Development of breeding goals for a dairy production system based on pastures, using a bio-economic simulation model

Abstract

Breeding goals for a dairy herd were developed by combining several of the traits of greatest economic impact on dairy farms; and a selection criterion based on the information available from genetic evaluations. A theoretical production system of 250 cows with a mean adult liveweight of 570 kg each, producing 5 000 L of milk, 173 kg of fat, and 163 kg of protein in 305 d was simulated. Feeding was based on grazing sown pastures, plus silage (maize and sorghum) and supplemental maize grain. The derivation of economic values of traits in the breeding goal was accomplished using a profit equation; and discounted expressions. Six scenarios were simulated by combining the proposed alternatives in concentrate feed costs {three levels: initial model (MI) (no change), MI + 20% and MI -20%} and product prices (two levels: ratios of protein/fat price of 1.33:1 and 2:1). Economic values generated by the base model were: - 0.045, 0.849, 1.412, and - 0.047 US$ kg-1 animal-1 for milk, fat, protein, and liveweight, respectively; they followed the same trend upon applying the remaining scenarios, and were sensitive to variations in costs and revenues. The selection index coefficients derived were -0.0477, 0.8317, and 1.4394 for additive genetic values of milk production, fat and protein, respectively. These coefficients were highly correlated with the objective under all six scenarios