Cold Stress in Cattle.

 By Heather Smith Thomas.

Weather is always a factor in cattle health.  Stressed animals are more vulnerable to stress-related illnesses.  Cattle need more care and feed during cold or wet weather.  Good management to prepare cattle for winter and minimize these stresses can save or make you money, and reduce the incidence of illness or loss of animals.

As days get shorter and weather is colder, body metabolism changes.  Feed intake increases and passage of feed through the digestive tract speeds up.  Feed requirements for cattle may go up as much as 10 to 15%.  All of these changes contribute to an increase in heat production so the animal can withstand winter temperatures.

Body condition is extremely important during winter.  Cows that get too thin during a cold or wet winter suffer more cold stress than fatter cows (since fat serves as insulation and a source of energy reserves).  A thin cow must rob body fat in order to keep warm.  It becomes a vicious cycle.  

Calves born to thin cows may be compromised in body condition and immune health, and more prone to disease during their first weeks of life.  Calves from thin cows may be born weak, unable to get up quickly and nurse—not getting colostrum soon enough.  Cold stress also hinders a calf’s ability to absorb antibodies from colostrum.  Thin cows may not produce adequate levels of antibodies in their colostrum if they have been short on protein.  Calf survivability is lower in thin cows, as is the cow’s ability to rebreed.

Shannon Williams, Lemhi County Extension Educator (Salmon, Idaho) says ranchers should make sure their cows are getting plenty of feed and adequate nutrition.  “If they are in a good body condition score, they will handle the cold much better.  When temperatures drop or it’s very windy, they need to eat more, to generate enough body heat to stay warm,” she says.

They need protection from wind, with windbreaks or trees for shelter.  “If you are hauling cattle in cold weather, they will be exposed to more wind chill than if they were simply outdoors.  Depending on how far you are hauling them, you need to consider the wind chill, and how much protection the trailer provides.  If it’s very open, there may be too much moving air around them,” says Williams.

Windbreaks and shelter for young calves is also crucial, but you also don’t want to congregate and confine them too much (with a lot of calves using the same shelter) or there will be more contamination and risk for scours.  In a barn or shelter they also need adequate ventilation.  “You walk a fine line between providing adequate protection and too much confinement,” she explains.

Cold weather brings additional challenges if it is accompanied by wind or wet weather.  Charles Stoltenow, Dean and Director of Extension, University of Nebraska (former Extension Veterinarian, North Dakota State University), says it’s important to provide windbreaks and bedding in those conditions.  “It all comes down to maintaining body heat, and nothing saps this out of the animal faster than wet and wind,” he says.  Once the hair gets wet and lies down flat rather than standing up fluffy (with air spaces between the hairs) it loses its insulating quality and it’s hard for the animal to keep warm.

“Many cattle died in the Atlas storm (when a lot of heavy, wet snow got dumped in South Dakota, Montana and Wyoming in early October, 2013).  Some got buried in drifts, but many died simply because they got wet and then weather turned cold.  They could not keep themselves warm enough, even though temperatures were not bitterly cold,” he says.

Without some kind of protection, bulls may also be vulnerable to scrotal frostbite and cows may suffer frostbitten teats.  If teats are sore, a cow won’t let her calf nurse, and this creates a double problem.  “In many parts of the country we must have windbreaks; otherwise cattle can’t get out of the wind,” Stoltenow says.

You also need to provide enough bedding so cattle to have a dry place to lie down so they are not losing as much body heat.  “Cattle are stressed if they are standing hunched up (too cold to lie down on frozen ground or mud).  If you have bedding for cattle, they are more comfortable, and tend to stay healthier,” he says.

Baby Calves
Cold stress in calves has more lethal consequences than in cows, says John Hall, Extension Beef Cattle Specialist, University of Idaho.  “Newborn calves are most at risk, but calves less than 2 weeks of age and sick calves or any age may also be at risk in severely cold weather,” he says.  Ranchers who calve in January/February are usually prepared for cold stress, but it can also affect calves born in late winter storms or an early spring downpour of rain.

Russ Daly, Extension Veterinarian/Associate Professor, South Dakota State University says newborns can handle fairly cold temperatures once they are dry and have the insulating effect of a dry hair coat.  Colostrum is also important.  After a calf has suckled, he has the energy to keep warm.

“A calf is born with less than a day’s worth of energy in the form of brown fat, to metabolize for body heat.  If he doesn’t get colostrum, once that brown fat is gone there is no energy available to maintain or regulate body heat.  Colostrum is high in fat, with 2 to 3 times more fat than regular milk.  This really makes a difference in getting the calf up and going,” he says.  A newborn calf that has had a full feeding of colostrum can stay warmer in cold weather.

Hall explains that lower critical temperature (LCT - the temperature below which the animal must burn extra energy to keep warm) is less for calves than cows, especially if they are wet.  “The LCT for calves is close to 60 degrees.  With a little rain or snow, the LCT moves closer to 70 degrees.  As little as 1/10th inch of rain on the day the calf is born can increase calf losses by 2 to 4%,” says Hall.

“Young calves dry off quickly on a dry day if the cow licks them immediately after birth,” says Daly.  “Sometimes in cold weather you have to help with that process.  It’s crucial to have bedding for baby calves.  There’s not much body mass in a small calf; these babies chill quicker than a large animal.  Bedding helps insulate the calf, making a separation between the calf and frozen ground, snow, cold concrete in a barn, etc.  This is important in helping calves stay warm,” says Daly.

Commercial calf blankets can increase survivability in young calves during extremely cold weather.  “Putting blankets on weak or chilled calves for a few days while they are in the barn may help calf survival,” says Hall.

Frostbite can be an issue in calves born during cold weather.  Extremities suffer first.  “Most people who calve early calve inside, but occasionally a calf freezes its ears,” says Daly.  “After the calf is born and dry there is much less risk for frostbite, unless a calf is suffering from a debilitating condition such as scours and dehydration,” says Daly.  In that situation, there is less blood flow to extremities.

Older Calves
Larger calves have more blood flow to extremities and are smarter about getting out of the wind.  As calves get older, windbreaks and temporary shelter can be helpful, along with good nutrition.  If they have adequate nutrition and are in good body condition they have more insulation against the cold, and enough energy to keep warm.  “We generally focus on protein, but energy for calves is crucial.  Weaning-age calves need a high-energy diet.  People here on the northern plains also recognize that these animals will increase their feed intake in response to the cold,” Daly says.

Affects On Cows
Lower critical temperature for cattle depends on hair coat; a heavy winter coat provides more insulation than summer hair and the animals won’t need extra energy to keep warm until temperature drops below that point.  “The LCT for Idaho cows with heavy dry winter coats is about 18 degrees, but the LCT of wet cows is 59 degrees,” says Hall.  If cows are not receiving extra nutrition to provide the needed body heat, they burn fat (to keep warm) and lose weight.  Weight loss during late gestation will result in lower pregnancy rates the next breeding season.

“Thin cows produce weaker calves, with reduced chance of survival.  Research from Colorado State University showed that first-calf heifers in body condition score 4 or less have reduced antibody levels in their colostrum, and their calves are more likely to become sick,” says Hall.

Increase in wind-chill or wet weather can dramatically increase cold stress on cows.  “Research from Kansas and Iowa indicates that maintenance energy requirements of a cow increase by 1% for each degree below her LCT.  For wet cows the rule of thumb is 2% for each degree below LCT.  For cows with wet coats, wind-chill temperature may easily be 20 to 30% below LCT.  Periods with high winds, snow or rain will dramatically increase energy requirements,” Hall explains.

“We must be sure we’re providing the additional feed they need,” says Daly.  For animals with a functional rumen—older calves, adult cattle--having adequate protein to utilize the energy is important.”  Microbes in the rumen break down the roughage in forage into useable energy, but they need protein to do this.

During a cold winter, stockmen can usually help cattle maintain themselves with extra feed, but prolonged cold makes it challenging to feed calves enough for weight gain.  “For mature animals, the best way to help them respond to cold stress is to feed enough energy and protein—especially as cows get into later gestation—to make sure the fetus isn’t shortchanged,” Daly says.  If any animal is putting all its resources into keeping warm, something will be shortchanged.

Hall says that during normal January/February weather in Idaho, cows need an additional 3 to 4 pounds of hay or 2 to 2.5 pounds of grain per day.  “Generally you can just feed more hay to compensate for weather stress, but hay that is low in protein will need supplemented with 1 to 2 pounds of protein.  Cows that don’t receive adequate nutrition to stay warm will lose ½ to 1 pound of weight per day,” he says.

“In extremely cold or wet conditions cows need to eat 7 to 8 more pounds of hay or 4 to 5 pounds of grain or high energy by-products, or they may lose 1.5 to 2 pounds of weight per day,” says Hall.  Windbreaks and bedding can help cattle maintain body temperature without as much extra feed, and also prevent frostbitten ears or teats, or scrotal frostbite in bulls.