Calves are much more sensitive to cold temperatures than cattle; they have a larger surface area relative to their body weight. This can result in rapid heat loss if not managed properly. As the calf ages and increases its energy intake, it develops heat producing abilities. Older calves also develop thicker skin and more subcutaneous fat, to act as insulation.
All animals have their own thermoneutral zone, which is a temperature range where enough heat is produced to match that which is lost, allowing body temperature to be maintained. When temperatures fall below the lower critical temperature (LCT) of the zone, maintenance requirements increase. If these requirements are not met, the calf has to rely upon its own body stores to produce heat. If this continues, the calf will experience decreased growth rates (or even weight loss) and a compromised immune system.
The LCT for calves older than 3 weeks is 5°C. However, younger calves (less than 3 weeks of age) have an LCT of 15°C, meaning their maintenance requirements increase much sooner with dropping temperatures. Newborn calves are particularly susceptible to cold stress – consider the following:
- Newborn calves have only 3% body fat (compared to 16% in human newborns), leaving them heavily dependent on nutritional energy sources for heat production (Alexander et al. 1975)
- Newborn calves have only 1.5% brown adipose tissue (BAT), a type of fat present at birth for the purpose of generating heat during cold stress. Without colostrum, BAT stores are depleted in 18 hours (Faulkner 1983)
- Newborn calves need to be dried off. Wet hair cannot insulate the calf, and as the water evaporates, it takes heat with it. This process of evaporative cooling is important for older animals during periods of heat stress, but is extremely energy-costly in young calves in the winter. Heat lamps can help keep newborn calves warm as well.
- Colostrum IgG absorption is also decreased with cold stress (Olson et al. 1981). Calves born during the cold face a more challenging start as they’re less likely to get the full protection they need from maternal antibodies – make sure to follow best management practices for colostrum feeding in the wintertime.
For all pre-weaned calves, it is recommended to feed more to meet the increased maintenance requirements associated with cold stress.
- A calf less than 21d (50kg) requires 1.8L more at 0°C than at 20°C (of a 20/20 MR mixed at 125g/L).
- It is important to feed more milk, as it is the most efficient source of feed for young calves.
- Some recommend increasing the concentration of milk replacer (MR). However, nutritionist Dr. Drew Vermeire of Nouriche Nutrition Ltd points out that increasing MR fat content will reduce lactose in the final product. As a result, significant increases in fat content will yield only minimal increases in energy. Switching to a higher energy MR may also increase scouring.
- It is recommended to increase the volume of milk fed, with a third daily feeding when possible
- Feed milk at a warm temperature (38.5°C) – otherwise the calf uses their own energy stores to warm the milk to body temperature
For recommendations on how much milk replacer to feed, based upon age and environmental temperature, visit http://calfcare.ca/calf-feeding/cold-weather-feeding/
Keep an eye out for shivering or raised hair amongst your calves – these are signs that they are suffering from cold stress. Ensure your calves are using as much of their milk for growth as possible, by making sure the rest of your management is working to keep your calves warm:
- Lots of straw bedding – it provides the best insulation to calves. Make sure straw is at least 3” (8cm) deep, and DRY. Kneel in the straw for 20s to see if your straw is in fact dry. There should be enough bedding that you cannot see the calves legs when it is lying down.
- Water consumption will encourage starter intake, providing another source of nutrients for warmth. Provide free access when possible; otherwise feed warm water between milk feedings.
- Keep facilities warm – while calves can thermoregulate quite well when kept dry and draft-free, their housing must be a couple of degrees warmer than the outside environment to facilitate ventilation. This principal is the same for hutches; the air inside must be warmer to rise and mix with the outside air.
- Calf jackets do an excellent job of keeping young calves warm (recommended for those under 3 weeks of age). However, be careful in fluctuating temperatures; look for calves that may be sweating underneath the jacket during the day, as this can cause them to develop chills in overnight temperatures.
It can be easy to overlook cold stress in calves. While we can bundle up in cold weather, calves can’t unless we manage them accordingly. Particularly if you are noticing a lack of growth and increased disease rates, consider whether your calves need help keeping warm.
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