Post-partum cows were housed in cubicles until 22 March. During this period they were fed grass silage ad libitum.
In addition, high NL cows received 7 kg/cow per day of concentrates and low NL cows received 4 kg/cow per day of concentrates. Between 23 and 29 March inclusive, cows were at pasture by day only. From then on cows were at pasture full time, and the high and low NL cows received 3 and 1 kg/cow per day of concentrate, respectively. Between 16 April and 9 October cows were at pasture full time and differences in NL were maintained by postgrazing sward height. Grazing management was based on a rotational grazing system, and cows were allocated fresh grass after morning milking. High and low NL cows grazed to a postgrazing sward height of 83 mm and 68 mm respectively. Herbage allowances were: high NL TAD=30.6; high NL OAD=32.0;low NL TAD=19.4 and low NL OAD=18.6 kg DM per cow/d,respectively. Actual grasses removed per cow/d in the groups were: high NL TAD=19.3; high NL OAD=19.7; low NL TAD=14.6 and low NL OAD=14.0 kg DM. Paddocks were topped by mechanical means to maintain pasture quality across treatments. Due to drought conditions and grass scarcity, between 1 July and 3 August cows on the high NL and low NL treatments were provided with 3 and 1 kg/cow per day of concentrates in addition to their grass allowance. This was reduced to 2 and 1 kg/cow per day between 4 and 11 August, when concentrate was again removed from the diet.