New Milk Replacer Quality Measure Improves Calf Performance

4 June 2019

By understanding the importance of osmolality and mixing milk replacers correctly, farmers will be able to support the health and performance of pre-weaned calves.

Georgina Thomas from Trouw Nutrition GB explains that osmolality is a measure of the concentration of particles in solution and is calculated by adding the concentration of sugars like lactose and minerals including sodium, magnesium and chloride.

“The osmolality of cow’s milk is close to 300mOsm/kg which is optimal for the absorption and digestion of nutrients by calves, but many milk replacers when mixed have levels above 400mOsm/kg, some closer to 600mOsm/kg. By comparison salt water has an osmolality of 1000mOsm/kg,” she warns. “Greatly increasing or decreasing osmolality from the target level can affect digestibility and increase the risk of gastrointestinal problems including nutritional scours.”

She says milk replacers with high levels of minerals and lactose tend to have higher osmolality. This can be a particular problem where lactose rather than fat is used as the primary energy source.

She also cautions that increasing the mixing rate from say 150g/litre to 175g/litre to increase the concentration of milk powder can have a detrimental effect by raising osmolality. She advises it will be better for the calf’s digestion to feed more volume at a lower concentration that to increase the mixing rate.

“In addition, osmolality can inadvertently be increased by doing what is thought best for the calf. Oral electrolyte solutions are usually based on minerals and sugar, but are usually recommended to be fed mixed in the milk which can send osmolality levels rocketing.

“New research by Trouw Nutrition into osmolality is resulting in milk replacers which are kinder for calves, being very close to the optimum level seen in cow’s milk which is after all what milk replacers should be designed to replicate as closely as possible.”


Dairy vet Dan Griffiths from Paragon Vets says it is important to understand the impact of osmolality of digestion in the pre-weaned calf.

He explains the gastrointestinal tract plays two crucial roles. First it absorbs nutrients from the diet to fuel growth and secondly, but equally important, it prevents unwanted compounds and pathogens from entering the blood stream.

“This intestinal barrier plays an essential role in calf health. Anything that alters the permeability of the gut wall can facilitate the onset of disease. Increasing osmolality affects the gut barrier function and integrity which can have detrimental effect.

“Where osmolality in milk replacer is too high it is also likely there will be an increased incidence of abomasal bloat. Finally, high osmolality levels can exacerbate the severity of scouring in sick calves.”

Mr Griffiths says that it is possible to take steps to limit the risk of osmolality causing problems in calves. He advises looking for a milk replacer with a higher fat content and reduced lactose. He says that by doing this and by ensuring the fatty acid in the replacer is balanced to resemble the profile found in cow’s milk, the overall digestibility of energy can be increased.

“New advances in technology mean that some milk replacers also have a smaller fat globule size which further improves by digestibility. It also helps reduce problems with fat deposits on buckets and feeding equipment.

“If you can lower the osmolality level closer to the levels in cow’s milk you can reduce the risk of gastrointestinal problems such as abomasal bloating and nutritional scours.”