Temperature C Extra TDN (lbs) Extra hay (lbs) Extra grain (lbs)
After chores, take a good look at your beef cows on a frigid winter morning, with a cutting northwest wind at your back. Most of them are probably up at the feed-bunk, bale-feeder or grazing forage swaths. All animals are eating more feed than usual. It’s a good thing to see, because they should be eating more of the feed that is put in front of them to keep warm, rather than burning up precious body fat reserves needed for the upcoming calving season. When you get back to the house, it’s a good idea to take time to look over your current rations. Determine if your cows are receiving enough dietary energy or whether a midwinter energy boost to their diets is required.
Most experienced producers know that more dietary energy must be fed to the cowherd, when arctic winds blow. Cows, like humans, feel the same effects of winter stress as measured by “windchill” (re: a combination of temperature and direct wind speed). It’s roughly a measure on how quickly heat energy is drawn away from cows’ body and the amount of energy that needs to be replaced in order to help them stay warm, maintain a critical 38C core body temperature, and keep in the same body condition. When the windchill falls below 0C, the cow is pushed out of her thermal comfort zone, and her energy requirements start to dramatically increase.
University and extension research has come up with a cold weather rule of thumb as follows: for every one degree Celsius drop in temperature below 0C, the beef cows’ TDN energy maintenance requirements are increased by about two per cent. Although, this is only an estimate and is based upon effective air temperatures, producers can also utilize windchill temperatures without adjustments, if the cows herd have little shelter. This means that if our early morning windchill temperature is -25C, there is an increase of about 50 per cent in the cows’ basic dietary energy needs.
Simply, feeding beef cows more of what they are already consuming during coldest weather often does not achieve these new energy requirements. When the thermometer drops, metabolic triggers in the cow stimulates her feed intake, but they will only increase dry matter consumption at the very most by 30 per cent; often limited by physical constraints of the rumen and a reversal in feed digestibility. Since, beef cows can eat only so much feed during very cold weather, it is wise to increase the energy density of their rations by using some high-energy and lower fibre feed ingredients.
This means, rather than feed cold-stressed cows more bulky feed such as more hay or more silage, it is sometimes better to substitute part of these forages with high-energy screening pellets or starch-enriched grains, such as barley or corn. University of Nebraska (2001) researchers found out that cold-stressed feedlot cattle derived more of a performance benefit by increasing the energy density of their ration with grain versus taking advantage of the extra heat increment (given off during rumen forage digestion) by feeding more forage.
Increasing the energy density of the beef cow ration might be as easy and convenient as feeding some grain during the coldest parts of the winter, but it is still more costly than feeding roughages. To help determine when extra grain should be fed instead of extra forage, the following table outlines a sample feeding guide dependent upon the weather conditions that might be used.
For illustration purposes, it is assumed that (1) hay is medium quality (TDN = 50 per cent and cows’ additional DMI stimulated by cold weather is maximized at 30 per cent or pluse-nine pounds of hay, daily); (2) extra grain is heavy barley (TDN = 75 per cent); and (3) late gestation beef cows have a basic TDN requirement of 11 lb./ head/day.
Based on the assumption that hay costs about 3/lb. and grain (barley) costs 6/lb., the cost of feeding a herd of 350 beef cows for one month of -20C temperatures (including windchill) costs approximately an extra $1,000 to feed extra barley instead of feeding extra hay.
Granted, there are a lot of mitigating factors built into this final calculated difference, but one might draw the conclusion to maximize forages such as hay when milder weather opportunities are presented and switch to extra grain only when precious body condition of the beef cows is threatened by very cold weather.
Whether choosing barley or hay, it becomes a matter of maintaining or achieving a Body Condition Score (BCS) of 2.5 to 2.75 (thin = 1, and 5 = obese) by calving time, while replacement heifers should calve out a little better BCS of 3.0. Furthermore, optimum BCS should parallel 150 to 180 lbs. of fetus and fetal membranes weight gain. Cows that successfully can get through the coldest winter months with an optimum BCS at calving have less calving problems, fewer days returning to estrus, and ultimately have higher conception rates. It is always a good idea to periodically review the BCS of the cows, and determine that any re-formulated diets for higher energy intake are working.
Maintaining mid-to late-gestation beef cow body condition is not solely based on increasing their dietary energy consumption. Sometimes, it means keeping them out of the cold in the first place!
For example, if a nine-foot slat windbreak can reduce windchill by only 5C, it saves 10 per cent in potential energy requirements added during cold winter weather. Open-faced pole-barns may also be used to allow beef cows to get out of the cold wind, and feed bunks/ bale feeders should be placed such that cows never have to eat facing into a bitter north-west wind. Similarly, elevated manure packs located away from a windbreak are a very effective means of not only keeping cows clean and dry, but can also generate a significant amount of heat for most of the winter. They should be well-bedded with straw or other insulating bedding, applied every few days.
By implementing these last recommendations in order to reduce energy loss, while at the same time increase their plane of dietary energy in a timely manner, should help gestating beef cows cope with any frigid weather. The payoff of this plan is a herd of healthy cows that come through such a typical western Canadian winter in good body shape should be ready for a successful calving season.
Peter Vitti is an independent livestock nutritionist and consultant based in Winnipeg. To reach him call 204-254-7497 or by email at [email protected]