Live-weight gain responses were investigated using 36 individually penned lambs (mean live weight 35·2 kg) given three sodium hydroxide treated straw-based diets: low-protein, low-rapeseed meal (control) diet; high protein, high-rapeseed meal (HR) diet; or high-protein, fish meal (FM) diet. The diets were formulated to provide 3 or 9 g undegradable nitrogen per kg dry matter (DM) respectively for the diets without or with fish meal. Diets were offered once a day in a 50: 50 forage-to-concentrate ratio in amounts calculated to support maintenance plus 150 g gain and were adjusted weekly according to live weight. Live-weight gain, measured for 7 weeks, was improved by the FM diet only (P < 0·05).

The three diets were given also to rumen-fistulated sheep. The FM diet maintained higher rumen ammonia concentrations during most of the day. The FM and HR diets reduced rumen solid particle outflow rate (P < 0·05) and increased the effective degradability of DM and acid-detergent fibre.

The response of 376 weaned bull calves to two different housing types was studied in a 2-year feedlot trial. Overall, animals with shelter had a higher rate of gain than animals with no shelter. The difference in the rate of gain between the housing types was, however, restricted to the coldest periods. No significant interaction between housing type and age of calf was observed. Regression analyses showed that whilst average daily temperature appeared to have a negligible effect on growth, temperature fluctuations between weighing days appeared to affect growth of calves in both housing types. Overall, climatic variables contributed more to the variance in gain of calves with shelter than of calves with no shelter.

A comparison was made between the Heal digestibility of the amino acids in pigs obtained by the use of a basal diet, the apparent Heal digestibility obtained with a semi-synthetic diet where peas were the sole protein source and the true Heal digestibility obtained with synthetic and nitrogen-free diets.