Summary 1. A growing number of ecologists are turning to the enumeration of white blood cells from blood smears (leukocyte profiles) to assess stress in animals. There has been some inconsistency and controversy in the ecological literature, however, regarding their interpretation. The inconsistencies may stem partly from a lack of information regarding how stress affects leukocytes in different taxa, and partly from a failure on the part of researchers in one discipline to consult potentially informative literature from another. 2. Here, we seek to address both issues by reviewing the literature on the leukocyte response to stress, spanning the taxa of mammals (including humans), birds, amphibians, reptiles and fish. 3. We show that much of the early literature points to a close link between leukocyte profiles and glucocorticoid levels. Specifically, these hormones act to increase the number and percentage of neutrophils (heterophils in birds and reptiles), while decreasing the number and percentage of lymphocytes. This phenomenon is seen in all five vertebrate taxa in response to either natural stressors or exogenous administration of stress hormones. For the ecologist, therefore, high ratios of heterophils or neutrophils to lymphocytes (‘H : L’ or ‘N : L’ ratios) in blood samples reliably indicate high glucocorticoid levels. Furthermore, this close relationship between stress hormones and N : L or H : L ratios needs to be highlighted more prominently in haematological assessments of stress, as it aids the interpretation of results. 4. As with hormone assays, there are challenges to overcome in the use of leukocytes profiles to assess levels of stress; however, there are also advantages to this approach, and we outline each. Given the universal and consistent nature of the haematological response to stress, plus the overwhelming evidence from the veterinary, biomedical and ecological literature reviewed here, we conclude that this method can provide a reliable assessment of stress in all vertebrate taxa.

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The use of leukocyte profiles to measure stress in vertebrates: a review for ecologists

Effects of climate changes on animal production and sustainability of livestock systems

Climate change and livestock: Impacts, adaptation, and mitigation

Elevated ambient temperatures affect animal production and welfare. Animal's reduced production performances during heat stress were traditionally thought to result from the decreased feed intake. However, it has recently been shown that heat stress disturbs the steady state concentrations of free radicals, resulting in both cellular and mitochondrial oxidative damage. Indeed, heat stress reorganizes the use of the body resources including fat, protein and energy. Heat stress reduces the metabolic rates and alters post-absorptive metabolism, regardless of the decreased feed intake. Consequently, growth, production, reproduction and health are not priorities any more in the metabolism of heat-stressed animals. The drastic effects of heat stress depend on its duration and severity. This review clearly describes about biochemical, cellular and metabolic changes that occur during thermal stress in farm animals.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/jpn.12379

Heat stress effects on livestock: molecular, cellular and metabolic aspects, a review.

https://pubag.nal.usda.gov/pubag/downloadPDF.xhtml?id=57392&content=PDF

Effect of supplementation of prebiotic mannan-oligosaccharides and probiotic mixture on growth performance of broilers subjected to chronic heat stress

The Effect of Temperature, Dietary Energy Level, and Corn Particle Size on Broiler Performance

Stress and Nutritional Quality of Broilers

Effect of Acclimation and Heat Stress on Thyroid Hormone Concentration

Although the use of tunnel ventilation is expanding, there remains some ambiguity about heat loss experienced
by broiler chickens at air speeds in the range commonly used with tunnel ventilation. A “wind tunnel”-type habitat
housing up to 500 broilers was created and instrumented to measure heat loss from the broilers subjected to a variety of
air speeds and ambient temperatures. Treatments included ambient temperatures of 29, 32, and 35°C (85, 90, and 95°F)
and air speeds of 61 to 183 m/min (200 to 600 ft/min) in 30 m/min (100 ft/min) increments. Results indicate that as air
speed increases, broilers experience increases in sensible heat loss and corresponding decreases in latent heat loss. The
sum of the two (total heat loss) tended to remain constant with increased air speed. A general decrease in sensible heat
loss accompanied by a general increase in latent heat loss was observed as temperature was increased.

J. D. May

Papers

The Effect of Temperature, Dietary Energy Level, and Corn Particle Size on Broiler Performance

Stress and Nutritional Quality of Broilers

Effect of Acclimation and Heat Stress on Thyroid Hormone Concentration

Heat loss from broiler chickens subjected to various air speeds and ambient temperatures

The effect of air velocity on broiler performance and feed and water consumption