Vidlund, Trinity2024-12-202024-12-202024-12-19vt_gsexam:41934https://hdl.handle.net/10919/123859Return to estrus following the postpartum interval to achieve pregnancy success on time is a considerable obstacle for beef females. Chromium supplementation increases available glucose and insulin sensitivity within cells. Two experiments were conducted to investigate the effects of supplementing Chromium propionate (CrP) during the peripartum until weaning on productive and reproductive performance in Bos taurus beef cows. In Exp. 1, 62 Angus-based beef cows were stratified by predicted calving date, body weight (BW) and randomly assigned to one of two treatments: 1) CON, (n=30) supplementation of corn gluten, soy hull pellet feed (50:50) with a mineral pack at 1 kg -1hd-1d; or 2) TRT, (n=32) supplementation at 1 kg -1hd-1d of corn gluten, soy hull pellet feed (50:50) with a mineral pack containing 1.4 g of Chromium Propionate (KemTRACE® Chromium 0.4%, Kemin Industries, Inc., Des Moines, IA). Cows remained on a single pasture equipped with SmartFeed trailers for individual supplement intake (SmartFeed®, C-lock Inc., Rapid City, SD). The experiment lasted 98 days, starting 63 days pre-breeding to 35 post-fixed-time artificial insemination (TAI). Ovarian ultrasonography was performed on days -10, -3, 0 (TAI Day), and 7 to determine the diameter of the largest follicle and corpus luteum (CL) volume. Age, days postpartum (DPP), initial and final BW, and supplement intake were similar (P>0.05) between treatments. However, TRT cows had a larger follicle (P=0.028) on d 0, increased CL volume (P=0.038), and increased (P=0.0213) circulating progesterone (P4) on day 7. In Exp. 2, 953 beef cows across nine locations were assigned to one of two treatments: 1) CON, supplementation of a mineral product at 113 g -1hd -1d (n=464 cows; 16 experimental units); or 2) TRT, supplementation of mineral product at 113 g -1hd -1d containing 1.4 g of CrP n=489 cows; 16 experimental units). Supplementation started approximately 37 days pre-calving and continued until weaning for 345 days. Age, DPP, d-10 body condition score (BCS), initial and final BW, BCS, calf birth and weaning weight, and mineral disappearance were similar (P>0.05) between treatments. However, CrP cows tended (P=0.081) to have greater estrus expression (68.3 and 60.2 ± 3.1 %, for CrP and CON, respectively) and greater (P=0.045) TAI pregnancy rates (55.2% vs. 49.9% ± 2, for CrP and CON, respectively). We conclude that supplementation of CrP to beef cows during the peripartum through weaning did not affect BW or BCS, but increased ovulatory follicle diameter, estrus expression, CL volume, and P4 concentration, and one or more of these positive effects of CrP likely contributed to the improvement in TAI pregnancy rate.ETDenIn Copyrightbovinereproductionchromium propionatefertilityThesis