Genetic resistance of Creole goats to cowdriosis in Guadeloupe. Status in 1995.

A genetic predisposition to resistance (R)/susceptibility (S) has been demonstrated for cowdriosis in certain goal lines. In order to identify genetic markers of R/S and to follow their transmission to the offspring, 4 groups of sires and dams were crossbred in 1991, 1992, and 1993: Rr, RS, SR, and SS. The offspring were challenged at the age of six months with subsequent challenge of the S parent. From 28 presumed S dams, 7 turned out R and from 2 presumed S sires, 1 was R and the other undefinable. The resistance rate was 76% for 21 RR kids and 45% for 20 RS kids. The R character seems to be better transmitted by dams than the S one. No difference was observed between R and S goats in terms of incubation period and body temperature level after challenge. There was no statistical effect found of sex, litter size, or birth mass on the R/S character; only a slight effect on daily mass gain was observed. Sperm has been collected from 4 S sires (died after challenge) and 5 R sires, and stored in liquid nitrogen in order to conceive additional SR and SS progeny. Several caprine leucocyte antigens seem to be genetic markers of R (Be 1, CLY) and of S (Be 9, Be 22, Be 23). Further powerful tools like microsatellites and probes defining other interesting loci possibly involved in disease pathogenesis are now at hand and will be included in future experiments.

Occurrence of caprine leucocyte antigens (CLA) in Creole goats susceptible/resistant to heartwater.

A genetic predisposition to the manifestation of disease symptoms has been demonstrated for heartwater in certain goat lines. In order to clarify a possible involvement of the major histocompatibility complex (MHC) in the pathogenesis of heartwater, over 100 Creole goats have been typed serologically for their CLA class I antigens coded by the caprine MHC. The MHC is a genetic system that influences different immunological processes, i.e. the individual immune response. With our alloantisera we were able to detect 13 different CLA alleles also present in the Swiss breeds, two non-MHC antigens, a new cluster defined by the splitting of two antigens and several specific reaction patterns of single reagents. The allele frequencies of the detected CLA antigens differed for the resistant and susceptible groups examined. Whether the differences represent regional sire effects or indicate pathogen-induced selection pressure remains to be clarified. Additional testing of resistant/susceptible goats originating from common environment as well as of specially crossbred (resistant x susceptible) animals are underway.

[Dermatophilus congolensis bovine dermatophilosis in the French West Indies. III. A comparison between infected and non-infected cattle]. / La dermatophilose des bovins à Dermatophilus congolensis dans les Antilles françaises. III. Comparaisons entre élevages infectés et indemnes.

The determination of the distinctive features between infected and uninfected cattle by Dermatophilus has been performed among 93 bovine stock in La Martinique, and 120 in La Guadeloupe and Saint-Martin Islands. Nearly half of the herds had been or were infected. Morbidity rates reach 33 per cent in La Martinique and 29 per cent in La Guadeloupe with a mortality ratio of 15 per cent and 5 per cent respectively. No frequency difference could be observed with respect to the season or the geographical area. Similarly, differences are little or nil as regards animal exposure toward aggressive factors such as sun, soil moisture, thorns, etc. On the other hand, the presence of Amblyomma variegatum is a determining factor considering the prevailing situation in La Martinique, where all breeds of cattle are sensitive to the disease. In this case, 63 per cent of the tick infested cattle develops dermatophilosis versus 2.5 per cent for the still uninfected animals. Conversely, in La Guadeloupe were Creole zebus are highly resistant (as a consequence of their natural selection), only 27 per cent of the infected stock suffers from this illness. In these two islands, regular dipping measures have proved to be beneficial in that it reduces the disease frequency. The study also reveals an underlying typology of the various rearing systems, thus allowing their classification as for their behaviour and response when meeting illness. In La Martinique, whatever they may be, quite none of them is infected in the tick free area. In the tick infested zones, the traditional small breeders rearing a sensitive cattle and who do not care with prophylactic rules, are mostly stricken, while more structured ones have succeeded in controlling the disease, owning to some appropriate measures together with a fair animal management. On the other hand, in La Guadeloupe where this tick is cosmopolitan, the small breeders who run a resistant Creole cattle, are not concerned, despite a rudimentary prophylactic behaviour. Conversely, the intensive rearing system, based upon improved imported breeds, meets great difficulties to master the infection.

Genetic resistance of Guadeloupe native goats to heartwater.

The resistance rate of different populations of the same breed of creole Guadeloupean goats to Cowdria ruminantium infection varied greatly depending on the previous heartwater history of each population. After experimental infection of goats removed decades ago from endemic areas, the observed resistance rate was 25%, while it was 54% in a population that had been isolated from the disease for 10 years and reached 78% in a flock actually exposed to heartwater. This resistance seems to be under genetic control as sex and paternity were the most important factors which could explain resistance in a group of 90 kids of the same flock, tested under controlled conditions. Resistance rate varied greatly (20-83%) depending on the sire, with a heritability estimate of 0.49 for half sibs and 0.85 for full sibs. A recessive sex-linked gene could be involved in the genetic determination of this resistance. From these observations, it can be stated that in endemic heartwater areas, each population, i.e. each flock, will have developed resistance at a definite rate according to population, age and the extent of past and present exposure to the disease, through a natural selection of resistant lines. Populations removed from exposure to heartwater will progressively lose their ability to resist infection through an increase in the frequency of susceptible stock. If our hypothesis of a recessive sex-linked gene is proved correct, it should be easy to select for improved resistance to the Guadeloupe breed of goat to heartwater.