Economic impact of mastitis in dairy cows

This thesis aims to assess the economic loss associated with clinical (CM) and subclinical (SCM) mastitis under current Swedish farming conditions. Stochastic simulation was used to investigate the impact of mastitis on technical and economic results of a 150-cow dairy herd. The yearly avoidable cost of mastitis, assuming that the initial incidence (32 and 33 cases of CM and SCM per 100 cow-years, respectively) could be reduced by 50%, was estimated at €8 095. This figure corresponded to 5% of the economic net return for the herd given the initial incidence of mastitis. Expressed as an average per cow/year, the avoidable cost of mastitis was estimated at €54. The economic loss associated with mastitis could not be reduced by discarding milk with high somatic cell count, because this resulted in a substantial decrease of the volume of sold milk which was not offset by the increase in milk price. Cases of CM and SCM were on average associated with an average economic loss of €275 and €60, respectively. Reduced milk production constituted the major cost component of the economic loss caused by mastitis. The magnitude of yield loss associated with mastitis occurring in different stages of lactation was assessed using mixed linear models. The dataset was collected in a research herd between 1987 and 2004, and consisted of weekly test-day records sampled in 1200 lactations. The most extensive yield loss was estimated when CM developed in early lactation and when SCM (modelled by means of increased somatic cell count) occurred in late lactation. The 305-day yield loss associated with CM varied between 0 and 705 kg milk in primiparous cows and between 0 and 902 kg milk in multiparous cows, depending on lactation week at onset. Most cases of CM developed in the first week of lactation and resulted in a yield loss of 578 and 782 kg milk in primiparous and multiparous cows, respectively. Daily yield loss at an SCC of 500 000 cells/ml ranged from 0.7 to 2.0 kg milk in primiparous cows and from 1.1 to 3.7 kg milk in multiparous cows. The yield loss in an average 305-day lactation affected by SCM was 150 and 450 kg milk in primiparous and multiparous cows, respectively