Mineral retention of growing and finishing beef cattle across different production systems1

Calcium, P, Mg, K, and S retention in carcass, offal, and viscera were measured in 2 beef cattle experiments. Experiment 1 used 30 steers (245 kg of BW; SE = 4 kg) wintered at 3 levels of gain: grazing wheat pasture at a (1) high or (2) low rate of gain or (3) grazing dormant native range, and all were finished on a common diet (71% corn, 9% cottonseed hulls, 5.35% soybean meal). Experiment 2 used 46 steers (240 kg of BW; SE = 4 kg) fed 3 growing diets with similar rate of gain: (1) sorghum silage, (2) program-fed high-concentrate diet, or (3) wheat-pasture grazing, or placed directly into the feedlot. In Exp. 1, retention of Mg, K, and S (g/100 g of protein gain) during the finishing period was greater for treatments wintered at a low rate of gain during the growing period (P ≤ 0.02). There were no treatment differences for P or Ca retention during the finishing period (P ≥ 0.39). In Exp. 2, no differences were noted due to treatment (P ≥ 0.25) or feeding period (P ≥ 0.37) for Ca, P, Mg, K, and S retention (g/100 g of protein gain). Concentrations of Cu, Fe, Mn, and Na were greater in offal than carcass tissues in both experiments (P < 0.01). In both experiments, expressing mineral retention on a protein gain basis minimized effects due to BW or rate of gain, allowing for a better comparison of mineral retention across a variety of animals and diets.