Pasture intake, milk production and grazing behaviour of dairy cows grazing low-mass pastures at three daily allowances in winter

Grazing low-mass pastures is almost inevitable when extending the grazing season into late winter to reduce feed costs, cows' performance being potentially affected. An experiment was carried out to estimate the performance, pasture intake (PI) and behavioural adaptation of dairy cows when grazing low-mass pastures at LOW, MEDIUM and HIGH pasture allowances (PA), corresponding to 19, 32 and 46 kg OM/cow per day above ground level, respectively. The study took place in the late winter of 2008 on good quality perennial ryegrass/white clover pastures with a mean pasture mass and a pre-grazing platemeter height of 2.3 t OM/ha above ground level and 5.8 cm, respectively. Each cow was supplemented with 4.4 kg OM of maize silage and 2.0 kg OM of cereal concentrate. Daily time at pasture was restricted to 9 h between the am and pm milkings. Eighteen midlactation Holstein cows (twelve multiparous and six primiparous) were used in a 3 × 3 orthogonal Latin square design with three consecutive periods of 13 days. On average, the cows produced 25.3 kg of milk and total OM intake was 14.4 kg/d. Pasture OM intake averaged 7.9 kg/d and linearly increased from LOW to HIGH (+ 0.04 kg/kg PA). Similarly, milk production per cow (+ 0.09 kg/kg PA) and milk protein concentration (+ 0.04 g/kg per kg increase in PA) linearly increased with increasing PA. Milk fat concentration, on the other hand, decreased by 0.10 g/kg per kg increase in PA. The daily grazing time (430 min) and the proportion of time spent grazing (79%) were not affected by PA. On average, pasture intake rate was low (19 g OM/min) and linearly increased from 16.9 g OM/min in LOW to 20.7 g OM/min in HIGH. In the present study, the PI was limited even at high PA because of the cumulative effect of the low-mass pasture (low intake rate) and the restricted access time (short grazing time). Consequently, the effect of PA on PI was low. However, the milk production response to variations in PI was high because of the low energy balance recorded in all treatments.