Effect of degradability of protein supplements on voluntary intake and nitrogen retention in young cattle fed grass silage

Grass silage was offered ad libitum to twelve 4-month-old British Friesian steers in an incomplete Latin-square experiment. The silage was given either alone or supplemented isonitrogenously with 50 g fish meal or 63 g groundnut meal per kg silage dry matter. Both protein supplements significantly increased the intakes of dry matter and organic matter by an amount about equivalent to the (calculated) contribution of the supplement ( P < 0·05); they also increased the intakes of digestible organic matter and nitrogen ( P < 0·001) but with no significant difference between supplements. Protein supplementation had no effect on the intake of indigestible organic matter. The digestibility coefficients of dry matter and of organic matter were significantly increased by supplementation ( P < 0·05) as were the digestibility coefficients of gross energy and of nitrogen ( P < 0·001). Nitrogen retention was also increased from 1·4 to 8·2 g/day ( P < 0·001), with no significant difference between supplements.