Interaction of Pre- and Postnatal Nutrition on Age at Puberty and Selected Aspects of Reproductive Phenotype in Sexually Mature Heifers

Two experiments were conducted to test if pre- and postnatal nutrition in the bovine female, independently or interactively, affect 1) age at puberty and 2) selected phenotypic characteristics of the estrous cycle of sexually mature offspring. Brangus and Braford (n=108) beef cows bearing a female fetus were fed to achieve body condition scores of 7.5-8 (H, obese), 5.5-6 (M, moderate) or 3-3.5 (L, very thin) by the start of the third trimester and maintained until parturition. Heifer offspring were weaned and fed to gain at either a high (H; 1 kg/d) or low (L; 0.5 kg/d) rate between 4 and 8 months of age, then fed a common growth diet until puberty, resulting in a 3x2 factorial arrangement of maternal x postnatal treatments (L/L, L/H, M/L, M/H, H/L, H/H). For Exp. 2, estrous cycles of a subgroup of postpubertal heifers (n = 53) from Exp. 1 were synchronized to evaluate selected ovarian, uterine, estrous behavior and hormonal characteristics, including antral follicle count (AFC), rate of growth and size of the pre-ovulatory follicle, size of corpus luteum (CL) and ovary, endometrial thickness, luteal phase concentrations of progesterone (P4), and follicular phase concentrations of estradiol-17β (E2). Heifers (n = 95) from the H postnatal dietary treatment reached puberty two months earlier (12 0.4 months; P = 0.0002) than those from the L postnatal diet (14 0.4 months). However, neither maternal diets nor their interaction with postnatal diets of offspring influenced age at puberty. In Exp. 2, maternal, postnatal and maternal x postnatal interactions failed to affect physiological or hormonal variables selected for evaluation, although there was a trend for AFC (P = 0.09) and peak concentrations of E2 before estrus (P = 0.08) to be greater in H than in L groups. Results confirm that early-weaned heifers fed a high-gain diet during the juvenile period reach puberty much earlier than those fed a low-gain (L) diet. However, neither maternal dietary treatments during the second and third trimesters of pregnancy nor their interaction with postnatal dietary treatments affected age at puberty or selected physiologic, morphologic, or behavioral characteristics of the estrous cycle