0601002015

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Heat Stress

BOVINE

Defining Heat Stress.

Temperature Humidity Index (THI)

How heat stress affects beef cattle and effective

support strategies.

Energy

Electrolytes

TempoF 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 10072 64 65 65 65 66 66 67 67 67 68 68 69 69 69 70 70 70 71 71 72 7273 65 65 66 66 66 67 67 68 68 68 69 69 70 70 71 71 71 72 72 73 7374 65 66 66 67 67 67 68 68 69 69 70 70 70 71 71 72 72 73 73 74 7475 66 66 67 67 68 68 68 69 69 70 70 71 71 72 72 73 73 74 74 75 7576 66 67 67 68 68 69 69 70 70 71 71 72 72 73 73 74 74 75 75 76 7677 67 67 68 68 69 69 70 70 71 71 72 72 73 73 74 74 75 75 76 76 7778 67 68 68 69 69 70 70 71 71 72 73 73 74 74 75 75 76 76 77 77 7879 67 68 69 69 70 70 71 71 72 73 73 74 74 75 76 76 77 77 78 78 7980 68 69 69 70 70 71 72 72 73 73 74 75 75 76 76 77 78 78 79 79 8081 68 69 70 70 71 72 72 73 73 74 75 75 76 77 77 78 78 79 80 80 8182 69 69 70 71 71 72 73 73 74 75 75 76 77 77 78 79 79 80 81 81 8283 69 70 71 71 72 73 73 74 75 75 76 77 78 78 79 80 80 81 82 82 8384 70 70 71 72 73 73 74 75 75 76 77 78 78 79 80 80 81 82 83 83 8485 70 71 72 72 73 74 75 75 76 77 78 78 79 80 81 81 82 83 84 84 8586 71 71 72 73 74 74 75 76 77 78 78 79 80 81 81 82 83 84 84 85 8687 71 72 73 73 74 75 76 77 77 78 79 80 81 81 82 83 84 85 85 86 8788 72 72 73 74 75 76 76 77 78 79 80 81 81 82 83 84 85 86 86 87 8889 72 73 74 75 75 76 77 78 79 80 80 81 82 83 84 85 86 86 87 88 8990 72 73 74 75 76 77 78 79 79 80 81 82 83 84 85 86 86 87 88 89 9091 73 74 75 76 76 77 78 79 80 81 82 83 84 85 86 86 87 88 89 90 9192 73 74 75 76 77 78 79 80 81 82 83 84 85 85 86 87 88 89 90 91 9293 74 75 76 77 78 79 80 80 81 82 83 85 85 86 87 88 89 90 91 92 9394 74 75 76 77 78 79 80 81 82 83 84 86 86 87 88 89 90 91 92 93 9495 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 9596 75 76 77 78 79 80 81 82 83 85 86 87 88 89 90 91 92 93 94 95 9697 76 77 78 79 80 81 82 83 84 85 86 87 88 89 91 92 93 94 95 96 9798 76 77 78 80 80 82 83 83 85 86 87 88 89 90 91 92 93 94 95 96 9899 76 78 79 80 81 82 83 84 85 87 88 89 90 91 92 93 94 95 96 98 99100 77 78 79 81 82 83 84 85 86 87 88 90 91 92 93 94 95 96 98 99 100101 77 79 80 81 82 83 84 86 87 88 89 90 92 93 94 95 96 98 99 100 101102 78 79 80 82 83 84 85 86 87 89 90 91 92 94 95 96 97 98 100 101 102103 78 79 81 82 83 84 86 87 88 89 91 92 93 94 96 97 98 99 101 102 103104 79 80 81 83 84 85 86 88 89 90 91 93 94 95 96 98 99 100 101 103 104105 79 80 82 83 84 86 87 88 89 91 92 93 95 96 97 99 100 101 102 103 105106 80 81 82 84 85 87 88 89 90 91 93 94 95 97 98 99 101 102 103 104 106107 80 81 83 84 85 87 88 89 91 92 94 95 96 98 99 100 102 103 104 106 107108 81 82 83 85 86 88 89 90 92 93 94 96 97 98 100 101 103 104 105 107 108109 81 82 84 85 87 89 89 91 92 94 95 96 98 99 101 102 103 105 106 108 109110 81 83 84 86 87 89 90 91 93 94 96 97 99 100 101 103 104 106 107 109 110111 82 83 85 86 88 90 91 92 94 95 96 98 99 101 102 104 105 107 108 110 111112 82 84 85 87 88 90 91 93 94 96 97 99 100 102 103 105 106 108 109 111 112113 83 84 86 87 89 91 92 93 95 96 98 99 101 102 104 105 107 108 110 111 113114 83 85 86 88 89 92 92 94 96 97 99 100 102 103 105 106 108 109 111 112 114115 84 85 87 88 90 92 93 95 96 98 99 101 102 104 106 107 109 110 112 113 115116 84 86 87 89 90 93 94 95 97 98 100 102 103 105 106 108 110 111 113 114 116117 85 86 88 89 91 93 94 96 98 99 101 102 104 106 107 109 111 112 114 115 117118 85 87 88 90 92 94 95 97 98 100 102 103 105 106 108 110 111 113 115 116 118119 85 87 89 90 92 94 96 97 99 101 102 104 106 107 109 111 112 114 116 117 119120 86 88 89 91 93 95 96 98 100 101 103 105 106 108 110 111 113 115 117 118 120

%  Relative  Humidity

Heat stress occurs when an animal’s attempt to dissipate heat is unsuccessful or overwhelmed. The result is poor health or performance. The thermoneutral zone is the range of temperatures in which an animal (including humans) does not use energy to stay warm or stay cool. When temperatures rise above the thermoneutral zone, animals must expend energy to cool their bodies.

High temperatures are not always the sole reason for heat stress conditions as humidity is also a factor. The Temperature Humidity Index (THI) illustrates this combination of conditions and provides a guideline of when cattle are susceptible to the negative effects of heat stress.

Entering the danger zone While feedlot cattle can generally handle air temperatures of up to 75-80 degrees without any negative effects on health or performance, every cattleman needs to know when to intervene. Cattle are in potential danger of death from heat exposure when the following occur:

• The heat index is 75 or greater for a 72 hour period

• The heat index during a 48 hour period is no lower than 79 during the day and no lower than 75 during the night

• The daytime heat index reaches 84 or higher for two consecutive days

Genetics make a difference Be aware that each genotype has a different and characteristic “zone of comfort”. For instance, lighter colored cattle generally show less heat stress than darker colored breeds - since darker colored breeds can be affected more quickly due to the absorption of heat by their darker hide.

In addition to genetics, response to heat stress is also affected by the following:

Health | Production Status | Previous Exposure to Heat StressEasy administration with 3 Bovine BlueLite PRODUCT FORMS available to fit any feedlot’s management needs

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>50% Relative humidity at which evaporative cooling effectiveness drops

>70ºF Overnight temperature signals likely heat stress conditions

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VitaminsGut Integrity

Performance

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Abatement practices

Hydration HealthBovine BlueLite helps cattle rehydrate in times of stress, including periods of heat stress, upon arrival to feedlots, and prior to shipping. As a high potassium electrolyte, Bovine BlueLite provides cattle with a source for quick replacement. Producers have seen increased profitability by using Bovine BlueLite as a way to improve carcass quality, reduce shrink loss, and reduce the potential for dark cutters.

Water and nutrition requirements Fluids, including water, comprise an average of 60% of the total body weight of a beef or dairy animal. Of this total body fluid, 66% is found in cells and the remaining third is found in the soft tissue compartment and vascular system.

For beef cattle in thermoneutral conditions daily water intake should be 8-9% of total body weight. Water intake increases when the THI goes above 75 and a temperature increase from 50º F to 90º F can increase daily water requirements by two and a half times. During heat stress events a 1,000 pound feedlot steer may require in excess of 20 gallons of water. Therefore, access to abundant and clean water is vital but note that the huge water flux resulting from increased water consumption causes heavy loss of electrolytes - and potassium is the first electrolyte that is excreted. Potassium loss from the hide increases by 500% in unshaded cattle and in attempts to conserve potassium, cows increase urinary excretion rates of sodium. However, if access to water is restricted or unavailable, intake can drop below what is required and feed intake also drops resulting in further compromises in health and performance.

Water loss All cattlemen need to keep in mind that increased water consumption will also increase fluid loss. Most of this loss is natural and happens due to: • urine • feces • sweat (to a limited degree) • evaporation (from the lungs and skin)

Be aware that fluid loss will also increase the loss of certain minerals, such as sodium, potassium and magnesium. Therefore, electrolyte supplementation is an important nutrient intervention to aid health and performance.

3Inches of linear water trough space per head per pen

Gallons of water per 100 lbs body weight required for normal cell function1. 2

• Bunching • Slobbering• High respiratory rates (panting)• Open mouth breathing• Seek shade or align themselves with the sun if there is

no shade• Eat and ruminate less• Thirst and water intake increase markedly

• Decreased activity• Agitation and

restlessness• Increased urination (with heavy

electrolyte loss)• Crowding over the water troughs• Refusal to lie down• Slower growth rates

Gut health challenges:• Ruminal pH is typically lower in heat stressed cattle• Rates of gut and ruminal motility are reduced, thus

slowing passage of feed through the digestive tract• Increased susceptibility to parasitic and non parasitic

diseases

Reproductive challenges:• Alters the production of reproductive hormones

essential for pregnancy• Changes the balance of developing follicles

in the ovary• Embryonic development is affected • Lower conception rates• Increased fetal and postnatal mortalities

Survival before production:• Resources diverted to survival functions to restore

balance rather than production• Production stops due to loss of homeostasis• The incidence of respiratory infections increases due to compromised immune response and an over-stressed respiratory system

• Higher mortality

Other challenges:• Gene function is disturbed• Stress hormones appear in the blood • Increased peripheral blood flow• Slower recovery from environmental and other

production stresses

Physiological effects of heat stress - long term

Visible signs of heat stress

BOVINE

Normal digestive processes create heat in cattle. Therefore, moving feeding time to late afternoon or evening will allow rumen fermentation to take place during the cooler temperatures. In turn, this will increase lung capacity for the cattle during the hotter daytime temperatures.

Other management practices that help cattle cope include: • Adding fans helps ensure

sufficient air movement and aids evaporative cooling

• Ensure easy access to abundant, clean water

• Introduce additional water tanks in anticipation of heat stress events so cattle get familiar with them

• Provide shade areas - preferably with generous ventilation

• Control flies to reduce the likelihood of grouping by the cattle - grouping reduces evaporative heat capacity

Proper hydration