Abstract

A penfeeding experiment, involving 29 lactating dairy cows, was undertaken to assess the use of Persian clover (Trifolium resupinaturn) herbage instead of perennial ryegrass (Lolium perenne)-dominant herbage as the basal ration in diets in which maize silage (0 to 10.6 kg DM/cow day-1) was used as a supplement. This was supported by a second experiment in which 16 cows grazed limited amounts of Persian clover pasture (herbage allowance of 16.5 kg DM/cow day-1) and were supplemented with various amounts of maize silage (0 to 8.3 kg DM/cow daym-1). In the pen experiment, feeding maize silage to cows grossly underfed with perennial ryegrass pasture resulted in a marginal response to additional feeding of 0.9 kg milk for each of the first 5 kg DM of supplement eaten. This level of supplementary feeding constituted about 40% of the diet. Thereafter, maize silage resulted in virtually no additional milk and the best fed cows only produced about 20 kg of milk. A much greater response in milk yield (1.4 kg milk/kg DM of additional maize silage eaten) was obtained when Persian clover was substituted as the basal ration. There were no differences in milk composition or changes in body condition between cows offered the different basal herbages. Milk fat content averaged 3.9% across all cows, while milk protein content and change in body condition increased by 0.03% and 0.13 units for each additional kg DM of maize silage eaten each day. In the grazing experiment, when a small amount of maize silage was fed to the cows, the marginal return was 1.2 kg milk for each additional kg DM of maize silage eaten. This is only slightly lower than that reported for the indoor feeding study. A major reason for the good response was the negligible substitution of maize silage for Persian clover that occurred with the first increment of supplement in the diet. With higher levels of maize silage feeding, no extra milk was produced. It was the increase in the level of substitution at the higher levels of maize silage that eliminated the possibility of additional responses in milk production.