Understanding Cold Stress in Cows

Cattle are naturally adapted to cold weather, but their ability to stay warm depends on factors such as their winter coat, body condition score (BCS), nutrition, and staying dry. Managing cows properly during winter is crucial to maintaining health and productivity. Cold stress increases their energy needs, and without sufficient energy intake, this can lead to weight loss and decreased body condition. 

Effects of Body Condition Score (BCS)

Body condition score, based on the cow’s external fat layer, is a critical factor in a cow’s ability to handle cold stress. A healthy cow with a body condition score of 5 (on a scale from 1 to 9) has a good layer of fat that helps insulate her body and reduce the amount of energy needed to stay warm. In such cows, the lower critical temperature (LCT)—the temperature at which they begin to use extra energy to maintain body heat—is around 19°F, when they have a dry, thick winter coat. Cows in good condition can handle cold temperatures without needing additional energy supplementation until the wind chill falls below their lower critical temperature (LCT).  

Since cows will lose weight due to winter conditions on low quality feeds, producers may consider adding extra external fat to cows in the fall, to achieve body condition scores 5.5 or 6.  If cold or blizzard conditions happen, cows can lose one full condition score in two weeks.  By starting with “fleshier” cows in BCS 5.5 or 6, producers can avoid cows turning thin (BCS 4).

The lower critical temperature (LCT) changes depending on the cow’s body condition and the weather conditions. A thin cow (body condition score of 4) has a higher LCT of about 27°F, meaning she will need to start using additional energy to stay warm at higher temperatures than a well-conditioned cow. If thin cows are exposed to cold weather, they will lose body condition more quickly and may not have enough stored fat to keep them warm. This can be particularly problematic during late gestation or calving, as cows in poor condition may give birth to weaker calves, or face difficulties during the breeding season. 

The fall of 2024 has been relatively mild in Nebraska, but winter storms are due to sweep across the Plains. Due to the unseasonably warm weather this fall, cows may also have lighter hair coats. This makes managing cattle even more important, as cows might already be in thin condition due to drought-related pasture shortages. A thin cow with a body condition score of 4, for example, could require 8% more energy than a cow in good condition (BCS 5) just to maintain body temperature at 21°F.  Consider feeding thin cows slightly more energy to gain condition during the fall to early winter, so that they have less energy needs during the rest of the winter.  

Wet Hair

Wet hair significantly increases the lower critical temperature (LCT), raising the critical temperature to 53°F for a cow in good condition. In wet winters, especially with freezing rain, maintaining body condition becomes challenging as cows expend extra energy to stay warm.

Wind Protection

Wind increases heat loss, raising energy requirements. Providing windbreaks reduces energy needs by minimizing heat loss, helping cows maintain condition. For cows with wind protection, the ambient temperature can be used to estimate energy needs.  Without wind protection, the wind chill temperature should be used to estimate energy needs.

Feeding Your Cows During Cold Weather

To meet the energy needs of cattle during cold stress, it’s important not to make drastic changes to their daily rations, but to provide consistent, high-energy feed during extended cold spells. Instead over a week or two, feed more of the same ration or supplement with higher-quality hay, grains like corn, or energy-rich feeds like distillers grains.  Good quality forage/hay can also help, as the fermentation in the rumen adds internal heat to the animal. 

When feeding lower quality hay, dormant range grazing or corn stalk grazing, additional feed will be needed. One option is to feed a higher quality hay source with higher total digestible nutrients (TDN), if available.  Free choice high quality hay (58 to 60% TDN) can work down to temperatures of 34°F below the LCT of the cow (-15°F for cows in good condition with dry hair or 19°F with wet hair). If cows are grazing cornstalks or winter range, then supplementation with a high energy feed may be desirable. While corn can be used to provide more energy, it comes with risk. Feeding more than 2 to 3 pounds per head can decrease forage digestion, especially if the forage is lower in protein. Feeding corn with some alfalfa on low protein forages can mitigate this issue. 

For corn supplementation, 3 pounds of corn (82% TDN) provides 2.5 pounds of TDN, which can offset energy requirements for a cow (BCS 5) down to 5°F with a dry coat or 38°F with a wet coat.

Distillers grains are another excellent choice-both high in energy and protein.  Distillers grains can reduce forage substitution effects. Compared to corn, the decision to feed distillers grains lean more towards cost than digestion limitations.  In the case of distillers and gestating cows, the pounds of TDN needed to account for energy used due to cold stress would be equal to the pounds of dry distillers that would need to be fed daily. 

When wind chill temperatures are extremely cold or the cow has a wet hair coat, a lot of supplement would be needed to make up the greater energy needs and maintain body condition. For instance, if the wind chill was -10°F and the cows had a wet hair coat, then 8.9 pounds of dry distillers would be needed to account for the increased energy requirement.  

However, feeding these levels can be impractical.  A better approach would be to provide a smaller amount of supplemental feed and to continue to feed the extra feed after the weather has moderated to allow cows to regain energy lost during the storm. 

It is also important to remember that lactating cows have a much greater energy requirement than pregnant cows. Given this, the combination of cold stress and lactation can pull down BCS quickly. 

For lactating cows, the energy demand is even greater, and cold stress can have a more immediate impact on their body condition. Ensuring that these cows have adequate nutrition before they start losing condition is key to preventing further complications, particularly during the harshest months of winter.

How to Calculate Extra Energy Needs for Cows

You will need to gather this information to figure the extra energy needs:

-the cow’s lower critical temperature (based on her body condition score)

-the outside temperature (ambient temperature) if a windbreak is provided 

or

            -the windchill temperature if no windbreak is provided.

Using a cow’s lower critical temperature (LCT), you can figure the percent increase in energy based on the outside temperature.  Use the windchill temperature if there is no wind protection.  If there is wind protection, use the ambient temperature in the formula.

There is a 1% increase in energy needs for every 1° below the LCT.

Let’s assume a cow is in body condition score 5, which means the BCS 5 cow’s lower critical temperature (LCT) is 19°F.  For this example, let’s assume the ambient temperature is 21°F, and the wind speed is 10 mph, which makes it feel like 11°F (the wind chill index).  

No windbreaks:

• Lower Critical Temperature – Wind Chill Index = Percent increase in energy requirements
• For our example: 19 – 11 = 8 percent increase in energy requirements for a  cow in good condition (BCS 5) with a dry winter coat.

If a windbreak is provided:

• Lower Critical Temperature – Ambient Temperature = Percent increase in energy requirements 
• For this example: 19 – 21 = No increase in requirements for a good condition cow (BCS 5) with a dry winter coat.

The energy needs of various classes of cattle can be found here. A 1200-pound dry cow in late gestation has an energy requirement of 13 pounds total digestible nutrients (TDN). The cold described above in the no-windbreak situation increased this need by an additional 8% which is equal to 1 pound of TDN, for a total of 14 pounds TDN per day.

Conclusion

Proactive management during cold weather is essential to reduce cold stress in cattle. Monitor body condition, provide wind and moisture protection, and adjust feed to meet increased energy needs. Ensuring cows are in good condition before winter and supplementing their diets as necessary will help maintain herd health and productivity through the cold months.