ESTIMATION OF INTAKE IN HIGH PRODUCING HOLSTEIN COWS GRAZING GRASS PASTURE

The objectives were to estimate intake of pasture and total DMI by hig h producing cows grazing grass pastures and to measure changes in nutr ient composition of grass pasture during the grazing season. Sixteen m ultiparous Holstein cows averaging 31 kg of 4% FCM/d at the start of t he trial grazed grass pastures at a stocking rate of 2.5 or 3.9 cows/h a from April until October 1990. Intake was estimated using Cr2O3 as a n indigestible fecal marker. Pasture samples were analyzed for nutrien t composition at six times during the grazing season corresponding to the times of intake estimation. Total daily DMI increased from 21.3 kg in early spring to 22.4 kg in late spring and then decreased as lacta tion progressed; however, DMI exceeded NRC recommendations during most of the grazing season. Daily pasture DMI varied with season, ranging from 11.6 to 15.6 kg and was lowest (11.6 kg) in the summer. Estimated NE(L) intakes were lower than NRC recommendations in early spring. Du ring the grazing season, pasture ranged from 39 to 48% NDF and from 22 to 30% CP with 15 to 20% ruminally degradable protein on a DM basis. Grazing cows consumed adequate DM from pasture except in early spring. Although nutrient composition of pasture varied with season, quality remained high.