White clover herbage in the vegetative stage of growth has a high nutritive value for milk production, but he high crude protein content could be better utilised if cows were given a suitable readily fermentable carbohydrate source. Six rumen fistulated Friesian cows in late lactation were housed in metabolism cages and fed either fresh white clover herbage or white clover and maize silage (50:50). The experiment was a cross over design that allowed measurement of nutrient intake, rumen function and milk production. At similar digestible organic matter intakes (9.6 kg/d vs 9.9 kg/d), replacing 50% of the white clover dry matter with maize silage reduced crude protein intake by 30% (3 kg/d vs 2.1 kg/d), and urinary N excretion from 251 gN/d to 137 gN/d without affecting milk yield (12.6 l/d vs 12.51 l/d) or milk protein output (400g/d vs 413 g/d). Rumen pH was similar for both treatments (6.1 vs 6.0) but there was a higher utilisation of neutral detergent fibre (2.6 kg/d vs 3.4 kg/d) when the cows were fed the mixed diet. The excess intake of nitrogen when the cows were fed white clover only was calculated to be largely wasted as ammonia absorbed from the rumen and excreted as urinary urea.
Proceedings of the New Zealand Society of Animal Production, Volume 53, , 29-32, 1993
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