Effect of replacing time available for grazing with time available for eating maize silage and soyabean meal on milk yield and feeding behaviour in dairy cows

Abstract

Low rates of herbage dry matter (DM) intake impose limits on total daily DM intake in grazing dairy cows. The objective of this study was to increase total daily DM intake and milk production by restricting daily time available for grazing (TAG) and replacing it with time available for eating a maize silage/soyabean meal (TAMS) diet indoors. The treatments (TAG + TAMS) were 20 + 0, 19 + 1, 10 + 10 and 5 + 15 h. Measurements were made of milk production, intake and feeding behaviour. The interactions of TAG + TAMS treatments with sward height (SH) and concentrate level (CL) were also examined. Two experiments, each lasting 42 days, were carried out in spring (Experiment 1) and autumn (Experiment 2) using forty-eight and twenty-four Holstein-Friesian cows respectively. Treatments were arranged in a factorial design with TAG + TAMS treatments, SH (Experiment 1 only) and CL as the independent variables and a TAG + TAMS of 20 h. Reducing TAG and increasing TAMS significantly reduced estimated herbage DM intake and significantly increased maize silage/soyabean meal intake in both experiments, but there were no significant main effects of TAG + TAMS treatments on milk yield (mean, 27·4 and 25·5 kg d−1 for Experiments 1 and 2 respectively), and yield of milk constituents. Increasing SH (Experiment 1) and CL (Experiments 1 and 2) significantly increased milk yield. In Experiment 1, there was a significant interaction between TAG + TAMS treatments and SH with the taller sward height of 8–10 cm and the 20 + 0 treatment having the highest milk yield (29·7 kg d−1) and the 5 + 15 treatment the lowest (27·2 kg d−1), whereas at the lower sward height of 4–6 cm, milk yield was lowest on the 20 + 0 treatment (25·5 kg d−1) with the other three treatments being higher (mean, 26·9 kg d−1). Replacing TAG with TAMS significantly increased liveweight gain in Experiment 1 but not in Experiment 2. Estimated rates of intake of herbage were lower in the autumn experiment (Experiment 2, 9·6 g DM min −1) than in the spring experiment (Experiment 1, 29·4 g DM min −1) but rates of intake of maize silage were higher in the autumn (112·4 g DM min−1) than in the spring (72·5 g DM min−1). In conclusion, in spring the response to replacing TAG with TAMS was dependent on sward conditions with the highest milk fat plus protein yield being on the 20 + 0 treatment at the high sward height and on the 19 + 1 treatment at the low sward height. The high liveweight gain of the 5 + 15 treatment could be an important means of restoring body condition in grazing lactating cows. In autumn, intakes of herbage were low in spite of its high estimated nutritive value with all treatments having a similar level of performance.