Effects of stocking density and concentrate supplementation of grazing dairy cows on milk production, composition and processing characteristics

The effects on milk composition and processing characteristics of varying g rass supply by changing stocking density and of offering a concentrate supp lement were investigated. The experiment was conducted over 28 weeks of the lactation (April-October) using 48 spring-calved Friesian-Holstein cows. T hree herds each of 16 cows were offered a restricted grass supply, a standa rd grass supply and a standard grass supply with a supplement of 3 kg conce ntrate/d. Treatment groups were grazed separately with a residence time of 3 d/paddock. Milk production, composition and processing characteristics su ch as renneting properties, ethanol stability and plasmin activity were mea sured weekly. Increasing stocking density above the standard system resulte d in significant reductions in milk fat and protein yields, the concentrati ons of total protein, casein and whey proteins, and a deterioration in most processing characteristics. Imposing concentrate supplementation on the st andard system increased total protein, casein and whey protein concentratio ns but generally did not improve processing characteristics except for etha nol stability. These results suggest that the standard grass supply in a ro tational grazing paddock system can support efficient production of quality milk, and concentrate supplementation will not improve processing characte ristics when an adequate supply of good quality herbage is available.