Effect of colostrum heat treatment and bacterial population on immunoglobulin G absorption and health of neonatal calves

Improved IgG absorption in calves fed heat-treated colostrum has been attributed to the reduced bacteria content in colostrum after heat treatment. However, at least one study reported that colostrum bacteria content did not affect IgG absorption. The main objective of the current study was a more conclusive test of the combined effects of colostrum bacteria content and heat treatment on IgG absorption. Comparison of conclusions from plasma IgG as measured by radial immunodiffusion and ELISA and comparison of health scores in the first week of life were secondary and tertiary objectives. Colostrum from individual cows was pooled, divided, either heat treated or unheated, and allowed to incubate for bacterial growth or not. The 4 treatments were unheated, low bacteria; unheated, high bacteria; heat-treated, low bacteria; and heat-treated, high bacteria. Plasma samples were collected from bull calves (n = 25-27 per treatment) before and 48 h after colostrum feeding for IgG and total protein analysis. Fecal, respiratory, and general health scores were assigned daily for the first 7 d. Plasma IgG, total protein, apparent efficiency of IgG absorption, and frequency of illness were analyzed using the MIXED and FREQ procedures in SAS (SAS Institute Inc., Cary, NC). Plasma IgG values from ELISA were lower than radial immunodiffusion; however, conclusions were similar. Greater colostrum bacteria content reduced total protein, plasma IgG, and efficiency of IgG absorption. Heat treatment tended to improve 48-h plasma IgG as measured by ELISA. Respiratory scores were not affected by colostrum treatment, but calves fed heat-treated, low-bacteria colostrum tended to experience fewer scour days. These results provide conclusive evidence for the benefits of minimizing bacterial contamination in colostrum for feeding calves.