The impact of cow nutrient status during the second and third trimesters on age at puberty, antral follicle count, and fertility of daughters

Abstract

Fluctuating feed resources to beef cows across the production cycle is a proven method for decreasing input costs; however, limiting nutrients during late gestation have been demonstrated to decrease ovarian follicle numbers in female offspring in some studies. We hypothesize that limiting nutrients to mature (≥3yr) crossbred beef cows during the second and third trimesters would result in daughters that would have decreased follicle numbers detectable by ultrasonography as yearlings. Over four breeding seasons, pregnant beef cows (n=397) were assigned to either Low (L), Moderate (M) or High (H) nutrient intake during the second or third trimester, resulting in four dietary treatment groups (L–H, L–L, M–H, and M–M). Heifers (n=416) born to these cows were weighed at weaning and moved to a dry lot where they were monitored for behavioral estrus with the aid of heat detection patches. Two weeks before their first breeding season, heifers were submitted for ultrasonographic examination of their ovaries to determine antral follicle numbers. Heifers were placed with bulls for 60d and pregnancy status was determined 45d after the bulls were removed. Growth and reproductive traits were analyzed using the MIXED Procedure of SAS with maternal diet and year as fixed effects. Maternal dietary intake did not affect heifer growth rates, age at puberty, or antral follicle counts (P≥0.40). However, an increased proportion of the heifers born to dams fed a high nutrient diet during the third trimester (L–H or M–H) calved in the first 21d of their first calving season (P=0.004). Antral follicle counts detectable by ultrasonography at yearling pre-breeding examination were greater in heifers that calved during the first 21d of their first calving season (P=0.02); however, these heifers did not differ in age at puberty (P=0.60). From this study, we conclude that: (1) limiting nutrient intake during late gestation in mature (≥3yr) beef cows does not influence the ovarian reserve or reproductive performance of daughters; (2) increasing maternal nutrient intake during the third trimester can improve the first service conception rates of daughters; and (3) pre-breeding ultrasonography to determine antral follicle counts is a good indicator of fertility for choosing replacement heifers.