At lower environmental temperatures, calf energy expenditure is concentrated on staying warm rather than on growth. Unless we provide them with additional energy, daily growth rates will be slowed and likely accompanied by concurrent disease. Calves have a thermal comfort zone, the lowest end of this is the Lower Critical Temperature (LCT). If ambient temperature drops below the LCT, additional feed should be given to maintain energy requirements.
The LCT varies with air speed and age of calf; for calves less than 3 weeks of age, the LCT is 15°C, for calves older than 3 weeks, the LCT is 10°C. The recommendation is to give an additional 50g per day of milk replacer, or 0.33 litres/day of whole milk, for each 5°C temperature drop below 15°C (if < 3 weeks), or below 10°C (if >3 weeks). (AHDB Calf Management Guide; Calves in cold weather). Always ensure milk is still warm at the point of feeding, and that concentrate, or creep feed, is offered ad lib.
As well as providing additional energy, as the temperature drops it is a good time to focus some attention on the calf shed. Deep straw bedding with good drainage will mitigate the impact of colder weather. Good ventilation is essential to reduce airborne pathogen challenge at the calf level, but draughts will increase air speed and lower the ambient temperature further. Having a couple of thermometers at different points in the shed is a good idea. Your vet can also help you perform a ventilation assessment and highlight any areas that might need adapting.
Calf jackets are another great option in younger calves if the temperature is predicted to fall below the LCT overnight. So long as the calf and the jacket are dry, it will preserve and insulate body heat (any moisture and it will become trapped). It’s essential these jackets are kept clean, if not they can contribute to the spread of scour pathogens (particularly Cryptosporidium).
