Economic impact of clinical mastitis in a dairy herd assessed by stochastic simulation

The main aim of the present study was to examine the economic consequences of a reduction of the incidence of clinical mastitis (CM) at herd level under current Swedish farming conditions. A second aim was to ask whether the estimated cost of CM alters depending upon whether the model reflects the fact that in different stages of lactation CM gives rise to different yield-loss patterns or postulates just one type of yield-loss pattern irrespective of when, during lactation, CM occurs. A dynamic and stochastic simulation model, SimHerd, was used to study the effects of CM in a herd with 150 cows. Technical and economic results given the initial incidence of CM (25.6 per 100 cow/year) were studied together with the consequences of reducing the initial risk of CM by 50% and 90% throughout lactation and the consequences of reducing the initial risk by 50% and 90% before peak yield. A conventional way of modelling yield losses-i.e. one employing a single yield-loss pattern irrespective of when, during the lactation period, the cow develops CM-was compared with a new modelling strategy in which CM was assumed to affect production differently depending on its lactational timing. The yearly cost of CM at herd level was estimated at 14,504, corresponding to 6.9% of the net return given the initial incidence of CM. Expressed per cow/year, the cost was 97. The cost per case of CM was estimated at 427. There were no major differences in the results obtained using the new and the conventional modelling strategy, with the exception of the yield loss per case of CM. The study, consequently, suggests that it is not worthwhile in decision making in CM prevention to put effort into deriving specific yield-loss patterns for different periods in lactation. (Less)