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RESPIRATORY MOVEMENTS OF THE CHICKEN DURINGTHE PARAFOETAL PERIOD

byc. ROMIJN

(Laboratory of Veterinary Physiology, Utrecht)Received June 27, I947

INTRODUCTION.From the work of ROMIJN and Roos (1938) we know that the air space of the hen'segg plays an important part in foetal development. Especially during the last day ofincubation when the chicken has perforated the membranous base of the air chamber andlungventilation has begun, the animal respires from an atmosphere with an extremelyhigh carbon dioxide percentage, (up to 9.11 %) and a very low oxygen percentage (9%or less). During this S.c. parafoetal period the respiration by means of the allantoic vesselsis gradually superseded by real lung ventilation.WINDLE and BARCROFT (1938) state that respiratory movements were never seenbefore the 17th or 18th day (sometimes not before the 19th), although movements of

the muscles involved in respiration appeared very much earlier. From the observationsof these authors on the effect of various amounts of carbon dioxide and oxygen on thegeneral movements of chickens during the second half of the incubation time, we mayconclude that the parafoetal period must be of great physiological importance for theinitiation of a respiratory rythm ofthe animal. The author studied theF development of the respiratory mo-vements during the last day of in-cubation and the results have beencollected in the present communi-cation.METHODS.

A series of 50 eggs of WhiteLeghorn hens were incubated at atemperature of 40 C. At the end ofthe 19th day of incubation someeggs (E) were isolated in a smallincubator at the same temperatureand a small funnel was fixed onthe blunt end of it, after artificial

TL2 0~ ........==

Inc

L,

sperforation of the shell on thatspot. The funnel was connected byFig. 1. Optical registration of fluctuations in pressure in means of narrow, flexible rubberthe air-chamber of the incubated egg. tube to a glass funnel (R), closenwith a very thin rubber membraneof about 0.01 mm thickness and a diameter of about 6 mm. Bij this method the air chamberof the incubated egg is connected with the air in the glass funnel and fluctuations in

From: Physiologica Comparata et Oecologia 1(1): 24-28 (1948)

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- - - - - - - - -

' - - - - ; -1 - - - - A

1 1 ~ . ~ ' 1 ~ ,., \ . ~ I ' I I 1 ' ~ ' (.' II' ,,'I,' .', I ~ , ~ ~ I .-"K!----- ;z /

B C

.-.

D

- - - - - - - - - - - - ------ ( /'E F

Fig. 2. Development of respiratory movements in the hen's embryo.

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25. ROMIJN: PARAFOETAL RESPIRATORY MOVEME:-ITS OF THE CHICKENpressure within the air chamber could be recorded optically. A silvercovered piece ofcoverglass, was fitted on a small segment of the rubber membrane and a beam of lightfrom lamp A, thrown on the mirror reflected by it on the slit of a camera with a cylindricallens (C) and a film of photographic paper (F). A second beam of light from lamp B wasprojected on the same film and was interrupted at regular intervals for time-recordingpurposes. RESULTS.

From the end of the 19th day till the end of the 20th day of incubation when thechicken perforates the egg shell which covers the air chamber, the movements of the embryocould be recorded. Some results have been collected in fig. 2. During the 19th day ofincubation embryonic movements are very rare and only one deflection of the beam oflight could be recorded every 10 minutes.Starting with the 20th day of incubation (A) there is an increase in rythm, though

the movements are still irregular in intensity and frequency. Probably at this momentthe membranous base of the air chamber is perforated by the beak of the animal andit respires directly from the air in the air space, together with the respiration by meansof the allantoic circulation which is still in full development. At this moment of foetaldevelopment lungventilation begins, a situation which is characteristic of the bird'sembryo and not comparable with any stage of development in the respiration of mammalfoetuses.A few hours after the beginning of these movements the rythm is more regular andthe fluctuations in pressure are of the characteristically respiratory type (B). Periodsof great frequency are followed by periods of slower rythm. The great sensitiveness ofthe recording technique could be demonstrated by increasing the speed of the paperfilm (D). The great fluctuations of the zero line coincide with the respiratory movements,the smaller with the heartbeat of the embryo. At this stage of development (19 days and10 hours) respiratory movements have a frequency of about 15 a minute, the heart beatswith a rythm of about 200 in the same space of time. During the following hours therespiratory rythm increases steadily and for some hours the frequency remains relativelyconstant (C). The respiratory movements are interrupted at irregular intervals bymovements of the body of the embryo ( t ) .

At the end of the 20th day of incubation, the frequency becomes faster and faster (E).A rythm of 60 respiratory movements per minute and more is not very rare. Generalmass movements of the embryo are more regular and appear at short intervals and duringthe last hour of the 20th day or at the beginning of the 21st day the movements of thebody are very energetic and frequent. At this stage of development the animal tries tobreak the shell and when succeeding, the fluctuations in pressure stop (F). During thelast minutes of the parafoetal period, when the movements of the body predominate,the respiratory rythm is of such high frequency, that an accurate recording was not verywell practicable. With six other eggs identical results were obtained; the results obtainedwith four of them have been collected in the following table (table J).

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26 C. ROMIJN: PARA FOETAL RESPIRATORY MOVEMENTS OF THE CHICKENTable 1. Development of respiratory movements in the chicken.

I Frequency of respiEgg(Nr) Incubation time ) ratory movements Remarks(per minute)

I!J days 23 hours I 6520 7520 2 min. 8020 15 9420 40 12020 55 15020 62 15020 100" 15020 2 hours 12020 2! " 13020 3 1352

3

4

20202020201919191919

1919191919202020191919191919191919

i 19

3hours

II!hours1314

14 ! "

16In "202123

II! "7 hours8

"9 "

10121313!15

15I I5269

2 -39-104025

3025203550606480I I

1513-1450

so80-2470 -3080--3070-30

th e animal squeaks within the shell

shell still intactth e animal squeaksCO2 content of the ai r in th e chamber 7%

egg shell perforatedth e animal squeaks (lungventilation from the air

chamber)

shell perforatedgeneral movements of the foetusirregular foetal movementsirregular body movements of low frequency.regular body movementsmovements of th e respiratory type, regular; th e

animal squeaks for the first time (Iungventilation I)

respiratory movements very regular, every 10 min.interrupted by squeaking movements. increasing muscular activity of th e chickenCO2 content of the air chamber gas 8.43%th e animal perforates th e shellregular movements of th e respiratory type, th emembranous base of th e air chamber still intact

animal respires from th e ai r in th e air chamber,lungventilationregular respiratory movements, interrupted bysqueakingperiods 0 f high frequency, followed by low activity

incl'easing intenSIty of body movementsperforating of th e shell

D l S C U S S l O ~ .

From the data obtained, some conclusions of general importance in relation to thedevelopment of respiration can be drawn. First of all, respjratory movements exist in thechick before lungventilation is established (eggs 3 and 4), though they are not of theregular type. In the White Leghorn chicken, incubated at a temperature of 40 C they

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27. ROMIJN: PARAFOETAL RESPIRATORY MOVEMENTS OF THE CHICKENcan be demonstrated during the first half of th e 20th day of incubation an d even earlier.From the figures collected in our first communication (1938) on th e composition of thegas in the air chamber (l.c. p. 374) we know that at the end of the 19th day of incubationthere is a sudden increase in CO 2 percentage an d decrease in O2 percentage. At this stageof development the CO 2 content takes up about 5% an d the oxygen content about 15%.As the total gas pressure in th e air chamber will be about atmospheric, the blood in theallantoic vessels is balanced with a gas mixture comparable with the alveolar air ofmammals.

Starting with the end of the 19th breeding day the composition of the gas alters, as aresult of th e increasing metabolism of th e foetus. Th e initiation of regular respiratorymovements during th e first hours of the last two breeding days is in accordance withthese findings. According to \\TINDLE and BARCROFT (1938) all movements are stimulatedby the carbon dioxide.

Perforation of the membranous base of th e air chamber by the beak of the animalshould be considered as a result of the increasing activity of the neck muscles. At thismoment lungventilation begins and the embryo respires directly from th e air in th e airchamber, together with the respiration by means of the allantoic vessels. Stimulationof the respiratory centre by the increasing CO 2 pressure in the blood may be the explan-ation, but there are some facts which are not in accordance with this supposition.First of all, alteration of the CO 2 pressure in the air chamber does not alter thefrequency of respiration worth mentioning. The following experiment was carried outwith an egg during the parafoetal period.

Egg nr. 5, breeding time 20 days, 5 hours; respiratory movements optically recorded,freq. 52/min. Air chamber ventilated with room air of 40 C for 5 minutes. After ventilationthe frequency of respiratory movements was 48/min. (no apnoe I), 20 minutes after stoppingthe ventilation of th e air chamber the CO 2 content of the gas in the air chambertook 4.10% and the respiratory rythm was 50/min.

The respiratory movements did not alter in rythm, though the CO 2 pressure of theaspirated air decreased from about 40 mm Hg to about zero an d afterwards increasedfrom zero to the original level. The reverse may be said about the oxygen pressure.I t seems probable that the chemical regulation of respiration in the chicken at thisstage of incubation is only poorly developed. We must however state that the exact

magnitude of th e tidal air could not be measured with our technique of registration an dour conclusions bear relation only to th e frequency of respiratory movements.

The insensibility of the respiratory centre to chemical stimulation from the aspiratedgases is illustrated by some other experiments.Egg nr. 6, in the small incubator, incubated 20 days; respiratory movements had afrequency of 68/min. A mixture of air and 6% CO 2 was driven through the small incubator(volume = 2 liter), replacing the normal air in it. Th e respiratory rythm of th e animaldid not alter during this experiment and after ventilating the incubator with 8 litersof the gas mixture (for 20 minutes) the frequency of respiratory movements was only72/min. [\ow, the gas volume of the incubator was quickly replaced by fresh room air(in 4 minutes) and the respiratory rythm continuously recorded. No alteration couldpu t on record, the frequency remained 68/min. an d did not change before the animalperforated the hard egg shell.

Perforation of the shell is another important moment in foetal development, especiallywhen the small window in th e shell is large enough to allow a gas exchange between th eair chamber and the incubator. A sudden fall in CO 2 content and consequent rise in O2content of the gas in the air chamber must result an d when the chemical regulation ofrespiration in the embryo should have its full development an apnoe would occur. Tocheck this supposition, the small window made by the embryo was enlarged artificiallyimmediately after perforation, and the respiratory movements of the animal observedwith the eye. In no case apnoe could be stated, the respiratory rythm was about the

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28 c. ROMIJN: PARA FOETAL RESPIRATORY MOVEMENTS OF THE CHICKENsame as before shell perforation, though general movements of the neck and other partsof the foetus were less frequent during some time.

We put another egg in an atmosphere of 40 C, containing 7% CO2, 12% O2 and81 % N2, a few minutes after perforation of the shell by the embryo. Hatching stated quitenormally, the chicken was completely free from the shell about 3 hours after the firstperforation and the respiratory movements had a frequency of fi8/min. shortly afterbirth. Brought under normal conditions the respiratory rythm did not alter and was fixedat GO/min. for about 15 minutes. When the animal is pu t back into the first gas mixturethe respiratory frequency does not change, no dyspnoe was observed. The same chicken,24 hours old, placed in an atmosphere containing 7% CO2, 12% O2 and 81 % N2, producesa distinct dyspnoe and the conclusion seems justif ied that has no effect on respiratoryactivity of the chicken during the parafoetal period and during the first hours after birth.To what extent the low oxygen percentage of the ai r chamber gas will be of importancefor the development of anoxaemia, consequently for the normal development of thewhole animal in general, is the subject of further research. It will be of importancein this connection to know the influence of CO2 on the O2 combining power of thechicken's blood.Moreover it is noteworthy to mention the redundance of the curious gas phase inthe air chamber for normal developm('nt. From three eggs, the ai r chambers of whichwere opened on the 12th day of incubation, two produced a normal chick; removal of theshell from the air chamber on the 17th breeding day in three other eggs did not preventnormal hatching. The chickens have grown up in the laboratory to normal 'White Leghornhens.

SUMMARY.The respiratory movements of the chicken during the last day of incubation (parafoetalperiod) have been recorded optically. The changes in respiratory activity before and after

the shell perforation have been described and the influence of CO 2 on it discussed.RESUME.

Les mouvements respiratoires du poussin pendant Ie dernier jour de la couvaisonont etc ctudics. L'activite de la respiration avant et apres la perforation de la coquilleet l'influence du CO2 on t ete discutees.

LITERATURE.ROMIJN, C. & Roos, J., 1938. The air space of the ben's egg and its changes during th e period of in-

cubation. J. Physiol., 94: 365-379.W I N D L E , W. F. & BARCROFT, J., 1938. Some factors governing the initiation of respiration in the chick.

A mer. J. Physiol., 121: 684-699.