The Effects of Age at Weaning and Length of Lipid Supplementation on Growth, Metabolites, and Carcass Quality of Young Steers

The objective of this study was to determine how weaning age and length of lipid supplementation effected growth, circulating metabolites, and carcass quality of young steers. Calves from a single AI sire were early-weaned (EW, n = 24) at 150 ± 11 d of age or traditionally weaned (TW, n = 24) at 210 ± 11 d of age. Following a two-wk adaptation period, steers were assigned to control (CON, n = 12/weaning group) or rumen by-pass lipid (RB, Essentiom™; n =12/weaning group) treatment and then fed for either 45 (45d; n = 6/treatment) or 90 (90d; n = 6/treatment) days. Treatments were formulated to be isocaloric and isonitrogenous. Steer BW was recorded on d -14 and -7 (relative to treatment), then BW and blood samples were taken on d 0, 22, 45, 66, and 90. After treatment, steers were harvested at a commercial processing plant. The right rib section of each animal was collected for proximate analysis. Data was analyzed in a 2 x 2 x 2 factorial with all significant interactions in the model using SAS. Circulating metabolites were analyzed as repeated measures. Steers fed RB had increased plasma glucose compared to CON steers (P = 0.03; 72.1 and 67.9 ± 1.7 mg/dL, respectively). Serum triglyceride concentrations were increased in RB steers vs CON steers (P = 0.02) and in TW compared to EW steers (P = 0.03; 14.3 ± 1.5). Serum cholesterol concentrations were increased (treatment * day P = 0.01) in RB steers over CON steers from d 22 to 90 of treatment. Traditionally weaned steers had a greater HCW than EW steers (143.7 ± 2.8 and 142.0 ± 2.8 kg, respectively; P < 0.0001). Steers fed for 90 d also had greater HCW than 45d steers (153.4 ± 2.8 and 132.3 ± 2.8 kg, respectively; P < 0.0001). The longissimus dorsi from RB steers had an increased EE compared to CON steers (3.6 ± 0. 2 vs 2.4 ± 0. 2 % on a wet basis; P <0.0001). Also, longissimus dorsi from 90d steers had greater (P = 0.02) concentration (3.3 ± 0.2 %) of lipid than those fed for 45 d (2.7 ± 0.2 %). These data show RB supplementation increases circulating glucose, cholesterol, and triglyceride concentrations as well as marbling content of the longissimus dorsi in young steers. Furthermore, a longer period of supplementation results in increased IM adipose concentration and increased HCW.