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Recent insights on how feeding whole milk or milk replacer affects the calf

Anna Welboren and Michael Steele for Progressive Dairy Published on 19 October 2021

The decision to feed whole milk or milk replacer to newborn calves continues to be a controversial topic among producers.

Although whole milk meets all nutrient requirements for development, milk replacer is largely considered beneficial in terms of cleanliness, cost and its consistent composition. Milk replacer and whole milk also differ in many other aspects, such as macronutrient composition and structure, and how these differences may affect calf growth, metabolism and health is currently unknown.

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Composition of whole milk and milk replacer

Milk-replacer formulations contain milk-borne ingredients, such as skim milk powder and whey products, and non-milk ingredients, such as vegetable protein, coconut oil, palm oil, tallow and lard. In addition, milk replacer generally contains more lactose (greater than 45%) and less fat (less than 20%) than whole milk because high-lactose products are relatively inexpensive and minimize fat deposition in replacement heifers. In this article, we highlight the potential effects of specific macronutrients in milk and milk replacer on growth and development of the heifer.

Differences and similarities between the macronutrient compositions of whole milk and milk replacer

Concerns about high-lactose milk replacers

Firstly, feeding high levels of a high-lactose milk replacer may negatively impact the calf’s ability to maintain stable blood glucose concentrations, which ultimately could decrease nutrient utilization. However, research groups from the Netherlands showed that partially replacing lactose with fat did not alter calves’ ability to maintain stable blood glucose concentrations during the pre-weaning phase when fed 8 litres of milk per day.

Secondly, feeding high-lactose milk replacers may negatively impact intestinal health due to their higher osmolality (the number of particles dissolved in 1 kilogram of fluid), which interferes with water absorption in the gut. Indeed, it has been demonstrated that partially replacing lactose with fat reduces the number of days with abnormal feces. However, the osmolality of both milk replacers did not differ and was relatively high compared with whole milk due to the relatively high content of minerals from the premix and the amount of powder dissolved per litre of milk replacer. For this reason, it is recommended to feed milk replacer between 12.5% (like whole milk) and 15% of solids.

Evaluation of milk replacer fat

Results from studies evaluating the effects of macronutrient composition of milk replacers on intestinal health and function do not show a clear preference for a specific composition. For instance, recent research showed that partially replacing lactose with fat increases the permeability of the digestive tract, which may facilitate the translocation of pathogens to gut tissue where they can cause infection.

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Evaluation of the fat sources most commonly used in milk replacers revealed differences in fatty acid composition and structure compared with whole milk. While whole-milk fat contains approximately 4% short-chain fatty acids, milk replacer fat contains none. Recent research conducted in Germany showed that adding short-chain fatty acids to milk replacer in the form of sodium butyrate increased surface area for nutrient absorption in the intestine.

Similarly, studies conducted by our group demonstrated that supplementing butterfat to milk replacer improved the microscopic anatomy of intestinal tissue, which may positively impact nutrient digestion and absorption. Therefore, inclusion of whole-milk fat or short-chain fatty acids in milk replacer formulations may promote intestinal development.

Another difference between whole-milk fat and milk replacer fat is that whole-milk fat consists of milkfat globules that are surrounded by a membrane, while milk replacer contains lipid droplets that are coated by milk proteins. Recent studies with human infants and rodents demonstrated that supplementing milkfat globule membrane (the membrane can be isolated by ultrafiltering buttermilk to yield a powder) may positively impact growth and intestinal development.

The mechanisms behind these effects are yet to be elucidated but may be related to the supply of bioactive phospholipids, oligosaccharides and membrane proteins present in the milkfat globule membrane fraction.

In summary, milk replacers generally contain higher levels of lactose and minerals and lower levels of fat. If diarrhea is a major contributor to morbidity and mortality of calves on your farm, evaluate the composition of your milk replacer and consider feeding a milk replacer with a lower lactose content or adjusting the concentration of solids (aim for 12.5% and not more than 15%). Furthermore, recent research has demonstrated that inclusion of whole-milk fat in milk replacer formulations may benefit the development of the digestive tract. Future research should provide insight into the importance of milk fatty acid composition and structure on the growth and development of calves during the pre-weaning phase. end mark

Dr. Michael Steele is an assistant professor at the University of Guelph. Email Dr. Michael Steele

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Anna Welboren is with the department of animal biosciences at the University of Guelph.

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