A cytogenetical study of cattle and pigs

Chromosome preparations were derived from short-term cultures of blood lymphocytes from 293 cattle and 99 boars. The cattle were of 9 breed-types involving 23 breeds and included the following groups:(i) 249 phenotypically normal bulls(ii) 15 cattle of both sexes with abnormal phenotypes(iii) 9 cattle (8 females and one male) descendants of a Charolais bull, with a presumptive 1/29 translocation(iv) 15 cattle (6 sets of twins and 1 set of triplets) of multiple birth origin.(v) 2 Banteng male cattle(vi) 3 phenotypically normal cows artificially inseminated with semen from a Charolais bull with a presumptive 1/29 translocation.The 99 boars, of which 76 were performance tested, were from 3 breeds: Large White (48), Landrace (20) and mixed breed (31).Lymphocytes were cultured in tissue culture medium 199 (C.S.L.) with 20% foetal calf serum (C.S.L.) and phytohaemagglutinin at 37.5°C for 48-72 hours, colchicine being added to the culture 2-5 hours before harvesting. Usually 0.075M potassium chloride solution for l6 minutes was used as hypotonic treatment; the cells were fixed in suspension with glacial acetic acid and methanol (l:3) spread on slides and stained with 4% Giemsa. The quality of mitotic metaphase chromosomes compared favourably with those prepared from other species including man. Characteristic morphological features of some chromosomes which aided in their recognition were found, but the identification of many homologous pairs by conventional staining techniques was difficult if not impossible. The normal karyotypes of cattle and pig as well as a bovine karyotype with a presumptive 1/29 translocation were characterised following Giemsa staining and C-banding.The chromosomes of all cattle were arranged into five rows of six pairs with the sex chromosomes occupying the position of the last pair in the karyotype. The autosomes were placed in order of descending size from pair no. 1 to pair no. 29.Analysis of mitotic chromosomes prepared from 249 phenotypically normal bulls showed that two bulls had sex chromosome mosaicism while the remainder possessed normal karyotypes. Fourteen cattle, of both sexes, with abnormal phenotypes also possessed normal karyotypes. All but one of fifteen cattle of multiple birth origin (6 sets of of twins and 1 set of triplets) showed sex chromosome chimaerism. The remaining female triplet partner possessed a female set of sex chromosomes only.Karyotypes of 9 descendants of a Charolais bull with a presumptive 1/29 translocation, showed that five cattle (3 daughters and 2 granddaughters) carried the translocation; all were phenotypically normal.Analysis of mitotic chromosomes prepared from 2 male Banteng cattle showed that their chromosomes were similar to those of Bos taurus cattle with a small submetacentric (sm) Y chromosome.For the nine cattle breed-types involved in the study, morphology of the autosomes and the X chromosomes was similar while that of the Y chromosome varied according to the derivation of the breed-type - all Bos taurus, Africander, Banteng and breeds derived from the former 2, possessed a submetacentric (sm) chromosome while all Bos indicus and derived breeds possessed an acrocentric (t) Y chromosome.The only variation of the submetacentric (sm) Y chromosome in Bos taurus breeds was that of the Jersey breed which was metacentric (m). One breed (Droughtmaster) was noted to have two forms of the Y chromosomes (acrocentric (t) and submetacentric (sm)) depending on the breed line. The morphology of the Y chromosome of bulls v;as similar to that of their sires.Analysis of 9394 mitotic cells prepared from 274 cattle with normal karyotypes revealed that 85% of cells possessed the modal chromosomal number (60), 12.8% cells were peridiploid with a marked bias towards hypodiploidy(11%) and polyploidy, which accounted for 2.2% cells, was chiefly tetraploidy (2.1%), triploidy (0.05%) and others (0.05%). The overall incidence of secondary constrictions was 0.7% while that for chromatid gaps was 5.5%.C-banding patterns of the autosomes and X chromosomes were similar for all breeds of cattle while that for the Y chromosome varied because of the difference in morphology of the Y chromosome between some breeds. After centromeric staining, the acrocentric (t) Y chromosome of Bos indicus and derived breeds v;as readily distinguished from acrocentric autosomes of similar size. The presumptive 1/29 translocation chromosome displayed a single darkly stained centromere usually of similar size to that of chromosome number 1.Fertility of bulls was determined where possible by 60-90 day non-return rates or pregnancy testing, while semen characteristics, including mean values of total sperm numbers per ejaculate, percent sperm abnormalities and percent live/normal sperm per ejaculate were recorded.Analysis of mitotic chromosomes prepared from 99 phenotypically normal boars involving 3 breeds, showed that the modal chromosome number for all pigs was 38 and this was observed in 84.5% cells, Peridiploidy accounted for 13.4% cells with a marked bias towards hypodiploidy (11.8%), while polyploidy (2.1%) involved tetraploid (1.8%), triploid (0.2%) and other cells (0.1%). Chromatid gaps were observed in chromosomes in 1.1?o of cells while chromosomes bearing secondary constrictions were observed in 89*9/^ cells. The presence of secondary constrictions helped in the identification of some chromosomes - chromosomes number 4 and 10. The 38 chromosomes of the pig were arranged into 4 groups according to centromeric position using the nomenclature and system proposed by Levan et al. (l964). Chromosomes of group 1 had sm morphology, group 2 st morphology, group 3 m morphology and group 4 t morphology. Both sex chromosomes with m morphology were placed in group 3. Difficulty was experienced with identification of several pairs of chromosomes using the conventional Giemsa staining technique while pair nos, 1, 6, 10, 13 and 16 and the Y chromosome were usually readily identified. All chromosomes of the pig karyotype, exhibited C-bands, some, (those with t morphology) displaying the bands earlier than others. Pale bands were also observed in the arms of chromosome numbers 14 and 16 while pair no. 1 exhibited dimorphism. The Y chromosome frequently appeared dark all over but in good preparations the short arm was palely stained.Reproductive performance and performance test scores of boars were measured.Results of chromosome analyses, their significance and C-banding patterns involving cattle and pig have been discussed in detail. Any association between karyotype and performance characters of the animals observed in this study appears to be indefinite if it exists at all. Also the relationship may be of little significance and its reliability for the selection of animals of superior genetic merit is doubtful.While this study adds to our knowledge and helps to define the norms of the karyotypes of both species, more detailed investigations are necessary in order that veterinary cytogenetics may play a role similar to that enjoyed by medical cytogenetics in man.