Document Type: Original Article


1 Department of Physiology, School of Medicine, Lorestan University of Medical Sciences, Khoramabad, Iran

2 Department of Clinical Studies, Faculty of Veterinary Medicine, Lorestan University, Khorram Abad, Iran


Objective- The objective of the present study was to define electrocardiographic data following intranasal administration of diazepam, midazolam and xylazine with or without Ketamine in Chough.
Design- To determine the heart effects of anesthetics in intranasal administration, an experimental in vivo study was employed.
Animals- Ten healthy Choughs were examined in the current study
Procedures- After intranasal administration of diazepam, midazolam and xylazine with or without Ketamine, electrocardigorams were recorded by a direct writing electrocardiograph. Then the heart rate, durations (seconds - s) and amplitude (millivolts - mv) of the P wave, QRS complex and T wave all measured in the bipolar II derivation
Results- There was a normal sinus rhythm after application of all drugs or combinations. The range of the heart rate of the birds was from 93 to 321 beats/min. The P wave was always positive in all recorded leads after administration. During anesthesia or sedation with all drugs, the T wave was positive in leads I, II, III and aVF and negative in leads aVR, and aVL. The amplitude and duration of P, QRS and T waves were changed after intranasal administration of all drugs or combinations.
Conclusion and Clinical Relevance- Based on the electrocardiographic hjfindings it seems that the xylazine is not a suitable drug to induce sedation and anesthesia of choughs via intranasal administration. Therefore, xylazine must be used for birds when its antagonists are accessible.


Main Subjects


Destruction of the wild animals’ habitat and consequent decrease in their popula­tion has stimulated studies regarding the acquisition of physiological and clinical data of wild species to help their survival in the nature .1Chough (Pyrrhocorax pyrrhocorax) like many wild animals has also suffered from environmental alterations.2 Anesthesia has been used to reduce stress during handling, capture, transport and surgery.3 Because of the proper anatomy and physiology of birds that greatly complicates anesthetic risk, anesthetizing a bird should never become a procedure to be taken easily.4 Monitoring the avian patient during anesthesia is the most critical aspect of the process and appropriate responses to the animal’s physiologic state must be performed correctly.5

Many advances in avian anesthesia are due to the use of better monitoring techniques. In this regard, studies have shown that electrocardiograms (ECG) can be effectively used to monitor the heart during anesthesia in birds. Moreover, to define the homeostatic ba­lance in wild species, information on the cardiac function is one of the important parameter to be achieved.6,7 Besides the difficulty involved in delivering a safe and effective volume, the use of injectable anesthetic agents have many disadvantages such as cardiopulmonary depression, prolonged and violent recoveries.8

The electrocardiogram is used in­creasingly in veterinary medicine as a non­-invasive and auxiliary diagnostic test.9-12 It is a useful method to determine the heart rhythm and frequency supplied by the P-QRS-T deflections of the elec­trocardiogram tracing.13,14 Since information on wild animal cardiac activity is very important and scarce, the objective of the present study was to define electrocardiographic data for Chough following intranasal

administration of diazepam, midazolam and xylazine with or withoutketamine.


Materials and Methods


Ten healthy adult domesticated Choughs (Pyrrhocorax pyrrhocorax) of both genders, weighing from 250 to 220gramswere used. The food management consisted of commercial feed and water ad libitum. The experimental protocol was approved by the Committee of Ethics in Animal Experimenta­tion of the Lorestan University.


Anaesthesia protocols

Each of the birds received seven drug combinations with an interval of one week. Briefly, ketamine (30 mg/kg, Daroupakhsh, Iran), xylazine (8 mg/kg, Daroupakhsh, Iran), diazepam (8mg/kg, Daroupakhsh, Iran), midazolam (8mg/kg, Daroupakhsh, Iran), ketamine –diazepam, ketamine -midazolam and ketamine -xylazine were administered intranasaly using a micropipette (Varipet 4810; Eppendorf, Hamburg, Germany).

In this study, standard bipolar and augmented unipolar leads were recorded. Alligator clip electrodes were attached to the skin at the base of the right and left wings and gastrocnemius muscle of the right and left limbs of the choughs in dorsal recumbence. Electrode gel was rubbed into the skin in the area where the alligator clips were attached to act as a conductive medium agent and thereby decrease the resistance of the skin. Electrocardigorams (ECGs) were recorded by a direct writing electrocardiograph (Kenz 110, Japan).The speed used was 50 mm per second, with voltage calibration of 1 cm for each millivolt (1mV=10mm). Leads I, II, III, aVR, aVL and aVF were recorded. The heart rate, durations (seconds - s) and amplitude (millivolts - mv) of the P wave, QRS complex and T wave all measured in the bi­polar II derivation.3,15,16

Experimental results were expressed as mean ± standard deviation (SD). All data were analyzed by one-way  analysis  of  variance  to  assess  statistical significance  between  experimental  groups  with the computer program SPSS 16.0 for Windows (SPSS, Inc., Chicago, Illinois, USA) and p value less than  0.05 was considered significant.



All of the choughs´ electrocardiograms during anesthesia with drugs are depicted in Figures 1 to 7. The durations


and amplitudes of all waves in lead II are shown in Table 1.

There was a normal sinus rhythm after application of all drugs or combinations (Fig.1-7). The range of the heart rate of the birds was from 93 to 321 beats/min with a mean (±SEM) of 215.7 ± 17.5 beats/min. xylazine and ketamine -diazepam induced the least (93 beats/min)  and the greatest (321 beats/min) heart rates, respectively.

The P wave was always positive in all recorded leads after administration of the used anesthetics. The choughs that received ketamine  and/or diazepam alone had the least P wave amplitudes (0.08 mv) and the other birds that were implicated with ketamine -xylazine and/or ketamine -diazepam showed the highest P wave amplitudes (0.11 mv). The difference between these minimum and maximum values was significant (P≤0.05). The least duration of the P wave (0.024 ± 0.002 sec) was showed during the anesthesia with xylazine which is significantly different from the highest one recorded for ketamine -diazepam (0.032±0.001 sec) (P≤0.05).

Implication of ketamine -xylazine and ketamine -diazepam resulted in the least (0.16 mv) and highest (0.32 mv) amplitudes of QRS waves, respectively. When results compared, significant difference between mean amplitudes of QRS in choughs administered with ketamine -xylazine and ketamine -diazepam was found (P≤0.05). The range of the mean QRS durations was 0.026-0.067 sec in lead II. The mean value for the QRS durations during the anesthesia with ketamine -xylazine (0.067 sec) was significantly higher than the values evaluated for ketamine -midazolam (0.026 sec) (P≤0.05).

During anesthesia with all drugs, the T wave was positive in leads I, II, III and aVF and negative in leads aVR, and aVL.

Comparing between the least (0.21 mv) and highest (0.34 mv) mean T wave amplitudes did not show significant difference. Intranasal administration of Ketamine-xylazine and ketamine-diazepam showed the least and highest mean T wave amplitudes, respectively.

Although ketamine-midazolam and ketamine-diazepam combinations induced the lowest mean duration of the T wave (0.046 sec), ketamine alone and ketamine-xylazine combination resulted in the highest values (0.056-0.06 sec). When compared the maximum and minimum values, significant difference (P≤0.05) between them was obvious.



Electrocardiography has been used to monitor heart rate and rhythm in anesthetized patients.15 Because the myocardium is very sensitive to hypoxia, the ECG can serve as a reliable indicator of the oxygenation of the bird’s myocardium under anesthesia.17To the author’s knowledge, this is the first report about the ECG on anesthetized chough.

In our study, all the birds had a normal sinus rhythm following the anesthesia induced by the intranasal administration of xylazine, diazepam, and midazolam alone or combined with ketamine.

The doses of drugs were chosen according to our previous studies on chough.18 In present study, choughs that received ketamine unexpectedly had significant lower heart rate than birds administered diazepam, midazolam alone or combined with ketamine. Salerno and van Tienhoven ( 1976) reported a dose dependent fall in heart rates following Ketamine administration in chickens.19The fall in heart rate in these birds is contrary to the behavior of ketamine in mammals in which case the drug is known to cause tachycardia.20 It is believed that the increase in the heart rate in animals anaesthetized by ketamine may be due to the action of this agent in the CNS, which causes an overflow of increased electrical activity in the limbic hypothalamic centers of the autonomic nervous system via medullary centers.21 This discrepancy may be due to the different physiological properties between mammals and birds. It has been suggested that Ketamine hydrochloride, a cyclohexamine, is a suitable anesthetic agent for birds, especially for chemical restraint and moderate analgesia for minor surgical and diagnostic procedures.22-25 Ketamine alone is not used in birds because of poor muscle relaxation and spontaneous movement, even at high dosages .26 It is often combined with other drugs to minimize these unwanted side effects. Significant species variation has been shown with ketamine when used in birds. For example, in several raptor species and waterfowl, the ketamine resulted in poor quality chemical restraint and anesthesia.22

Ketamine is generally used in conjunction with other drugs such as diazepam or xylazine to improve the quality of the anesthesia by providing more muscle relaxation or increased analgesia.22 In previous study we showed that intranasal use of xylazine, diazepam, and midazolam alone or combined with ketamine provides reliable sedation in chough.18In this experiment, diazepam - ketamine given to choughs resulted in significant enhanced heart rate when compared with ketamine, xylazine or diazepam - ketamine combination. Maiti et al also reported that the heart rate of white leghorn cockerels that received diazepam – ketamine was significantly higher than the values for birds were anaesthetized by midazolam or xylazine with ketamine.21

The least heart rate in the present study was pronounced during the anesthesia with xylazine. Depression of the heart rate after intravenous administration of xylazine-ketamine in the anaesthetized chickens has been reported .21Xylazine is a non-narcotic, sedative, muscle relaxant and analgesic alpha-2-adrenergic agonists that have been used in wide range of wild and domestic animals and birds.27-30 This agent can cause cardiopulmonary effects such as second-degree heart block, bradyarrhythmias and increased sensitivity to catecholamine-induced cardiac arrhythmias.4 Its cardiopulmonary depressive effects are not compensated by the effects of ketamine.31 Severalmechanisms contribute to the xylazine-induced bradycardia such as decreased sympatheticactivity, inhibition ofnoradrenaline release from sympatheticnerve terminals, direct depression of cardiacpacemaker and conduction tissue,increased vagal tone and direct increasein the release of acetylcholine from parasympatheticnerves in the heart.32 When used in combination with ketamine, thesedative and analgesic effects of xylazine are increased.4

Our results showed that the heart rate following intranasal administration of diazepam and midazolam in choughs was very near to those with ketamine-diazepam and ketamine-midazolam. Like other benzodiazepines, midazolam and diazepam act on the benzodiazepine binding site of GABAAreceptors. When bound they enhance the binding of GABA to the GABAA receptor whichin turn results in inhibition of central nervous system.33 Midazolam with the least cardiopulmonary effects is slightly more potent thandiazepam.8 Intramuscular injection of midazolamhas caused no significant changes in cardiopulmonary function in Canada geese, pigeons and quail .29,34,35

We observed that the P wave was constantly positive during the anesthesia with all agent or combinations. It has been documented that the P wave morphology may vary in the ECG of healthy birds, which is a possible physiologic variation.36,37 Moreover, different morphologies (biphasic, inverted and etc) in P wave have been described in healthy domestic fowls.38Negative P waves may be seen in the ketamine-xylazine induced anesthesia. For example, a negative P wave on lead II in a red-tailed hawk during the anesthesia with ketamine-xylazine has been shown.39

The mean amplitude of the P wave in choughs anesthetized by ketamine-xylazine and ketamine-diazepam was 0.11mv, which is significant higher than values obtained following administration of ketamine and/or diazepam.One of the effects of anesthesia on heart function could be the smaller P waves.15,36,40 The mean duration of the P wave was 0.024- 0.032 sec which is comparable with the value described by Espino et al., who had utilized isoflurane for anesthetizing the buzzards in his study.15 An increase in duration of the P wave has been suggested in biatrial enlargement and birds infected by influenza virus.41

In agree with studies on many avian species (15,37,39,40,42,43,44,45,46-53 ), our findings showed that the QRS polarity was negative in leads I, II, III, and aVF after anesthesia induced by all drugs and combinations. Themaximum (0.32 mv) and minimum (0.16 mv) amplitudes of the QRS were observed in choughs anesthetized with ketamine-diazepam and ketamine-xylazine, respectively.An increased voltage in QRS complexesmay be indicative of heart muscle hypertrophy and developed ascites in birds. 15,47

With all anesthetic agents and combinations utilized here, the T wave was positive in all leads except in leads aVR and aVL. The mean duration (0.046-0.6 sec) and amplitude (0.21-0.34 mv) of the T wave were almost the same as values for buzzard which anesthetized with isoflorane.15 Elevated and peaked T waves can be observed in shocked raptors and after electrocution as a result of hyperkalemia.48 The same T patternhas been demonstrated as a sign of hyperkalemia in ducks.49 If anesthesia is too deep, the T-waves will become smaller and eventually disappear. As the depth further increases, the R-waves will increase in magnitude and S-waves will decrease.50 When we compare our results with reports about other wild birds like buzzard, it will be able to note that the amplitude and duration of T waves and QRS complex was not very weak.15 Based on the electrocardiographic findings that mentioned above and complementary data from our previous study on choughs, it is obvious that the anesthesia with drugs used in this study is not deep. Although we did not record the ECG deflections in conscious choughs, our findings may be used as the first reference values for the ECG parameters in chough. Recording an ECG in undomesticated animals can be a problematic procedure and it may be a source of interferences.15 It has been demonstrated that anesthesia may alter only slightly the values of the ECG.15 Previously, electrocardiographic reference values for wild birds like buzzard and African grey parrots have been established on anesthetized birds.15,43 To choose the best drug for anesthesia in wild animals many parameters must be investigated. Based on the electrocardiographic findings it seems that the xylazine is not a suitable drug to induce sedation and anesthesia of choughs via intranasal administration. Therefore, xylazine must be used for birds when its antagonists such as atipamezole and yohimbine are easily accessible.



This research was supported by grant from Lorestan University. The authors are most grateful to Milad Rostami and Elham Hajitabar for their kind cooperation in Faculty of Veterinary Medicine, Lorestan University.


Conflicts of interest


  1. Diniz AN, da Silva Júnior JR, Guerra PC, Barreto-Júnior RA, Almeida HM, Freire LD, Carlos E. Alves AFR. Electrocardiogram assessment in non-anaesthetized clinically healthy agouti (Dasyprocta primnolopha, Wagler 1831). Pesquisa Veterinária Brasileira. 2013; 33:8-14.
  2. Gray N, Thomas G, Trewby M, Newton SF. The status and distribution of Choughs Pyrrhocorax pyrrhocorax in the Republic. Irish Birds. 2003; 7: 147-156.
  3. Machin KL, Caulkett NA. Evaluation of isoflurane and propofol anesthesia for intraabdominal transmitter placement in nesting female canvasback ducks.. Journal of Wildlife Diseases. 2000; 36: 324–334.
  4. Edling, T.M. Updates in anesthesia and monitoring. In: Harrison, G.I:, Lightfoot, TL (Eds), Clinical Avian Medicine.2006; vol. 2: pp 747—760.
  5. Abou-Madi N. Avian Anesthesia. In Heard DJ (ed): Veterinary Clinics of North America: Exotic Animal Practice. 2001; 4:147-167.
  6.  Bodmer RE, Eisenberg JF,Redford KH. Hunting and the likeli­hood of extinction of Amazonian mammals. Conservation Biology. 1997;  2:460-466.
  7.  Leal IR, Da Silva JMC, Tabarelli M. Lacher Jr TE. Changing the course of biodiversity conservation in the caatinga of northeastern Bra­zil. Conservation Biology. 2005; 19:701-706.
  8.  Ludders JW, Mathews N. Birds. In Thurmon JC, Tranquilli WJ,Benson JG (eds): Lumb and Jones Veterinary Anesthesia 3rd ed. Baltimore, MD, Williams &Wilkins. 1996;  645-669.
  9. Tilley LP. Basic canine and feline electrocardiography. The Canadian Veterinary Journal. 1981; 22:23-24.
  10.  Aptekmann KP, Vailati MCF, Fortuna TOM,  Schwartz DS. Preva­lence of cardiac arrhythmias and conduction disturbances in dogs and cats in Botucatu. Brazilian Journal of Veterinary Research and Animal Science. 2010; 47:371-379.
  11.  Neto GBP, Márcio A, Brunetto MA, Sousa MG, Carciofi AC, Camacho AA. Effects of weight loss on the cardiac parameters of obese dogs. Pesquisa Veterinária Brasileira. 2010; 30:167-171.
  12.  Gava FN, Paulino-Junior D, Pereira-Neto GB, Pascon JPE, Sousa MG, Champion T, Camacho AA. Computerised electrocardiograph in Beagle dogs. Arquivo Brasileiro de Medicina Veterinária e Zootecnia. 2011; 63:317-321.
  13.  Hanton G. & Rabemampianina Y. The electrocardiogram of the Bea­gle dog: reference values and effect of sex, genetic strain, body position and heart rate. Laboratory Animal. 2006; 40:123-136.
  14. Scheer P, Svoboda P, Sepsi M, Janecková K, Doubek J. The electro­cardiographic Holter monitoring in experimental veterinary practice. Physiological Research. 2010; 1:59-64.
  15.  Espino L, Suárez ML, López-Beceiro A, Santamarina G. Electrocardiogram reference values for the buzzard in Spain. Journal of Wildlife Diseases. 2001; 37:680-685.
  16. Çınar A, Belge F, Donmez N, TaA, Selçuk M, Tatar M. Effects of stress produced by adrenocorticotropin (ACTH) on ECG and some blood parameters in vitamin C treated and non-treated chickens. Veterinarski Arhiv. 2006;76, 227-235.
  17. Degernes LA, Kreeger TJ, Mandsager R, Redig PT. Ketamine-xylazine anesthesiain red-tailed hawks with antagonism byyohimbine. Journal of Wildlife Diseases. 1988; 24: 322–326.
  18. Raisi A, Taati M, Rostami M, Hajitabar E. Anesthesia and Sedation in Chough (Pyrrhocorax pyrrhocorax) FollowingIntranasal Administration of Diazepam, Midazolam, Xylazine with or withoutKetamine: Clinical Evaluation. Iranian Journal of Veterinary Surgery. 2016; 11; 2: 23-27.
  19. Salerno A, van Tienhoven A. Comparative biochemistry and physiology. C: Comparative Pharmacology. 1976; 55 :69-75.
  20.  Ajadi RA, Olusa TA, Smith OF, Ajibola ES, Adeleye OE, Adenubi OT, Makinde FA. Tramadol improved the efficacy of ketamine–xylazine anaesthesia in young pigs. Veterinary Anaesthesia and Analgesia. 2009; 36:562–566.
  21.  Maiti SK, Tiwary R, Vasan P,  Dutta A. Xylazine, diazepam and midazolam premedicated ketamine anaesthesia inWhite Leghorn cockerels for typhlectomy. Journal of the South African Veterinary Association. 2006; 77: 12–18.
  22.  Ludders JW, Rode JA, Mitchell GS.Effects of ketamine, xylazine and a combination of ketamine and xylazine in Pekin ducks. American Journal of Veterinary Research. 1989; 50: 245-249.
  23.  BoeverWJ,WrightW. Use of ketamine for restraint and anesthesia of birds. Veterinary Medicine, Small Animal Clinics 1975; 70: 86–88.
  24.  Kittle EL. Ketamine HCL as an anesthetic for birds. Modern Veterinary Practice. 1971; 52: 40–41.
  25. Mandelker L. Ketamine HCL as an anesthetic for parakeets. Veterinary Medicine,Small Animal Clinics. 1972;67: 55–56.
  26. Bigham Sadegh A, Shafiei Z, Mahmoudi T, Shariati E, Bahadoran Sh , Zamani Moghaddam A. Ketamine-xylazine with diazepam or midazolam anesthesiain eagles (Aquila Chrysaetos).Online Journal of Veterinary Research. 2011; 15: 414-419.
  27. Allen JL, Oosterhuis JE. Effect of tolazoline on xylazine-ketamine-induced anesthesia in turkeyvultures. Journal of American Veterinary Medicine Association. 1986; 189:1011-1012.
  28. Ali BH, Silsby JL, el Halawani ME. The effect of magnesium aspartate, xylazine and morphine onthe immobilization-induced increase in the levels of prolactin in turkey plasma. Journal ofVeterinary Pharmacology Therapeutic. 1987; 10:119-126.
  29. Valverde A, Honeyman VL, Dyson DH. Determination of a sedative dose and influence ofmidazolam on cardiopulmonary function in Canada geese. American Journal of VeterinaryResearch. 1990; 51:1071-1074.
  30. Varner J1, Clifton KR, Poulos S, Broderson JR, Wyatt RD. Lack of Efficacy of Injectable Ketamine with Xylazine orDiazepam for Anesthesia in Chickens. Laboratory Animals. 2004; 33:36-39.
  31. Miller, Wendy and Buttrick, Martha. Current Anesthesia Recommendations for Companion Birds.Iowa State UniversityVeterinarian. 1999; 61: 3.
  32.  MacDonald E, Virtamen R.  Review ofthe pharmacology of the medetomidineand detomidine: chemically similar alpha-2adrenoceptor agonists used as veterinarysedatives. In Short C E, Poznak A V (eds),Animal pain (1st edn). Churchill Livingston,London. 1992;
  33.  Skerritt JH, Johnston GA. Enhancement of GABA binding by benzodiazepines and relatedanxiolytics. European Journal of Pharmacology. 1983; 89:193-198.
  34.  Smith J, Muir WW. Cardiopulmonary effects of midazolam and flumazenil in racing pigeons.Veterinary Surgery. 1992; 21:499.
  35. Day TK, Roge CK. Evaluation of sedation in quail induced by use of midazolam and reversed byuse of flumazenil. Journal of American Veterinary Medicine Association. 1996; 209:969-971.
  36. Hassanpour H, Zamani Moghaddam AK, Cheraghchi Bashi M. The Normal Electrocardiogram of Conscious Golden Eagles(Aquila chrysaetos). Journal of Zoo and Wildlife Medicine. 2010; 4:426-431.
  37. Talavera J, Guzma´n MJ, del Palacio MJF, Albert AP, Bayo´n A. The normal electrocardiogram of four species of conscious raptors.Research in Veterinary Science. 2008; 84: 119–125.
  38. Hill JR, Goldberg MJ. P-wave morphology and atrial activation in the domestic fowl .American Journal of Physiology-Regulatory, Integrative and Comparative Physiology. 1980; 239: 483–488.
  39. Burtnick NL, Degernes LA. Electrocardiography on fifty-nine anesthetized convalescing raptors. Raptor Biomedicine. 1993; 20: 111–121.
  40. Edjtehadi M, Rezakhani DVM, Szabuniewicz M. The electrocardiogram of thebuzzard, Buteo buteo. Zentralblatt fuer Veterinaermedizin.Reihe 1977; 24: 597–600.
  41. Mitchell BW, BrughRUGHM. 1982. Comparisonof electrocardiograms of chickens infectedwith viscerotropic velogenic Newcastle diseasevirus and virulent avian influenza virus. American Journal of Veterinary Research. 1982; 43(12):2274-2278.
  42. Casares M, Enders F, Montoya JA. Comparative electrocardiography in four species of macaws (Genera Anodorhynchus and Ara). Journal of Veterinary Medicine. 2000; 47: 277–281.
  43. Nap AMP, Lumeij JT, Stokhof AA.Electrocardiogram of the African grey (Psittacuserithacus) and Amazon (Amazona spp.) parrot. Avian Pathology. 1992; 21: 45–53.
  44. Rodrı´guez R, Prieto-Montan˜a F, Montes AM, Bernal LJ, Gutierrez-Panizo C, Ayala I. The normal electrocardiogram of theunanesthetized peregrine falcon (Falco peregrinus brookei).Avian Diseases. 2004; 48: 405–409.
  45. Sturkie PD, Whittow GC. Sturkie’s Avian Physiology. Academic Press, Amsterdam,Holland. 2000.
  46. Szabuniewicz M, Mcgrady JD. Theelectrocardiogram of the Japanese (Coturnix coturnixjaponica) and Bobwhite (Colinus virginianus) Quail.Zentralblatt fur Veterinarmedizin Reihe. 1974; A 21: 198–207.
  47. Odom TW, Rosenbaum LM, Hargis BM.Evaluation of vectorelectrocardiographicanalysis of young broiler chickens as a predictiveindex for susceptibility to ascites syndrome. Avian Diseases. 1992; 36:78–83.
  48.  Blanko JM. Avian electrocardiography: Acontribution for the practitioner. In Proceedingsof the 1993 European Conference on AvianMedicine and Surgery. European Committee ofthe Association of Avian Veterinarians, Utrecht, The Netherlands 1993; pp. 137–154.
  49. Anderson HT. Hyperpotassemia and electrocardiographicchanges in the duck during prolongeddiving. Acta Physiological Scandinavia. 1975; 63:292–295.
  50. Ritchie B, Harrison G, Harrison L. Avian Medicine:Principles and Applications. Lake Worth, FL:Wingers Publishing. 1994; 1066-1080.