Early lactation pasture allowance and duration: the effect on yield of milk fat and protein

Early spring pasture growth can be low, resulting in a pasture availability deficit. The objective of this experiment was to investigate if different pasture allowances offered to early lactation grazing dairy cows for varying time durations influenced yield of milk fat and protein. The two year experiment offered cows one of four pasture allowances (PA; 60, 80, 100 or 120% of intake capacity) for either 2 or 6 weeks. Once the 2- and 6-week time durations had elapsed, the treatments were offered 100% of intake capacity. During the first 2 weeks of the experiment yield of milk fat and protein increased linearly with increasing PA (1.73, 1.77, 1.84 and 1.98 kg cow-1 day-1; 60, 80, 100 and 120% PA, respectively). At the end of the 6 weeks there was an effect of the interaction between pasture allowance and duration on yield of milk fat and protein on milk solids yield. All 2-week cows had similar cumulative milk yields for the first 6 weeks of the experiment (78 kg); although they were similar to the 100x6 cows they were different to all other 6-week treatments. The 60 and 80% 6-week cows produced similar yields of milk fat and protein to each other (70 kg), but lower than the 100 and 120% 6-week cows, who differed significantly from each other (80 and 87 kg, respectively). This suggests that in early lactation the effect of PA yield of milk fat and protein depends on the severity and duration of the reduction in feed allowance