The utilization of silage by dairy cows with special reference to supplementation

A series of six feeding experiments with Ayrshire dairy cows was conducted to investigate the effect of different types and amounts of feeds when used as supplements for grass silage offered ad libitum. The effects of the supplements on feed intake, milk yield, milk composition and liveweight were measured. In three experiments, the effects of giving concentrates at different frequencies per 24 hrs was investigated also. A study of the feeding behaviour of the cows was made in one of these experiments. The experiments had cyclic, Latin Square and crossover designs with experimental periods of either 3 or 4 weeks. In Expt 3.1 grass silage with an vitro D-value of 69.8 was offered ad libitum to twelve cows in a 16-week experiment. In addition, supplements of hay in the long, short (12.1 mm) and ground and cubed form (modulus of fineness = 0.80) with in vitro D-values of 59.7, 59.4 and 61.9, and concentrates (203 g CP/kg DM) at either 2 or 4 kg per 10 kg milk were given. The hay in the ground and cubed form gave marked increases in the total intakes of forage dry matter of 9.9 and 8.6% compared with the long and short hays respectively at the low concentrate rate, and 14.2 and 14.9% at the high concentrate rate. The average reduction in the forage DM intake per kg concentrate DM consumed was 0.50 kg. At the low rate of concentrate intake, hay in the ground and cubed form gave marked increases in milk yield of 10.2 and 7.8% compared with the long and short hays respectively. At the high rate of concentrate intake, the ground and cubed hay gave smaller increases of 1.5 and 3.1%. The hay treatments had only small and non-significant effects on milk composition. In Expt 3.2, grass silage with an in vitro D-value of 61.6 was offered ad libitum to six cows in a 12-week experiment. On the control treatment, the silage was supplemented with soyabean meal only, and on the other two treatments barley and sugarbeet pulp were given in equal amounts on a dry matter basis plus the same weight of soyabean meal as on the control treatment. The highest daily silage DM intake of 11.26 kg per cow occurred on the soyabean meal only treatment, and the differences in silage intake between barley and sugarbeet pulp treatments were not significant. On average, for 1 kg of barley and sugarbeet pulp DM consumed, the reductions in the intake of silage DM were 0.44 and 0.36 kg respectively. The daily milk yields were 20.5 and 20.8 kg per cow on the barley and the sugarbeet pulp treatments respectively and were not significantly different. The fat, solids-not- fat, crude protein and lactose concentrations in the milk, and the liveweight of the cows were not significantly different on the barley and sugarbeet pulp treatments. In Expt 3.3, grass silages with low D-values of 62.6 and 65.5, and high D-values of 69.7 and 68.6 were offered ad libitum to twelve cows in a 16-week experiment. In addition, a supplement of high-protein concentrates (362 g CP/kg DM) was given at a flat rate of 1.5, 3.0 and 4.5 kg per cow/day. There were no significant changes in the daily silage DM intakes when increasing amounts of the concentrate supplement were consumed. The milk yields increased significantly as the concentrate intake increased with both the low and the high D-value silages. The fat, total solids and the lactose concentrations in the milk were not significantly different on the different treatments