Cow-calf producers generally recognize that winter weather is a stressor which increases cow nutrient requirements.  The practical questions that must be asked when managing cowherds through cold stress events are “What is cold to cow?”, “What nutrients increase and by how much?”, and “How should the feeding program be adjusted to offset the increase?”. 

What is cold to a beef cow?

Cattle are most comfortable and perform optimally, when effective temperatures are neither too warm nor too cold.  This is also referred to as thermoneutral and beef cows begin to experience cold stress when effective ambient temperatures drop below the lower critical temperature (Table 1).

Essentially, once effective temperatures are below this point the cow must generate additional heat just to maintain her body temperature.  Effective ambient temperatures account for factors such as wind chill, humidity, and solar radiation and lower critical temperatures are influenced by both environmental (wind speed, precipitation, humidity) and animal (hair depth or thickness, hide thickness, the amount of mud present on the hair, body condition score) factors.  Windchill factors for varying combinations of wind speeds and temperatures for beef cows in a body condition score 5 with a dry, winter hair coat are provided in Table 2.

What nutrients increase and by how much?

Cold stress increases maintenance energy requirements of the cow to offset her need to produce extra body heat.  Energy demands increase but there is no clear impact on protein, mineral, or vitamin requirements.  A good, practical rule of thumb to follow for a cow in a body condition score 5 or greater with a dry hair coat is that her energy needs increase by 1% for each point (°F) below the lower critical temperature.  For example, if the lower critical temperature was 32°F and she requires 12.0 lb. of TDN (total digestible nutrients) daily, then her needs would increase to 13.2 lb. if the effective temperature was 22°F.  This would be determined by the following:

• 32 (lower critical temperature) – 22 (effective temperature) = 10 degree difference.
• A 10 degree difference is a 10% increase in TDN, which equals 1.2 lb. (12 lb. × 0.10.)
• 1.2 lb. + 12.0 lb. = 13.2 lb. TDN needed per day accounting for cold stress when dry.

If she has a wet (regardless of hair length) coat, then energy requirements increase by 2% for each point (°F) below the lower critical temperature.  So, for a cow requiring 12.0 lb. of TDN, her energy needs would now increase by 74% with a wet hair coat (lower critical temperature of 59°F and a 22°F effective temperature (59-22 = 37 × 2 = 74).

How should the feeding program be adjusted to offset the increase?

Feeding additional pounds of an average quality hay can typically offset increased energy needs during periods of moderate cold stress (Table 3).  In cases of severe or prolonged cold stress, hay alone is usually not sufficient and providing additional energy by feeding higher quality, more energy dense feedstuffs may be required.  When supplementing grains such as corn, wheat, or sorghum, avoid feeding more than 0.5% of body weight to reduce negatively impacting forage digestion and risks with founder unless cows are slowly and gradually introduced to higher amounts.

Consider using feedstuffs with highly digestible fiber and lower starch content such as distillers grains, wheat middlings, soybean hulls, or corn gluten feed if available.  It is typical that beef cows in a confinement or pen-fed setting respond to cold stress by increasing voluntary forage intake.  However, beef cows on pasture may spend less time grazing during cold stress events which reduces forage intake and makes it challenging to meet the cow’s additional energy requirement solely through voluntary forage intake.  It is critical that cows have access to sufficient water during cold stress events because water restriction will further reduce forage intake and subsequent body heat production.

Important points to consider when managing cowherds through cold stress

1. Body condition is key, cows in a BCS ≥ 5.0 are better able to withstand cold stress.
2. It is very difficult to add body condition after calving, even more so during cold weather.
3. Thin cows (BCS ≤ 4.0), cows without wind protection, and with wet hides are at greatest risk.
4. The lower critical temperatures are simply a guide for when cold stress may occur.
5. When the hair coat is dry, energy needs increase 1% for each °F below the lower critical temperature.
6. When the hair coat is wet, energy needs increase 2% for each °F below the lower critical temperature.
7. Start with conservative amounts of grains (0.2% of body weight) and gradually increase.
8. Feed low starch feedstuffs (distillers grains, wheat middlings…etc.) if available.
9. Provide bedding to help insulate from cold, frozen ground surfaces.

10. Ensure cows have sufficient access to clean, fresh water.