Effect of winter pasture residuals' and grazing- off on subsequefit milk production and pasture performance

Abstract

Concern at the effect of winter pasture residuals on pasture productivity led to the comparison of different wintering systems at the DRC No. 3 Dairy from May-December 1993. Three farmlets were designed to have 2000 kg DM/ha average farm cover at calving, but with pastures grazed to either 900, 1400 or 1800 kg DM/ha at least once during the winter. A fourth farmlet was spelled from grazing from 25 May-4 July to give an average farm cover at calving of 2900 kg DM/ha. Pasture regrowth, composition and structure, milk yield, liveweight and reproductive performance were measured. A simulation model UDDER was used to generalise from the specific experimental results. Pasture regrowth in July-August was greater on the wintering-off treatment than those grazed during winter, but treatment differences in late spring were inconsistent. Wintering-off decreased ryegrass tiller and white clover growing point densities in August but differences had disappeared by November. Winter grazing treatment had no effect on any component of milk production from calving to late October. From late October until m&December-milk-protein-and.milksolids y i e l d were less on the wintering-off treatment than the mean of the other three treatments (0.62 vs 0.68 kg/cow/day) and (1.49 vs 1.59 kg/cow/day), respectively. Grazing to different winter pasture residuals had no consistent effects on subsequent pasture productivity, composition or milk yield. Simulation showed that wintering-off can lead to increased milksolids production when average farm cover in September is predicted to fall below 1750 kg DM/ha. Timing and amount of conservation become c&i&i1 slfterwintering;off if pasture quality and hence milk production are to be maintained in late spring. Keywords: dairy cow, milksolids, milk yield, pasture regrowth, pasture residual, pasture structure