Controlling bacteria levels in colostrum is an important aspect of managing this important first feed for calves. Once it is collected, colostrum can be refrigerated, frozen, or have potassium sorbate added to control bacterial growth (though the latter is seldom used). When done correctly, each of these methods can keep bacteria from growing, but none of these strategies reduces the amount of bacteria already present in colostrum. Bacteria can get in to colostrum through contamination from milking dirty udders, reservoirs in dirty milking equipment or colostrum storage containers, and by direct shedding from the mammary gland.

Pasteurization, which is often used for milk or waste milk, can be used to reduce bacteria levels and has been shown to be very effective at killing a variety of pathogenic bacteria including Salmonella, E. coli, Mycobacterium avium subspecies paratuberculosis, Mycobacterium californicum, Mycobacterium bovis, and Listeria monocytogenes. We are learning that pasteurization can be used for colostrum also.

We first must remember that the nutrient density of colostrum is different from whole milk. Fat, solids-not-fat, and protein typically affect how heat is transferred through colostrum or milk. Early attempts at pasteurizing colostrum using the same time and temperature used in pasteurizing whole milk were largely unsuccessful due to the large reduction in immunoglobulin levels or the creation of a thick, pudding-like mass that was hard to feed and even harder to clean out of pasteurization equipment.

More recently, University of Minnesota and Penn State researchers have shown that colostrum can be heat-treated or perhaps termed ‘pasteurized’ successfully, if different time and temperature criteria are used. Since colostrum can be quite varied from cow to cow, it is unlikely that a true definition of time and temperature can be found for considering true pasteurization for all colostrum. However, a study using a wide variety of colostrum samples conducted at Penn State and published in the Journal of Dairy Science early this year showed that on average heating colostrum at 140°F for 30 minutes is the optimum combination to reduce bacteria counts without affecting colostrum IgG levels or viscosity. Other research from the University of Minnesota confirms that if higher levels of some disease-causing organisms are present in the colostrum, 140°F for 60 minutes will give a more reliable kill of these harmful bacteria; however, slightly more IgG will be lost in the process.

An unexpected finding in the Minnesota research was that calves fed pasteurized colostrum absorbed more IgG. In this study, 24-hour serum IgG was 22.3 mg/mL in calves fed pasteurized colostrum compared to 18.1 mg/mL in calves fed raw colostrum. Apparent efficiency of IgG absorption was also improved in the calves fed pasteurized colostrum (35.6 versus 26.1%). This phenomenon has also been observed in two different experiments conducted at Penn State. In one study, calves fed colostrum heated at 140°F for 30 minutes had serum IgG of 22.6 mg/mL at 24 hours compared to 19.6 mg/mL for calves fed raw colostrum. The higher blood Ig levels remained for the first 5 weeks of age.

All calves in these studies were generally healthy and calf body weight was similar for the two treatments through 6 weeks of age. None of the studies specifically targeted sick or immune suppressed calves. In a second study done at Penn State, calves fed pasteurized colostrum had IgG of 26.7 mg/mL compared to 20.2 mg/mL for calves fed unheated colostrum. In these three studies combined, feeding pasteurized colostrum increased 24-hour serum IgG level by 20 to 25%.

The results of this research suggest that heat-treating or pasteurization of colostrum may present an excellent opportunity to reduce bacterial populations in colostrum and increase IgG absorption, thereby reducing the percentage of dairy calves that experience failure of passive transfer. The explanation of why IgG absorption is improved when colostrum is pasteurized is not yet clear, although it may be due to changes in colostrum components when they are exposed to heat or possibly to reduced competition between proteins for absorption.

Past research has shown that bacteria introduced into the gut before colostrum feeding can reduce the amount of IgG absorbed by calves. But, in a recent Penn State study calves fed colostrum that contained a high bacterial load (measured by standard plate count and coliform count) absorbed similar amounts of IgG as calves fed colostrum with a low bacterial load. Although further research is required to explain why heat-treatment increases IgG absorption, it seems clear that heating colostrum does offer advantages in providing cleaner colostrum for calves along with improved IgG absorption. This could be particularly helpful in herds working to limit the spread of Johne's.

Source: Coleen Jones, Research Associate, and Jud Heinrichs, Professor of Dairy and Animal Science, Department of Dairy and Animal Science Penn State University