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Evidence for Genetic Variation in Resistance to a Respiratory Infection in Chickens
Evidence for Genetic Variation in Resistance to a Respiratory Infection in Chickens I. M I C H A E L L E R N E R AND L E W I S W.
TAYLOR,
Division of Poultry Husbandry AND BEACH*
Department of Veterinary Science, University of California, Berkeley (Received for publication April 25, 1950)
/ ^ * E N E T I C differences in resistance to ^ - * different infectious diseases of chickens have been extensively studied by a large number of investigators. Since Hutt (1949) has recently reviewed the field it is not necessary to cover the same ground here, except to list the particular diseases for which genetic information is available. They include avian diphtheria (Frateur, 1924), fowl typhoid (Lambert and Knox, 1932), pullorum (Roberts and Card, 1935), and lymphomatosis (Asmundson and Biely, 1932; Taylor, Lerner, DeOme and Beach, 1943; Hutt and Cole, 1948; and many others). Although the various respiratory diseases to which chickens are subject are extremely common in the field, so far apparently no demonstration of genetic variation in resistance to any of them has appeared in the literature. The purpose of the present report is to record the evidence for the existence of such variation in the University of California flock of Single Comb White Leghorns. This flock has been maintained by the Division of Poultry Husbandry for approximately twenty years in a relatively isolated canyon which is a part of the Berkeley campus of the University. Also * Now at College of Agriculture, Davis.
in this canyon at a distance of 0.3 mile from the poultry plant are the buildings of the Department of Veterinary Science at which extensive experimental work on poultry diseases, including those affecting the respiratory organs, has been pursued throughout this time. The precautions taken to prevent spread of infectious diseases (particularly the method of handling birds used in disease experiments at Veterinary Science, avoidance of all unnecessary intercourse between the personnel of Veterinary Science and Poultry Husbandry, barring entrance of visitors to pens containing poultry, and adherence by Poultry Husbandry to the policy of making additions to its flock only with hatching eggs) sufficed to keep the experimental flock in question free of infectious disease other than lymphomatosis and coccidiosis from 1932 to 1949, when the disease discussed herein spontaneously appeared. During this 17-year period the flock has shown no clinical evidence of any infection, other than mentioned above, nor was any detected by the systematic laboratory examination made at Veterinary Science of all removals from the Poultry Husbandry flock by death or culling. 862
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J. R.
GENETIC VARIATION IN RESISTANCE TO RESPIRATORY INFECTION
863
DESCRIPTION OF THE DISEASE gling or loud shrill rales. The data given On September 23, 1949, an attendant in Table 1 show the distribution of the reported the presence of respiratory symptoms and course of the disease symptoms in a few of 106 caged layers in through this group of chickens. The experimental units of Row A. That eve- attitude of the birds remained good but ning one of us (L. W.T) inspected the entire there was a decline in feed consumption. plant and detected coughing and rales in There were no deaths. The birds were one pullet of a house in Row H (the one laying too few eggs to enable definite farthest removed from Row A), and in observation of the effect of the disease on several birds in Row F. The number of egg production. Thirteen of the 106 birds clinical cases increased rapidly and within^apparently escaped the infection.
Sept. 26
Sept. 28
Sept. 30
Oct. 3
nadc* only,
34
55
31
6
40 birds had nasal discharge only
dyspf only,
32
30
1
0
9 birds had dyspnea only
nadc and dysp,
15
8
0
0
no symptoms,
25
13
74
100
The nasal discharge tended to persist longer than the dyspnea 13 birds shows no symptoms at any time. There were no deaths
Date of examination Birds with number Birds with number Birds with number Birds with number
Remarks
* nadc=nasal discharge. t dysp=dyspnea, cough, rales.
a week birds with symptoms could be found in practically all houses and pens. The disease spread in a "hit and miss" fashion rather than by contiguity or the route of travel followed by attendants. In fact the birds in Row A, the first affected, were under the complete care of an attendant who at no time entered another house or had contact with any other birds. The outbreak ran a rapid course and by October 7,1949, two weeks after the onset visible recovery of the flock was nearly, complete. The recovery of individuals was likewise complete, there being found only two birds which were removed as hopeless cases because of chronic involvement of the nasal sinuses. The symptoms and course of the disease were best observed in the caged layers of Row A which could easily be examined individually. They consisted of nasal discharge, dyspnea, coughing, and gur-
General observation showed that the disease ran a similar course among groups of birds on the floor. Dyspnea and rales were the most prominent symptoms observed in these groups, perhaps because a nasal discharge could not be readily detected without individual examination of the birds. For example, among the pullets in Row H on September 30 there were numerous birds having dyspnea and loud rales or coughing, but few with a nasal discharge could be detected. On October 3 respiratory difficulty was less prominent but a few droopy birds were noted. By October 7 the flock appeared to have almost completely recovered so far as the respiratory disturbances were concerned. It may be noted that within a week of the first appearance of symptoms in a pen, feed consumption declined severely and normal appetite was not regained for at least a week thereafter.
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TABLE 1.—The distribution and duration of respiratory symptoms in 106 caged pullets in row A
864
I. MICHAEL LERNER, LEWIS W. TAYLOR AND J. R. BEACH
and incubated in an atmosphere containing 10 percent carbon dioxide. Practically pure cultures of an organism which was DIAGNOSIS morphologically like Hemophilus galliUnfortunately there were no chickens narum were obtained in all plates inocuon hand which were suitable for use in lated with the nasal or tracheo-bronchial attempts at artificial transmission at the exudate of several of the diseased chickonset of the outbreak. By the time a sup- ens. Coryza was produced in baby chicks ply of birds was obtained the outbreak was which were inoculated intranasally with so nearly terminated that suitable ma- the culture and from them the organism terial for transmission attempts was was readily reisolated in blood agar culnot available. Consequently indirect tures. On the basis of these findings the means had to be employed to differentiate tentative diagnosis was that the disease the disease from, or to identify it as, any was atypical infectious coryza resulting of the four known infectious respiratory from uncomplicated H. gallinarum infecdiseases of chickens, i.e. infectious laryn- tion. The disease may be considered atypigotracheitis, infectious bronchitis, avian cal of coryza in that its spread through the pneumoencephalitis (PE) and infectious flock was so rapid and apparently by incoryza, with each of which it had, direct contact. It was not necessarily symptomatically, something in common. atypical of coryza with respect to its Autopsy of several birds, which were nature, however, since it was of rapid sacrificed, showed only mucous exudate in onset and short duration. This is the type the nasal chambers, trachea, and large of disease which Nelson (1933 a and b, bronchi, and in one case, caseous exudate 1938), states, and Schalm and Beach in the thoracic air sacs. It was differenti- (1936) have observed, is induced by pure ated from laryngotracheitis by the fact cultures of H. gallinarum. It might also that recovered birds were susceptible to be mentioned that one of us (J. R. B.) that virus; from infectious bronchitis by has previously encountered two similar the inability to demonstrate neutralizing outbreaks in flocks from which coryza had antibodies for that virus in the serum of been eradicated by depopulation and recovered birds in tests made with chicken which had been free from the disease embryos; and from avian pneumoencepha- for several years. The source of the infeclitis by the negative results of hemaggluti- tion which precipitated the outbreak nation-inhibition tests using serum of under discussion was and continues to be recovered birds and a good hemagglutinat-, a mystery. ing strain of PE virus, and by the fact that recovered birds proved susceptible THE POPULATION USED LN THE to inoculation with PE virus. Further GENETIC ANALYSIS evidence that none of these three viruses For the purposes of the genetic analysis were involved in the etiology of the disease we shall consider only one row of laying was the failure to isolate any of them in houses (H) which in 1949, as in other embryos inoculated with the nasal and years, contained the bulk of the pullet tracheo-bronchial mucous exudates. To population. The row consists of five check for the presence of infectious double laying pens, two in one, and three coryza, fresh-blood agar plates were in a second house. Approximately 275 streaked with the pathological exudate pullets are placed in each of the double The effects on egg production will be discussed later.
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GENETIC VARIATION IN RESISTANCE TO RESPIRATORY INFECTION
865
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pens at the time of legbanding (about 5 ered to have manifested themselves in months of age). In the fall of 1949 the two approximately the first three weeks of double pens in one house were occupied by October. In addition to the effects on egg pullets originating from eight inbred production, egg quality and hatchability lines (designated as inbreds in Table 3), by following resumption of lay were also offspring of a series of crosses between affected by the disease. These will be these lines (inbred crosses in Table 3), and reported upon separately. by pullets from a line selected for shank PAUSING AS A CRITERION OF length (size in Table 3). The second house RESISTANCE contained the pullets from the productionbred flock and the pullets from lines For the purposes of the present study selected for a high incidence of winter the production records between September pausing and blood-spotting respectively, 26 and October 25 were subjected to as well as those from a cross between the scrutiny. It became apparent immedilatter and the production-bred flock. The ately that the probable effect of the designations of these sub-populations in Table 3 are self-apparent. One of the three double pens in this latter house was divided into two separate units. In this manner it was possible to carry out a subsidiary nutritional test, by providing two different diets to the two groups of birds ( 1 | pen in each) in this house. Birds carrying odd numbered SEPTEMBER OCTOBER wing bands were assigned to one group, FIG. 1. Daily percent production. and those with even numbered wingbands to another. Thus the populations on the two different diets were randomized with disease was not in reducing the rate of respect to origin. The difference between production of laying birds, but rather in the two diets consisted in one ingredient complete cessation of production of most only, and since, as it will be shown later, birds previously in lay. Thus the presence the diet had no effect on the incidence of of a pause of an arbitrary number of the disease in question, this difference is consecutive non-laying days (selected as irrelevant for the present discussion. 10) within the designated period sugFigure 1 illustrates the daily percentage gested itself as a criterion of susceptibility production for the whole population of to the disease. No claim, of course, is pullets considered. It may be seen that the made that all birds exhibiting such pause normal seasonal increase in gross rate of were clinical cases of the disease. It may lay, apparent in the extreme left of the be recalled, however, that a certain procurve, was checked very early in October. portion of the birds in the A row (13 out This was followed by a precipitous drop of 106) failed to exhibit any respiratory in production which reached its floor in symptoms. Thus, the birds which did not the middle of October, whereupon the pause may have been either escapes or trend was reversed and gradual recovery resistant to disease in the sense of being initiated. The main effects of the disease able to maintain production after infecon egg production may be thus consid- tion. In either event specific definition of
866
I. MICHAEL LERNER, LEWIS W. TAYLOR AND J. R. BEACH
TABLE 2.—Percentage distribution in the production-bred flock Year Total birds banded a. Immature on 9/26 b. In pause on 9/26 c. Died before 9/26 d. Died 9/26-10/25 e. Affected f. Unaffected g. Affected as percent of sample*
1948
1949
549 8.2 4.9 2.7 1.1 5.3 77.8
625 17.3 1.9 2.1 3.5 71.2 4.0
6.4
94.7
computations of pausing incidence. A further question arose with respect to the birds which died in the course of the period between September 26 and October 25. These will be considered further in the discussion to follow.
In order to make certain that the pausing behavior in 1949 was, indeed, related to the presence of the disease in the flock, a comparison was made between pause incidence in the production-bred flock in that year and in 1948. The distribution of pullets in different categories is shown in Table 2. Whereas 5.3 percent of all birds paused in 1948, 71.2 percent did so in 1949. The difference becomes even more extreme (largely due to the later sexual maturity of the 1949 flock) when only the birds in lay on September 26 are considered. If we also exclude the birds dying in the subsequent 30 days, the comparative percentage incidence of pausing is 6.4 and 94.7 for 1948 and 1949. The odds on the reality of this difference are, of course, astronomical. COMPARISON BETWEEN LINES
Having thus satisfied ourselves that pausing is at least a reasonable criterion of some form of susceptibility to the respiratory disease in the flock, comparison of pausing incidence between different lines was undertaken. The results are presented in Table 3. The last two lines of the table are complementary to each other. It may be seen that the range of incidence of pausing in the different lines extended from 86 to 100 per cent. Whether or not the differences between the lines are sig-
TABLE 3.—Distribution of birds in different lines
Line or cross
Total birds banded (Immature on 9/26 Birds excluded 1 In pause on 9/26 from sample] Died before 9/26 (Died 9/26-10/25 Birds in sample Birds affected Birds unaffected Percentage unaffected Percentage affected
Production 625 108 12 13 22 470 445 25 5.32 94.68
Inbreds 245 158 11 7 5 64 61 3 4.69 95.31
Inbred crosses 213 99 10 3 1 100 86 14 14.00 86.00
Size
104 72 2 4 3 23 22 1 4.35 95.65
Bloodspots 168 32 6 0 4 126 109 17 13.49 86.51
ProductionX Winter Total blbod- pause spots 13 3 0 0 1 9 8 1 11.11 88.89
1393 25 485 13 0 41 0 27 2 38 10 802 10 741 61 0 0 7.61 100.00 92.39
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the two types of birds, although of course, desirable, is not possible and actually not essential to demonstrate the genetic differences, the existence of which is indicated here. A more difficult problem is presented by birds which were not in production at the beginning of the period, either because they were still immature or because they were already in winter pause. These individuals, together with any that died before September 26, were excluded from
GENETIC VARIATION IN RESISTANCE TO RESPIRATORY INFECTION
nificant may be best determined by x2 tests, the results of which are shown in Table 4. Since the numbers of pullets in several of the lines are rather small, only the four groups with 50 or more birds in each were included in the first comparison. The x2 was found to be 14.74 which for three degrees of freedom indicates a high prob-
867
including or excluding the birds dying from reproductive disturbances, must be deemed to be highly significant. OTHER COMPARISONS
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It may be recalled that the inbred lines were housed together with the progeny of crosses between them. Similarly the production-bred birds were in the same units as the pullets from the bloodTABLE 4.—Homogeneity tests spot line. The total x2 can then be partitioned to determine if the differences J Comparison made £g£a°' x° P between the lines were due to differences Production, Inbred, Inbred between houses. As it may be seen in Table crosses, Blood-spot 3 14.74 <0.01 As above, including reproduc4, the x2 for the comparison between the tive mortality 3 15.20 <0.01 Production, Blood-spot 1 10.13 <0.01 production and the blood-spot lines is Inbred, Inbred crosses 1 3.64 0.055 Rations 1 0.44 0.5 highly significant (x2 of 10.13), while for Sire families within production line 9 7.66 0.6 the inbred and inbred crosses compairson it only verges on significance (x2 of 3.64). 2 ability that the differences between the Since this leaves a x of only 0.97 between lines compared are significant. In order, houses, it must be concluded that the line however, to make certain that the exclu- differences, in the main contributed to by sion of the birds dying during the period the difference between the production and studied did not unduly affect this conclu- the blood-spot lines, are independent of the differences between disease conditions sion, a second comparison was made. in the two groups of units. Autopsies of the 38 birds dying between The next comparison made was that September 26 and October 25 indicated that the deaths of 14 birds were probably between the two rations and, as the x2 independent of the presence of the respira- of 0.44 convincingly demonstrates, no tory infection. Death was due to lympho- differences in pausing induced by the matosis in four of these, four others died difference in diets appear to be present. of accidental injuries, two had digestive Finally, a comparison between pausing disturbances, one had an involvement of incidences in different sire families within the excretory system, and the remaining the production line was undertaken. As three cases were of a doubtful nature. The shown in the last line of table 4, no signifiremainder of the dead birds, 24 in number, cant differences were found here. In fact, were all characterized by disturbances of an attempt to compute the heritability of the genital system. Whether or not their pausing in this group by the method of death may have been related to the res- Robertson and Lerner (1949) led to a negpiratory disease is of little import, since, ative estimate, indicating smaller variaas shown in the second line of Table 4, tion between sire families than would be the inclusion of such birds together with expected by chance on the average. The their pausing flock-mates did little to significance of the low x8 for the producchange the picture. The x2 here was found tion flock will be commented upon in the to be 15.20 and hence line differences, following section.
868
I. MICHAEL LERNER, LEWIS W. TAYLOR AND J. R. BEACH
THEORETICAL CONSIDERATIONS
The possible argument that what is being dealt with here is a general resistance rather than one specific to the disease which appeared in the flock in September, 1949, is not valid for two reasons. Firstly, should this have been the case, the genetic variability in the production line might have been expected to be of the same magnitude as for the resistance to death in the first year from all causes. This was found by Robertson and Lerner (1949) to lead to a heritability estimate of 0.089 ±0.028, whereas, as noted, in the present case the heritability estimate fell below a value of zero. Secondly, should general vigor have been the sole differential determining presence or absence of pausing, it might have been expected that the group of inbred birds (with an average coefficient of inbreeding of 43.3 percent and lacking vigor by other criteria) would have had a significantly lower percentage of unaffected birds than the productionbred flock. In reality, as shown by the figures in Table 3, this was not the case. It is true, however,that the border-line significance of the difference between the
inbred and the hybrid populations (inbred crosses) suggests that general vigor enhances resistance to the disease, but the fact remains that inbreeding degeneration, a property characteristic of general vigor, is not exhibited by the character under discussion. Since no artificial or natural selection for resistance could have taken place in the 17 years preceding the outbreak of the disease, the only reasonable possibility of finding genetic differences in a population of non-interbreeding isolates, such as represented by the different lines in the flock, would lie in chance differentiation of genotypes. Under such circumstances, absence of genetic differences would not be surprising. Their presence, on the other hand, is no cause of surprise but simply a gratifying accident. It is true that the greatest chance of finding differences in resistance would be in the group of inbred lines, but the numbers available for study within the lines are too small to make this possible. The blood-spot line itself is slightly inbred (average F of 10.02 percent), so that the operation of genetic drift in differentiating it from the production line was somewhat facilitated. The main factor, however, lies in the breeding isolation of this line from the production-bred one. The immediate practical consequences of the material reported upon are not clearly apparent. It is obvious that any attempt at increasing resistance in the production line by selection would be extremely difficult. Added to other complications of breeding for disease resistance when the incidence is close to 95 percent, (see Lush, Lamoreux and Hazel, 1948) is the fact that the genetic variation in this group is at the present not discernible. Migration from the blood-spot line would, of course, be a rather dubious procedure: the superiority of this line in resistance is
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The particularly interesting feature of the results from the genetical standpoint lies in the fact that differences in resistance to the disease, as adjudged by the ability of a bird to continue production in the course of the epidemic described, were found between lines of common origin which differentiated while there was no exposure to this or any other respiratory disease. The blood-spot line originated from the production-bred flock during the period when no direct selection for resistance was practiced or, indeed, was possible. Hence, the genetic differences in resistance cannot be due to adaptation as a result of directed selection, but to chance possession of particular genotypes by the different lines.
ASSOCIATION NOTES
relatively slight, while its blood-spotting tendencies are much greater than in the production-bred line (by a factor of approximately 17 in 1948). SUMMARY
REFERENCES CITED Asmundson, V. S., and J. Biely, 1932. Inheritance of resistance to fowl paralysis (Neurolymphatosis gallinarum) I. Differences in susceptibility. Can. J. Res. 6: 171-175. Frateur, J. L., 1924. The hereditary resistance of the fowl to the bacillus of diphtheria. Proc. 2d World's Poultry Congr., Barcelona: 68-71. Hutt, F. B., 1949. Genetics of the fowl. Xl-f 590 pp. McGraw-Hill. New York.
Hutt, F. B., and R. K. Cole, 1948. The development of strains genetically resistant to avian lymphomatosis. Proc. 8th World's Poultry Congr., Copenhagen, 1: 719-725. Lambert, W. V., and C. W. Knox. 1932. Selection for resistance to fowl typhoid in the chicken with reference to its inheritance. la. Agr. Exp. Sta. Res. Bull. 153: 263-295. Lush, J. L., W. F. Lamoreux and L. N. Hazel, 1948. The heritability of resistance to death in the fowl. Poultry Sci. 27: 375-388. Nelson, J. B., 1933a. Studies of an uncomplicated coryza of the domestic fowl. I. Jour. Exp. Med. 58: 289-295. Nelson, J. B., 1933b. Studies of an uncomplicated coryza of the domestic fowl. n . Jour. Exp. Med. 58: 297-304. Nelson, J. B., 1938. Studies of an uncomplicated coryza of the domestic fowl. IX. Jour. Exp. Med. 67: 847-855. Roberts, E., and L. E. Card, 1935. Inheritance of resistance to bacterial infection in animals. 111. Agr. Exp. Sta. Bull. 419: 467-493. Robertson, A., and I. M. Lerner, 1949. The heritability of all-or-none traits: Viability of poultry. Genetics, 34:395-411. Schalm, O. W., and J. R. Beach, 1936. Studies of infectious coryza with special reference to its etiology. Poultry Sci. 15: 473-481. Taylor, L. W., I. M. Lerner, K. B. DeOme and J. R. Beach, 1943. Eight years of progeny-test selection for resistance and susceptibility to lymphomatosis. Poultry Sci. 22: 339-347.
Association Notes {Continued from page 851)
of the Recommended Nutrient Allowances for Poultry. He is the senior author or co-author of numerous scientific papers dealing with the nutrition of poultry. He is an Associate Editor of POULTRY SCI-
Isabel Karrasch and they have three children.
ENCE.
The Poultry Science Association's Research Prize of one hundred dollars for the outstanding research paper published during the preceding fiscal year of the Association was presented to Dr. Robert J.
In addition to the Poultry Science Association, Professor Cravens is a member of the Chemical Society and the Institute of Nutrition. He was married in 1939 to
POULTRY SCIENCE RESEARCH PRIZE
(Continued on page 873)
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Evidence for genetic differences in specific resistance to a respiratory disease, tentatively diagnosed as atypical infectious coryza resulting from uncomplicated H. gallinarum infection, as measured by the ability to maintain production during an epidemic is presented. Of particular interest is the fact that the flock in which these observations were made was free of any respiratory disturbances for 17 years prior to the outbreak. The demonstrated differences were thus due to chance differentiation of genotypes in non-interbreeding lines.
869
TAYLOR,
Division of Poultry Husbandry AND BEACH*
Department of Veterinary Science, University of California, Berkeley (Received for publication April 25, 1950)
/ ^ * E N E T I C differences in resistance to ^ - * different infectious diseases of chickens have been extensively studied by a large number of investigators. Since Hutt (1949) has recently reviewed the field it is not necessary to cover the same ground here, except to list the particular diseases for which genetic information is available. They include avian diphtheria (Frateur, 1924), fowl typhoid (Lambert and Knox, 1932), pullorum (Roberts and Card, 1935), and lymphomatosis (Asmundson and Biely, 1932; Taylor, Lerner, DeOme and Beach, 1943; Hutt and Cole, 1948; and many others). Although the various respiratory diseases to which chickens are subject are extremely common in the field, so far apparently no demonstration of genetic variation in resistance to any of them has appeared in the literature. The purpose of the present report is to record the evidence for the existence of such variation in the University of California flock of Single Comb White Leghorns. This flock has been maintained by the Division of Poultry Husbandry for approximately twenty years in a relatively isolated canyon which is a part of the Berkeley campus of the University. Also * Now at College of Agriculture, Davis.
in this canyon at a distance of 0.3 mile from the poultry plant are the buildings of the Department of Veterinary Science at which extensive experimental work on poultry diseases, including those affecting the respiratory organs, has been pursued throughout this time. The precautions taken to prevent spread of infectious diseases (particularly the method of handling birds used in disease experiments at Veterinary Science, avoidance of all unnecessary intercourse between the personnel of Veterinary Science and Poultry Husbandry, barring entrance of visitors to pens containing poultry, and adherence by Poultry Husbandry to the policy of making additions to its flock only with hatching eggs) sufficed to keep the experimental flock in question free of infectious disease other than lymphomatosis and coccidiosis from 1932 to 1949, when the disease discussed herein spontaneously appeared. During this 17-year period the flock has shown no clinical evidence of any infection, other than mentioned above, nor was any detected by the systematic laboratory examination made at Veterinary Science of all removals from the Poultry Husbandry flock by death or culling. 862
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J. R.
GENETIC VARIATION IN RESISTANCE TO RESPIRATORY INFECTION
863
DESCRIPTION OF THE DISEASE gling or loud shrill rales. The data given On September 23, 1949, an attendant in Table 1 show the distribution of the reported the presence of respiratory symptoms and course of the disease symptoms in a few of 106 caged layers in through this group of chickens. The experimental units of Row A. That eve- attitude of the birds remained good but ning one of us (L. W.T) inspected the entire there was a decline in feed consumption. plant and detected coughing and rales in There were no deaths. The birds were one pullet of a house in Row H (the one laying too few eggs to enable definite farthest removed from Row A), and in observation of the effect of the disease on several birds in Row F. The number of egg production. Thirteen of the 106 birds clinical cases increased rapidly and within^apparently escaped the infection.
Sept. 26
Sept. 28
Sept. 30
Oct. 3
nadc* only,
34
55
31
6
40 birds had nasal discharge only
dyspf only,
32
30
1
0
9 birds had dyspnea only
nadc and dysp,
15
8
0
0
no symptoms,
25
13
74
100
The nasal discharge tended to persist longer than the dyspnea 13 birds shows no symptoms at any time. There were no deaths
Date of examination Birds with number Birds with number Birds with number Birds with number
Remarks
* nadc=nasal discharge. t dysp=dyspnea, cough, rales.
a week birds with symptoms could be found in practically all houses and pens. The disease spread in a "hit and miss" fashion rather than by contiguity or the route of travel followed by attendants. In fact the birds in Row A, the first affected, were under the complete care of an attendant who at no time entered another house or had contact with any other birds. The outbreak ran a rapid course and by October 7,1949, two weeks after the onset visible recovery of the flock was nearly, complete. The recovery of individuals was likewise complete, there being found only two birds which were removed as hopeless cases because of chronic involvement of the nasal sinuses. The symptoms and course of the disease were best observed in the caged layers of Row A which could easily be examined individually. They consisted of nasal discharge, dyspnea, coughing, and gur-
General observation showed that the disease ran a similar course among groups of birds on the floor. Dyspnea and rales were the most prominent symptoms observed in these groups, perhaps because a nasal discharge could not be readily detected without individual examination of the birds. For example, among the pullets in Row H on September 30 there were numerous birds having dyspnea and loud rales or coughing, but few with a nasal discharge could be detected. On October 3 respiratory difficulty was less prominent but a few droopy birds were noted. By October 7 the flock appeared to have almost completely recovered so far as the respiratory disturbances were concerned. It may be noted that within a week of the first appearance of symptoms in a pen, feed consumption declined severely and normal appetite was not regained for at least a week thereafter.
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TABLE 1.—The distribution and duration of respiratory symptoms in 106 caged pullets in row A
864
I. MICHAEL LERNER, LEWIS W. TAYLOR AND J. R. BEACH
and incubated in an atmosphere containing 10 percent carbon dioxide. Practically pure cultures of an organism which was DIAGNOSIS morphologically like Hemophilus galliUnfortunately there were no chickens narum were obtained in all plates inocuon hand which were suitable for use in lated with the nasal or tracheo-bronchial attempts at artificial transmission at the exudate of several of the diseased chickonset of the outbreak. By the time a sup- ens. Coryza was produced in baby chicks ply of birds was obtained the outbreak was which were inoculated intranasally with so nearly terminated that suitable ma- the culture and from them the organism terial for transmission attempts was was readily reisolated in blood agar culnot available. Consequently indirect tures. On the basis of these findings the means had to be employed to differentiate tentative diagnosis was that the disease the disease from, or to identify it as, any was atypical infectious coryza resulting of the four known infectious respiratory from uncomplicated H. gallinarum infecdiseases of chickens, i.e. infectious laryn- tion. The disease may be considered atypigotracheitis, infectious bronchitis, avian cal of coryza in that its spread through the pneumoencephalitis (PE) and infectious flock was so rapid and apparently by incoryza, with each of which it had, direct contact. It was not necessarily symptomatically, something in common. atypical of coryza with respect to its Autopsy of several birds, which were nature, however, since it was of rapid sacrificed, showed only mucous exudate in onset and short duration. This is the type the nasal chambers, trachea, and large of disease which Nelson (1933 a and b, bronchi, and in one case, caseous exudate 1938), states, and Schalm and Beach in the thoracic air sacs. It was differenti- (1936) have observed, is induced by pure ated from laryngotracheitis by the fact cultures of H. gallinarum. It might also that recovered birds were susceptible to be mentioned that one of us (J. R. B.) that virus; from infectious bronchitis by has previously encountered two similar the inability to demonstrate neutralizing outbreaks in flocks from which coryza had antibodies for that virus in the serum of been eradicated by depopulation and recovered birds in tests made with chicken which had been free from the disease embryos; and from avian pneumoencepha- for several years. The source of the infeclitis by the negative results of hemaggluti- tion which precipitated the outbreak nation-inhibition tests using serum of under discussion was and continues to be recovered birds and a good hemagglutinat-, a mystery. ing strain of PE virus, and by the fact that recovered birds proved susceptible THE POPULATION USED LN THE to inoculation with PE virus. Further GENETIC ANALYSIS evidence that none of these three viruses For the purposes of the genetic analysis were involved in the etiology of the disease we shall consider only one row of laying was the failure to isolate any of them in houses (H) which in 1949, as in other embryos inoculated with the nasal and years, contained the bulk of the pullet tracheo-bronchial mucous exudates. To population. The row consists of five check for the presence of infectious double laying pens, two in one, and three coryza, fresh-blood agar plates were in a second house. Approximately 275 streaked with the pathological exudate pullets are placed in each of the double The effects on egg production will be discussed later.
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GENETIC VARIATION IN RESISTANCE TO RESPIRATORY INFECTION
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pens at the time of legbanding (about 5 ered to have manifested themselves in months of age). In the fall of 1949 the two approximately the first three weeks of double pens in one house were occupied by October. In addition to the effects on egg pullets originating from eight inbred production, egg quality and hatchability lines (designated as inbreds in Table 3), by following resumption of lay were also offspring of a series of crosses between affected by the disease. These will be these lines (inbred crosses in Table 3), and reported upon separately. by pullets from a line selected for shank PAUSING AS A CRITERION OF length (size in Table 3). The second house RESISTANCE contained the pullets from the productionbred flock and the pullets from lines For the purposes of the present study selected for a high incidence of winter the production records between September pausing and blood-spotting respectively, 26 and October 25 were subjected to as well as those from a cross between the scrutiny. It became apparent immedilatter and the production-bred flock. The ately that the probable effect of the designations of these sub-populations in Table 3 are self-apparent. One of the three double pens in this latter house was divided into two separate units. In this manner it was possible to carry out a subsidiary nutritional test, by providing two different diets to the two groups of birds ( 1 | pen in each) in this house. Birds carrying odd numbered SEPTEMBER OCTOBER wing bands were assigned to one group, FIG. 1. Daily percent production. and those with even numbered wingbands to another. Thus the populations on the two different diets were randomized with disease was not in reducing the rate of respect to origin. The difference between production of laying birds, but rather in the two diets consisted in one ingredient complete cessation of production of most only, and since, as it will be shown later, birds previously in lay. Thus the presence the diet had no effect on the incidence of of a pause of an arbitrary number of the disease in question, this difference is consecutive non-laying days (selected as irrelevant for the present discussion. 10) within the designated period sugFigure 1 illustrates the daily percentage gested itself as a criterion of susceptibility production for the whole population of to the disease. No claim, of course, is pullets considered. It may be seen that the made that all birds exhibiting such pause normal seasonal increase in gross rate of were clinical cases of the disease. It may lay, apparent in the extreme left of the be recalled, however, that a certain procurve, was checked very early in October. portion of the birds in the A row (13 out This was followed by a precipitous drop of 106) failed to exhibit any respiratory in production which reached its floor in symptoms. Thus, the birds which did not the middle of October, whereupon the pause may have been either escapes or trend was reversed and gradual recovery resistant to disease in the sense of being initiated. The main effects of the disease able to maintain production after infecon egg production may be thus consid- tion. In either event specific definition of
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I. MICHAEL LERNER, LEWIS W. TAYLOR AND J. R. BEACH
TABLE 2.—Percentage distribution in the production-bred flock Year Total birds banded a. Immature on 9/26 b. In pause on 9/26 c. Died before 9/26 d. Died 9/26-10/25 e. Affected f. Unaffected g. Affected as percent of sample*
1948
1949
549 8.2 4.9 2.7 1.1 5.3 77.8
625 17.3 1.9 2.1 3.5 71.2 4.0
6.4
94.7
computations of pausing incidence. A further question arose with respect to the birds which died in the course of the period between September 26 and October 25. These will be considered further in the discussion to follow.
In order to make certain that the pausing behavior in 1949 was, indeed, related to the presence of the disease in the flock, a comparison was made between pause incidence in the production-bred flock in that year and in 1948. The distribution of pullets in different categories is shown in Table 2. Whereas 5.3 percent of all birds paused in 1948, 71.2 percent did so in 1949. The difference becomes even more extreme (largely due to the later sexual maturity of the 1949 flock) when only the birds in lay on September 26 are considered. If we also exclude the birds dying in the subsequent 30 days, the comparative percentage incidence of pausing is 6.4 and 94.7 for 1948 and 1949. The odds on the reality of this difference are, of course, astronomical. COMPARISON BETWEEN LINES
Having thus satisfied ourselves that pausing is at least a reasonable criterion of some form of susceptibility to the respiratory disease in the flock, comparison of pausing incidence between different lines was undertaken. The results are presented in Table 3. The last two lines of the table are complementary to each other. It may be seen that the range of incidence of pausing in the different lines extended from 86 to 100 per cent. Whether or not the differences between the lines are sig-
TABLE 3.—Distribution of birds in different lines
Line or cross
Total birds banded (Immature on 9/26 Birds excluded 1 In pause on 9/26 from sample] Died before 9/26 (Died 9/26-10/25 Birds in sample Birds affected Birds unaffected Percentage unaffected Percentage affected
Production 625 108 12 13 22 470 445 25 5.32 94.68
Inbreds 245 158 11 7 5 64 61 3 4.69 95.31
Inbred crosses 213 99 10 3 1 100 86 14 14.00 86.00
Size
104 72 2 4 3 23 22 1 4.35 95.65
Bloodspots 168 32 6 0 4 126 109 17 13.49 86.51
ProductionX Winter Total blbod- pause spots 13 3 0 0 1 9 8 1 11.11 88.89
1393 25 485 13 0 41 0 27 2 38 10 802 10 741 61 0 0 7.61 100.00 92.39
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the two types of birds, although of course, desirable, is not possible and actually not essential to demonstrate the genetic differences, the existence of which is indicated here. A more difficult problem is presented by birds which were not in production at the beginning of the period, either because they were still immature or because they were already in winter pause. These individuals, together with any that died before September 26, were excluded from
GENETIC VARIATION IN RESISTANCE TO RESPIRATORY INFECTION
nificant may be best determined by x2 tests, the results of which are shown in Table 4. Since the numbers of pullets in several of the lines are rather small, only the four groups with 50 or more birds in each were included in the first comparison. The x2 was found to be 14.74 which for three degrees of freedom indicates a high prob-
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including or excluding the birds dying from reproductive disturbances, must be deemed to be highly significant. OTHER COMPARISONS
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It may be recalled that the inbred lines were housed together with the progeny of crosses between them. Similarly the production-bred birds were in the same units as the pullets from the bloodTABLE 4.—Homogeneity tests spot line. The total x2 can then be partitioned to determine if the differences J Comparison made £g£a°' x° P between the lines were due to differences Production, Inbred, Inbred between houses. As it may be seen in Table crosses, Blood-spot 3 14.74 <0.01 As above, including reproduc4, the x2 for the comparison between the tive mortality 3 15.20 <0.01 Production, Blood-spot 1 10.13 <0.01 production and the blood-spot lines is Inbred, Inbred crosses 1 3.64 0.055 Rations 1 0.44 0.5 highly significant (x2 of 10.13), while for Sire families within production line 9 7.66 0.6 the inbred and inbred crosses compairson it only verges on significance (x2 of 3.64). 2 ability that the differences between the Since this leaves a x of only 0.97 between lines compared are significant. In order, houses, it must be concluded that the line however, to make certain that the exclu- differences, in the main contributed to by sion of the birds dying during the period the difference between the production and studied did not unduly affect this conclu- the blood-spot lines, are independent of the differences between disease conditions sion, a second comparison was made. in the two groups of units. Autopsies of the 38 birds dying between The next comparison made was that September 26 and October 25 indicated that the deaths of 14 birds were probably between the two rations and, as the x2 independent of the presence of the respira- of 0.44 convincingly demonstrates, no tory infection. Death was due to lympho- differences in pausing induced by the matosis in four of these, four others died difference in diets appear to be present. of accidental injuries, two had digestive Finally, a comparison between pausing disturbances, one had an involvement of incidences in different sire families within the excretory system, and the remaining the production line was undertaken. As three cases were of a doubtful nature. The shown in the last line of table 4, no signifiremainder of the dead birds, 24 in number, cant differences were found here. In fact, were all characterized by disturbances of an attempt to compute the heritability of the genital system. Whether or not their pausing in this group by the method of death may have been related to the res- Robertson and Lerner (1949) led to a negpiratory disease is of little import, since, ative estimate, indicating smaller variaas shown in the second line of Table 4, tion between sire families than would be the inclusion of such birds together with expected by chance on the average. The their pausing flock-mates did little to significance of the low x8 for the producchange the picture. The x2 here was found tion flock will be commented upon in the to be 15.20 and hence line differences, following section.
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I. MICHAEL LERNER, LEWIS W. TAYLOR AND J. R. BEACH
THEORETICAL CONSIDERATIONS
The possible argument that what is being dealt with here is a general resistance rather than one specific to the disease which appeared in the flock in September, 1949, is not valid for two reasons. Firstly, should this have been the case, the genetic variability in the production line might have been expected to be of the same magnitude as for the resistance to death in the first year from all causes. This was found by Robertson and Lerner (1949) to lead to a heritability estimate of 0.089 ±0.028, whereas, as noted, in the present case the heritability estimate fell below a value of zero. Secondly, should general vigor have been the sole differential determining presence or absence of pausing, it might have been expected that the group of inbred birds (with an average coefficient of inbreeding of 43.3 percent and lacking vigor by other criteria) would have had a significantly lower percentage of unaffected birds than the productionbred flock. In reality, as shown by the figures in Table 3, this was not the case. It is true, however,that the border-line significance of the difference between the
inbred and the hybrid populations (inbred crosses) suggests that general vigor enhances resistance to the disease, but the fact remains that inbreeding degeneration, a property characteristic of general vigor, is not exhibited by the character under discussion. Since no artificial or natural selection for resistance could have taken place in the 17 years preceding the outbreak of the disease, the only reasonable possibility of finding genetic differences in a population of non-interbreeding isolates, such as represented by the different lines in the flock, would lie in chance differentiation of genotypes. Under such circumstances, absence of genetic differences would not be surprising. Their presence, on the other hand, is no cause of surprise but simply a gratifying accident. It is true that the greatest chance of finding differences in resistance would be in the group of inbred lines, but the numbers available for study within the lines are too small to make this possible. The blood-spot line itself is slightly inbred (average F of 10.02 percent), so that the operation of genetic drift in differentiating it from the production line was somewhat facilitated. The main factor, however, lies in the breeding isolation of this line from the production-bred one. The immediate practical consequences of the material reported upon are not clearly apparent. It is obvious that any attempt at increasing resistance in the production line by selection would be extremely difficult. Added to other complications of breeding for disease resistance when the incidence is close to 95 percent, (see Lush, Lamoreux and Hazel, 1948) is the fact that the genetic variation in this group is at the present not discernible. Migration from the blood-spot line would, of course, be a rather dubious procedure: the superiority of this line in resistance is
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The particularly interesting feature of the results from the genetical standpoint lies in the fact that differences in resistance to the disease, as adjudged by the ability of a bird to continue production in the course of the epidemic described, were found between lines of common origin which differentiated while there was no exposure to this or any other respiratory disease. The blood-spot line originated from the production-bred flock during the period when no direct selection for resistance was practiced or, indeed, was possible. Hence, the genetic differences in resistance cannot be due to adaptation as a result of directed selection, but to chance possession of particular genotypes by the different lines.
ASSOCIATION NOTES
relatively slight, while its blood-spotting tendencies are much greater than in the production-bred line (by a factor of approximately 17 in 1948). SUMMARY
REFERENCES CITED Asmundson, V. S., and J. Biely, 1932. Inheritance of resistance to fowl paralysis (Neurolymphatosis gallinarum) I. Differences in susceptibility. Can. J. Res. 6: 171-175. Frateur, J. L., 1924. The hereditary resistance of the fowl to the bacillus of diphtheria. Proc. 2d World's Poultry Congr., Barcelona: 68-71. Hutt, F. B., 1949. Genetics of the fowl. Xl-f 590 pp. McGraw-Hill. New York.
Hutt, F. B., and R. K. Cole, 1948. The development of strains genetically resistant to avian lymphomatosis. Proc. 8th World's Poultry Congr., Copenhagen, 1: 719-725. Lambert, W. V., and C. W. Knox. 1932. Selection for resistance to fowl typhoid in the chicken with reference to its inheritance. la. Agr. Exp. Sta. Res. Bull. 153: 263-295. Lush, J. L., W. F. Lamoreux and L. N. Hazel, 1948. The heritability of resistance to death in the fowl. Poultry Sci. 27: 375-388. Nelson, J. B., 1933a. Studies of an uncomplicated coryza of the domestic fowl. I. Jour. Exp. Med. 58: 289-295. Nelson, J. B., 1933b. Studies of an uncomplicated coryza of the domestic fowl. n . Jour. Exp. Med. 58: 297-304. Nelson, J. B., 1938. Studies of an uncomplicated coryza of the domestic fowl. IX. Jour. Exp. Med. 67: 847-855. Roberts, E., and L. E. Card, 1935. Inheritance of resistance to bacterial infection in animals. 111. Agr. Exp. Sta. Bull. 419: 467-493. Robertson, A., and I. M. Lerner, 1949. The heritability of all-or-none traits: Viability of poultry. Genetics, 34:395-411. Schalm, O. W., and J. R. Beach, 1936. Studies of infectious coryza with special reference to its etiology. Poultry Sci. 15: 473-481. Taylor, L. W., I. M. Lerner, K. B. DeOme and J. R. Beach, 1943. Eight years of progeny-test selection for resistance and susceptibility to lymphomatosis. Poultry Sci. 22: 339-347.
Association Notes {Continued from page 851)
of the Recommended Nutrient Allowances for Poultry. He is the senior author or co-author of numerous scientific papers dealing with the nutrition of poultry. He is an Associate Editor of POULTRY SCI-
Isabel Karrasch and they have three children.
ENCE.
The Poultry Science Association's Research Prize of one hundred dollars for the outstanding research paper published during the preceding fiscal year of the Association was presented to Dr. Robert J.
In addition to the Poultry Science Association, Professor Cravens is a member of the Chemical Society and the Institute of Nutrition. He was married in 1939 to
POULTRY SCIENCE RESEARCH PRIZE
(Continued on page 873)
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Evidence for genetic differences in specific resistance to a respiratory disease, tentatively diagnosed as atypical infectious coryza resulting from uncomplicated H. gallinarum infection, as measured by the ability to maintain production during an epidemic is presented. Of particular interest is the fact that the flock in which these observations were made was free of any respiratory disturbances for 17 years prior to the outbreak. The demonstrated differences were thus due to chance differentiation of genotypes in non-interbreeding lines.
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