Respiratory evaporation of poultry – the development of a ventilated hood system

The main function of the respiratory system is the gas exchange, carrying oxygen to the tissues and removing carbon dioxide from them and supplying the metabolic requirements of the animals. Furthermore the respiratory system is essential to the thermoregulation because the loss of water is a way to the maintenance of body temperature in conditions of high air temperature. When there is an increase of the air temperature, consequently it is observed a decrease in the temperature gradient with the body temperature, birds like broiler chickens, quails and turkeys increase their respiratory evaporation to increase the loss of heat to the environment. Thus, the increase of respiratory evaporation to the maintenance of body temperature results in an energy expenditure greater than the sensible flow, and consequently we can observe changes in the acid-basic equilibrium of blood and in the content of water of the body. Some techniques are described in the literature to the settlement of the respiratory evaporation of poultry, but all used in controlled environments (chambers). Two-compartment metabolic chambers are described to calculate separately the cutaneous and respiratory losses of small birds. However, the measurements must be done in the dark to avoid the animals to shake inside the chamber. Other technique is the intubation of birds using an endotracheal tube connected to a pneumotachograph but this can be considered an invasive technique. Masks can be developed to the settlement of respiratory evaporation and connected to a spirometer can be used to the study of respiratory functions of poultry in similar conditions of facilities (tidal volume, respiratory frequency, temperature of expired air). The use of masks coupled to gas analyzers enables the measurement of oxygen consumed and carbon dioxide produced, and it is possible to measure the metabolic heat production. Previous experiments showed that a mask isolating only the beak of broilers is not appropriate because it causes discomfort and the leakage of the expired air. Therefore we developed a plastic and transparent hood to envelop the head and neck of the birds to permit their vision sealed with a rubber sheet. The Animal Biometeorology Laboratory developed the System of Physiological Measurement to the continuous measurement of respiratory gases (oxygen; carbon dioxide; water vapour), respiratory functions (tidal volume, respiratory flow and respiratory rate) and body temperatures (skin, feather, rectal and expired air). The system used for poultry is composed by: the hood (developed by the Laboratory); oxygen and carbon dioxide analyzers (model FMS-1201-05, Field Metabolic System); two water vapour analyzers (one for the atmosphere and one for the expired air of broilers, model RH-300, Sable System); two pumps (model SS4 sub-sample, Sable System); a dessicant column (Magnesium Perchlorate); spirometer (model ML141, ADInstruments); chamber to the mixture of gases (developed by the Laboratory); one breathing tube; a flow head (model MLT10, ADInstruments); a probe for the expired air temperature (model MLT415/AL, ADInstruments). Respiratory evaporation (W m-2) can be calculated by eq. (1): q_ER^"=(λ RF( φ_A-φ_exp ))/A, where: λ is the latent heat of water vaporization (J g-1); RF is the respiratory flow (m3 s-1); φA is the absolut humidity of air (g m-3); φA is the absolut humidity of expired air (g m-3); A is the surface body area (A=0.000819 (〖BW〗^0.705), m2, BW is the body weight, kg). Metabolic heat production (W m-2) can be calculated by eq. (2): q_M^"=RF[(QO_2 DO_2 0.75)+(Q〖CO〗_2 D〖CO〗_2 0.25)]/A, where: RF is the respiratory flow (L s-1); QO2 is the caloric coefficient of oxygen (kJ L-1); ΔO2 is the difference between oxygen concentrations in the atmosphere and in the expired air (%);QCO2 is the caloric coefficient of carbon dioxide (kJ L-1); ΔCO2 is the difference between carbon dioxide concentrations in in the expired air and in the atmosphere (%). Some tests were made to validate the methodology. Considering broilers as very uniform animals (from a same strain) we chose a 15 minutes sampling of a broiler at 23ºC, with a temperature of expired air of 30ºC and with a body weight of 1.6 kg. We observed the following mean values (±SE): respiratory rate, 24±0.17 breaths min-1; respiratory flow, 0.00779±0.001 L s-1; ventilation, 0.467±0.002 L min-1; tidal volume, 0.01977±0.0001 L breath-1. All the observed values are in accordance to data described in literature, mainly tidal volume and ventilation. These results show our system has no leakage of the expired air during measurements. The mean value of metabolic heat production was 53.61±0.23 W m-2 and we observed an average of respiratory evaporation of 1.14±0.005 W m-2. The results of metabolic heat production are in agreement with values described in literature for broilers with similar body weight. The respiratory evaporation little contributed to the heat loss considering the air temperature of the test. We can consider as the most valuable result of our work the evidence of a reliable technique to measure respiratory evaporation of poultry, considering the animals exposed to environmental conditions and not under controlled environments as respiratory chambers. We are performing an assay to the study of respiratory functions, metabolic heat production and respiratory evaporation of broilers during all the rearing period.