By Dr Gillian Scoley (Dairy Youngstock Research Team, AFBI Hillsborough)
and Naomi Rutherford (Beef Research Team, AFBI Hillsborough)
WITH autumn upon us and the colder weather creeping in, we are all reaching for our coats before we head out the door. But do we need to consider doing the same for our calves?
At birth, and for the first few weeks of life, calves are unable to properly regulate their own body temperature and are vulnerable to low environmental temperatures. At low temperatures, calves have to expend energy to maintain their body temperature, which can have a negative impact on performance and health.
The simplest way to keep calves warmer is to provide them with deep dry bedding. However, consideration of housing design and materials, or using external heat sources such as heat lamps or calf jackets can also have a role to play.
Calf jackets are now more commonly seen across dairy farms, and present an opportunity to provide calves with a barrier to environmental conditions such as low temperatures and draughts without restricting airflow through the house.
Additionally, some farmers have observed increased daily live weight gains, improved coat condition and less health issues – but what does the science say?
In environmental temperatures below the lower critical temperature (LCT), calves have to divert energy from growth and immune system function in order to maintain their body temperature.
The LCT of calves has been estimated as ranging from 13°C at birth to 8°C at three weeks of age, and as reported by the MET Office, average environmental temperature in Northern Ireland between September 2018 and April 2019 ranged from 5.1 to 11.5°C, highlighting how calves are vulnerable to the effects of cold stress.
Two studies conducted by AFBI researchers Gillian Scoley and Naomi Rutherford were set up to examine the impact of using calf jackets on calf performance and health across the typical Northern Irish calving season temperatures.
In the first study, conducted within the calf rearing accommodation at AFBI Hillsborough, 90 homebred Holstein Friesian calves were group housed in pens of 15, with half of the calves provided with a commercially available calf jacket for the first three weeks of life. The study was conducted between September and January when temperature in the calf house ranged from 1-17.4°C, and was 10°C or below for more than 60 per cent of the time.
Calves were offered a moderate level of 5.1 litres of milk replacer per day at a rate of 150g/l via automatic milk feeder and had free access to concentrate and drinking water.
In the first three weeks of life, skin temperature was 6.4°C higher in jacketed calves, but there was no difference in performance between jacketed and non-jacketed calves (Table 1). However, calves without jackets visited the automatic milk feeder more frequently, indicating that they were hungrier than calves with jackets.
In the week following removal of the jackets (21-28 days of age), daily live weight gain was 0.12kg lower in calves that had been provided with jackets (Table 1).
This suggests that calves have to acclimatise to low temperatures and use energy from feed for heat production as opposed to growth. If using jackets, delaying their removal until at least the fourth week of life when calves are consuming more solid feed and therefore increasing energy intake may therefore be beneficial.
The second study was conducted at a specialised commercial calf rearing unit over a period of one year, starting in April 2017 and ending in May 2018. Over the course of the year five batches of dairy-origin beef calves were brought onto the farm in an all in-all out system. Calves were purchased from a number of suppliers and only calves that were healthy and of a minimum age of 10 days were purchased.
On arrival at the specialised rearing unit, calves were spilt into four treatments:
n I. Control – no calf jacket
n II. Arrival – calf jacket for two weeks post arrival
n III. Weight – calf jacket for a minimum of two weeks and until 65kg live weight
n IV. Weaning – calf jacket until five days post weaning
Calves were provided with approximately 620g/day fresh weight of a commercially available milk replacer at an inclusion rate of 12.3 per cent and had free access to drinking water and pelleted concentrate feed. Ambient temperature within the rearing accommodation ranged from -2.78 to 28.6°C throughout the year-long study.
Similarly to the first study, skin temperature of calves with jackets was on average 4.3°C higher than those without jackets.
Again, no differences in performance were noted between treatments, with daily live weight gain averaging 0.86 kg/day (Table 2), nor were there any differences in calf health.
No beneficial effects of jackets on performance or health of dairy or dairy origin beef calves were found in either study despite calves being exposed to temperatures below the LCT.
However, in both studies, calves were group housed in well-designed calf rearing accommodation, so although the sheds were ventilated, they were draught-free and calves always had a deep, dry straw bed allowing them to nest and huddle, thus helping to minimise the effects of cold temperatures.
It must also be remembered, that calves in the second study were an average of one month of age when the study started and were therefore more able to withstand lower temperatures without detriment to performance even without a jacket.
However, results from both studies clearly indicate that calves are exposed to cold temperatures throughout the calving season, which puts them at a greater risk for problems in early life.
As indicated by the differences in skin temperature between jacketed and non-jacketed calves, calf jackets create a micro-environment for the calf and therefore act as a barrier to cold temperatures and draughts.
In systems where calves are exposed to less than ideal conditions such as increased windspeed, draughts or wet bedding, it may be expected that jackets would be beneficial to both performance and health.