Winter Weather Factors

BY JIMMY PARKER

There are many factors that determine how much feed an animal will eat each day. We have touched on many of them, from heat stress to feed quality. We have not spent a great deal of time discussing what is more relevant for this time of year. The environmental things that we see playing major roles this time of year are generally temperature, wind, rain and mud. Of course, feed or forage quality will still play a major role.

When we talk about winter weather factors that influence nutritional demands, we normally think of energy demands, and rightfully so. That is what changes the most. Typically, the other nutrients do not really change a great deal with the colder weather environmental changes, although you could see the slightest increase in protein needs as hair growth ramps up.

We have talked about energy sources before. The bulk of energy nutrition is centered around fat, starches and fiber digestion. Fat is the densest energy source and works well to increase the total calories provided, but has limitations for many reasons and can only be used sparingly. Starches are really good sources of energy as well and we find them added usually in the form of normal grains like corn. Fibers are a bit more complex and some are better sources than others. They do generally provide the base of caloric intake in ruminants. Some are easy to digest and some are almost impossible to use. The less digestible fibers also tend to hang around the rumen for longer periods of time and limit total intake. This is where putting up really mature grasses as hay will haunt you the most and probably causes as many problems in our cow herd as any one factor each year.

Animals burn calories to maintain body temperature. Animals in good body condition are good at staying warm in cold weather. Hair and fat provide a great deal of insulation. Cattle don’t go into cold stress with normal winter hair until temperatures fall to around 32 degrees, but their energy needs go up considerably during wet windy conditions at temperatures below the mid-50s Fahrenheit. Animals’ energy requirements go up about 1% as the environmental conditions worsen and temperatures fall below a critical point with dry conditions, and requirements go up about 2% in wet windy conditions for each degree of temperature change. So, in dry, calm conditions with a body score of 5 and a normal hair coat, cattle would not see a real change in energy needs until temperatures reach the freezing mark or just a bit below, especially on a nice sunny day. That does change rapidly as temperatures fall further, 1% for each degree, so, at 25 degrees you would be 7 degrees below freezing and you would need to increase the animal’s caloric intake by 7%. That is pretty straightforward.

When rain, wind and muddy conditions are factored in, the change is much more significant and starts in the mid- to high- 50s. Using 55 degrees as the benchmark for where cold stress starts on wet, windy days, we need to add 2% more energy for a cow to maintain her temperature. So, at 42 degrees on a wet, windy day, cattle would need a great deal more energy. 55-42=13 times 2 would be 26% more energy, just to maintain body temperature. At 36 degrees, 55- 36=19 times 2 would be 38% more energy needed.

Under wet, windy conditions, it is highly unlikely that cattle can maintain themselves on hay alone and unless additional calories are provided they will pull from their fat reserves to meet their energy needs. That is very effective when fat reserves are plentiful, but as those fat reserves disappear and body condition suffers, then their ability to insulate themselves goes way down and they will need even more energy to stay warm. It is a vicious cycle and one that costs producers a great deal of production each year.

When we talk about body condition and an animal’s ability to stay warm, we can think of their body condition as like our clothing choices. Cattle with a body condition score (BCS) of 5 would be like you wearing a really heavy coat and you would be comfortable at reasonably cold temps. Cattle with a BCS of 3 would be like you wearing a light jacket and you would start to burn more calories at a higher temperature. BCS scores of 2 would be like you wearing shorts and a tee shirt and you would notice cold, rainy weather well before your friend with the heavy coat. Cattle with a BCS of 1 would be like a naked person out in the cold and survival would be questionable well before temperatures reach the freezing mark.

Hopefully, your animals have started the winter with a good hair coat and a high BCS. If so, they are well-equipped to survive the cold, wet days to come. They will still need a little help on those hardest days and will probably need a bit more than just hay, or at the very least they will need your best hay on the worst days. If your animals enter the winter in less than ideal body condition, expect to need to supplement them on the nice days and feed them heavily as cold, wet weather becomes more common.

Under wet, windy conditions, it is highly unlikely that cattle can maintain themselves on hay alone and unless additional calories are provided they will pull from their fat reserves to meet their energy needs.