Cow-calf producers generally recognize that severe 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.