References
Calf jackets: a review of science and practice
Abstract
In the ideal world in which we do not live, where all births are easy, all nutrition balanced, and environmental conditions clean and without thermal stress, calf jackets would never be needed. In reality, however, calves — particularly those born in the winter months in the UK — will likely fall below their thermoneutral zone, requiring a solution. While some added insulation for a cold period might have positive physiological responses, trial data on the value of calf jackets do not often show clear benefits, despite the confidence of some UK producers that they produce benefits for their farms. There are also concerns about the extent of effective hygiene routinely applied to jackets. This article presents and discusses literature related to calf jacket use, and suggests protocols for safe use.
Most veterinarians are familiar with the idea of thermoneutral zones (TNZ) for animals, outlined by a lower critical temperature (LCT) and upper critical temperature (UCT). The subject is covered, for example, by Silva and Bittar (2019), and relates to the interaction between animal physiological states, nutrition, and external environment. It is broadly understood that when an animal moves outside its TNZ, there will be behavioural, energetic and physiological changes until TNZ is regained. What is not so clear is whether or not the cattle sector understands the dynamic nature of TNZ within and between 24-hour periods.
One example of the constant variability of the LCT/UCT limits of TNZ is the change in sensible heat production throughout a 24-hour period. Figure 1 shows the change in heat production during the first 15 hours of life for three different breeds of calf (Vermorel et al, 1983). The daily pattern of milk feeding, typically twice a day, will also influence daily changes in heat production (Hill et al, 2016). Body temperature will fluctuate as well, from the impact of depressed body temperature in dystocial calves (Vermorel et al, 1983) to the daily rhythmicity that establishes around day 9 in calves (Figure 2; Piccione et al, 2003). LCT and UCT may also change within 24 hours due to environmental variations in ambient air speeds and moisture levels in bedding.
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