Partitioning of evaporative heat loss in poultry: phenotypic flexibility in response to thermal acclimation

Clinton Bukho Tshingilane (M.Sc. student)

Supervisors: Dr. Thobela Nkukwana, Prof. Andrew McKechnie

Temperatures in the 21st century are expected to increase by ~4.0 oC compared to the 20th Century average, with a concomitant increase in temperature-related challenges like heat stress. Poultry are sensitive to heat stress, in part because of artificial selection for rapid growth and the associated metabolic heat production. Increasing air temperatures are especially alarming for rural poultry farming compared to large-scale commercial farming, because the hotter parts of South Africa are regularly exposed to air temperatures approaching or exceeding chickens’ normothermic body temperature (~40 C). Under these conditions, evaporative heat loss becomes the sole avenue whereby heat can be dissipated and lethal hyperthermia avoided. Evaporative water loss can broadly be partitioned into respiratory evaporative water loss (REWL) and cutaneous evaporative water loss (CEWL). Research on evaporative water loss partitioning has largely focused on wild bird species. Although some studies have quantified respiratory evaporation under moderate temperatures in poultry, quantification of CEWL is lacking. Moreover, available data on wild birds reveals that the relative contributions of CEWL and REWL have far-reaching implications for thermoregulation in the heat, with, the contributions of REWL versus CEWL varying widely amongst taxa.  Furthermore, data from wild birds also reveals phenotypic flexibility in CEWL, and the capacity for individuals to enhance evaporative cooling efficiency via increases in rates of CEWL following acclimation / acclimatisation to hot conditions. The aims of this project are to make use of a partitioning chamber in quantify the contribution CEWL and REWL at a range of air temperatures above Tb in indigenous chickens (Boschveld breed) and evaluate phenotypic flexibility in CEWL in response to thermal acclimation. These data will allow us to develop predictive relationships for how thermoregulatory efficiency varies with heat stress and better quantify the risks posed during periods of high environmental temperatures. 

Contact the Research Group! hotbirdsresearchproject@gmail.com
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