Response to grazing pressure and supplementation on milk production by dairy cows

Resumen

An experiment with two systems of milk production using rotationally grazed pasturesof perennial ryegrass and white clover was carried out to study the effect of differentgrazing pressures in spring/early summer on subsequent herbage composition. Seventytwo Holstein-Friesian dairy cows were randomly assigned to four treatments: two stocking rates were applied, medium (M, 3.9 cows ha–1) and high (H, 5.2 cows ha–1) at twodifferent stages of lactation, spring-calving (S) and autumn-calving (A). Milk yieldand composition were analyzed for five months (March to August). Pasture production, quality and sward utilization were measured for each treatment. The objective ofthis experiment was to achieve high herbage intake per animal, high herbage utilizationand to maintain high sward quality throughout the period. Increasing grazing pressureduring the spring period resulted in a significant decrease in herbage intake per cow andincrease in herbage utilization. This lower intake was compensated for by significantlyimproved grass quality in HS. Total nutrient intake was sufficient to maintain high milkproduction per cow. The H stocking rate had increased grass intake and improved grassquality which reduced the substitutive effects of supplementation and maintained highmilk production.