Effects of supplementary concentrate composition on milk yield, milk composition and pasture utilization of rotationally grazed dairy cows

Twenty eight lactating cows were used in a randomized block design experiment to evaluate the effects of supplementary nitrogen source and heat treatment of rapessed meal containing concentrate compound on pasture utilization under a controlled rotational grazing system. The four supplemental concentrates were: 1) a cereal by-product based basic dairy concentrate (BDC); 2) BDC with 0.9% additional urea (UREA); 3) BDC with 12% rapeseed meal (RSM); and 4) expanded (heat treated) concentrate compound containing BDC and 12% rapeseed meal (EDC). The crude protein (CP, g kg−1 DM) content in the supplement was 124 (BDC), 150 (UREA), 154 (RSM) and 156 (EDC) respectively. The supplementary concentrate was fed at a fixed rate of 0.30 kg−1 of milk. Daily milk yield and concentrate consumption were recorded. No differences existed among four concentrate supplements for energy corrected milk yield (27.4, 26.9, 27.1, 27.7 kg d−1) and fat content, (39.9, 38.2, 38.1, 39.8 g kg−1). Milk protein content tended to decrease (P < 0.06) on UREA supplement compared to RSM and EDC. Milk lactose content was significantly (P < 0.01) low on BDC compared to the other three supplements. Both herbage height (HH) and herbage mass (HM) data indicated that there was a good amount of herbage ha−1 before grazing. The mean herbage organic matter (kg OM per cow per day > 4 cm) available (HOMA) was 13.8, 24.5, 17.2 and 18.2 for the months of May, June, July and August-September, respectively. The mean in vitro organic matter digestibility (IVOMD, g kg−1) was 788 and 770 for the periods of May and June and then dropped to 696 and 686 in the second half of the experimental period.