Maternal Dietary Effects on Embryonic Ovarian Development in Cattle
Ovarian gametogenesis and folliculogenesis begins early in fetal development with peak numbers of follicles present in bovine fetal ovaries in the second trimester of gestation and may be altered by maternal nutrition. The objective was to determine whether maternal dietary energy intake by replacement beef heifers prior to breeding affects ovarian development in female progeny. Over 3 breeding seasons, puberal heifers were fed either a high (HE) or low (LE) energy diet for 6 mo before breeding plus the first 22 d of a 47-d breeding period to achieve 55 vs. 65% of mature BW; heifers were subsequently managed together on pasture. Female progeny (n = 68 LE and 67 HE) were developed on a standard management protocol for replacement beef heifers. Numbers of antral follicles (AFC), corpora lutea (CL), and ovarian length and height were measured in progeny ovaries by transrectal ultrasonography at 14 mo of age prior to a 29-d breeding period with fertile bulls; pregnancy was diagnosed at about 75 d of gestation. Data were analyzed by ANOVA with diet, year and diet x year as fixed effects. Progeny of LE vs. HE dams did not differ in birth (33.8 vs. 34.4 ± 0.6 kg, respectively) or prebreeding BW (381.2 vs. 385.0 ± 3.6 kg, respectively). Ovaries of LE progeny contained fewer small (2 to 5 mm) (18.0 vs. 21.9 ± 1.0, LE vs. HE; P = 0.02) and total antral follicles (AFC, 19.9 vs. 24.0 ± 1.0, LE vs. HE; P = 0.01). Overall, 96.5% of progeny had a CL at examination. Although AFC was correlated positively (r = 0.36; P < 0.01) with ovarian size (length x height), size did not differ between diets (357.4 vs. 348.4 mm2 ± 12.6, LE vs. HE, P > 0.10). The AFC was similar between left and right ovary (r = 0.77; P < 0.01), but not between progeny and dam AFC (r = 0.05). Proportion of daughters pregnant to the 29-d breeding period did not differ between maternal diets (72.4 vs. 70.7 ± 0.5%, LE vs. HE) and was not influenced by prebreeding AFC. Results indicate that nutrient intake by first-parity heifers during early embryonic development may affect fetal ovarian development. USDA is an equal opportunity provider and employer.
Keywords: beef heifers, diets, developmental programming