Hypothermia is a profound drop in body temperature to below normal levels. While potentially serious in any age animal, it can be devastating and likely to be fatal in the newborn calf. Calves less than 48 hours are often hypoglycemic (low blood sugar) with inadequate fat reserves, and may be unable to restore both temperature and blood sugar to normal with their own homeostatic mechanisms. Newborn calves do not have the benefit of a functioning rumen to generate heat.
Faced with a cold environment, any mammal will try to maintain body temperature with two automatic methods; shivering, to increase muscle heat production, and blood shunting, which diverts blood flow away from the extremities to the body core, thus reducing heat loss and maintaining vital functions for a longer period of time.
Hypothermia may be classed in one of two ways. Exposure (gradual) hypothermia is the steady loss of body heat in a cold environment through normal bodily means such as respiration and evaporation and transference. Lack of adequate body hair coat, body flesh or weather protection can increase heat loss dramatically and this can affect all classes of livestock, but particularly the young, the old and the thin animals. Immersion (acute) hypothermia is the rapid loss of body heat due to a saturated hair coat in a cold environment. This is most often the case in newborn calves saturated with birthing fluids, but can also occur when born in deep snow or on wet ground, falling into a creek or being soaked by heavy rains followed by chilling winds. First-calf heifers may lack the experience to lick and dry their calf, and may not stand well for the calf to nurse. Calves resulting from a slow or hard birth may be born with a lower than normal level of oxygen in their blood. This may result in an inability to stand or to nurse, or both, and sets the calf up for hypothermia.
Mild hypothermia occurs as the body’s core temperature drops below normal, which would be below 100 degrees F for a calf. Early on, vigorous shivering will usually be accompanied by increased heart and respiratory rate. The nose and hooves will be cold and pale, indicating rerouting of blood away from the extremities. In the case of a just-born calf, severe shivering may actually interfere with the calf’s ability to stand and nurse. This only further accentuates the problem and sets the animal up for a never ending cycle of worsening and worsening hypothermia. Erratic behavior, confusion and clumsiness are all signs of so-called “dummy calves” and mild hypothermia. If you put your fingers in the calf’s mouth and it feels cold, and the calf has no sucking reflex, it needs to be dried and warmed immediately.
Severe hypothermia occurs as the core temperature drops below 94 degrees F. Shunting of blood flow continues, resulting in very cold extremities. Decreased circulation also results in a buildup of acid metabolites (waste products) in the muscles of the legs. After shivering stops, it is replaced by muscle stiffening or rigidity. Below 94 degrees, the vital organs are beginning to get cold. As the brain cools, brain cell metabolism slows, resulting in severe alterations in brain function. The level of consciousness deteriorates from confusion to incoherence to coma. Below 86 degrees, and signs of life are very difficult to detect. The calf may be mistaken for dead as the pulse may be undetectable, the respiratory rate may be reduced to a gasp 4-5 times a minute or less. The pupils of the eyes may be fixed and dilated.
Treatment of hypothermia needs to begin immediately upon discovering a chilled calf. The goal is to return the core body temperature to normal (100 degrees) and dry the haircoat. Sources of heat may include a warm water bath, an electric blanket, heat lamps or hot water bottles. Warming and drying boxes may be used, but it is absolutely critical that excellent ventilation be maintained as the calf is both warmed and dried. Poorly ventilated plywood boxes with external heat sources result in extreme humidity predisposing the calf to pneumonia. Left unattended, boxes with a propane heater or heat lamp can overheat a calf, resulting in burns or even heatstroke. It is not surprising that such homemade devices were nicknamed “death boxes.”
Calves with hypothermia need to be warmed slowly over about the course of 60-90 minutes. They also require a source of energy as they warm up. They should be fed either warm colostrum or a warm electrolyte solution that includes dextrose or glucose as a primary ingredient. This serves to further warm the calf from the inside out, and helps to prevent acidosis as the calf warms up. Acidotic calves will be predisposed to scours and pneumonia.
Hypothermic calves will generally be too weak to nurse, and may not suck from a bottle. It is essential that these calves be tubed with an esophageal feeder as soon as they are conscious if they will not suck. Any liquid should be at least 98 degrees, but not hotter than 102 degrees. I personally would tube with 2 quarts for most calves, although smaller calves could make do with 1 ½ quarts. This should be repeated in 6-12 hours if the calf is not up and nursing off its mother by that time.
Warm water immersion is probably the fastest way to rewarm calves that are chilled. Calves that are warmed at warm room temperature with added insulation (blankets) and heat lamps will use more stored body energy to produce body heat that calves warmed in a warm water bath. Water needs to be about 100 degrees F, and checked frequently to ensure that the water bath maintains that temperature. Needless to say, calves immersed in warm water must be maintained with their head above water, and must be dried thoroughly prior to being returned to the outside environment.
Warm blankets should not be so hot that they cause skin burns. An electric blanket may be used, but the calf should not be allowed to lie on the electric blanket or burns may occur. Blankets can also be warmed in an oven (with caution) or a clothes dryer (ideal). Blankets in contact with the calf should be easily touched by human hands or they are too hot. They also must be rotated frequently as they cool to maintain a temperature close to 100 degrees.
Hot boxes can be purchased with a heat source and fan for circulation, or can be homemade. Temperature should be about 105-108 degrees, but care must be exercised as the calf warms not to overheat it. Hyperthermia (heat stroke) can kill very rapidly. Homemade boxes must be adequately ventilated to prevent buildup of carbon dioxide and moisture, either of which will add further problems to the calf’s condition. Fans to circulate the warm air around the calf’s body are essential.
Any calf left with an external source of heat on it or directed at it should be carefully monitored. Burns and heat stoke are very serious conditions, and may be more difficult to treat than the original hypothermia. The body temperature of the calf should be checked frequently with a rectal thermometer and should be no lower than 100 degrees when warming efforts stop. The calf must be totally dry and well fed with colostrum before it is returned to its mother. Ideally, the pair would be confined to a clean, dry stall or pen where they can then bond and the calf can be monitored to make sure that it will nurse off the cow.
I have used warm water immersion on chilled calves. This works particularly well if the calf has become soaked with mud because I can rinse the mud off as I am warming them with each new change of water. I have also successfully warmed calves by bringing them inside to our mudroom and “superheating” it up to about 85 degrees with an electric space heater. This latter technique is not ideal, but it certainly has worked for me. It is a large enough area that the calf can be kept well away from the heat source, so there is no danger of burns, and there is no significant ventilation problem because of the size of the room. It is not the fastest method, but it saved a comatose calf that was literally stuck to the frozen ground when he was found. Needless to say, I always tube or bottle feed chilled calves colostrum. It helps to warm them and I do not trust their ability to nurse on their own. If I am not happy with the calf’s progress, I would not hesitate to keep it in the house overnight, and feed it again by bottle or tube before it is returned to its dam.
Common sense plays a pivotal role in preventing severe hypothermia in calves. Cows that calve in severe cold should be monitored carefully, and brought in to shelter prior to calving. Calves that do not stand and nurse within 2 hours should be monitored for hypothermia, and fed colostrum if cold. Cows that have prolonged labor, and first calf heifers that may not have a clue as to how to care for their newborn calf should have their calves carefully observed for evidence of hypothermia. Highland calves are born with a heavy haircoat, but that hair must be dry before it will protect the calf against the cold and rain. Until it is dry, all that hair is a liability. If the cow does an inadequate job of licking the calf, old towels and vigorous rubbing can help dry and stimulate a newborn calf. It takes a lot of towels, however, to remove and dry all the fetal fluids in which the calf was born. Commercial calf blankets would seem redundant on a Highland calf, but if you have to treat one for hypothermia, it would do no harm to put it in such a blanket (“Woolover” for example) for a few days after birth.
Remember that hypothermia is not restricted to winter weather. Cool weather with a brisk wind may be all that is needed to chill an otherwise healthy calf, let alone one stressed from a long and difficult birth. Use any technique to warm the calf that is available to you, even if not the ideal. A calf with severe hypothermia will not survive without you. Keep your eyes open and be diligent in treatment, and many of these calves can be saved.