Feeding milk to calves

The importance of a good start

Healthy, well-grown calves become productive herd replacements. Feeding strategies should also support calves in developing a strong immune response and provide enough energy for natural behaviours such as grooming, sucking, and playing.

Calves fed approximately 20% of their initial body weight (6-10 L/day for calves 25 to 50 kg) from day one can achieve strong average daily weight gains due to the efficiency of young calves at converting milk nutrients into body tissue. There is growing evidence around the benefits of feeding heifer calves more milk, with research finding:

Feeding volume and frequency

How much and how often calves are fed milk are closely linked - total daily volume only delivers its full benefit when spread across enough feeds for adequate digestion. Calves consuming at least 20% of their bodyweight in milk each day, split across a minimum of two feeds, are more likely to achieve high average daily growth rates. Feeding milk at 20% of body weight more closely mimics the milk consumption of a calf on a cow and ensures good daily growth rates and wellbeing outcomes.

A New Zealand study compared the impact of differing allowances of milk replacer on early growth and development of dairy heifers. Calves were fed either 4 L/day, 8 L/day or ad-lib (unrestricted) from birth until weaning. Those that were fed 8 L/day and ad-lib achieved significantly higher preweaning body weights compared to calves fed 4 L/day.

Feeding calves once a day (OAD) during the first two weeks does not fully meet their nutritional and behavioural needs. Young calves need multiple feeds throughout the day to meet their daily energy requirements, as their abomasum only holds around 1.5 litres.

Increasing feeding frequency to at least twice daily (TAD) during the first few weeks of life allows calves to consume and digest adequate amounts of milk. This provides the energy they need to maintain good health, growth and to exhibit natural behaviour, such as running and playing.

Ad-lib feeding systems also provide these benefits and have the potential to reduce labour.

Some farms use automated calf rearing systems, which allow the calf to choose when and how often they feed. This mimics the natural feeding behaviour of a calf on a cow. Properly managed, automated systems have been found to reduce nutritional or non-infectious scours and the need for additional labour.

CMR and whole milk

Calves can be reared economically on both whole milk and high-quality, reputable calf milk replacers (CMR). In seasonal dairy systems there is often an abundance of surplus milk over spring, and many farms may not justify the use of milk replacers on economic grounds. Whole milk also supports the development of a calf's gut by providing natural growth factors and bioactive compounds that stimulate the intestinal lining, something milk replacers are unable to replicate.

Raw milk can be a high-risk pathway for the spread of some infectious diseases. Ensure any milk you sell, or purchase is traceable by completing a record of raw milk movement. See the OSPRI website on raw milk traceability for more information.

There are several reasons milk replacers may be used, including:

• Surplus milk is not readily available.
• High milk price.
• Disease control e.g. M. bovis and Johne's.
• Automated calf feeding systems.

Changes in liquid diet

If you need to swap between different milk replacers throughout the season, or to and from vat milk, give calves time to adapt to these changes. This can be achieved by initially mixing the CMR with transition/whole milk to let them adjust between the two feeds. Consistency is key to the success of milk replacers. Always read the label and mix according to the directions. Keep in mind:

• The digestive system of the calf takes some time to adapt to a new diet, and the risk of nutritional scours is higher when this is done suddenly.
• When changing feeds, avoid placing other stressors on calves at the same time. Allow them to adjust to the new diet before changing feeding frequency, disbudding, or moving them outside.
• Older calves adapt more easily to dietary changes. When adjusting diets, choose older mobs where possible, and keep younger calves on the same milk type.

Swapping from CMR to vat milk

• This is an easier transition for calves and can be done suddenly if needed, but a gradual change over several days is preferred, i.e. feed a 50:50 blend for a few days.
• Ensure vat milk remains undiluted to support optimal curding (a normal part of calf digestion, which forms solid clots) in the stomach and reduce the risk of scours.

Swapping between different CMRs

• To maintain calf health, gradually adjust the feed ratio over several days when introducing dietary changes, i.e. use a mixture ratio of current CMR to new CMR of 75:25 on day 1, 50:50 on day 3, and 25:75 on day 5. If calves become unwell, stay on the same ratio longer, or go back to the previous ratio.
• Mixing rates vary between products – always read the label and mix according to the manufacturer’s directions. Non-curding milk powders are suitable for older calves (e.g. 2-3 weeks).
• Monitor calves closely during the process and be ready to treat scouring calves with electrolytes to prevent dehydration. Talk to your veterinarian if you need advice on managing scours.