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This article was published in 1953
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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.
Sterility in Boars: Probable Genetic Origin
G. CHARLES. B.V.Sc., Inspector of Stock, Forbes
Introduction
Lethal factors are known to exist in pigs, and a case involving a possible further factor is reported.
History
A stud pig-breeder in this District has a Berkshire stud in which he has been breeding along certain lines to achieve and fix certain characteristics which he considers desirable. During this breeding programme he selected a sow of similar breeding to his boar and mated them. The resultant offspring approached his ideal fairly closely and in his efforts to try and fix these characteristics he then mated the boar with a sow from this litter; in other words a father-daughter mating. The resultant litter consisted of four pigs; three boars and one sow.
The owner reported that as the boars grew, two of them showed slightly less testicular development than the third. In due course, one of these two was sold, but was returned as he failed to fertilise any sows with whom he was mated. The fault was not with the sows, which conceived when mated with another boar. This faulty boar was castrated by the breeder, who then tried the second of the two boars on some of his own sows. Again the sows failed to conceive. The third boar, previously mentioned as showing better testicular development, was joined successfully with these same sows. As a result of the failure of the second boar, the owner sought advice.
Examination
At the time of examination the boar was 14 months old and in good condition. The testes appeared less well developed than those of his normal litter-mate and on palpation felt rather flabby. When put with a sow on heat he exhibited all the normal reactions of a boar on such occasions, and achieved penetration. An unsuccessful attempt was made to collect semen at this time. However, it was noted that the ejaculum appeared watery and small in volume.
The boar then was castrated and the testes examined. The epididymis appeared to be well developed but the testicular tissue was flabby and on section did not appear as vascular as usual. Sections of the testis and epididymis were submitted for histological examination, and a tentative diagnosis of testicular hypoplasia of genetic origin was made.
Histological Examination
Subsequent histological examination revealed very few spermatozoa to be present. The semeniferous tubules showed some spermatogonia and what appeared to be Sertoli cells, but little sign of further spermatogenic stages. From this it was apparent that spermatogenesis was not proceeding beyond the first stage.
Discussion
Although there is no proof that this condition was of genetic origin, and the original father-daughter mating could not be repeated owing to the death of the sow, it is considered that the most likely explanation does lie in the genetic theory, particularly since undesirable factors are determined generally by recessive genes. Hagedoorn (1944) states, “test mating a sire with his own daughters is not only a good way to recognise heterozygosis in respect of vital factors, but it brings out every sort of impurity". Although this breeder did not realise it, he was following this practice of test mating, as whenever stock with a lethal genotype are born, it is obvious that a condition of heterozygosity exists in the herd.
The finding or this condition, assuming it to be genetic in origin, reveals the need for test mating in pigs, and breeders would do well to undertake such matings, as they quickly reveal undesirable recessive factors, if present, and so enables their elimination by culling the heterozygotes. Such heterozygotes, if allowed to continue breeding, would result eventually in a high proportion of their like being present within the breed, to the ultimate detriment of the breed.
It would be of interest to know if similar cases have occurred in other parts of the State, but unfortunately some breeders suppress such information and by deliberately disregarding such happenings in their herds continue to propagate these heterozygous individuals. The extent to which such propagation reaches can be demonstrated best by again quoting Hagedoorn (1944): "if a male happens to be heterozygous for a vital gene, half his daughters must necessarily be also heterozygous". In the course of several years this could amount to a considerable number of heterozygous sows, in the case of pigs.
Acknowledgement
Thanks are due to Mr. D.C. Christie. B.VSc., D.V.O. (West), for permission to quote from official reports.
Reference
1. Hagedoorn. A.L. (1944), Animal Breeding. Crosby Lockwood and Son. London.