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Airborne-Particle Deposition in the Respiratory Tract of Chickens1
Airborne-Particle Deposition in the Respiratory Tract of Chickens1 R. B . HAYTER AND E . L . BESCH
Institute for Environmental Research College of Engineering, and Department of Physiological Sciences, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas 66506 (Received for publication November 16, 1973)
POULTRY SCIENCE 53: 1507-1511, 1974
INTRODUCTION HE physiological effects of dust on man and the control of dust particles in man's environment have been the subject of indepth study (Dautrebande, 1962). Until recently the need for controlled environments to improve the health and production efficiency of domestic animals, including poultry, has been largely ignored. The deposition of inhaled aerosols generally is a function of aerosol concentration in the animal's environment. Viable particle concentrations as high as 2.4 x 105 per cubic meter (m.3) have been measured in poultry units (Anderson et al., 1964). Mass concentrations may be 25 times greater (Wolfe et al, 1968) than those reported in urban atmospheres. Because such viable particulates can cause such diseases as Newcastle, and air sacculitis
T
1. This work was supported in part by the U.S.P.H.S. Training Grant No. 2-T01-EL-0024-06; and the Kansas Agricultural Experiment Station. Contribution number 121, Department of Physiological Sciences, Kansas Agricultural Experiment Station, Kansas State University, Manhattan, Kansas 66506.
(Anderson et al., 1964; Hinshaw, 1961; Horton and Dingle, 1961), acceptable environmental conditions in animal rooms cannot be maintained without controlling airborne particles. Moreover, knowledge of the regional deposition of such particles in the respiratory tract might allow us not only to characterize toxicity of the contaminants but also to design optimal air-cleaning equipment. Those considerations were the basis for this study. MATERIALS AND METHODS Animals. Thirty adult, fasted, anesthetized Single Comb White Leghorn roosters—six for each particle size—averaging 2.03 ± 0.05 kg. body weight were used. To measure respiratory frequency and volume, we suspended each bird in an upright posture (Figure 1) in a plexiglas, whole-body plethysmograph (modified after Boecker et al., 1964). At the end of each experiment, the bird was euthanatized (I.V., sodium pentobarbital) and the plethysmograph calibrated. To detect the inhaled, radioactive aerosol externally for each of seven, equal-length sections along the axis of the body (Figure 2), we used a lead shielded Na-I scintillation detector (Harshaw Scientif-
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Downloaded from http://ps.oxfordjournals.org/ at University of Ulster at Coleraine on April 12, 2015
ABSTRACT Thirty anesthetized, male White Leghorn chickens, approximately six months old (average body weight, 2.030 ± 0.048 kg.), individually inhaled radioactively labeled (1-128) monodispersed latex particles. Six birds each were exposed to one of five particle sizes (0.091, 0.176, 0.312, 1.1, and 3.7 to 7 microns). During exposure, the respiratory rate and tidal volume were monitored by a whole-body plethysmograph. Inhaled aerosol was detected externally for each of seven, equal-length sections along the axis of the body. Percentages of deposition for each section were calculated from the corrected time-decay activity. Significant differences (P < 0.05) were found for regional deposition as a function of particle size. The largest particles (3.7 to 7 |x.) were captured in the head and anterior trachea; other particles were deposited uniformly throughout the remainder of the system. The 1.1-micron-size particles were deposited primarily in the lung and posterior air sacs; those of 0.312-microns (having weak interception, impaction, and diffusion-capture mechanisms) tended to pass through the posterior to the anterior sacs (assuming the Hazelhoff-Bethe gas pathway theory); and smallest particles, influenced by diffusion, were captured in the birds' caudal regions.
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R. B. HAYTER AND E. L. BESCH
ic, Model 12 SW12W4). The time-decay corrected activity for each section of the bird gave a relative estimate of the aerosol concentration for that section. Aerosol. Five discrete particle sizes were used: 0.091, 0.176, 0.312, 1.1, and 3.7 to 7 microns. 2 A polymerized layer of iodine on the particle surfaces allowed radioactive la-
beling of the particles by neutron bombardment (Bogen, 1970). The labeled particles were atomized (Fraser et al., 1969), deionized (3M Model 7330, Whitby and Liu, 1968), and carried in the airstream to the plenum, which was at or near ambient barometric pressure. The bird was allowed to breath for 30 minutes through a demand-actuated unidirectional valve from the plenum.
2. Polystyrene latex spheres; Diagnostic Products, Dow Chemical Company, Indianapolis, Indiana 46206.
Particle Capture. Four principles of collecting (Whitby and Lundgren, 1965) or capturing
Downloaded from http://ps.oxfordjournals.org/ at University of Ulster at Coleraine on April 12, 2015
FIG. 1. Whole body plethysmograph containing bird. The animal breathed radioactive particles from the plenum through the mask (arrow). Insert shows detail of the mask.
PARTICLE DEPOSITION IN RESPIRATORY TRACT
particles mechanically are identified: /. Straining: important for large particles (larger than used in this study); 2. Inertial impaction: involves heavy particles that tend to leave the airstream and impact with an obstacle; 3. Interception: involves large-diameter particles that pass within less than one radius from the obstacle; and 4. Diffusion: affects small particles diverted by bombardment of gas molecules; their random path may cause the particles to come in contact with obstacles.
branous flap covered with many small feathers (McLeod et al., 1964) and also mucous membrane-covered turbinate bodies that have a large surface area relative to that of the nostril opening. Quite likely impaction and interception on the turbinates, the feather-covered membrane flap, the cranial larynx, and the mucous-covered walls of this area all entrapped particles 3.7 to 7.0 (JL. in size. On the other hand, for particles of 1.1 (JL. or less (Figure 3b), which tend to follow streamlines around obstacles (Whitby and Lundgren, 1965), inertial impact had markedly less influence. Though that reduced the
Least affected by such mechanisms are the 0.3-micron particles (too small to be influenced by impaction and interception and to large to be diffused). RESULTS AND DISCUSSION The largest particles (3.7 to 7 microns), were deposited primarily in the anterior portion of the respiratory system (Figure 3a); the remainder of the particles were distributed equally throughout the rest of the system. Thus, most particles were deposited in the vicinity of the cranial larynx, on the cranial end of the trachea where the diversion of the airstream could have caused increased impaction and interception of the large particles. The avian nasal cavity contains a mem-
FIG. 3. Relative deposition of particles in various body sections (Figure 2). Similar crosshatching in adjacent sections show nonsignificant differences in relative deposition (P > 0.05). Number at the top of each column of the histogram shows average percent of total body deposition for that section.
Downloaded from http://ps.oxfordjournals.org/ at University of Ulster at Coleraine on April 12, 2015
Fio. 2. The seven anatomical sections of the bird. The use of an appropriately constructed plexiglass mold permitted similar positioning, by section, for each animal.
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Diffusion appears to have been the primary collection mechanism for the two smallestsize particles (Figure 3d and 3e). For the 0.176-micron diameter particles, diffusion increased at the syrinx, where the airstream velocity dropped. Reduced concentrations in the airstream resulted in reduced particle capture in the caudal areas of the bird. Most 0.91-micron particles avoided capture until they reached the extremely low-velocity areas of the posterior sacs, where diffusion caused their capture. These results could, under certain conditions, be extrapolated to liquid aerosols, assuming those of the same size and density (1.05 gm./cc.) would be deposited in similar manner. However, the degree of ionization developed in dispersing the liquid aerosol could cause large variation in their collection sites compared with the neutralized particle used in this study. Ionization is a function not only of atomizing techniques used but also of the solution employed. In addition, antagonistic compounds used as aerosol dispersing agents may cause marked changes in airway constriction or dilation and breathing patterns (Dautrebande, 1962).
These results seem to be supported by the work of others (Hazelhoff, 1951) who concluded that gas apparently flows through the avian lung unidirectionally during both inspiration and expiration. During inhalation, approximately 35% of the air flowing through the primary bronchus is directed through the lung via the dorsobronchi, 4% to the anterior sacs, and 61% directly to the posterior sacs (Zeuthen, 1942). The lung clears into the anterior sacs via the ventrobronchi. On exhalation, 65% of the expired gas passes through the lung from the posterior sacs; the remainder passes directly out the primary bronchus and trachea; and that gas in the anterior sacs clears via the ventrobronchi, primary bronchus, and trachea.
Special thanks are given to Michael J. McEwan, Department of Nuclear Engineering, Kansas State University for the radioactive labeling of the aerosol used in this study.
ACKNOWLEDGEMENTS
REFERENCES Anderson, D. P., F. L. Cherms and R. P. Hanson, 1964. Studies on measuring environment of turkeys in confinement. Poultry Sci. 42: 305-318. Boecker, B. B., F. L. Agrilar and T. T. Mercer, 1964. The design of a canine inhalation exposure apparatus incorporating a whole body plethysmograph. AEC. Res. & Develop. Rpt. LF-16, Lovelace Foundation, Alburquerque, N.M., 60 p. Bogen, D. C , 1970. Preparation of radioactive-labeled poly strene latex monodispersed submicron aerosols. Amer. Ind. Hyg. Assoc., May-June: 349-352. Dautrebande, L., 1962. Microaerosols. Academic Press, New York, N.Y., pp. 291-353.
Downloaded from http://ps.oxfordjournals.org/ at University of Ulster at Coleraine on April 12, 2015
effect of interception, interception appeared to be the dominant collection mechanism because the capture of the 1.1-micron particles increased as the trachea bifurcated to form the primary bronchi. Those particles not captured in the lung region passed to the abdominal sacs and were captured— probably by inertia—on the walls of the sacs as the airstream reversed direction when the bird exhaled. The capture 0.3-micron particles—those least affected by the collection mechanisms (Whitby and Lundgren, 1965)—in the respiratory system was difficult to predict. There probably was deposition in the upper tract (Figure 3c). It may be assumed that during expiration, the free aeorsol in the posterior sacs passed predominantly through the lung and partially back out the primary bronchi and trachea, resulting in some particle capture. Those particles previously entering the lungs, but not captured, were transported to the anterior sacs (including the cervicals parallelling the trachea). Therefore, high particle concentration in that area was expected. In addition, any particles not captured in the anterior sacs probably were captured when they were exhaled back out the primary bronchi and trachea.
PARTICLE DEPOSITION IN RESPIRATORY TRACT
Service, U.S. Department of Agriculture ARS 45-2: 91-95. McLeod, W. M., D. M. Trotter and J. W. Lumb. 1964. Avian Anatomy. Burgess Publishing Co., Minneapolis, Minn., pp. 47-56. Whitby, K. T., and D. A. Lundgren, 1965. Mechanics of air cleaning. Trans. A.S.A.E. 8: 342-344, 351352. Whitby, K. T., and B. Y. H. Liu, 1968. Polystyrene aerosols—electric charge and residue size distribution, Atmos. Environ. 2: 103-116. Wolfe, R. R., D. P. Anderson, F. L. Cherms and W. E. Roper, 1968. Effect of dust and ammonia air contamination on turkey response. Trans. A.S.A.E. 11:515-522. Zeuthen, E., 1942. The ventilation of the respiratory tract in birds. Kgl. Danske Videnskab Selskub Biol. Medd. 17: 1-50.
The Influence of Breed and Sex on Live Performance, Dressing and Yield of Meat from 12-Week Old Broilers ABUL WAHIDf. T . K . MuKHERJEEft AND SYED jALALUDINf
(Received for publication November 16, 1973)
ABSTRACT The performance of four purebred and four crossbred broilers were compared in regard to their dressing and ready-to-cook percentages of live weight and yield of edible cooked meat. Analysis of variance of the eviscerated carcass weight showed a highly significant difference due to progeny groups and sex with the purebred Cornish giving the highest yield. The yield of cooked edible meat was also found to be statistically significant among the progeny groups and sex. The meat-to-bone ratio was highest in White Cornish purebred (W.C. 2 x W.C. 6") females and New Hampshire x White Cornish crossbred (N.H. 2 x W.C. <$) females and lowest in White Rock purebred (W.R. 2 x W.R.
INTRODUCTION HE continued growth of the broiler industry in Malaysia has aroused great
T
fPresent Address: Department of Animal Science, Faculty of Agriculture, University of Malaya, Kuala Lumpur 22-11, Malaysia. ttPresent Address: Division of Genetics, School of Biological Sciences, University of Malaya, Kuala Lumpur 22-11, Malaysia.
interest in the type and strain of chickens to be used for obtaining maximum yields in eviscerated and edible meat. Quite a number of researchers in the western countries have reported works dealing with comparisons of meat yields between breeds, strains and crosses of broilers but a thorough review of literature available revealed that practically no work at all has been done in this country to assess the yields of meat in the common
Downloaded from http://ps.oxfordjournals.org/ at University of Ulster at Coleraine on April 12, 2015
Fraser, D. A., R. E. Bales, M. Lippman and H. E. Strokmeyer, 1969. Exposure Chambers for Research in Animal Inhalation. PHS Monograph No. 57. Government Printing Office, Washington, D.C., pp. 30-31. Hazelhoff, E. H., 1951. Structure and function of the lung of birds. Poultry Sci. 30: 3-10. Hinshaw, W. R., 1961. Physical factors that can influence transmission of poultry diseases. Symposium: Disease, Environmental, and Management Factors Related to Poultry Health, Agricultural Research Service, U.S. Department of Agriculture ARS 45-2: 81-85. Horton, J. M., and A. N. Dingle. 1961. The role of air in the transmission of disease. Symposium: Disease, Environmental, and Management Factors Related to Poultry Health, Agricultural Research
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Institute for Environmental Research College of Engineering, and Department of Physiological Sciences, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas 66506 (Received for publication November 16, 1973)
POULTRY SCIENCE 53: 1507-1511, 1974
INTRODUCTION HE physiological effects of dust on man and the control of dust particles in man's environment have been the subject of indepth study (Dautrebande, 1962). Until recently the need for controlled environments to improve the health and production efficiency of domestic animals, including poultry, has been largely ignored. The deposition of inhaled aerosols generally is a function of aerosol concentration in the animal's environment. Viable particle concentrations as high as 2.4 x 105 per cubic meter (m.3) have been measured in poultry units (Anderson et al., 1964). Mass concentrations may be 25 times greater (Wolfe et al, 1968) than those reported in urban atmospheres. Because such viable particulates can cause such diseases as Newcastle, and air sacculitis
T
1. This work was supported in part by the U.S.P.H.S. Training Grant No. 2-T01-EL-0024-06; and the Kansas Agricultural Experiment Station. Contribution number 121, Department of Physiological Sciences, Kansas Agricultural Experiment Station, Kansas State University, Manhattan, Kansas 66506.
(Anderson et al., 1964; Hinshaw, 1961; Horton and Dingle, 1961), acceptable environmental conditions in animal rooms cannot be maintained without controlling airborne particles. Moreover, knowledge of the regional deposition of such particles in the respiratory tract might allow us not only to characterize toxicity of the contaminants but also to design optimal air-cleaning equipment. Those considerations were the basis for this study. MATERIALS AND METHODS Animals. Thirty adult, fasted, anesthetized Single Comb White Leghorn roosters—six for each particle size—averaging 2.03 ± 0.05 kg. body weight were used. To measure respiratory frequency and volume, we suspended each bird in an upright posture (Figure 1) in a plexiglas, whole-body plethysmograph (modified after Boecker et al., 1964). At the end of each experiment, the bird was euthanatized (I.V., sodium pentobarbital) and the plethysmograph calibrated. To detect the inhaled, radioactive aerosol externally for each of seven, equal-length sections along the axis of the body (Figure 2), we used a lead shielded Na-I scintillation detector (Harshaw Scientif-
1507
Downloaded from http://ps.oxfordjournals.org/ at University of Ulster at Coleraine on April 12, 2015
ABSTRACT Thirty anesthetized, male White Leghorn chickens, approximately six months old (average body weight, 2.030 ± 0.048 kg.), individually inhaled radioactively labeled (1-128) monodispersed latex particles. Six birds each were exposed to one of five particle sizes (0.091, 0.176, 0.312, 1.1, and 3.7 to 7 microns). During exposure, the respiratory rate and tidal volume were monitored by a whole-body plethysmograph. Inhaled aerosol was detected externally for each of seven, equal-length sections along the axis of the body. Percentages of deposition for each section were calculated from the corrected time-decay activity. Significant differences (P < 0.05) were found for regional deposition as a function of particle size. The largest particles (3.7 to 7 |x.) were captured in the head and anterior trachea; other particles were deposited uniformly throughout the remainder of the system. The 1.1-micron-size particles were deposited primarily in the lung and posterior air sacs; those of 0.312-microns (having weak interception, impaction, and diffusion-capture mechanisms) tended to pass through the posterior to the anterior sacs (assuming the Hazelhoff-Bethe gas pathway theory); and smallest particles, influenced by diffusion, were captured in the birds' caudal regions.
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R. B. HAYTER AND E. L. BESCH
ic, Model 12 SW12W4). The time-decay corrected activity for each section of the bird gave a relative estimate of the aerosol concentration for that section. Aerosol. Five discrete particle sizes were used: 0.091, 0.176, 0.312, 1.1, and 3.7 to 7 microns. 2 A polymerized layer of iodine on the particle surfaces allowed radioactive la-
beling of the particles by neutron bombardment (Bogen, 1970). The labeled particles were atomized (Fraser et al., 1969), deionized (3M Model 7330, Whitby and Liu, 1968), and carried in the airstream to the plenum, which was at or near ambient barometric pressure. The bird was allowed to breath for 30 minutes through a demand-actuated unidirectional valve from the plenum.
2. Polystyrene latex spheres; Diagnostic Products, Dow Chemical Company, Indianapolis, Indiana 46206.
Particle Capture. Four principles of collecting (Whitby and Lundgren, 1965) or capturing
Downloaded from http://ps.oxfordjournals.org/ at University of Ulster at Coleraine on April 12, 2015
FIG. 1. Whole body plethysmograph containing bird. The animal breathed radioactive particles from the plenum through the mask (arrow). Insert shows detail of the mask.
PARTICLE DEPOSITION IN RESPIRATORY TRACT
particles mechanically are identified: /. Straining: important for large particles (larger than used in this study); 2. Inertial impaction: involves heavy particles that tend to leave the airstream and impact with an obstacle; 3. Interception: involves large-diameter particles that pass within less than one radius from the obstacle; and 4. Diffusion: affects small particles diverted by bombardment of gas molecules; their random path may cause the particles to come in contact with obstacles.
branous flap covered with many small feathers (McLeod et al., 1964) and also mucous membrane-covered turbinate bodies that have a large surface area relative to that of the nostril opening. Quite likely impaction and interception on the turbinates, the feather-covered membrane flap, the cranial larynx, and the mucous-covered walls of this area all entrapped particles 3.7 to 7.0 (JL. in size. On the other hand, for particles of 1.1 (JL. or less (Figure 3b), which tend to follow streamlines around obstacles (Whitby and Lundgren, 1965), inertial impact had markedly less influence. Though that reduced the
Least affected by such mechanisms are the 0.3-micron particles (too small to be influenced by impaction and interception and to large to be diffused). RESULTS AND DISCUSSION The largest particles (3.7 to 7 microns), were deposited primarily in the anterior portion of the respiratory system (Figure 3a); the remainder of the particles were distributed equally throughout the rest of the system. Thus, most particles were deposited in the vicinity of the cranial larynx, on the cranial end of the trachea where the diversion of the airstream could have caused increased impaction and interception of the large particles. The avian nasal cavity contains a mem-
FIG. 3. Relative deposition of particles in various body sections (Figure 2). Similar crosshatching in adjacent sections show nonsignificant differences in relative deposition (P > 0.05). Number at the top of each column of the histogram shows average percent of total body deposition for that section.
Downloaded from http://ps.oxfordjournals.org/ at University of Ulster at Coleraine on April 12, 2015
Fio. 2. The seven anatomical sections of the bird. The use of an appropriately constructed plexiglass mold permitted similar positioning, by section, for each animal.
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R. B. HAYTER AND E. L. BESCH
Diffusion appears to have been the primary collection mechanism for the two smallestsize particles (Figure 3d and 3e). For the 0.176-micron diameter particles, diffusion increased at the syrinx, where the airstream velocity dropped. Reduced concentrations in the airstream resulted in reduced particle capture in the caudal areas of the bird. Most 0.91-micron particles avoided capture until they reached the extremely low-velocity areas of the posterior sacs, where diffusion caused their capture. These results could, under certain conditions, be extrapolated to liquid aerosols, assuming those of the same size and density (1.05 gm./cc.) would be deposited in similar manner. However, the degree of ionization developed in dispersing the liquid aerosol could cause large variation in their collection sites compared with the neutralized particle used in this study. Ionization is a function not only of atomizing techniques used but also of the solution employed. In addition, antagonistic compounds used as aerosol dispersing agents may cause marked changes in airway constriction or dilation and breathing patterns (Dautrebande, 1962).
These results seem to be supported by the work of others (Hazelhoff, 1951) who concluded that gas apparently flows through the avian lung unidirectionally during both inspiration and expiration. During inhalation, approximately 35% of the air flowing through the primary bronchus is directed through the lung via the dorsobronchi, 4% to the anterior sacs, and 61% directly to the posterior sacs (Zeuthen, 1942). The lung clears into the anterior sacs via the ventrobronchi. On exhalation, 65% of the expired gas passes through the lung from the posterior sacs; the remainder passes directly out the primary bronchus and trachea; and that gas in the anterior sacs clears via the ventrobronchi, primary bronchus, and trachea.
Special thanks are given to Michael J. McEwan, Department of Nuclear Engineering, Kansas State University for the radioactive labeling of the aerosol used in this study.
ACKNOWLEDGEMENTS
REFERENCES Anderson, D. P., F. L. Cherms and R. P. Hanson, 1964. Studies on measuring environment of turkeys in confinement. Poultry Sci. 42: 305-318. Boecker, B. B., F. L. Agrilar and T. T. Mercer, 1964. The design of a canine inhalation exposure apparatus incorporating a whole body plethysmograph. AEC. Res. & Develop. Rpt. LF-16, Lovelace Foundation, Alburquerque, N.M., 60 p. Bogen, D. C , 1970. Preparation of radioactive-labeled poly strene latex monodispersed submicron aerosols. Amer. Ind. Hyg. Assoc., May-June: 349-352. Dautrebande, L., 1962. Microaerosols. Academic Press, New York, N.Y., pp. 291-353.
Downloaded from http://ps.oxfordjournals.org/ at University of Ulster at Coleraine on April 12, 2015
effect of interception, interception appeared to be the dominant collection mechanism because the capture of the 1.1-micron particles increased as the trachea bifurcated to form the primary bronchi. Those particles not captured in the lung region passed to the abdominal sacs and were captured— probably by inertia—on the walls of the sacs as the airstream reversed direction when the bird exhaled. The capture 0.3-micron particles—those least affected by the collection mechanisms (Whitby and Lundgren, 1965)—in the respiratory system was difficult to predict. There probably was deposition in the upper tract (Figure 3c). It may be assumed that during expiration, the free aeorsol in the posterior sacs passed predominantly through the lung and partially back out the primary bronchi and trachea, resulting in some particle capture. Those particles previously entering the lungs, but not captured, were transported to the anterior sacs (including the cervicals parallelling the trachea). Therefore, high particle concentration in that area was expected. In addition, any particles not captured in the anterior sacs probably were captured when they were exhaled back out the primary bronchi and trachea.
PARTICLE DEPOSITION IN RESPIRATORY TRACT
Service, U.S. Department of Agriculture ARS 45-2: 91-95. McLeod, W. M., D. M. Trotter and J. W. Lumb. 1964. Avian Anatomy. Burgess Publishing Co., Minneapolis, Minn., pp. 47-56. Whitby, K. T., and D. A. Lundgren, 1965. Mechanics of air cleaning. Trans. A.S.A.E. 8: 342-344, 351352. Whitby, K. T., and B. Y. H. Liu, 1968. Polystyrene aerosols—electric charge and residue size distribution, Atmos. Environ. 2: 103-116. Wolfe, R. R., D. P. Anderson, F. L. Cherms and W. E. Roper, 1968. Effect of dust and ammonia air contamination on turkey response. Trans. A.S.A.E. 11:515-522. Zeuthen, E., 1942. The ventilation of the respiratory tract in birds. Kgl. Danske Videnskab Selskub Biol. Medd. 17: 1-50.
The Influence of Breed and Sex on Live Performance, Dressing and Yield of Meat from 12-Week Old Broilers ABUL WAHIDf. T . K . MuKHERJEEft AND SYED jALALUDINf
(Received for publication November 16, 1973)
ABSTRACT The performance of four purebred and four crossbred broilers were compared in regard to their dressing and ready-to-cook percentages of live weight and yield of edible cooked meat. Analysis of variance of the eviscerated carcass weight showed a highly significant difference due to progeny groups and sex with the purebred Cornish giving the highest yield. The yield of cooked edible meat was also found to be statistically significant among the progeny groups and sex. The meat-to-bone ratio was highest in White Cornish purebred (W.C. 2 x W.C. 6") females and New Hampshire x White Cornish crossbred (N.H. 2 x W.C. <$) females and lowest in White Rock purebred (W.R. 2 x W.R.
INTRODUCTION HE continued growth of the broiler industry in Malaysia has aroused great
T
fPresent Address: Department of Animal Science, Faculty of Agriculture, University of Malaya, Kuala Lumpur 22-11, Malaysia. ttPresent Address: Division of Genetics, School of Biological Sciences, University of Malaya, Kuala Lumpur 22-11, Malaysia.
interest in the type and strain of chickens to be used for obtaining maximum yields in eviscerated and edible meat. Quite a number of researchers in the western countries have reported works dealing with comparisons of meat yields between breeds, strains and crosses of broilers but a thorough review of literature available revealed that practically no work at all has been done in this country to assess the yields of meat in the common
Downloaded from http://ps.oxfordjournals.org/ at University of Ulster at Coleraine on April 12, 2015
Fraser, D. A., R. E. Bales, M. Lippman and H. E. Strokmeyer, 1969. Exposure Chambers for Research in Animal Inhalation. PHS Monograph No. 57. Government Printing Office, Washington, D.C., pp. 30-31. Hazelhoff, E. H., 1951. Structure and function of the lung of birds. Poultry Sci. 30: 3-10. Hinshaw, W. R., 1961. Physical factors that can influence transmission of poultry diseases. Symposium: Disease, Environmental, and Management Factors Related to Poultry Health, Agricultural Research Service, U.S. Department of Agriculture ARS 45-2: 81-85. Horton, J. M., and A. N. Dingle. 1961. The role of air in the transmission of disease. Symposium: Disease, Environmental, and Management Factors Related to Poultry Health, Agricultural Research
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