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

- Heifers with diminished numbers of antral follicles have smaller reproductive tracts.
- Uterine protein production is decreased in heifers with diminished numbers of antral follicles.
- There does not appear to be a change in the number of endometrial glands.
- This suggests a decrease in protein production or secretion.

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 355 d 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 (25 mg) administered 11 d apart, and heifers were slaughtered on d 6 (n = 26 heifers/group) or d 16 (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.