THE EFFECTS OF PROTEIN AND ENERGY CONTENT OF COMPOUND SUPPLEMENTS OFFERED AT LOW-LEVELS TO OCTOBER-CALVING DAIRY-COWS GIVEN GRASS-SILAGE AD-LIBITUM

Ninety-six October calving, multiparous Friesian dairy cows were given from week 2 of lactation perennial ryegrass silage ad libitum, supplemented with one of four compound foods, offered at a flat rate of 3 kg/day. The compound foods differed in crude protein (CP) concentration (210 (LP) and 350 (HP) g/kg dry matter (DM)), achieved by including fish meal at 50 and 250 kg/t respectively, and in metabolizable energy (ME) concentration (12.8 (LE) and 14-0 (HE) MJ/kg DM), achieved by adding protected fat (approx. 100 kg/t). There were no significant interactions between supplement type in terms of animal performance. Over an average feeding period of 152 days, milk yields were significantly increased by 0-49 kg/day per 100 g supplementary CP (P < 0.01) and 0.50 kg/day per MJ of supplementary ME (P < 0.05). Increasing the level of supplementary CP had no effect on milk composition but significantly increased yield of milk protein (67 g/day). An increase in supplementary ME significantly reduced protein concentration in the milk (1.1 g/kg) but had no effect on protein yield. Yield of milk fat was significantly increased (76 g/day), The additional energy also significantly improved cow fertility in terms of a reduced interval from calving to both first service and conception.