Calf Milk Replacer Guide – What to Use and Why

It is important that you read the product labels. Ingredients will be listed in descending order of inclusion. Milk-based proteins should be higher on the ingredient list compared to plant-based proteins.

Plant-Based Proteins

Plant-based protein sources are commonly found in CMR’s. Calves will always perform better on milk-based proteins compared to plant-based proteins, which are a cheaper alternative but generally less digestible. The most common plant-based sources are hydrolysed wheat gluten, pea protein, soy protein (soy flour, soy protein isolate and soy protein concentrate) and potato protein.

Hydrolysed wheat gluten is the most used non-milk protein in the UK. It is a high quality, economical protein source, manufactured from wheat flour by separating the gluten protein from wheat starch.

Pea protein is also favourable for its high digestibility and absence of anti-nutritional factors. However, it does not tend to mix as well and sediments out rapidly. If included in a CMR, check the buckets after feeding to see if residual solids remain.

Soy protein has low digestibility and amino acid content. It can cause an allergic reaction in the gut tissue, decrease available protein to the calf and result in diarrhoea. This source of protein is best used in calves over three weeks of age. Soy proteins may contain anti-nutritional factors which can cause scours if fed in excess. If it is on the label, it should be present at very low levels (low down on the ingredient list).

Potato protein isolates have had the carbohydrate fraction (fibre) removed through special processing. This also removes the allergens, inhibitors and other anti–nutritional factors usually associated with plant proteins. They are low in fibre and lower in cost than milk proteins, making them a good choice for milk replacer.

Egg proteins are commonly used in commercial milk replacers with excellent results. Egg proteins are often referred to as the perfect protein, given their excellent amino acid content and digestibility. They are also less expensive than milk proteins, thereby helping reduce the cost of CMR.

Understanding Fats

Fat is present in cow’s milk in the form of triglycerides, surrounded by a membrane to make a milk fat globule. The most common fatty acid in milk triglycerides is palmitic acid, a saturated fatty acid. The best source of palmitic acid among vegetable fat sources is palm oil. Milk fat also contains short and medium-chain fatty acids. These are readily available energy sources and have helpful bacteriostatic and bactericidal effects in the gut.

Milk replacers often include coconut oil to provide medium chain fatty acids. As coconut and palm oil tend to be the most digestible fat sources, they are commonly used. Fat sources rich in unsaturated fatty acids, such as soya oil or sunflower oil, give lower growth rates and can increase diarrhoea, so are best avoided.

Understanding Osmolality For Optimal Digestion

Osmolality refers to the concentration of a solution expressed as the total number of solute particles per kilogram. Cow’s milk has an osmolality of around 300mOsm/kg, which is the same as a calf’s blood. As these are similar, this enables optimal digestion and the absorption of nutrients into the bloodstream.

The osmolality of a CMR will vary depending on the concentration of lactose and minerals in the product but can often be higher than that of the calf’s blood, potentially leading to problems when the CMR is mixed at a high inclusion rate.

If a CMR uses fat as its main energy source, its osmolality will be lower than one that is relying more on lactose to provide energy. Whey based powders will have varying osmolality depending on their lactose content.  Better quality whey-based milk replacers will have a lower percentage of lactose and thus a higher fat percentage, resulting in a lower osmolality.

If the osmolality of milk is too high, fluid is effectively drawn from the calf’s blood into the intestine. This can cause diarrhoea and lead to dehydration. In extreme cases, there is delayed abomasal emptying, putting calves at risk of bloat. Regular feeding of high osmolality CMR has also been shown to damage the lining of the gut. This not only has an effect on the calf’s ability to digest nutrients properly, but can increase the permeability of the gut lining, making it easier for pathogens to transfer into the bloodstream, causing disease.

To avoid high osmolality, it is recommended that CMR’s are mixed at a maximum concentration of 15% (unless advised otherwise by the manufacturer/supplier) and plentiful fresh water is available. Even if the CMR is mixed properly, the osmolality in the calf’s gut is dependent on the calf drinking enough water and the health of the calf, whether it is scouring and dehydrated.