Implications of adapting autumn grazing management on spring herbage production––The effect on late lactation milk production and the subsequent response in early lactation animal performance

Abstract

The importance of increased grass availability in the diet of the early lactation dairy cow in spring-calving pasture-based systems is widely reported. To combat the effect of low over winter growth rates, closing swards earlier in autumn can allow for greater accumulation of herbage for grazing in spring. The aim of this study was to identify the impact of three autumn closing treatments (varying closing rotation dates); (1) Early – September 25th to November 9th, (2) Normal – October 10th to November 24th and (3) Late – October 25th to December 9th, on late lactation milk production and early lactation milk production in the subsequent spring. The goal was to identify the optimum recommendations for autumn closing management to achieve increased milk production in spring resulting from increased grass availability, without compromising on animal performance in late lactation. There was no effect of autumn closing treatment on late lactation milk yield or milk solids yield. There was, however, a decline in milk protein concentration, associated with the diet change at housing of the early closed treatment (−1.6 g/kg milk) and normal treatment (−0.7 g/kg milk) in autumn compared with the late closed treatment (41.5 g/kg milk), as a result of the increased silage fed during this period (473.2, 345.8 and 163.8 kg DM/cow, respectively). Each one day increase in closing resulted in an extra 16 kg DM/ha in pre-grazing herbage mass on February 1st of the subsequent year (R2 = =0.502). The resulting increases in pre-grazing herbage mass contributed to increased daily herbage allowance (DHA; +2.9 kg DM/cow) and total dry matter intake (+1.3 kg DM/cow) for the early treatment in spring compared with the normal and late closed treatment. Each 1 kg increase in DHA resulted in an increase of 0.38 kg milk/cow/day. A greater proportion of silage was required cumulatively on the early closed treatment (628 kg DM/cow) in contrast to the late closed treatment (419 kg DM/cow) between the autumn and spring period. However, the increased milk production associated with the increased grass availability in spring outweighed the cost associated with the increased silage requirement. Closing the farm early in autumn offers significant advantages in terms of higher DHA, increased dry matter intake and higher milk yields the following spring. Therefore, it is recommended the closing rotation should begin in late September and cease by mid-November, where there is a high demand for grass in early spring.