The influence of the legume Leucaena leucocephala and formal-casein on the production and composition of milk from grazing cows

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Abstract
Twenty-four lactating Jersey cows, grazing a 3-week regrowth of nitrogen-fertilized Chloris gayana cv. Pioneer pastures selected a diet containing 18% crude protein and were given 0, 2 or 4 kg/day of fresh Leucaena leucocephala or 250 g/day of formal-casein. The effect of the treatments on milk production was measured in a 4 × 4 latin-square design experiment with experimental periods of 14 days.Mean milk yield of unsupplemented cows was 9·6 kg/day, 10·1 kg/day when cows were supplemented with formal-casein and 10·3 kg/day when fed 2 or 4 kg Leucaena/day. Yields of solids-not-fat, protein, casein, butterfat and short and medium-chain (C4–C16) fatty acids in milk fat were higher when cows were fed supplements (P < 0·01). Intake of digestible organic matter was lowest on the unsupplemented diets although feed in excess of 40 kg D.M./cow/day was offered and cows had little difficulty harvesting feed with a mean bite size of 350 mg organic matter/bite and mean grazing time of 507 min/24 h.It was concluded that a tropical grass diet containing 18% crude protein was deficient in protein for lactating cows and that small quantities of the legume Leucaena can alleviate such a deficiency.