Supplementation of calcium magnesium carbonate, tylosin phosphate, or both on growth performance, carcass traits, liver outcomes, and rumination activity of yearling beef steers fed a finishing diet*

The objective of this study was to evaluate the effects of supplementation with calcium magnesium carbonate (CMC), tylosin phosphate (TYL), or both on rumination behavior, growth performance, liver abscess prevalence, and carcass characteristics of yearling beef steers. Treatments were arranged as a 2 × 2 factorial including CMC and TYL. Beef steers (n = 156; 469 ± 18 kg) were assigned to 1 of 20 pens. Di- etary inclusion of CMC was included at 1.5% of the diet (DM basis) in replacement of dry-rolled corn, and TYL was provided at 90 mg per steer/d. Growth performance was calculated on a carcass-adjusted basis (hot carcass weight/0.625). Data were analyzed as a randomized com- plete block design with fixed effects of CMC, TYL, and their interaction; block was a random effect. Dry matter intake was 4.9% less when CMC was fed and 1.6% greater when TYL was fed. Carcass weight tended to be lighter with CMC supplementation compared with CON (432 vs. 439 kg). Supplementation of TYL tended to reduce the percentage of abscessed livers by 55.7%. These results indi- cate that supplementation of CMC did not result in any improvements in growth, carcass, or dietary net energy utilization, but TYL supplementation tended to reduce liver abscess prevalence.