Use of calf jackets to mitigate cold stress and improve calf welfare
Dairy bred calves in N. Ireland, as with most parts of the world, are reared artificially. Most calves are separated from their dams within the first 24 hours of birth. This is done to optimise calf health and the productivity of the dairy herd management system. However, where calves are reared artificially, farmers have a responsibility to optimise the health and welfare of the dairy bred calf for sound economic reasons and increasingly from a societal demand perspective.
Creating the optimum calf environment is a major challenge for many dairy farmers. Calf jackets have gained considerable popularity amongst farmers in recent years as a way of mitigating cold stress. This technology investigation assesses the need for cold temperature mitigation measures for calves and evaluates the research evidence supporting their use.
Thermoneutral zone and lower critical temperature
Calves have a temperature range known as the thermoneutral zonewithin which they can comfortably maintain their body temperature without needing to expend excessive energy on thermoregulation. The lower limit of the thermoneutral zone is generally known as the lower critical temperature. Up to one month old, the thermoneutral zone is around 10-25ºC, after this age they are equipped to cope with temperatures down to 0ºC. However, this temperature range can vary in relation to housing, air speed (draughts), humidity, nutrition and breed.
The lower critical temperature is the temperature at which the calf starts to feel cold. This does not necessarily mean that a calf at this temperature is severely stressed, but it is the temperature below which the calf will physiologically start to use energy to keep itself warm. The newborn calf, sick calves, and calves just transported to the farm are those that are most likely to be affected by low temperatures.
At temperatures higher than the thermoneutral zone, a calf will experience heat stress and will physiologically use energy to cool itself down. Similarly, when ambient temperatures drops below the lower critical temperature, there is a risk of cold stress. Calves will physiologically create heat to raise their temperature back to an acceptable level.
Both of these mechanisms will divert energy from production, potentially compromising immunity and growth rates. To mitigate cold stress in the winter, there is often a temptation to block sidewalls and doors or to use straw bales or boards to create calf ‘micro-climates’ inside a larger building. The risk with this practice however, is that there will be areas of stale air created which can lead to outbreaks of pneumonia.
Table 1. Lower critical temperature of calves
|0.2 m/s (draught free)||2.0 m/s|
|5 week old calf||2oC||11oC|
|6 month old calf||-6oC||5oC|
Source: Webster, 1984
Where calves are exposed to draughts (air movement speeds above 0.2 m/s), the lower critical temperature at which a calf starts to feel cold increases considerably as indicated in Table 1. The floor or bedding the calf lies on also has a considerable impact on the calf lower critical temperature as shown in Table 2.
Table 2. Floor type and lower critical temperature of newborn calf
|Lower critical temperature (oC)|
|Lying on concrete||18|
|Lying on wooden slats||11|
|Lying on damp straw||11|
|Lying in deep, dry straw||<6|
Source: Webster, 1984
Temperature within calf houses
Young calves do not generate sufficient body heat to have an appreciable impact on the temperature inside an enclosed calf house. This has been verified by ongoing research work by AFBI Hillsborough on commercial dairy farms in N. Ireland through the DAERA and Agrisearch funded ‘Optihouse project’ in collaboration with CAFRE. The initial unpublished data indicates that the average difference between the inside temperature of commercial farm calf houses and the ambient external temperature is approximately +1.0oC. This is similar to findings from Teagasc research where the reported difference in temperature between the inside of calf houses and the ambient outside temperature was +2.0oC.
Table 3. National Met Office National Climate Information Centre, Air Temperature, N. Ireland
Source: Met Office National Climate Information Centre
Met office data presented in Table 3 indicates that for between 6 and 8 months of the year, average mean and or average minimum temperatures in N. Ireland are lower than the lower critical temperature for young calves of 10oC.
Calf jackets – mitigation of cold stress
The effect of calf jackets was studied at AFBI Hillsborough from Sep to Nov 2016. Measurement of skin temperature of calves fitted with jackets (over a 24-h period) was found to be 6.3°C higher than that of calves without jackets, with mean skin temperatures measured of 35.3°C and 29.0°C, respectively. In the AFBI study, ambient air temperature measurements were recorded as being ≤10°C throughout 61.4% of the study period.
Calf jackets – impact on calf performance
The benefits of calf jackets on calf performance have also been studied by AFBI, Teagasc, Harper Adams and the Kingshay Farming Trust.
The AFBI study was carried out between Sep and Nov 2016 with 90 Holstein Friesian calves born at the Hillsborough research centre. Half of the calves were fitted with ‘Cosy Calf’ jackets within 12 hours of birth. Calves were reared in an individual pen and fed whole milk for 5 days before being moved to a straw bedded group pen. Groups of 15 calves per pen were fed 5.1 litres (750 grams/litre) per day of milk replacer (26% crude protein; 17% fat), concentrate (ad libitum) through automatic calf feeders and straw (ad libitum) from racks. Calf jackets were removed at 21 days of age. Calves were weaned at 56 days of age.
Table 4. Performance of calves in AFBI study. (*Statistically significant )
|Average daily liveweight gain, age 7 to 20 (kg/day)||0.48||0.49|
|21 to 28 (kg/day)||0.49||0.61*|
|28 to 55 (kg/day)||0.67||0.69|
|0 to 56 (kg/day)||0.57||0.61|
|Liveweight at weaning (56 days of age) (kg)||72.6||74.7|
|Total dry matter intake days 5 to 20 (kg DM)||9.54||10.07*|
Performance of calves with and without jackets in the AFBI study was similar at all stages, apart from the period after the jackets were removed at 21 days of age (Table 4). Performance of the calves that had been fitted with jackets was reduced in the week following jacket removal. This suggests that the calf jackets were removed at too young an age. Calves not fitted with jackets consumed 5% more feed dry matter (milk replacer plus concentrate) in the 5 to 20 days of age period, than calves fitted with jackets. This suggest that the calves not fitted with jackets consumed more feed to maintain core body temperature as a result of the low ambient temperature.
In the Teagasc 1999 study, the working hypothesis was that, (a) calves reared outdoors fitted with a calf jacket would be less susceptible to respiratory disease than calves reared indoors, and that (b) calves reared outdoors fitted with calf jackets would be more resistant to disease than calves reared outdoors without jackets.
In the Teagasc study, calves were purchased into the research centre between one and two weeks of age and had an average liveweight on arrival of 55kg. The calves were managed in three study groups:
- Outdoors fitted with an all-weather jacket
- Outdoors without an all-weather jacket
- Indoors without an all-weather jacket
The temperatures of the rearing environments between February and March ranged from –0.1 °C to 13.2 °C (average 6 °C) for the indoors, and from –2.1 °C to 11.1 °C (average 4 °C) for the outdoors, respectively. All calves were fed 25kg of milk replacer in buckets over a 42 day period with ad libitum access to a concentrate ration. The outdoor calves were reared in groups of 10, accommodated in 0.1 hectare paddocks with a 40m2 dry sand lying area which was wind sheltered with Tildnet double skinned fencing 1.2m high on three sides plus a wooded natural shelter on the fourth side.
Table 5. Performance of calves in Teagasc study
|Treatment||Outdoor +Jacket||Outdoor No Jacket||Indoor No Jacket|
|Liveweight day 0 (kg)||55.2||54.9||55.1|
|Liveweight day 63 (kg)||105.7||106.0||108.2|
|Liveweight gain (kg/day)||0.80||0.81||0.84|
|Total food intake (kg)||28.5||26.7||30.1|
The statistical analysis found no significant difference in calf performance between the treatments in the Teagasc study. Calves on this study had a high incidence of disease with 70% of calves treated for pneumonia and 34% of calves treated for scours. Calves housed indoors had a higher incidence of pneumonia, while outdoor reared calves had a higher incidence of scour.
Harper Adams study
The Harper Adams study involved fitting calf jackets to purchased Holstein and Holstein x Continental bull calves arriving at the beef rearing unit at 17 days of age on average. The study found consistent trends towards increased growth rates in calves fitted with jackets, despite eating slightly less concentrate over the rearing period. However, the increases in growth rates measured were not statistically significant.
Kingshay “Tried and Trusted”
Kingshay have produced a “Tried and Tested” report assessing practical aspects of eight different types of calf jacket. The report is available to subscribers at www.kingshay.com. The Kingshay report includes an assessment of how readily calf jackets can be machine washed. To avoid jackets becoming a disease transfer risk, washing and drying jackets between calves is essential.
Mitigating cold stress – other methods
Ventilation should never be compromised to raise the temperature of a calf building. The focus needs to be on implementing other measures to keep the calves warm including:
- Providing plentiful quantities of deep, dry bedding in which calves can nest should be a top priority especially in cold weather, as it traps a layer of warm air around the calf, which acts as a heat insulator.
- The University of Wisconsin have developed a calf nesting score to evaluate the adequacy of bedding. At score 1, calf legs are fully visible; score 2, calf legs partially visible; score 3, calf legs are obscured by bedding. Score 3 should be the target in very cold weather with bedding topped up, ideally at night.
- Calf jackets may help as they can prevent heat loss through convection, conduction, radiation and evaporation.
- Feed intake should be increased in cold temperatures to replace energy being burnt for heat and to prevent growth rates being compromised. The Agricultural and Horticulture Development Board (AHDB) recommend feeding an extra 50g of milk replacer per day for each 5oC drop in temperature below 10oC.
From reviewing the evidence from the research studies carried in the UK and Ireland, there is little evidence to suggest that calf jackets have a significant impact on the growth rate of artificially reared calves. There is however some local evidence to show that calf jackets can provide calves with cold tolerance protection, through increases in skin temperature when average ambient temperatures are below 10 °C.
In an era when some negative social media commentary is highly critical of the manner in which dairy bred calves are artificially reared, the visual impact of group reared calves fitted with ‘cute’ calf jackets bedded in deep clean straw is a highly positive image which may help to offset some deliberately negative online content.