Economic weights for major milk constituents of Manchega dairy ewes

The objective of this study was to estimate economic weights of major components of milk (fat and protein) for the Manchega dairy sheep breed. An economic study was carried out and the profit associated with fat and protein yields of milk was calculated as the difference between incomes and costs. Incomes were obtained from milk sales to cheese industry and a reference marked price was used. Costs were calculated considering the energy necessary to produce each of the components of milk, and the price per milk forage unit was calculated as the total expense in feedstuff divided by the total (theoretical) needs of the flock. Economic values were defined as partial derivatives of the profit function with respect to each trait. Economic weights for fat and protein yields were similar, being slightly greater for protein in all cases. For carrier, economic weights were close to zero and negative because an increase in carrier production without changes in fat and protein composition leads to an increase in energy demands, holding the sale price of milk constant. When genetic standard deviations were taken into account and standardized economic values were calculated, an increase in economic value of protein and a decrease in economic value of fat yields were observed. The consequences that different changes in production system conditions have on the estimated economic weights were also studied. In general, economic weights were relatively insensitive to changes in production levels and market prices except for changes on milk price. Given the economic importance shown for fat and protein, milk components should be taken into consideration when breeding objectives for dairy sheep are established.This work was financed by project INIARTA-02-002-C2.Peer Reviewe