USE OF SERUM-PROTEIN CONCENTRATION TO PREDICT MORTALITY IN MIXED-SOURCE DAIRY REPLACEMENT HEIFERS

The relationship between serum protein concentration in the Ist week o f life and survival to 16 weeks of age was examined in 3,479 Holstein replacement heifers over a period of 10 years on a farm with endemic s almonellosis. Thirty-four percent of calves studied had serum protein concentrations <5.0 g/dL and 60.5% of calves had serum protein concent rations <5.5 g/dL. Cumulative mortality was 7.9%, indicating that calv es with marginal passive transfer status can be reared successfully un der conditions of endemic salmonellosis. Optimal survival was observed in calves with serum protein concentrations >5.5 g/dL. Calves with se rum protein concentrations of 5.0-5.4 g/dL had only a slightly increas ed relative risk (RR) of mortality (RR = 1.3) compared to calves with serum protein concentrations >5.5 g/dL. The highest RR was experienced by calves with serum protein concentrations <4 g/dL (RR = 4.6) and 4. 0-4.4 g/dL (RR = 3.1). Calves with inadequate passive transfer (serum protein concentration <5.0 g/dL), experienced increased mortality unti l at least 10 weeks of age, indicating that failure of passive transfe r has an effect on calf health that extends into the juvenile period. Models in which serum protein concentration was treated either as a co ntinuous variable or as a categorical variable failed to demonstrate a ny significant interaction between baseline mortality and the RR of mo rtality. This finding suggests that the RR derived in the present stud y should be applicable to farms with dramatically different baseline m ortality rates.