Fats in Powdered Milk Replacers

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Dietary considerations

 

Fats provide essential energy that are needed to grow, develop and function property. The body needs fats for brain and neurological development, blood clotting, and controlling inflammation. The body cannot make fats by itself nor work without them. Different types of fats work in varied ways.

 

While there has been extensive research on the importance of milk fat needed for growth and development, far less is known about their structures and exactly how fat is digested. Fat digestion involves the body making the fats more soluble so they can be absorbed into the intestine and transferred into the circulatory system. Digestive enzymes, called lipases, break down dietary fats so they can be absorbed in the small intestine. While bile plays a role in breaking the fats down further into an emulsion, newborns and infants have reduced bile production. Research shows that milk fats are unique in that they enter the digestive tract as an emulsion and “self-assemble” into tiny nanometer-sized structures with a high surface area, rather than large globules as seen in other fats. Those smaller milk fat droplets are more rapidly digested by the lipase enzyme, some believe this is an adaption of the digestive chemistry of the infant gut to facilitate fat digestion. Vegetable and animal fats have different structures, and thus are digested differently.

 

As mentioned elsewhere, the components and chemistry of milk is worthy of extensive research. While this section briefly describes a few topics relevant to feeding wild mammals a substitute formula in captivity, the subject is complex and absolutely deserving of significantly more study.

 

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Milk fats

 

Milk fat is one of the major components of mammal milk. It is one of most complex natural fat and includes about 400 different fatty acids in trace quantities. The major function of milk fat is to provide high energy to infants during their early development. The essential fatty acid components vary amongst mammal species milks and are based on their requirements and metabolic features. In addition to the nutrient values, milk fat plays a major role in growth and brain development, gastrointestinal development and health, protection against infection, and delivery of nutrients.

 

The proportions of fats in milks also vary widely among species. For example, rabbit mothers feed their young infrequently, so the fat content of rabbit milk is exceptionally high. Such a high fat content may be necessary to sustain young rabbits in between feeds. Other species may need the exceptionally high fat values in milk to build thick layers of subcutaneous fat to help cope with extreme cold, such as seals and whales. Other species that are able to suckle more frequently and face less severe environments may have lower fat levels in the mothers' milks. Research continues on factors that influence the proportions of fats in the species milks, including the following: during different stages of lactation, diets consumed by the mothers, times of year, and more.

 

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Vegetable fats

 

Various plants are highly refined and processed into fat products, including corn, cottonseed, canola, soy, palm, sunflower, and rice. The vegetable oils used in animal foods, including milk replacer powders, are unlikely to be from higher priced or quality vegetables, seeds or nuts. AAFCO defines vegetable oil as "...the product of vegetable origin obtained by extracting the oil from seeds or fruits which are processed for edible purposes." This all-encompassing definition of 'vegetable oil' allows for manufacturers to reformulate their source or type of oil without any updated disclosures or printing of new labels. Therefore, it is impossible to determine the source of the oil from the product label. Some vegetable oils have fewer nutrients than others. Also, vegetable oils have substantially less variety of the important fatty acids than cow’s milk. The processing, uses, digestibility and subsequent results of consumption of vegetable oils are being researched.

 

Processing vegetable oils involves the use of heat that can exceed their heat tolerance, putting them at risk of rancidity. Vegetable oils can oxidize and degrade, especially when exposed to heat during storage. Some manufacturers add preservatives to the milk powders to reduce the chance of spoilage, but some may still become rancid. This suggests that there are benefits to storing milk replacer powders in a cooler environment and that the formula be monitored by the consumer for signs of an 'off’ odor, which can indicate rancidity (described as an odor similar to crayons, soap, or metals).

 

 

Animal fats

 

There are several different categories of animal fats, including rendered fats, fish oils and milk fats. They all have different compositions, calories and energy. For a number of years, people assumed that the animal fats in high-fat milk powders were dairy-based milk fats, such as cream. That assumption was revealed to be wrong, as the animal fat in in some milk replacers is lard (e.g., Multimilk®).

 

Lard stays in solid form until it melts at 109 degrees F. People feeding formula prepared with one of the milk replacers containing lard have reported that some issues.  The young animals have been more reluctant to eat it unless it is much warmer than the normal temperature that would be similar to the mother’s natural milk. In addition, there have been concerns expressed regarding: the lard taste, digestibility, and the concept of feeding it to herbivores. Like with vegetable oils, oxidation and degradation can occur, especially when these fats are exposed to heat.  Storing these products in a cooler environment and monitoring for signs of rancidity (as described above) would be suggested as well.

 

 

Milk replacer analysis

 

Since almost all of the milk fat (cream) is removed in the processing of whole milk, manufacturers of animal milk replacer products combine varieties of the wet or dry forms of fat (discussed above) with other ingredients to create a replacer product. These are sold, either in wet or dry form, to feed target species, mostly in the commercial livestock and companion animal industries. The chart below indicates the various sources of fats used in formulation of some of the various powdered milk replacer products available from Fox Valley Animal Nutrition and PetAg® that are used by wildlife rehabilitators: