Bent-limb disease in lambs. Apparent transmission with an autosomal recessive gene linked to the OL-Z minor lymphocyte antigen locus and the I locus involved in the expression of R and O antigens in sheep.

In crossbred Charmois lambs, Bent-limb disease appears to be associated with the phenotype 'z,i' which corresponds to a doubly recessive genotype at the two loci OL-Z (a minor lymphocyte antigen locus independent of OLA, the major histocompatibility complex of the sheep) and I (involved in genetic control of the expression of R and O antigens found in various body fluids and on erythrocytes). The disease seems to be controlled by a single autosomal recessive gene, provisionally named bl (its normal or healthy allele Bl being dominant) which is distinct from, though linked to, the genes at the OL-Z and I loci (observed haplotype: bl,z,i). In the Lacaune breed, besides the already observed bl,z,i haplotype, there is an additional one: bl,z,I. In Vendéen sheep, and in animals which belong to two other breeds, the bl,Z11,I haplotype (bl linked to the two dominant alleles) appears to be relatively frequent. Further studies are needed in order to confirm the genetic hypothesis suggested by the present data.