Trop. Anita. Hlth Prod. (1981) 13, 217-221
HAEMOGLOBIN POLYMORPHISM AND RESISTANCE TO HELMINTHS IN RED SOKOTO GOATS V. BUVANENDRAN1, T. SOORIYAMOORTHY2, R. A. OGUNSUSls and I. F. ADU1 1National Animal Production Research Institute, PMB 1096, Zaria, Nigeria, 2Department of Veterinary Physiology and Pharmacology, Ahmadu Bello University, Zaria, Nigeria and aDepartment of Veterinary Parasitology and Entomology. Ahmadu Bello University, Zaria, Nigeria SUMMARY
Haemoglobin variants were studied in a population of 104 Red Sokoto goats of over I year of age and in 49 kids. Three haemoglobin variants and 5 phenotypes were detected. The observed proportions of haemoglobin phenotypes in animals over 1 year of age differed from the expected numbers calculated on the basis of genetic equilibrium, while in kids there was good agreement between observed and expected values. There were significant differences in helminth egg counts among haemoglobin phenotypes. The heterozygotes had significantly lower egg counts than homozygotes. It is postulated that the discrepancy in the observed ratios of haemoglobin phenotypes of the older group was probably due to the differential susceptibility to helminth infection. INTRODUCTION
Three haemoglobin variants have been reported in the Red Sokoto goat of Nigeria (Enyenihi, 1974) the relatively fast moving Hb F, the slower Hb S and the intermediate Hb N. Enyenihi (1974) also described the detection of 4 haemoglobin phenotypes, 1 having only Hb N which he considered as the homozygote Hb-NN and 3 others having mixtures of 2 haemoglobin types Hb N/Hb F, Hb N/Hb S and Hb F/Hb S which he considered as heterozygotes Hb-NF, Hb-NS and Hb-FS respectively. The fact that 2 haemoglobin types appear in some while only 1 appears in others is indirect evidence that each haemoglobin type is controlled by an allele and that these are co-dominant. An examination of the distribution of the frequencies of the different genotypes in the above study showed that 2 homozygotes Hb-FF and Hb-SS were missing although some animals of these types were expected to be present on the basis of gene frequencies. Such an apparent disturbance from the expected frequencies may occur due to selective forces operating on some genotypes. It may also occur due to chance since small numbers of animals were drawn from different parts of the country for this study and the samples may not have been representative of the populations. It was therefore felt that a study of the distribution of the different haemoglobin types in a closed population was desirable to confirm the findings of Enyenihi (1974). This paper reports the results of a study clone in a closed flock of Red Sokoto goats at Shika in Nigeria. MATERIALS AND METHODS
The animals used in this study were from the experimental flock of Red Sokoto goats at the National Animal Production Institute. The flock was introduced into Shika in 1976 and has been kept as a closed flock since that time. Animals are bred once every year. All mature does are generally used for breeding while in choosing breeding bucks some attention is given to growth rates. 217
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BUVANENDRAN, SOORIYAMOORTHY, OGUNSUSI AND ADU
Blood samples were collected during November to December 1978 from all does over 1 year of age. Sixty animals from this population were bred at this time and blood samples collected from their progeny born during April to May 1979. Haemolysates were prepared according to the method described by Friedman (1962). Eleetrophoresis was carded out on cellulose acetate paper using a Tris-EDTA-borate buffer with a pH of 8.4 at a constant voltage of 400 for a pedod of 10 rain (Briere, Tipton and Batsakis, 1965). Four faecal samples were taken at weekly intervals from the animals whose blood samples were obtained in 1978. Samples were obtained in June to July 1979 during the height of the rainy season when helminth infestation is known to be high. Animals were given anthelmintic treatment 4 weeks before the first sample was obtained. Helminth eggs per gram (epg) of faeces were determined using the modified McMaster technique (Whitloek, 1948). No attempt was made at differential egg counts but the main helminth species represented were Haemonchus and Trichostrongylus species. Egg counts were subjected to an analysis of variance partitioning the variance into haemoglobin types, weeks and haemoglobin-week interaction. The data were also analysed after transforming the epg to log (epg+ 10) to reduce the dependence of the variance on the mean (Turner and Short, 1972). As the results of transformed and untransformed values were essentially the same the results of the latter analysis are presented here. RESULTS
A total of 104 does over 1 year of age was studied. The number of animals of each haemoglobin phenotype observed is shown in Table I. Five of the 6 possible phenotypes were detected, the missing class being Hb-FF. From the distribution of the phenotypes the gene frequencies of the 3 alleles Hb F, Hb N and Hb S are calculated as 0"077, 0-591 and 0-327 respectively. The expected numbers of each phenotype, if the population is in genetic equilibrium, will be according to the proportion Hb F ~, Hb N 2, Hb S~, 2Hb F. Hb N, 2Hb S- Hb N and 2Hb F. HbS for phenotypes Hb-FF, Hb-NN, Hb-SS, Hb-FN, Hb-SN and Hb-FS respectively (Falconer, 1961) (Table I). It is obvious that there is a discrepancy between observed and expected values, there being excess animals in classes Hb-NS and Hb-FS over the expected numbers while the observed numbers of Hb-SS are lower than expected. The difference between observed and expected values approaches significance (x2(.~)--10-03, 0.05 > P < 0.10). The distribution of the observed and expected numbers of the haemoglobin phenoT~t~ I Observed and expected numbers of haemoglobin phenotypes in Red Sokoto goats
Age of goats Over 1 year Haemoglobin phenotype NN NS FS NF SS FF
Kids
Observed Expected Observed Expected 34 48 10 7 5 0
36"4 40-2 5"2 9"5 11-1 0-6
18 17 2 7
18.4 17.7 2.7 5.5
5
4.3
0
O.4
HAEMOGLOBINPOLYMORPHISMIN GOATS
219
types in the kids is shown in Table I. The expected numbers are very close to the observed values in all classes (X2¢s)= 1.14, P > 0.95) indicating that the population is in genetic equilibrium. Some of the animals which were used for haemoglobin studies were disposed of before studies on helminth infections could be undertaken. Eighty two animals were available for this study. The mean helminth egg count for each of the haemoglobin phenotypic classes is shown in Table II. There are significant differences in egg counts between haemoglobin types, Hb--SS animals having significantly greater counts than the 3 heterozygntes. Hb-NN also differed significantlyfrom types Hb--FS and Hb-NF. There was also a progressive increase in egg counts over time, the mean counts from week 1 to week 4 being 523, 742, 978 and 1,253 respectively. The interaction between haemoglobin type and time was not significant. TABL~II Mean helminth epg o f faeces among haemoglobin phenotypes in Red Sokoto goats
Haemoglobin phenotype
No. of animals
NN NS FS NF SS
29 33 9 7 3
Mean egg count1 1138 ab 872 b 430 e 456e 1475 a
1Valueswith differentsuperscripts are significantly different,P < 0-05. TABLEIII Observed and expected numbers of haemoglobin phenotypes in the population o f Red Sokoto goats studied by Enyenihi (1974)
Haemoglobin phenotype
0 bserved
Expected
NN NS FS NF SS FF
10 30 10 10 0 0
15-0 20.0 6.7 10-2 6.5 1.7
DISCUSSION This study has demonstrated the presence of animals of type Hb-SS which were missing in the populations studied by Enyenihi (1974). Animals of type Hb-FF are absent in this study as was reported by Enyenihi but this is not surprising in view of the low gene frequency of gene Hb F in this population. The chief interest of the present study lies in the comparison of the proportions of the different phenotypes among kids and older populations. The fact that in kids the observed ratios are close to expected values and that in adults there are discrepandes between observed and expected values is very strong evidence of differential mortality in the period from kid to adult stage. The discrepancy arises chiefly from an
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BUVANENDRAN, SOORIYAMOOKTHY, OGUNSUSI AND ADU
excess of the heterozygotes Hb-NS and Hb-FS and a deficiency of homozygote Hb-SS. It is also significant that almost the same pattern of distribution of phenotypes was found in Enyenihi's study. Using his data the expected frequencies were calculated and are shown in Table III. The same classes that were either deficient or in excess in the present study were observed in his study as well but the discrepancies were more pronounced (x~(s)= 16-5, P < 0.01). The forces that disturb a population from genetic equilibrium are mutation, migration, selection and random drift (Falconer, 1961). In the present instance, where the disturbance in genetic equilibrium appears to occur between different stages in the life of the animals, selection offers the most plausible explanation. A possible selective force could be the differential susceptibility of haemoglobin phenotypes to helminth infections. Egg counts are regarded as rather inaccurate measures of parasitic burdens but they remain the only convenient method of assessing helminth burdens in large populations. The results of the relative egg burdens show that with the exception of Hb--NF it is those haemoglobin phenotypes that are in excess which had the least egg burdens and vice versa. It is therefore tempting to postulate that the heterozygotes are relatively more resistant to helminth infections than the homozygotes. The association between genes controlling haemoglobin type and resistance to helminthiasis is well documented in sheep. Of the 2 haemoglobins occurring in sheep, Hb A and Hb B, Hb A is reported to be associated with resistance to haemonchosis (Evans, Blunt and Southcott, 1963). Recently it has been shown that a similar relationship occurs even with non-haematophagic species such as Ostertagia (Altair and Dargie, 1978). The relationship found in this study between haemoglobin type and helminth infection is therefore not surprising. The present study was done in an experimental herd where good veterinary care is provided and anthelmintic treatments are given at monthly intervals during the wet season. Animals owned by private farmers rarely receive anthelmintic treatments and therefore the differences in susceptibility to helminth infections among the haemoglobin phenotypes may be more pronounced. A study done on such privately owned flocks should throw more light on this relationship. ACKNOWLEDGEMENTS
The authors are grateful to Professor S. Nuru, the Director of the National Animal Production Research Institute for facilities to carry out this work. Accepted for publication July 1980 REFERENCES AL'r~aF,K. L & DAI~CIE,J. A. 0978). Research In Veterinary Science, 24, 39. BRIEI~, R. O., TIFrON, G. & BAT~KiS,J. G. (1965). American Journal of Ch'nicalPathology, 44, 695. ENYENIHI,U. K. (1974). Research in Veterinary Science, 17, 360. EVANS,J. V., BLu~rr, M. H. & SOUTHCCYI'r,W. H. (1963). Australian Journal of Agricultural Research, 14, 549. FALCONER,D. S. (1961). Introduction to Quantitative Genetics, 1st edn, Oliver and Boyd, Edinburgh. FgIF.D~N, H. S. (1962). Clinica chimica aeta, 7, 100. Tt~R~R, H. G~ & SHORT,A. J. (1972). Australian Journal of Agricultural Research, 23, 177. WHITLOCK,J. H. (1948). Journal of the Council of Science and Industrial Research of Australia, 21, 177. HEMOGLOBINE ET RESISTANCE AUX HELMINTHES CHEZ LES CHEVRES SOKOTO R ~ m $ - - L c s h~moglobines ant 6t~ 6tudi~es dans une population de 104 chtvres Sokoto de plus de un an et chez 49 cabris. Trois variantes et cinq phtnotypcs ant 6t6 d~couverts. I.~ proportions des ph~notypes chez Its animaux de plus d'un an sont difftrentcs de ce qui ~tait attendu en se basant sur
HAEMOGLOBIN POLYMORPHISM IN GOATS
221
l'6quilibre g6n~.tique, tandis que, chez les cabris, il existe une bonne correlation entre ce qui a ~t~ constat6 et ce qui ~tait escompt6, Parmi les ph~notypes, on note des differences significatives en ce qui concerne le nombre d'oeufs ~limin~s: celui-ci est moins ~lev~ chcz les h~t~rozygotes que chez les homozygotes. Darts le groupe des ch/:vres les plus ~q~es, les ~..arts observ(:s sent probablement imputables/t une sensibilit6 diff6rente/t l'infestation par les helminthes. POLIMORFISMO DE LA HEMOGLOBINA Y KESISTENCIA A HELMINTOS EN CABRAS SOKOTO ROJAS Resumen---Seestudiaron variantes de la hemoglobina en una poblaci6n de 104 cabras Sokoto Rojas con 49 cabritillos. El estudio tuvo 1 a t e de duracibn. Se detectaron tres variantes y 5 fenotipos en la hemoglobina. La propercibn observada de fenotipos en la hemoglobina en animals de mM de 1 ate fueron diferentes a los ndmeros esperados calculados con base en el equilibrio gen6tico; mientras que en los cabritillos hubo una buena correlacibn. Tambi6n hubo diferencias significativas en el ndmero de huevos de helmintos entre los fenotipos de hemoglobina. Los heterocigotes tuvieron un ndmero de huevos menor que los homocigotes. Se postula, que la discrepancia en los valores de fenotipos de hemoglobina observados en el grupo de m/ts edad, se debe probablementea la diferente susceptibilidad infecciones per helmintos.
HANDBOOK OF TROPICAL VETERINARY LABORATORY DIAGNOSIS Section 2. General Techniques 35 Pages
5 Figures
The second part of the C.T.V.M. Handbook concerned with the laboratory diagnosis of tropical animal diseases is now available. It summarises the general techniques likely to be routinely required in small district veterinary investigation laboratories in tropical and subtropical countries and concentrates on those which do not require sophisticated laboratory equipment or advanced laboratory training. Contents include post-mortem examination procedures, maintenance and use of equipment, cultivation and staining of micro-organisms, histological and haematological methods and helminthological techniques. The price including postage by surface mail is £2.50 per copy and orders should be sent to: Executive Officer Centre for Tropical Veterinary Medicine, Easter Bush, Roslin, Midlothian, SCOTLAND Cheques, which should accompany the order, should be made payable to the C.T.V.M.
