North Dakota State University Agriculture Communication
(Previously published online with North Dakota State University Extension and Ag Research News: December 16, 2014)
(Image Source: Farm Advisory Service)
Sheep are tolerant to cold weather with proper care.
Production systems in upper Midwest sheep operations often revolve around winter. Sheep producers need to make sure their flock is prepared for the cold weather, according to North Dakota State University Extension Service sheep and livestock stewardship experts.
“Well-adapted sheep are quite tolerant to cold weather, given a few management factors are adequately addressed,” sheep specialist Reid Redden says.
Due to wool’s insulative properties, the lower critical temperature for a sheep with a full fleece is below freezing, whereas the lower critical temperature of a freshly shorn sheep is near room temperature.
Sheep managed below their lower critical temperature will begin to use additional feed resources or bodily tissues to maintain body heat. A general rule of thumb is to add 1/4 pound of total digestible nutrients for every 10 degrees below the lower critical temperature, Redden says.
For example, when temperatures fall to minus 15 F (roughly 40 degrees below the lower critical temperature), sheep should be supplemented with an additional 1 pound of corn per day to avoid a loss of body condition.
Newborn lambs are very susceptible to cold stress, hypothermia and frostbite. During cold weather, lambs are able to maintain normal body temperature for only a few hours after birth. Lambs must nurse shortly after birth to be able to fuel their metabolic need to maintain body heat. Producers whose flocks lamb in the winter should confine ewes in barns that provide a clean, warm area for newborn lambs.
“The ability to nurse quickly in cold temperatures is also critical to the immune status of newborn lambs because hypothermia will inhibit absorption of immune components, which protect the lamb from infectious pathogens,” veterinarian and livestock stewardship specialist Gerald Stokka says.
Moisture alters the level of cold stress on sheep. Newborn lambs are born covered in a liquid (amniotic fluid) that works against them. This fluid works as a conduit to exchange heat and cools their body temperature quickly.
“Fortunately, ewes have a natural instinct to lick off this fluid and reduce the rate of heat loss,” Redden says. “This behavior also stimulates the lambs to stand up and nurse.”
Similarly, lambs that are born outside in wet conditions (rain, sleet, or wet snow) are more susceptible to hypothermia than lambs born outside in dry or below-freezing conditions. However, subzero ambient temperatures are detrimental to lamb survival, regardless of moisture, he adds.
Wind also is a factor that affects cold stress in sheep. Wind speeds above 5 mph can increase the risk of hypothermia drastically in newborn lambs and cold stress in all classes of sheep. Stokka recommends providing protection by strategically placing hay stacks, providing bedded areas, constructing wind fences or planting shelter belts.