Effect of source of carbohydrate in concentrate on the performance of high producing dairy cows during spring grazing

Abstract

Two experiments were conducted to evaluate two different sources of carbohydrate (fibrous and starchy) in concentrate supplement for high producing dairy cows fed spring pasture. In experiment 1, 12 Friesian cows producing a daily milk yield of 33.0 kg were assigned to a 3x3 Latin Square design with 21 day periods each. In experiment 2, 27 Friesian cows yielding 29.3 kg/d were assigned to a completely randomized design for 45 days. In both experiments, the treatments included: grazing only (GO), grazing plus 6 kg/d of sugar beet pulp- based concentrate (beet pulp), and grazing plus 6 kg/d of cereal-based concentrate (barley). The cows were supplemented twice a day and managed under a strip grazing system on a pasture consisting mainly of perennial ryegrass. In experiment 1 and 2 the crude protein (CP) content of the concentrates was 17.0 and 11.9%, respectively. In experiment 1, average milk yield and milk composition were similar for the sugar beet pulp-based concentrate and the cereal-based concentrate. In experiment 2 average milk yield and milk fat were similar for the supplemented treatments. The type of concentrate did not affect body weight, bodyweight gain, or body condition score. Concentrate supplementation increased average milk yield (5.0 and 6.0 kg/d for experiments 1 and 2, respectively) and milk protein concentration (0.12 and 0.15 percent units for experiments 1 and 2, respectively).These results were only significant in experiment 1, when compared to grazing only. In experiment 2 the starchy concentrate produced an increase in plasma glucose concentration and a decrease in plasma BHBA and urea-N concentrations. Under these conditions, the results suggest that carbohydrate source did not affect the productive performance of dairy cows but it did improve the metabolic condition.