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.