INTERSEXUALITY IN PIGS - CLINICAL, PHYSIOLOGICAL AND PRACTICAL CONSIDERATIONS

Veterinary surgeons and practical pig farmers need to be aware of a co ndition that can have important deleterious consequences in a breeding herd. The animals in question have sometimes been referred to as herm aphrodites but would more correctly be termed intersexes. Whilst there is a complete spectrum of phenotypic sexual development within a popu lation of such animals, the most common form is that of a putative fem ale with a prominent up-turned vulva. Reflection of the vulval lips re veals a much-enlarged clitoris. There may be scrotal development, in c onjunction with an enlarged penile and preputial sheath. Coarse hair a nd incipient tusk development may further indicate differing degrees o f masculinization. Surgical exploration of intersex animals confirms a complete spectrum of gonadal types, ranging from 2 ovaries with a pro portion of testicular tissue in one of them (i.e., an ovotestis) to 2, much-enlarged testicular-like structures with no detectable ovarian t issue. The gonads usually remain within the abdomen, but those with te sticular tissue may descend to an inguinal or even scrotal location. T he genital tract invariably comprises a bicornuate uterus, a partially vestigial Fallopian tube, and some development of one or both Wolffia n ducts adjoining an ovotestis or testicular-like structure to form a convoluted epididymis. Spermatozoa are never present, either in abdomi nal or scrotal testicular tissue, nor are there any germ cells within the seminiferous tubules, only Sertoli-like cells. Due to the spectrum of gonadal types, sexual behaviour ranges from male-type aggressivity on the one hand to regular oestrous cycles on the other, with periods of standing oestrus during which intromission may be achieved. In ani mals with functional ovarian tissue in both gonads, foetal development has been observed at least until days 25-30 of gestation. Almost all intersex pigs possess XX sex chromosomes and usually 36 autosomes; onl y a very small proportion are chimaeras or mosaics. Chromosome banding techniques have failed to demonstrate a portion of the Y chromosome t ranslocated onto an X chromosome nor has molecular probing revealed th e presence of the sex determining gene Sry or other classical Y-relate d DNA sequences, except in one instance. Breeding records suggest that the intersex condition results most frequently from the influence of an autosomal recessive gene carried by certain boars. Identification o f such boars is therefore essential, as the incidence of intersexualit y in their offspring may reach 4-5% or more. In terms of the pig indus try, economic losses may result from: 1. Lack of fertility in intersex animals. 2. Aggressive behaviour in groups of growing/fattening pigs. 3. Boar taint in the carcase of animals possessing ovotestes. 4. Prop agation of the deleterious condition, either by mating or more widely by artificial insemination.