By Dr Lorna MacPherson,

Dairy consultant, SAC Consulting

There are various options when it comes to feeding calves, but it is important that farmers think about developing the animal’s rumen and don’t forget that a supply of drinking water is equally important.

Rumen development is critical if the young dairy heifer calf is going to be successfully weaned without the stresses that can lead to growth check. Whilst milk makes up the majority of a calf’s diet the significant contributor to rumen growth is the starter feed.

The key lies in developing the rumen’s internal lining, made up of tiny finger-like projections called papillae. These massively increase the surface area for absorbing the nutrients which provide the energy for growth.

Forage also plays an important part. It is the pieces of long fibre touching the papillae, or 'scratch factor', which create the muscle contractions vital for good rumination.

The provision of forage will promote muscular development and help prevent the clumping together of papillae which can affect the efficiency of nutrient absorption.

While whole milk may be cheaper to feed at the moment than calf milk replacer, there are many reasons why calves will perform better on replacer, compared to whole milk. Calves like consistency and, depending on its source, whole milk can vary in quality, increasing the risk of scours.

The transfer of Johne’s through milk should also be considered and pasteurisation of whole milk does not guarantee it is safe to feed.

Whole milk has a higher fat content (33% on dry matter basis) than calf milk powders (which are typically 16-20% fat). Feeding too high a level of fat can reduce starter feed intake, leading to poorer rumen development.

Calves reared on milk replacer are usually heavier at weaning (see table below).

Milk feeding regime

Whole milk Milk replacer

Average 56-day weaning weight (kg) 75.5 81.5

Average 70-day weight (kg) 86.8 95.1

Average overall weight gain (kg) 47.7 55.4

Source: Teagasc Moorepark research centre/Volac

There are various milk powders available for calves, which are generally classified as being either whey, or skim-based. This refers to the type of milk protein and whole milk is approximately 80% skim.

Skim-based milk replacers are often recommended where there is a known veterinary challenge on farm. It allows slower and safer digestion as it clots in the abomasum and there is less risk of milk spilling over into the small intestine, causing nutritional scours.

Whether skim or whey-based milk replacers are used, calves can have a similar performance. Research by Harper Adams University, using Holstein bulls, showed no difference in liveweight gain and coat bloom scores reared on either a whey or skim based milk replacer until weaning.

However, calf performance will depend on the quality of whey proteins and how well they are processed.

Calves will always perform better on milk-based proteins, compared to plant based proteins, which are a cheaper alternative but generally less digestible.

Hydrolysed wheat gluten is most commonly used and is highly digestible, as is pea protein, although it doesn’t tend to mix as well and sediments out rapidly. Soya protein is much less digestible particularly for calves under three weeks of age.

As a rule of thumb, a calf needs 800g milk powder plus ad-lib starter feed to achieve a growth rate of about 800g/day. The target liveweight gain from birth to calving should be in the region of 0.75kg-0.85kg/day for Holstein-Friesian calves.

Aim to double birth weight at weaning, so the calf should be 80kg by eight weeks of age assuming a 40kg birth weight. Growth rates should be maximised in the pre-weaning phase when feed conversion efficiency is highest.

At this stage, feed conversion is about 50%, so 100g of starter feed gives 50g growth. After this, feed conversion efficiency rapidly declines and, from 11 months of age until calving, feed conversion efficiency is only about 10%.

Remember the forgotten nutrient – water! Milk is not a source of water, which is required for the rumen to function properly and digest starter feed. A calf requires four litres of water to digest 1kg of starter feed and, therefore, insufficient water intake will slow rumen development.