Submitted to: Livestock Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 3, 2014
Publication Date: April 1, 2014
Citation: Cushman, R.A., McNeel, A.K., Freetly, H.C. 2014. The impact of cow nutrient status during the second and third trimesters on age at puberty, antral follicle count, and fertility of daughters. Livestock Science. 162:252-258. Interpretive Summary: Minimizing supplementation to spring calving cows during the second trimester of pregnancy has been demonstrated to be an effective method of decreasing feed costs without negatively impacting the re-breeding performance of the cows. However, recent research into the impacts of maternal nutrition on development of the fetus has suggested that altering maternal nutrients during pregnancy could negatively impact the performance of the offspring. To investigate this, we performed a four-year study in which mature cows were fed at low (L, 75% of maintenance) or moderate (M, 100% of maintenance) levels during the second trimester and at low, moderate, or high (H, 125% of maintenance) levels during the third trimester, resulting in four treatment groups (L-H, L-L, M-H, and M-M). Heifers born to these cows were evaluated for age at puberty, antral follicle counts, and heifer pregnancy rate. Cow performance was not impacted by nutrition during pregnancy as we have demonstrated in the past. Age at puberty, antral follicle counts, and heifer pregnancy rates were not different in the daughters born to cows from these four nutritional regimens. However, heifers born to cows that were fed a high level of nutrition during the third trimester (L-H and M-H) conceived earlier in their first breeding season and calved earlier. This supports other reports that improved maternal nutrition during the third trimester improves first service conception rates in daughters and eliminates a decreased age at puberty or alteration of the numbers of follicles in the ovaries as mechanisms behind this enhanced fertility. Subsequent analysis will determine if this early calving in these heifers results in increased lifetime productivity.
Technical 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 (>/= 3 yr) 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 60 d and pregnancy status was determined 45 d 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 21 d 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 21 d 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 (>/= 3 yr) 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.