Effect of Supplementation of Chelated Trace Minerals on Reproductive Performance of Beef Cattle

To evaluate the effect of supplementing two different chelated trace mineral sources on reproductive performance of beef cows, 204 spring-calving, Angus and Simmental × Angus cows (BW = 649±129 kg) were utilized. Cows received 1 of 2 glycine ligand chelated trace minerals (MAAC; MAAC^®, Novus International; TRAX; B-TRAXIM 2C, Pancosma), both formulated to replace 50% of the Cu, Mn, and Zn inorganic trace mineral. Cows were housed at two locations, and a complete randomized block design was used (8 pens/location; 12-13 cows/pen). Cows were stratified by BW, age, and BCS across treatment. Treatments were applied in two stages. During the dry-lot phase, cows were provided a TMR, targeted to provide 113.4 g of trace mineral·cow^-1·d^-1. Cows were moved to pasture on d 31 and mineral was provided free choice. Body weight and BCS were collected at trial initiation, breeding, AI pregnancy confirmation, and final pregnancy confirmation. Liver samples were collected at trial initiation, AI synchronization, and final pregnancy confirmation for mineral, metallothionein (MT) and actin analysis. On d 32 and 42, cyclicity was determined based on plasma progesterone levels. On d 42, cows were enrolled in the 7-d Co-Synch + CIDR and timed-AI protocol. Following AI, cows were exposed to one bull/pen for a 44 d breeding season. Conception rates to AI and overall pregnancy rates were determined on d 91 and d 147, respectively. Cow BW did not differ (P ≥ 0.17) across all time points, and BCS was not different (P ≥ 0.50) at initiation, breeding, or final pregnancy confirmation. However, there was a tendency (P = 0.07) for BCS to be greater for TRAX cattle at the time of AI confirmation. Liver trace mineral concentrations were not different (P ≥ 0.11). Liver MT/actin expression was not different (P ≥ 0.24) at trial initiation or breeding. However, TRAX cattle did have greater (P = 0.03) MT/actin expression compared to MAAC cattle at the time of final pregnancy confirmation. There was no difference (P ≥ 0.69) between treatments in percent of cows exhibiting estrous cyclicity, or in AI conception rates (MAAC=72.2% and TRAX=71.2%). However, overall pregnancy rate was greater (P = 0.03) for TRAX (98.4%) compared to their MAAC (90.1%) counterparts. While supplementation source did not affect BW, liver trace mineral concentrations or AI pregnancy rates, cows supplemented with TRAX prior to breeding did have improved MT/actin expression at pregnancy confirmation and improved overall pregnancy rates.