Costs of clinical mastitis with special reference to premature culling

Bovine mastitis is an economic and a welfare problem on dairy farms. The objective of this study was to estimate the costs of clinical mastitis (CM), having a special focus on the cost variation related to culling decisions. A dynamic optimization model was developed to determine an optimal replacement time of a mastitic cow and to estimate the costs of CM, taking into account the risk of premature culling and the uncertainty in CM prevalence. Six lactations were analyzed at monthly periods for Ayrshire and Holstein-Friesian breeds. The estimates reflect Finnish production conditions where mastitis is treated only by veterinarians. Biological parameters of the model were adapted from the literature and the Finnish dairy herd health recording system. Field data were used to produce the risk parameters of culling due to mastitis on commercial dairy farms. The model recommended treating the cows with CM and keeping them in most cases until their fifth lactation. A cheaper (-20%) heifer transferred the optimum to the previous lactation and a more expensive (+20%) heifer to the following lactation. Conditional on optimal replacements, the average cost of CM of an Ayrshire (Holstein-Friesian costs in parentheses) cow was (sic)485 ((sic)458), varying from (sic)209 ((sic)112) to (sic)1,006 ((sic)946). The costs were at the highest when the occurrence of CM was at a top yield phase. In the scenario where the risk of culling due to mastitis was included in the model, the average cost of CM was (sic)596 ((sic)623). Disposing of a young cow at the end of her first lactation month caused the highest costs. The costs converted to figures per cow-year were (sic)121 ((sic)147) with optimal cullings and (sic)155 ((sic)191) in the current Finnish conditions. Thus, the increase in the costs of CM due to premature cullings was 28% (30%.) The main cost sources were long-term production losses regardless of the culling decisions. Premature culling formed 20% (23%) of the total costs. To decrease the costs of CM, more emphasis should be given to hid-den costs, especially the high cost of premature culling should be underlined.