The effect of grazing intensity in late summer/autumn on sward characteristics and milk production of spring-calving dairy cows

The effects of different grazing intensities imposed during late-summer/autumn on subsequent herbage composition and milk production were examined. The treatments involved two stocking rates, 4.55 and 3.54 cows/ha, from 26 June to 20 August (Period I). Subsequently, from 21 August to 6 December (Period II), each of the above stocking rates was adjusted to either 2.89 or 2.45 cows/ha. A total of 56 spring-calving dairy cows were used. Rotation length was maintained at 21 days or greater, depending on grass supply. Where grass supply was not adequate, grass silage was offered as a buffer feed. There was no interaction between stocking rate in Period I and subsequent stocking rate in Period II for either milk yield, milk composition or live-weight change. Milk yield (19.2 v. 18.2 kg/day; P < 0.01), fat yield (0.73 v. 0.69 kg/day; P < 0.001), protein yield (0.65 v. 0.61 kg/day; P < 0.001) and lactose yield (0.86 v. 0.80 kg/day; P < 0.001) were all reduced during Period I at the lower stocking rate. Milk protein concentration was also reduced with the lower stocking rate (34.0 v. 33.4 g/kg; P < 0.01) as was Lactose concentration (44.8 v. 44.1 g/kg; P < 0.001). Reducing stocking rate during Period II had no effect on milk production, except protein concentration which was increased (P < 0.05). The lower milk yields in Period I were associated with significantly higher pre-grazing herbage yield, lower organic matter digestibility, lower proportion of live leaf in herbage offered and longer rotation length.