Studies were conducted to: (1) identify the optimal temperature and time, at which heat treatment of bovine colostrum would produce the least significant changes in viscosity and IgG concentrations yet produce a significant reduction in bacterial count, (2) describe the effect of heat treatment of colostrum at 60°C for 30 min on colostrum characteristics including bacterial counts, IgG1 and IgG2 concentrations (g/L), and viscosity (Pa·s), (3) describe the effects of feeding heat-treated (vs. unheated) colostrum to neonatal dairy heifers on passive transfer of colostral immune parameters, health, and growth characteristics to 8 wk of age, and (4) determine the effects of feeding heat-treated colostrum and unheated colostrum with two different bacterial counts on passive transfer of immunity in neonatal bull calves.
In the first study, 10-mL colostrum samples were heat-treated for 0, 30, 60, or 90 min at 63, 60 or 57°C and evaluated for IgG1 and IgG2 concentrations, standard plate (SPC) count, preliminary incubation count (PIC), coagulase-negative staphylococci (CNS) count, environmental streptococci (ES) count, coliform (CC) count, Gram-negative noncoliform (NC) count, Streptococcus agalactiae (SAG) count, and Staphylococcus aureus (SA) count. The results of the study showed that all heat treatments resulted in a significant reduction of SPC, CC, NC, ES, CNS, SA, and PIC. Heat-treatment at 60°C and above resulted in significant denaturation of colostral IgG1; however, colostral IgG2 concentrations were not significantly reduced when the temperature was held at 60°C for 30 or 60 minutes. Viscosity was not significantly affected when temperature was held at 60°C for 30 or 60 minutes.
In the second study, unheated or heat-treated colostrum was fed to newborn Holstein heifer calves to determine the effect on immunoglobulins G absorption, serum total IgG and serum total protein concentrations, lymphocyte counts, health scores, growth measurements, and starter intake. Batch heat treatment of colostrum at 60°C for 30 min resulted in lower colostrum bacteria concentrations while maintaining colostral IgG concentration and viscosity. Calves fed heat-treated colostrum had significantly (P < 0.01) greater IgG concentrations at 24 h, plus greater apparent efficiency of IgG absorption (IgG = 23.4 g/L; apparent efficiency of absorption = 33.2%) compared with calves fed unheated colostrum (IgG = 19.6 g/L; apparent efficiency of absorption = 27.7%). There was no difference between treatment groups when examining lymphocyte counts, growth measurements, calf starter intake, or health scores.
In the third study, heat-treated colostrum or unheated colostrum with two different bacterial concentrations were fed to newborn Holstein bull calves to determine the effect on immunoglobulins G absorption, serum total IgG and serum total protein concentrations. Batch heat treatment of colostrum at 60°C for 30 min resulted in lower colostrum bacteria concentration while maintaining colostral IgG concentration. Calves fed heat-treated colostrum had significantly (P < 0.01) greater serum total protein IgG concentrations at 24 h, plus greater apparent efficiency of IgG absorption (total protein = 62.5 g/L; IgG = 26.7 g/L; apparent efficiency of absorption 43.9%) compared with calves fed unheated-low bacteria colostrum (total protein = 57.0 g/L; IgG = 20.2 g/L; apparent efficiency of absorption = 35.4%) or unheated-high bacteria (total protein = 56.2 g/L; IgG = 20.1 g/L; apparent efficiency of absorption = 32.4%). High bacteria load in colostrum did not interfere with IgG absorption.
