Abstract:
Dairy cows in early lactation were fed a maize-silage-based supplement at either 3 or 8 kg DM/cow.day, while grazing irrigated perennial pastures at 45 or 30 kg pasture DM/cow.day. The supplement consisted of maize silage, alone or with 16% DM replaced by cottonseed meal. A fifth group grazed at the higher pasture allocation with no supplements. Milk yield and composition, liveweight and body condition, and pasture intake were monitored over 10 weeks during late spring-early summer. Samples of pre- and post-grazed pasture, supplement, rumen fluid, and faeces were collected for chemical analyses. Supplemention increased total feed intake and milk yield of grazing cows, except at the higher level of silage without cottonseed meal. From data on nitrogen content of the grazed pasture and the supplement, together with rumen ammonia concentrations, it was concluded that low dietary protein levels limited milk yield in cows supplemented with 8 kg maize silage DM/day without the additional cottonseed meal. Liveweight and body condition score increases were greater in supplemented animals, while their rumen volatile fatty acid profiles suggested greater partitioning of nutrients towards lipogenesis in body tissue. Pasture was substituted at the rate of 0.67 kg DM for every kg maize silage DM consumed.