Commercial Poultry Production and Hatchery Management

ADVERSE EFFECTS

• The various physiological and pathological changes that take place in the flock, during high summer temperature are as follows:
  • Energy intake and thereby feed consumption and other nutrients intake reduce as the environmental temperature increases. This is because birds need less energy for maintenance of body temperature, when the ambient temperature is high. Consequently, growth rate and body weight of birds will become lower.
  • There will be early two-fold increase in the water consumption of birds during summer; because during high environmental temperature the major way to lose the excess heat produced in the body is by loss of water vapour through expired air.
  • High ambient temperature increases the respiratory rate and body temperature. Since there are no sweat glands in Poultry, they will start panting vigorously, in order to lose the excess body heat produced. As the outside temperature increases the heat production as well as the heat loss from the body decreases.
  • For every 1^oC increase in ambient temperature, the heat production in the body decreases by about one per cent.
  • On the other hand, water loss through respiration increases, with increase in ambient temperature.
  • High environmental temperature on the other hand decreases oxygen consumption, blood pressure, pulse rate, thyroid size and activity, blood calcium level and body weight.
  • The problems with ectoparasites will be more during summer and the following monsoon.
  • Moreover, high environmental temperature associated with high relative humidity (>70%) may lead to outbreaks of Coccidiosis.
  • Low feed intake and thereby low coccidiostat consumption will further aggravate Coccidiosis outbreaks.
  • Incidences of Fatty Liver Haemorrhagic Syndrome and other metabolic disorders like heat stroke, liver rupture etc. are more during summer; especially in case of heavy broilers.
  • Birds will shed more feathers during summer, in order to lose the excess body heat produced.
  • At high environmental temperatures, nearing the body temperature of the birds, vapourisation of body water through respired air is the only way to lose substantial amount of heat from the body. However, this is possible only when the inspired air has very low moisture levels. But if both temperature and relative humidity are high, birds will not be able to lose the excess body heat and will finally die of heat prostration.
  • Fatty birds succumb first, perhaps because their air sacs are rather constricted and thereby not able to evaporate moisture and produce coolness efficiently.
  • Caged birds and birds reared on slatted floors will suffer more due to high environmental temperature than birds reared on litter floors; because birds on litter can cool themselves to some extent by dusting themselves in the litter.
  • Heavy mortality due to heat stroke will be noticed among heavy broilers, in the late afternoon and evening.
  • Temperature affects egg breakage. Elevated environmental temperature is associated with decrease in shell quality.
  • Reduction of shell thickness produced by heat stress is apparently due to respiratory alkalosis which causes lowering of partial pressure of carbon dioxide in the lungs and raises blood pH.
  • As the ambient temperature increases above 26^oC, the egg size declines.