[Urea and acetone content in milk as indicators for nutritionally caused fertility disorders of dairy cows].

In 915 records of cows of the breeds German Simmental and German Brown the relationships between fertility parameters and milk urea as well as acetone content were analysed with linear models regarding systematic effects of herd, month, lactation number and breed-Brown-Swiss blood proportion. Milk urea concentration showed significant curvilinear associations to following fertility parameters: days open, days between first and last breeding as well as number of inseminations per service period, conception rate at first insemination after calving and lactational incidence of endometritis. The reproductive traits showed an optimum at a milk urea concentration between 15 and 25 mg/dl. The regression of the fertility parameters on acetone content in milk was nearly linearly decreasing and with the exception of days to first breeding after calving significantly different from zero. An increase of milk acetone by 0.01 mmol/l lead to a prolongation of days from first to last breeding in the service period by more than one day, and to a decrease of conception rate at first insemination by nearly one percent. An approach was developed which is suitable to quantify the influence of milk constituents on fertility traits. The model developed can consider nonlinear relationships, more than one metabolic parameter and systematic effects. Thresholds for milk parameters are no longer needed as the negative effects of the metabolic influences caused by nutritional factors are quantified in terms of fertility parameters.