BRIEF COMMUNICATION: A case study of the effects of diet and winter management on dairy production, profit and nitrate leaching in Rotorua

Feed and winter management options were modelled for a dairy farm and its adjoining support land in the Lake Rotorua catchment. The base farm fed turnips, fodder beet, oats, palm kernel expeller (PKE) and pasture silage on the milking platform, with cows wintered on the dry-stock unit on pasture, kale and fodder beet. Scenarios investigated removing crops from the milking platform whilst either: A) reducing stocking rates; B) feeding additional PKE; C) replacing crops, PKE and pasture silage with purchased maize grain and maize silage; or D) wintering cows on the milking platform at a reduced stocking rate. Under a milk price of $6.00/kg MS, D was the only scenario that increased profitability of the milking platform (7%). Compared to the base scenario, nitrate leaching on the milking platform increased for scenario D and decreased for scenarios A, B and C. When including the dry-stock unit, total N leaching was reduced by 5, 0, 13 and 15%, for A, B, C and D, respectively, compared to the base farm. These results reiterate the importance of investigating the impact of off-farm grazing when wintering cattle in nitrogen sensitive catchments.