Abstract

Two experiments were conducted to assess aspects of the feeding value of winter pasture for lactating dairy cows. During May 1989, three groups of 10 Friesian cows were offered daily herbage allowances of 43 (High, H), 20 (Medium, M) and 13 (Low, L) kg dry matter (DM) per cow, for a four week period in early lactation. Daily herbage intakes, assessed by cutting pastures before and after grazing, were 12.4, 9.1 and 7.6 kg DM per cow, respectively. "Covariance adjusted" daily milk yields (15.6, 12.4 and 9.4 litres/cow), milkfat yields (0.64, 0.54 and 0.41 kg/cow) and protein yields (0.50, 0.36 and 0.28 kg/cow) differed significantly (P<0.01) between treatments. Responses/kg extra herbage DM eaten were 1.0 and 1.9 litres, 31 and 84 g milkfat and 43 and 52 g protein for the H-M and M-L increments, respectively. Apparent liveweight gains and proportion of cows showing oestrus were also positively related to allowance. During June 1990, two groups of 15 Friesian cows in early lactation were transferred from a herbage and grass silage ration to a high herbage allowance of 63 kg DM/cow daily. The yields of milksolids and especially protein immediately increased substantially (P<0.01); the protein concentration increasing from 3.02 to 3.70%. For a period of two weeks, the cows in one of the groups (Treatment) also consumed 2.7kg DM daily of a high protein concentrate supplement (Brewers' grain and soyabean products). Daily milk yields (Control 20.3, Supplemented 22.5 litres), milkfat yields (C 0.87, S 0.94 kg) and protein yields (C 0.75, S 0.82 kg) were increased significantly (P<0.05) by the supplement. Herbage intakes were measured and substitution rates of 0.71 and 0.45 kg pasture DM/kg concentrate DM were estimated using two alternative techniques. The combined results indicate that the nutritive value for milk production of winter pasture is relatively high, provided that a high daily allowance is offered from pastures with more than 2,000 kg DM/ha pre-grazing mass. However, the relatively large increase in milk production caused by the concentrate supplement suggests that aspects of its nutritive value may constrain high levels of milk production where allowance is high.

W, Suksombat, CW Holmes, and GF Wilson

Proceedings of the New Zealand Society of Animal Production, Volume 54, , 83-86, 1994