28 Investigating the effects of Chromium Propionate supplementation on reproductive performance of beef cows

Abstract The objective of this study was to explore the effects on reproductive performance of beef cows supplemented with Chromium Propionate during the post-partum and breeding periods. A total of 955 multiparous suckled beef cows located at eight locations were enrolled in the study. Within location cows were stratified based on parity, body condition score (BCS), and days postpartum (DPP) and randomly assigned to one of two treatments: 1) Control- supplementation of a mineral product at 113 g animal/d (n = 484 cows; 16 experimental units); or 2) CrP - supplementation of mineral product at 113 g animal/d containing Chromium Propionate (0.4% animal/d, KemTRACE, Kemin Industries; n = 471 cows; 16 experimental units). Mineral supplementation was offered starting at 45 d pre-breeding, during the breeding season, and until weaning for a total of approximately 150 d. Cows were enrolled in a fixed-time artificial insemination (TAI) using the 7-d CO-Synch+CIDR protocol followed by natural service with clean-up bulls 7 d after TAI, for a 70-d total breeding season. Pregnancy diagnosis was performed by ultrasonography 55 d after TAI and again approximately 40 d after the end of the breeding season. Cow body weight (BW) and BCS were recorded at the beginning of the experiment (d -45), at the initiation of the TAI protocol (d -10), at each pregnancy diagnosis (d 55 and 110), and at weaning (d 150). Mineral intake was estimated based on the difference in weight between offered mineral and refusals. Data were analyzed using the GLIMMIX, for binomial data, and MIXED, for continuous data, procedures of SAS. Cow initial BW and DPP were similar (P 0.10) between treatments (584 ± 198 kg and 78 ± 3 d, respectively). Estimated mineral intake was similar (P = 0.52) between treatments (119.6 ± 10.3 g and 124.5 ± 10.4 g animal/d, for Control and CrP, respectively). Supplementation of CrP did not influence estrus expression (58.3% vs 61.0% ± 2.5 %; P = 0.45), TAI pregnancy rates (63.1% vs 60.1 % ± 2.9 %; P = 0.56), or final breeding season pregnancy rates (94.2% vs 94.7% ± 2.9 %; P = 0.86), for CrP and Control, respectively. Chromium Propionate supplementation did not affect (P 0.10) final cow BCS and BW (5.2 ± 0.03; 562.9 ± 169.93 kg). In conclusion, Chromium Propionate supplementation delivered via an oral mineral supplement during the pre-breeding and breeding periods did not influence reproductive performance and changes in BW and BCS of beef cows.