The effect of restriction of pasture intake in late lactation on the milk production and body condition of dairy cows

The effect of restricting the intake of pasture on the performance of dairy cows was studied in two 28-day phases in the eighth and ninth months of lactation. Intakes ranged from 12.4 to 4.9 kg of dry matter/cow day-1. After the 28-day restriction phases, all cows were grazed ad libitum at pasture. Production of milk, butterfat, protein and solids-not-fat all declined linearly with reduction in intake (0.569, 0.0286, 0.0206 and 0.0525 kg per kg of dry matter intake, respectively). Butterfat concentration increased curvilinearly with reduction in intake, but there was no effect on protein and solids-not-fat concentrations. In addition to the decreased production, there was a decrease in body condition score of 0.160 units for each kg reduction in dry matter intake. During the post-experimental period, with ad libitum grazing, cows that had previously been restricted recovered most of their daily milk yield and some of their body condition. The cows in this experiment required an extra 35 kg of dry matter to produce an extra kg of butterfat, but this efficiency ignores potential extra production in the following lactation from improved body condition.