The results of a study of the economic losses caused by paratuberculosis in dairy cattle are reported. The losses in production and the determination of lost future income due to premature disposal are emphasised. A decrease in milk production of 19.5 per cent compared with the lactation two years before culling was recorded in animals showing clinical signs of paratuberculosis. The decrease in production in the last lactation but one compared with the previous lactation was 5 per cent. In animals with non-clinical forms of paratuberculosis these decreases in production were 16 per cent and 6 per cent, respectively.
This paper is confined to the first question; the second will be worked out in a subsequent paper.First, the principle underlying the replacement decision is discussed. Then, the basic data of the model are given. The age-associated probability of disposal has also been included in the model.A reduction of the involuntary replacement rate was found to he of major importance on the farm level. In the model a herd showing average production and an average herd life of 5.3 lactations will have approximately 20% more earned income each year than a similar herd with an average productive life of 3.3 lactations. However, the yield resulting from a longer herd life is subject to the law of diminishing returns.The economic importance of a long herd life appeared to be remarkably stable, i.e., hardly affected by: (a) the average productive capacity of the herd as regards milk and/or meat; (b) the presence or absence of a moderate genetic improvement (1% per annum) in milk yield; or (c) changes in price ratios between milk and meat.
Dijkhuizen, A.A.. Renkema, l.A. and Stelwagen, l .• 1991. Modelling to support animal health control. Agric. Econ .• 5: 263-277.Animal Health Economics is a relatively new subject. being developed to provide a quantitative insight into the economic effect of disease and disease control in livestock. Research in this field is focussed on both the further development of a more solid scientific framework of concepts and methods and its applications in quantitative model calculations. Three issues are especially of interest: (a) the losses of disease. (b) the profitability of preventive measures. and (c) the replacement decision of individual affected animals. All three issues concern complex problems, which have to be studied under imperfect veterinary knowledge and under a high degree of uncertainty. In this paper the basic economic framework and its applications in the underlying field are discussed and illustrated. 0169-5150/91/$03.50 ® 1991 -Elsevier Science Publishers B.V.
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