Effects of pasture type and grazing management in autumn on the performance of dairy cows in late lactation and on subsequent pasture productivity

Abstract

An experiment at Kyabram, Victoria, studied the effects of pasture allowance on the production of grazing dairy cows in late lactation (autumn). Cows strip-grazed paspalum dominant or ryegrass-white clover perennial pastures for 60 d from March to May. Mean pasture allowances were 23.2, 13.3 or 6.9 kg digestible dry matter/cow.d. Reduced pasture allowance during late lactation reduced milk yield and body condition. This occurred because pasture intake was positively related to pasture allowance. Each additional kilogram of dry matter (DM) eaten produced 0.93 kg milk and 0.045 kg milk fat. Cows grazing ryegrass-white . clover pastures produced more milk and milk products at equivalent DM intakes than did cows grazing paspalum dominant pastures, and they were in better condition. This was due to herbage quality: cows grazing ryegrass-white clover pastures were able to select higher quality diets than could those grazing paspalum dominant pastures. When the results were compared with those from two previous stall-feeding experiments, the marginal efficiencies for milk production in all experiments were not significantly different; an extra 1.19 kg fat corrected milk was produced for each additional kilogram of digestible dry matter of pasture eaten. . The pastures were not grazed from May to September but their growth and quality were measured during this period. The amount of pasture left at drying off influenced the growth and quality of the pastures throughout winter: daily growth declined by 3.31 kg DM/ha between May and July, and by 6 56 kg DM/ha between July and September, as herbage yield at drying off (May) increased by each additional tonne of DM per hectare. Also, the ryegrass-white clover pastures grew more herbage at equivalent DM yields than did the paspalum dominant pastures. The implications of these results for grazing management are discussed.