Effect of supplementing barley straw with lucerne silage or cottonseed meal on diet digestibility and growth rate of steers

In Experiment 2, thirty six steers were fed barley straw ad libitum and were supplemented with 1.9 (L2), 3.9 (L4) or 5.7 (L6) kg lucerne silage DM/d, or 0.8 kg CSM DM/d for 49 d. Proportions of straw eaten in the BS + CSM, L2, L4 and L6 diets were 811, 586, 326 and 166 g/kg respectively. L2, L4, L6 and BS + CSM diets were estimated to contain 97.5, 144.0, 172.4 and 106.2 g CP/kg DM and 7.1, 8.0, 8.5 and 6.8 MJ ME/kg DM respectively. There were significant treatment effects on total DMI (P < 0.001), straw intake (P < 0.001) and LW gain (P = 0.018). Total DMI was 4.66, 5.80, 6.91 and 4.28 kg/d (l.s.d. = 0.485); straw intake 2.73, 1.89, 1.15 and 3.47 kg/d (l.s.d. = 0.493); LW gain 0.06, 0.23, 0.45 and 0.49 kg/d (l.s.d. = 0.248) for L2, L4, L6 and BS + CSM diets respectively. NDF intake was similar between diets. Straw intake declined (P < 0.05) with increasing silage supplementation, but total intake increased (P < 0.05). LW gain on BS + CSM was higher (P < 0.05) than L2 and L4, and considerably higher than predicted from feeding standards.