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.

Effects of preovulatory estradiol on uterine environment and conceptus survival from fertilization to maternal recognition of pregnancy.

Preovulatory estradiol is known to impact embryo quality and survival. The objective of this study was to determine the effects of preovulatory estradiol on the uterine environment and conceptus survival through maternal recognition of pregnancy. Beef cows/heifers were AIed following induced ovulation. Cows were grouped into high and low preovulatory estradiol. Conceptuses were collected on day 16 nonsurgically (Rep 1; n = 20), or following slaughter (Rep 2; n = 29). Blood was collected to determine plasma glucose concentrations, and uterine luminal fluid (ULF) was analyzed for protein, glucose, and interferon tau (IFNT) concentrations. Total cellular RNA was extracted from caruncular (CAR) and intercaruncular (INCAR) endometrial tissue. There was no effect of preovulatory estradiol on conceptus recovery rate (P = 0.38) or on apoptosis rate in the trophectoderm (P = 0.64). Cows in which a conceptus was recovered had greater concentrations of protein in the ULF (P = 0.04). Animals with elevated preovulatory estradiol had greater endometrial abundance of SLC2A1 (P = 0.05) and SLC5A1 (P = 0.04) in both INCAR and CAR tissue. Presence of a conceptus also tended to increase (P = 0.10) abundance of SLC5A1 in INCAR. In CAR tissue, cows with a conceptus had decreased SLC2A4 abundance (P = 0.05). In summary, conceptus recovery rates, apoptosis in the trophectoderm, IFNT, glucose, and protein concentration in ULF did not differ between cows that did or did not have an increase in preovulatory estradiol concentrations. Thus, there is no indication of increased conceptus survival to day 16 of pregnancy based on estradiol concentrations.

Beef heifers with diminished numbers of antral follicles have decreased uterine protein concentrations.

Previous research demonstrated a favorable relationship between the number of follicles detectable in the bovine ovary by ultrasonography and fertility, and bovine females with diminished numbers of antral follicles had smaller reproductive tracts. Therefore, we hypothesized that uterine function would be compromised in beef heifers with diminished numbers of antral follilcles. Angus heifers (n=480) were submitted for ultrasonographic evaluation of antral follicle number at 325 and 355d of age. After the second ultrasonographic examination, 40 pubertal heifers with the greatest average number of antral follicles (30.9±0.7) and 40 pubertal heifers with the lowest average number of antral follicles (14.2±0.7) were synchronized with two i.m. injections of prostaglandin F2α (25mg) administered 11d apart, and heifers were slaughtered on d6 (n=26 heifers/group) or d16 (n=14 heifers/group) of the resultant estrous cycle. The uterus was weighed, flushed for determination of protein content, and representative samples were fixed for determination of endometrial gland morphometry. Heifers in the Low group had fewer surface antral follicles and smaller reproductive tracts than heifers in the High group (P<0.01). Protein content of the uterine flushes was decreased in heifers in the Low group (P<0.01); however, there was no difference in the percent area of the endometrium occupied by endometrial glands. From these results, we conclude that the uterine environment of beef heifers with diminished numbers of antral follicles is less conducive to supporting early embryonic survival.