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Fat in colostrum: The cream of the crop

Koryn Hare, Amanda Fischer-Tlustos and Michael Steele for Progressive Dairy Published on 15 July 2019
New born calf

What’s your dairy cow’s milkfat content? It’s an easy question, right? You likely have milkfat records from generations on your farm and could readily explain how your milk components have changed over the years or pinpoint what management and feeding practices caused reductions or increases in milkfat.

What about your colostrum fat percentage? Are you able to give an exact, or even a ballpark, answer? You might be thinking, “Does it matter?”

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We generally focus on colostral immunoglobulins to define quality since IgG in colostrum is necessary for passive immunity. Yet by doing so, we limit ourselves to take advantage of everything colostrum has to offer. Our lab and others have been working to characterize all of colostrum’s benefits for the calf and, in this article, we are going to start back at square one: nutrients. In particular, we are going to highlight the importance of fat in colostrum for newborn calves and show you why you need to be measuring colostrum fat just as frequently as you measure your milkfat.

The same equation we use to calculate milk energy output based on fat, protein and lactose can be used to calculate the gross energy content of colostrum. Yet gross energy does not equal digestible energy, nor energy the calf uses for growth and maintenance. From an internal review of recent data our group collected from 20 cows on a commercial dairy farm in Alberta, we calculated that protein, fat and lactose respectively account for 58%, 36% and 6% of gross energy in colostrum.

However, 70% to 80% of the protein fraction is composed of immunoglobulins that will not be fully digestible due to colostrum-containing compounds that block proteins, like IgG, from digestion. Additionally, the newborn calf gut is immature and relatively inefficient at digesting protein. Accounting for these factors, we approximated that the proportions from which protein, fat and lactose contribute to gross energy shift from 58% to 25% for protein, 36% to 63% for fat and 6% to 12% for lactose. Therefore, fat, and not protein, actually represents the primary energy source the cow packages into colostrum for the calf.

As the famous saying goes, “Mom knows best,” so why has she decided fat is the cream of the crop? It is actually quite clear. The term fat broadly encompasses related compounds that have multiple roles in the neonatal calf:

1. Fuel: Fat compensates for the relatively lesser concentration of lactose in colostrum than mature milk, ultimately complementing the calf’s digestion and metabolism at this age.

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2. Thermoregulation: When burned, fat releases 1.6 and 2.4 times more energy than protein and lactose, respectively. This released heat (energy) maintains the calf’s optimal body temperature, which is particularly important for calves born in winter.

3. Hormonal signaling: The colostral fat fraction contains specific fats that can be used as hormones in the body. For example, researchers showed in 2001 and 2014 that cholesterol is higher in colostrum than in milk. Cholesterol is the precursor for steroid hormones that have vast roles ranging from expression of sex-specific traits to controlling stress responses within the body.

4. Inflammation and immune response: Recent data from our lab has shown that omega-6 and omega-3 fatty acids (FA) are elevated in colostrum. Omega-6 and omega-3 FA are essential FA and precursors to compounds that regulate inflammation, immune response and brain development. Researchers at Michigan State University have been exploring supplementing fish and flax oil (high in omega-3 FA) in colostrum and have shown prolonged benefits in terms of antioxidant status and immune responses from a single feeding. Following further research, perhaps supplemental omega-FA could become part of your on-farm colostrum management in the near future.

These are just a few examples, but it is clear colostrum fat should not be overlooked. With this in mind, we will highlight an important concern about colostrum fat. Figure 1 shows the wide range in colostrum fat concentration that has been reported to be as low as 0.3% in 1950 to as high as 26.5% in 2007.

Numerous studies (noted in Figure 1) have consistently reported that colostrum fat concentration is highly variable from cow to cow, and this variation is similarly demonstrated across studies.

Fat concentration (96) reported in 12 studies from 1950 to present

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This variation is critical. For example, based on the minimum and maximum concentrations reported from 1950 until now, a newborn calf could receive between 0.1 to 9.8 Mcal of energy from fat alone in the 4 litres of colostrum fed at birth. If you considered your TMR, would a similar range of net energy delivery to your lactating herd ring alarm bells? Of course.

Research has captured some prepartum factors that impact colostrum fat output, namely parity, dry period length and nutrition, immunization protocols and the season of calving. Researchers from both Cornell University and the University of Saskatchewan find nutrient intake can alter colostrum fat output without impacting colostrum yield. In terms of fat components, prepartum fat supplementation, such as omega-FA feeding, causes in corresponding changes in the colostrum FA profile. In a 2014 study from Florida, they found the fat source fed to the dam can alter her newborn’s efficiency of IgG uptake without altering the colostral IgG content.

We still have a lot of work to do in terms of understanding the cow-level and management factors that can alter colostrum fat, as well as what these changes will mean for the newborn calf. But by the preliminary work and the known importance of fats for energy and development, it is time we start paying more attention to this macronutrient. It would be a great step forward for research to investigate the levels of colostrum the calf needs for optimal growth and maintenance.

This topic has not been the focus of current colostrum research and, at present, there is no recommended threshold for colostrum fat levels. We would recommend your colostrum fat should be higher than the fat levels of your bulk milk tank, and to be safe you should feed colostrum that contains more than 5% fat. For now, improving colostrum management can be as simple as sending a cow’s colostrum sample for component analysis just as you would when testing your monthly milk samples. After all, knowledge is power.  end mark

PHOTO: We still have a lot of work to do in terms of understanding the cow-level and management factors that can alter colostrum fat, as well as what these changes will mean for the newborn calf. Photo by Mike Dixon.

Amanda Fischer-Tlustos is a research assistant at the University of Guelph. Michael Steele is an assistant professor at the University of Guelph. Email Michael Steel.

Koryn Hare is a Ph.D. student at the University of Guelph.

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