Positive relation between substitution rate and pasture allowance for cows receiving concentrates

Pasture substitution rates were measured when cows were offered a grain-based concentrate at pasture allowances of 8, 17 and 33 kg DM/cow.day. Thirty-six cows in their first month of lactation were allocated to 6 groups in a 6x6 Latin square design. There was a significant interaction between supplementation and pasture allowance for pasture intake and milk yield. Pasture intake decreased by 0,0.25 and 0.69 kg pasture DM/kg concentrate DM eaten, at pasture allowances of 7.6, 17.1 and 33.2 kg DM/ cow.day. The increases in milk yield from feeding concentrates were greater at lower pasture allowances: 0.97, 0.69 and 0.28 L/kg concentrate DM eaten at pasture allowances of 7.6, 17.1 and 33.2 kg DM/ cow.day respectively. A highly significant linear relation between pasture intake at zero concentrate intake and pasture substitution rate (SR) was established from these and other published data [SR = -0.445 + 0.3 15 (¦0.057)PI, where PI is pasture intake (kg DM/ cow.day. 100 kg liveweight)]. This relation quantifies the effect of unsupplemented pasture intake on pasture substitution rate and consequently on the milk yield response to supplementing the diet of cows with concentrate.