The Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) has a rich history. Over the 50 plus years we have existed, TVMDL professionals have worked tirelessly to provide the most accurate and up to date resources to our clients. The following excerpt is part of an ongoing series of articles written by TVMDL’s first director, Dr. William Sippel, and other professionals from the earlier days of TVMDL. Some articles were written for features in The Cattleman publication where others were case studies over recent diagnoses. We hope you enjoy this look back on TVMDL’s history.
Veterinary Outlook: Starvation from the Cold
By William L. Sippel, V.M.D.
A large number of cattle died in January and February as a result of cold weather and inadequate food intake. January 1978 was the coldest month on record in many years of Texas. The very prolonged cloudy, cold weather with rain, sleet, snow and persistent wind resulted in conditions that required substantially increased amounts of energy feeds just to maintain body heat. Many cows presented to the laboratory for autopsy revealed a total absence of fat and few, if any, other lesions. Some had the added burden of pregnancy and a few were parasitized.
A review of the mechanism of resistance to cold might explain what happened to these cattle.
The body of the animal has several defenses against cold. The first is the hair coat which grows longer in winter and offers considerable help in conserving heat and repelling cold. In this regard, the different breeds vary greatly in the effectiveness of the protection from their coat. A must ox has a much thicker and more dense coat than a Brahman. This is a genetic difference derived from centuries of adapting to arctic and temperate zones respectively.
The thickness of the layer of fat beneath the skin is another important cold defense in which breeds vary as above. These two defense are physical or mechanical types of protection.
A third type is more chemical and is the ability of the animal to generate more heat in response to the demand of low atmospheric temperature. Here, the differences between breed are less marked. Shivering is another cold defense mechanism that produces heat by muscular exertion; however, when the body temperature gets low enough, shivering ceases. These activities are controlled by the heat regulating center or “thermostat” in the brain that calls for high heat production in cold weather and minimal amounts in hot weather. This heat must come from the metabolism of food eaten by the animal, in days or weeks previously, that has already been digested and stored as fat and muscle. Forage that is consumed in the previous 24 hours, or possibly longer, will not be of much help as it must be digested to be used, a process that also requires energy. High energy feeds provide internal heat but enough cannot be utilized to immediately overcome the heat deficiency encountered in weather such as experienced this winter.
Most of the animals examined at our laboratory had food in the rumen and true stomach but it was “too little and too late.”
Cattle that succumbed probably went into the winter in relatively poor condition. They were probably on a subsistance [sic] ration that in normal winter weather would enable them to come into the spring with a weight loss of 150 to 250 pounds. Spring grass would “pout them on the mend’ and hopefully in early summer they would be back to normal.
However, the cold, wet, windy weather of January and February demanded more energy to maintain body heat than they had available. Ordinarily one-third more heat is required for maintenance of body temperature in January than in July. This winter if portably approached twice as much. The body fat deposits were completed used up and music tissue, which is a less efficient heat, was being utilized. Energy from intake of amounts of feed that are adequate for maintenance in normal winters fell short of the requirement. Cold by itself is and enough but when rain wind are added, heat loss is multiplied several times by the effect of conduction and evaporation. Under these circumstances the “wind chill factor” referred to by the weatherman has real meaning to a range animal. It is a common practice to feed cattle in an open field near the road. Regardless of weather, cattle will gather in this area awaiting the feed truck. Some exposure could be prevented if the feed were distributed in a wooded or other protected area.
I recall a winter several years ago in Florida when a cold, north wind and rain lasted several successive days. Cattle drifted to the south fence of pastures and thin animals died in piles from loss of heat that resulted in the body temperature dropping below the level required for normal function of the body systems. Under these extreme conditions the heat regulating center in the brain calls for maximum heat production and available fat and even muscle is converted to heat. When the fat is depleted, heat production and body temperature drop rapidly. Muscle cannot be converted fast enough to maintain body temperature. When body temperature gets below critical levels, certain vital enzyme reactions cease to take place and the animal dies. This phenomenon is what resulted in the death of many Texas cattle this year. Mercifully, it is painless.
One wonders how cattle in northern states and Canada withstand the extreme cold to which they are exposed each year. Some don’t, but most have acclimatized to the severe weather and are better able to survive. Also, rancher in these areas put their herds in “winter pastures” closer to headquarters and possibly look after them better because they if they don’t, they will lose them. Severe weather is expected every year in the north and ranchers keep their cattle in an nutritional state that will enable them to withstand it. The animals have heavier coats of hair, thicker layers of fat under the skin and usually have areas or buildings where they can get protection from the wind. Such facilities are seldom needed in most parts of Texas except in unusually severe winters.
The price of cattle last fall probably influenced the decision regarding how much money to budget for winter feed. The severity of the weather could not be predicted. These factors contributed to the problem.
Hopefully, the above information will explain the physiological process so that losses can be prevented in future years.