The effects of supplementary Chinese milk vetch silage on the growth rate of cattle and their intake of ammoniated rice straw

Thirty-two Holstein heifers were allocated to four groups and used to investigate the response in growth rate to supplementing ammonia bicarbonate-treated rice straw (ABRS) with Chinese milk vetch (Astragalus sinicus L.) silage (MVS). All groups were offered ABRS ad libitum with 1 kg of a concentrate mixture per head per day, and the MVS was supplemented at levels of 0, 10, 20 or 30% of the calculated dietary dry matter intake. Intake of ABRS was not affected by a 10% inclusion rate of MVS but inclusion at each of the higher levels reduced ABRS intake. Dry matter intakes were higher in all three supplemented groups, and daily liveweight gains were 588 g, 692 g, 800 g and 777 g in the groups supplemented with MVS at levels of 0%, 10%, 20% and 30%, respectively. When MVS accounted for 20 or 30% of the diet, the liveweight gains were significantly higher than in the non-MVS group (P < 0.05). Concentrate consumption per kilogram liveweight gain was 1.70 kg, 1.45 kg, 1.25 kg and 1.30 kg for the 0%, 10%, 20% and 30% levels, respectively. It is concluded that supplementation of an ABRS-based diet with MVS may improve the growth rate of ruminants and save concentrate consumption. The results of orthogonal contrasts indicate that the optimal level of supplementary MVS in this study was 23% of the dietary dry matter intake.