The effect of initial spring grazing date and subsequent stocking rate on the grazing management, grass dry matter intake and milk production of dairy cows in summer

The objective of this study was to investigate the effects of an early (February; F) or delayed (April; A) primary spring grazing date and two stocking rates, high (H) and medium (M), on the grazing management, dry matter (DM) intake of grass herbage and milk production of spring-calving dairy cows grazing a perennial ryegrass sward in the subsequent summer. Sixty-four Holstein-Friesian dairy cows (mean of 58 d in milk) were assigned to one of four grazing treatments (n = 16) which were imposed from 12 April to 3 July 2004. Cows on the early spring-grazing treatment were grazed at 5.5 cows ha ^-1 (treatment FH) and 4.5 cows ha^-1 (treatment FM) while cows on the late-grazing treatment were grazed at 6.4 cows ha^-1 (treatment AH) and 5.5 cows ha^-1 (treatment AM). The organic matter digestibility and crude protein concentration of the grass herbage were higher on the early-grazing treatment than on the late-grazing treatment. The cows on the FM treatment had significantly (P < 0.001) higher milk (24.5 kg), solids-corrected milk (22.5 kg), fat (P < 0.01, 918 g) and protein (831 g) yields than the other three treatments. Cows on the FM treatment had a higher (P < 0.001) DM intake of grass herbage by 2.3 kg DM per cow per day than cows on the AH treatment, which had a DM intake significantly lower than all other treatments (15.2 kg DM per cow per day). The results of the present study showed that grazing in early spring has a positive effect on herbage quality in subsequent grazing rotations. The study also concluded that early spring-grazed swards stocked at a medium stocking rate (4.5 cows ha^-1; FM) resulted in the highest DM intake of grass herbage and milk production.