August 2, 2023
By Jerad Jaborek, Michigan State University Extension
Cattle are often viewed as hardy creatures because they spend their lives outdoors exposed to a vast range of temperatures and environmental conditions. In the Upper Midwest, we get to experience the extremes on both ends of the temperature spectrum, from extremely cold and wet winters to extremely hot and humid summers. Cattle facilities vary in design and amenities, particularly by location, regarding the protection and comfort provided to the animal from these environmental elements. In the Upper Midwest region, it is probably fair to say a greater number of cattle producers have a structure of some form to provide cattle with an escape or protection from the sun, wind or precipitation.
The thermoneutral zone is where cattle do not have to expend extra energy to maintain their regular body temperature. Factors such as hair coat thickness, hide color, degree of fatness and cleanliness, along with environmental factors such as being wet, relative humidity, or exposure to the wind can change the range of temperatures representing the thermoneutral zone of cattle.
With the idea of cattle producers having some protection to mitigate environmental stressors, let’s focus for a moment more specifically on heat stress. Producers must consider amenities such as shade structures to escape from the sun, air flow that can be created naturally or artificially with fans and the possible use of sprinklers to allow for evaporative cooling. Some of these options may be limited due to facility design and energy or resource cost. However, different nutritional management decisions can be used as cost effective strategies to help mitigate heat stress for cattle.
Cattle produce a metabolic heat load from tissue metabolism and homeostasis, activity and fermentation of feed in the digestive tract. Cattle dissipate heat to their surroundings through conduction, convection and radiation when the ambient temperature is less than that of their skin. If the temperature is higher than their normal skin temperature, cattle lose heat in less effective ways, by evaporation via the skin or respiration via panting. The total heat load experienced by cattle is the combination of metabolic heat produced and absorption of heat from the environment. If cattle are unable to dissipate the excessive heat load experienced, hyperthermia can occur, and cattle health will suffer.
Cattle nutrition can be managed in a way that has the potential to change the metabolic heat produced by the animal. Energy intake and different feedstuffs (i.e., grain, forage, fat) can have differing effects on cattle performance and physiological responsiveness to elevated temperatures and excessive heat loads.
In a research study conducted by Mader and others, published in The Professional Animal Scientist journal, performance of cattle exposed to an excessive heat load versus thermoneutral conditions was recorded. Hereford steers were fed either:
ad libitum (free-choice) of a grain-based diet containing 6% forage (high energy; HE), the same grain-based diet with 6% forage at 90%
ad libitum (restricted energy; RE), or
ad libitum of a grain-based diet containing 28% forage (high forage; HF)
All cattle were housed in a climate-controlled facility to induce either thermoneutral or excessive heat load conditions. Under thermoneutral conditions, steers fed the HE and HF diets had a greater feed intake compared with steers that were fed the RE diet. This resulted in a greater energy intake for steers fed the HE diet compared with steers fed the RE and HF diets. However, under hot conditions where steers experienced an excessive heat load, steers fed the RE diet maintained their feed and energy intake (-4.6%), while steers fed the HE diet decreased 15% and the HF diet decreased 18%. Steers fed the RE and HF diets also drank the greatest amount of water, which can have beneficial cooling effects. Steers fed the HE diet had greater respiratory rates, body temperatures and signs of greater heat stress, compared with steers fed RE and HF diets. These experimental results demonstrated that limit-feeding can be used as a strategy to mitigate heat stress in cattle.
Additionally, forage inclusion in the diet can help reduce body temperatures as well, even though forages have a higher heat increment during digestion compared with grains and fat. During the 17-day transition period to a finishing diet, steers were transitioned from a diet containing 55% forage to 40%, to 25%, and finally 10%, with diet changes occurring after 5, 5 and 7 days. Relative to steers raised under thermoneutral conditions, steers exposed to an excessive heat load had elevated body temperatures and a reduced feed and energy intake after being switched to the 10% forage diet. Decreasing feed and energy intake is a common coping mechanism for cattle when they experience an excessive heat load. In this particular case, the cattle were not able to dissipate the excessive heat load because there was no night-time cooling period. The greater inclusion of forage as opposed to grain reduces the energy intake, possibly in part due to gut fill, by the animal and inherent heat production contributing to the excessive heat load experienced by cattle in hot environmental conditions.
Another heat mitigation strategy may be to increase the percentage of fat within the diet when cattle are exposed to extreme heat. Huffman and others investigated the effects of fat and forage inclusion in finishing diets for cattle in a Journal of Animal Science publication. Crossbred yearling steers and heifers were fed one of four diets with either 0% or 4% added fat in combination with 0% or 7.5% forage during the summer feeding period. Total diet fat concentrations were about 5.5 to 6.0% and 9.0 to 9.5% fat for the 0% and 4% added fat diets, respectively. Regarding forage inclusion concentration, cattle with 7.5% forage had a greater feed intake, greater rate of gain and similar feed efficiency compared with cattle consuming the 0% forage diet. Cattle consuming the diet with 4% added fat had a similar feed intake but increased average daily gain (4.3%) and improved feed efficiency (9.7%) compared with cattle fed the diet with no added fat. Fat has a lower heat increment during fermentation and is also very energy dense (2X) relative to carbohydrates provided by grains and forages.
As cattle feeders and nutritionists, we need to be aware that the microbes responsible for rumen fermentation can be negatively impacted when dietary fat concentrations get greater than 8 to 10%. Gaughan and others fed Murray Grey × Hereford steers in a climate-controlled facility to induce heat stress and measure the effects of supplemental dietary fat (+5%) and the timing of cooling strategies (morning or evening with sprinklers and fans) on the response of cattle. Steers that were day-cooled experienced greater heat stress compared with evening cooled cattle. Fat supplementation increased feed intake for heat stressed steers that were day cooled, there was no difference for feed intake of evening cooled steers. Fat supplementation did not impact respiratory rate or body temperature, but evening cooling was beneficial compared with day cooling. The data indicated that cooling strategies, such as the use of sprinklers and fans, were far more effective than fat supplementation for managing heat stress in feedlot cattle.
Another study conducted by Mader and others, published in the Journal of Animal Science, aimed to confirm the positive benefits of limit-feeding on elevating heat stress and investigate different durations of limit-feeding during the finishing period. Crossbred steers were fed a corn-based finishing diet either at ad libitum for 63 days, 75% of ad libitum for 21 days followed by ad libitum feeding for the remaining 42 days, or 75% of ad libitum for 42 days followed by ad libitum feeding for the remaining 21 days. Over the course of the 63-day feeding period the average THI was 71 but ranged from 64 to 79. By design, the limit-fed groups had a lesser feed intake compared with steers offered feed ad libitum. Interestingly, this pattern was persistent even after limit-fed steers were switched to ad libitum feeding after either 21 or 42 days and compensatory feed intake was not observed. Restricting feed intake reduced body temperature 0.4 degrees Fahrenheit to 0.7 degrees F compared with steers offered feed ad libitum. Unfortunately, a carry-over effect of reduced body temperatures for the 21-day restricted feeding group was not maintained after being switched to ad libitum feeding during the following 21-days. Steers with restricted feed intakes began to reduce their body temperatures around 5 p.m. and had lower body temperatures until feeding the next morning at 6 a.m., whereas the decline in body temperature for steers fed ad libitum didn’t occur until 2 to 4 hours later than restricted fed steers. Therefore, restricted fed steers experienced heat stress for a shorter period of time relative to steers fed ad libitum.
Published in the Journal of Animal Science, Mader and Davis investigated the effect of feeding time on the ability of Angus × Charolais crossbred steers to cope with heat stress during the summer. Steers were either fed a corn-based finishing diet ad libitum at 8 a.m.; ADL), fed the same diet at 4 p.m. at an amount where all feed was consumed by 8 a.m. the next day (SLK), or steers were limit-fed 85% of ad libitum at 4 p.m. (LIM). These feeding treatments were imposed for the first 23 days of an 83-day feeding period, then all steers were fed ad libitum for the remaining 59 days of the feeding period. No differences were found for body weight gain, feed intake or feed efficiency during the first 23 days when the treatments were imposed. However, SLK steers consumed the same amount of feed compared with ADL steers even though the time feed was made available in the bunk was less (16 hours vs. 24 hours). Limit-fed cattle had a lesser feed intake by design and experienced compensatory performance during the remaining 59-days of the feeding period, where they had a greater average daily weight gain (14%), average daily feed intake (5.7%), and a 6.5% improvement in feed conversion.
In contrast to the findings by Mader and Davis in the previously mentioned study, a Kansas Research Report by Reinhardt and Brandt found that evening feeding at 8 p.m. versus morning feeding at 8 a.m. of limit-fed Holstein steers improved rate of body weight gain and feed efficiency. Differences between the two research studies may be due to the extent of feed restriction imposed on cattle. Feeding cattle in the morning may add the heat load of peak fermentation with the peak heat exposure during the day, while evening feeding would allow peak fermentation to take place once cattle are past the hottest part of the day and beginning to lower their body temperature. However, when night-time cooling is limited evening feeding may not be beneficial at alleviating the excessive heat load experienced by cattle.
The USDA Agricultural Research Service and National Oceanic and Atmospheric Administration (NOAA) National Weather Service have partnered to provide a 7-day forecast map. The color-coordinated map identifies areas of the U.S. where cattle are at risk of experiencing heat stress based on the predicted environmental conditions. Use this tool to help plan ahead for the following week’s feed deliveries.
Overall, limit-feeding cattle may be an effective approach to help feedlot cattle manage heat stress throughout the summer. This is a feeding management practice that could be implemented in early summer to allow cattle time to adapt to the heat. It could also be implemented ahead of forecasts for extremely hot and humid weather. Consider double-checking the fat concentration in your feedlot diet as well. With many producers feeding distillers grains, fat concentrations may already be close to the 8 to 10% recommended maximum. However, if your finishing diet fat concentration is less, around 2 to 4%, you may consider adding some supplemental fat to increase the energy content and reduce the heat increment of the diet. Remember to always keep clean fresh water available for cattle. Other cooling methods, such as fans and sprinklers, can be very effective at helping to cool cattle down, particularly in the evening.
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