Abstract:
Dairy cows in early lactation grazed irrigated annual pastures during 14 weeks in autumn and winter. They were grazed for either 2 or 6 h each day and then restricted to a feedpad and offered ad libitum maize silage. Other cows were fed 1 of 2 diets while in yards: a feedlot diet based on cereal grain, maize silage, and protein supplement; a mixture of conserved legume and maize silage. Feed intakes and cow performance were monitored. Cows in metabolism cages were fed the feedlot diet with various combinations of red clover and maize silage. Digestibility and rate of disappearance of test feeds from nylon bags were measured in the metabolism trials. Rumen samples were analysed for pH, ammonia, and volatile fatty acids. Dietary constituents were evaluated in vitro and in vivo using sheep. The cows on the feedlot diet recorded the highest DM intakes and the highest liveweight gain, and initially produced the most milk and milk protein. Their milk yields eventually fell to levels similar to those of the grazing cows. Cow performance was poorest on the pasture silage-maize silage mixture, and this treatment was discontinued after only 8 weeks. The poor performance was partly attributed to reduced silage quality from heat damage during ensiling the pasture. Supplementing red clover with increasing levels of maize silage did not influence digestibility but reduced DM intakes and cow performance. Cows grazing for 2 h/day produced 1-2 L/day less milk, and lost more weight, than cows grazing for 6 h/day; their rumen ammonia fell below critical levels. The grazing of high-clover pastures between morning and afternoon milking, combined with maize silage supplementation, is convenient and sustains high milk yields during early lactation.