Effect of variability in response to superovulation on donor cow selection differentials in nucleus breeding schemes

Short communication: Greater intensity of estrous expression is associated with improved embryo viability from superovulated Holstein heifers

The aim of this study was to determine the association between estrous expression, measured using a breeding indicator and an automated activity monitor (AAM), and the success of embryo collection after superovulation. Holstein heifers (n = 51; 10.5 to 14.5 mo, and 325.0 ± 21.1 kg of body weight) were superovulated (n = 69 events) for the collection of embryos using a protocol based on sequential administration of FSH for follicle superstimulation and GnRH to induce ovulation. Artificial insemination (AI) was performed twice, once at the moment of GnRH administration and again 12 h later, using thawed, sexed semen. Ovaries were scanned via ultrasonography on the day of the first AI to count the total number of preovulatory follicles and 7 d later for the total number of corpora lutea present. Embryos were collected 7 d post-AI, counted, and assessed for viability. A breeding indicator (Estrotect, Rockway Inc., Spring Valley, WI) and a collar-mounted AAM (CowScout Activity Monitoring System, GEA, Dusseldorf, Germany) were used to measure standing mounts and an algorithmic estimate of estrous expression, respectively. A score for the breeding indicator was given as follows: score 1 = 100% of the indicator was intact; score 2 = 50% of the indicator was rubbed off; score 3 = greater than 50% of the indicator was rubbed off. Estrous expression detected by the AAM was quantified through the relative increase in physical activity and duration of time spent above a set threshold. Data were analyzed by ANOVA using the MIXED procedures of SAS (SAS Institute Inc., Cary, NC). The number of follicles present at AI was not affected by estrous expression. The mean (± SD) ovulatory response was 67.5 ± 26.3%. We found an effect of estrous expression as detected by the breeding indicator on the ovulatory response (42.1 ± 8.0, vs. 78.2 ± 9.0, vs. 74.0 ± 4.9%, for scores 1, 2, and 3, respectively) but not from the AAM. Heifers that had a score of 3 (versus those with scores of 1 and 2) on the breeding indicator had a greater number of embryos (4.1 ± 0.5, vs. 1.2 ± 1.0, vs. 1.8 ± 1.0 embryos), and a greater percentage of these embryos were viable (43.1 ± 0.05, vs. 35.5 ± 0.1, vs. 34.3 ± 0.1%). Similarly, heifers that showed a greater intensity of activity (as measured by the AAM) had a greater number of embryos collected (10.2 ± 1.2 vs. 6.0 ± 1.3 embryos), and a greater percentage of those embryos were viable (53.1 ± 5.0 vs. 23.4 ± 5.1%). Longer-duration estrus episodes were associated with a higher percentage of viable embryos (51.2 ± 5.2 vs. 25.3 ± 5.3%). In conclusion, stronger estrous intensity was associated with a greater number of total embryos collected and a greater percentage of viable embryos. These results suggest that monitoring the intensity of estrus could be used to predict superovulatory response as well as embryo quality in Holstein heifers.

Effect of the interval from follicle aspiration to initiation of lengthened FSH treatment on follicular superstimulatory and superovulatory responses and embryo production in lactating Simmental cows

The present study evaluated follicular superstimulatory (FSS) and superovulatory (SOV) responses and in vivo embryo production in lactating Simmental cows treated with FSH starting 1 or 2 days after follicle aspiration (FA). The performance of a lengthened superovulation program, named 6dFSH-P36-hCG60, is described. At random stages of the estrous cycle, cows (n = 52) were subjected to ultrasound-guided transvaginal aspiration of all follicles ≥ 5 mm. After FA, cows were randomly assigned to one of two groups in which FSH treatments started 1 or 2 days after FA (groups FA-1D and FA-2D, respectively). Cows were superstimulated with a total of 500 μg pFSH over 6 days on a decreasing dose schedule and were pre-treated with a single dose of 400 IU of eCG 24 h before the start of FSH treatments. Follicular superstimulatory (the mean numbers of follicles ≥ 8 mm on the day of hCG treatment) and SOV responses (the mean numbers of CL and cows with ≥ 3 CL at the time of collection) were similar in FA-1D and FA-2D groups. However, when compared to FA-1D group, the number of unfertilized ova tended to decrease (0.4 vs 1.7; P = 0.065) and percentage of fertilized ova tended to increase (95.8% vs 84.6%; P = 0.066) in FA-2D group. Moreover, the mean numbers and percentages of both transferable embryos (8.0 and 77.6% vs 6.4 and 57.7%) and freezable embryos (5.3 and 51.5% vs 3.5 and 31.1%) were numerically higher in FA-2D group than FA-1D group. The results of the study suggest that starting a lengthened superovulation programs in Simmental cows 2 days after FA has potential to increase percentage of fertilized ova and the number of transferable and freezable embryos, although new studies may be needed to confirm this findings.

Differential expression of LHCGR and its isoforms is associated to the variability in superovulation responses of Gir cattle

The aim of this study was to evaluate the pattern of expression of LHCGR isoforms in Gir heifers characterized as good (10.3 ± 1.2 ova/embryos per flush, n = 5) or poor responders (1.1 ± 0.3 ova/embryos per flush, n = 5) to superovulation protocols. In both groups, an adapted ultrasound-guided follicular aspiration system was used to collect granulosa cells from 8 mm follicles formed either during a synchronized, non-stimulated follicular wave (no stimulation control, NS) or on the fourth day of a superovulation protocol (SOV) induced with 200 IU of pFSH. The recovered follicular fluid was centrifuged and granulosa cells were washed with NaCl 0.9% and kept in RNAlater^®. RNA extraction was performed using a commercial RNeasy Micro Kit and eluted samples were quantified and reverse transcribed using the commercial Superscript III kit. cDNA samples were amplified by real-time PCR using a primer to target LH/hCG receptor gene - not selective for LHCGR isoforms (total LHCGR) - and four sets of isoforms selective primers (S1, S10, S10 + 11, and S11). Analyses were performed using the REST software and expression levels are shown as mean ± SEM. Under physiological conditions (NS), poor responders had a higher expression of total LHCGR (4.9 ± 1.7 fold-change, P < 0.01) as well as isoforms S10, S11 and S10 + 11, compared to good responders. In both phenotypes, superovulation down-regulated total LHCGR expression (-0.5 ± 0.2 and -0.9 ± 0.0 for good and poor responders, respectively; P < 0.05). However, in poor responders the exogenous FSH treatment up-regulated the S10 (2.4 ± 2.0; P < 0.05), S10 + 11 (3.8 ± 3.2; P < 0.01), and S1 isoforms (1.8 ± 1.3; P < 0.05), compared to good responders We conclude that down-regulation of total LHCGR, associated to up-regulation of their inactive isoforms, may have compromised follicle development and thus contributed to the low efficiency of superovulation in heifers with a poor responder phenotype.

Characterization of polymorphism in the FSH receptor gene and its impact on some reproductive indices in dairy cows

Follicle stimulating hormone (FSH) is released from the anterior pituitary gland and has an important role in female fertility. As FSH is a glycoprotein polypeptide hormone which cannot pass through the cell membrane, its influence on target cells must be mediated by the FSH receptor (FSHR). Accordingly, any kind of mutation in FSHR can affect reproduction in dairy cows. In this study, the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique was used for recognition of a point mutation (A/G: position -278) located in the FSHR gene in Iranian dairy cows. The association was evaluated of this mutation with reproductive performance. Blood samples were collected from 79 cows in a dairy farm in Iran and genotyped based on this single nucleotide polymorphism (SNP). The 5'-flanking regions of FSHR gene were successfully amplified and produced a fragment of 211bp in all cases. Three different patterns were, however, produced following restriction digestion with FaqI enzyme. The molecular results showed the existence of three different genotypes of AA, AG and GG among examined cows. In this study percentages of genotypes were 51.9%, 43.2% and 4.9% for AA, AG and GG genotypes, respectively. Allele frequencies were 73.5% and 26.5% for A and G, respectively. Results indicate that cows lacking allele G had desirable fertility in which a greater percentage (53.7%) of cows lacking Allele G (AA) had services per conception (SPC) of <2 in the previous lactation; while a lesser percentage of cows with Allele G (28.9%) had SPC of <2 (P<0.05). There was no difference in the days non-pregnant (DNP) and calving to first service interval among cows with these genotypes (P>0.05). Calving to first service interval was 69.9 ±12.3 in cows with Allele G and 74.73±13.9 in cows without Allele G (P>0.05). Percentage of cows with repeat breeder syndrome (SPC >3) was also 15.6% and 27.6% in cows without Allele G and with Allele G, respectively, but these values were not different (P>0.05). It can be concluded that the A to G mutation within the upstream region of FSHR gene (position -278) may affect some reproductive variables in Holstein dairy cows.

Embryo production in heifers with low or high dry matter intake submitted to superovulation

This study investigated the influence of feed intake on superovulatory response and embryo production of Nelore heifers. Pubertal heifers were kept in a feedlot and were submitted to the same diets, but with different levels of feed consumption: High (1.7 M; n = 20) or Low (0.7 M; n = 19) feed intake. Heifers in the 1.7 M treatment consumed 170% (2.6% of body weight [BW] in dry matter) and the 0.7 M heifers ate 70% (1.1% of BW in dry matter) of a maintenance diet. After 7 wk on these diets, heifers were treated with eight decreasing doses of follicle-stimulating hormone (FSH) given every 12 h, totaling 133 mg Folltropin (Folltropin-V; Bioniche Animal Health, Canada) per heifer. Seven d after AI, heifers had their uteri flushed and embryos were recovered and graded according to the International Embryo Technology Society standards. Data were analyzed using the GLIMMIX procedure of SAS and results are presented as least-squares means ± SEM (P < 0.05). At the onset of the FSH treatment (Day 0 of the protocol), 1.7 M heifers had greater body condition score (BCS), BW and serum insulin concentrations than 0.7 M heifers (4.1 ± 0.1 vs. 3.0 ± 0.1; 462.5 ± 10.1 vs. 382.7 ± 10.4 kg; and 14.3 ± 1.7 vs. 3.5 ± 0.8 μIU/mL, respectively). The 0.7 M heifers had more follicles ≥6 mm at the time of the last FSH (Day 7; 47.9 ± 6.4 vs. 23.5 ± 4.3 follicles), related to a better follicle superstimulatory response to FSH. Similarly, 0.7 M heifers had more corpora lutea at the time of embryo collection (33.6 ± 1.4 vs. 15.7 ± 0.9) than the 1.7 M heifers, which resulted in greater number of recovered embryos and ova (9.9 ± 0.7 vs. 6.7 ± 0.6) and viable embryos (5.3 ± 0.5 vs. 3.8 ± 0.4), despite having similar proportions of viable embryos (∼62%). A negative correlation between circulating insulin and follicle superstimulatory response to FSH was observed (r = -0.68). Therefore, we conclude that high feed intake, for a long period of time, compromised the superovulatory response and embryo production potential of Bos indicus heifers possibly related to the elevation in circulating insulin.

In vivo embryo production in cows superovulated 1 or 2 days after ovum pick-up

The present study evaluated superovulatory responses and in vivo embryo production in cows treated with FSH starting 1 or 2 days after ovum pick-up (OPU). Thirty-three non-lactating Nelore cows were subjected to aspiration of all follicles ≥3mm for OPU. After OPU, cows were randomly divided into two groups in which the follicle superstimulatory treatments with FSH started 1 or 2 days after OPU (Groups D1 and D2, respectively). Data are presented as the least squares mean±s.e.m. The number of follicles ≥3mm before OPU was similar between groups (~34); however, cows in Group D2 had more follicles ≥3mm on the first day of FSH (15.2±2.3 vs 7.6±1.7; P=0.04) and a higher ratio of the number of follicles at first FSH/number of follicles before OPU (0.41±0.04 vs 0.24±0.02; P=0.01). In addition, Group D2 cows had a greater superovulatory response than did cows in Group D1 (18.9±2.8 vs 9.1±1.9 corpora lutea, respectively; P<0.03). However, there was no difference in the total number of recovered ova and embryos from cows in Groups D2 and D1 (5.1±1.4 vs 4.9±1.3, respectively; P>0.10). Nevertheless Group D2 cows had more freezable embryos than Group D1 cows (3.2±1.1 vs 1.3±0.5, respectively; P<0.05). Cows from Group D2 had a much higher proportion (P<0.001) of follicles ≥8mm compared with follicles ≥6mm and <8mm at the time of the last treatment with FSH. In conclusion, to obtain a greater production of viable embryos in superovulated cows after OPU, it is recommended to wait at least 2 days before starting FSH treatment.

The use of increased female reproductive rates in dairy cattle breeding schemes

The effect of increased female reproductive rates on selection response, on efficiency of progeny testing and on the openness of the nucleus was investigated in open nucleus breeding plans. Conventional progeny testing plans and closed nucleus plans are special classes of open nucleus plans. In the open nucleus plans, generation intervals and selection across tiers were optimized. The number of offspring per elite dam was varied from 1 to 41, progeny testing of young bulls in the female base population was varied from 0 to 100 test records and the size of the nucleus was varied from 250 to 2000 young bulls born per year. Also efficiency of selection was varied: efficient selection in T(heoretical)-schemes and less efficient selection in P(ractical)-schemes. Especially, selection of base parents was less efficient i n P-schemes.

The deterministic prediction model took account of variance reduction due to selection and reduction of selection differentials due to correlations between estimated breeding values of relatives (order statistics). For closed nucleus plans, the results of the model were verified with Monte Carlo simulation results.

By increasing female reproductive rates, genetic gain increased by a factor 0·08 and 0·16 for the T- and P-schemes respectively. The nuclei in P-schemes were less open, due to the less efficient selection in the female base population. Schemes that were less open benefited more from increased female reproductive rates because selection differentials in small nuclei increased more than those in large base populations. The optimal open nucleus plan became less open with increasing female reproduction. Generally, progeny testing of bulls reduced genetic gain (by up to a factor 0·1) but it also reduced inbreeding rates. Progeny testing was more efficient in schemes that were less open: in P-schemes with 41 offspring per dam, progeny testing increased genetic gain. With many offspring per dam there were fewer full-sib families, causing lower selection differentials due to order statistics effects. This effect could be prevented by increasing the size of the nucleus.

Effects of female reproductive rate and mating design on genetic response and inbreeding in closed nucleus dairy herds

Hierarchical (each dam mated to one sire) and factorial (each dam mated to several sires) designs involving juvenile selection in a closed nucleus breeding programme were compared for rates of genetic response and inbreeding using stochastic simulation. Numbers of sires and dams selected and herd sizes varied. Generations were discrete. Sires and dams were selected at 15 months on the basis of an estimated breeding value (EBV) calculated using selection index which considered information on close relatives. Selection was for total merit index. Matings were carried out assuming use of multiple emulation and embryo transfer (MOET) or in vitro embryo production (1VEP) technologies, over a range of reproductive parameters. Reproductive rates assumed a fixed number of potential offspring per collection with IVEP and MOET. Comparison of mating designs using MOET showed that rates of genetic response and inbreeding with factorial designs voere from 88 to 431% and 36 to 111% of those with the hierarchical design. Generally rates of genetic response were increased and inbreeding decreased by increasing the number of mates per dam due to a reduction of correlations among EBV. Reduced rates of genetic response were occasionally observed in factorial designs involving the mating of dams to large numbers of sires. This increased the generation interval due to the time to carry out the matings. Factorial designs were found to be most efficient for increasing genetic response and or decreasing inbreeding, for breeding programmes involving the selection of equal numbers of sires and dam. For the breeding programmes considered, rates of genetic response with IVEP equalled the best of the MOET designs, achieved at highest MOET rates, at the lowest level of IVEP. But at the equivalent rate of genetic response, rate of inbreeding was increased by 8%. The increased rate of inbreeding was due to the shorter generation interval with IVEP, and the increased probability of selecting related individuals assuming all donors respond to IVEP.

Polymorphisms in the 5' upstream region of the FSH receptor gene, and their association with superovulation traits in Chinese Holstein cows

To identify a predictor to forecast superovulation response on the basis of associations between superovulation performance and gene polymorphism, variation in the bovine follicle stimulating hormone receptor (FSHR) gene was investigated using PCR-single-strand conformational (PCR-SSCP) and DNA sequencing. One single nucleotide polymorphism (SNP) of G-278A located in the 5' upstream region of bovine FSHR gene was found in 118 Chinese Holstein cows treated for superovulation. Two SNPs of G-278A (GU253337) and A-320T (rs43676359) were analyzed. In polymorphic locus -278, all cows without superovulation response were mutations with genotypes of CD and DD. Cows with CC genotype had a significant increase in the total number of ova (TNO) (P<0.01), and produced more transferable embryos (NTE) than those of the CD and DD genotypes (P<0.01). At this locus, the additive effects seemed to be highly significant (P<0.01) and allele C was associated with an increase in the TNO and NTE. These results indicated that the FSHR is a potential marker for superovulation response and can be used as a predictor for superovulation in Chinese Holstein cows.

Association between numbers of ovarian follicles in the first follicle wave and superovulatory response in ewes

The aim of this study was to examine the variability in the number of ovarian follicles in sheep and to determine if the average number of follicles per day influences the response to superovulation and resulting embryo quality. Ewes (n=83) were synchronized and the number of follicles (> or =2 mm diameter) in the ovaries were counted daily between Days 0 and 4 of the oestrous cycle using transrectal ultrasonography. Fourteen to 21 days later, 47 ewes were randomly chosen from the group and were treated with an intravaginal progestagen pessary for 12 days and superovulated with 1500 IU eCG administered as a single injection 10 days after sponge insertion. Ewes were mated and reproductive tracts were recovered after slaughter on Day 6 of pregnancy. The number of corpora lutea was counted, uterine horns were flushed and the morphology and developmental stage of the recovered oocytes/embryos was assessed. The mean daily number (+/-S.D.) (> or =2 mm diameter) of follicles per ewe was 8.5+/-2.8 (ranging between 3 and 16). After superovulation animals with few follicles (Low group: <8 follicles/day; n=21) had fewer (P<0.005) corpora lutea, total structures (unfertilized oocytes and embryos), good quality and total embryos compared to animals with many follicles (High group: > or =8 follicles/day; n=23). No difference was found in the proportion of good quality embryos (relative to the total number; Low 0.68+/-0.11 versus High 0.79+/-0.08; P=0.21) between the two groups, or the recovery rate, the number of unfertilized oocytes or the number of poor quality embryos per animal. We conclude that ewes with a higher number of follicles (> or =8) during the first follicular wave had a better superovulatory response (in terms of corpora lutea and high quality embryos) 2-3 weeks later; however, there was no relationship between the number of follicles and the proportion of good quality embryos per animal.

The Effect of Active Immunization against Inhibin on Gonadotropin Secretions and Follicular Dynamics during the Estrous Cycle in Cows

The hypothesis of the present study is that active immunization of cows against inhibin would neutralize endogenous inhibin, increase circulating levels of follicle stimulating hormone, and subsequently affect follicular dynamics and the ovulation rate during the estrous cycle. Thirteen cows were immunized against inhibin alpha-subunit and, 6 cows were immunized with a placebo. Both groups were given 4 booster immunizations 7, 14, 21, and 34 weeks after the primary injection. Ovaries were examined daily after the 2nd, 3rd, and 4th booster immunizations by transrectal ultrasonography for 25 days. After the 4th booster immunization, blood samples were collected daily for one complete estrous cycle to measure FSH and LH. The results showed that the immunized cows generated antibodies against inhibin, and that they had higher FSH levels compared with the controls. The number of follicular waves during the estrous cycle was higher in the immunized cows (3 or 4 waves) than in the controls (2 or 3 waves). Moreover, the immunized cows had a greater number of follicles during the estrous cycle compared with the control cows. The maximum number of follicles was 14.8 +/- 1.7 vs 5.4 +/- 0.2 in inhibin-immunized and control cows, respectively, during the first follicular wave and 13.9 +/- 1.9 vs 5.6 +/- 0.7, respectively, during the ovulatory wave. Multiple ovulations were increased in the immunized cows. However, the ovulation rate varied greatly in the immunized animals. In conclusion, immunization against inhibin increased FSH secretions during the estrous cycle in the cows. Moreover, the immunized cows had a greater number of follicular waves during the estrous cycle and a greater number of follicles, and this could be used as a potential source of oocytes for use in IVF/embryo transfer programs.

Seleção para produção de leite em núcleos MOET das raças zebuínas: um estudo de simulação

Um programa estocástico de seleção em núcleo MOET, esquema adulto, com geração discreta e população panmítica finita, foi simulado para uma característica influenciada por grande número de locos, mediante um modelo estocástico. Foram consideradas as herdabilidades de 0,25, 0,35 e 0,45 e a repetibilidade de 0,50. Os fatores utilizados na definição dos esquemas alternativos de núcleo MOET estudados foram: tamanho da população (N), estratégia de acasalamento (A), número de progênies MOET nascidas (P) e número de reprodutores selecionados por grupo de irmãos completos (R). Os tamanhos de população que constituíram a geração base do núcleo foram: 16 doadoras/8 reprodutores; 16 doadoras/4 reprodutores e 32 doadoras/4 reprodutores. Na estratégia hierárquica (H) de acasalamento, cada doadora foi acasalada com apenas um reprodutor, enquanto na estratégia fatorial de acasalamento, cada doadora foi acasalada com dois (F-I) ou quatro (F-II) reprodutores por geração. Considerou-se o nascimento de quatro ou oito progênies MOET por doadora a cada superovulação. O número de reprodutores selecionados foi limitado a um ou dois de cada grupo de irmãos completos. Para as três estratégias de acasalamento (H, F-I e F-II), foi utilizado o intervalo de gerações (IG) de 3,89 anos e, para a estratégia F-II, o IG de 4,15 anos. Todos os fatores utilizados na definição dos esquemas alternativos influenciaram (P<0,05) os resultados do ganho genético nas três herdabilidades consideradas. O efeito de algumas interações (N×A, N×R e P×A) também foi significativo (P<0,05). A interação A×R influenciou (P<0,05) apenas nas herdabilidades de 0,25 e 0,35. Para a taxa de endogamia, verificou-se influência (P<0,05) de todos os fatores estudados para as três herdabilidades. O efeito das interações N×P, N×A, N×R e P×A também foi significativo (P<0,05) sobre a taxa de endogamia. Verificou-se que a eficiência do MOET em produzir estruturas viáveis e prenhezes positivas, bem como o grau de redução no IG, constituem os principais aspectos responsáveis pela taxa de progresso genético nos esquemas de seleção em núcleos MOET.

Active immunization against inhibin improves superovulatory response to exogenous FSH in cattle

The effect of active immunization against inhibin on the response to superovulatory treatment by porcine FSH (pFSH) was investigated in cattle. Japanese black cows were sc injected with 1 mg of porcine inhibin alpha-subunit fragment (1-26) conjugated with rabbit serum albumin (inhibin-immunized group; n=14) or rabbit serum albumin alone (control group; n=12) in Freund's complete adjuvant. Booster injections (half the amount of the primary injection) were given 35 and 70 days after the primary injection. All cows were superovulated three times with pFSH. Three days after each injection of the antigen, a progesterone-releasing intravaginal device (CIDR-B) was inserted vaginally into all animals and left in place for 10 days. Forty-eight hours before CIDR-B removal, all animals were sc injected with 30 mg pFSH dissolved in 40% polyvinylpyrrolidone, and im injected with 750 microg of PGF2alpha at CIDR-B removal. Cows were artificially inseminated twice during estrus, and ova or embryos were collected 7 or 8 days after estrus. The number of corpora lutea, the number of ova or embryos and the number of transferable embryos in inhibin-immunized cows (12.1+/-1.2, 11.1+/-1.3 and 6.2+/-1.0, respectively) were significantly greater than those in the controls (8.2+/-1.0, 5.7+/-1.1 and 3.1+/-0.7, respectively). These results indicate that active immunization against inhibin enhanced ovarian response to the usual superovulatory treatment in cattle. Therefore, immunization against inhibin may be a useful approach for improving the response to superovulation in cattle.

A simple ultrasound test to predict the superstimulatory response in cattle

We tested the hypotheses that: (1) the superstimulatory response is related to the intrinsic number of follicles recruited into a follicular wave; and (2) the number of follicles recruited into a wave is correlated to the number of follicles recruited into the successive wave. A positive correlation will form the basis of a test for predicting the superstimulatory response. Cows (n = 141) were treated with estradiol and progesterone to synchronize follicular wave emergence (first synchronization) and ranked according to the number of follicles > or =2mm at wave emergence to select the upper and lower 10% of the herd. Follicular wave emergence was synchronized again in the high-end (n = 16) and low-end (n = 20) groups (second synchronization), and cows were treated with FSH twice daily for 3 days. High-end cows had a greater number of follicles (P < 0.001) than low-end cows at the time of wave emergence after both the first and second synchronizations in the 2-3 and 4-6mm categories. The numbers of 2-3 and 4-6mm follicles at wave emergence after the first and second synchronizations were positively correlated (P < 0.001; r = 0.77 and 0.71, respectively). Endogenous FSH peak at the time of wave emergence was higher in the low-end group than in the high-end group. Superstimulatory treatment resulted in more than double the number of follicles (P < 0.003) in the 5-7mm and > or =8mm categories in the high-end group than in the low-end group (16.8 +/- 2.2 versus 8.1 +/- 0.9 and 22.7 +/- 4.1 versus 9.7 +/- 1.6, respectively). The number of follicles > or =5 and > or =8mm at the end of superstimulation was positively correlated (P < 0.001) with the total number of follicles > or =2mm at the time of wave emergence after both the first (r = 0.64 and 0.54, respectively) and second ( r = 0.65 and 0.5, respectively) synchronizations. Based on the results of this study, the superstimulatory response can be predicted by the number of follicles > or =2mm at wave emergence. For practical purposes, practitioners can expect the number of follicles > or =5mm after ovarian superstimulation to be approximately 71% of the number of follicles > or =2mm at the time of wave emergence. Results validated the proposed simple ultrasound-based test for predicting the superstimulatory response of individual cows.

Estimates of pregnancy outcomes based on selection of bovine embryos produced in vivo or in vitro

The objective of this study was to estimate the degree of variation among experienced evaluators selecting in vivo- or in vitro-produced embryos for transfer and to determine how this affects both the proportion of recipients becoming pregnant after transfer, and the number of embryo transfers required per pregnancy. Data from 6 experienced evaluators who graded Day 7 embryos produced either in vivo (n = 15) or in vitro (n = 15) were used to estimate these effects. The evaluators viewed video recorded images of the embryos and classified each embryo for stage of development and quality grade (1 = excellent, 2 = good, 3 = fair, 4 = degenerated and nontransferable). The statistical model considered transfer of embryos of the following individual or combined grades: Grade 1 only, Grade 2 only, Grade 3 only, Grades 1 and 2, Grades 2 and 3, and Grades 1, 2 and 3. Probabilities of pregnancy after embryo transfer were based on pregnancy rates of recipients at the facility of 1 of the 6 evaluators where the percentages of heifers pregnant after the transfer of Grade 1, 2 and 3 embryos, by embryo source, were 76, 65 and 54% (in vivo), and 59, 45 and 30% (in vitro). Within most grades, the proportion of embryos selected for transfer differed (P < 0.05) among the 6 evaluators. Although no significant differences (P > 0.10) were found among evaluators in the proportion of recipients pregnant after transfer within any embryo grade, there was substantial variation among evaluators in the proportion of recipients becoming pregnant, especially for embryos produced in vitro. Estimated percentages of heifers becoming pregnant for embryos classified as Grade 1, 2 or 3 were 66 to 76, 62 to 69, and 54 to 60%, respectively, for in vivo-produced embryos; and, 39 to 59, 15 to 45, and 24 to 32%, respectively, for in vitro-produced embryos. Approximately twice as many transfers were needed per pregnancy for embryos produced in vitro as for those produced in vivo regardless of the grade.

Structure of breeding programs to capitalize on reproductive technology for genetic improvement

Potential rates of genetic progress are limited by biological constraints, which along with genetic parameters determine the structure of breeding programs to be employed for maximum genetic improvement. The objective here is to determine whether current progeny-testing programs in dairy cattle, which have been dictated and constrained by low female reproductive rates, need to be changed to capitalize on new reproductive technologies and how these changes should be implemented. Many differences between breeding programs diminish when selection on animal model genetic evaluations across all age and population groups is adopted as a strategy. Progeny-testing schemes then evolve toward dispersed open nucleus breeding schemes when multiple ovulation and embryo transfer is used on bull-dams. Nucleus breeding schemes have been advocated to capitalize on embryo transfer technology. In nucleus breeding schemes utilizing high reproductive rates, inbreeding, rather than reproductive rate, poses a limit to genetic progress, and strategies that maximize response to selection while limiting inbreeding need to be employed. One strategy is mating each dam to several sires rather than only one sire. In vitro embryo production techniques can be used to facilitate such mating strategies. Large-scale in vitro embryo production programs, in which large numbers of embryos per female are tested in the commercial population, offer the greatest potential for genetic gain with low rates of inbreeding. Cloning has an impact mainly on methods for dissemination of genetic improvement. Breeding herds, genetically inferior to marketed clones, are needed for continuous genetic gain. Reproductive technologies offer the potential for genetic improvement. Whether new breeding programs require changes in population structure, e.g., by creation of nucleus breeding herds, depends mainly on logistics and on quantity and quality of field information.