Possible role of IGF2 receptors in regulating selection of 2 dominant follicles in cattle selected for twin ovulations and births

Abundance of IGF-2 receptor (IGF2R), FSH receptor (FSHR), and LH receptor (LHCGR) mRNA in granulosa cells (GCs) or theca cells (TCs) or both cells as well as estradiol (E2), progesterone (P4), and androstenedione concentrations in follicular fluid were compared in cows genetically selected (Twinner) or not selected (control) for multiple ovulations and twin births. Cows were slaughtered at day 3 to 4 (day 3) and day 5 to 6 (day 5) of an estrous cycle, and ovaries, follicular fluid, GCs, and TCs were collected. The two largest (F1 and F2) E2-active (EA) and E2-inactive (EI) follicles were selected according to their E2-to-P4 ratio and diameter. Androstenedione levels in EA F1 and F2 follicles were 5-fold greater (P < 0.05) in Twinner cows than in control cows on day 3 but did not differ on day 5. Twinner cows also had greater (P < 0.05) E2 and P4 concentrations, whereas steroid levels in EI follicles did not differ (P > 0.10) between genotypes. In EA F2 follicles, IGF2R levels in GCs were greater (P < 0.05) in control cows than in Twinner cows on day 3 and day 5, whereas IGF2R mRNA in TCs did not differ (P > 0.10). On day 3, FSHR mRNA levels were greater (P < 0.05) in GCs of EA F1 and EI F2 follicles of control cows than of Twinner cows. LH receptor mRNA expression was less in GCs and greater in TCs of EA F2 follicles in control cows than in Twinner cows (P < 0.05). We hypothesize that reduced GC IGF2R expression in F2 follicles of Twinner cows may play a role in the development of 2 or more dominant follicles.

Identification of an ionotropic glutamate receptor AMPA1/GRIA1 polymorphism in crossbred beef cows differing in fertility

A proposed functional polymorphism in the ionotropic glutamate receptor AMPA1 (GRIA1) has been reported to influence antral follicle numbers and fertility in cows. Repeat breeder cows that fail to produce a calf in multiple seasons have been reported to have reduced numbers of small (1 to 3 mm) antral follicles in their ovaries. Therefore, we tested the hypothesis that this GRIA1 polymorphism was affecting antral follicle numbers in repeat breeder cows. Repeat breeder cows (n = 64) and control cows (n = 72) that had always produced a calf were housed in a dry lot and observed twice daily for behavioral estrus. Blood samples were collected, and cows were genotyped for this GRIA1 polymorphism and for a polymorphism in the GnRH receptor (GnRHR) that was proposed to influence age at puberty. On d 3 to 8 after estrus cows were slaughtered, and reproductive organs were collected to determine antral follicle count, ovary size, and uterine horn diameter. Repeat breeder cows were older at first calving than control cows (P = 0.006). The length (P = 0.03) and height (P = 0.02) of the ovary contralateral to the corpus luteum (CL) were greater in control cows than repeat breeder cows. The endometrial diameter in the horn ipsilateral to the CL was greater in the control cows than the repeat breeder cows. Repeat breeder cows had fewer small (1 to 5 mm) antral follicles than control cows (P = 0.003); however, there was no association between GRIA1 genotype and antral follicle number. The GnRHR polymorphism was associated with age at first calving because cows that were homozygous for the C allele had a greater age at first calving than heterozygous cows or cows that were homozygous for the T allele (P = 0.01). In the granulosa cells from small (1 to 5 mm) antral follicles, mRNA abundances of 2 markers of oocyte quality, anti-Müllerian hormone and pentraxin 3, did not differ between fertility groups (P ≥ 0.12). We conclude that this GRIA1 polymorphism exists in beef cows but that it does not influence antral follicle numbers. The association between GnRHR genotype and age at first calving is likely not causal as this polymorphism is not functional. The utility of this polymorphism as a genetic marker for early conception in heifers will require further validation. Screening postpartum cows by ultrasonography to determine antral follicle numbers may aid in making culling decisions.

Increased abundance of aromatase and follicle stimulating hormone receptor mRNA and decreased insulin-like growth factor-2 receptor mRNA in small ovarian follicles of cattle selected for twin births

Cattle genetically selected for twin ovulations and births (Twinner) exhibit increased ovarian follicular development, increased ovulation rate, and greater blood and follicular fluid IGF-1 concentrations compared with contemporary cattle not selected for twins (Control). Experimental objectives were to 1) assess relationships among aromatase (CYP19A1), IGF-1 (IGF1), IGF-2 receptor (IGF2R), and FSH receptor (FSHR) mRNA expression in small (≤5 mm) antral follicles and 2) determine their association with increased numbers of developing follicles in ovaries of Twinner females. Ovaries were collected from mature, cyclic (d 3 to 6) Twinner (n = 11), and Control (n = 12) cows at slaughter and pieces of cortical tissue were fixed and embedded in paraffin. Expression of mRNA was evaluated by in situ hybridization using (35)S-UTP-labeled antisense and sense probes for CYP19A1, FSHR, IGF1, and IGF2R mRNA. Silver grain density was quantified within the granulosa and theca cells of individual follicles (2 to 7 follicles/cow) by Bioquant image analysis. Follicles of Twinners tended to be smaller in diameter than Controls (1.9 ± 0.1 vs. 2.3 ± 0.1 mm; P = 0.08), but thickness of granulosa layer did not differ (P > 0.1) by genotype. Relative abundance of CYP19A1 (P < 0.01) and FSHR (P < 0.05) mRNA was greater in granulosa cells of Twinners vs. Controls, respectively, whereas IGF2R mRNA expression was less in both granulosa (P < 0.01) and theca (P < 0.05) cells in follicles of Twinners vs. Controls, respectively. Abundance of CYP19A1 mRNA in granulosa cells was correlated negatively with IGF2R mRNA expression in both granulosa (r = -0.33; P < 0.01) and theca (r = -0.21; P = 0.05) cells. Expression of IGF1 mRNA was primarily in granulosa cells, including cumulus cells, and its expression did not differ between Twinners vs. Controls (P > 0.10). Detected increases in CYP19A1 and FSHR, but not IGF1, mRNA expression along with decreases in IGF2R mRNA expression in individual follicles of Twinners support the hypothesis that increased follicular development and steroidogenesis in Twinner females result from increased extra-ovarian IGF-1 production. Furthermore, a reduction in follicular IGF2R mRNA expression accompanied by a reduction in receptor numbers would increase availability of free IGF-2 and its stimulation of follicular development in Twinners.

174 MicroRNA EXPRESSION PROFILE IN BOVINE CUMULUS-OOCYTE COMPLEXES DURING LATE OOGENESIS

During late oogenesis, the mammalian oocyte synthesizes and stores mRNA necessary to guide the early stages of embryo development before the activation of embryonic transcription. The oocyte also contains many post-transcriptional regulatory mechanisms that coordinate mRNA stability and translation before specific activation. MicroRNAs (miRNAs) are short noncoding RNAs (17–25 nucleotides) that repress translation of target genes through sequence complementation and have recently been identified in murine oocytes. The objective of the current study was to identify and characterize the expression of miRNAs in bovine cumulus–oocyte complexes (COC) during late oogenesis as a potential mechanism for post-transcriptional regulation of mRNA in developing bovine oocytes. Ovaries from beef cattle (mixed populations) were obtained at a local abattoir. The COC were aspirated from 2- to 10-mm follicles and were pooled from each of 5 replicate collections for RNA extraction (n = 2241 total COC). Small RNA in the 16- to 27-bp range was isolated and used to construct cDNA libraries for sequencing, producing 2529 successful sequences that were clustered based on matching 14 consecutive bases to the most common member of the cluster. The consensus sequences of the clusters were screened for mitochondrial RNA, rRNA, tRNA, and snoRNA contaminants, leading to removal of 774 (31%) sequences from consideration. The remaining 1755 putative miRNA sequences were compared with known miRNA in miRBase, revealing 62 bovine COC miRNA clusters matching previously known sequences and 4 with no match. The cluster with the largest number of sequences identified in bovine COC matched the sequence of the let-7 miRNA family (657 sequences or 37% of putative miRNA). Within the let-7 family, let-7b (459 sequences or 26%) was the most abundant followed by let-7i (135 sequences or 8%). The four clusters that did not match sequences in miRBase represent putative novel miRNA. One of these four clusters had relatively high expression in bovine COCs (308 sequences or 18%), whereas the other 3 clusters had relatively low expression (total of 55 combined sequences or 3%). Expression of several putative miRNAs (let-7b, let-7i, miR-106a, and the abundant novel miRNA) in bovine COC were confirmed using TaqMan miRNA assays. These results demonstrate the presence of miRNA within bovine COC during late oogenesis, which suggests that these post-transcriptional regulatory elements may play a role in coordinating mRNA stability and translation in bovine oocytes.

Confirmation of quantitative trait loci using a low-density single nucleotide polymorphism map for twinning and ovulation rate on bovine chromosome 5

Traditional genetic selection in cattle for traits with low heritability, such as reproduction, has had very little success. With the addition of DNA technologies to the genetic selection toolbox for livestock, the opportunity may exist to improve reproductive efficiency more rapidly in cattle. The US Meat Animal Research Center Production Efficiency Population has 9,186 twinning and 29,571 ovulation rate records for multiple generations of animals, but a significant number of these animals do not have tissue samples available for DNA genotyping. The objectives of this study were to confirm QTL for twinning and ovulation rate previously found on BTA5 and to evaluate the ability of GenoProb to predict genotypic information in a pedigree containing 16,035 animals when using genotypes for 24 SNP from 3 data sets containing 48, 724, or 2,900 animals. Marker data for 21 microsatellites on BTA5 with 297 to 3,395 animals per marker were used in conjunction with each data set of genotyped animals. Genotypic probabilities for females were used to calculate independent variables for regressions of additive, dominance, and imprinting effects. Genotypic regressions were fitted as fixed effects in a 2-trait mixed model analysis by using multiple-trait derivative-free REML. Each SNP was analyzed individually, followed by backward selection fitting all individually significant SNP simultaneously and then removing the least significant SNP until only significant SNP were left. Five significant SNP associations were detected for twinning rate and 3 were detected for ovulation rate. Two of these SNP, 1 for each trait, were significant for imprinting. Additional modeling of paternal and maternal allelic effects confirmed the initial results of imprinting done by contrasting heterozygotes. These results are supported by comparative mapping of mouse and human imprinted genes to this region of bovine chromosome 5.

Large variation in steroid concentrations and insulin-like growth factor binding proteins exists among individual small antral follicles collected from within cows at random stages of the estrous cycle

Variation in the biochemical status of individual small (< or = 5 mm diameter) antral follicles within the ovaries of a cow at any given time likely influences the capacity for undergoing recruitment, selection, and establishing dominance. The objectives of this study were to provide insight into the magnitude of variation in follicular fluid concentrations of steroids and activities of IGFBP that exists among individual small antral follicles within and between cows, and to determine the relationships between follicular fluid IGFBP and steroid concentrations in these follicles. A total of 108 small antral follicles were collected from 6 cows at random stages of the estrous cycle, with 10 to 26 follicles/cow. Concentrations of steroids (ng/mL of follicular fluid) in the overall population of follicles ranged from 0.1 (lowest detectable limit) to 51 for estradiol (E2), 4 to 1,149 for progesterone (P4), and 5 to 504 for androstenedione (A4). Concentrations of E2 and A4 were associated positively (r = 0.2; P < 0.02), but E2 (r = -0.4) and A4 (r = -0.4) were associated negatively, with P4. The proportion of variation in steroid concentrations accounted for by differences among animals (P < 0.05) was small for E2 (12%), moderate for P4 (43%), and greatest for A4 (74%). Least differences between minimum and maximum concentrations of steroids observed in follicles from within a cow were 21-, 5.5-, and 3.5-fold for E2, P4, and A4, respectively, whereas the greatest differences between minimum and maximum concentrations were 505-, 108-, and 26-fold for E2, P4, and A4, respectively. Ranges of IGFBP concentrations (arbitrary densitometer units) detected in fluid from a sub-sample of 43 follicles were 1.18 to 4.50 for IGFBP-3, 0.54 to 4.68 for IGFBP-2, 0.07 to 2.56 for IGFBP-4, and 0.01 to 6.71 for IGFBP-5. Concentrations of E2 were correlated negatively with each IGFBP (r = -0.4 to -0.8; P < 0.05) except IGFBP-3. In contrast, concentrations of A4 were correlated positively with IGFBP-3 (r = 0.4; P < 0.05) but were not correlated with other IGFBP. Concentrations of P4 were correlated positively (r > 0.4; P < 0.05) with IGFBP-4 and -5. The results indicate that steroid concentrations and IGFBP activities vary substantially among small antral follicles collected from within and among individual animals and that increasing production of E2, the hallmark of a developing follicle, was associated with reduced activity of all IGFBP except IGFBP-3, thereby implicating these IGFBP in the regulation of follicular recruitment.

Increased calf production in cattle selected for twin ovulations1,2

The effects of increasing fetal numbers and their distribution between the left and right uterine horns on calf survival, calf BW at birth and weaning, gestation length, dystocia, and calf sex ratio were evaluated for single (n = 1,587), twin (n = 2,440), and triplet calves (n = 147) born to primiparous and multiparous females in the Twinner population at the US Meat Animal Research Center between 1994 and 2004. Cattle were distributed equally between the spring and fall breeding seasons. Fetal number and distribution in utero were determined by real-time ultrasonography at 40 to 70 d postbreeding. For cows and heifers combined, number of calves per parturition increased from 1.34 in 1994 to 1.56 in 2004. Gestation length was 6.8 d shorter (P < 0.01) for twins compared with singles (277.5 +/- 0.2 vs. 284.3 +/- 0.2 d) and 12.7 d shorter for triplets (271.6 +/- 0.8 d). Survival and BW of individual calves at birth decreased (P < 0.01) but total calf BW per dam increased (P < 0.01) as fetal number increased from single to triplet births. Twins resulting from bilateral twin ovulations had increased (P < 0.01) survival and BW at birth, a longer (P < 0.01) gestation length, and less (P < 0.01) dystocia than twins resulting from unilateral twin ovulations. Calf survival and BW at birth were 97.2 +/- 0.3% and 48.0 +/- 0.1 kg for singles, 92.0 +/- 0.4% and 39.0 +/- 0.2 kg for bilateral twins, 83.2 +/- 0.4% and 36.7 +/- 0.2 kg for unilateral twins, 73.8 +/- 1.4% and 30.6 +/- 0.7 kg for bilateral triplets, and 51.9 +/- 3.2% and 31.7 +/- 1.6 kg for unilateral triplets. Birth weight of single calves increased by 0.51 kg/d for each additional day of gestation length vs. 0.38 kg/d for individual twins. Calf BW at birth increased (P < 0.01) with age of dam from 2 to 4 yr. Twin and triplet births had a greater (P < 0.01) incidence of dystocia than single births. The ratio of male:female calves (0.52:0.48) at birth was not affected by type of birth. Postnatal calf survival was similar for all 3 types of birth. Total progeny BW at weaning for single, twin, and triplet births was 217.7 +/- 2.5, 328.3 +/- 3.2, and 378.4 +/- 15.0 kg, respectively (P < 0.01). Although most bovine females have the uterine capacity to gestate twin calves, decreased survival and BW of unilateral twins and of all triplets indicate that their growth and development may have been compromised by uterine crowding.

Effects of ovulation rate and fetal number on fertility in twin-producing cattle

Effects of ovulation rate and of fetal number and distribution within the uterus on pregnancy rate and fetal survival were evaluated in nulliparous (n = 1,331) and parous (n = 3,517) cattle selected for twinning. Cattle were divided into a spring (70 d) and fall (60 d) breeding season and bred by a combination of AI and natural service. Ovulation rate, pregnancy status, and fetal number and distribution were determined by transrectal, real-time ultrasonography of the uterus and both ovaries at the end of the breeding season. Pregnancy was reconfirmed by rectal palpation at 75 to 135 d of gestation. For heifers and cows combined, ovulation rate increased (P < 0.01) from 1.46 +/- 0.4 in 1994 to 1.89 +/- 0.4 in 2004; number of calves per parturition increased (P < 0.01) from 1.34 +/- 0.3 to 1.56 +/- 0.3, respectively, which included an increase in triplet and quadruplet ovulations and triplet births. Bilateral twin ovulations yielded proportionately more (P < 0.01) twin births than unilateral twin ovulations. Ovulation rate was greater (P < 0.01) in the fall than spring breeding season. Pregnancy rate at ultrasound diagnosis did not differ among females with 1, 2, or 3 ovulations (89.1 +/- 0.7, 91.2 +/- 0.7, or 91.5 +/- 2.8%, respectively), but rates at calving decreased (P < 0.01) with increasing ovulation rate (85.1 +/- 0.6, 82.7 +/- 0.6, or 64.2 +/- 2.7%, respectively). Pregnancy rate was less (P < 0.01) after twin or triplet births than single births. For dams birthing twins or triplets, pregnancy rate was less in the fall vs. spring, but rates were similar between seasons for dams with a single birth (type of birth x season, P < 0.05). Cows </= 50 d postpartum had a decreased (P < 0.01) pregnancy rate compared with cows > 60 d, regardless of type of birth. Maintenance of pregnancy to term differed (P < 0.01) among females diagnosed with 1, 2, or 3 fetuses (95.7 +/- 0.6, 87.8 +/- 0.8, and 54.9 +/- 2.3%, respectively). The reduced survival of twin and triplet fetuses in heifers had occurred (P < 0.01) by d 75 to 135 of gestation, and fetal losses were greater (P < 0.01) for unilateral than bilateral twins or triplets, whereas loss of twin or triplet fetuses in cows occurred later in gestation, and losses were not affected by uterine location. Thus, increased calf production from selecting for increased ovulation rate in beef cattle is tempered by increased fetal mortality, partially associated with the crowding of 2 or 3 fetuses within 1 uterine horn, especially in heifers.

Localization of Period 1 mRNA in the ruminant oocyte and investigations of its role in ovarian function

The clock gene Period 1 (Per1) may be a prolificacy gene, because it localized to the mouse oocyte and Per1-null drosophila shed fewer eggs. Because Per1 mapped to a region of mouse chromosome 11 syntenic to bovine chromosome 19 where a quantitative trait loci (QTL) for ovulation rate existed, we hypothesized that Per1 influenced folliculogenesis and ovulation rate in ruminants. Ovarian cortex was collected at slaughter on days 5, 12, 15, 17, and 20 after estrus for real-time RT-PCR evaluation of Per1 mRNA expression in Dorset (n = 18), Romanov (n = 10), Romanov/Dorset (n = 21), and Composite (n = 22) ewes. Ovarian cortex was also collected from cows selected for increased ovulation rate (n=37) or unselected controls (n = 28) on days 4, 5, and 6 of the estrous cycle for in situ hybridization and real-time RT-PCR. To examine the role of Per1 in early follicular development, ovarian cortex from neonatal calves (n = 5) was cultured for 10 days and Per1 mRNA levels were measured on day 0 and on day 10 of culture. The primers generated a 483bp amplicon with 100% sequence homology to bovine RIGUI-like protein (Per1). In silico mapping of this sequence placed Per1 on bovine chromosome 19; however, it was 20cM from the QTL. Per1 mRNA expression was unaffected by prolificacy, day of the cycle, or pregnancy status in ewes or cows. The riboprobe hybridized to oocytes of bovine preantral and antral follicles. In bovine ovarian cortical cultures on day 0, the tissue contained mostly primordial follicles (5.6+/-0.6 follicles/section); however, after 10 days in culture, the number of primordial follicles per section decreased (0.5 follicles/section) and the number of primary follicles increased as follicles activated (day 0 = 0.5+/- 0.6 versus day 10 = 10.4 +/-0.6 primary follicles/section; P < 0.001). Per1 mRNA did not change over time in culture. We conclude that Per1 mRNA is expressed by ruminant oocytes in preantral and antral follicles; however, its physiological role in mammalian ovarian function remains to be elucidated.

Association of a single nucleotide polymorphism in SPP1 with growth traits and twinning in a cattle population selected for twinning rate

Continued validation of genetic markers for economically important traits is crucial to establishing marker-assisted selection as a tool in the cattle industry. The objective of the current study was to evaluate the association of a SNP (T(9)/T(10)) in the osteopontin gene (SPP1) with growth rate in a large cattle population spanning multiple generations and representing alleles from 12 founding breeds. This population has been maintained at the US Meat Animal Research Center since 1981 and subjected to selection for twinning rate. Phenotypic records for this population included twinning rate and ovulation rate, providing an opportunity to examine the potential effects of SPP1 genotype on reproductive traits. A set of 2,701 animals was geno-typed for the T(9)/T(10) polymorphism at SPP1. The geno-typic data, including previously genotyped markers on chromosome 6 (BTA6), were used in conjunction with pedigree information to estimate genotypic probabilities for all 14,714 animals with phenotypic records. The genotypic probabilities for females were used to calculate independent variables for regressions of additive, dominance, and imprinting effects. Genotypic regressions were fit as fixed effects in a mixed model analysis, in which each trait was analyzed in a 2-trait model where single births were treated as a separate trait from twin births. The association of the SPP1 marker with birth weight (P < 0.006), weaning weight (P < 0.007), and yearling weight (P < 0.003) was consistent with the previously reported effects of SPP1 genotype on yearling weight. Our data supports the conclusion that the SNP successfully tracks functional alleles affecting growth in cattle. The previously undetected effect of the SNP on birth and weaning weight suggests this particular SPP1 marker may explain a portion of the phenotypic variance explained by QTL for birth and HCW on BTA6.

Increased vascular endothelial growth factor and pregnancy-associated glycoproteins, but not insulin-like growth factor-I, in maternal blood of cows gestating twin fetuses1,2

Differences in placental mass and vascularity exist between cows gestating single vs. multiple fetuses. Therefore, the association between fetal number and placental development or function was assessed by comparing concentrations of vascular endothelial growth factor (VEGF), pregnancy-associated glycoproteins (PAG), IGF-I, and progesterone in the maternal blood of cattle selected for twin births and gestating 1 (n = 23) vs. 2 (n = 17) fetuses. Samples of jugular venous blood were collected serially at a mean of 57, 121, 192, and 234 d (range within groups was 20 d) after AI. Plasma concentrations of VEGF, IGF-I, and progesterone were measured by double-antibody RIA, and of PAG by an indirect sandwich ELISA. Concentrations of VEGF and progesterone were greater (P < 0.05) in dams with twin vs. single fetuses. Maternal VEGF concentrations did not differ among collection times, but progesterone concentrations increased (P < 0.01) between d 192 and 234. Conversely, PAG concentrations were low at d 57 and 121 and did not differ between dams carrying singles or twins. However, the subsequent increase (P < 0.01) in PAG was greater in dams with twins, resulting in greater (P < 0.01) PAG concentrations for dams with twins at d 192 and 234 (type of birth x time; P < 0.01). Maternal IGF-I concentrations were unaffected by fetal number. Because corpora lutea persisted for the duration of the evaluation period, maternal progesterone concentrations were likely related to the number of corpora lutea rather than the number of fetuses. It is postulated that the greater PAG and VEGF concentrations in the blood of dams gestating twins are the result of a larger uteroplacental mass, including increased numbers of binucleate cells and increased angiogenesis and vasculogenesis associated with a twin pregnancy. Although PAG and VEGF were elevated in dams gestating twins, variability within and among birth groups limits the use of PAG or VEGF measurements for the diagnosis of twins.

Evaluation of ovulation rate and ovarian phenotype in puberal heifers from a cattle population selected for increased ovulation rate1,2

Long-term selection for increased ovulation rate (1984 to 2002) has resulted in a unique ovarian phenotype in the MARC Twinner cattle population. Ovulation rate and frequency of bilateral ovulations were examined by rectal palpation in 29,547 estrous cycles for 3,910 heifers (12 to 18 mo of age) in this population. Bilateral ovulations (one corpus lutuem [CL] on each ovary) were of interest because bilateral twin pregnancies result in decreased dystocia and increased calf survival. Ovulation rate increased linearly at a rate of 0.026 CL per year, and it currently averages 1.48 +/- 0.04 CL per estrous cycle. Concurrent with the increase in ovulation rate, the frequency of triplet ovulations increased from 0% to 2.3 +/- 0.8% (P < 0.001). Ovulation rate of both the right and left ovary increased equally at a rate of 0.013 CL per year, and mean ovulation rate of the right ovary remained greater than mean ovulation rate of the left ovary throughout the study (0.66 vs. 0.55 +/- 0.003 CL per estrous cycle; P < 0.001). Although correlations were low, ovulation rate of one ovary was negatively correlated (P < 0.001; r = -0.07) with ovulation rate of the same ovary in the previous estrous cycle, but positively correlated (P < 0.001; r = 0.13) with the contralateral ovary of the previous estrous cycle. The proportion of bilateral ovulations averaged 55.7 +/- 0.7%, a value greater than the predicted 49.5% (P < 0.001). In addition to dystocia and retained placenta, triplet pregnancies increase the incidence of pregnancies gestating fetuses of opposite sexes and subsequent incidence of freemartins; thus, selection pressure on ovulation rate may need to be adjusted in the MARC Twinner population. The proportion of bilateral ovulations in the population is greater than expected, and this may be an economically important trait, which will respond to selection and be beneficial for improving bovine reproductive efficiency. Understanding factors controlling the increased functional activity of the right ovary and bilateral ovulations may provide further insights into the mechanisms controlling follicle selection and methods to improve reproductive management of cattle.

Characterization of gene expression in double-muscled and normal-muscled bovine embryos

Myostatin, a member of the transforming growth factor-beta superfamily, is a negative regulator of skeletal muscle growth. Cattle with mutations that inactivate myostatin exhibit a remarkable increase in mass of skeletal muscle called double muscling that is accompanied by an equally remarkable decrease in carcass fat. Although a mouse knockout model has been created which results in mice with a 200% increase in skeletal muscle mass, molecular mechanisms whereby myostatin regulates skeletal muscle and fat mass are not fully understood. Using suppressive subtractive hybridization, genes that were differentially expressed in double-muscled vs. normal-muscled cattle embryos were identified. Genetic variation at other loci was minimized by using embryonic samples collected from related Piedmontese x Angus dams or Belgian Blue x Hereford dams bred to a single sire of the same breed composition. Embryos were collected at 31-33 days of gestation, which is 2-4 days after high-level expression of myostatin in the developing bovine embryo. The suppressive subtraction resulted in 30 clones that were potentially differentially expressed, 19 of which were confirmed by macroarray analysis. Several of these genes have biological functions that suggest that they are directly involved in myostatin's regulation of skeletal muscle development. Furthermore, several of these genes map to quantitative trait loci known to interact with variation in the myostatin gene.

Ovarian follicular development in cattle selected for twin ovulations and births12

Comparisons of numbers of antral ovarian follicles and corpora lutea (CL), of blood hormone concentrations, and of follicular fluid steroid concentrations and IGFBP activity were conducted between cows selected (twinner) and unselected (control) for twin births to elucidate genetic differences in the regulation of ovarian follicular development. Ovarian follicular development was synchronized among cows by a single i.m. injection of PGF2alpha on d 18 of the estrous cycle; six cows per population were slaughtered at 0, 24, 48, and 72 h after PGF2alpha. Jugular vein blood was collected from each animal at PGF2alpha injection and at 24-h intervals until slaughter. Ovaries of twinner cows contained more small (< or = 5 mm in diameter, P < 0.05), medium (5.1 to 9.9 mm, P < 0.05), and large (> or = 10.0 mm, P < 0.01) follicles and more (P < 0.01) CL than ovaries of controls. Follicular fluid concentrations of estradiol, androstenedione, testosterone, and progesterone reflected the stage of follicular development and were similar for twinner and control follicles at the same stage. Earlier initiation of follicular development and/or selection of twin-dominant follicles in some twinner cows resulted in greater concentrations of estradiol in plasma at 0, 24, and 48 h and of estradiol, androstenedione, and testosterone in follicular fluid of large follicles at 0 h after PGF2alpha for twinner vs. control cows (follicular status x time x population, P < 0.01). Binding activities of IGFBP-5 and -4 were absent or reduced (P < 0.01) in follicular fluid of developing medium and large estro-gen-active (estradiol:progesterone ratio > 1) follicles but increased with atresia. Only preovulatory Graafian follicles lacked IGFBP-2 binding, suggesting a possible role for IGFBP-2 in selection of the dominant follicle. Concentrations of IGF-I were twofold greater (P < 0.01), but GH (P = 0.10) and cholesterol (P < 0.05) were less in blood of twinners. Three generations of selection of cattle for twin ovulations and births enhanced ovarian follicular development as manifested by increased numbers of follicles within a follicular wave and subsequent selection of twin dominant follicles. Because gonadotropin secretion and ovarian steroidogenesis were similar for control and twinner cattle, enhanced follicular development in twinners may result from decreased inhibition by the dominant follicle(s), increased ovarian sensitivity to gonadotropins, and/or increased intragonadal stimulation, possibly by increased IGF-I.

Insulin-like growth factor binding proteins in granulosa and thecal cells from bovine ovarian follicles at different stages of development1,2

Because IGFBP inhibit IGF-stimulated cellular proliferation and differentiation, it is hypothesized that variations among IGFBP in individual follicles might contribute to the regulation of recruitment, selection, dominance, and turnover of ovarian follicles. Sources of IGFBP in fluid of bovine follicles are not well established; thus, objectives of this study were to determine levels of IGFBP binding activities and messenger RNA (mRNA) in granulosa and theca interna cells at different stages of follicular development (small [< 6 mm], medium [6 to < 8 mm], and large [> or = 8 mm]) and to characterize associations of these levels measured in the cells with levels of IGFBP and steroids in follicular fluid. Thecal and granulosa cells from large healthy follicles contained two- to twentyfold less (P < 0.05) IGFBP-2, -3, and -5 than cells from small, medium, and large atretic follicles. Thecal cells from small, medium, and large atretic follicles contained more (P < 0.05) IGFBP-3 and -4 than granulosa cells from these follicles, whereas granulosa cells from these follicles contained more IGFBP-2 activity than thecal cells. Differences in IGF binding activity were paralleled by differences in levels of mRNA for the respective IGFBP. Developmental differences in IGFBP activity in follicular fluid were positively associated with activity in granulosa and/or thecal cells, with the exception of IGFBP-4, which was low in fluid from large healthy follicles but markedly increased (mRNA and binding activity) in granulosa cells from these follicles. It is concluded that developmental changes in follicular fluid IGFBP-2 and -5 binding activities seem to be controlled in part by alterations in synthesis of these IGFBP by granulosa and thecal cells, whereas diminished IGFBP-4 in fluid from large healthy follicles occurs concomitantly with increased levels of IGFBP-4 mRNA and activity in granulosa cells, implicating posttranslational regulation by specific proteases.

Initial results of genomic scans for ovulation rate in a cattle population selected for increased twinning rate

Genomic scans were conducted with 273 markers on 181 sires from a cattle population selected for increased twinning rate to identify chromosomal regions containing genes that influence ovulation rate. Criteria used for selecting markers were number of alleles, ease of scoring, and relative position within linkage group. Markers were multiplexed or multiple-loaded on the gels to reduce the costs and labor required to obtain genotypic data. This approach reduced the number of gels by 45% when compared with running each marker independently. Male animals selected for the genomic scan sired the majority of the population. A modified interval analysis was used in a granddaughter design to compare effects of each allele within sire for 10 different sire families. The midparent deviation of the son's estimated breeding value for ovulation rate was used as the phenotype. Forty-one potential peaks were identified with a nominal significance level < or = 0.05. The 10 peaks with the highest significance levels (P < 0.02) were selected for further analysis. Markers were genotyped across daughters of the sire where nominal significance was found for each of the 10 peaks. One peak (BTA5, relative position 40 cM) was found to be nominally significant in the daughters. The nominal significance levels were P = 0.01 for the sons (n = 32) and P = 0.02 for the daughters (n = 94) of sire 784403. A combined genomewide significance value (P = 0.07) was calculated that accounted for the 10 analyses with sons and the 10 analyses with daughters. These results strongly suggest that this region contains a gene(s) that is involved in the follicular recruitment and development process.

Evaluation of numbers of microscopic and macroscopic follicles in cattle selected for twinning

We hypothesized that the number of microscopic follicles present in the ovaries of cattle selected for twin births (Twinner) would be greater than in the ovaries of contemporary Controls. Ovaries were collected from seven Control and seven Twinner cows at slaughter. The number of Small (1 to 3.9 mm), Medium (4 to 7.9), and Large (> 8 mm) surface follicles was counted and one ovary was fixed for histological evaluation. Fifty to sixty consecutive 6-microm slices were taken from a piece of cortical tissue, approximately 1 cm x 1 cm in area, located between the surface follicles. Microscopic follicles were classified as primordial (oocyte surrounded by a single layer of squamous pregranulosa cells), primary (oocyte surrounded by a single layer of one or more cuboidal granulosa cells), secondary (oocyte surrounded by two or more layers of granulosa cells), or tertiary (oocyte surrounded by multiple layers of granulosa cells with initiation of antrum formation to < or = 1 mm in diameter). The total number of follicles was counted in 200 fields (2 mm x 2 mm) per ovary. A field containing no follicles was classified as empty. There were significantly more secondary follicles in Twinner compared with Control ovaries (12.9 vs 6.3; P < .05). Twinners also tended to have more small surface follicles (35.4 vs 49.0; P < 0.1). We conclude that ovaries of Control and Twinner cows do not differ in the number of primordial follicles or in the number of follicles activated into the growing pool; however, Twinner cows are able to maintain more growing follicles at the secondary and subsequent stages of development.

Effects of twinning on postpartum reproductive performance in cattle selected for twin births

The effects of twinning, dystocia, retained placenta, and body weight on postpartum reproduction were evaluated for 3,370 single and 1,014 twin births. Females were bred by AI for 40 d followed by 20 or 30 d of natural service with equal numbers bred and calved in spring and fall. Percentage of dams cyclic by the end of the AI period was lower (P<.05) for dams birthing and nursing a single calf (92.4%) than for dams birthing twins and nursing zero (98.7%) or two (94.7%) calves. Whereas the interval from parturition to first estrus was shorter (P<.01) for dams birthing and nursing a single (56.9 d) than for dams birthing twins and nursing one (68.5 d) or two (69.6 d) calves, length of the interval was further reduced by dystocia in nonlactating dams of either twins or singles (type of birth x dystocia, P<.05). Ensuing pregnancy rates were also affected by type of birth and dystocia. Without dystocia, dams birthing and nursing a single calf had a higher pregnancy rate (79.2%) than dams birthing twins and nursing one (61.7%) or two (66.3%) calves, whereas the lower ensuing pregnancy rates associated with dystocia in dams of singles (71.9%) resulted in similar rates among dams of singles and twins with dystocia (type of birth x dystocia; P<.01). Having a retained placenta resulted in a lower incidence of (93.5 vs. 96.4%, with vs. without; P<.05) and a longer interval to (64.7 vs. 59.2 d; P<.01) estrus while reducing subsequent pregnancy rates (X = 9.6%) in 3 of the 7 yr evaluated (retained placenta x year, P<.01). Because all parous females were bred during the same calendrical period, the shorter gestation length for twin calves (275.6 vs. 281.3 d) resulted in a longer interval from parturition to conception for twin births, whereas means for conception date differed by only 2 d between dams of twins and singles. Furthermore, a reduction (P<.01) in the interval to conception occurred with dystocia in dams of singles (89.3 vs. 85.0 d, without vs. with dystocia) and of twins nursed by zero (116.9 vs. 83.5 d), one (100.2 vs. 92.8 d), or two (96.1 vs. 97.2 d) calves. Another detriment to fertility was the higher incidence of fetal mortality or abortions associated with twin vs. single pregnancies (12.4 vs. 3.5%; P<.01). However, despite the lower conception rates for dams of twins, the increased prolificacy provides an opportunity to increase total beef production with a twinning technology.

Effects of twinning on gestation length, retained placenta, and dystocia

Constraints to maximal productivity from twinning in beef cattle include increased incidence of dystocia and retained placenta, longer postpartum interval, and lower conception rate. Incidence and cause(s) of the shorter gestation length and of the increased retained placenta and dystocia associated with twinning were evaluated for 3,370 single and 1,014 twin births produced in a population of cattle selected for natural twin births. Gestation length was shorter for twin than for single pregnancies (275.6 vs. 281.3 d, P<.01) and likely contributed to the higher incidence of retained placenta associated with twin births (27.9 vs. 1.9%; P<.01). Incidence of retained placenta was also higher in the spring (March-April) than in the fall (August-September) calving season (18.3 vs. 11.4%; P<.01). The higher incidence of dystocia with twins than with singles (46.9 vs. 20.6%, P<.01) was primarily due to abnormal presentation (37.0 vs. 4.5%, respectively) of one or both twin calves at parturition. First- (40.5%) and second- (22.7%) parity dams with a single birth had more (P<.01) dystocia than older dams (13.4%), whereas dystocia was not affected (P>.10) by parity with twin births. Because of the shorter gestation length and the increased incidence of retained placenta and(or) dystocia, achievement of increased productivity with twinning in cattle necessitates intensive management of twin-producing dams and their calves during the calving season. Management of the increased dystocia can be facilitated by preparturient diagnosis of twin pregnancies, enabling timely administration of obstetrical assistance to facilitate delivery of twin calves and to increase their neonatal survival.

A model of litter size distribution in cattle

Genetic increases in twinning of cattle could result in increased frequency of triplet or higher-order births. There are no estimates of the incidence of triplets in populations with genetic levels of twinning over 40% because these populations either have not existed or have not been documented. A model of the distribution of litter size in cattle is proposed. Empirical estimates of ovulation rate distribution in sheep were combined with biological hypotheses about the fate of embryos in cattle. Two phases of embryo loss were hypothesized. The first phase is considered to be preimplantation. Losses in this phase occur independently (i.e., the loss of one embryo does not affect the loss of the remaining embryos). The second phase occurs after implantation. The loss of one embryo in this stage results in the loss of all embryos. Fewer than 5% triplet births are predicted when 50% of births are twins and triplets. Above 60% multiple births, increased triplets accounted for most of the increase in litter size. Predictions were compared with data from 5,142 calvings by 14 groups of heifers and cows with average litter sizes ranging from 1.14 to 1.36 calves. The predicted number of triplets was not significantly different (chi2 = 16.85, df = 14) from the observed number. The model also predicted differences in conception rates. A cow ovulating two ova was predicted to have the highest conception rate in a single breeding cycle. As mean ovulation rate increased, predicted conception to one breeding cycle increased. Conception to two or three breeding cycles decreased as mean ovulation increased because late-pregnancy failures increased. An alternative model of the fate of ova in cattle based on embryo and uterine competency predicts very similar proportions of singles, twins, and triplets but different conception rates. The proposed model of litter size distribution in cattle accurately predicts the proportion of triplets found in cattle with genetically high twinning rates. This model can be used in projecting efficiency changes resulting from genetically increasing the twinning rate in cattle.

Genetic and environmental parameters for ovulation rate, twinning rate, and weight traits in a cattle population selected for twinning

A project was implemented in 1981 with the objective of increasing twinning rate in cattle. Daughters of foundation sires had twin calves at a frequency of from 8 to 13%, and foundation females had twin calves at an average frequency of 50%. Data were analyzed on twinning rate, ovulation rate, and weight traits. The h2 of ovulation rate increased from .11 to .38 for a single estrous cycle to the mean of eight estrous cycles. From all data, h2 for single observation of ovulation rate and twinning rate were .10 and .09, respectively. The r(g) between them was .75. The h2 of weight traits ranged from .42 to .54 when weight traits were analyzed pair-wise with ovulation rate and with twinning rate. The r(g) between weight traits with ovulation rate ranged from .15 to .30 and with twinning rate ranged from .24 to .39. Phenotypic mean twinning rate increased from 1.07 to 1.29 calves per parturition for females born 1981 through 1993, and adjusted mean predicted breeding value (PBV) increased from 1.07 to 1.33 calves per parturition. Phenotypic mean ovulation rate for fall of 1984 through fall 1994 birth groups increased from 1.11 to 1.26 per estrous cycle, and adjusted mean PBV for ovulation rate increased from 1.11 to 1.29 per estrous cycle. Because of the high r(g) (i.e., .75) between ovulation rate and twinning rate, and because of a h2 of .35 for ovulation rate for the mean of six estrous cycles, repeated records of ovulation rate in puberal heifers is an effective indirect selection criterion for twinning rate. The positive r(g) between growth traits and ovulation and twinning rate suggest the need for some compromise when the selection goal is increased twinning rate with no increase in growth and size.

Levels of insulin-like growth factor (IGF) binding proteins, luteinizing hormone and IGF-I receptors, and steroids in dominant follicles during the first follicular wave in cattle exhibiting regular estrous cycles

Objectives of this study were to determine if concentrations of steroids, insulin-like growth factor -I (IGF-I), and IGF binding proteins (IGFBP) in follicular fluid and numbers of LH and IGF-I receptors change during growth of the dominant follicle. Ovarian follicular development was monitored daily via ultrasound in lactating Holstein cows. Animals underwent bilateral ovariectomy when the dominant follicle was first identified (days 4-6; estrus = day 0; early; n = 5) or when it stopped growing (days 8-12; late; n = 8). All follicles were classified as dominant (DF), large (LG; > = 6 mm in diameter, excluding DF) or small (SM; < 6 mm), follicular fluid was aspirated, and theca and granulosa cells were collected. Levels of IGFBP-2, assessed via ligand blotting, were greater (P < 0.05) in LG and SM follicles compared with DF in early cows. Levels of IGFBP-3 in follicular fluid were unaffected by follicle class. Numbers of specific 125I-hCG/LH binding sites in thecal cells were greater (P < 0.01) in DF compared with LG and SM follicles of both early and late cows. Numbers of specific 125I-hCG/LH binding sites in granulosa cells were similar for follicle sizes in early cows, but, in late cows, were greater (P < 0.01) in DF compared with SM follicles and were severalfold greater (P < 0.01) in late DF compared with early DF. Numbers of receptors for IGF-I in thecal cells were 2-fold greater (P < 0.05) in DP and LG compared with SM in late cows. Numbers of IGF-I receptors in granulosa cells were unaffected by size or growth of follicles, but were severalfold greater than in theca cells. Concentrations of estradiol were severalfold greater (P < 0.01) in DF compared with LG and SM in both early and late cows. Concentrations of androstenedione in early cows were greater (P < 0.05) in DF and SM compared with LG follicles. Concentrations of progesterone and IGF-I did not differ (P > 0.10) among follicle classes, but both were greater (P < 0.10) in late LG compared with early LG follicles. Concentrations of IGF-II in follicular fluid did not differ (P > 0.10) between early and late cows but were greater (P < 0.10) in SM than DF or LG follicles. We conclude that low amounts of IGFBP-2 and increased thecal binding sites for hCG/LH appear to be related to establishment of the dominant follicle during the first follicular wave in cattle exhibiting regular estrous cycles during late lactation.

Effects of twinning on dystocia, calf survival, calf growth, carcass traits, and cow productivity

This paper reports results from a long-term experiment with a primary objective to increase twinning rate in cattle at the Roman L. Hruska U.S. Meat Animal Research Center. Survival of singles was 13% higher (P < .01) than that of twins at birth, and the difference in survival in favor of singles was of similar magnitude at 72 h (12.9%, P < .01), 150 d (14.8%, P < .01), and 200 d (15.2%, P < .01). Survival of calves with no dystocia was higher than survival of calves with dystocia: 8.6% (P < .01) at birth, 10.8% (P < .01) at 72 h, 12% (P < .01) at 150 d, and 12.2% (P < .01) at 200 d. The effect of dystocia on survival was greater (P < .01) in twins than in singles at birth and at 72 h. Least squares means for dystocia were 20.4% in singles compared with 42.2% in twins. Most of the dystocia in singles resulted from a traction requirement (84.7%) of normal presentations, whereas most of the dystocia in twins (77.8%) resulted from malpresentations, with 59.2% of the malpresentations accompanied with a requirement for traction. Survival in singles ranged from 10.7% to 15.3% greater than in twins at different ages when there was no requirement for assistance in either singles or twins. Calves born as singles were 8.8 kg heavier (P < .01) at birth and 28 kg heavier (P < .01) at 200 d than calves born and reared as twins. Calf weight produced per cow calving was 53.1%, 54.7%, and 58.4% greater (P < .01) at birth, 150 d, and 200 d, respectively, in cows producing twins than in cows producing singles. Cows producing twins had 65.2% more (P < .01) live calves at 200 d than cows producing singles. Single male calves gained 74 g more per day than twin males from birth to 200 d, 45 g more (P < .01) per day from 200 d to slaughter and 57 g more (P < .01) per day from birth to slaughter. Differences between twin and single males in carcass traits were small. A sample of steers from the Twinning Project gained significantly faster and produced significantly more desirable carcasses than a sample of steers from a high performance reference population. Freemartins did not differ (P < .05) from normal females in growth traits, but freemartins had higher (P < .05) scores for marbling with a higher percentage (P < .05) of USDA Choice or better quality grade carcasses and lower estimated percentage retail product.

The ovarian insulin and insulin-like growth factor system with an emphasis on domestic animals

Insulin and insulin-like growth factors (IGFs) have direct effects on cultured ovarian cells. These effects include stimulation of granulosa cell mitogenesis, granulosa and luteal cell progesterone production, and thecal cell androgen production and appear similar among species. However, species differences exist with regard to insulin and IGF-I effects on granulosa cell estradiol production. In addition to endocrine effects of insulin and IGFs, IGFs are produced by granulosa, thecal, and luteal cells, allowing for an intraovarian autocrine and paracrine system. Granulosa, thecal, and luteal cells contain receptors for insulin and IGFs, and these receptors appear to mediate the effects of insulin and IGFs. Adding to the complexity of the regulatory role of IGFs is the presence of IGF-binding proteins (IGFBPs) within the ovary. These IGFBPs are produced by granulosa, thecal, and luteal cells, and their production is hormonally regulated. Evidence for a coherent mechanism by which insulin, IGFs, and IGFBPs interact and regulate ovarian function in vivo has yet to be found.

Serum hormones, follicular fluid steroids, insulin-like growth factors and their binding proteins, and ovarian IGF mRNA in sheep with different ovulation rates

Ovulation rate, serum hormone concentrations, follicular fluid (FFL) concentrations of steroids and IGF, IGF binding protein (IGFBP) activity in FFL, and follicular IGF-I and -II mRNA were compared during the follicular phase among five genotypes of ewes: Finn (F), Composite III (C), 1/2 Booroola Merino (B) x 1/2 F (B x F), 1/2 F x 1/2 C (F x C), 1/2 B x 1/2 C (B x C). Composite III ewes were a Columbia x Suffolk x Hampshire crossbred. Ovulation rates for F (n = 7), C (n = 5), B x F (n = 6), F x C (n = 3), and B x C (n = 8) ewes were 3.1, 1.6, 3.8, 2.9, and 2.9 (Pooled SEM = .5), respectively. Concentrations of IGF-I in FFL were 53% greater (P < .05) in large (> or = 4.1 mm) than in small (< 4.1 mm) follicles but did not differ (P > .10) among genotypes. In contrast, FFL IGF-II concentrations were greater (P < .05) in B x C and B x F ewes than in C or F x C ewes but did not differ between small and large follicles. Ligand blotting revealed that IGFBP activity of three species (34, 27 to 29, and 24 kDa) were lower (P < .05) in FFL of large than in FFL of small follicles but did not differ (P < .10) among genotypes. Follicular wall IGF-I mRNA and IGF-II mRNA was detected in 5 and 32% of the samples from preovulatory follicles, respectively, using reverse transcriptase-PCR and ethidiumbromide staining. Ovarian IGF-I mRNA levels, assessed by Northern analysis, in B x F and B x C ewes were greater (P < .05) than those in C ewes; ovarian IGF-I mRNA levels in F and F x C ewes were intermediate and did not differ (P > .10) from those in C ewes. Small follicles from B x C and B x F ewes had severalfold greater (P < .05) estradiol concentrations than those from F or C ewes, whereas large follicles from B x F ewes had twice (P < .05) the estradiol concentrations of follicles from F or C ewes. Progesterone in FFL did not differ among genotypes. Serum LH, FSH, inhibin, IGF-I, and progesterone did not differ (P > .10) among genotypes.(ABSTRACT TRUNCATED AT 400 WORDS)

Relationships among concentrations of steroids, insulin-like growth factor-I, and insulin-like growth factor binding proteins in ovarian follicular fluid of beef cattle

The relationship between ovarian follicular steroidogenesis and insulin-like growth factor binding protein (IGFBP) activity was evaluated during the follicular phase of the bovine estrous cycle. In experiment 1, follicles were collected from cyclic cows (n = 11) slaughtered at 48 h after administration of prostaglandin F2 alpha (PGF; 35 mg i.m.). In experiment 2, cows were injected twice daily with saline (control) or FSH (FSH cows; total dosage = 42 mg) from Day 2 to Day 6 (estrus = Day 0) and with PGF (35 mg i.m.) on Day 7; follicles were collected from control cows (n = 20) slaughtered at 0, 24, 48, or 72 h and from FSH cows (n = 8) at 0 and 48 h after PGF. Follicular fluid was assayed for estradiol (E2), androstenedione (A4), progesterone (P4), and insulin-like growth factor-I (IGF-I) by RIA and for IGFBP activity by ligand blotting and densitometry. Intensities of the 34-kDa (IGFBP-2), 29-27-kDa, and 22-kDa IGFBP bands in follicular fluid were nondetectable or were lower (p < 0.01) in the fluid of large (> or = 8 mm) E-active (E-A; E2 > 50 ng/ml and > P4) follicles than in large E-inactive (E-I), medium (5-7 mm), or small (< 5 mm) follicles. IGFBP-3 (44-40-kDa doublet) was unaffected by follicle stage in experiment 1, but IGFBP-3 was lower (p < 0.01) in follicular fluid of E-A vs. E-I large follicles in experiment 2. Profiles of IGFBP activity were similar in follicular fluid of small, medium, and E-I large follicles. In experiment 2, E2 concentrations in large E-A follicles increased (p < 0.01) from 0 to 48 h after the PGF injection for control cows but decreased (p < 0.01) for FSH cows, whereas follicular fluid IGFBP-2 binding activity decreased from 0 to 48 h after PGF in controls and increased in FSH cows (treatment x time, p < 0.05). IGFBP-3 binding was unaffected by FSH treatment or time after administration of PGF. Profiles of IGFBP activity in homogenates of granulosa or theca cells were similar to follicular fluid profiles except for the absence of IGFBP-3 binding activity. The disappearance of binding activities for IGFBP-2 and smaller-molecular-mass IGFBPs in E-A follicles suggests a possible regulatory role for IGFBPs in follicular maturation and on aromatase activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Follicular development and superovulation response in cows administered multiple FSH injections early in the estrous cycle

To determine whether follicular development, superovulation and embryo production were affected by the absence or presence of a dominant follicle, cows were administered injections of FSH twice daily in the early (Days 2 to 6, estrus=Day 0) or middle stage (beginning on Day 10 or 11) of the estrous cycle. Treatment with FSH early in the cycle stimulated follicular development in 83 to 100% of all cows from 4 groups evaluated at different times after PGF2alpha treatment on Days 6 and 7. However, the proportion of cows with >2 ovulations varied from 31 to 62.5%, indicating that induction of follicular development may occur in the absence of superovulation. When compared with cows treated in the middle of the cycle, no differences were observed in the proportion of cows with >2 ovulations (31 vs 20%), ovulation rate. (26.0+/-6.3 vs 49.6+/-25.8), production of ova/embryos (13.3+/-3.2 vs 14.4+/-3.4), or the number of transferable embryos (8.0+/-3.6 vs 5.4+/-1.5; early vs middle, respectively). The proportion of the total number of embryos collected that were suitable for transfer was greater (P<0.01) in cows treated early in the cycle (60%) than at midcycle (37.5%). The diameter of the largest follicle observed by ultra-sound prior to initiation of FSH treatment in the early stage of the cycle (10.0+/-2.0 mm) was smaller (P<0.05) than at midcycle (16.8+/-1.3 mm). These results demonstrate that superinduction of follicular development is highly consistent after FSH treatment at Days 2 to 6 of the cycle and that superovulation and embryo production are not less variable than when FSH is administered during the middle of the cycle. However, superovulation in the early stage of the cycle may increase the proportion of embryos suitable for transfer.

Administration of porcine somatotropin by a sustained-release implant: effect on follicular growth, concentrations of steroids and insulin-like growth factor I, and insulin-like growth factor binding protein activity in follicular fluid of control, lean, and obese gilts

Prepubertal gilts of control (n = 30), obese (n = 30), or lean (n = 29) genetic lines were implanted with no, one, or two implants of porcine somatotropin (pST, each delivers 2 mg/d) for 6 wk starting at 160 d of age to determine whether pST affects ovarian function. At 4 mg/d, pST increased (P < .01) numbers of 4.0- to 6.9-mm (medium) follicles but not (P > .10) numbers of 1.0- to 3.9-mm (small) follicles per gilt. Both doses of pST increased (P < .01) serum and follicular fluid (FFL) concentrations of IGF-I and activity of IGF binding protein (IGFBP)-3 and 36-kDa IGFBP in all three lines; IGFBP-3 was the predominant IGFBP. In comparison, binding activity of IGFBP-2 was decreased (P < .01) in serum by 4 mg of pST but increased (P < .05) in FFL by 4 mg of pST. Lean gilts had lower (P < .05) serum concentrations of IGF-I and less (P < .05) total binding activity of IGFBP than control and obese gilts. Concentrations of estradiol in FFL of small and medium follicles tended (P < .08) to be increased by 2 mg/d of pST, whereas FFL concentrations of progesterone were unaffected by pST. Obese and control gilts had twofold greater (P < .05) FFL progesterone concentrations than lean gilts. We conclude that sustained-release implants of pST can stimulate follicular growth, increase concentrations of IGF-I in serum and FFL, and increase IGFBP activity in serum of genetically divergent lines of gilts without an adverse effect on ovarian function.

In vitro production of estradiol by bovine granulosa cells: evaluation of culture condition, stage of follicular development, and location of cells within follicles

In vitro estradiol (E2) production by bovine granulosa cells was evaluated under several culture conditions, which included the presence or absence of fetal bovine serum (FBS; 2.5 and 10%), serum substitutes (1% Nutridoma [Boehringer-Mannheim, Indianapolis, IN], 2% UltroSer G [IBF Biotechnics, Villenue-la Garenne, France]), selenium (Se; 10 ng/ml), lipoprotein (0.25% Excyte/ml), O2 concentration (5 and 20%), and two attachment factors (Pronectin F and PepTite-2000). Dulbecco's Modified Eagle's medium:Ham's F-12 medium (1:1 mixture) containing 1 microM androstenedione, 1 microgram/ml insulin, and 0.1% BSA was the basal medium evaluated. The optimum conditions determined were the basal medium in 5% O2. These conditions were then used to ascertain whether or not E2 production by granulosa cells varied with respect to location of cells within a follicle. Follicular fluid was aspirated and centrifuged to obtain granulosa cells expected to be primarily luminal and cumulus cells. Follicles were then bisected, and remaining mural granulosa cells were removed by scraping the follicle wall with a fine plastic loop. Aspirated granulosa cells secreted more (p < 0.01) E2 than scraped cells. Production of E2 during Days 0 to 2 of culture by aspirated (0.15 +/- 0.05 ng/microgram DNA) and scraped (0.02 +/- 0.01 ng/microgram DNA) granulosa cells from small follicles (< 8 mm) was less than that by aspirated (6.30 +/- 2.20 ng/micrograms DNA) and scraped cells (1.90 +/- 1.00 ng/microgram DNA) from large follicles (> or = 8 mm). During Days 2 to 4 of culture when compared to Days 0 to 2, E2 production increased for aspirated (but not scraped) granulosa cells from small follicles (0.66 +/- 0.23 ng/microgram DNA)). In contrast, E2 production decreased (p < 0.05) over time in culture for aspirated (2.10 +/- 0.50 ng/microgram DNA) and scraped (0.16 +/- 0.07 ng/microgram DNA) granulosa cells from large follicles. Thus, granulosa cells proximal to the basement membrane may be less differentiated with regard to E2 production than cells distal to the basement membrane. In addition, aspirated granulosa cells from small follicles appear to continue to differentiate toward E2-producing cells during culture, a characteristic difficult to obtain with bovine granulosa cells.

Effects of insulin, insulin-like growth factor I, and gonadotropins on bovine granulosa cell proliferation, progesterone production, estradiol production, and(or) insulin-like growth factor I production in vitro

The objectives of the present studies were to determine the effect of insulin, insulin-like growth factor I (IGF-I), testosterone, and FSH on proliferation, progesterone production, and(or) estradiol production of bovine granulosa cells. In addition, existence of IGF-I mRNA in granulosa cells and in vitro IGF-I production by granulosa cells were assessed. Cells from small (1 to 5 mm) and large (> or = 8 mm) follicles were collected from cattle and cultured for either 3 or 4 d. When cells from small follicles were cultured, insulin (.1 to 10 micrograms/mL) and IGF-I (100 to 400 ng/mL) increased (P < .05) cell numbers compared with controls. Insulin alone or IGF-I alone increased (P < .05) progesterone production per cell by severalfold on d 4. In cells from both sizes of follicles, insulin (1 microgram/mL), in the presence of FSH, increased estradiol production per cell. In contrast, IGF-I (100 ng/mL) inhibited estradiol production by cells from small follicles and stimulated estradiol production by cells from large follicles. Insulin-like growth factor II (100 ng/mL) and insulin at higher doses (> or = 5 micrograms/mL) had no effect on estradiol production by cells from small and large follicles. Granulosa cells contained four IGF-I mRNA transcripts and produced IGF-I in vitro. These results support the hypothesis that insulin and IGF-I may have direct local effects on bovine ovarian function, and that these effects are influenced by dose and size of follicle.

Effect of porcine somatotropin on number of granulosa cell luteinizing hormone/human chorionic gonadotropin receptors, oocyte viability, and concentrations of steroids and insulin-like growth factors I and II in follicular fluid of lean and obese gilts

Prepubertal gilts of obese (n = 24) or lean (n = 24) genetic lines were injected (s.c.) daily with 0, 2, or 4 mg of porcine somatotropin (pST) for 6 wk starting at 160 d of age to determine whether pST affects follicular function. Blood and ovaries were collected at slaughter 24 h after the last injection. Surface follicles greater than or equal to 1.0 mm in diameter were counted, and pools of follicular fluid (FFL) and granulosa cells were collected from 1.0- to 3.9-mm (small) and 4.0- to 6.9-mm (medium) follicles. Oocytes were collected from small and medium follicles and evaluated for maturational stage and viability. Porcine somatotropin increased (P less than .08) the numbers of small but not the numbers of medium follicles per gilt (P greater than .10). Oocyte maturation and viability were not affected by pST or genetic line. Porcine somatotropin increased (P less than .05) concentrations of insulin-like growth factor I (IGF-I) in serum and FFL of both obese and lean gilts; IGF-I was lower (P less than .01) in lean gilts. Treatment with pST decreased (P less than .05) IGF-II in FFL of lean but not in that of obese gilts. Dose of pST and line had no effect on concentrations of progesterone in FFL of small or medium follicles or on concentrations of estradiol in FFL of small follicles.(ABSTRACT TRUNCATED AT 250 WORDS)

Fetal development in cattle with multiple ovulations

Treatment of lactating and nonlactating parous cows (n = 379) with 12 mg of FSH-P to evaluate development of multiple bovine fetuses resulted in ovulation rates ranging from 1 to 27 corpora lutea (CL). Fertilization rate (i.e., ova fertilized at 6 to 8 d postmating, 80.0%) was not affected by ovulation rate. The percentage of fetuses developing normally at 51 to 53 d postmating decreased (P less than .01) as ovulation rate increased; 1 CL, 100.0%; 2 CL, 100.0%; 3 CL, 66.7%; 4 CL, 45.8%; 5 CL, 33.3%; 6 to 10 CL, 13.6%; and greater than 10 CL, 8.9%. Of the 86 cows permitted to calve, 47 produced singles, 22 twins, 9 triplets, 7 quadruplets, and 1 quintuplets. Calf birth weight and gestational length decreased (P less than .01) as the number of calves born increased from one to two to three. Smaller decreases (P less than .05) in birth weight occurred among triplets, quadruplets, and quintuplets, whereas gestational length did not differ (P greater than .1) among these groups. Systemic progesterone concentrations in the dam were proportional (P less than .01) to the number of fetuses in utero between d 126 and 266 for dams gestating one, two, or three or more fetuses; estrone sulfate was lower (P less than .01) in dams with one than in those with two or more fetuses. Placental weight (i.e., cotyledons plus intercotyledonary membranes) per fetus at 52 +/- 1 d of gestation and at term decreased as the number of fetuses increased. The chorioallantoic membranes were often fused among multiple fetuses and contained either all viable or all dead fetuses, but not both, within the same anastomosed placental unit. These results suggest that ovulation rate is the first limiting factor to increasing cow productivity for beef cattle because some bovine females had the capacity to gestate up to three fetuses per uterine horn, or a total of five fetuses, above which pregnancy was terminated.

Prediction of breeding values for twinning rate and ovulation rate with a multiple trait, repeated records animal model

A genetic correlation near unity between ovulation rate in heifers and later twinning frequency led to consideration of using measures of ovulation rate in heifers for each estrous cycle, beginning at puberty, to increase accuracy of selection for twinning rate. An initial evaluation with a multiple trait animal model for predicting breeding values included six genetic groups: 1) selected Scandinavian bulls, 2) transfers from other populations at the Research Center to a twinning project, 3) early-purchased Holsteins, 4) late-purchased Holsteins, 5) early purchases-other breeds, and 6) late purchases-other breeds. For ovulation and twin measures, heritabilities of .100 and .070 and repeatabilities of .120 and .092 were assumed. Assumed phenotypic correlation between ovulation and twin measures of .08 was accounted for by genetic correlation of .89 and permanent environmental correlation of .19. The number of animals evaluated was 1,745; 6,912 estrous cycles were measured for ovulation rate on 840 heifers and 1,929 parturitions were observed for occurrence of twinning on 851 cows, of which 346 had ovulation rate measured as heifers. The remaining 400 animals were foundation animals that created relationships among those with records or were sires of animals with records. The Scandinavian genetic group effect was substantially greater than that of the others. Joint evaluations were compared to evaluations using only twinning measures. For animals with twin evaluations based only on parents but with ovulation rates measured, the multiple trait evaluation increased accuracy of evaluation from .62 (twin information only) to .81.(ABSTRACT TRUNCATED AT 250 WORDS)

Failure of embryos from bluetongue infected cattle to transmit virus to susceptible recipients or their offspring

Sixty heifers were infected with bluetongue virus (BTV) by the bites of the vector and by inoculation with insect origin virus. During the acute and convalescent stages of the infection, embryos were collected nonsurgically from these animals and washed according to the recommendations of the International Embryo Transfer Society (1). No BTV was isolated from 77 of these embryos when they were inoculated onto cell culture and into embryonating chicken eggs. There was no evidence of lateral BTV transmission when 231 of these embryos were transferred into susceptible recipients, nor was there evidence of vertical BTV transmission to the 88 calves resulting from these transfers. Another six donors that were assumed to have recovered from a natural infection of BTV, were added to the study to increase the probability of obtaining embryos from a persistently infected BTV carrier. However, it was determined later that these animals had not been infected with BTV but with the closely-related epizootic hemorrhagic disease virus (EHDV). Embryos were collected from these donors and washed as above. Neither BTV nor EHDV was isolated from 26 of these embryos by the inoculation of cell culture and embryonating chicken eggs. There was no evidence of lateral BTV or EHDV transmission to recipients of 15 of these embryos or of vertical BTV or EHDV transmission to the resulting 7 calves. However, two recipients of embryos from one of these donors developed antibodies to BTV 6 to 9 months after transfer. Passive antibodies to BTV were also detected in their calves. There is good evidence that these two recipients acquired BTV from natural exposure to infected insect vectors and not from the transferred embryos.

Ovulation rate and twinning rate in cattle: heritabilities and genetic correlation

Repeated measures of ovulation rate on puberal heifers should be an effective way to select for increased twinning rate. A reliable estimate of the genetic correlation between ovulation and twinning rates is needed to implement such selection and to predict its efficiency. Restricted maximum likelihood was used to estimate genetic correlations from subsets of data collected from the twinning project at the Roman L. Hruska U.S. Meat Animal Research Center. The animal model included numerator relationships among the animals and fixed effects of year-season of measurement, age at measurement, and birth group. Genetic correlations between averages of ovulation rates for three, four, five, six, seven, and eight estrous cycles and the occurrence of twins were, respectively, .62, .76, 1.00, 1.00, 1.00, and .98 based on observations on 200 to 325 puberal heifers. Corresponding phenotypic correlations ranged from .06 to .26. Genetic correlations between ovulation rate in a single estrous cycle and occurrence of twins were .38, .98, and .98, respectively, for 323, 430, and 283 cows with ovulation rate measured after measurement of twinning, in the same season as measurement of twinning, and more than 1 yr before measurement of twinning. Phenotypic correlations were .00, .07, and .00. Genetic and phenotypic correlations among ovulation rates at six consecutive estrous cycles averaged, respectively, .66 and .12 for 610 heifers. Heritabilities for ovulation rates in individual cycles averaged .16. No evidence of negative environmental covariance between ovulation rates in adjacent cycles was found. These results support the approach of indirectly selecting for twinning rate by measuring ovulation rates in estrous cycles of puberal heifers.

Superovulation and embryo quality in beef cows using PMSG and a monoclonal anti-PMSG

The long half-life of pregnant mare serum gonadotrophin (PMSG) reduces its application in the superovulation of cattle; thus, a monoclonal antibody to PMSG (anti-PMSG) was administered at the onset of estrus to increase the number of transferable embryos. Angus, Hereford and Angus x Hereford cows (n = 149) 3 to 9 yr old were assigned randomly to one of three dosages of PMSG (1500, 3000 or 6000 IU) with or without an equivalent dosage of anti-PMSG. Embryos were collected nonsurgically on Day 8 (estrus = Day 0), and all cows were ovariectomized on Day 9. The percentage of cows exhibiting estrus and ovulating decreased (P<0.05) with an increasing dosage of PMSG (82, 76 and 44% for 1500, 3000 and 6000 IU, respectively). Ovarian and total corpora lutea (CL) weight increased (P<0.001) linearly as PMSG dosage increased, but were reduced (P<0.001) curvilinearly by anti-PMSG, resulting in a PMSG by anti-PMSG interaction (P<0.001); the interaction was also significant (P<0.05) for ovulation rate (14.0 vs 14.3, 21.5 vs 24.4 and 29.2 vs 6.6 CL for 1500, 3000 and 6000 IU PMSG, without vs with anti-PMSG, respectively). Anti-PMSG increased (P<0.001) the number of small ovarian follicles (1 to 3 mm diameter) and decreased (P<0.001) the number of large follicles (>10 mm) at ovariectomy; the number of large follicles increased (P<0.001) with PMSG dosage. The number of total and transferable embryos recovered did not differ among PMSG and anti-PMSG dosages; however, the percentage of transferable embryos decreased (P<0.01) with increasing PMSG dosage. In general, neither PMSG dosage nor anti-PMSG influenced embryo quality.

Twinning in cattle: III. Effects of twinning on dystocia, reproductive traits, calf survival, calf growth and cow productivity

An evaluation of natural twinning in beef cattle revealed that cows birthing twins had shorter (P less than .01) gestation lengths, more (P less than .01) retained placentas, more (P less than .01) dystocia, more (P less than .01) days to estrus, lower (P less than .01) conception rates and more (P less than .01) days to pregnancy than cows birthing singles. Days to estrus, conception rate and days to pregnancy were not affected by number of calves reared (1 vs 2) in cows birthing twins. Survival at birth was greater (P less than .01) for single- than for twin-born calves, but twins and singles did not differ (P greater than .05) in postnatal survival. When dystocia was experienced, calf survival at birth was 95% vs 73% for singles vs twins compared with 99% vs 92% when no dystocia was experienced. Calves born twins were lighter (P less than .01) at birth, 100 d and 200 d, but twins and singles did not differ in postweaning gains. Total calf weights at 100 d per cow calving were 12% greater (P less than .01) in cows birthing twins vs singles when twin calves reared by foster dams were excluded. The potential increase in cow productivity for total calf weight at 100 d is 40% if calf survival rates of twins with dystocia relative to survival rates of twins without dystocia were comparable to survival rates of singles with and without dystocia, and if cows birthing twins were fed and managed to obtain conception rates equal to those of cows birthing singles. Identification of cows gestating twins to provide for their higher prepartum nutritive requirements and calving assistance at parturition is necessary to make twinning in cattle an economically viable technology.

Twinning in cattle: II. Genetic and environmental effects on ovulation rate in puberal heifers and postpartum cows and the effects of ovulation rate on embryonic survival

The potential of ovulation rate before 18 to 21 mo of age in puberal heifers as an indirect selection criterion for twinning rate was considered. Heritability (h2) was .07 +/- .03 for single observations and .34 +/- .18 for the mean of 7.9 estrous cycles per heifer. Estimated repeatability (r) of ovulation rate was less than or equal to h2, indicating negligible permanent environmental effects. Expected h2 for mean ovulation rate (assuming h2 = r = .07 for single observations) for increasing numbers of estrous cycles would be as follows: 4, .23; 6., 31; 8, .38; and 10, .43. About 50% of the heifers produced no multiple ovulations, but 27% produced multiple ovulations in more than 15% of their estrous cycles. Ovulation rate varied seasonally and increased about .01 per month of age (P less than .05). Genetic correlation of mean ovulation rate with adjusted 368-d weight was low (.08 +/- .32). Ovulation rate in postpartum cows was higher (P less than .05) in fall than in spring (1.15 vs 1.08). In postpartum cows, estimated h2 = .24 +/- .13 and r = .17. Mean ovulation rate for postpartum cows was 1.12 vs 1.09 in puberal heifers, accounting in part for the higher h2. Pregnancy rate was higher (P less than .05) in multiple- than in single-ovulating cows. Effects of ovulation rate on embryonic survival were small (P greater than .05). Unilateral and bilateral multiple ovulations were not different in embryonic survival. Accuracy of ovulation rate determination by palpation per rectum was lower in multiple- than in single-ovulating postpartum cows, because some unilateral multiple corpora lutea, especially, were recorded as singles. Results suggest that use of ovulation rate in puberal heifers should permit effective indirect selection for twinning rate among yearling heifers based on individual performance and among young sires based on ovulation rate of sibs and daughters.

Twinning in cattle: I. Foundation animals and genetic and environmental effects on twinning rate

Foundation cows were selected using prior records from one of two sources, private herds or other projects at the Research Center. Comparing twinning rates before and after selection, the repeatability was lower for those from the first (.08) than for those from the second (.16) source with a combined value of .12. Realized heritability of single-parity twinning rate estimated from selection of parents and response in daughters of foundation females was .06. Paternal half-sib estimate of heritability of twinning rate was .02 +/- .07. Estimates of repeatability computed from calving records of females born in the project indicate that permanent environmental effects on twinning rate in cattle are small. Mean calving rate of females born in the project was 1.11 in the data set that included all data and 1.09 in the data set that excluded females from highly selected parents. Twinning rate was greater (P less than .05) in fall than in spring calving (1.13 vs 1.06). Data on twinning rate of a sample of the Swedish Friesian breed were summarized. Mean twinning rate of the Swedish Friesian breed is 2.57%. Age adjusted mean twinning rate of daughters of 32 half-sib sons of one particular Swedish Frieisan sire averaged 5.4% and ranged from .9% to 13.6%. There was no indication of a bimodal distribution, which would be expected if a single gene with a major effect on twinning rate were segregating. The estimated genetic standard deviation (sigma-xn) for mean twinning rates of the 32 sire progeny groups was 1.8%. Observed range among son progenies was .127 or 7.2 sigma-xn, in reasonable agreement with the hypothesis that twinning rate in this population is inherited as a quantitative trait.

Concentrations of insulin-like growth factor-I in blood and ovarian follicular fluid of cattle selected for twins

Recent studies have implicated insulin-like growth factor I (IGF-I) as an intraovarian regulator of follicular growth and differentiation. Therefore, we investigated the possibility that cattle selected for twin births may have increased concentrations of IGF-I within the ovarian follicle and(or) in peripheral blood. The estrous cycles of 14 cows with histories of producing twins and 12 control monotocous cows were synchronized with 35 mg of prostaglandin F2 alpha (PGF2 alpha). Blood and follicular fluid were collected 48-50 h post-administration of PGF2 alpha (follicular phase of the estrous cycle). Concentrations of IGF-I were measured by RIA after acid-ethanol treatment of serum or follicular fluid. Twin-producing cows had a greater (p less than 0.05) number of large (greater than or equal to 4 mm) follicles and 47% greater (p less than 0.05) concentrations of IGF-I in peripheral blood than control cows. Cattle selected for high twinning frequency also had greater (p less than 0.05) concentrations of IGF-I (+/- SE) in the two largest follicles than control (unselected) cows (327 +/- 28 vs. 243 +/- 29 ng/ml). IGF-I concentrations in pooled small (1-3.9 mm) follicles were less (p less than 0.05) than in large follicles but did not differ between control and twin-producing cattle. In addition, the percentage of IGF-I concentrations measured in follicular fluid to that of serum was lower (p less than 0.05) in small follicles than in large follicles, and was greater (p less than 0.05) in large follicles of control (93.2 +/- 5.3%) than twin-producing (76.2 +/- 4.4%) cattle.(ABSTRACT TRUNCATED AT 250 WORDS)

Ovarian responses to intramuscular or intravenous administration of prostaglandin F2 alpha in control and FSH-treated beef heifers

Sixty Simmental crossbred heifers 18 to 20 mo of age were detected in estrus and assigned at random to a 2 x 2 factorial design study with 30 controls, and 30 given FSH. Half of each group was given prostaglandin F2 alpha (PGF) i.v. and the rest i.m. Injections of follicle-stimulating hormone were started on d 7 to 14 of an estrous cycle and continued for 5 d or until ovariectomy; PGF was administered either i.v. or i.m. at 48 (25 mg) and 60 (15 mg) h after the initial FSH injection. Control females received a similar PGF treatment on a day between d 9 and 15 of the estrous cycle. Blood samples were collected from all animals immediately before PGF administration and every 12 h thereafter until ovariectomy. Within each of the four experimental subgroups, ovariectomies were performed at either 24, 48 or 72 h (five/time group) after initial PGF injection. Ovarian and corpus luteum (CL) weights were recorded as well as number and size of follicles and number of ovulations. Regression of the CL was slower (P less than .05) after administration of PGF i.v. than i.m. (CL weight was 2.6 vs 3.3 +/- .2 g for i.m. and i.v. groups, respectively). Exogenous FSH increased estradiol-17 beta (E2) concentrations, and FSH-treated heifers had more (P less than .05) early ovulations than control heifers did. Ovulations in FSH-treated heifers had begun to occur by 24 h after i.v. and i.m. PGF injection.(ABSTRACT TRUNCATED AT 250 WORDS)

Exposure of bovine embryos to trypsin during washing does not decrease embryonic survival

The objective of this study was to assess whether the exposure of zona pellucida-intact bovine embryos to the proteolytic enzyme, trypsin, during embryo washing has a detrimental effect on their subsequent survival and development. Embryos were collected nonsurgically from superovulated cows (n = 19) 7.5 d after insemination. Grade 1 and Grade 2 embryos were washed 12 times in modified Dulbecco's phosphate buffered saline (PBS) containing 0.4% bovine serum albumin (BSA), or in a series of five washes in BSA-PBS (without Ca++ and Mg++), two in 0.25% trypsin in Hank's solution (without Ca++ and Mg++) and five in PBS-BSA medium. Within 30 min after washing, embryos were either transferred nonsurgically into recipient cows, 7 to 8 d post estrus, or cryopreserved and transferred later. Frozen-thawed embryos from five of the donors were cultured for 72 h in vitro and their development was evaluated. Pregnancy rates did not differ (P>0.1) between recipient cows receiving control-washed and trypsin-washed embryos transferred fresh (51.0 vs 56.3%). However, pregnancy rates were higher (P<0.05) for frozen-thawed embryos treated with trypsin before cryopreservation than for frozen-thawed, control-washed embryos (68.2 vs 38.5%). Survival and development of embryos in vitro after cryopreservation did not differ between embryos subjected to the control- and trypsin-wash procedures. These results suggest that exposure of bovine embryos to trypsin for 2 to 3 min during washing did not have a detrimental effect on embryonic development, but may have enhanced cryopreservation of the embryos.

The influence of the BoLA-A locus on reproductive traits in cattle

Associations between the major histocompatibility complex (MHC) and reproductive performance have been reported in humans, mice, rats, pigs and chickens. Only the A locus of the bovine major histocompatibility complex (BoLA-A) has been well characterized, and 42 alleles of this locus have been identified in American cattle. Four studies were conducted to examine the association between alleles of the BoLA-A locus and reproductive performance. Testis size, which is an indicator of early puberty and increased fertility in young bulls, was examined in 440 yearling bulls from nine breeds with a gene substitution model that included the effects of breed, sire, age of dam and age or weight of the bull. Estimated breeding value for twinning was examined with a gene substitution model with 204 cattle from a herd with a high frequency of twinning. Fertility of potential partners having BoLA-A locus alleles in common was examined in a prospective study involving 101 pure-bred Hereford cows mated by artificial insemination to four pure-bred Hereford bulls. The effect of homozygosity on birth weight, preweaning weight gain and post-weaning weight gain was estimated in a sample of 683 calves from nine breeds; 22% of the calves were apparently homozygous and 78% were heterozygous at the BoLA-A locus. There were significant and large effects of some BoLA-A locus alleles on paired testicular volume, but the analyses on the other traits did not show significant associations. Substitution of the W6.1 allele for the W9A allele reduced paired testicular volume by 150 +/- 44 cm3. The W6.1 allele has now been shown to influence a reproductive trait, a production trait and susceptibility to an economically important disease. Selection for these traits may influence the frequency of the large number of alleles at the BoLA-A locus.

Relationship between concentrations of immunoreactive insulin-like growth factor-I in follicular fluid and various biochemical markers of differentiation in bovine antral follicles

Three experiments were conducted to determine the relationship between concentrations of insulin-like growth factor-I (IGF-I) in ovarian follicular fluid and various biochemical markers of follicular differentiation in bovine follicles. In Experiment I, ovaries were removed on Days 7, 14, 28, 42, or 56 after parturition from a total of 21 cows. In Experiment II, ovaries of 31 cows were removed between Days 20 and 30 postpartum after 48 or 96 h of either saline (0.9% NaCl, 5 ml) or luteinizing hormone-releasing hormone (LHRH, 500 ng/5 ml saline) injections given every 2 h via jugular cannulae. In Experiment III, ovaries of six cows were removed 48-50 h after a 35-mg injection of prostaglandin F2 alpha during the midluteal phase of an estrous cycle. In Experiments I and II, all follicles greater than or equal to 8.0 mm in diameter were removed from each ovary (n = 33 and 46, respectively). In Experiment III, fluid from all follicles greater than 4 mm in diameter were removed individually (n = 10), and fluid from follicles 1-4 mm in diameter were pooled for each cow. Follicles for each experiment were further categorized as either estrogen-active (E-A, concentration of estradiol greater than progesterone in follicular fluid) or estrogen-inactive (E-I, concentration of progesterone greater than estradiol in follicular fluid). Measurements of immunoreactive IGF-I (i-IGF-I) were made after separating IGFs from their binding proteins with an acid-ethanol extraction.(ABSTRACT TRUNCATED AT 250 WORDS)