AGRICULTURAL NEWS

(940)716-5580 FAX:(940)716-5589

December 19, 2009
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
problems.  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. 

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. 

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 posters or increase the hay rations 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 eat
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,)
can keep her warm, since the fermentation and breakdown of cellulose
creates heat energy.   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
cold.  With a summer hair coat the typical beef cow may chill when
temperature drop below the mid 50's 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
increase 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 (mammals must maintain a constant body
temperature to keep up the proper metabolic processes).

If a cow has good winter hair, she does find 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.

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 a 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 wind chill and stress of continuous bad weather.

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 condition (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 50 degrees F

04/15/09