Effect of stage of lactation and feeding level on milk yield response by stall-fed dairy cows to change in pasture intake

Abstract

Three separate experiments were carried out to determine the effects of stage of lactation and feeding level on marginal production response by dairy cows to change in feeding level. In each experiment cows were individually offered cut pasture in stalls, ad libitum initially for 10 days, and for a further 28-day period when feeding treatments were imposed. In experiment 1, a total of 37 cows in early or late lactation were offered the same high quality pasture diet either ad libitum or at 0.60 x ad libitum intake. In experiments 2 and 3, 35 and 31 cows which were in early (experiment 2) or late lactation (experiment 3) were offered pasture at 1 of 3 feeding levels: ad libitum, 0.75 x ad libitum. 0.50 x ad libitum intake. In experiment 1 the marginal response was similar, 23.5 and 25.0 g milk fat/kg change in dry matter intake, for cows offered the same diet in early or late lactation. In experiment 2, cows in early lactation showed marginal responses which ranged from 0 to 80 g milk fat/kg dry matter intake and were greater at lower feeding levels and for cows with greater initial milk production. In experiment 3, the marginal response for cows in late lactation was similar to that in experiment 1 (24.4 g milk fat/kg change in DM intake) and was not significantly affected by the level of feeding or by the initial milk production of the cow. Reduced levels of feeding in late lactation appeared to accelerate the changes in milk composition which occur normally in late lactation: increases in the concentration of milk fat and protein; a decrease in lactose concentration. It is concluded that in early lactation, much of the published variation in marginal response can be explained by differences between experiments in levels of feeding studied and in the initial milk yield of the cows. In late lactation there was much less variation in the reported magnitude of the marginal response, and the variation which did exist can be explained by experimental error.