Influence of season and stocking rate on pasture herbage availability and milk yield

Abstract

This experiment evaluated the effect of season of the year and stocking rate (SR) on pasture availability to lactating dairy cows supplemented with concentrates. In study 1, herbage mass (HM) and pasture allowance (PA) were evaluated on a commercial dairy farm during the months of July to February. Regression analysis indicated a significant and quadratic negative relationship between time and HM (P < 0.05; R²  = 0.65) and a weaker linear relationship between time and PA (P < 0.05; R² = 0.47). Herbage mass and PA were lower from October to February, when the climate is dryer and cooler in the Caribbean tropics. Pasture allowance declined from 48.7 (July to September) to 21.1 kg/cow (December to February). However, estimated pasture consumption increased from 6.4 to 8.1 kg of dry matter per cow over the same period. In a second study, the effect of SR on HM, PA and concentrate supplementation was evaluated on 12 farms. As expected, HM (P < 0.05; R² = 0.31) and PA (P < 0.01; R² equal 0.80) declined as SR increased. There was no significant relationship between SR and concentrate intake (Cl) or between Cl and milk yield. On most farms pasture herbage appeared to be underutilized because of relatively high levels of concentrate supplementation. Pasture management and supplementation strategies should be modified to account for seasonal variability of pasture yield and intake. This modification would improve nutrient utilization from pasture and would reduce the need for purchased feeds and ultimately ration costs.