The effect of grass silage harvesting strategy and concentrate level on feed intake, diet digestibility and milk production of dairy cows

Two experiments were conducted under Northern European conditions to quantify dairy cow responses to variable grass silage quality and concentrate feed supplementation. Experiment 1 included 3 primary growth grass silages (early, intermediate and late maturity stage) supplemented with three concentrate levels (9, 12 and 15 kg d-1). Experiment 2 included three consecutive harvests (first, second and third harvest from the same sward within the growing season) and three levels of concentrate supplementation (9, 11 and 13 kg d-1). Dairy cows responded clearly to changes in the harvesting time of silage in primary growth (quadratic effect) and amount of concentrate (linear effect) in the diet in Experiment 1. Milk yield was the lowest with third harvest silage in Experiment 2, and responses to increasing concentrate allowance were linear. Interactions between silage quality and concentrate supplementation were detected in Experiment 1, where milk production responses to additional concentrate decreased with increasing silage digestibility. No interactions were found in Experiment 2, probably due to the small range of differences in nutritional quality between the silages prepared from different harvests. The results demonstrated that it is difficult to compensate for low silage digestibility by increasing the amount of concentrate. The variable ECM response (from -0.01 to 0.85 kg ECM per kg DM incremental concentrate in the diet) is explained by the concomitant decrease in silage intake and negative effect on diet neutral detergent fibre digestibility.