Evaluation of weaning regimen and seminal plasma biology on reproductive management in cattle

Abstract

The goal of any reproductive management system in cattle is to ensure that cows breed at the earliest opportune time and maintain their pregnancy to term. However, delayed resumption of postpartum ovarian cyclic activity in primiparous beef cows and pregnancy losses in dairy cows continue to impede progress in obtaining sound reproductive efficiency in these species. Three studies were designed to test the following hypotheses: 1) Does removal of lactational stress in beef cows by early weaning of calves improve cow energy profile and postpartum reproductive performance? 2) Does artificial insemination (AI) with adjunctive seminal plasma (SP) or transforming growth factor beta-1 (TGF-β1) improve conception rates in lactating dairy and beef cows? 3) Does seminal plasma of dairy bulls differ in expression of proteins that might be used as potential biomarkers of male fertility? In experiment 1, pregnant and lactating beef cows (n = 408) were assigned randomly to wean calves either at 180 d of age (early weaning) or 45 d later (normal weaning). Body energy status was evaluated by periodic measurements of body weight (BW), body condition score (BCS), rib and rump fat. Reproductive performance was determined by calving intervals (CI), intervals from breeding to calving (BCI), retention in herd, and adjusted 205-d weaning weight of the subsequent calf. In experiment 2, lactating beef (n = 1090) and dairy (n = 800) cows received 0.5 mL SP, 40 ng recombinant human TGF-β1, or 0.5 mL bovine serum albumin (BSA) or were left untreated at insemination. Pregnancy was determined by transrectal ultrasonography 35 to 40 d post insemination or from records of calves born in the subsequent calving season. In experiment 3, seminal plasma from high (n = 8) and low (n = 6) fertility bulls at Select Sires Inc. (Plains City, OH) were assayed for TGF-β1 content, and subsequently analyzed by 2-D fluorescence difference gel electrophoresis (2-D DIGE) for presence of potential biomarkers of male fertility. Early weaning and cow age improved (P < 0.001) energy partitioning and production efficiency in beef cows. Rump fat measurements predicted body energy status better than BW or BCS (P < 0.001). Inseminations with SP and/or TGF-β1 numerically increased (P = 0.07) conception rates in beef and dairy cows. Concentrations of TGF-β1 in seminal plasma were numerically greater (P = 0.25) in high fertility dairy bulls than those of low fertility. Expression of fertility associated proteins did not differ (P > 0.05) between high and low fertility bulls. However, their expression patterns were altered by semen processing. In conclusion, reproductive efficiency in primiparous beef cows can be improved by removal of lactational stress during mid to late pregnancy, while in dairy cows inseminations with adjunctive SP and/or incorporation of some seminal plasma proteins into semen during processing might improve conceptions rates after AI. iii DEDICATION This dissertation is dedicated to my departed sister, Ms. Lillian Achieng whom I'll always miss dearly.