Genetic relationships between reproductive disorders, operational days open and milk yield

The data on 23 196 Ayrshire cows were extracted from the Finnish health register for dairy cattle to study the relationships of veterinary diagnoses of ovulatory disorder and metritis within 150 d postpartum across the first three lactations. A subset of 11 173 disease recordings was merged with information on 305 d milk yield and operational days open to study the genetic correlations between reproduction disorders, daughter fertility, and milk production. (Co)variance components were estimated using linear multitrait REML and the expectation-maximization algorithm with a sire model. The estimates of genetic correlations between different lactations were positive and from moderate to high for operational days open (0.77 to 0.93) and ovulatory disorder (0.60 to 0.94). The high genetic correlation between ovulatory disorder and operational days open (0.80) indicates that the both traits are expressions of the same trait complex. A moderately high unfavourable genetic association was found between milk yield and both reproductive disorder and operational days open. Based on the results, a genetic improvement of 500 kg in milk yield would, as a correlated response, result in an increase of 1.7%-units, 0.9%-units and 4.2 d in the frequency of ovulatory disorder and of metritis, and in operational days open, respectively.