THE EFFECT OF CLOSING DATE OF PASTURE IN AUTUMN AND TURNOUT DATE IN SPRING ON SWARD CHARACTERISTICS, DRY-MATTER YIELD AND MILK-PRODUCTION OF SPRING-CALVING DAIRY-COWS

Studies in Ireland and elsewhere have shown that grazed grass can make a major contribution to the diet of lactating dairy cows and is less expensive than silage or concentrates. Therefore, the provision of a l arge supply of grass in spring for cows in early lactation is an impor tant management objective. The aim of this study was to investigate th e effect of closing date of pasture in autumn and subsequent turnout d ate in spring on the performance of spring-calving dairy cows in early lactation. Fifty-two spring-calving dairy cows were randomly assigned to one of four treatments in the spring of 1994. The treatments invol ved two closing dates in the autumn, 20 October 1993 (early closing) a nd 2 December 1993 (late closing), and two turnout dates in spring, 4 March 1994 (early turnout) and 25 March 1994 (late turnout). The durat ion of milk production measurement in Spring was 12 weeks (4 March to 27 May, 1994). Delaying closing date in the autumn significantly (P < 0.001) reduced the availability of herbage in the following spring. Li kewise, early turnout in spring significantly reduced pre-grazing herb age yields. In late May when the experiment finished the effect of clo sing date on pre-grazing herbage yields was still present whereas the effect of turnout date had disappeared. There was no interaction betwe en closing date in autumn and turnout date in spring for milk yield, m ilk composition or live-weight change. Closing date did not have a sig nificant effect on milk yield or milk composition. Early turnout incre ased milk yield (P < 0.05) and fat and protein concentrations (P < 0.0 1) during the 3-week period when the late-turnout group were housed. I t is concluded that in a compact, spring-calving herd, at stocking rat es of 2.7 to 3.0 cows/ha, in the south of Ireland, all animals should be removed from pasture by late November to early December and turnout to pasture in spring should be from early March.