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Title: Does reduced peri-pubertal nutrient intake influence the ovarian reserve in beef heifers?

item Cushman, Robert - Bob
item FORBES, ELIZABETH - University Of Connecticut
item SWANSON, OLIVIA - South Dakota State University
item McNeel, Anthony
item Chase, Chadwick - Chad
item Lents, Clay
item Freetly, Harvey

Submitted to: Society for the Study of Reproduction Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 3/28/2013
Publication Date: 7/1/2013
Citation: Cushman, R.A., Forbes, E.D., Swanson, O.L., McNeel, A.K., Chase, C.C., Lents, C.A., Freetly, H.C. 2013. Does reduced peri-pubertal nutrient intake influence the ovarian reserve in beef heifers? [abstract]. Biology of Reproduction Supplement (46th Annual Meeting of the Society for the Study of Reproduction). pp. 44-45 (Abstract #48).

Interpretive Summary:

Technical Abstract: Reducing nutrient intake in beef heifers after weaning decreases production costs; however, the impact of reduced nutrient intake on the ovarian reserve has not been investigated in this species. In rodent models, caloric restriction increased the number of primordial follicles and decreased the number of antral follicles in the ovaries. Therefore, we hypothesized that reducing nutrient intake to heifers after weaning would increase the number of primordial follicles and decrease the number of antral follicles in the ovaries. In Experiment 1, crossbred beef heifers (n = 255/treatment) were fed to obtain 65% of mature weight by breeding (Control) or fed a calorie-restricted diet for 84 days following weaning; then stepped up to a greater amount of energy for 60 days before breeding (Stair-Step). Heifers were submitted for ovarian ultrasonography monthly from 12 to 14 months of age to determine pubertal status and at 14 months of age heifers were given a complete reproductive tract examination that included counting antral follicles and measuring the ovaries and the uterine horn. In Experiment 2, crossbred beef heifers (n = 6/treatment) were developed in the same way and slaughtered at 14 months of age. Ovaries were weighed and measured and all surface follicles were counted. The uterus was weighed and uterine horn diameters were measured. A cross section of one ovary was fixed and morphometric analysis was performed to determine the numbers of preantral follicles by a trained technician who was unaware of the treatments. In Experiment 1, there was no difference between treatments in the percentage of heifers that were identified with a CL at any of the ultrasonographic examinations, indicating no difference in the age at puberty between the treatments. At pre-breeding ultrasonographic examination, Control heifers had larger uterine horn diameters (29.8 ± 0.4 vs. 28.3 ± 0.4 mm, P = 0.003) and greater ovarian lengths (12.3 ± 0.2 vs. 11.4 ± 0.2 mm, P = 0.005); however, there was no difference in the number of antral follicles observed. Heifer pregnancy rates and Julian day of calving did not differ between the treatment groups (P > 0.05). In Experiment 2, there was no difference in reproductive tract measurements or anterior pituitary weights (P > 0.05). However, there was a greater number of primordial follicles/section in the ovaries of Stair-Step heifers than Control heifers (112.5 ± 14.0 vs. 52.4 ± 14.0, P = 0.004). There was no difference in the number of primary, secondary, or antral follicles. These data support previous studies that demonstrate that reducing peri-pubertal nutrient intake does not negatively impact heifer reproductive performance. Furthermore, the results indicate that reducing the nutrient intake to beef heifers in the peri-pubertal period increases the number of primordial follicles in the ovaries, a novel finding for this species. This is most likely because depletion of the primordial follicles is slowed when nutrient intake is decreased based on previous results in rodents. However, it is also possible that the increased nutrient intake during re-feeding stimulated oogonial stem cells to form new primordial follicles. USDA is an equal opportunity provider and employer.