An experiment was designed to establish the growth response of young housed steers to the feeding of stack-ammoniated low-quality hay, and to a range of different supplements for 16 weeks, and any carry-over effects during the following 24 weeks at pasture. Ammoniated hay was offered alone (TA), or with daily supplements of either 0·75 kg barley (TLB), 1·50 kg barley (THB), 0·1125 kg fish meal (TF), 0·75 kg or 1·50 kg of a barley-based concentrate (TLC and THC, respectively). Untreated hay was offered with either urea (UU) or with a daily supplement of 0·75 or 1·50 kg concentrates (ULC and UHC respectively).
Ammoniation increased the total nitrogen concentration of the hay from 13·4 to 24·2 g/kg dry matter, and resulted in a small increase in the organic matter digestibility measured in vivo (0·597 to 0·653), compared with that measured in vitro (0·572 to 0·667). Digestibilities of the fibre fractions, measured in vivo, were also increased by ammoniation (0·626 to 0·734, 0·637 to 0·761, 0·678 to 0·771 for acid-detergent fibre, neutral-detergent fibre and cellulose, respectively). Intakes of hay were reduced by supplementation, with the exception of TF, although total intakes were increased. During the housed period, live-weight gains of steers given ammoniated hay were 0·58, 0·71, 0·81, 0·69, 0·80, 0·86 kg/day for treatments TA, TLB, THB, TF, TLC, THC, respectively. The live-weight gains of steers offered the untreated hay were 0·49, 0·66, 0·87 kg/day for treatments UU, ULC, UHC, respectively. There was no carry-over effect of treatments on live-weight gains over the grazing season (mean 0·66 kg/day). It is concluded that when high levels of supplementation are available, no benefit is to be gained by ammonia treatment of ihe hay. However, without supplementation stack ammoniation of hay produces a marked improvememt in performance, compared with the addition of urea at feeding.