The Cow/Calf Manager "Extra Energy Needed During Cold Weather"

Livestock Update, February 2001

John Hall, Extension Animal Scientist, Beef, Virginia Tech

This November and December were among the coldest on record, and despite a break in the weather, the forecast is for a cold winter. This extreme cold, for Virginia, means cows are more likely to be stressed and need extra feed this winter. It is important to supplement your feeding program to insure cows don't lose weight.

Cows and heifers that are not fed extra during long cold snaps (more than 2 weeks) are in danger of reduced reproductive performance. Problems with cows not fed extra during extreme cold include weak calves, increased calving difficulty, poor colostrum and reduced pregnancy rates. In addition, calves born to these cows often have more health problems such as scours and respiratory infections.

The Lower Critical Temperature (LCT) is the temperature below which a cow must use energy to keep warm. The average cow in Virginia does not expend extra energy to keep warm between the temperatures of 30° and 50° F during the winter. She stays warm because of her hair coat and the heat produced by fermentation in the rumen. So, 30° F is her LCT.

If the average of the high and low temperature for the day is below 30° F, then a cow must spend energy to keep warm. Lately, the average temperature has been much colder than 30° F throughout much of Virginia. Every degree below 30° increases the amount of energy needed. In order to keep warm, cows must either eat more energy or burn fat. If cows are wet, then the LCT rises to 45° - 50°, so a 40° day with rain causes a cow to need extra energy.

Cows will need about 1% more TDN in the diet for every degree below LCT. Generally, cows will need a 20 to 40% increase in total energy when they are cold or wet than if they are dry and the temperature is above LCT. For example, a cow in late gestation needs 13.2 lbs of TDN per day. If the temperature, drops to an average of 25°F then she will need an extra 5% TDN in her diet. This means she needs 13.9 lbs of TDN per day or an extra 0.7 lbs of TDN.

Table 1 shows the pounds of various grains needed to meet the added requirements due to decreasing temperatures in dry cattle. Cows must already be eating a hay or a diet that is 54.6% TDN and 8.6% crude protein.

Lactating cows already need a better diet than late gestation cows. They need a diet that is 59.2% TDN and 10.5% crude protein. Lactating cows need an additional _ pound of grain above what would be needed by late gestation cows (Table 2). Late gestation heifers need to be supplemented like lactating mature cows.

Table 1. Amount of grain needed to be added to an adequate diet* of 1200 lbs. cows in late gestation (60 - 90 days before calving) to compensate for cold temperatures.

	Average Environmental Temperature
Grain Source	25°F (5° below LCT)	20°F (10° below LCT)	15° F (15° below LCT)
Corn	1.0	2.0	3.0
Barley	1.1	2.2	3.3
Corn gluten	1.0	2.0	3.0
Soybean Hulls	1.0	2.0	3.0

*Diet must be 54.6 % TDN and 8.6 % CP before adding grain

Lactating first calf heifers will need the most energy of all. They should get an additional 0.2 lbs of grain per day for every 5°F below LCT. Extra attention should be paid to these milking two-year-olds. Don't forget cows will need even more energy if they are wet. Also, make sure you test your forages for nutrient content.

Table 2. Amount of grain needed to be added to an adequate diet* of late gestation heifers or 1200 lbs. cows in early lactation (0 - 90 days after calving) to compensate for cold temperatures.

&nsbp;	Average Environmental Temperature
Grain Source	25° F (5° below LCT)	20°F (10° below LCT)	15° F (15° below LCT)
Corn	1.5	2.5	3.5
Barley	1.6	2.7	3.8
Corn gluten	1.5	2.5	3.5
Soybean Hulls	1.5	2.5	3.5

*Diet must be 59.2 % TDN and 10.5 % CP before adding grain

If you forget to cut out these tables, use this rule of thumb:

• 1 pound of corn for every 5 degrees below 30°F for late gestation cows
• 1.5 pounds of corn for every 5 degrees below 30°F for lactating cows and late gestation heifers.
• 1.7 pounds of corn for every 5 degrees below 30°F for lactating heifers.

So put another log on the fire and feed the cows some extra grain, and you'll both be warm!

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