Due to their weight to surface area ratio, neonatal calves are susceptible to significant heat loss which can impact on health and daily live weight gain (DLWG).
The thermoneutral zone for calves is 15C under 3 weeks of age, meaning calves must use energy in order to stay warm below this temperature. The average temperature in the UK across the year is 9C. Studies have generally found calf housing to be of a similar temperature to the environmental temperature, unless heat sources are supplied.
Environmental temperatures affect calf mortality - female dairy calf death rates rise to ~6% in colder months, and drop to <4% in warmer summer months.
How do we tackle this issue?
Supplementing calves in cold weather with extra milk/ milk replacer can help to maintain growth rates.
Calves will require around 15% extra feed in 0C compared to 20C. It is best to increase the volume of milk replacer rather than concentration to prevent issues of nutritional scour or abomasal bloat from an increased osmolality.
Despite their popularity, the literature supporting calf jackets is lacking. A study by the University of Nottingham released 2022 looked at the effects of calf jackets and heat lamps on growth during the months Jan-April. As in previous studies, the calf jackets were not associated with improvements with DLWG.
The study did however find significantly increased growth rates attributed to the use of heat lamps. They used 1KW heat lamps which were positioned over 4 individual calf pens. The mean daily temperature was 5C higher in pens with heat lamps than those with out. The use of 1KW heat lamps are expected to increased growth rates of 90g/day in colder months.
The study calculated the use of heat lamps for 21 days cost £17 per calf.
Strategic use of straw bales around the outside of calf pens can prevent calves losing heat by convection when sitting against cold concrete walls. Straw bales as pen dividers will be difficult to clean, so it may be useful to cover with plastic sheets so they can be easily cleaned between groups.
Sufficient bedding allowing calves to nest will put some distance between them and the cold and wet floor.
If the environment of the most optimal, warmer, months could be replicated in calf sheds it is estimated >37 000 calf deaths could be prevented per year. Efforts made to increase environmental temperatures during the winter months can reduce mortality and improve growth rates. Unfortunately, it seems it is time to look beyond calf jackets as the solution.
Hyde, R. M., Green, M. J., Hudson, C., & Down, P. M. (2022). The effect of environmental temperature on average daily gain in preweaned calves: A randomized controlled trial and Bayesian analysis. Journal of Dairy Science.
Hyde, R., M. J. Green, V. E. Sherwin, C. Hudson, J. Gibbons, T. Forshaw, M. Vickers, and P. M. Down. 2020. Quantitative analysis of calf mortality in Great Britain. J. Dairy Sci. 103:2615–2623.