Defining
Heat Stress. 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
Temp o F 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120
% Relative Humidity 0 64 65 65 66 66 67 67 67 68 68 69 69 70 70 71 71 72 72 72 73 73 74 74 75 75 76 76 76 77 77 78 78 79 79 80 80 81 81 81 82 82 83 83 84 84 85 85 85 86
5 65 65 66 66 67 67 68 68 69 69 69 70 70 71 71 72 72 73 73 74 74 75 75 76 76 77 77 78 78 79 79 79 80 80 81 81 82 82 83 83 84 84 85 85 86 86 87 87 88
10 65 66 66 67 67 68 68 69 69 70 70 71 71 72 72 73 73 74 74 75 75 76 76 77 77 78 78 79 79 80 80 81 81 82 82 83 83 84 84 85 85 86 86 87 87 88 88 89 89
15 65 66 67 67 68 68 69 69 70 70 71 71 72 72 73 73 74 75 75 76 76 77 77 78 78 79 80 80 81 81 82 82 83 83 84 84 85 85 86 86 87 87 88 88 89 89 90 90 91
20 66 66 67 68 68 69 69 70 70 71 71 72 73 73 74 74 75 75 76 76 77 78 78 79 79 80 80 81 82 82 83 83 84 84 85 85 86 87 87 88 88 89 89 90 90 91 92 92 93
25 66 67 67 68 69 69 70 70 71 72 72 73 73 74 74 75 76 76 77 77 78 79 79 80 80 81 82 82 83 83 84 84 85 86 87 87 88 89 89 90 90 91 92 92 93 93 94 94 95
30 67 67 68 68 69 70 70 71 72 72 73 73 74 75 75 76 76 77 78 78 79 80 80 81 81 82 83 83 84 84 85 86 86 87 88 88 89 89 90 91 91 92 92 93 94 94 95 96 96
35 67 68 68 69 70 70 71 71 72 73 73 74 75 75 76 77 77 78 79 79 80 80 81 82 82 83 83 84 85 86 86 87 88 88 89 89 90 91 91 92 93 93 94 95 95 96 97 97 98
40 67 68 69 69 70 71 71 72 73 73 74 75 75 76 77 77 78 79 79 80 81 81 82 83 83 84 85 85 86 87 87 88 89 89 90 91 92 92 93 94 94 95 96 96 97 98 98 99 100
45 68 68 69 70 71 71 72 73 73 74 75 75 76 77 78 78 79 80 80 81 82 82 83 84 85 85 86 87 87 88 89 89 90 91 91 92 93 94 94 95 96 96 97 98 98 99 100 101 101
50 68 69 70 70 71 72 73 73 74 75 75 76 77 78 78 79 80 80 81 82 83 83 84 85 86 86 87 88 88 89 90 91 91 92 93 94 94 95 96 96 97 98 99 99 100 101 102 102 103
55 69 69 70 71 72 72 73 74 75 75 76 77 78 78 79 80 81 81 82 83 84 85 86 86 87 87 88 89 90 90 91 92 93 93 94 95 96 96 97 98 99 99 100 101 102 102 103 104 105
60 69 70 70 71 72 73 74 74 75 76 77 78 78 79 80 81 81 82 83 84 85 85 86 87 88 88 89 90 91 92 92 93 94 95 95 96 97 98 99 99 100 101 102 102 103 104 105 106 106
65 69 70 71 72 73 73 74 75 76 77 77 78 79 80 81 81 82 83 84 85 85 86 87 88 89 89 90 91 92 93 94 94 95 96 97 98 98 99 100 101 102 102 103 104 105 106 106 107 108
70 70 71 71 72 73 74 75 76 76 77 78 79 80 81 81 82 83 84 85 86 86 87 88 89 90 91 91 92 93 94 95 96 96 97 98 99 100 101 101 102 103 104 105 106 106 107 108 109 110
75 70 71 72 73 74 74 75 76 77 78 79 80 80 81 82 83 84 85 86 86 87 88 89 90 91 92 92 93 94 95 96 97 98 99 99 100 101 102 103 104 105 105 106 107 108 109 110 111 111
80 70 71 72 73 74 75 76 77 78 78 79 80 81 82 83 84 85 86 86 87 88 89 90 91 92 93 93 94 95 96 97 98 99 100 101 102 103 103 104 105 106 107 108 109 110 111 111 112 113
85 71 72 73 74 75 75 76 77 78 79 80 81 82 83 84 85 86 86 87 88 89 90 91 92 93 94 94 95 96 98 98 99 100 101 102 103 104 105 106 107 108 108 109 110 111 112 113 114 115
90 71 72 73 74 75 76 77 78 79 80 81 82 83 84 84 85 86 87 88 89 90 91 92 93 94 95 95 96 98 99 100 101 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117
95 72 73 74 75 76 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 96 98 99 100 101 102 103 103 104 106 107 108 109 110 111 111 112 113 114 115 116 117 118
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 Stress
>70ºF >50% Overnight temperature signals likely heat stress conditions
Heat Stress
Temperature Humidity Index (THI)
Relative humidity at which evaporative cooling effectiveness drops
100 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120
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How heat stress affects beef cattle and effective support strategies.
Proper hydration makes everything
work better
Visible signs of heat stress
• 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
Physiological effects of heat stress - long term 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
Abatement practices
Hydration Health
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 • E nsure easy access to abundant, clean water • I ntroduce additional water tanks in anticipation of heat stress events so cattle get familiar with them •P rovide shade areas - preferably with generous ventilation •C ontrol flies to reduce the likelihood of grouping by the cattle - grouping reduces evaporative heat capacity
3
Inches of linear water trough space per head per pen
1.2
Bovine BlueLite helps cattle rehydrate in times of stress, including periods of BOVINE 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.
Gallons of water
per 100 lbs body weight required for normal cell function