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PREPARE CATTLE FOR WINTER TO MINIMIZE COLD STRESS

by: Heather Smith Thomas

Cattle need care during cold or wet weather to make sure they stay healthy and perform well. A well managed program to prepare cattle for winter and minimize cold stress can save money and reduce the number of sick animals.

Pregnant cows

Body condition should be assessed as a cow goes into winter; she should be fed to maintain or regain moderate to good condition -- to withstand the rigors of bad weather without loss of production. Body condition is generally rated on a score of 1 to 9 (1 denotes emaciation; 9 is obese). Most stockmen try to keep cows at score 5 to 6, for best health and fertility.

Thin cows suffer more cold stress and rob body fat stores to keep warm. Calves may be born weak, cows may not produce adequate colostrum, calf survivability is lowered, as is the cow's ability to breed back on time. To help cows maintain health and body condition, vaccinations should be kept up to date, parasite populations should be determined (and cattle dewormed and deloused if necessary) and windbreaks and bedding should be provided during the worst of winter's storms.

In most herds the cows should be sorted into groups - by body condition and/or age -- and fed accordingly (or utilizing different types of pasture). Then you can feed the thin or young ones (or have them in the best pastures) for weight gain without overfeeding the rest. Feeding the whole herd your best pastures or extra rations (the high level of nutrition needed by the young or thin ones) is costly and wasteful, so it pays to separate the cattle.

How much feed or supplement a cow needs depends on weather, body condition, available pasture or crop residue (quantity and quality), age of cows, whether they are still nursing calves, dry, or ready to calve again soon, or fall calved and need extra nutrition to milk well and breed back again.

Some herds do well in fall and winter on good native pasture (unless snow covers the feed) especially if cows are dry and not nursing calves. Some dryland bunch grasses (on good soils) will meet all the nutrient requirements of the dry cow except salt. Salt should always be provided for cattle since this is the only mineral not found in feeds and forages. Other kinds of pasture, especially "tame" or irrigated pastures or crop residues, lose some of their nutritional value if they dry up or freeze, and cows will need supplemental feed -- hay, silage, grain, or supplemental protein and a mineral mix. Cows on mature grass or crop residues may need phosphorus, a mineral that is most important to the cow in the last two months of gestation and the first three months after calving.

After calving, the cow's energy requirements increase anywhere from 17 percent to 50 percent, depending on her milk production. Inadequate feed at this time can lower weaning weights and reduce conception rates when cows start to rebreed. If cows calve during winter (January, February, early March), care must be taken to ensure adequate nutrition. How much feed a cow needs during early lactation depends on her milking ability and upon the weather -- how cold or wet it is. If the cow is shortchanged on feed during cold or wet weather and isn't able to supply her needs for lactation and body warmth, she'll lose weight and have trouble rebreeding.

Results from a three year study in South Dakota show that cows with higher body condition scores tend to return to heat earlier in the breeding season and are also more likely to settle. Thin cows (condition score 3 or less) have the poorest chance of becoming pregnant. Several other studies have shown that average body condition (score 5) at calving and at the beginning of the breeding season results in high reproductive performance. Ideal body condition can vary with cow type, season, and geographic location. As a general rule, cows in cold climates need more flesh covering to perform well than do cows in warm climates.

Sort cattle by nutrient needs

Young cows need extra nutrition for growth as well as reproduction especially pregnant yearlings and two year olds that have just weaned their first calves. The two year old cow is at the most difficult age (growing, milking, putting energy into the developing fetus of her second calf, shedding the last of her baby teeth). Most stockmen give special attention to a two year old as she calves and prepares to breed back, but they don't always take into consideration that she needs pampering through the next pregnancy (especially during winter) until she is safely bred back again as a three year old. Her two year old winter is a critical time.

By contrast, mature cows, especially if they enter winter in good body condition, can get by on plainer feed, available fall pasture or crop residue (with supplements added if conditions warrant) until they get close to calving again. Old cows may need to winter separately or with the young ones, if they are thin. But mature cows in good flesh can actually lose weight during winter with no adverse affect on productivity; as long as they have good feed and proper nutrition after calving. It's cheaper to prevent severe weight loss before calving, however, than to put it back on after calving when their needs are so much greater.

Adjust for cold weather

Closely monitor condition of cows as they go through winter. If some start to lose weight, you have time to correct this by feeding hay to supplement dwindling or snowed under pastures, or increase the hay ration if weather turns cold.

If weather is cold and windy, cows need extra feed just to keep warm. They may stand around or huddle behind windbreaks instead of grazing. Even if pasture is available, they may not graze until mid day when temperatures are warmest -- losing weight because they don't cat enough. This problem can be solved by giving some hay or supplement early in the day to get them going -- then they will start grazing.

A cow needs to eat more roughage in cold weather, to give her the calories for heat energy. If she doesn't have enough roughage, the pounds will melt off her as she robs body fat to create energy for warmth. More total pounds of roughage in her diet (extra grass hay, or even straw) can keep her warm, since the fermentation and breakdown of cellulose creates heat energy. High quality alfalfa hay supplies protein, calcium, vitamin A and other important nutrients, but not enough roughage for heat energy in cold weather. Alfalfa alone is not adequate for cattle in cold temperatures; cows will gobble it up and stand around shivering, losing weight. If a cow is cold, she should be given all the roughage she will clean up. Even for lactating cows, a mix of alfalfa and grass hay is more ideal than straight alfalfa. Cattle who have a chance to acclimate gradually to winter will develop a good hair coat, and put on body fat if feed sources are adequate. Hair and fat serve as good insulation against the cold. With a summer hair coat the typical beef cow may chill when temperatures drop below the mid 50s, whereas with a heavy winter coat she can stay comfortable at much lower temperatures. She can also adjust by increasing her metabolic rate to increase heat production, which also increases her appetite. But if she gets too cold, heat loss and cold stress reduces appetite and efficiency of feed conversion since the body's metabolism is adversely affected (mammals must maintain a constant body temperature to keep up the proper metabolic processes).

Critical temperature

If a cow has good winter hair, she does fine until temperatures drop below 20 to 30 degrees F. Below that, she compensates for heat loss by increasing energy intake; she must increase heat production to maintain body temperature. Healthy cows, in average body condition and acclimated to cold weather have a "lower critical temperature point" (point at which maintenance requirements increase and you need to feed them more) of about 20 degrees F. Lower critical temperature is defined as the lower limit of the "comfort zone" (below which the animal must increase its rate of heat production; it's also the temperature at which performance begins to decline as temperatures become colder).

For example, a 1100 pound pregnant cow needs 11.2 lbs. of TDN per day when temperatures are above freezing. If temperature drops 20 degrees below her lower critical temperature, she needs 20 percent more MN or 2.2 more lbs. of digestible nutrients. To supply that, you can feed her 3 lbs. of grain, or 5 lbs. of hay containing 50 percent TDN.

Wind or moisture makes effective temperature (the temperature felt by the body) lower than the temperature on the thermometer. You must figure the wind chill factor when arriving at amount of degrees below a cow's critical temperature point. There are many wind chill charts available. Kansas State University researchers have developed a wind chill index for cattle. For example, a 10 mile per hour wind at 20 degrees has the same effect as a temperature of 9 degrees with no wind. If the temperature drops to zero (or equivalent of zero, with wind chill) energy requirement of a cow increases between 20 percent and 30 percent - about one percent for each degree of coldness below her critical temperature. Cattle can't eat enough extra feed to compensate for heat production loss at minus 50 degrees F with wind chill; they need windbreaks under these conditions to reduce heat loss during winter storms. During severely cold weather, cattle also need bedding to insulate them from the frozen ground, which will help conserve their body heat.

Cows with normal winter hair coats need about one third more feed when exposed to wind chill temperatures at or near zero. Critical temperature for any cow or calf will vary according to hair coat, moisture conditions, age, size of animal, fatness (fat under the satin is good insulation against cold), length of time exposed to adverse conditions, and amount of wind. Feedlot steers, with their extra fat and access to windbreaks, are usually more tolerant of cold weather than grazing cows. Cold stress is also less severe if a storm is brief, compared with the chill and stress of continuous bad weather. Temperatures and wind chill charts (in figuring cold stress) are based on 24 hour average temperatures.

A rough rule of thumb to compensate for cold is to increase the amount of feed (energy source) by one percent for each two degrees F of cold stress. For thin cows with poor hair coats, or in wet conditions (wet hair coat) figure a one percent increase for each degree of temperature drop. A wet storm is worse than dry cold. Wet hair loses insulating quality; the cow will chill sooner. When hair coat is wet, the critical temperature is about 59 degrees F.

When dry, the hair is fluffy and traps body heat in tiny air spaces between the hairs, creating a blanket of insulation between the cow's body and the cold air. Hair tends to shed water fairly well for awhile, but once it gets completely wet and lies flatter, its insulating quality is lost and the cow is more easily chilled. A cow can suffer more cold stress in wet weather than in dry cold.

With severe wind chill and wet conditions, it is impractical or impossible to feed a cow enough additional energy to provide the calories she needs to keep warm (and inadvisable, if you are using grain to increase energy; that much grain would cause digestive disorders). It's better to provide windbreaks to offset the wind chill, and to have the cows in adequate body condition to provide stored energy for these critical times.

Many stockmen overlook the effects of wet weather, because the temperature isn't really cold. Yet a cow's nutrient requirements may be greatly affected, since she has more trouble keeping warm (try soaking your coat in water and see how poorly it insulates you from the wind or cold temperatures). Cows who have lost weight or who are losing weight are very susceptible to cold or wet weather stress, so keep track of body condition as you winter your cows.

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