Heat and Colostrum, Friend and Foe

Mrs. Dianne Shoemaker, Extension Dairy Specialist, OSU Extension Center at Wooster 

Hot environmental temperatures, combined with high humidity, can negatively impact colostrum production in first calf heifers. Conversely, heat treatment of colostrum can have more than one benefit according to data presented at the 2006 American Dairy Science Association (ADSA) Annual Meetings.

Generous colostrum feeding guidelines ensure that most calves will receive sufficient immunoglobulins (IgG; antibodies) to achieve a successful transfer of immunity. Success depends on the individual calf's ability to absorb IgG and the calf being fed enough IgG. We know that the calf's ability to absorb antibodies is negatively effected by the time that has elapsed since birth and the relative difficulty of the birth process. While absorption rates can approach 50% shortly after birth, they decline rapidly towards zero within the first 24 hours.

Environmental heat

Heat stress of first calf heifers is likely to cause a drop in IgG concentrations in their first milking. An Italian study using 12 Holstein heifers kept in environmentally controlled rooms reported a 19% decrease in IgG production from the heifers exposed to higher temperatures (89°F daytime and 79°F nighttime) compared to the control heifers (65°F, all heifers experienced 72% relative humidity.) Heifers were exposed to these environments for approximately 3 weeks before calving.

Is this happening with your heifers? The only way to know for sure is to measure the IgG concentrations in each dam's colostrum before feeding it to the calf. In the Italian study, yield (volume) of colostrum did not differ between heifers subjected to heat stress and the control heifers. Evaluating quality of colostrum based on volume produced will be useless. Simple on-farm methods of quality evaluation include using either a colostrometer or commercial "quick tests". These tools are readily available from farm supply catalogs or stores.

Heat treatment

Pasteurization of colostrum is generating increased interest as herds seek additional tools to control the transfer of disease pathogens, such as Johne's bacteria, through colostrum.
Godden at the University of Minnesota reported new data at this year's ADSA meeting from a study on the impact of pasteurizing colostrum on the apparent efficiency of IgG absorption.

Early attempts at pasteurization of colostrum were frustrating as the HTST (high temp, short time) pasteurization methods created a pudding like mass that plugged up the equipment and was impossible to feed. Longer time, lower temp methods are more successful, although some thickening can also occur.

Two important questions are: "Will the heat treatment harm the IgG?" and "Will pasteurization impede a successful transfer of immunity?" To help answer these questions, batches of colostrum were divided in half. Using a 60 min, 140oF pasteurization method, one half of the batch was pasteurized and one half of each batch was not. Pairs of calves were fed either the pasteurized or the fresh colostrum.

All fifty calves achieved a successful passive transfer of immunity. However, calves fed the pasteurized colostrum achieved significantly higher blood IgG concentrations than the calves fed fresh colostrum (22.3 mg/ml for pasteurized and 17.5 mg/ml for fresh). After calves were tested for blood IgG levels, the apparent efficiency of absorptions were calculated. Calves fed the fresh colostrum averaged 27% apparent absorption, while calves fed pasteurized colostrum averaged 35%.

Bottom line, the higher the efficiency of absorption, the better chance a calf has to achieve a successful transfer of passive immunity. Based on this study, the pasteurization process not only did not reduce the IgG concentration in colostrum, but the bacteria "kill" of the pasteurization appeared to allow more IgG to be absorbed compared to unpasteurized colostrum.

It has been demonstrated that bacteria that get into the calf's gut before colostrum is fed can interfere with IgG absorption. This study provided a strong indicator that bacteria may interfere with IgG absorption when they are fed with the colostrum as well. Dairy farms must have protocols and practices in place to ensure that colostrum is harvested and handled as cleanly as possible.

*A list of research references is available on request.