Why would a calf need a jacket?

The obvious answer is to keep warm in cold weather. But what's "cold" to a newborn calf? There's a temperature range where the amount of body heat a calf produces is balanced by the heat she loses — that range is called thermoneutral.

For an 85lb newborn calf, that range is roughly 55–78°F, assuming she's dry and in a draught-free environment. As temperatures fall below 55°F for an extended period, she has to burn extra energy just to maintain her core body temperature.

Four ways heat escapes a calf

Evaporation

Body heat is used to evaporate water on her skin and hair coat. This is easy to solve at birth — once her dam has licked her off, finish the drying and fluff up her coat. But does her housing keep her dry through the first month? A water-repellent jacket helps keep her dryer for longer.

Conduction

Calves under a week old spend around 90% of their time lying down. Direct contact with wet straw causes three times as much heat loss by conduction as dry wood shavings. A moisture-repellent jacket slows conduction losses through damp bedding.

Radiation

Heat transfers through the air from a warm calf to a cold surface — concrete or snow. A jacket acts as an insulating barrier, reducing heat moving away from the calf's body.

Convection

Losses occur when air passes over the calf. In draught-free housing where a calf can nest into straw, losses are minimal; in open, greenhouse-style or pole-barn housing, convection losses can be much higher. A jacket minimises the radiated heat that convection would otherwise carry away.

How jackets benefit the calf

  • The smaller the calf, the greater her potential to lose body heat — her surface-to-body-mass ratio is much higher than an older heifer's. This especially matters for the youngest calves, or those with low birth weights, like twins.
  • The greater the air movement around calves, the greater the benefit of a jacket. Housing that doesn't let calves find a draught-free spot has real potential for jackets to help.
  • The bigger the gap between a calf's body temperature and the air around her, the greater the benefit. In very cold weather, North Dakota State University researchers recorded an increase from 1.2lb to 1.4lb average daily gain, birth to four weeks, using jackets in hutch-housed calves.

Management tips

  • The drier and cleaner the jacket, the better it insulates — aim for bedding that keeps jackets relatively clean and dry.
  • The optimum age range for jackets is birth to 4–5 weeks, once calves are well grown and onto concentrates, reaching the thermo-neutral zone described on our Thermo-Neutral Zone page. Jackets can stay on longer with no ill effects if needed.

Information adapted from Attica Veterinary Associates.