QUALITY EVALUATION AND CONCENTRATE SUPPLEMENTATION OF ROTATIONAL PASTURE GRAZED BY LACTATING COWS

The effects of pasture quality and the amount and nutrient composition of a concentrate supplement on performance of lactating cows were investigated under a controlled rotational grazing system. Pasture samples were collected for two consecutive summers, and the relationship was positive between wet chemistry and near infrared reflectance spectroscopy for CP, ADF, and NDF. During yr 2, 54 Holstein cows averaging 82 d postpartum were used in a randomized block design to evaluate three methods of supplementing grain for a 24-wk trial. A 16.2-ha area of primarily orchardgrass pasture was divided into paddocks of approximately .40 ha each. The three supplemental grain rations were 1) 1 kg of grain/3 kg of milk; 2) 1 kg of grain/4 to 5 kg of milk adjusted weekly, depending upon the quantity of pasture available; and 3) 1 kg of grain/4 to 5 kg of milk. The amount fed in ration 3 was adjusted weekly, depending upon the quantity of pasture available, and reformulated biweekly based on analysis of pasture. No differences existed among treatments for milk production (24.7, 23.2, and 24.1 kg/d) or 3.5% FCM (25.3, 24.8, and 24.9 kg/d) over the 24-wk trial. Cows fed more grain (ration 1) gained more BW. Adjusting nutrient density of the grain to changes in pasture quality resulted in similar milk production and a lower ration cost.