A partial budget model to estimate economic benefits of lactational treatment of subclinical Staphylococcus aureus mastitis.

Subclinical Staphylococcus aureus mastitis is rarely treated during lactation because it is widely believed to be uneconomical, although there are no economic studies that support this view. Partial budgeting was used to develop a deterministic simulation model to estimate the net cost or benefit of antibiotic treatment of subclinical S. aureus mastitis during lactation. Direct and indirect effects of treatment were taken into account, including prevention of clinical flare-ups and contagious transmission. Input variables were based on literature and on 2003-2004 prices in the Netherlands. When contagious transmission of S. aureus was likely (reproductive ratio R = 5.3), 3- and 8-d treatments resulted in an average net profit of 95.62 euros and 142.42 euros, respectively, compared with no treatment. When the probability of S. aureus transmission was low (R = 0.32), the average economic benefit of 3- or 8-d treatment was -21.12 euros and -57.70 euros, respectively. On low-transmission farms, 3-d treatment was profitable when the appropriate cows were selected for treatment using known risk factors for cure. Sensitivity analysis showed that the 6 most influential input variables in the model were chance of bacteriological cure, R, probability of culling, retention pay-off, and cost of antibiotics and bacterial culture. Although the economic outcome of lactational treatment of subclinical S. aureus mastitis is highly herd-, cow-, and strain-dependent, treatment is economically justified in many situations.