Steve Paisley: Weather’s impact on cattle performance
Occasionally there are examples that dramatically illustrate the impact that weather can have on cattle performance.
Last week we weighed consignor bulls on our residual feed intake (RFI) bull test at the SAREC facility. Weight gains during the last three weeks of December were exceptional for a forage-based test, with daily gains approaching 4 pounds per day.
Over the last four years, we have evaluated bulls for feed efficiency and RFI on very similar predominantly forage diets. The late December and early January performance was especially interesting when compared to last year’s performance over the same time period.
While this December has been mild to say the least, late December of last year had a lengthy cold spell with temperatures dipping down to -30 degrees at times. Bull performance also dipped, hovering around 2 pounds per day. These differences tend to average out over the length of the test, but the interim weights still illustrate the impact that weather, especially cold weather, can have on animal performance.
This second week of January 2012 is another example of weather extremes. In southeast Wyoming, temperatures on Monday approached 50 degrees, but by Wednesday it was a 15-degree day with 30 mile per hour winds, (a -5 degree wind chill). How do we manage cattle during these extremes, and what impact does the big temperature shift have on animal requirements?
Cattle with a heavy winter hair coat certainly have the ability to withstand very cold temperatures. However, as the coldness, or wind chill, decreases, the amount of energy cattle use just to maintain normal body temperature goes up. Most information suggests that the lower end of a cow’s comfort zone is 10 degrees F. to 20 degrees F. This means that as long as the wind chill is above 20 degrees, the cow, heifer, feedlot steer, yearling, etc. is not using any additional energy to stay warm. Once the animal drops below 20 degrees F., their energy requirements go up.
The rule of thumb is, for every 1 degree below 20 degrees, the cow’s energy requirements increase by 1 percent. This means that on a day when wind chill is -5 degrees, the cow’s requirements have gone up approximately 25 percent. In feed terms, this roughly translates to up to 10 pounds of prairie hay to meet that additional requirement.
Just to illustrate the effect of cold weather, I took this week’s temperature swing, from calm and 45 degrees on Monday to 15 degrees with a 30 mile per hour wind on Wednesday. I also used three different cattle types, or situations, to illustrate the effect. The three scenarios include: a 1,300-pound cow in late pregnancy (to simulate current conditions); the same cow with a one-month-old calf to illustrate the same temperature effect in April; and a 550-pound stocker steer being wintered on pasture.
In the two cow examples, the sudden shift in weather resulted in a 6.5 pound increase in their TDN requirement (see Table 1). This translates to approximately 10 pounds of additional prairie hay if we chose to try and meet that additional requirement. Hopefully these cold, windy days are rare and very temporary.
These numbers also illustrate the positive impact that wind protection can have on the herd. The same table could be used to show that proper wind protection can potentially save that same 10 pounds of hay per head on cold blustery days. This is increasingly important given current feed and hay prices.
Probably the biggest impact of cold, windy weather is on stocker calves. Because of their smaller size and reduced feed capacity, a stocker calf’s requirement can almost double during cold weather. Often we are unable to feed enough supplemental hay to meet this increased requirement. Comparing the additional feed required for all three situations to actual body size of the animal, the additional hay required for stocker steers and heifers would be approximately 1.68 percent of their body weight, a considerable amount of roughage for a growing animal. While mature beef cows are often able to increase their forage intake to compensate for cold weather, this example illustrates that increased forage intake often won’t meet the additional cold weather requirements of growing steers and heifers.
We tend to manage or maintain weaned calves in tougher environments, such as pastures that are less protected and further away from the calving grounds. Because these are growing calves, they will often rebound from these cold periods and cold winters by improved gains during the spring. A little “tough love” is probably acceptable as long as heifers grow normally and reach puberty prior to breeding season. However, delaying the growth curve of replacement heifers also increases the risk associated with having the heifer crop cycling and ready for breeding season.
Cold weather can also impact the future calf crop, affecting calving success, colostrum intake and proper immune transfer to the calf. Cold weather is unavoidable, but wind protection, proper planning and a sound nutrition program all help to reduce the impacts of weather on the herd.
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