What is osmolality and why is it important in calf rearing?

Osmosis (the movement of molecules through a membrane, or in and out of a cell) is important for absorption of minerals and nutrients, as well as for gastrointestinal health.

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.

A milk replacer with high osmolality, typically above 500mOsm/kg may affect osmosis and hence present the following challenges to calves:

Decreased abomasal emptying rate (the gut has a control mechanism to prevent too much of a high osmolality fluid coming in at once), which can lead to diarrhoea in mild cases, and abomasal bloat and death in severe cases.
Interfere with water absorption, leading to scours. (Less water is being absorbed by the gut, therefore it is excreted at the back end.)
Causes damage to the cells in the gut, which may result in “leaky gut”. This condition is very risky as it leads to pathogens leaking from the gut into the body, causing inflammation and other issues.

So, the lower the osmolality of a CMR, the better it is for osmosis and hence digestibility.

The osmolality of cow’s milk is close to 300mOsm/kg which is optimal for the absorption and digestion of nutrients by calves.

The lactose content in CMR is the main contributor to the osmolality value. High levels of minerals and lactose tend to increase the osmolality of the product.

Sprayfo Delta Energised Calf Milk (calf milk replacer) was developed with a low level of lactose, reducing the osmolality of the product by 20% and thus bringing it closer to whole milk.

Sprayfo Delta has an osmolality of 350mOsm/kg when mixed at 135g/L. In contrast, many calf milk replacers (when mixed) have levels above 400mOsm/kg, some closer to 600mOsm/kg.

By comparison, salt water has an osmolality of 1000mOsm/kg.

Mixed at the recommended rate of 135g/L, Sprayfo Delta has an osmolality of 350mOsm/L - making it the closest alternative to cow’s milk.

A higher mixing rate would increase osmolality but, compared to other CMRs mixed at the same rate, Sprayfo Delta will still have a lower osmolality.

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