Effect of daily herbage allowance on the performance of spring-calving dairy cows

The aim of this study was to investigate the relationship between daily herbage allowance (DHA) and the performance of dairy cows. Forty-eight multi-parous spring-calving (mean date, 19 February) Friesian cows were divided into three equal groups and assigned to one of three levels of DRA (above a cutting height of 35 mm) of 16 W, 20 (M) and 24 (H) kg dry matter per head from May to August, 1995. The daily allowances were equivalent to 14.5, 18.1 and 21.9 kg organic matter (OM) per head. The cows grazed to sward heights (mm) of 44, 55 and 65 (s.e. 0.6) and residual herbage masses (above 35 mm) of 276, 404 and 509 kg OM/ha (s.e. 14.2) for L, M and H DRA, respectively. Pastures were mechanically topped post-grazing. Cows consumed 13.5, 14.6 and 15.1 kg OM (s.e. 0.30) at L, M and H DRA, respectively. Mean daily milk production of the cows grazing at L, M and H DRA was 20.8, 22.3 and 23.0 kg (s.e. 0.31), respectively, and the corresponding milk protein concentrations were 32.4, 32.8 and 33.6 g/kg (s.e. 0.25). Daily milk yield could be predicted from pre-experimental yield and DHA according to the following model: y = Delta + 0.66 (s.e. 0.052) X pre-experimental milk yield + 0.304 (s.e. 0.0410) X DHA (r.s.d. 1.68; R-2 0.74), where Delta = 2.04, 0.62, -2.88 and -3.12 as the intercepts for May, June, July and August, respectively. The results indicate that good individual cow and herd production levels can be achieved from high quality herbage without concentrate supplement during the summer at a daily allowance of 24 kg herbage dry matter above 35 mm.