Pretty much all farmers have heard of calf coats, they have gained popularity in recent years as a way to control cold stress but do we know how to use them correctly?
Let’s take humans for example, when the temperature drops, we put more layers on, right? And vice versa when the temperature rises; should we consider this for our calves too? First, let’s understand why we use calf coats.
Thermoneutral zone and lower critical temperature
What is the purpose of a calf coat? Simply put, it’s to keep the calf warm in colder temperatures. For the first few weeks of life, the calf struggles to regulate its own body temperature. There is a temperature range where the amount of body heat produced by a calf is balanced by the calf’s body heat losses, this is known as the thermoneutral zone (TNZ). The lower limit for the TNZ is known as lower critical temperature (LCT). For a 40kg newborn healthy calf at four weeks of age, the LCT can range from 5ºc to 15ºc (Robertson, 2021). This will vary from calf to calf depending on a number of things body weight, genetics, health, nutrition, environment etc, keeping in mind that a sick calf is likely to have a much lower LCT.
Once the LCT has been reached the calf will then use energy to keep itself warm which can have a negative effect on performance and health. Similarly, at temperatures higher than the TNZ the calf becomes heat-stressed and will use energy to cool itself down.
Read more: Heat stress in calves - how to avoid it?
Read more: Too Hot to Handle - The Detrimental Effects of Heat Stress
Starting Point
- Use a wall thermometer to monitor the min/max temperature in the calf shed; reset every day
- Discuss with your calf rearer/staff the temperature at which to begin to use the calf jacket (most commonly it is 10°C)
- Young calves are more susceptible to cold stress, so assess them first
- Put a clean coat on every calf below one week of age
- Adjust straps accordingly to get a good fit
Lower critical temperature of calves
Table 1. Lower critical temperature of calves
| 0.2 m/s (draught free) | 2.0 m/s (meters per second) | |
| New-born calf | 12ºC | 20ºC |
| 5 week old calf | 2ºC | 11ºC |
| 6 month old calf | -6ºC | 5ºC |
(webster 1994)
Interestingly the above table indicates that the calf’s lower critical temperature is increased considerably when exposed to air movement speeds above 0.2 meters per second, meaning the calf will begin to feel colder at higher temperatures if wind speeds increase above 0.2m/s.
As the calf gets older, they are able to withstand colder temperatures, therefore, the calf’s lower critical temperature is less. When the calf reaches five weeks of age it is not necessary for the use of a calf jacket.
Requirements when choosing a calf coat:
- Breathable
- Well fitted
- Water repellent
- Washable
- Hardwearing
Calf coat protocols
If you are thinking of using calf jackets then I would suggest having protocols in place for your calf rearers/staff.
Hygiene
If you’re not going to bother cleaning the jackets properly then I strongly recommend you have a look at another way of keeping your calves warm, that might be blunt but it’s true!
5 Steps of washing the coats
Jackets on/off
Calves can wear the jackets from birth to four weeks of age; when to remove the jackets is the tricky bit and depends on each individual calf, taking into account the current condition and performance of the calf and most importantly the current weather conditions.
Jamie Robertson recommends putting a max/min thermometer in the calf shed, and then decide what temperature you will start using the calf jackets (10ºc is most commonly used) agree on a protocol with your calf rearer/ staff that once the calf shed has reached 10ºc for three consecutive nights, you then put the calf coats on. Reset the thermometer every morning during the colder months.
When removing the calf coats keep an eye on the weather forecast and make sure you’re checking the nighttime temperatures too. There’s no point taking them off if it’s looking like the weather is going to drop again or if the nights are still chilly. Consider the overall health of the calves and remove the jacket in the morning, not the afternoon.
Key take home messages
- Each individual calf will have a different thermal neutral zone depending on breed, genetics, nutrition, health
- Damp straw is very cold
- Choose your calf jacket wisely
- Have protocols in place for your calf rearer/staff
- Make sure to clean and disinfect the jackets after each use
- Putting a min/max thermometer in the calf shed will goa long way when you are deciding when to put the calf coats on/off
- Keep an eye on the weather forecast!
