Effects of offering a concentrate or silage supplement to grazing dairy cows in late lactation on animal performance and on milk processability

Grass growth declines during the autumn period. The issue arises as to when silage and/or concentrate feeding of cows at pasture should commence. The present study was undertaken to compare the effects of two levels of silage and two levels of concentrate, offered as supplements to pasture towards the end of the grazing season, on production and processability characteristics of milk. Seventy cows were assigned to one of the following treatments for a 10-week period: (1) pasture only, (2) pasture + 2 kg grass silage dry matter (DM)/day, (3) pasture + 4 kg silage DM /day, (4) pasture + 2 kg concentrate DM/day, and (5) pasture + 4 kg concentrate DM/day. The cows were stocked at 2.69/ha and grazed as one group. Pasture was grazed to a sward surface height of 6 to 7 cm. Supplementation with silage reduced (P < 0.05) the yield of milk constituents. This effect was linear. The concentrations of protein and lactose in milk were also reduced (P < 0.05). Concentrate supplementation resulted in a significant linear increase (P < 0.001) in the yield of milk and milk constituents and in lactose concentration but fat concentration was reduced at the higher level of supplementation. Free fatty acid concentrations in milk were significantly reduced by both silage (P < 0.05) and concentrate (P < 0.01) supplementation in weeks 6 and 10 only. Milk casein number was similar for all treatments. Rennet coagulation time, rate of curd aggregation and curd firmness were also similar for all treatments.