Cold Stress in Cows
Table of Contents
When temperatures start to decline in winter, particularly as we get closer to 0°C (or 32°F), it is time to think about what effect this is having on cow productivity and efficiency.
Like all mammals, cows are warm blooded and need to maintain a constant core body temperature. Normal rectal temperature for a cow is around 38°C (101°F).
Within a range of environmental temperatures called the thermoneutral zone, animals do not have to expend any extra energy to maintain their body temperature. At the lower end of this range, normal metabolic processes supply enough heat to maintain body core temperature. Within their thermoneutral zone, animals may modify their behaviour, such as seeking shelter from wind, and respond over the long term by growing a thick hair coat for winter, without affecting their nutrient requirements. However, below the lower limit of the thermoneutral zone, in the lower critical temperature, the animal experiences cold stress. To combat cold stress, the animal must increase its metabolic rate to supply more body heat. This increases dietary requirements, particularly for energy. Typical lower critical temperatures for beef cattle are affected by a number of factors. Table 1, below, shows the impact that different hair coat types can have on lower critical temperature.
Table 1. Lower Critical temperatures for Beef Cattle, Assuming No Wind Chill
Cattle, like humans, actually experience the effective temperature, which takes into account both air temperature and the effect of wind chill. Cool or cold wind passing over an animal draws heat away from it much more quickly than still air at the same temperature. Wind chill effects for cattle are shown in Table 2, below. These figures assume a dry, clean hair coat. If the animal is wet and/or dirty, consider the data to be an underestimation of the effect of the wind.
Table 2. Wind Chill Effects for Cattle with Winter Coats (values are effective environmental temperatures)1 2
1 Assumes that hair coat is dry and clean.
2 For example, when air temperature is 18°C and wind speed is 24 kph, the effective temperature experienced by the animal is the equivalent of a still air temperature of 26°C.
If cows are exposed to wind or drafts, it is important to adjust for the effective temperature and take the appropriate steps to ensure that the cows can maintain body temperature and weight.
Hypothermia occurs when the body temperature drops well below normal. In general terms, with cattle, mild hypothermia occurs with a body temperature of 30°C32°C, (86°F89°F), moderate hypothermia at 22°F29°C, (71°F85°F) and severe hypothermia below 20°C (68°F). As rectal temperature drops below 28°C (82°F), cows are not able to return to normal temperature without assistance through warming and the administration of warm fluids. As hypothermia progresses, metabolic and physiological processes slow down, and blood is diverted from the extremities to protect the vital organs. Teats, ears and testes are prone to frostbite. In extremes, respiration and heart rate drop, animals lose consciousness and die.
In most situations, a more insidious and costly problem occurs. Cows are subjected to an environmental temperature below the lower critical temperature, but without obvious signs of hypothermia. This increases the maintenance energy requirement of these animals as they adjust to the conditions and divert more energy to maintaining body temperature. There are two potential responses to this situation.
1. Cows have access to higher quality feed and/or increased intake, and therefore maintain their body weight.
Cows try to increase feed intake in an effort to meet their energy requirements. Given the opportunity and gut capacity, cows will eat more feed to help meet their increased energy demands. Practically, it is usually expedient to feed grain as well. This increases feed costs, increasing the cost of keeping cows, however the expectation is that cows will maintain their body weight!
It is generally accepted that for every 1°C drop below the lower critical temperature, there is an approximately 2% increase in energy requirements. The amounts of additional feed required for a cow under cold stress can be calculated, but as a rule of thumb, a cow with a dry winter coat should be fed the additional feed as presented in Table 3, below.
Table 3. Effective Temperature and the Additional Feed Required to Meet the cow's Energy Requirements
2. Cows dont have increased feed quality and intake and lose body weight.
If cows are not fed additional feed or the quality does not allow them to eat enough to meet their additional energy requirements, body mass will be burned to produce metabolic heat. These cows lose weight as both feed energy and stored fat are diverted to maintain body temperature and vital functions. Cows in this situation that start to lose weight soon enter a downward spiral the more weight (fat) they lose, the less insulation they have, the more susceptible they are to further cold stress, and they lose weight even faster.
Cows, and especially heifers that lose weight, calve in poor condition. The consequences are increased calving difficulties, an increase in the number of lighter, weak calves and higher calf mortality. These dams produce a reduced amount of colostrum (of lower quality) and have lower milk production, increased neonatal mortality and reduced growth rate in surviving calves. These cows usually have delayed return to estrus, longer days open and poorer reproductive success.
We cant control the weather but we can do everything reasonably possible to reduce the effects of cold on cows. This will help reduce costs and improve production efficiency.
This Factsheet was authored by Brian Tarr, Ruminant Nutritionist, Shur Gain, and reviewed by Craig Richardson, Animal Care Specialist, OMAFRA, Kemptville, and Christoph Wand, Beef, Sheep and Goat Nutritionist, OMAFRA, Woodstock.
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