Role of the placenta in developmental programming: Observations from models using large animals

Developmental programming, which proposes that "insults" or "stressors" during intrauterine or postnatal development can have not only immediate but also long-term consequences for healthy and productivity, has emerged as a major biological principle, and based on studies in many animal species also seems to be a universal phenomenon. In eutherians, the placenta appears to be programmed during its development, which has consequences for fetal growth and development throughout pregnancy, and likewise has long-term consequences for postnatal development, leading to programming of organ function of the offspring even into adulthood. This review summarizes our current understanding of the placenta's role in developmental programming, the mechanisms involved, and the challenges remaining.

Effects of administration of a growth promoting implant during the suckling phase or at weaning on growth, reproduction, and ovarian development in replacement heifers grazing native range

Management strategies utilized during pre-breeding development of replacement heifers can impact fertility and the ovarian reserve. Angus-Hereford crossbred heifers (n = 233) were utilized over a three-year period to determine the effects of administration of a growth promoting implant at either branding or weaning on growth, reproduction, and ovarian development. Heifer calves were randomly assigned to one of three treatments: 1) non-implanted controls (CON; n = 79), 2) implanted at approximately 2 mo of age (average calf age = 58 d) with Synovex-C (BIMP, n = 82), or 3) implanted at approximately 7mo of age (average calf age = 210 d) with Synovex-C (WIMP; n = 72). In yr 2 and 3 a subset of heifers (yr 2 n = 16; yr 3 n = 14) were unilaterally ovariectomized. Heifers implanted at 2 mo of age were heavier at weaning, yearling (mid-February; average calf age = 332 d), and at the beginning of the breeding season (P < 0.01) compared to CON and WIMP heifers. Average daily gain (ADG) was similar among treatments from weaning to yearling and weaning to the start of the breeding season (P ≥ 0.61), however, WIMP heifers had increased (P = 0.05) ADG from yearling to the start of the breeding season compared to BIMP heifers. Antral follicle count and reproductive tract scores were not influenced by implant treatment (P ≥ 0.18). Response to synchronization of estrus was increased (P = 0.02) in WIMP compared to CON heifers, with BIMP heifers similar to all other treatments. First service conception rates tended to be increased (P = 0.09) in CON heifers compared to WIMP heifers, with BIMP heifers similar to CON and WIMP. Final pregnancy rates were similar (P = 0.54) among treatments. A treatment × yr interaction was detected (P = 0.01) for the number of primordial follicles/section with increased primordial follicles in WIMP heifers in yr 3 compared to BIMP and WIMP heifers in yr 2 and CON heifers in yr 3, as well as in BIMP compared to WIMP heifers in yr 2. Utilization of growth promoting implants did not negatively impact postweaning reproductive development or compromise pregnancy rates in beef heifers. Based on these results, administration of a growth promoting Synovex-C implant at 2 mo of age may allow for increased body weight at weaning, without hindering reproductive performance.

Review: Perspective on high-performing dairy cows and herds

Milk and dairy products provide highly sustainable concentrations of essential amino acids and other required nutrients for humans; however, amount of milk currently produced per dairy cow globally is inadequate to meet future needs. Higher performing dairy cows and herds produce more milk with less environmental impact per kg than lower performing cows and herds. In 2018, 15.4% of the world's dairy cows produced 45.4% of the world's dairy cow milk, reflecting the global contribution of high-performing cows and herds. In high-performing herds, genomic evaluations are utilized for multiple trait selection, welfare is monitored by remote sensing, rations are formulated at micronutrient levels, health care is focused on prevention and reproduction is managed with precision. Higher performing herds require more inputs and generate more waste products per cow, thus innovations in environmental management on such farms are essential for lowering environmental impacts. Our focus is to provide perspectives on technologies and practices that contribute most to sustainable production of milk from high-performing dairy cows and herds.

iTRAQ-based proteomic analysis of bovine pre-ovulatory plasma and follicular fluid

Bovine follicular fluid (FF) creates a unique microenvironment in follicles necessary for follicle growth, oocyte maturation, and estradiol (E2) production. The objective of this study was to analyze changes in proteins in FF and plasma (PL) from animals with high E2 (HE2) or low E2 (LE2) during the preovulatory period. Beef cows were synchronized, and follicular dynamics and ovulatory response were monitored using transrectal ultrasonography. Nine cows were selected and slaughtered, blood samples were collected at slaughter and FF was aspirated from dominant follicles (DF; >10 mm). Abundant proteins (albumin, IgG, IgA, and alpha-1-antitrypsin) were depleted from both PL and FF. Peptides were labeled with iTRAQ reagents and quantified using 2-dimentional liquid chromatography ESI-based mass spectrometry. Estradiol was associated with protein changes in PL and FF. Protein expression changes between FF HE2 and FF LE2 were greater than between PL HE2 and PL LE2. There were 15 up-regulated proteins and 10 down-regulated proteins in FF HE2 compared to FF LE2, and 7 proteins up-regulated and 9 proteins down-regulated in PL HE2 compared to PL LE2. Several of the differentially expressed proteins function in follicle development and were mainly categorized under cellular process and metabolic process. Pathway analysis identified the up- and down-regulated proteins were predominantly associated with the complement and coagulation cascades. The data demonstrate E2 regulates a wide range of reproductive associated proteins in bovine PL and FF and can provide the basis for further investigation of specific processes involved in such regulation.

iTRAQ-Based proteomic dataset for bovine pre-ovulatory plasma and follicular fluid containing high and low Estradiol

This is isobaric tags for a relative and absolute quantification (iTRAQ)-Based Proteomic Data on bovine plasma (PL) and follicular fluid (FF) containing high and low pre-ovulatory circulating concentration of estradiol (E2). The PL and FF were collected from nine beef cows that were identified to initiate a new follicular wave on day -4 during synchronization. Follicular dynamics and ovulatory response were monitored using transrectal ultrasonography. Blood samples were collected at slaughter and FF was aspirated from dominant follicles (DF; >10 mm). Estradiol concentrations in PL and FF were measured by radioimmunoassays. Plasma and FF were labeled as containing high E2 (PL HE2 and FF HE2) or low E2 (PL LE2 and FF LE2). Abundant proteins (albumin, IgG, IgA, and alpha-1-antitrypsin) were depleted from the four PL and FF samples. Peptides were labeled with iTRAQ reagents and analyzed using 2-dimentional liquid chromatography ESI-based mass spectrometry. Proteins were identified and quantified using SEQUEST^TM search engine embedded in Proteome Discoverer. The proteins matched with at least one unique peptide at minimum 95% confidence were considered positive identifications. Protein expression levels were determined by assigned fold change of >2.0 or <0.5 between any pair from the four sample types. The paired comparisons made were PL HE2 and PL LE2, FF HE2 and FF LE2, PL HE2 and FF HE2, and PL LE2 and FF LE2. Protein Analysis Through Evolutionary Relationships (PANTHER) and Database for Annotation, Visualization and Integrated Discovery (DAVID) were used to classify protein functions. This dataset includes the overview of workflow for identification and quantification of proteins and details on 231 proteins identified which includes 103 up- and down-regulate proteins. This dataset can be useful for further probing of the identified regulated proteins to better understand folliculogenesis and ovulation, particularly in bovine. This dataset is related to the article ‘iTRAQ-Based Proteomic Analysis of Bovine Pre-ovulatory Plasma and Follicular Fluid’ by P. A. Afedi, E. L. Larimore, R. A. Cushman, D. Raynie, G. A. Perry. Domestic Animal Endocrinology. https://doi.org/10.1016/j.domaniend.2021.106606

Invited review: Learning from the future-A vision for dairy farms and cows in 2067

The world's population will reach 10.4 billion in 2067, with 81% residing in Africa or Asia. Arable land available for food production will decrease to 0.15 ha per person. Temperature will increase in tropical and temperate zones, especially in the Northern Hemisphere, and this will push growing seasons and dairy farming away from arid areas and into more northern latitudes. Dairy consumption will increase because it provides essential nutrients more efficiently than many other agricultural systems. Dairy farming will become modernized in developing countries and milk production per cow will increase, doubling in countries with advanced dairying systems. Profitability of dairy farms will be the key to their sustainability. Genetic improvements will include emphasis on the coding genome and associated noncoding epigenome of cattle, and on microbiomes of dairy cattle and farmsteads. Farm sizes will increase and there will be greater lateral integration of housing and management of dairy cattle of different ages and production stages. Integrated sensors, robotics, and automation will replace much of the manual labor on farms. Managing the epigenome and microbiome will become part of routine herd management. Innovations in dairy facilities will improve the health of cows and permit expression of natural behaviors. Herds will be viewed as superorganisms, and studies of herds as observational units will lead to improvements in productivity, health, and well-being of dairy cattle, and improve the agroecology and sustainability of dairy farms. Dairy farmers in 2067 will meet the world's needs for essential nutrients by adopting technologies and practices that provide improved cow health and longevity, profitable dairy farms, and sustainable agriculture.

Anti-Müllerian hormone inhibits activation and growth of bovine ovarian follicles in vitro and is localized to growing follicles

STUDY QUESTION

Does anti-Müllerian hormone (AMH) inhibit activation (initiation of growth) of primordial follicles and attenuate the growth of primary follicles in cattle, an excellent animal model for human ovarian follicular development?

SUMMARY ANSWER

AMH inhibited activation of bovine primordial follicles and attenuated the growth of activated follicles in vitro.

WHAT IS KNOWN ALREADY

In mice null mutant for AMH, the pool of primordial follicles is depleted prematurely and AMH inhibits follicle activation in vitro. Results of studies with human ovarian tissue in vitro were inconsistent. Our previous work provided indirect evidence that AMH inhibits follicle activation in bovine ovaries.

STUDY DESIGN, SIZE, DURATION

Pieces of fetal bovine ovarian cortex (2 pieces/culture well), obtained during mid or late pregnancy, were cultured in control medium or with graded doses of AMH for 2, 10 or 12 days. Effects of treatment on follicle activation and growth were determined by histological morphometry; follicles in every 20th histological section were staged (primordial or primary), counted, and measured. In addition, AMH was immunolocalized in bovine ovaries obtained at various times during pregnancy (n = 20 ovaries).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Bovine fetal ovaries at mid or late gestation were obtained at a commercial abattoir. Pieces of ovarian cortex were cultured without or with AMH and fixed for histological morphometry on Day 0 and at the end of culture. Treatments were applied to duplicate cultures from each of two or three fetuses. In 12-day cultures, addition of AMH was delayed until the third day. Histological analysis provided information about the types, numbers and sizes of follicles in cortical pieces before and after treatments. Ovaries obtained during the second and third trimesters were assessed for the presence of AMH by immunohistochemistry.

MAIN RESULTS AND THE ROLE OF CHANCE

AMH (100-500 ng/ml) inhibited follicle activation in response to an activator (insulin) in ovarian cortical pieces from fetal ovaries in late gestation. Dose-dependent inhibitory effects on the diameters of primary follicles and their oocytes were also observed. These results were obtained only when AMH was added to cultures in advance of insulin (presumably because it penetrates tissue more slowly than insulin). Results of experiments with cortical pieces from fetal ovaries at mid-gestation, when follicles are forming, showed that AMH did not inhibit the formation of follicles. Immunohistochemical localization of AMH showed that it is not present in fetal ovaries until the third trimester, when it was localized to the granulosa cells of secondary and small antral follicles.

LIMITATIONS REASONS FOR CAUTION

The experiments were performed with fetal ovaries because follicles form and follicle activation begins during fetal life in cattle (as it does in humans), so fetal ovarian cortex of later gestation provides tissue rich in primordial follicles. We assume, but have no experimental evidence, that our findings also apply to post-natal ovaries.

WIDER IMPLICATIONS OF THE FINDINGS

Although circulating AMH is used as an indication of the follicular reserve in women, little is known about AMH in human ovaries. Cattle are an excellent non-primate model for human ovarian follicular development and, hence, the findings suggest similar roles for AMH in human follicular development.

LARGE SCALE DATA

Not applicable.

STUDY FUNDNG/COMPETING INTEREST(S)

This research was supported by National Research Initiative Competitive Grants no. 00-35203-9151, 2003-35203-13532, and 2008-35203-05989) from the U.S. Dept. of Agriculture's National Institute of Food and Agriculture to JEF and by an NIH National Research Service Award (F32 HD08264) to RAC. There are no conflicts of interest or competing interests.

144 EFFECT OF ANTRAL FOLLICLE COUNT IN BEEF HEIFERS ON IN VITRO FERTILIZATION/PRODUCTION

Our objective has been to compare the IVF and in vitro production (IVP) of embryos from low and high antral follicle count (AFC) heifers. This is the fourth year of the study with years 1 to 3 reported individually. For this report, we add data for the fourth year and present a combined analysis (years 1 to 4) for the first time. Each year, AFC was determined on ~120 Angus heifers using transrectal ultrasonography. Ten heifers with the lowest AFC and 10 heifers with the highest AFC and all with evidence of oestrous cyclicity were synchronized with two 5-mL injections of PGF2α 11 days apart. Half were harvested on Day 5 to 6 and half on Day 15 to 16 of the oestrous cycle. The IVF procedure was slightly modified each year. For year 4, the IVF procedure included protocols for semi-defined media and was as described (IVP Protocol, P. J. Hansen’s Laboratory, University of Florida). Cumulus-oocyte complexes (COC) from follicles less than 8 mm in diameter were cultured in maturation medium (5% CO2; 38.5°C) for 24 h. Matured COC were fertilized using thawed frozen semen from a bull that was purified using isolate. Motile spermatozoa were added to COC in fertilization medium at a final concentration of 1 × 106 spermatozoa per mL. About 24 h later, presumptive zygotes were placed in micro drops of development medium under oil, and cultured (5% CO2; 5% O2; balance N2; 38.5°C). On Day 3 and 8 after fertilization, cleavage and blastocyst development rates, respectively, were assessed. Data were analysed using the MIXED procedure of SAS (SAS Institute Inc., Cary, NC, USA) and the model included the effects of year (1 to 4), group (high or low AFC), and their interaction. The year × group interaction was not significant (P > 0.10). Low AFC heifers, compared with high AFC heifers, had fewer numbers of COC (P < 0.0001; 12.8 ± 1.83 v. 31.9 ± 1.86), fewer numbers of COC that cleaved (P < 0.0001; 8.0 ± 1.38 v. 21.6 ± 1.40), and fewer numbers of COC that developed to the blastocyst stage (P < 0.0001; 1.7 ± 0.58 v. 5.7 ± 0.58). Year affected the numbers of COC that cleaved (P < 0.003) and the numbers of COC that developed to the blastocyst stage (P < 0.0001). Year also influenced the percentage of COC that cleaved (P < 0.0002) and the percentage of COC that developed to blastocysts (P < 0.0001). Group (AFC) did not influence (P > 0.19) the percentage of COC that cleaved (61.2 ± 2.83 v. 66.4 ± 2.83%, for low v. high AFC, respectively). Low AFC heifers had a lower (P < 0.002) percentage of COC that developed to blastocysts (10.3 ± 1.52%) than high AFC heifers (17.6 ± 1.52%). These results indicate that high AFC heifers, compared to low AFC heifers, have more COC recovered, more COC cleaved, and more COC developed to the blastocyst stage. The percentage of COC cleaved did not differ between AFC groups; however, the percentage of COC that developed to the blastocyst stage was greater for high than low AFC heifers. This suggests a potential advantage in maternal to embryonic transition for high compared with low AFC heifers.

Litter-of-origin trait effects on gilt development

The preweaning litter environment of gilts can affect subsequent development. In a recent experiment designed to test the effects of diet on gilt development, litter-of-origin traits including individual birth weights, immunocrits (a measure of colostrum intake), sow parity, number weaned, and individual weaning weights were collected for approximately 1,200 gilts that were progeny of approximately 300 sows. Subsequently, BW, LM area, and backfat were measured at 100 d of age and at 28-d intervals until slaughter (260 d of age). From 160 d of age to slaughter, gilts were observed daily for estrus. At slaughter, the reproductive tract and 1 mammary gland were recovered. The reproductive tract was classified as cyclic or prepubertal; the number of corpora lutea was counted. Uterine horn lengths and ovarian dimensions were measured. Uterus and ovary samples from every 10th gilt were prepared for histological evaluation of uterine gland development and follicle counts, respectively. Mammary gland tissue protein and fat were assayed. Day of the estrous cycle at slaughter was calculated using the first day of the most recent standing estrus (d 0) recorded previous to slaughter. Each gilt development trait was analyzed for association with each litter-of-origin trait, after adjusting for dietary treatment effects. Uterine length, ovarian dimensions, mammary gland protein and fat, and uterine gland development were also adjusted for day of the estrous cycle at slaughter. All litter-of-origin traits were associated ( < 0.05) with growth traits. Top-down (backward elimination) multiple regression analysis indicated that BW and LM accretion in gilts was positively associated with immunocrit ( < 0.01), birth weight ( < 0.01), preweaning growth rate ( < 0.01), and parity ( < 0.01). Backfat accretion was positively associated with preweaning growth rate ( < 0.01), number weaned ( < 0.05), and parity ( < 0.05). Age at puberty was associated with birth weight (positive; < 0.01) and preweaning growth rate (negative; < 0.01). Total uterine length was positively associated with only birth weights ( < 0.05). Mammary gland protein was negatively associated with preweaning growth ( < 0.01). Mammary gland fat was positively associated with birth weight and number of piglets weaned ( > 0.05). These results indicate that colostrum consumption, birth weights, preweaning growth rate, number weaned, and parity are associated with gilt development traits during later life.

Changes in ovarian function associated with circulating concentrations of estradiol before a GnRH-induced ovulation in beef cows

These studies were conducted to evaluate causes for differences in circulating concentrations of estradiol before a GnRH-induced ovulation. Beef cows were synchronized by an injection of GnRH on day -7 and an injection of prostaglandin F2α (PGF2α) on day 0. In experiment 1, blood samples were collected every 3 h from PGF2α on day 0 to hour 33 after PGF2α and at slaughter (hour 36 to 42; n = 10). Cows were assigned to treatment group based on circulating concentrations of estradiol (E2): HighE2 vs LowE2. At slaughter, follicular fluid (FF) and granulosa cells were collected from the dominant follicle. In experiment 2, blood samples (n = 30) were collected every 8 h from PGF2α until the dominant follicle was aspirated via ultrasound-guided follicular aspiration to collect FF and granulosa cells (hour 38 to 46). In experiment 1, HighE2 had increased abundance of 3β-hydroxysteroid dehydrogenase, cytochrome P450 aromatase, and LHR (P ≤ 0.02), and greater concentrations of estradiol and androstenedione (P ≤ 0.02) in the FF. In experiment 2, HighE2 had increased abundance of CYP11A1, 3β-hydroxysteroid dehydrogenase, cytochrome P450 aromatase, and LHR (P ≤ 0.03) vs either LowE2 or GnRHLowE2. There was a tendency (P = 0.07) for LH pulse frequency to be increased in both the GnRHLowE2 and HighE2 compared with LowE2. HighE2 cows experienced increas in circulating concentrations of estradiol compared with LowE2. In conclusion, animals with greater concentrations of circulating estradiol before fixed-time AI experienced an upregulation of the steroidogenic pathway during the preovulatory period.

Estimates of epistatic and pleiotropic effects of () and () genetic markers on beef heifer performance traits enhanced by selection

Genetic marker effects and type of inheritance are estimated with poor precision when minor marker allele frequencies are low. A stable composite population (MARC II) was subjected to marker assisted selection for 2 yr to equalize and genetic marker frequencies to evaluate the epistatic and pleiotropic effects of these markers on BW, reproduction, and first calf performance traits in replacement beef females ( = 171) managed under 2 postweaning development protocols. Traits evaluated on the heifers were birth BW, weaning BW, 11-mo BW, 12-mo BW, 13-mo BW, first breeding season pregnancy evaluation BW, first calving season BW, 11-mo puberty, 12-mo puberty, 13-mo puberty, first breeding season pregnancy, and first calf weaning rate. Additionally, heifer's first calf performance traits of ordinal calving date, first calf birth BW, and first calf weaning BW (with and without age adjustment) were analyzed. Selection to increase minor allele frequencies and balanced sampling across genotype classes enhanced the ability to detect all genetic effects except dominance × dominance epistasis. The × genotype effect was significant ( < 0.05) for 11-mo BW and 12-mo BW and tended to be significant ( = 0.08) for 13-mo BW. Consistently, for all 3 traits, the most significant effect among epistatic × genotype effects was the additive effect, with the G allele decreasing BW. There were no associations between × genotype and fertility related traits ( ≥ 0.46) in this study. Additionally, there were no × genotype associations with first progeny performance traits ( ≥ 0.14). The large effect of the additive × additive interaction on first calf weaning BW was imprecisely estimated, which may warrant further investigation.

181 IN VITRO FERTILIZATION (IVF) USING SEMI-DEFINED CULTURE CONDITIONS FROM LOW OR HIGH ANTRAL FOLLICLE COUNT PUBERTAL BEEF HEIFERS

To compare the in vitro fertilization (IVF) and production (IVP) of embryos from low and high antral follicle count (AFC) heifers, AFC were determined on 106 heifers using transrectal ultrasonography. Ten heifers with the lowest AFC (avg. 13.2) and 10 heifers with the highest AFC (avg. 27.4) with evidence of oestrous cyclicity were synchronised with 2 injections of prostaglandin F2α (PGF2α); half were harvested on Days 5 to 6 and half on Days 15 to 16 of the oestrous cycle. The IVF procedures included protocols for semi-defined media and were as described (IVP Protocol, P. J. Hansen’s Laboratory, University of Florida, Gainesville, FL, USA). Cumulus-oocyte complexes (COC) from follicles less than 8 mm in diameter were cultured in maturation medium (5% CO2; 38.5°C) for 24 h. Matured COC were fertilised using thawed frozen semen from a crossbred bull that was purified using Percoll gradient separation procedures. Motile spermatozoa were added to COC in fertilization medium at a final concentration of 1 × 106 spermatozoa per mL. About 24 h later, presumptive zygotes were placed in microdrops of development medium under oil, and cultured (5% CO2, 5% O2, balance N2, 38.5°C). On Days 3 and 8 after fertilization, cleavage and blastocyst development rates, respectively, were assessed. Data were analysed using the mixed procedure of SAS (SAS Institute, Cary, NC, USA) and the model included the effects of collection day, group (high or low AFC), and their interaction. More COC (P < 0.0005) were collected from high than low AFC heifers (30.3 v. 9.3 ± 3.12 per heifer). Both the number and percentage of COC that cleaved had an interaction between collection day and group (P < 0.03). The interaction appeared to be due to low cleavage and development rates on 1 of 4 collection days (appeared not related to day of oestrous cycle). Although high compared to low AFC heifers had more COC that cleaved (18.7 v. 4.4 ± 1.84 per heifer), the percentage of cleaved COC did not differ (59.2 v. 49.8 ± 3.36%). There were no significant differences between high and low AFC heifers in the number of blastocysts (3.1 v. 0.6 ± 1.21 per heifer) or in the percentage of COC that developed to blastocysts (8.8 v. 5.2 ± 3.60%). In previous replicates (years), we reported that high AFC heifers had more COC collected, more COC that cleaved, and more COC that developed to blastocysts than low AFC heifers. In contrast, in this study numbers of COC that developed to blastocysts did not significantly differ between high and low AFC heifers. Additionally, the percentage of COC that cleaved, and that developed to blastocyst have been similar between high and low AFC heifers. Therefore, high compared to low AFC heifers may produce more IVP embryos; however, AFC does not appear to affect the competence of an oocyte to develop and mature to the blastocyst stage.

Relationship of follicle size and concentrations of estradiol among cows exhibiting or not exhibiting estrus during a fixed-time AI protocol

Cows exhibiting estrus near fixed-time artificial insemination (AI) had greater pregnancy success than cows not showing estrus. The objective of this study was to determine the relationship between follicle size and peak estradiol concentration between cows that did or did not exhibit estrus during a fixed-time AI protocol. Ovulation was synchronized in beef cows by applying the CO-Synch protocol [GnRH (100 μg) on day-9, prostaglandin F2α (PGF2α; 25 mg) on day-2, and a second injection of GnRH 48 h after PGF2α (day 0)] to both suckled (experiment 1) and nonsuckled (experiment 2) cows. Follicle size (day 0) and ovulation (day 2) was determined by ultrasonography. Blood samples were collected every 3 or 4 h beginning at the time of PGF2α injection (0 h). Estrus was detected by visual observation with the aid of estrus-detection patches, and cows that ovulated were classified as exhibited estrus (n = 46) or did not exhibit estrus (n = 63). In both suckled and nonsuckled cows, there was a positive relationship between all cows (P < 0.05) and among those that exhibited estrus (P < 0.05) between follicle size and peak estradiol concentration, but no linear relationship (P > 0.50) between follicle size and peak estradiol concentration was observed among cows not exhibiting estrus. Cows that exhibited estrus had greater (P < 0.01) peak estradiol concentrations than cows that did not exhibit estrus. Suckled cows exhibiting standing estrus had greater (P < 0.001) preovulatory concentrations of estradiol beginning 6 h (replicate 1) or 4 h (replicate 2) after the injection of PGF2α on day-2 compared with cows not exhibiting standing estrus. Nonsuckled cows exhibiting standing estrus had greater (P < 0.001) preovulatory concentrations of estradiol beginning at the injection of PGF2α on day-2 compared with cows not exhibiting standing estrus. Furthermore, cows that exhibited estrus had an increased (P < 0.01) rate in the rise in concentrations of estradiol following the PGF2α to peak estradiol than cows not exhibiting estrus. In summary, follicle diameter had a positive relationship with peak concentrations of estradiol, but only among cows that exhibited standing estrus, and estradiol increased earlier in cows that exhibited estrus compared with cows that did not.

142 EFFECT OF HIGH AND LOW ANTRAL FOLLICLE COUNT IN PUBERTAL BEEF HEIFERS ON IVF

Pubertal heifers can be classified between those with high (n = 25) or low (n = 15) antral follicle counts (AFC). The objective of this study was to determine oocyte development and maturation (e.g. fertility) in an IVF system for high- and low-AFC heifers. From a pool of 120 heifers, 10 high- and 10 low-AFC heifers were determined by transrectal ultrasonography; all heifers with evidence of oestrous cyclicity (i.e. pubertal) were synchronized with two 5-mL injections of prostaglandin F2α 11 days apart. Heifers were euthanized over 4 days on Days 15 to 16 of the synchronized oestrous cycle. A total of 15 heifers (n = 7 high and n = 8 low AFC) were at the appropriate stage of the oestrous cycle. Ovaries were collected and transported to the laboratory. Follicles less than 8 mm in diameter were aspirated. The IVF procedures and media were as previously described (Miles et al. 2004. Biol. Reprod. 71, 1919–1926). Cumulus-oocyte complexes (COC) were identified and washed in oocyte collection medium and then in maturation medium and were cultured (5% CO2; 38.5°C) for 24 h. Following maturation, COC were transferred and washed in fertilization medium. Thawed frozen semen from a crossbred bull was subjected to the swim-up procedure. Motile spermatozoa were collected and added to COC to yield a final concentration of spermatozoa per milliliter of fertilization medium. About 24 h later, presumptive zygotes were washed in development medium, placed in microdrops of development medium, and cultured for 8 days. On Days 3 and 8 after fertilization, cleavage and blastocyst development, respectively, were assessed. Data were analysed using the Proc Mixed procedure of SAS (SAS Institute Inc., Cary, NC, USA) and the model included the effects of day of collection (n = 4), group (n = 7 high- or n = 8 low-AFC heifers), and the interaction. The interaction did not differ (P = 0.10). Day of collection influenced (P < 0.05) the number of COC and the number of oocytes cleaved. High- compared to low-AFC heifers had the greater (P < 0.05) numbers of COC (42.7 ± 4.66 v. 22.1 ± 4.59), oocytes that cleaved (28.1 ± 3.60 v. 15.9 ± 3.55), and developed to blastocysts (13.2 ± 1.71 v. 6.2 ± 1.69). However, there was no difference (P > 0.10) in the percentage of COC that cleaved (65.3 ± 5.58 v. 66.2 ± 5.50%, high v. low, respectively) or that developed to blastocysts (46.7 ± 6.75 v. 42.2 ± 6.65%). In conclusion, AFC did not appear to affect oocyte maturation and development through the blastocyst stage.

Heifer calving date positively influences calf weaning weights through six parturitions

Longevity and lifetime productivity are important factors influencing profitability for the cow-calf producer. Heifers that conceive earlier in the breeding season will calve earlier in the calving season and have a longer interval to rebreeding. Calves born earlier in the calving season will also be older and heavier at weaning. Longevity data were collected on 2,195 heifers from producers in South Dakota Integrated Resource Management groups. Longevity and weaning weight data were collected on 16,549 individual heifers at the U.S. Meat Animal Research Center (USMARC). Data were limited to heifers that conceived during their first breeding season. Heifers were grouped into 21-d calving periods. Heifers were determined to have left the herd when they were diagnosed not pregnant at the end of the breeding season. Heifers that left the herd for reasons other than reproductive failure were censored from the data. Heifers that calved with their first calf during the first 21-d period of the calving season had increased (P < 0.01) longevity compared with heifers that calved in the second 21-d period, or later. Average longevity for South Dakota heifers that calved in the first or later period was 5.1 ± 0.1 and 3.9 ± 0.1 yr, respectively. Average longevity for USMARC heifers that calved in the first, second, or third period was 8.2 ± 0.3, 7.6 ± 0.5, and 7.2 ± 0.1 yr, respectively. Calving period as a heifer influenced (P < 0.01) unadjusted weaning BW of the first 6 calves. Estimated postpartum interval to conception as a 2-yr-old cow was greater for females that calved in the first period as heifers but did not differ between heifer calving periods in subsequent calving seasons. In summary, heifers that calved early in the calving season with their first calf had increased longevity and kilograms weaned, compared with heifers that calved later in the calving season.

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.

Contributions of the maternal uterine environment and piglet genotype on weaning survivability potential: I. Development of neonatal piglets after reciprocal embryo transfers between Meishan and White crossbred gilts

In commercial pigs, the greatest susceptibility for pre-weaning mortality occurs in low birth-weight piglets. Despite their overall decreased birth weight, Meishan (MS) piglets have decreased pre-weaning mortality rates compared with contemporary Western breeds. The objective of the current study was to determine the contributions of the maternal uterine environment, piglet genotype, and their interaction on the development of neonatal piglets pertaining to pre-weaning survivability using reciprocal embryo transfer between MS and White crossbred (WC) pigs. Twenty-five successful pregnancies were produced from 2 farrowing seasons, generating litters of maternal uterine environment (MUE) by piglet genotype (PigG) combinations; MS × MS (n = 4 litters), MS × WC (n = 7 litters), WC × MS (n = 7 litters), and WC × WC (n = 7 litters). At approximately 24 h of age (Day 1), piglets (n = 173) were weighed and a blood sample was taken. Hematocrit, hemoglobin, glucose, plasma urea nitrogen, albumin, NEFA, lactate, and cortisol were measured in all blood samples. Representative piglets (n = 46) from each litter were harvested and body measurements (i.e., organ weights, tissue glycogen content, and body composition) were determined. Piglet data were analyzed by ANOVA using MIXED model procedures. Both MUE (P < 0.001) and PigG (P < 0.01) affected piglet BW, illustrating that piglets gestated in WC gilts were heavier than piglets gestated in MS gilts, and WC piglets were heavier than MS piglets. Serum albumin concentrations were increased (P < 0.05) in MS piglets compared with WC piglets, indicating greater liver maturity. Significant MUE × PigG interactions were observed for hematocrit and hemoglobin, in which the greatest concentrations were observed in MS piglets gestated in MS and WC gilts, and the lowest concentrations were observed in WC piglets gestated in WC gilts, demonstrating increased oxygen-carrying capability. The percentage of fat and nitrogen, as well as the GE of the body, were greater (P < 0.05) in MS piglets, indicating greater energy stores. Liver, bicep femoris, and LM glycogen concentrations were greater (P < 0.01) in WC piglets compared with MS piglets, demonstrating increased glycogen catabolism in MS piglets. This study demonstrated limited interactions between the maternal uterine environment and piglet genotype on weaning survivability potential, suggesting that the MS piglet is a viable model for pre-weaning survivability.

Physiology and Endocrinology Symposium: How single nucleotide polymorphism chips will advance our knowledge of factors controlling puberty and aid in selecting replacement beef females

The promise of genomic selection is accurate prediction of the genetic potential of animals from their genotypes. Simple DNA tests might replace low-accuracy predictions for expensive or lowly heritable measures of puberty and fertility based on performance and pedigree. Knowing with some certainty which DNA variants (e.g., SNP) affect puberty and fertility is the best way to fulfill the promise. Several SNP from the BovineSNP50 assay have tentatively been associated with reproductive traits including age at puberty, antral follicle count, and pregnancy observed on different sets of heifers. However, sample sizes are too small and SNP density is too sparse to definitively determine genomic regions harboring causal variants affecting reproductive success. Additionally, associations between individual SNP and similar phenotypes are inconsistent across data sets, and genomic predictions do not appear to be globally applicable to cattle of different breeds. Discrepancies may be a result of different QTL segregating in the sampled populations, differences in linkage disequilibrium (LD) patterns such that the same SNP are not correlated with the same QTL, and spurious correlations with phenotype. Several approaches can be used independently or in combination to improve detection of genomic factors affecting heifer puberty and fertility. Larger samples and denser SNP will increase power to detect real associations with SNP having more consistent LD with underlying QTL. Meta-analysis combining results from different studies can also be used to effectively increase sample size. High-density genotyping with heifers pooled by pregnancy status or early and late puberty can be a cost-effective means to sample large numbers. Networks of genes, implicated by associations with multiple traits correlated with puberty and fertility, could provide insight into the complex nature of these traits, especially if corroborated by functional annotation, established gene interaction pathways, and transcript expression. Example analyses are provided to demonstrate how integrating information about gene function and regulation with statistical associations from whole-genome SNP genotyping assays might enhance knowledge of genomic mechanisms affecting puberty and fertility, enabling reliable DNA tests to guide heifer selection decisions.

148 PIGLET GROWTH AND BLOOD COMPONENTS DURING LACTATION FOLLOWING RECIPROCAL EMBRYO TRANSFER BETWEEN MEISHAN AND WHITE CROSSBRED GILTS

Sow productivity has a significant economic impact on the swine industry and is influenced by several factors, including preweaning piglet mortality. In Western breeds, low birth weight piglets exhibit the greatest susceptibility to preweaning mortality. In contrast, Meishan (MS) piglets have decreased birth weights but lower preweaning mortality rates, suggesting that birth weight is not the sole component of preweaning survival. The objective of the current study was to determine the contributions of the maternal and piglet breed and their interactions on piglet growth and blood components pertaining to survivability during lactation following reciprocal embryo transfer between MS and White crossbred (WC) gilts. Twenty-five successful pregnancies were produced by embryo transfer in 2 farrowing seasons that represented all maternal and piglet breed combinations; MS × MS (n = 4 litters), MS × WC (n = 7 litters), WC × MS (n = 7 litters), and WC × WC (n = 7 litters). At Day 1, 10, and weaning (average weaning age = 18 days), piglets (n = 147, 97, and 94, respectively at Day 1, 10, and weaning) were weighed and blood samples were taken. Hematocrit, hemoglobin, glucose, nitrogen, nonesterified fatty acids, albumin, and cortisol were measured in all blood samples. All data were analysed for ANOVA using mixed model procedures. Piglet weights were greater (P < 0.001) throughout lactation in piglets from WC dams regardless of piglet breed. As a result, average daily gains from Days 1 to 10 and weaning were greater (P < 0.05) in piglets from WC dams. There were significant (P < 0.001) maternal × piglet × day interactions for hematocrit and hemoglobin levels in which levels were greatest at Day 1 in MS piglets from WC dams and at Day 10 in MS piglets from MS dams but decreased in WC piglets from WC dams at Day 1. Glucose was greater (P < 0.05) at Day 1 in piglets from WC dams regardless of piglet breed but was greater (P < 0.05) at weaning in WC piglets regardless of maternal breed. Nitrogen was similar at Day 1 for all maternal and piglet breed combinations, but at Day 10 and weaning, nitrogen levels were greater (P < 0.001) in MS piglets regardless of maternal breed. Nonesterified fatty acid was greater throughout lactation in piglets from MS dams irrespective of piglet breed. Albumin was greater (P < 0.05) in MS piglets throughout lactation regardless of maternal breed. Cortisol was not different between the maternal and piglet breed combinations throughout lactation, but cortisol was greater (P < 0.001) at Day 1 compared with Day 10 and weaning. This study demonstrated that piglet growth during lactation was influenced more by maternal breed in favor of WC dams, which supports previous crossbreeding studies. However, blood components pertaining to survivability displayed complex interactions between the piglet and maternal breed, which may signify possible mechanisms for improved preweaning survivability of MS pigs.

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.

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.