Straight From the Horse's Mouth

Duane A. Lienemann, UNL Extension Educator, Webster County January 2, 2010 Edition Well it is here, the second decade of the millennium year. I am sure it will take awhile to get used to saying or writing “ought 10” on checks, letters, etc., but I guess I will get used to it. I know that I am not really getting used to the cold and the snow. We have been kind of spoiled the last several years with open and relatively warmer winters. With this kind of weather, my mind always gravitates to thinking about how the livestock are faring in this. This kind of weather is really hard on livestock and especially the cows out in stalks. I think it is time to revisit wind chill index and feeding cattle. Critical Temperature and Wind Chill: December thermometers have shown temperatures well below freezing, and winds have created “wind chills” which pushed the effective temperature to below zero marks. It is continuing so far into January and more cold weather is probably on the way, which will create added or continual stress for cattle. Unfortunately I believe that some cattle producers may not aware of the added nutritional needs of cattle that cold weather brings. Or, if they recognize that their cattle are stressed, they aren't sure how, or if, they should compensate for the stress. Cold stress occurs when an animal is exposed to weather conditions that put them below their lower critical temperature. The wind chill index, rather than ambient temperature, is used to estimate effective temperature when considering the severity of cold stress. Wind or moisture makes effective temperature (the temperature felt by the body) lower than the temperature on the thermometer. You must figure the wind chill factor when arriving at amount of degrees below a cow's critical temperature point. How can you determine this? You can find a handy wind chill chart in Excel form at: http://www.cattle-manager.com/downloads/Cattle%20-%20Wind-Chill%20Index.xls or give me a call and I will email it to you. You may also want to check out this site for cattlemen: http://www.ranchweather.com/weather_computer.shtml. It should be noted that temperatures and wind chill charts in figuring cold stress are based on 24 hour average temperatures. Remember to use the temperature as result of wind chill when making your decisions. When conditions result in an effective temperature below the animal's lower critical temperature, the animal must increase the rate of heat production to maintain a constant body temperature. In order to produce more heat, the animal must receive an increase in ENERGY from the ration or “draw” on body stores. Protein, vitamin, and mineral requirements are usually not altered, as long as energy is provided. A cow needs to eat more roughage in cold weather, to give her the calories for heat energy. If she doesn't have enough roughage, the pounds will melt off her as she robs body fat to create energy for warmth. More total pounds of roughage in her diet (extra grass hay, or even straw) can keep her warm, since the fermentation and breakdown of cellulose creates heat energy. She also needs accessible water. Starving your cattle will obviously give you bad results, however, believing that "keeping hay in front of them will take care of the problem", may not be true all the time. If the quality of hay is good (good being hay harvested before it is mature and baled before it is rained on) cattle will probably make it through cold weather in good condition. But if hay quality is not good, the cattle may be in trouble, both short term and long term. Be careful when you talk hay quality. High quality alfalfa hay supplies protein, calcium, vitamin A and other important nutrients, but not enough roughage for heat energy in cold weather. Alfalfa alone is not adequate for cattle in cold temperatures; cows will gobble it up and stand around shivering, losing weight. If a cow is cold, she should be given all the roughage she will clean up. Cows with normal winter hair coats need about one third more feed when exposed to wind chill temperatures at or near zero. A rough rule of thumb to compensate for cold is to increase the amount of feed (energy source) by one percent for each two degrees F of cold stress. For thin cows with poor hair coats, or in wet conditions (wet hair coat) figure a one percent increase for each degree of temperature drop. A wet storm is worse than dry cold. Wet hair loses insulating quality; the cow will chill sooner. Another rule of thumb for beef cattle is that the energy requirement increases 13 percent for each 10-degree drop in temperature below 30 degrees for cattle with moderate body condition and a winter hair coat. Energy requirements increase 30 percent for each 10-degree drop in temperature below 30 degrees when cows are wet, thin or have a thin coat. Basically, an 1100 pound pregnant cow in the pre-calving stage needs about 23 pounds of DM (dry matter) or 12.5 lbs. of TDN (total digestible nutrients) per day when temperatures are above freezing. If the temperature drops 20 degrees below her lower critical temperature, she needs 20 percent more dietary net energy for maintenance (NEm) or 2.4 more lbs. of digestible nutrients. To supply that, you can feed her 5-6 lbs. of hay containing 50 percent TDN extra per day. If the temperature is at +10 F, that 1100 pound cow will need 20% more TDN which amounts to about 3.5-4 lbs/cow/day of extra hay needed or 2-2.5 lbs/cow/day of extra grain. Now if it gets to -10 F, then the cow will need 40% more TDN which amounts to 7-8 lbs/cow/day of extra hay needed or 4-6 lbs/cow/day of extra grain. Cow size has a direct effect on feed requirements, in that a bigger cow needs more pounds of TDN. A 1400 lb cow would need 28 lbs lf DM and 15 lbs of TDN or 20% more feed over and above. I don’t normally like feeding corn as it can mess up their dietary system if they are not used to it, however that is better than not getting energy to them. Your cow will work for you, but you will need to take care of her, especially in this weather, if you expect any returns! The preceding information comes from the research and personal observations of the writer which may or may not reflect the views of UNL or UNL Extension. For more further information on these or other topics contact D. A. Lienemann, UNL Extension Educator for Webster County in Red Cloud, (402) 746-3417 or email to: dlienemann2@unl.edu or go to the website at: http://www.webster.unl.edu/home