Bovis ISSN 2398-2993

Heat stress

Synonym(s): Hyperthermia

Contributor(s): George Lindley, Mike Reynolds

Introduction

  • Cause: when body heat gain cannot be compensated by physiological mechanisms designed to cause heat loss, resulting in an overall increase in body temperature.
  • Signs:
    • Individual animal: tachypnea, open mouth breathing, hyperthermia and hypersalivation, collapse, coma and death
    • Herd level: reduced dry matter intakes, reduced milk production and reduced fertility performance.
  • Diagnosis: clinical signs in the presence of a high environmental temperature/humidity.
  • Treatment: fluid thereapy and environmental modification.
  • Prognosis: guarded. Response to therapy is often variable.

Pathogenesis

Etiology

  • Heat stress is defined as the sum of external forces acting on an animal that causes an increase in body temperature and evokes a physiological response (Dikmen & Hansen, 2009).
  • External forces that may lead to an increased body temperature may include:

Predisposing factors

  • Bos taurus breeds.
  • Lactating cattle: high yielding cattle are more at risk of heat stress than lower lactating cows.
  • Multiparous cows.
  • Cattle close to finished weight were found to be at the highest risk of heat stress-related mortality in feedlot systems in Australia (Sparke et al, 2001). Whilst an exact mechanism was not determined, it is of the authors opinion that it may be related to greater adipose/muscle tissue coverage, smaller lung capacity relative to bodyweight, and possibly greater amount of concentrates fed. Very young animals may not have the physiological reserves required to withstand extreme heat.
  • Animals with dark colored hides are over-represented.
  • Cattle with other clinical disease: bronchointerstitial pneumonia may predispose to heat stress related mortality Adult respiratory disease: overview.

Pathophysiology

  • Cattle are homeothermic and maintain a normothermic body temperature of 39 ± 0.5°C/102.2 ± 32.9°F.
  • The thermoneutral zone of mature cattle is generally accepted to be between -15°C/5°F (Lower Critical Temperature) and +25°C/77°F (Upper Critical Temperature).
  • When in the thermoneutral zone, cattle can maintain their core body temperature through regulation of dry heat loss methods alone; conduction, convection and radiation. When outside of the thermoneutral zone the animal must take further steps to redress the balance. These steps can have both animal welfare and economic repercussions:
    • When experiencing temperatures below the LCT the cow will increase her dry matter intake to convert feed to heat, rather than directing these food resources to produce milk.
    • When experiencing temperatures above the UCT cows will engage measures to reduce her core body temperature, these may include increasing heat dispersal (panting, drooling, etc) and limiting heat production (reducing movement, rumination, feed ingestion, etc)
  • Dry heat loss is proportional to the temperature difference between the body and the environment, ie dry heat loss will be greater when environmental temperatures are lower.
  • When cattle are exposed to temperatures above 25°C/77°F dry heat loss mechanisms are ineffective. Instead, they will increase heat loss through evaporative mechanisms (sweating, panting, drooling) and by limiting heat production (reduced movement, rumination, etc). High relative humidity reduces the effectiveness of sweating.
  • Cattle that are unable to maintain thermal balance will become heat stressed.

Timecourse

  • Clinical disease in an individual may appear to be sudden in onset, however it is usually the result of sustained heat load and preceding subclinical disease.
  • Time course will be reduced in neonatal animals.

Epidemiology

  • Clinical disease in an individual may be an indicator of more extensive clinical or subclinical disease within the herd/management group.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed Papers

  • Recent references from PubMed and VetMedResource.
  • Fabris T F, Laporta J, Skibiel A L, Corra F N et al (2019) Effect of heat stress during early, late, and entire dry period on dairy cattle. J Dairy Sci 102 (6), 5647-5656 PubMed.
  • Gernand E, König S & Kipp C (2019) Influence of on-farm measurements for heat stress indicators on dairy cow productivity, female fertility, and health. J Dairy Sci 102 (7), 6660-6671 PubMed.
  • Herbut P, Angrecka S, Godyn D & Hoffman G (2019) The physiological and productivity effects of heat stress in cattle - a review. J Natl Res Inst Anim Prod 19, 579-593.
  • Lacetera N (2019) Impact of climate change on animal health and welfare. Anim Front 9, 26-31 PubMed
  • Summer A, Lora I, Formaggioni P & Gottardo F (2019) Impact of heat stress on milk and meat production. Anim Front (1), 39-46 PubMed.
  • Chen S J, Wang D, Peng G, Chen Li J & Gu X (2018) Exposure to heat-stress environment affects the physiology, circulation levels of cytokines, and microbiome in dairy cows. Sci Rep (1), 14606 PubMed
  • Dahl G E (2018) Impact and mitigation of heat stress for mastitis control. Vet Clin North Am Food Anim Pract 34 (3), 473-478 PubMed.
  • Sullivan K F & Mader T L (2018) Managing heat stress episodes in confined cattle. Vet Clin North Am Food Anim Pract 34 (2), 325–339 PubMed.
  • Kamal R, Dutt T, Patel M, Dey A, Bharti P K & Chandran P C (2018) Heat stress and effect of shade materials on hormonal and behavior response of dairy cattle: a review. Trop Anim Health Prod 50 (40), 701-706 PubMed.
  • Paudel T P, Acharya B R, Karki D B & Shrestha B S (2018) Effect of heat stress on crossbred dairy cattle in tropical Nepal: Impact on blood parameters. J Agric Nat Resour 1, 223-230.
  • Wang X, Bjerg B S, Choi C Y, Zong C & Zhang G (2018) A review and quantitative assessment of cattle-related thermal indices. J Therm Biol 77, 24-37 PubMed.
  • Curtis A K, Scharf B, Eichen P A & Spiers D E (2017) Relationships between ambient conditions, thermal status, and feed intake of cattle during summer heat stress with access to shade. J Therm Biol 63, 104-111 PubMed.
  • Polsky L & von Keyserlingk M A G (2017) Invited review: effects of heat stress on dairy cattle welfare. J Dairy Sci 100 (11), 8645-8657 PubMed.
  • Dash S, Chakravarty A K, Singh A, Upadhyay A, Singh M & Yousuf S (2016) Effect of heat stress on reproductive performances of dairy cattle and buffaloes: A review. Vet World 9 (3), 235-244 PubMed.
  • Adams J (2015) Fluid therapy in adult cattle. Livestock 20 (1), 32-37 VetMedResource.
  • Mader T L & Griffin D (2015) Management of cattle expose to adverse environmental conditions. Vet Clin Food Anim 31 (2), 247-258 VetMedResource.
  • Mader T L & Griffin D (2015) Management of cattle exposed to adverse environmental conditions. Vet Clin North Am Food Anim Pract 31 (2), 247-258 PubMed.
  • Roussel A J (2014) Fluid Therapy in Mature Cattle. Vet Clin North Am Food Anim Pract 30 (2), 429-439 PubMed
  • Schüller L K, Burfeind O & Heuwieser E (2014) Impact of heat stress on conception rate of dairy cows in the moderate climate considering different temperature-humidity index thresholds, periods relative to breeding, and heat load indices. Theriogenology 81 (8), 1050–1057 PubMed.
  • Landaeta-Hernández A, Zambrano-Nava S, Hernández-Fonseca J P et al (2011) Variability of hair coat and skin traits as related to adaptation in Criollo Limonero cattle. Trop Anim Health Prod 43 (3), 657–663 PubMed
  • Bourke C A (2003) Evidence that enforced sunlight exposure can cause hyperthermia in cattle ingesting low levels of ergot of rye (Claviceps purpurea), when air temperature and humidity conditions are only moderate. Aust Vet J 81 (9), 553–8 PubMed
  • West J (2003) Effects of heat-stress on production in dairy cattle. J Dairy Sci 86, 2131-44 VetMedResource.
  • Kadzere C, Murphy M, Silanikove N & Maltz E (2002) Heat stress in lactating dairy cows: a review. Livest Prod Sci 77, 59-91.
  • West J (1999) Nutritional strategies for managing the heat-stressed dairy cow. J Anim Sci 77, 21-35 PubMed.
  • Coppock C E, Grant P A, Portzer S J, Charles D A & Escobosa A (1982) Lactating dairy cow responses to dietary sodium, chloride, and bicarbonate during hot weather. J Dairy Sci 65 (4), 566-576 PubMed.

Other sources of information

  • Hansen P J (2011) Dairy Production Medicine. Blackwell Publishing Ltd.
  • Srikandakumar A & Johnson E (2004) Effect of Heat Stress on Milk Production, Rectal Temperature, Respiratory Rate and Blood Chemistry in Holstein, Jersey and Australian Milking Zebu Cows. Kluwer Academic Publishers.
  • NADIS (online) Managing Heat Stress in Dairy Cows. Website: https://www.nadis.org.uk.
  • NDSU (online) Dealing With Heat Stress in Beef Cattle Operations. Website: https://www.ag.ndsu.edu.


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