Young dairy calves are particularly susceptible to hypothermia because of poor insulation and high surface area to volume ratio. Tessa Markovich, BVSc, MS, Dipl. ABVP, Te Puke Veterinary Centre, Te Puke, New Zealand, says on grazing dairies, calf hypothermia can be a big problem in those herds with early-spring calving.
She adds that small crossbred or Jersey calves tend to tolerate the cold less than Friesian calves.
Traditionally in temperate climates it is possible to collect calves once or twice daily from the calving paddock, Markovich told attendees at the 2012 Western Veterinary Conference this week. “If calving occurs during periods of inclement weather more regular collection (hourly) of newborns is critical to their survival.”
Lower critical temperature is the environmental temperature below which heat production increases in response to decreasing temperature. The critical temperature decreases with age ~13 °C (55°F) at < 1 week and ~ 8 °C (46°F) at 3 weeks. As calves age and increase tissue insulation, they are more resistant to hypothermia.
Wind and rain can reduce growth rates and efficiency of food utilization in young calves and increase mortality caused by hypothermia, she said, and will be more severe in Jersey calves. “Rain increased heat production of calves <4 weeks old by 12% without wind and 28% with wind.”
Markovich says if young calves are dry, out of drafts and eating well, they are able to withstand cold fairly well until the air temperature falls below about 5°C (41F). Intermittent cold (0°C [32°F]) seldomly increases heat loss and food requirements more than about 25%.
However, it’s a good idea to provide supplemental heating to sick calves or those that are prevented from getting a normal energy intake because of their lower metabolic heat production and reduced cold tolerance.