Effects of passive immunity on subsequent production in dairy heifers.

Dairy Herd Improvement data from a large, commercial dairy farm were used to evaluate the relationships of first lactation milk and fat yield and age at first calving on passively acquired immunity in Holstein heifers. Total serum Ig concentration was measured 24 to 48 h postpartum (mean = 25.5 mg/ml, SD = 19.2) on calves allowed to suckle their dams freely through 24 h postpartum. No additional colostrum was supplied and no attempt was made to ensure adequate colostrum intake. Calves were raised in Tucson, AZ until 6 mo of age, then transferred to Idaho to complete the growing phase and to be bred. Heifers were returned to Tucson during their 7th or 8th mo of gestation. Serum Ig concentration, measured shortly after birth, was an important source of variation for mature equivalent milk (b = 8.5 kg/Ig unit) and mature equivalent fat (b = .24 kg/Ig unit) production in the first lactation but did not affect age at first calving. It is impossible to ascertain from these data whether Ig concentration at birth was directly or indirectly related to production; regardless, supplying an adequate amount and concentration of colostrum at the appropriate time to dairy heifers may enhance their future productivity.