Daily herbage allowance: Effect on yield and quality of pasture and on milk production per cow and per hectare

Abstract

A deeper knowledge on the effects of herbage allowance (HA) on pasture characteristics and animal performance is necessary to improve efficiency of dairy production systems based on intensive grazing of pasture. The objectives of this study were to assess the effect of two levels of HA on  pasture characteristics and milk performance during a three years period. Holstein Friesian dairy cows were selected from a dairy herd owned by the Universidad Austral de Chile and randomly assigned to one of two homogeneous groups. Each group was managed with different HA (high or low), measured at ground level, in a grazing system with half day strip. Grazing management variables (pre and postgrazing herbage mass, stocking rate, and proportion of pasture harvested), and animals variables (body weight, body condition score, milk production and composition), were measured and the results were averaged for each season of the year. Pre-grazing herbage mass did not differ between treatments averaging 2,313, 2,261, 2,069 and 1,315 kg DM ha-1, for spring, summer, autumn and winter, respectively. Cows grazing at low HA had a lower post-grazing herbage mass (-146 kg DM ha-1), especially in summer and spring. Consequently the proportion of pasture harvested was greater at low HA (+5.5%). Milk production per cow was not significantly reduced when a low level of HA was
offered. However, due to higher stocking rate, milk production per hectare increased in low HA by 26% as average of the three-year period. Results suggest that the restriction on herbage allowance might be a useful grazing management tool to improve the profitability of dairy systems based on intensive grazing of pasture.