ASSOCIATIONS BETWEEN THE FAT TO PROTEIN RATION IN MILK, HEALTH STATUS AND REPRODUCTIVE PERFORMANCE IN DAIRY CATTLE

The aim of the present study was to evaluate pregnancy rates of 232 dairy cows in relation to fat to protein ratio (FPR) in milk, using survival analysis. Pregnancy rates of cows inseminated within 90 and 120 days postpartum in a group of clinically healthy cows were 38 and 68 %, respectively. Lower pregnancy rates are observed in groups of cows with ketosis and reproductive disorders, 44 and 28 % for pregnancy rate within 120 days. The highest correlation between FPR and calving to conception interval (CC) was observed between 30 and 60 days postpartum (r = 0.411, P < 0.001). Diagnostic evaluation of FPR using ROC (receiver operating characteristics) analysis showed that FPR at 1.37 discriminates cows with CC below and above 120 days with an accuracy of 71 %. Survival curves for the subgroups of animals with FPR below or above 1.37 differed significantly in the case of clinically healthy cows, where CC in subgroups were 87 +/- 28 and 122 +/- 42 days, respectively. Although survival curves for subgroups for cows with diseases did not differ significantly we observed longer CC in all subgroups with FPR > 1.37 than in subgroups with FPR < 1.37. In all groups pregnancy rates within 90 and 120 days were lower in subgroups with FPR > 1.37 than in subgroups with FPR < 1.37. Therefore, FPR can be used by bovine practitioners to predict fertility problems in dairy herds.