An extreme model of fertility in sheep demonstrates the basis of controversies surrounding antral follicle count and circulating concentrations of anti-Müllerian hormone as predictors of fertility in ruminants.

Ovarian ultrasonography and measurement of circulating concentrations of anti-Müllerian hormone (AMH) have been used to estimate follicle number and predict fertility in mammalian females, but no study has evaluated follicle number and circulating concentrations of AMH in ewes known to differ in fertility. We tested the hypothesis that ewes that had failed to lamb (BARREN) in four consecutive annual breeding seasons of 21-35 d have fewer follicles and diminished circulating concentrations of AMH compared to closely matched ewes that consistently produced lambs (FERTILE) under the same breeding protocols. Once identified, BARREN ewes (n = 19) were paired by breed and sire to a FERTILE control ewe (n = 19) and reproductive tracts were recovered at necropsy. Visible antral follicles in both ovaries were counted and a representative cross section of one ovary was embedded for histological evaluation of pre-antral follicle numbers. Paired t-tests indicated that BARREN ewes had fewer antral follicles, fewer primordial follicles, and decreased circulating concentrations of AMH compared to FERTILE ewes (P ≤ 0.01), but there were ewes in each fertility classification that had ovarian phenotypes like the opposite fertility classification. The best technologies we have currently for estimating follicle numbers are ultrasonography and measurement of circulating concentrations of AMH, but no single technique is perfect for predicting fertility. A better understanding of the under-lying biological mechanisms linking AMH, folliculogenesis, and fertility is required to improve the use of measurements of follicle number for predicting fertility in livestock.

Polymorphism of the follicle stimulating hormone receptor does not impact reproductive performance or in-vitro embryo production in beef heifers.

Assisted reproductive technologies are used to propagate desirable genetics in a shortened timeframe. Selected females undergo ovarian stimulation with the use of follicle stimulating hormone (FSH) to increase embryo recovery for subsequent transfer programs. The FSH receptor (FSHR) c.337 C > G variant was reported to have a reduction in viable embryo numbers in an ovarian stimulation protocol. We, therefore, hypothesized that FSHR c.337 C > G would result in reduced in-vitro blastocyst development. Beef heifers were genotyped and selected based on the c.337 C > G FSHR genotype (CC, CG, GG; n = 15-16/genotype). Estrus was synchronized with a Select Synch protocol and heifers were slaughtered 5 days after induced ovulation. Anterior pituitaries, serum and reproductive tracts were collected at slaughter for analysis. Cumulus oocyte complexes (COCs) were collected and pooled within genotype for in-vitro fertilization (IVF) and subsequent blastocyst development. No differences were observed in carcass weights, anterior pituitary weights, serum progesterone, corpus lutea weight, surface follicle counts, histological follicle counts or follicular fluid estradiol concentration (P > 0.1) due to FSHR genotype. Differences were observed for ovulation rates in the GG FSHR genotype group (P < 0.01). However, cleavage and blastocyst rates were not affected due to FSHR genotype (P > 0.1), following standard IVF protocols. The FSHR variant does not influence antral follicle counts, estradiol production, or in-vitro blastocyst development in beef heifers. The GG FSHR genotype had an increased ovulation rate, which may indicate a greater potential for twinning, but research with a larger population is warranted to support this hypothesis.

Prenatal transportation stress did not impact ovarian follicle count for three generations of female Brahman offspring.

As prenatal transportation stress altered behavior and adrenal glucocorticoid secretion of calves, we hypothesized that prenatal transportation stress would decrease ovarian reserve size and negatively impact female offspring fertility. The impact of prenatal transportation stress on ovarian follicle numbers in female offspring for three generations was studied. Brahman cows were transported for 2 h on day 60 ± 5, 80 ± 5, 100 ± 5, 120 ± 5, and 140 ± 5 of gestation. Ovaries were collected from offspring of transported or non-transported dams at multiple ages. Primordial, primary, secondary, and antral follicles were histologically analyzed. Antral follicle numbers were determined by ultrasound in a subset of offspring. Numbers of primordial, primary, secondary, and antral follicles were analyzed using the MIXED procedure, while the CORR procedure of SAS was used to determine the correlation between follicles observed by ultrasonography and histology. There were no differences (P > 0.05) in the number of primordial, primary, secondary, antral, or total follicles observed histologically due to treatment. Younger females had significantly greater numbers of follicles than older females (P < 0.0001). Antral follicles tended to be correlated with total histological ovarian follicles (P = 0.10). There was no difference in the number of antral follicles observed at ultrasound due to treatment (P = 0.3147), or generation (P = 0.6005) when controlling for age at observation. These results show that short-term transportation stress during early- to mid-gestation did not impact fertility as measured by ovarian follicle numbers in female Brahman offspring for three generations.

Brangus cows have ovarian reserve parameters more like Brahman than Angus cows.

Bos indicus females have more surface antral follicles than Bos taurus females; however, histological studies demonstrated no difference in total number of primordial follicles between these two biological types of cattle. Primordial follicle density in the ovary was less in Nelore ovaries compared to Angus ovaries, but no studies have examined the primordial follicle density in Bos indicus cross-bred females. It, therefore, was hypothesized that primordial follicle density in the ovary would decrease as percentage Bos indicus increased. Ovaries were collected from cross-bred Angus (n = 32, no Bos indicus influence), Brangus (n = 15), or Brahman (n = 9) cows and prepared for histological evaluation. There was no difference in total number of primordial follicles per ovary between breeds (P > 0.10). When numbers of primordial follicles were expressed on a per gram of ovarian tissue basis, there were fewer primordial follicles per gram of ovarian tissue in Brangus and Brahman cows than in Angus cows (P < 0.05). Brangus cows did not differ from Brahman cows in primordial follicle density (P > 0.10). Differences in primordial follicle density could indicate differences in capacity of ovarian stroma to produce factors necessary for oogonial proliferation and primordial follicle formation among breeds. Identifying these factors could improve the aprroach for culturing pre-antral follicles of cattle. Furthermore, these results explain why ultrasonographic antral follicle counts may need to be adjusted to a greater threshold to predict size of the ovarian reserve and determine ovarian reserve related reproductive traits in Bos indicus females.