Cold stress in beef cattle

CUSTER COUNTY - When temperatures begin to drop into the single digits, ranchers/farmers should think about the effect that severe cold weather will have on herd health. The bovine can be very tolerant of cold temperatures. The cow that has a good winter hair coat, adequate body condition, and readily available feed and water can withstand cold extremes that would be fatal to a human. However, even if the cow temporarily withstands these extremes she will pay a price. The price can range from loss of body condition to death from hypothermia.

The environmental temperature at which the cow will begin to experience hypothermia will vary. Short hair coats, high winds, and wet cattle will amplify the actual environmental temperature and induce hypothermia sooner. As hypothermia sets in, all metabolic and physiologic processes begin to slow. Blood is shunted away from the extremities in an attempt to protect vital organs. Frostbite of the udder and ear tips will occur at this stage. As hypothermia progresses, respiration rate and heart rate decrease and blood pressure drops. Eventually, the cow loses consciousness and death is imminent if rewarming does not occur.

In most cases if windbreaks and adequate nutrition are provided, hypothermia can be avoided. However, additional health problems should be considered in the winter. Cattle are good weather predictors and will change eating habits before a large storm. Research has shown that cattle will increase grazing activity prior to a storm, ingest little feed during the storm, and increase grazing activity after the storm. If the cattle are on high-quality pasture, this will increase the chances for bloat.

Make sure that water is available. If water is not supplied, cattle will reduce feed intake. If the winter is exceptionally hard, the pregnant animals may spend all winter using energy to generate heat. If nutrients are shunted to heat production, cattle begin to lose body condition. Cows, and particularly heifers, in poor body condition are at risk for calving problems. Also, these animals may provide inferior colostrum for the calf, and neonatal mortality may increase. In addition, these animals do not cycle on time and delay breeding in the spring and summer. Monitor body condition scores throughout the winter and be prepared to supplement the ration with increased energy, protein, vitamins, and minerals when the cattle are exposed to cold temperatures for extended periods. Adult functioning ruminants will survive long periods of cold, but may pay the price at calving or rebreeding.

When backgrounding calves or caring for beef cows, the easiest strategy during a snowstorm or blizzard is to provide the cattle with plenty of hay, often of low quality. The cattle eat their fill, it stays in the digestive tract for a longer period of time than grain or high-quality forage and the leftovers provide bedding to protect them against the weather. Windbreaks are essential to keeping animals safe from frigid conditions.

Experimental work done at Oklahoma State University shows that wet, windy winter weather greatly increases energy required by cattle. The

researchers determined what they called the critical temperature, the outside temperature at which the animals are comfortable without above-normal energy intake. When cattle are dry, the critical temperature is 32 degrees Fahrenheit. Below that, they need extra energy to maintain body condition. When their coats are wet, the critical temperature jumps to 50 degrees F. Wind chill must be considered, too. In general, cattle with a dry winter hair coat need an additional one percent increase in energy requirements for each degree the wind chill is below the 32 degrees Fahrenheit critical temperature level. Cattle with wet hair coats require even greater energy boosts. Cows that have a heavy winter hair coat that is dry and are in a body condition score of 5 have a lower critical temperature of 19°F.

What about the calf ? The calf has very little fat reserve, is born with a wet hair coat, and does not have the benefit of a functioning rumen to generate heat. Calves can go through the stages of hypothermia quickly and if rewarming does not occur death cannot be avoided. Cows expected to calve in extreme weather must be given shelter or be under constant surveillance to prevent calf loss from hypothermia.

With the onset of cold weather, try to minimize the effects of cold weather on your cattle through proper management.

Jess Taylor At right, a Charolais cow and her calf stand in the cold and the snow at the Taylor ranch last week. Calves are born with little fat reserve. Cows that calve during extreme weather must be given shelter to prevent calf loss from hypothermia.