Dairy cattle breeding objectives combining yield, survival and calving interval for pasture-based systems in Ireland under different milk quota scenarios

Abstract

Economic values in Irish pounds (IR£) were calculated for milk, fat and protein yields (IR£ cow −1 year −1 kg −1), survival (IR£ cow −1 year −1 % survival −1), and calving interval (IR£ cow −1 year −1 day −1) using a farm model for pasture-based systems in Ireland. Economic values for yield were calculated by changing one of these traits whilst keeping the other traits at the default level, i.e. the economic value for calving interval does not include the costs of higher culling due to a longer calving interval. Herd parameters (e.g. number of milking cows, replacements, youngstock and calving pattern), milk production, energy requirements, feeding ration, land use and labour requirements were re-adjusted to calculate economic performance. Three scenarios were simulated as follows: (S1) milk and fat% quota with a fixed number of cows per farm and quota leasing; (S2) non-quota scenario with a fixed number of cows per farm; and (S3) milk and fat% quota with a fixed output per farm. Sensitivity analysis showed that, with high quota costs and/or lower fat prices, the weighting of fat yield was close to becoming negative in the quota leasing scenario (S1). There was major re-rankings among the top 1000 bulls due to a negative weighting on fat. The results for S1 suggested that the economic values in profit per cow per year are −IR£0.06 per kg milk, IR£0.68 per kg butterfat, IR£4.49 per kg protein, IR£8.98 per % survival, and −IR£1.63 per day calving interval, and the corresponding values in additive genetic standard deviation units were −0.47, 0.19, 1.00, 0.56 and −0.21, respectively.