Effect of heat treatment and bacterial population of colostrum on passive transfer of IgG
Heat treatment of colostrum has been shown to increase apparent efficiency of IgG absorption (AEA) in newborn dairy calves. It has been hypothesized that this may be partially due to reduction in bacteria that occurs during heat treatment. This study’s objective was to test the effect of bacteria concentration in unheated and heat-treated colostrum on IgG absorption. Colostrum treatments were created by pooling colostrum from individual cows to create a single batch. Half of the colostrum was heated to 60o C and held for 30 min before cooling and rebottling (heat-treated). The remaining half of the colostrum was rebottled without heating (unheated). Half of each treatment was frozen immediately after bottling. Remaining heat-treated colostrum was inoculated with 20 mL of unheated colostrum. Remaining unheated and inoculated heat-treated colostrum were stored at 20o C for 60 and 72 h, respectively, to achieve similar final bacteria populations and subsequently frozen until needed for feeding. Samples were collected from each colostrum treatment for IgG and bacteria analysis prior to freezing. Bull calves (n = 104) were randomly assigned to treatment at birth. Plasma samples were collected 48 h after birth and assessed for IgG concentration. Data were analyzed using the mixed procedure in SAS. Initial SPC was 4.59 log cfu/mL and reduced to 2.79 log cfu/mL following heat treatment. High bacteria treatments of unheated and heat-treated colostrum contained 8.65 and 8.56 log cfu/mL, respectively. Mean AEA (48-h plasma IgG concentration) was 31.25% (20.7 mg/mL) and 15.86% (10.4 mg/mL) in calves fed unheated colostrum of low and high bacteria concentration, respectively; and 37.27% (24.0 mg/mL) and 13.94% (9.3 mg/mL) in calves fed heat-treated colostrum of low and high bacteria concentration, respectively. Bacteria level significantly reduced AEA and 48-h plasma IgG concentration (P < 0.01). No effect of heat treatment was observed for 48-h IgG concentration or AEA (P = 0.42 and 0.36, respectively); however, there tended to be an interaction between bacterial population and heat treatment for AEA (P = 0.08). Slicing the interaction indicated a tendency of heat-treatment to increase 48-h IgG concentration and AEA in low bacteria colostrum treatments (P = 0.10 and 0.07, respectively). In this study, concentration of bacteria in colostrum had greater effect on calves' ability to absorb IgG than heat treatment of colostrum.
Keywords: IgG, calf, colostrum