Considerations for adjusting TMR feeding for cold weather

Published on Thu, 01/25/2018 - 3:26pm

Considerations for adjusting TMR feeding for cold weather

Dr. Alan S. Vaage Ph.D.

When cattle are fed quality forages or mixed rations free-choice, changes in nutritional requirements associated with stage of production or weather are generally compensated for by the animal through a change in intake.  When a TMR ration is fed, intake is normally adjusted by the feeder; this includes needing to adjust feed delivery for changes in weather, such as cold exposure.  However, ration adjustments can also be required where poorer quality forages are fed, as intake may be limited by the digestibility of the feed (e.g. when feeding straw or stubble).

Lower Critical Temperature:  There exists a lower critical temperature (LCT) for each animal, below which it must actively generate metabolic heat, at a nutritional energy cost, to maintain its normal body temperature, if it can.
The USDA Cooperative Extension Program defines such a “cold stress” as follows:
“Cold stress (lower critical temperature) occurs when an animal is exposed to weather conditions that put it below its lower critical temperature. To maintain core body temperature when it is cold, cattle shiver to maintain body temperature, and that requires energy. For cattle with a normal winter coat that is dry, the lower critical temperature is 32°F [0°C]. If the coat is extra heavy, it drops to 18°F [-8°C]. If the normal coat is wet, however, the lower critical temperature may become 60°F [16°C].”
The LCT and point where cold stress occurs is mainly a function of feed intake and efficiency of use through digestion and metabolism which produce heat that keeps the animal warm. When this heat production is insufficient to balance heat loss associated with cold weather and coat condition, cold stress occurs and increased energy intake is required to stay warm and maintain production.
Effects of cold on animal performance: Some older Canadian research showed that exposing calves to cold (-17oC and -28oC) increased maintenance energy requirements by 39 to 43 %, respectively.  Other research, demonstrated that Saskatchewan feedlot cattle in December had growth rates, feed intake and feed:gain ratios that were 70, 140 and 149%, respectively of those during March and April.

More recent research has shown that switching the time of feeding from the morning to the afternoon can be used to improve the growth performance and/or feed efficiency in growing feedlot cattle during cold weather (daily average temperatures <-10oC).  It is believed the change in intake behavior that occurs, especially with limit fed cattle, moves the peak in heat production associated with feed intake and subsequent digestion to the colder part of the day, the nighttime and early morning, effectively lowering the animals’ LCT.   Interestingly, comparable data does not appear to be available for beef cows, but similar results might be expected.
Adjusting TMR feeding for cold weather: While it is easy to understand how cattle can undergo cold stress, as well as its effect on animal performance, it is often harder to know when feeding adjustments are required to prevent reductions in animal performance.  Once you see visible signs of cold stress such as crowding together, shivering, and difficulty walking with backs hunkered to conserve heat, much performance has already been lost.
Feedlot cattle: Animals that are being fed to appetite in a feedlot will simply increase intake during cold stress, and such changes in intake will usually become part of the normal adjustment in feed calls over time. Special attention may be needed, however, if there are abrupt changes in temperature, or the animals are being limit fed for a specific rate of gain.
The attached table shows the proportion of dietary intake that is used for maintenance, versus body weight gain, for animals of differing shrunk body weights, Note that the proportion of the diet used for maintenance decreases as rate of gain increases (combined effect of dilution of maintenance and increasing ration energy density), but not with body weight. Using this table, an appropriate cold stress adjustment can be calculated as follows:
DMIadj = DMI + (DMI x PIM x Tcs x 0.009)
Where:  DMIadj = cold stress adjusted dry matter intake;  DMI = current dry matter intake;  PIM= proportion of intake used for maintenance (from Table);  Tcs = number of degrees Celsius of cold stress;  and 0.009 represents 0.9% increase in maintenance requirement per degree Celsius of cold stress.
For example, for 300 kg calves normally requiring 10 kg DMI to achieve 1.5 kg body weight gain, at -20oC (10oC cold stress) they would require 10.35 kg DMI (i.e. 10 + (10 x 0.386 x 10 x 0.009)), i.e. an extra 0.35 kg DMI per day, to maintain their growth performance (38.6% of daily intake used for maintenance, 61.4% for gain).
Beef cows: For beef cows in mid gestation after weaning (i.e. dry cows), 90-95% of their daily intake is used for maintenance, with the remainder used for fetal development.  During late gestation and calving, 60-70% of daily intake is used for maintenance, while the remainder is used for either fetal growth or milk production.
Thus, as temperatures drop below -10oC:  for dry cows, feed allocation should increase about 8-9 % for every ten degrees of cold stress to prevent body weight loss or reduced body weight recovery; while for late gestation and calving cows, feed allocation should increase 5-7% to prevent decreased milk production and impaired calf growth and associated health problems. This assumes all nutritional requirements were otherwise being met before the advent of the cold stress.
Cold weather below the lower critical temperature of beef cattle will impair performance unless adjustments are made, either in the amount of ration being fed, or even to the ration being fed if forage quality is low. Feeding with a vertical TMR mixer allows one to know what cattle are eating at a given time and to easily make the necessary adjustments when required, such as during cold stress… ”Because Nutrition Matters™”.

Dr. Alan Vaage is a Ruminant Nutritionist with over 30 years of experience in the beef industry, and currently provides technical support for Jaylor Fabricating Inc., Orton, Ontario.  Dr. Vaage can be contacted by email: nutrition@jaylor.com