In a year of high feed prices and colder than average winter weather, produces have been challenged by the decision on how to best meet the nutritional needs of their herds economically. Evaluating cold stress and cow body condition is an important task because it can have a significant impact on cow and calf health.
Cold stress in beef cattle results when environment conditions drive an animal's metabolic rate higher requiring more energy to sustain basic metabolic functions.
A cow's thermoneutral zone is the temperature when an animal does not require, or expend, energy to cool or warm herself while maintaining basic needs. During the winter, a temperature of 18°F is the lowest threshold a cow with a heavy, dry winter coat will be before it is susceptible to cold stress (Table 1). The three main environmental events that cause cold stress in cattle are lot conditions, physical activities, and weather/wind conditions.
Poor loafing and feeding conditions during the winter results in "extra work" for cows. Poor lot conditions, including deep snow, inadequate dry loafing, and mud, will result in poorly insulating, matted, and wet hair coats.
Feed intake will increase and energy needs will increase to meet the animal needs caused by these conditions.
Although often overlooked, a lack of dry feeding areas and dry loafing areas (bedding) can be significant contributions to cold stress. Providing dry feeding and loafing areas will decrease the energy needs (and ultimately your feed bill) because it allows cattle to utilize feed nutrients for basic metabolic demands and fetal development instead of battling cold stress
In addition to lot factors, cow body condition can easily decay when they are simply not receiving their required nutritional needs, especially when feedstuffs are chosen by price and not nutrient value. Even if cows are dry, their metabolic demand increases during extremely cold and windy conditions.
If this energy is not provided during extremely cold conditions, the cow will mobilize body fat and potentially muscle to meet her basic required energy needs. If this happens for an extended period of time, cows consume all body fat, significant amounts of muscle and can die.
In some instances, hungry, cold-stressed cows can become impacted with forages (usually low quality hay) and die. Low quality forages and lack of access to unrestricted water could result in impaction due to reduced rate passage.
Wind and bitterly cold weather play large roles in influencing an animal's energy needs (Table 2). Producers can reduce the effects of wind chill by providing windbreaks for cattle to loaf behind, or, in the best case scenario, to provide a covered shelter, which can drastically reduce the effect of cold stress caused by wind chill.
To help meet nutrient requirements during cold stress, a producer should first know gestating cow requirements and how those requirements change as the weather changes. A beef cow weighing 1400 lbs in second trimester needs 21.0 lbs DM at 10.1 TDN a day at 30°F (Table 3).
For every 2°F the temperature drops 1.1 lbs of TDN increase needed to meet their daily requirements. Greater energy needs may have to be met using supplemental energy source other than hay.
It has been shown that 2.0% of a cow's body weight is the typical DMI of a beef cow, so with the lower quality hay and larger body weight cows will need other sources of energy such as distillers or corn to meet their needs. This is why it is very important that producers know the nutrient requirements of their cattle and to have analyses of their feedstuff inventory.
Additionally, it is important for them to know what alternative energy-containing feeds are available at reasonable prices to ensure that the best supplementing strategy is applied.
Analyzing feedstuffs often is overlooked on many operations; but, for less than $20 a sample you can determine the nutrient profile of your feed. Just a few percent point difference in TDN energy value can make a large difference in what you need to feed to meet the requirements of your herd.
With gestating cows, there is an increase of 1.5 lb DM and 1.8 lb TDN in the last trimester at thermoneutral zone temps that must be accounted for too, especially when calving during the first four months of the year.
Failing to adjust diets to each winter can cause great financial loss to you as a producer from over feeding in unseasonal warm winters. Most importantly, underfeeding during critical cold temperatures can also result in loss of body fat and in extreme situations has been associated with the death of gestating beef cows this winter.