[The decision to replace dairy cows in case of difficult-to-achieve pregnancy: an economic evaluation].

The question approached is, 'How long will it be profitable to continue breeding dairy cattle in cases of poor reproductive performance, differing in age and milk production potential, until it has to be decided to cull them?' This question was expressed in an economic replacement model for dairy cattle. The essence of the model is a comparison of anticipated incomes from a cow present in the herd an a replacement cow. For herd cows, the critical production level (expressed as a percentage of the herd level, after correction for age and stage of lactation) below which it is no longer profitable to breed empty cows was calculated. This was done at ten stages in each lactation. It was found to be profitable to continue breeding cows with poor reproductive performance for a long period: even up to 8-9 months after calving in young cows showing an average production level or higher. The most important factor affecting the calculated critical production levels was found to be the repeatability of an unduly long calving interval of the cow concerned: if problems regarding reproductive performance are also expected in future lactations, breeding should be stopped earlier in lactation.