[Productive life-span of dairy cows and its economic significance. III. Economic evaluation: results obtained by model calculations (authors transl)].

A reduction of the forced replacement rate is found to be of major economic importance on the farm level. In the model, the income earned from a fifth lactation of a cow showing an average production is approximately Dfl 440 higher than the earned income per annum over the average herd life of 4.3 lactations. A farm with a herd of fifty cows showing average production and an average herd life of 5.3 years will have approximately Dfl 9600 more earned income each year than a similar farm with an average herd life of 3.3 years. The yield resulting from a longer herd life is subject to the law of diminishing returns. For the annual income from a dairy herd, a sixth lactation is of less importance than a fifth lactation, etc. The economic importance of a long herd life appears to be remarkably stable, i.e. hardly affected by: (a) The average productive capacity of the herd as regards milk and/or meat. (Note: Differences in milk-producing capacity within a herd have a marked effect on the economic value of an additional lactation by an individual cow). (b) The presence or absence of a moderate genetic improvement (1 per cent per annum) in milk-yield.