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consequence of level of nutrition on heifer ovarian and mammary development

H. C . Freetly, K. A. Vonnahme, A. K. McNeel, L. E. Camacho, O. L. Amundson, E. D. Forbes, C. A. Lents, R. A. Cushman
Journal of animal science 2014 v.92 no.12 pp. 5437-5443
DNA methylation, animal nutrition, animal ovaries, anterior pituitary, beef, breeding, calves, cattle feeds, cows, feed quality, heifers, herds, livestock feeding, mammary development, mammary glands, milk production, puberty, small cereal grains
Replacing cows in the herd is second only to nutrition as the single greatest input cost in cow/calf beef production. The increased availability of cereal grains for feeding livestock has allowed replacement heifers to enter the production system at younger ages. Many heifer development programs feed heifers large quantities of feed to ensure they reach puberty before breeding. Nutrition level during development has been associated with altered milk production and stayability. We hypothesized that heifers exposed to different levels of nutrition during the peripuberal period would differ in methylation of the DNA in the mammary gland and ovarian cortex. We also hypothesized that the ovarian reserve would decrease in heifers fed for rapid growth compared to heifers fed for slow growth during puberty. At 257 ± 1 d of age, heifers in the Stair-Step treatment (n = 6) receive 157 kcal ME/BW kg0.75 for 84 d, and heifers in the Conventional treatment (n = 6) were offered 228 kcal ME/BW kg0.75. At d 84, heifers were fed for an additional 83 d. Stair-Step heifers were offered 277 kcal ME/BW kg0.75, and heifers on the Conventional treatment received 228 kcal ME/BW kg0.75. Mammary weights (P = 0.43), capillary area density (P = 0.74), and capillary surface density (P = 0.18) did not differ between treatments; nor did alveolar number (P = 0.55) and alveolar density (P = 0.49). Reproductive tract weights (P = 0.69) and ovarian weight (P = 0.68), and ovarian size (P > 0.75) did not differ between treatments. In histological sections, Stair-Step heifers had more primordial follicles than Conventional heifers (P = 0.02), but primary (P = 0.59) and secondary (P = 0.15) follicles did not differ. Global methylation of parenchymal tissue (P = 0.82), mammary fat pad (P = 0.45), and ovarian cortex (P = 0.14) did not differ between treatments. Anterior pituitary weight did not differ between treatments (P = 0.16). Our hypothesis that modifying peripubertal nutrition modifies global methylation of the mammary and ovary is not supported; however, our hypothesis that it modifies the ovarian reserve is supported.