Energy Expenditure During Thermoregulation in Birds
The thermoregulatory mechanism of birds varies from mammals with regard to their higher metabolic rate and reduced ability for heat dissipation due to plumage and absence of sweat glands.
Metabolic heat production occurs especially during digestive processes starting form feed intake, digestive break down of feed resources, its absorption and utilization. During pleasant and comfortable environmental conditions, the metabolic heat generated ensures normal productivity in birds, indicating their comfort zone. However, several factors influence the impact of metabolic heat produced. For example, the maintenance metabolism is higher in growing birds which therefore contributes severely to the heat increment. The composition and texture of feed also influence the energy expenses in association with feeding activities. In addition, the inability to convert feed into protein and lipid above maintenance requirement contributes 20-25% of heat production. Heat production in broilers mainly dependent on genetics that the breeds preferred for fast growth with a low feed conversion ratio (FCR) produces lower heat than either of slow growth with a low FCR or slow growth with a high FCR. Further, heat production is high in broilers due to their higher growth rate that is associated with more feed intake.Heat stress manifests a wide range of physiological, behavioural, neuroendocrine and molecular responses in birds to restore their core body temperature within the normal limits. The metabolic activities regulate the physiological functions of maintenance, growth and egg production which increases the heat production and it depends upon the species, breed, body weight, production, feed intake and feed quality in birds. The regulation of body temperature in birds is established by radiation, conduction, convection, evaporation and excretion.
The heat loss through radiation is an electromagnetic process where body temperature is transmitted to cooler surroundings without a medium by air. The evaporative heat loss mechanism is a significant way of heat dissipation in birds through respiratory tract which majorly rely on panting and nasal cavity acts as heat exchanger. In addition, a small quantity of heat also lost through skin surface and comb of birds. The radiative heat loss occurs from featherless regions of birds by raising their wings during hot environmental conditions. The high wind velocity favours the removal of heat load from bird’s body by convection where there is optimum ventilation. Further, birds drink double the quantity of water during heat stress to eliminate the heat load through urine and wet faeces. Further, few responses are also evolved to establish for a long period of time to acclimatize the bird to that particular environmental condition which falls within the upper limit of the thermoregulatory zone. However, climatic extremes beyond the threshold limit in birds may lead to deleterious situation in birds wherein none of the adaptive mechanisms can sustain the bird’s survivability, finally culminating to death.Know More......................
• Birds’ feathers provide remarkable insulation against the cold.
• Emperor penguins are the most climate resilient birds.
• Birds lack sweat glands.
• Average body temperature of birds: 40 °C.
• Gular fluttering is common mechanism in birds used to facilitate heat loss.
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