We are at the end of fall and looking at the beginning of winter. While we may grumble at times about cold temperatures or a combination of cold with wind, rain or snow, livestock owners need to be aware of the effect environmental conditions can have on livestock nutrient requirements.
Specifically, cold temperatures, cold rains, and muddy conditions can all significantly increase the energy requirement of livestock. All animals have what is termed a thermo neutral zone, that is, a range in temperature over which the animal is most comfortable and is not under any temperature stress. This is the temperature range that is considered optimum for body maintenance, animal performance and health. The lower boundary of this zone is referred to as the lower critical temperature (LCT). Livestock experience cold stress below the LCT. Below the LCT, animal metabolism must increase to provide adequate heat to maintain body temperature.
When the temperature falls below the lower critical level, the animal must increase energy intake to maintain body temperature and basic body maintenance functions. The general rule of thumb is that energy intake must increase by 1% for each degree of cold below the LCT. This is where the nutritional level of the animal's diet becomes a factor. If average to good quality hay is being fed, the animal might be able to increase intake enough to meet the additional need for energy. If forage quality is low it is unlikely that the animal can increase intake enough to meet increased energy demands. In the short run, if animals are in good body condition they can burn fat reserves to compensate. If poor quality forage is the only forage option or if there is an extended period of very cold weather then some additional energy supplementation will need to be provided to the animals.
The LCT is influenced by such factors as size of the animal, breed, age, housing conditions, hair coat or wool thickness and nutrition. For livestock that live outdoors with little or no access to a barn during the winter and fall months, the hair coat or wool thickness and nutrition level are the factors we are most concerned with. As hair coat or wool thickness is increased, the LCT decreases. Quite a bit of research and study has been done with beef cattle on this topic and the following chart describes the relationship between hair coat thickness and the LCT.
Lower Critical Temperatures (LCT) for Beef Cattle
The LCT for goats is generally considered as 32 degrees F, and for sheep the LCT is 50 degrees F if freshly shorn or 28 degrees F with 2.5 inches of fleece.