The effect of silage type on the performance of lactating cows and the response to, high levels of protein in the supplement

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Abstract
A change-over design experiment, comprising four periods each of 4 weeks' duration, was used to evaluate three silage types each fed with two levels of protein in the supplement in a 3×2 factorial arrangement. The three silages were high digestibility unwilted (A), high digestibility wilted (B) and low digestibility unwilted (C). The supplements had crude protein contents of 152 and 240 g/kg dry matter, and were offered at a standard rate of 10 kg undried weight daily. The mean silage intakes were 9·3, 9·5 and 8·6 ±0·19 kg dry matter/day for A, B and C respectively, but protein content of the supplement had no significant effect on the intake of silage. Milk yield was significantly affected by both silage type and protein content of the supplement, with the mean yields being 23·6, 23·9 and 22·0 ± 0·49 kg/day for A, B and C respectively, and 22·4 and 24·0 ±0·40 kg/day for the medium and high protein supplements respectively. Although there was no significant interaction between silage type and protein content of the supplement, the greatest response to increased protein was obtained with B. Neither silage type nor protein content ofthe supplement affected animal live weight or milk composition (other than fat content, which was significantly affected by silage type). Blood plasma urea levels were 281 and 405 ± 28·0 mg/1 for the medium and high protein supplements respectively.Total ration digestibility and nitrogen balances were carried out on three animals per treatment. The digestibility of dry matter, organic matter and nitrogen was significantly affected by both silage type and level of protein in the supplement. The output of nitrogen in the urine was also significantly affected by both these factors.