Winter Calf Management Tips for Mitigating Illness
Although in our region we are not typically subjected to the brutally cold winters that are characteristic of the Upper Midwest, we are challenged by temperatures that fluctuate dramatically throughout the winter months. It is not uncommon for us to see temperature swings of 30 or 40°F on a given day, making management of pre-weaned calves difficult. However, reinforcing some basic housing and management concepts can help producers mitigate risks of calf illness throughout the winter.
Concept of Thermal Stress
Thermal stress occurs when animals are exposed to temperatures outside of their thermoneutral zone. The thermoneutral zone is the temperature range between which animals do not have to expend additional energy to maintain their body temperature. This temperature range varies depending on an animals’ size, age, and physiological state. Lactating cows are often the focus when it comes to the topic of heat stress because their thermoneutral zone is lower than that of other animals on the farm and thus, are more sensitive to higher temperatures. In contrast, young calves are more sensitive to cold temperatures because they have a higher thermoneutral zone. This is due to their high surface area to volume ratio, which reduces their capacity to retain body heat, and their lack a functioning rumen, which reduces their heat production capacity via digestion and fermentation. For these reasons, calves under 3 weeks of age begin to require additional energy to maintain body temperature when temperatures drop below 68°F; for calves over 3 weeks of age, this temperature threshold is closer to 50°F.
...deep straw bedding has been shown to reduce cold stress in calves and improve daily gains when temperatures are below 50°F.
Pre-weaned calves experience cold stress at temps below 68-50°F
For calf barns, ensure 4 total air exchanges per hour without producing a draft
Deep-bedded straw is superior to sawdust
Increased energy consumption can be accomplished by:
Increasing daily milk or milk replacer consumption
Increasing energy density of milk replacer
Good ventilation is critical for calf health, particularly with regard to respiratory disease management. Without adequate ventilation, pathogens and harmful gases, such as ammonia, can linger near the calf and lead to health problems. While adequate ventilation is important for calves in all types of housing, calf barns are usually the focal point for ventilation discussions because it is one of the biggest challenges for that type of housing system.
A good ventilation system will provide fresh air to remove excessive heat, moisture, dust, pathogens, and volatilized gases without creating a draft. This can be a tall order, particularly for retro-fitted or repurposed calf barns. According to University of Wisconsin Veterinary School, natural ventilation is often insufficient for calf barns, especially on days when there is minimal wind. In such cases, properly designed positive pressure ventilation systems can help bring fresh air into the barn without creating a draft on the calf. During cold weather (<50°F), a full barn air exchange every 15 minutes can provide sufficient ventilation for young calves. However, it is important to ensure that wind speed at the calf-level does not exceed 50 feet per minute when temperatures are less than 50°F.
As always, bedding should be kept clean and dry. However, closer attention to bedding during the winter is needed because wet, dirty bedding can promote pathogen growth and increase cold stress. A wet hair coat substantially increases energy requirements for maintaining body temperature during cold weather. Assessment of bedding dryness can be accomplished by conducting the “kneeling test” in the calf pen. If your knees are damp upon standing, the bedding is too wet.
Bedding material is also important. Although sawdust is a good choice for bedding material due to its ability to absorb moisture, using it alone during the winter is not recommended. Relative to sawdust, deep straw bedding has been shown to reduce cold stress in calves and improve daily gains when temperatures are below 50°F. Unlike sawdust, straw or hay can help mitigate cold stress during the winter by allowing calves to “nest”, which helps to create a surrounding layer of warm air. The University of Wisconsin Veterinary School has developed a “nesting” score system to help producers evaluate bedding depth by examining the visibility of the rear leg when calves are laying down: a score of 1 indicates that the leg is completely visible; a score of 2 indicates that the leg is partially visible; and a score of 3 indicates that the leg is completely concealed by bedding. During the winter, producers should aim for a score of 3.
Many producers elect to utilize calf jackets during the winter months. These can be helpful, especially during situations when nesting score is inadequate. According the University of Wisconsin Veterinary School, putting a jacket on a calf with a bedding nesting score of 2 can provide cold stress reduction equivalent to that of a nesting score of 3. However, a calf jacket cannot substitute for a nesting score of 1, wet and/or dirty bedding, or poor ventilation.
When temperatures drop below a calf’s thermoneutral zone, energy requirements increase. This increase is directly related to the amount of additional energy (i.e., calories) required by the calf to maintain its body temperature. Without increasing energy consumption, growth rate will suffer. This is why taking steps to reduce temperature stress on the calf, through means of good bedding management and ventilation, is so important. These measures can help mitigate the amount of additional nutrition a calf requires during the winter in order to maintain performance.
It may sometimes be necessary to increase the energy intake of calves during the winter. This can be accomplished by: 1) increasing the amount of milk or milk replacer fed at each feeding; 2) increasing the energy content of the milk replacer by increasing the fat content; or 3) adding an additional milk or milk replacer feeding. Regardless of the approach, keep in mind that the goal is to increase energy consumption in order to compensate for the increased energy requirements resulting from cold stress so that calves can remain healthy and continue to grow at an acceptable rate.
Newborn calves are especially vulnerable to cold stress because they have very little body fat stores. Ensuring that cows calve in clean, dry areas that are sheltered from wind is important for preventing cold stress in newborn calves. Drying calves as quickly as possible after birth is also important. In some situations when calves are born in very cold temperatures and/or are exposed to wind, mud, precipitation, etc., it can be beneficial to place calves in a warming box, warm room, or something similar, for a few hours until they are dry and active. It is also critical to ensure sure that calves receive at least 3-4 liters of high quality (>50 IgG or 22% Brix) colostrum within 4 hours of birth. Not only does colostrum contain antibodies for immune system development, but it also includes high levels of fat, protein, and growth factors that jumpstart the calf’s metabolism.
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