Differences in Thermotolerance Between Temperate and Tropical Birds

Characterisations of thermoregulation both in tropical and temperate birds are very much important to predict their vulnerability to climate change. Upper critical temperature (UCT) is used to assess the latitudinal variation in heat tolerance and susceptibility to heat stress.

Heat tolerance limits (HTL): the air temperature at which an endotherm loses the ability to regulate its body tempera­ture. Tropical birds have higher HTL (ΔHTL = 2.2 °C;

45.2 vs. 43.0 °C) and upper critical temperature (ΔUCT = 1.1 °C; 38.7 vs. 37.6 °C) which indicate that tropical birds have better thermotolerance ability than the temperate birds. However, these differences between tropical and temperate birds do not seem to impact susceptibility to thermal stress neither thermal safety margins nor thermal tolerances (the difference between HTL and Tmax) vary between temperate and tropical species. Temperate birds show consistent seasonal changes in thermoregulatory traits especially during winter seasonal changes showed by tem­perate birds seem to be primarily aimed to conserve heat making them acclimatized to cold temperature (Pollock et al. 2019). However, tropical birds do have capability of seasonal adjustment and are rather more phenotypic flexible than the temperate birds. Temperate birds have wider TNZ, whereas tropical birds showed idiosyncratic patterns of sea­sonal variation in LCT, UCT and TNZ. Total feather mass and density of downy feathers were significantly high in temperate birds which provide insulation to tolerate cold temperature and making the survivability of these birds in warmer tropical regions very difficult.

Learning Outcomes

• High or low ambient temperature initiates various physiological, behavioural and endocrine responses to maintain the thermal balances in birds.

• Heat/cold stress affects the growth performance, egg and meat production in birds as a result of reduced feed intake and impaired digestion and absorption of nutrients.

• Heat/cold stress stimulates the production of highly conserved molecular heat shock proteins that helps in protein folding and unfolding and maintenance of cellular homeostasis.

Exercises

Objective Questions

Q1. What is the temperature range of thermoneutral zone for poultry?

Q2. What is the crucial temperature point in poultry for thermoregulation?

Q3. How heat and cold stress activates the stress response in poultry?

Q4. Impacts of heat stress on productive performance of poultry?

Q5. Why heat stress is very critical in birds?

Q6. The first sign of heat stress in poultry? Q7. What does enhanced panting lead to?

Q8. What is the ideal temperature for optimum production in birds?

Q9. Which is the stress hormone in birds?

Q10. Mention is the thermogenic hormone in birds?

Q11. What is the biomarker for oxidative stress?

Q12. Haematological indicator of heat stress in birds?

Q13. Which is the cellular and molecular biomarker of heat stress in birds?

Subjective Questions

Q1. What is the impact of heat stress on productive perfor­mance of poultry?

Q2. How heat stress impairs the productive performance in birds?

Q3. How the egg shell quality is affected during heat stress?

Q4. What are the heat dissipation of mechanism in birds?

Q5. How the acid base balance is disturbed in birds during heat stress?

Q6. How does metabolic acidosis occur in birds during heat stress?

Q7. What is the neuroendocrine response in birds?

Q8.

Q9. Explain the molecular response to heat stress in birds? Q10. What is major impact of lipid peroxidation in heat stressed birds?

Answer to Objective Questions

A1. 18-22

A2. 30

A3. Activates the hypothalamo-hypophyseal-adrenocorti- cal (HPA) axis

A4. Reduced feed intake, decrease in body weight, reduc­tion in egg production and shell quality

A5. Lack of sweat glands and higher metabolic rate

A6. Increased respiration rate

A7. Respiratory alkalosis

A8. 19-22

A9. Corticosterone

A10. Thyroid hormones

A11. Malondialdehyde

A12. Decrease in haemoglobin (g/dL) and haematocrit percent

A13. Heat shock proteins in particularly HSP70

Answer to Subjective Questions

A1. Decrease in feed intake, reduced body weight gain, decrease in number eggs and poor egg shell quality.

A2. Reduced feed intake, decreased digestive enzymes and biological activities, inflammation in the digestive tissues.

A3. The increased CO2 elimination results in decreased HCO₃ which is essential for the formation of egg shell.

A4. Evaporative heat loss, convection, conduction and radiation.

A5. The increase in respiration rate during heat stress results in respiratory alkalosis which disrupts the acid base balance and leads to increase blood pH in associ­ation with reduced pCO₂.

A6. The enhanced excretion of fluid in the urine with more concentration of electrolytes and the disproportion of dietary Na, K and Ca may lead to metabolic alkalosis with increased blood pH, HCO₃ and base excess.

A7. The activation of hypothalamic-pituitary-adrenal axis enhanced the glucocorticoids particularly corticoste­rone and decrease in triiodothyronine.

A8. The levels of blood total lipids and cholesterol are reducing with increasing environmental temperature. The haematological values such as haemoglobin con­centration (g/dL) and haematocrit percent (Ht%) are decreasing during heat stress depending upon the age of birds.

A9. Heat stress enhances the production of HSPs which selectively bind to the degenerated proteins or aggregated proteins and newly synthesized polypeptides.

A10. The lipid peroxidation is a major consequence of heat stress where protein carbonyl, MDA, 8-hydroxy-2^,- -deoxyguanosine and advanced glycation end product are considered as biomarkers of protein, lipid, DNA and carbohydrate oxidation in birds.

Further Reading

Ajakaiye JJ, Perez-Bello A, Mollineda-Trujillo A (2011) Impact of heat stress on egg quality in layer hens supplemented with l-ascorbic acid and dl-tocopherol acetate. Vet Arhiv 81:119-132

Chowdhury VS (2018) Heat stress biomarker amino acids and neuro­peptide afford thermotolerance in chicks. J Poult Sci 56:0180024

Chowdhury V, Tomonaga S, Nishimura S, Tabata S, Furuse M (2012) Physiological and behavioral responses of young chicks to high ambient temperature. J Poult Sci 49:212-218

Deeb N, Cahaner A (1999) The effects of naked neck genotypes, ambient temperature, and feeding status and their interactions on body temperature and performance of broilers. Poult Sci 78(10):1341-1346

Etches RJ, John TM, Verrinder Gibbins AM (1995) In: Daghir NJ (ed) Behavioural, physiological, neuroendocrine and molecular responses to heat stress. CAB International, pp 31-65

Goel A (2021) Heat stress management in poultry. J Anim Physiol Anim Nutr 105:1-10. https://doi.org/10.1111/jpn.13496

Hafez ESE (1964) Behavioral thermoregulation in mammals and birds. Int J Biometeorol 7(3):231-240

Imik H, Atasever MA, Urgar S, Ozlu H, Gumus R, Atasever M (2012) Meat quality of heat stress exposed broilers and effect of protein and vitamin E. Br Poult Sci 53:689-698

Jastrebski SF, Lamont SJ, Schmidt CJ (2017) Chicken hepatic response to chronic heat stress using integrated transcriptome and metabolome analysis. PLoS One 12(7):e0181900

Liu L, Ren M, Ren K, Jin Y, Yan M (2020) Heat stress impacts on broiler performance: a systematic review and meta-analysis.

Lu Z, He X, Ma B, Zhang L, Li J, Jiang Y, Zhou G, Gao F (2018) Serum metabolomics study of nutrient metabolic variations in chronic heat- stressed broilers. BrJ Nutr 119(7):771-781

Mack LA, Felver-Gant JN, Dennis RL, Cheng HW (2013) Genetic variation alter production and behavioral responses following heat stress in 2 strains of laying hens. Poult Sci 92:285-294

Marder J, Arad Z (1989) Panting and acid-base regulation in heat stressed birds. Comp Biochem Physiol A Physiol 94(3):395-400

Pollock HS, Brawn JD, Agin TJ, Cheviron ZA (2019) Differences between temperate and tropical birds in seasonal acclimatization of thermoregulatory traits. J Avian Biol 50(4). https://doi.org/10.1111/ jav.02067

Pollock HS, Brawn JD, Cheviron ZA (2021) Heat tolerances of temper­ate and tropical birds and their implications for susceptibility to climate warming. FunctEcol 35(1):93-104

Ranjan A, Sinha R, Devi I, Rahim A, Tiwari S (2019) Effect of heat stress on poultry production and their managemental approaches. Int J Curr Microbiol App Sci 8(2):1548-1555

Ruuskanen S, Hsu BY, Nord A (2021) Endocrinology of thermoregula­tion in birds in a changing climate. Mol CellEndocrinol 519:111088. https://doi.org/10.1016Zj.mce.2020.111088

Saeeda M, Abbas G, Alagawany M, Kamboh AL, El-Hack MEA, Khafaga AF, Chaoa S (2019) Heat stress management in poultry farms: a comprehensive overview. J Thermal Biol 84:414-425

Smit B, Zietsman G, Martin RO, Cunningham SJ, McKechnie AE, Hockey PAR (2016) Behavioural responses to heat in desert birds: implications for predicting vulnerability to climate warming. Clim Change Responses 3:9. https://doi.org/10.1186/s40665-016-0023-2

Vandana GD, Sejian V, Lees AM, Pragna P, Silpa MV, Maloney SK (2021) Heat stress and poultry production: impact and amelioration. Int J Biometeorol 65:163-179

Wang S, Edens FW (1993) Stress-induced heat-shock protein synthesis in peripheral leukocytes of turkeys (Meleagris gallopavo). Comp Biochem Physiol 106(3):621-628