Effect of production system on mineral retention within serially slaughtered cattle

Abstract Text: Data from 3 serial harvest experiments were utilized to calculate mineral (Ca, P, Mg, K, and S) retention in cattle.  Experiment 1 evaluated 3 rates of gain during a growing period (grazing wheat pasture at a high or low rate of gain and grazing dormant native range) followed by a common finishing diet utilizing British crossbred steers (n = 48; 244 ± 23 kg).  Serial harvest consisted of 4 steers per treatment following the growing period (120 d) and 6 steers per treatment following the finishing period (89-163 d).  Experiment 2 utilized British crossbred steers (n = 46; 237 ± 34 kg) fed 3 growing diets (sorghum silage, program fed a high concentrate diet, and grazing wheat pasture) or placed directly into the feedlot as calf-feds.  Serial harvest included 4 steers prior to the growing phase at d 0, 6 steers from each of 3 growing treatments at d 112, and 6 steers from all 4 treatments at the end of the finishing period (104-196 d).  Experiment 3 evaluated zilpaterol hydrochloride inclusion in a finishing cattle diet utilizing calf-fed Holstein steers (n = 115; 449 ± 20 kg).  A baseline group of 5 steers was harvested after 226 days on feed.  Remaining cattle were assigned to 11 harvest groups, with slaughter every 28 d.  At harvest, carcasses were broken down into lean, bone, internal cavity, hide, and fat trim tissues.  Retention of minerals during the growing phase was not affected by diet fed to cattle (P ≥ 0.20; Exp. 2).  Finishing beef cattle, gaining 1.63-2.02 kg/d retained 7.9-17.3 g Ca, 3.2-6.2 g P, -0.03-0.4 g Mg, 0.5-2.9 g K, and 0.3-1.9 g S/100 g protein gain (Exp. 1 and 2).  Retention of Mg, K, and S during the finishing period was greater (P ≤ 0.02; Exp. 1) for cattle grown slowly (< 0.6 kg/d) during the growing phase.  Mineral retention was not affected by zilpaterol hydrochloride inclusion in the finishing ration when retention was expressed relative to protein gain (P ≥ 0.14; Exp. 3).  Expressing retention relative to protein gain resulted in no differences across days on feed (P ≥ 0.11; Exp. 3) averaging 14.4 g Ca, 7.5 g P, 0.45 g Mg, 1.3 g K, and 1.0 g S/100 g protein gain.  In all experiments, expressing mineral retention on a protein gain basis minimized differences due to BW or rate of gain.

Keywords: cattle, mineral, retention