Effect of different heating times of high-, medium-, and low-quality colostrum on immunoglobulin G absorption in dairy calves

The objective of this study was to determine the effect of different durations of heat treatment on passive transfer of IgG from high-, medium- and low-quality colostrum. Colostrum was collected from The Pennsylvania State University dairy herd and divided by quality (high, medium, or low) based on colostrometer measurements. Colostrum was pooled by quality to create 3 unique batches. Each batch was further divided in thirds as follows: frozen to be fed without heat treatment, heated at 60°C for 30 min, or heated at 60°C for 60 min. Colostrum samples from each treatment were collected and analyzed for standard plate count, gram-negative noncoliforms, coliforms, and total IgG concentration. Serum samples were collected from 108 Holstein calves before feeding colostrum and 24 h after birth. Blood samples were analyzed for total protein, total IgG, and hematocrit. Colostrum quality (high, medium, or low), heat treatment (unheated, 60°C for 30 min or, 60°C for 60 min), and their interaction were analyzed as fixed effects, with calf sex included as a random block effect. Colostrum IgG was different between quality groups (92.5, 59.4, and 48.1 mg/mL of IgG). Heating colostrum reduced IgG concentration compared with the control by 9% when heated for 30 min and by 12% when heated for 60 min. Colostrum heated for 60 min had a lower standard plate count than colostrum heated for 30 min or not heated (1.8, 2.0, and 3.6 log cfu/mL, respectively). Serum IgG concentration at 24 h increased as colostrum quality increased (18.0, 22.2, and 24.8 mg/mL) and tended to increase as heat treatment time increased (19.7, 20.3, and 25.0 mg/mL of IgG). Apparent efficiency of IgG absorption was greater in calves that received medium-quality colostrum compared with calves fed high-quality colostrum (38.1 and 25.0%, respectively). These results suggest an upper limit may exist to the amount of IgG absorption in a given time period and that medium- or high-quality colostrum yields similar blood IgG concentration given the same volume of intake.