The effect of level of concentrate supplementation in winter and grazing allowance on the milk production and financial performance of spring-calving cows

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Abstract
An experiment with a 2 × 2 factorial design was used to assess the effects of offering either 6 (L6) or 12 (H12) kg concentrates daily from day 13 of lactation until turnout to grazing with grass silage (600 to 620 g digestible organic matter per kg dry matter (DM)) ad libitum and either ad libitum (G) or restricted (g) quantities of grass from turnout to the end of August. In each of 3 years, 60 to 70 January- to March-calving British Friesian cows were used. From calving until turnout to grazing the mean daily DM intakes of silage were 7·2 and 8·9 kg, and of concentrates 8·5 and 4·9 kg for the H12 and L6 groups respectively, giving a mean substitution rate of 0·47 kg silage DM per kg concentrate DM. Mean daily milk yields were 26·7 and 22·9 kg giving a direct response of 0·85 kg/kg additional concentrate DM. Milk from the L6 group had a higher fat concentration and these cows were also lighter at the end of the winter. At pasture, there were no significant interactions for milk variates between winter treatments and grass availability. The stocking rate of cows with restricted grass availability was 0·33 higher from turnout to the end of August. It resulted in a 0·10 proportional reduction in milk yield per cow but per ha there was a 0·21 proportional increase. At pasture, the H12 cows gave more milk at both grass availabilities. The total responses to concentrates were 1·59 and 2·11 kg milk per kg concentrate DM at the ad libitum and restricted grass availabilities respectively. The good response to concentrate coupled with a 0·35 cow per ha increase in annual stocking rate as a result of restricting the grazing area ensured that gross margins and grass utilization were highest for the H12g cows. Conception rates were similar on all treatments and there were no significant differences in live weight at the end of lactation.