MILK-PRODUCTION FROM GRASS-SILAGE DIETS - THE RELATIVE IMPORTANCE OF THE AMOUNTS OF ENERGY AND CRUDE PROTEIN IN THE CONCENTRATES

To identify the separate and combined effects of energy and crude prot ein (CP) from concentrates on responses to concentrate feeding, 42 mul tiparous Friesian cotes were given fixed amounts of concentrates with primary growth grass silage (194 g CP per kg dry matter (DM)) ad libit um for weeks 4 to 22 of lactation. A basal treatment of 3 kg DM per da y of a standard concentrate (197 g CP per kg DM) was compared with 6 k g DM per day of the same concentrate (doubling energy and CP intake), 6 kg DM per day of a low-protein concentrate (106 g cp per kg DM) (dou bling energy intake alone), or 3 kg/day of a high-protein concentrate (383 g CP per kg DM) (doubling CP intake alone). Results are presented in terms of main effects as interactions were not significant except for energy apparent digestibility. Silage intake was reduced by energy but increased by CP; in consequence extra energy from concentrates in creased digestible energy (DE) intake but reduced CP intake and concen tration whereas extra CP from concentrates increased not only DE intak e but also CP intake and concentration. The ratio of the responses to CP compared with the responses to energy mere 1.7 for milk yield, 0.9 for fat yield, 3.2 for protein yield and 1.4 for lactose yield. Energy reduced milk protein concentration and tended to increase milk fat co ncentration whereas CP had the opposite effect. The efficiency of conv erting food nitrogen to milk nitrogen teas unaffected by extra CP but was increased, from 0.195 to 0.229, by extra energy. he poor response in milk protein yield and the reduction in its concentration with extr a energy reflected the lower CP intake due to the reduced silage consu mption. The experiment emphasizes the importance of concentrate Cp sup ply in stimulating silage intake and yields of all milk constituents f or diets containing fairly small amounts of concentrates.