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.
Note that once the coat is wet, regardless of how heavy it is, the lower critical temperature increases to 59 degrees F. This is because hair coats lose their insulating ability when wet. This would apply to cattle, horses and goats, but not sheep, since wool has the ability to shed water and maintain its insulating properties. Due to the effect of moisture on hair coats, dry, cold weather is easier on cattle, horse and goats than cool wet weather.
Wind speed produces wind chill and can further increase energy requirements for livestock when those values are below the LCT. For livestock that are housed in the open, the wind chill factor must be used to calculate additional energy needs. Providing a windbreak is another option that can be explored.
Fall and winter weather can vary considerably and one of those variations is muddy conditions. Mud also reduces the insulating ability of the hair coat, leading to a need for increased energy. The relationship between mud and its effect on energy requirements is not as well defined as the temperature charts, but depending upon the depth of the mud and how much matting of the hair coat it causes, energy requirements could increase 7 to 30% over dry conditions. In addition, there is research that suggests that mud may also be associated with decreased feed intake. Thus the worst situation for livestock is cold stress combined with mud.
Source: Rory Lewandowski, Extension Educator Wayne County and Crossroads EERA