Assessing efficiency of passive immune transfer in dairy herds.

Blood serum immunoglobulin concentrations of calves during their 2nd wk of life had a .97 correlation with 1st wk concentrations. Correlations between 1st wk concentrations and those in the 3rd, 4th, 5th, and 6th wk of life were .91, .90, .81, and .69. Ten herds were divided into those with mortality rates above and below the median. The major difference in distributions of immunoglobulin concentration between the two groups was percent of calves with concentrations less than 2.5 mg/ml during the 1st wk of life. Calves were sampled monthly for a full year in 19 herds, and all but one herd had one or more calves with immunoglobulin concentrations under 5.0 mg/ml. Overall, calves having immunoglobulin concentrations under 5.0 mg/ml were exposed to excess mortality risk; however, most of the excess risk was concentrated in three herds with high mortality rates (16 to 20%). Evaluating the efficiency of passive immune transfer through the use of management data was unreliable in comparison with assaying serum samples for immunoglobulin concentration.