Genetic partitioning of variation in ovulatory follicle size and probability of pregnancy in beef cattle

The objectives of this research were to partition variation in ovulatory follicle size into genetic and nongenetic components and to assess the utility of ovulatory follicle size as an indicator trait associated with reproductive success in beef cattle. Data were collected during the years 2002 to 2005 from 780 beef females that ranged in age from 1 to 12 yr (mean of 2.4 observations per female). Data were analyzed with a multiple trait Gibbs sampler for animal models to make Bayesian inferences from flat priors. A chain of 500,000 Gibbs samples was thinned to every 200th sample to produce a posterior distribution composed of 2,500 samples. Heritability estimates (posterior mean +/- SD) were 0.16 +/- 0.03 for follicle size and 0.07 +/- 0.02 and 0.02 +/- 0.01 for pregnancy rate as a trait of the female and service sire, respectively. Posterior means of genetic correlations were all <0.10, with 0.00 contained within the respective 90% probability density posterior intervals. Results indicate that whereas follicle size is of greater heritability than pregnancy rate, its usefulness to improve reproductive rate is greatest as an ancillary phenotype in multiple trait selection.     

Effect of ovulatory follicle size and expression of estrus on progesterone secretion in beef cows

Induced ovulation of small dominant follicles (SF, < 12 mm; CO-Synch protocol) in postpartum beef cows resulted in formation of corpora lutea (CL) that exhibited a delayed rise in progesterone (P4) compared with CL from large dominant follicles (LF, > 12 mm). Experiment 1 characterized P4 concentrations from ovulation to subsequent estrus among GnRH-induced or spontaneously ovulated SF (or= 12 mm) to determine if P4 secretion by CL formed from GnRH-induced SF remains lower postovulation in nonlactating beef cows. Nonlactating beef cows were induced to ovulate 48 h after PGF(2alpha) (CO-Synch; GnRH on d - 9, PGF(2alpha) on d - 2, and GnRH on d 0) or exhibited estrus and spontaneously ovulated after PGF(2alpha). Follicle size was measured at the second GnRH in cows induced to ovulate or approximately 3 h after the onset of estrus for cows that ovulated spontaneously. Cows were classified into 1 of 4 groups: 1) GnRH-induced ovulation-SF (or= 12 mm; Ind-LF; n = 16); 3) spontaneous ovulation-SF (or= 12 mm; Spon-LF; n = 22). Serum concentrations of P4 from d 3 to 15 were reduced in the Ind-SF compared with the Ind-LF (P = 0.05), Spon-SF (P = 0.07), and Spon-LF (P = 0.03). Experiment 2 characterized P4 concentrations (0 to 60 d postAI) among GnRH-induced or spontaneously ovulated SF (or= 13 mm) to determine if P4 secretion by CL formed from GnRH-induced SF remained lower during early gestation. Ovulation was induced with GnRH 48 h after PGF(2) (CO-Synch) or occurred spontaneously, and ovulatory follicle size was measured at AI. Lactating cows were classified into 1 of 3 groups: 1) GnRH-induced ovulation-SF (or= 13 mm; Ind-LF; n = 43); or 3) spontaneous ovulation-LF (>or= 13 mm; Spon-LF; n = 27). The increase in P4 concentrations was greater (P = 0.06) in pregnant (d 2 to 12) compared with nonpregnant cows. Also, the increase in P4 from d 2 to 12 was greater (P = 0.01) in the Ind-LF compared with the Ind-SF groups, but there was no difference (P = 0.94) among groups in P4 from d 14 to 60 in pregnant cows. Follicle size at AI influenced the increase in P4 in cows that failed to conceive (P = 0.007), but not among cows that became pregnant (P = 0.32) to AI. In summary, P4 secretion after GnRH-induced ovulation of SF was decreased from d 2 to 12 compared with that of LF, but was similar among pregnant cows from d 14 to 60 postAI (d 0).     

Effect of duration of dominance of the ovulatory follicle on onset of estrus and fertility in heifers.

In cattle, prolonged progestogen treatments following luteolysis result in persistent dominant follicles (DF) that are associated with precise onset of estrus but marked reductions in pregnancy rate (PR). The aim was to determine whether increasing duration of dominance of the ovulatory follicle in heifers affected 1) precision of onset of estrus and 2) the timing and nature of the decline in PR. In Exp. 1, duration of dominance of the ovulatory follicle was controlled by causing corpus luteum (CL) regression at emergence of the second follicle wave (mean duration of dominance of 2.1+/-.3 d, Dm2, n = 11) or first day of dominance of the second DF of the cycle; the latter was combined with insertion of a 3-mg norgestomet ear implant for 2 to 10 d to maintain the second DF for 4 (Dm4, n = 32), 6 (Dm6, n = 19), 8 (Dm8, n = 49), 10 (Dm10, n = 28), or 12 d (Dm12, n = 20). Heifers detected in estrus were inseminated approximately 12 h later with frozen-thawed semen. Durations of dominance of the ovulatory follicle of up to 8 d did not affect (P>.05) PR (Dm2 8/9, Dm4 19/28, Dm6 14/18, and Dm8 34/48 heifers pregnant), but PR in Dm10 heifers (12/23 heifers pregnant) was reduced (P = .05) compared with Dm2 heifers; PR in Dm12 heifers (2/17 pregnant) was less compared with all other treatments (P<.01). Fitting a logistic regression model to the pooled PR data to examine the trend in PR showed that extending the duration of dominance from 2 to 9 d and from 10 to 12 d resulted in a predicted decline in PR of 10 to 25% and a further decline of 35 to 75%, respectively. Onset of estrus was delayed in heifers assigned to Dm4 treatment relative to all other treatments (P<.001); it was less variable than that for heifers on Dm6, Dm8, and Dm10 treatments (P<.1). In Exp. 2, heifers received a PGF2alpha analogue and a norgestomet implant on d 12 of the cycle for 3 or 7 d to give approximate durations of dominance of the preovulatory follicle of 2 to 4 d (Dm2-4, n = 29) or 6 to 8 d (Dm6-8, n = 24), respectively. The PR did not differ (P>.05) between heifers on Dm2-4 (22/29) and Dm6-8 (15/24) treatments, but the interval to onset of estrus was delayed (P<.05) by 7 h in the Dm2-4 heifers. In conclusion, restricting the duration of dominance of the preovulatory follicle to < or =4 d at estrus, results in a precise onset of estrus and a high PR following a single AI at a detected estrus.     

Influence of the length of progestagen treatment and the time of oestradiol benzoate application on the ovulatory follicle size and ovulation time in anoestrous and cyclic beef cows

Previous research from our laboratory in beef cattle suggests that the pre-ovulatory follicle size, maturity and subsequent susceptibility to gonadotropin are influenced by the length of progestagen treatment in artificial insemination programme in beef cows. To test this hypothesis, two experiments were conducted. In experiment 1, 35 anoestrous beef cows received an intravaginal sponge containing 200 mg of medroxyprogesterone acetate. The treatment lasted for 7 (n = 12), 8 (n = 11) or 9 (n = 12) days. Half of the animals in each group were injected with 0.7 mg of oestradiol benzoate (EB) at device removal (0 h) and the other half 24 h later. In experiment 2, 38 cycling beef cows were treated with the same protocols as in experiment 1. Ultrasound examinations were performed to determine the follicular diameter at device removal (dominant follicle), interval to ovulation and ovulatory follicle diameter. The dominant follicle of anoestrous cows with progestagen for 7 days (8.4 ± 1.6 mm) resulted smaller (p < 0.05) than the cows treated for 8 (10.5 ± 1.6 mm) and 9 days (10.6 ± 1.2 mm). However, regardless of the length of the treatments, ovulation time after device removal was longer (p < 0.05) when EB was injected 24 h after withdrawal than at 0 h in anoestrous cows (EB0 = 52.7 ± 4.0 h; EB24 = 70.8 ± 6.2 h) and in cyclic cows (EB0 = 50.0 ± 21.0 h; EB24 = 73.0 ± 20.0 h). In anoestrous cows, the treatment with progestagen for 9 days and EB at 24 h increased the diameter of the ovarian follicle (p = 0.033) but did not affect the diameter of the ovulatory follicle in cyclic cows. In conclusion, increasing the length of progestagen treatment for 8 or 9 days compared to 7 days increased the diameter of the dominant follicle, in anoestrous and cyclic beef cows. Oestradiol benzoate administered at device removal resulted in a shorter interval from device removal to ovulation compared with EB injection 24 h after the end of a progestagen treatment.     

The effect of pregnancy on visceral growth and energy use in beef heifers

Beef heifers (24 mo; 378 +/- 32 kg of BW; 22 pregnant, PR; 17 nonpregnant, NP) were grouped in common pens and fed corn silage- and hay-based diets formulated to provide an ADG of 0.45 kg in NP heifers. Both PR and NP heifers were slaughtered on d 40, 120, 200, and 270 of the study. Intestinal and hepatic tissues were analyzed for protein, DNA, RNA (mg/g of fresh tissue), and in vitro oxygen use. Jejunal samples were analyzed for cellular proliferation via immunohistochemical analysis. For ileum, DNA, which provides an estimate of cell number per unit of tissue, revealed an interaction (P = 0.06) between pregnancy and slaughter day; both PR and NP decreased with time, but NP increased on d 270 (P = 0.09). Cell number in the ileum was reduced at d 200 and 270 in the PR heifers (P < 0.09). Liver protein concentration was less (P = 0.07) in PR than in NP heifers (NP = 291.1 vs. PR = 210.5 +/- 33.9 mg/g). Hepatic protein:DNA ratio was not affected (P > 0.10) by pregnancy or day. Energy use (kcal/d) of duodenum and jejunum, calculated from in vitro oxygen consumption, increased linearly (P < 0.02) with time for both PR and NP. Pregnant and NP ileal energy use increased linearly (P < 0.01), but ileal energy use by PR was less throughout gestation (P = 0.07) than ileal energy use by NP. Cellular proliferation in the crypt region of the jejunum was decreased on d 120 and 200 (P < 0.02). These data indicate that the small intestine and liver of PR heifers may conserve energy expenditure compared with NP heifers. Energy conservation can partially be explained by differences in growth and cell proliferation and by energy use of the liver and small intestine.     

The vaginal and fecal microbiomes are related to pregnancy status in beef heifers

Background: The greatest impact on profitability of a commercial beef operation is reproduction. However, in beef heifers, little is known about the vaginal and fecal microbiota with respect to their relationship with fertility. To this end, we followed heifers through gestation to examine the dynamics of vaginal and fecal microbial composition throughout pregnancy.Results: Heifers were exposed to an estrus synchronization protocol, observed over a 12-day period, artificially inseminated 12 h to 18 h after observed estrus, and subsequently exposed to bulls for a 50-day breeding season.Vaginal samples were taken at pre-breeding(n = 72), during the first(n = 72), and second trimester(n = 72) for all individuals, and third trimester for individuals with confirmed pregnancies(n = 56). Fecal samples were taken at prebreeding(n = 32) and during the first trimester(n = 32), including bred and open individuals. Next generation sequencing of the V4 region of the 16 S rRNA gene via the Illumina Mi Seq platform was applied to all samples.Shannon indices and the number of observed bacterial features were the same in fecal samples. However,significant differences in vaginal microbiome diversity between gestation stages were observed. No differences in beta-diversity were detected in vaginal or fecal samples regarding pregnancy status, but such differences were seen with fecal microbiome over time. Random Forest was developed to identify predictors of pregnancy status in vaginal(e.g., Histophilus, Clostridiaceae, Campylobacter) and fecal(e.g., Bacteroidales, Dorea) samples.Conclusions: Our study shows that bovine vaginal and fecal microbiome could be used as biomarkers of bovine reproduction. Further experiments are needed to validate these biomarkers and to examine their roles in a female's ability to establish pregnancy.     

Evaluation of the factors that affect the pregnancy rates during embryo transfer in beef heifers

The aim of this study was to evaluate the effects of the transfer side, transfer location, cervix transfer score, type and diameter of corpus luteum (CL) during embryo transfer on pregnancy rates in beef heifers. Progesterone-based synchronization and superovulation protocol were applied to Simmental cows used as donors (n = 168). Uterine flushings were performed on day 7 following artificial insemination. Obtained Code I (excellent or good) and II (fair) quality embryos were transferred to recipient beef heifers (n = 561). During embryo transfer, side of transfer (right or left), transfer location (the cranial or middle third of uterine horn), cervix transfer score (easy, moderate or difficult) and type (CLa, CLb and CLc) and diameter of CL were determined. Pregnancy rates following the transfer of Code I and II embryos were 44.66% and 33.07%, respectively (p < .05). The rates of pregnancy after transfers to the right and left uterine horn were 37% and 42.2%, respectively (p > .05). The pregnancy rates were 41.2%, 34.9% and 30.3% for cervix transfer scores as easy, moderate and difficult, respectively (p > .05). Pregnancy rates after transfer to the cranial third and middle third were 41.06% and 29.67%, respectively (p < .05). According to types of CL, pregnancy rates were 31.7%, 40.4% and 45.3% for CLa, CLb and CLc, respectively (p < .05). Moreover, it was found that as the CL diameter increased, the pregnancy rates increased. As a result, it was concluded that there was no effect of side of transfer and cervix transfer score, but embryo quality, transfer location, type and diameter of CL had significant effects on the pregnancy rate during embryo transfer in beef heifers.     

Nonpuberal estrus in beef heifers

The frequency of occurrence of behavioral estrus without subsequent development of functional luteal tissue (termed nonpuberal estrus, NPE), was determined in 43 Simmental X Hereford-Brahman heifers. Blood samples were collected weekly from the start of the study to first behavioral estrus and then daily from d 1 (d 0 = estrus) through d 14 following first and subsequently observed estrous behaviors. All blood samples were analyzed for serum progesterone (P4) concentrations by radioimmunoassay. More heifers (62.8%) exhibited NPE than had luteal development after their first behavioral estrus (37.2%). There was a tendency for fewer light-weight heifers (less than or equal to 240 kg at the start of the experiment) to exhibit a puberal first estrus compared with the heavy-weight (greater than 240 kg at the start of the experiment) heifers (31.2% vs 68.8%, respectively; P = .12). Heifers that had a puberal first estrus were older (376 +/- 12 d vs 334 +/- 9 d, P less than .05) compared with heifers that had NPE. Weight at first behavioral estrus was similar between heifers that had a puberal first estrus and those that had NPE (298 +/- 8 kg and 289 +/- 6 kg, respectively). More heifers that had a puberal first estrus also had an elevation in serum P4 concentrations before that first estrus (64.3% vs 20.0%, P less than .05), and the serum P4 elevation was greater (2.5 +/- .4 ng vs 1.2 +/- .1 ng, P less than .05) than heifers that had NPE. We have concluded from these results that NPE is a common occurrence in heifers approaching puberty.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of acute nutritional change on follicle wave turnover, gonadotropin, and steroid concentration in beef heifers

The effects of acute nutritional change on endocrine and ovarian characteristics were studied in cyclic (intact; n = 20) and long-term ovariectomized (ovx; n = 18) heifers being fed 1.2 x maintenance (1.2M). On d 7 of an 8-d progesterone and estradiol treatment, intact and ovx heifers were randomly allocated to diets providing .4, 1.2, or 2.0M until emergence of the second follicular wave after ovulation in intact heifers. In intact heifers, two of eight fed .4M failed to ovulate. In the other six, growth rate and maximum diameter (1.1+/-.09 mm/d and 10.1+/-.7 mm, respectively) of the first dominant follicle (DF) postovulation were less (P<.05) than in heifers fed either 1.2 (1.6+/-.18 mm/d; 12.9+/-.44 mm) or 2.0M (1.6+/-.08 mm/d; 12.7+/-.7 mm). In intact heifers, LH pulse frequency and amplitude were not affected by diet (P>.10). In ovx heifers, the frequency of LH pulses was unaffected by diet (P>.10), but heifers fed .4M had a greater pulse amplitude (P<.05) and mean concentration of LH (P<.001) than those fed 1.2 or 2.0M. Plasma concentrations of FSH were greater (P<.05) in ovx heifers fed .4M than in those fed 1.2 or 2.0M and increased linearly with time (P<.01). The FSH concentrations in heifers fed 1.2 and 2.0M were similar (P>.10) and decreased linearly with time (P<.001). In intact heifers, concentrations of FSH preceding follicle wave emergence were greater in heifers fed .4M (P<.001), but basal concentrations were not affected (P>.10). Concentrations of progesterone and estradiol were unaffected by diet (P>.10). Significant diet x ovarian status interactions in plasma IGF-I concentrations existed. Plasma concentrations of insulin increased as the level of nutrition increased, whereas concentrations of NEFA decreased. In conclusion, growth rate and maximum diameter of the DF were decreased by acute nutritional restriction, without affecting the concentration of LH. The magnitude of the FSH increase preceding new follicle wave emergence increased following dietary restriction, but concentrations of FSH were unaffected during the other stages of DF growth. The results of this study may have important implications for the feeding strategies adapted for high-yielding dairy cows in the early postpartum period when feed intake is often physiologically restricted.     

Energy metabolism in lactating beef heifers

To obtain measurements of energy balance in lactating beef cows, respiration calorimetry and digestion trials were conducted using seven lactating (613 kg BW) and three nonlactating (598 kg BW) Hereford x Angus heifers fed a pelleted 75% alfalfa:25% concentrate diet. Five measurements of energy balance were obtained at 6- to 7-wk intervals beginning 6 to 10 wk postpartum in lactating heifers and at 6-wk intervals in nonlactating heifers. Milk yield was measured using a combination of weigh-suckle-weigh and machine milking to adapt heifers to milking by machine without the use of oxytocin. Heifers were milked only by machine during measurements of energy balance. Weekly milk yield averages ranged from 8.2 kg/d at wk 5 postpartum to 3.2 kg/d at wk 32 postpartum. When scaled to BW(.75), the regression of NE1 on ME intake and the regression of ME intake on NE1 were remarkably similar to previously published regressions for measurements obtained from lactating Holstein-Friesian cows. The average daily maintenance energy requirement from these regressions was 503 kJ ME/kg BW(.75), a value similar to the average value reported previously for lactating Holstein-Friesian cows (488 kJ/kg (BW.75)). This is in contrast to numerous published comparisons of the maintenance requirements of cattle breed types in the nonlactating state and current NRC standards for estimating maintenance energy requirements of beef and dairy cattle. The results of the present study suggest that when expressed on the basis of BW(.75) the efficiency of utilization of incremental ME above maintenance for milk and tissue energy (i.e., NE1) is similar among lactating Hereford x Angus heifers and lactating Holstein-Friesian cows. The breeds differ in terms of their propensity for milk yield and the resulting partition of ME between milk synthesis and tissue energy retention.     

Relationship between ovarian weight and follicular population in heifers

The size of the ovary varies substantially among cattle. This variation may influence the potential of the ovary to produce follicles. In the present study, we examined whether a relationship exists between the weight of the ovary and the number of antral follicles >or=1 mm. Paired ovaries were obtained from Holstein x Japanese Black F1 heifers. Follicles were classified into three size categories (small: 1.0-<5.0 mm, medium: 5.0-<8.5 mm and large: >or=8.5 mm), and the number of follicles in each category was recorded. Large variations in the weight of ovaries and the number of follicles were observed among animals. Significant positive correlations (r>or=0.4, P<0.001) were found between the weight of intact ovaries and the number of follicles in all three categories for the ovary contralateral to CL (OCC) and in the small follicles for the ovary ipsilateral to CL (OIC). Significant positive correlations (r>0.4, P<0.0001) were also observed between the weight of ovaries devoid of CL and follicles and the number of small and medium follicles in both OIC and OCC, indicating that the correlation is not due to the increase in ovarian weight associated with the increase in follicular number. Paired ovaries contained a similar number of small and medium follicles, and significant positive correlations were observed between them (r>0.6, P<0.0001). There were significant positive correlations between the weight of OCC and the number of small and medium follicles in paired ovaries (r>0.4, P<0.0001). These results suggest that 1) the weight of an ovary reflects the potential of the ovary to produce antral follicles, and 2) a rough estimation of follicular population might be possible by using the weight of the ovary contralateral to CL in heifers.     

Serum copper concentrations in beef cows and heifers

OBJECTIVE: To characterize serum copper status of cows and heifers in beef cow-calf herds throughout the United States and to evaluate use of copper supplements in those herds. DESIGN: Cross-sectional survey. ANIMALS: 2,007 cows and heifers from 256 herds in 18 states. PROCEDURES: Producers participating in a health and management survey conducted as part of the National Animal Health Monitoring System voluntarily allowed serum samples to be obtained from cows and heifers for determination of copper concentration. Results were categorized as deficient, marginally deficient, or adequate. The proportion of cattle and herds (on the basis of mean value of the tested cattle) in each category was determined. Copper concentrations were compared between herds that reportedly used copper supplements and those that did not. RESULTS: Overall, 34 of 2,007 (1.7%) cows and heifers were deficient in copper, and 781 (38.9%) were marginally deficient. In each region, at least a third of the cattle were deficient or marginally deficient. For herds, 92 of 256 (35.9%) were marginally deficient, and 22 (0.8%) were deficient. Approximately half of the producers reported use of copper supplements, but a sizeable proportion of those producers' cattle and herds were classified as marginally deficient or deficient. CONCLUSIONS AND CLINICAL RELEVANCE: Copper deficiency is not restricted to a single geographic region of the United States. Copper deficiency can persist despite reported use of supplements by producers. Veterinarians dealing with beef cow-calf herds that have problems consistent with copper deficiency should not rule out copper deficiency solely on the basis of geographic region or reported use of copper supplements for the herd.     

Comparative study of mammary gland development and differentiation between beef and dairy heifers

Sixteen Hereford and 16 Holstein heifers were used to study the relationship of milk production potential to mammary development and differentiation. Heifers were slaughtered 150, 180, and 260 days of first gestation and at 49 days of first lactation. Prolactin binding capacity of mammary tissue was 2.5 fold higher in dairy than beef heifers at day 260 of gestation (27.2 vs 11.0 fmols/mg protein). In both breeds, maximal growth hormone binding in liver coincided with the beginning of the rapid phase of mammary growth at 180 days. Mammary tissue from dairy heifers released more casein and alpha-lactalbumin during in vitro incubations than tissue from beef heifers. No differences were observed between breeds with respect to incorporation of [¹⁴C]acetate into lipids. Mass of dairy mammary tissue at 49 days of lactation was 3.3 times greater (16.4 vs 4.9 kg) and produced 5.7 times more milk (20.3 vs 3.5 kg/day) than its beef counterpart. The total DNA content and the RNA/DNA ratio of lactating dairy mammary tissue was approximately twice that of lactating beef mammary tissue. The data suggested that the higher milk production observed in dairy cattle is a result of a greater number of secretory cells and greater activity per cell.     

Relationship between nutrition and reproduction in beef cattle

The primary nutrient consideration for optimum reproductive performance in beef cattle is energy. Low energy intake delays the onset of puberty in heifers and bulls. Heifers should reach approximately 66 per cent of mature body weight by 14 to 15 months of age and be bred 30 days prior to breeding the main cow herd. Body conditioning scores (BCS) (1 = emaciated, 9 = obese) should be used to evaluate pregnant cows entering their third trimester. Cows should calve with body conditioning score 5 to 7. Forage quality and environmental factors influence maximum dry matter intake and nutrient requirements and must be considered in the clinical setting. Crude protein dietary content should be 11 to 12 per cent for lactating beef cattle. Mineral (calcium, phosphorus, magnesium, potassium, sulfur, sodium, chloride) nutrition is not a major cause of decreased reproductive performance in beef cattle. Trace mineral deficiencies (particularly selenium, copper, and zinc) can cause decreased reproductive performance. Diagnosis of these trace mineral deficiencies can be confirmed by elemental analysis of blood or tissues.