Winter Environment and Nutrition

By: Rory Lewandowski, Extension Educator, Athens County, Buckeye Hills EERA

Cold temperatures, wind chill, snow, freezing rain, and mud are all terms that come up at some point in describing our winter weather here in Ohio. The cattleman needs to pay attention to the terms because they play a role in determining the nutrient requirement of cattle. Specifically these conditions increase the energy requirement of cattle, can reduce the efficiency of utilization of dietary energy, can decrease voluntary intake, and can change cattle behavior.

As temperature falls below a critical level, the cow must increase energy intake to maintain body temperature and basic body maintenance functions. Cattle have a comfort zone of 59 to 77 degrees F. that is considered optimum for body maintenance, animal performance and health. At temperatures lower than the comfort zone, that is, below 59 degrees F, the animal can make use of a thickening hair coat and heat from normal tissue metabolism and rumen fermentation to conserve body heat without any increase in energy intake requirements. This is known as the thermoneutral zone. The lower boundary of this zone is referred to as the lower critical temperature (LCT). Below the LCT, animal metabolism must increase to provide adequate heat to maintain body temperature. This can be accomplished through increased energy intake. The general rule of thumb is that energy intake must increase by 1% for each degree of cold below the LCT. The LCT is usually described by the coat description of cattle as in the following table:

Lower Critical Temperatures for Beef Cattle

Coat Description	Degrees F
Summer (or wet)	59
Fall	45
Winter	32
Heavy Winter	18

Note that once the coat is wet, regardless of how heavy it is, the lower critical temperature increases to 59 degrees F. Dry, cold weather is easier on cattle than cool wet weather. Wind speed produces wind chill and can further increase energy requirements for cattle when those values are below the LCT. The following chart provides wind chill values at various wind speeds when combined with a range of ambient temperatures:

	Temp., Degrees F
Wind, mph	0	5	10	15	20
0	0	5	10	15	20
5	-6	-1	3	8	13
10	-11	-6	-1	3	8
15	-15	-10	-5	0	4
20	-20	-15	-10	-5	0
25	-27	-22	-17	-12	-7
30	-36	-31	-26	-21	-16

At this point, let's take a look at some examples of how winter temperatures can affect energy requirements. Consider a 1200 lb cow in late gestation with a 10 degree air temperature and a 10 mph wind on a dry day. The cow has a moderately heavy winter coat, providing a LCT of 20 degrees F. The wind chill value is -1 degrees F. According to NRC nutrient requirement tables, this cow requires a TDN concentration of about 56% in her diet or 13 lbs of TDN per day within the thermoneutral zone. Providing a 56% TDN hay with an intake between 1.9 to 2.0 percent of the body weight in dry matter will meet this energy requirement in terms of pounds of TDN required. The -1 degree wind chill temperature is 21 degrees below the LCT of the thermoneutral zone. Following our general thumb rule, energy intake must increase by 21%. This cow must consume an additional 2.6 lbs of TDN (15.6 lbs total) to maintain body temperature. This additional energy requirement can be met in two ways. Either the intake of the current feedstuff must increase so more total energy is consumed, or a feedstuff with a higher nutrient density can be provided.

Hay with a TDN value of 56% is low quality forage. To get an intake of 15.6 lbs of TDN from this forage the cow will need to consume this hay at about 2.4% of her body weight. Is this realistic? If total dry matter intake is to remain at about the same number of pounds, the energy concentration of her diet must increase to a TDN level of about 66.5%. Another way of meeting this need is to add about 2.5 lbs of shelled corn with a TDN value of 88% to the ration. This, along with a hay intake of about 2% of body weight of the 56% TDN hay, will provide the added energy that is needed.

Now, what happens if the air temperature is 35 degrees F with a freezing rain and no wind? The insulating ability of the coat is lost because of the rain and the CLT is 59 degrees F. The cow requires a 24% increase in energy intake to maintain body temperature. As in the first example, this additional energy requirement will have to be met through either an increased intake of whatever feedstuff is being provided or through the addition of some higher energy density feedstuff, such as shelled corn.

In real life, practical terms there are very few beef farmers that are constantly monitoring the weather, thinking about lower critical temperature and adjusting the ration for daily weather fluctuations. Those increased energy requirements that adverse winter weather brings are handled in a number of ways including: providing forage that has more than the minimum required nutrient density. This forage could be stockpiled grass, hay, or a combination of the two. The key is that it is more than just the minimum nutrient density. In a free-choice situation, the cow is likely consuming more than the minimum pounds needed to meet nutrient needs. The cow is able to self-regulate to some extent, her nutrient needs with regard to weather conditions. Cows in a pasture situation may also change their behavior instead of changing intake. For example, they may seek shelter on the side of a wind break to avoid the full effect of a wind chill.

In the event of a predicted longer-term adverse winter weather condition, for example, a week or longer spell of temperatures in the 5 to 10 degree range, the cattleman may want to provide some higher energy in the ration. This is most important when low quality forages are being provided, because the nutrient density is low and they provide limited potential for increased intake. This is another example of why the cattleman should use forage testing to know the nutrient level of hay that is being fed.

A final winter condition that beef cattle managers must be aware of is mud. As in the case with rain, mud reduces the insulating ability of the hair coat, leading to a need for increased energy. In addition, there is research that suggests that mud may decrease feed intake in the 15% and up to 30% range. In an Oklahoma Panhandle Research and Extension Center beef cattle research update from January of 2007, there is a table that lists mud at 4-8 inches deep as decreasing intake by 15% and mud at 12-24 inches deep decreasing intake by 30%. Thus the worst situation for cattle is cold stress combined with mud.

Winter provides challenges for both the beef cow and the cattle manager. Understanding the effects of winter weather conditions upon cattle nutrient requirements combined with the knowledge of the nutrient content of the feedstuffs being provided to the cow herd can help the manager to better care for the cows, and maintain potential profitability.