Breeding and calves special: Osmolality key to increasing calves' intakes
Maximising calves’ intakes can be vital to improving herd growth rates, and measuring the osmolality of milk replacers can be a key step in this achieving this, according to Georgina Thomas of Trouw Nutrition GB.
Osmolality is a measure of the concentration of particles in a solution.
It is calculated by adding the concentration of sugars, such as lactose, and minerals, including sodium, magnesium, and chloride.
Ms Thomas says: “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.
Target level
“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 150g/litre to 175g/litre to increase the concentration of milk powder can have a detrimental effect by raising osmolality.
She says it is better for the calf to feed more volume at a lower concentration than 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.”
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Digestion
Dairy vet Dan Griffiths, of 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. Firstly, it absorbs nutrients from the diet to fuel growth and secondly, but equally important, it prevents unwanted compounds and pathogens from entering the bloodstream.
“This intestinal barrier plays an essential role in calf health. Anything which 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.”
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