Effect of feeding supplements on the intake and live-weight gain of male red deer given silage during winter

The live-weight gain (LWG) of young male red deer in New Zealand naturally slows during winter and feeding diets of mainly silage appears to exacerbat e this effect. We aimed to quantify the effect of feeding silage on intake and LWG during winter and the ability to improve LWG by feeding supplements , mainly in the form of barley. Seven groups of eight deer were maintained outside in gravelled enclosures and offered silage ad libitum for 94 days d uring winter. Six groups were given supplements (950 g barley with 50 g rap eseed meal per kg to make all diets isonitrogenous) at rates of proportiona tely 0.2, 0.4, 0.5, 0.6, 0.7 and 0.9 of the metabolizable energy (ME) intak e of the group given only silage (0). The study also examined the effect of the winter treatments on subsequent LWG to slaughter weight whilst grazing on pasture during spring and into summer (102 days). Increasing supplement intake resulted in a decrease in silage dry matter (D M) and ME intake (P < 0.001) and an increase in total ME intake (P < 0.01). The substitution rate for silage DM was 0.84 (s.e. 0.079). LWG during sila ge feeding was positively related (P < 0.01) to supplement intake with an i ncrease of 6.21 g/day per MJ per day. LWG on pasture was not related to eit her supplement feeding rate or LWG during winter. LWG over the entire exper iment was related (P < 0.01) to supplement feeding rate, with a final diffe rence in live weight of 6 kg between 0 and 0.9 groups. This study has confirmed that the LWG of young male deer is low during wint er when given only silage and that feeding supplements increases total ME i ntake and LWG. The reduced LWG due to silage feeding was not compensated fo r on pasture during spring and summer, thus delaying the time to reach Slau ghter weight by approximately 1 month. High proportions of silage in the di et appear unsuitable for young male deer if the aim is to achieve rapid LWG during winter.