Title: Improving Reproductive Performance: Long and Short Term Authors
Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: March 11, 2011
Publication Date: March 17, 2011
Citation: Geary, T.W., Roberts, A.J. 2011. Improving Reproductive Performance: Long and Short Term. Proceedings of the XV Course on New Approaches to Production and Reproduction in Cattle. Pp. 370-385. Uberlandia, Brazil, March 17, 2011. Interpretive Summary: Several papers have been written during the past 50 years to include strategies to improve short term (current year) reproductive performance in beef cows, but very few papers have revealed strategies that improve long term reproductive performance as measured by longevity in a cowherd. The information in the present paper includes short term strategies (including heifer development, dystocia management, nutritional management, early weaning, and hormonal manipulation of estrous cycles) and long term strategies (including genetic selection and epigenetic control) to improve herd reproductive performance and guidelines when both should be used to obtain the maximal benefit.
Technical Abstract: Improvements in reproductive performance for beef herds can be classified as short term (current year) or long term (lifetime production) and can be applied to and measured in individual animals or the entire herd. In other species, results show that rearing young animals under caloric restriction increased lifespan. An objective of the current study was to determine the effects of restricted feeding (80% of adequate) in utero and during pubertal development on reproductive performance and longevity. Data was collected over an eight year period in cows that were culled from the herd if they failed to have a calf at their side at the beginning of the breeding season or were not pregnant after the end of the breeding season. Heifers reared on reduced nutrient availability consumed 27% less feed and were lighter at the onset of breeding at approximately 14 months of age, but were more efficient in conversion of feed to gain. Reproductive performance during their first breeding season was not different than heifers fed the adequate diet. During the first 3 years of production, retention was greater for adequate fed cows than restricted cows. However, a greater retention is being observed in restricted fed cows that were restricted in utero. Cows that were nutritionally restricted in utero are heavier and in better body condition at the start of breeding in their 5th year. Taken together, these data indicate an epigenetic effect on metabolic efficiency based on in utero nutrition. Short term strategies that could be used to decrease the decline in retention of nutritionally restricted heifers include providing additional nutrient supplementation during and after their first pregnancy, hormonal induction of estrous cycles, and early weaning of calves. Genetic selection for earlier age of puberty and crossbreeding are other long term strategy to improve reproductive performance and longevity. The mechanisms by which crossbreeding improve reproductive performance warrant further study.