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The cold weather has finally reached us. These arctic blasts can cause problems for livestock operations ranging from frozen waterers to sick cattle. In these situations, hindsight is often 20/20 due to lack of preparation. I encourage folks to jot down the “little things” in these instances that could be prepared for during the warmer days of fall leading up to winter. The key is to remember to dig these notes out in the fall and start the preparation before the cold hits. The lower critical temperature (LCT) value for cattle is the adjusted ambient temperature or wind chill temperature at which no additional energy for heat production is required to maintain core body temperature. As the temperature declines below this lower critical value, the maintenance energy value for 4 the animal is increased to maintain core body temperature. Core body temperature is maintained by increasing metabolism resulting in greater heat production as well as other heat conservation strategies such as reducing blood flow to the extremities, shivering, and increased intake. Cold stress results in approximately a 1 percent increase in the maintenance energy requirement for each Celsius degree or two degrees Fahrenheit below the LCT. For instance, if the net energy for maintenance (NEm) for a late gestating beef cow is 12 mcal of NEm with no cold stress, a cow experiencing temperatures 10 degrees Fahrenheit below the LCT would require approximately 5 percentmore energy or another 0.6 mcal of NEm. If one was feeding decent grass hay that contained 49 mcal NEm/cwt, this cow would require an additional 1.25 lb of hay or about a 5 percent increase in hay intake to offset her energy need from the colder temperatures. Lower critical temperature value can be influenced by several factors. Both external and internal insulation influences the LCT. External insulation is basically the depth and thickness of the hair coat, condition of the hair coat and thickness of the hide. Thin hided breeds such as dairy breeds tend to have a lower insulating factor than thick hided breeds like Herefords. The condition of the hair coat is extremely important as an external insulation barrier. The hair coat acts as insulation similar to insulation we put in our attics as it traps air enhancing the insulating value. If the hair is wet and full of mud, air is excluded reducing the insulating value and increasing heat loss from the skin to the environment. Below the impact of hair condition is shown with respect to modeling cold stress on cattle. Note that the density of the hair coat and if it is wet or dry impacts the wind chill temperatures at which cold stress is considered mild, moderate or severe. The impact of rain used in the above model is such that if a 0.10 inch of rain was received within the last hour of the time of interest, the wet hair condition is used. For example, if the actual temperature was 40 F and it was raining, the cattle would be considered to be experiencing moderate cold stress. Acclimation time, hide thickness, fat cover and other factors will influence the degree of cold stress experienced and these values are simply baseline figures.
Ambient temperatures can impact dry matter intake of cattle providing an opportunity to compensate for increased maintenance energy needs. The intake adjustment factors suggested by the recent Beef NRC are shown below. These are expected adjustments which may or may not occur depending upon other factors such as feed quality, bunk space, lot conditions, and others. This can be important when limit feeding animals to ensure adequate nutrient intake to compensate for the increased maintenance energy needs during cold stress. One either needs to increase feed intake or increase the energy density of the diet by feeding higher quality hay or adding more grain or fat to the grain mix.
Big deal, right? Looking at the December 2009 Kentucky Mesonet daily average temperature combined with average wind speed for wind chill temperature and average daily precipitation a teachable moment is seen. Taking the straight average temperature and the days when precipitation was 0.10 inch plus, thirty percent of the month of December cows would have been experiencing some degree of cold stress. Taking into account the days with windchill, this is increased to 12 out of 31 days or 39 percent of the month.
Lesson to be learned. Continue to monitor the cows during the winter time and ensure body condition is being maintained. Poor quality hay may not provide adequate energy to maintain gestating cows that are entering the third trimester. Consider having the hay tested to determine if supplementation may be needed during times of possible cold stress, especially for the enduring cold spells. Consider separating younger and thinner cows that may not have the internal insulation as well conditioned older cows and supplement them accordingly or offer them higher quality forage if available. Move cows to fields with natural wind breaks or provide man-made windbreaks which are not the same as a barn. Poorly managed barns combined with poor ventilation may actually hamper efforts of improving the environmental conditions. Lastly, remember it is energy or calories that are really needed. If the protein level in the forage is adequate, do not make supplement purchase decisions based on protein level rather purchase the most affordable calories. Stay warm and keep the waterers flowing.