Impact of breed and colostrum replacer quantity on IgG kinetics in Holstein and Holstein-Angus crossbred bulls

The objective of this study was to explore the effect of colostrum replacer quantity and breed on serum immunoglobulin G (IgG) kinetics in Holstein and Holstein-Angus calves. Holstein (n = 24; 12/trt) and crossbred (n = 24; 12/trt) bulls were assigned to 1 of 2 diets for the 0 h and 12 h meals: low colostrum replacer (LOW; 2.5 g of IgG/kg birth body weight; BW) or high colostrum replacer (HIGH; 5 g of IgG/kg BW). Acetaminophen was administered in the 0 h meal to measure abomasal emptying. Calves received milk replacer at 6% BW per meal twice daily from 24 h to d 7. Frequent blood samples were taken to assess serum IgG concentrations, apparent efficiency of absorption (AEA), IgG persistency, and abomasal emptying rate. Serum IgG concentrations were increased in the HIGH calves but were not impacted by breed. However, there was an interaction of colostrum and breed, where LOW crossbred calves had increased serum IgG concentrations from 4 h to d 7 compared with LOW Holstein calves. Apparent persistency of IgG at 48 h was increased in HIGH calves compared with LOW, however by d 7 apparent persistency of IgG did not differ by treatment. Additionally, apparent persistency of IgG at d 7 was increased in crossbred calves compared with Holsteins, while HIGH Holstein calves had increased apparent persistency of IgG at 48 h compared with LOW Holstein calves. Calves on the LOW treatment had increased AEA at 24 h compared with HIGH, while LOW crossbred calves had increased AEA at 12 h compared with LOW Holsteins. Similarly, HIGH calves had decreased first-order slow gastric emptying constant (KSP2) compared with LOW calves and LOW crossbred calves had increased KSP2 compared with LOW Holstein calves. These results suggest that crossbred calves may have a physiological mechanism that allows them to better absorb IgG, particularly when fed low levels of colostrum.