Bulldog Dwarfism in Dexter Cattle (Vind Afrikaanse weergawe hieronder)
Bulldog Dwarfism (Chondrodysplasia)
Bulldog dwarfism in Dexter cattle is one of the earliest single-locus disorders described in animals and has been documented in Dexter cattle since the early 1900s. Affected fetuses display among other defects, severe disproportionate dwarfism, short vertebral column and a large head. Typically, they die around the seventh month of gestation, precipitating a natural abortion.
Heterozygotes have one copy of the defective allele produces the favoured short-legged phenotype of Dexter cattle and showing a milder form of dwarfism, most noticeably having shorter legs. Thus, selection for the preferred Dexter phenotype may maintain a lethal allele in high frequency in the population. Breeding carrier animals together will produce 25% affected fetuses and leads to a reduction in the number of live born offspring.
In homozygotes the defect is a major problem for Dexter breeders as the these animals result in a loss of a calf for that season.
Bulldog Dwarfism is inherited in an autosomal recessive trait. This means, that the individual can be free of the disease (homozygote normal), affected (homozygous affected) or carrier (heterozygous, one mutant gene and one normal gene).
Carriers may spread the mutation in a population without showing symptoms themselves. Because of this, it is extremely important to identify carriers correctly and prevent the mutation spreading in the herd. No treatment is available for this disease.
The DNA test is available for the following breeds: Dexter and Dahomey and Brahman cattle. Bulldog dwarfism in Dexters is caused by mutations in the aggrecan gene (ACAN). The most common mutation is BD1. A diagnostic test for BD1 has been developed and is available to help Dexter breeders avoid production of bulldog calves. This mutation has also been found in the Brahman breed of cattle.
For the DNA test the following samples are accepted: hair, sperm, EDTA blood or any other tissue.
An animal can be disease free and has in this instance two healthy genes,. If used in breeding programs, this animal will not become ill due to the disease and also cannot spread the disease in the herd or any other herd either.
Carrier animals have one healthy and one disease gene. When used in breeding 50% of the offspring will receive the disease copy of the gene. Carriers will not become ill and perform at the same level as normal animals.
An affected animal has inherited two disease genes and will be aborted by the 7 th month op pregnancy.
Results are usually available within 7 working days from receipt of samples.
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Bulldog dwergisme By Dexter Beeste
Bulldog Dwergisme (Chondrodysplasie)
Bulldog dwergisme by Dexter beeste was een van diie eerste enkellokus genetiese toestande wat reeds in die vroeë 1900's beskryf is. Aangetasde fetusse toon verskeie afwykings wat insluit erge dwergisme, 'n kort ruggraat en 'n groot kop. Die erge dwergisme word toegeskryf aan abnormale kaakbeenvorming genoem chrondroplasie. Tipies vrek die fetusse teen sewe maande dragtigheid wat dan aanleiding gee tot aborsie.
Heterosigote (draer diere met een kopie van die defektiewe geen) toon minder erge vorme van dwergisme en diere het gewoonlik opsigtelike korter bene. Hierdie diere toon die verkose fenotipe vir Dexter telers en seleksie van sulke diere behou dus 'n potensiale letale geen in die beespopulasie teen hoë frekwensie. Teling met draer diere het teoreties 'n 25% kans vir geaffekteerd nageslag wat tot 'n verlies van 'n kalf vir daardie seisoen kan lei.
Bulldog Dexter dwergisme word as 'n ressesiewe genetiese eienskap oorgeërf. Dit het tot gevolg dat individuele diere vry van die toestand (homosigoties normal) kan wees, draers van die toestand (heterosigoties) of geaffekteerd (homosigoties geaffekteerd) kan wees. Draers (heterosigote) kan dus die siekte in die kudde versprei sonder om self simptome van die siekte te toon. As gevolg hiervan is die baie belangrik om draers (heterosigote) te identifiseer en nie as suiwer stoetteeldiere te gebruik nie aangesien die defektiewe geen vinnig in kuddes versprei kan word. Daar is geen behandeling vir die bulldog dexter toestand nie.
Is die Bulldog dwergisme rasgebonde?
Chondroplasie (Bulldog dwergisme) is reeds in Dexters, Dahomey en Brahman beeste beskryf. Bulldog dwergisme in Dexters word veroorsaak deur mutasies in die aggrecan geen (ACAN). Die algemene mutasie is die BD1 mutasie en kan met behulp van 'n DNA toets opgespoor word. Dexter telers kan dus die genetiese toestand uit hul kuddes teel deur diere te toets en parings korrek te bestuur.
DNA toetse kan voltooi word op DNA verkry vanaf bloed, haarwortels, semen of ander weefsel soos vleis.
Resultate sal aandui of die dier siekte vry is (geen mutasie teenwoordig) en dus kan die siekte nie versprey in 'n kudde nie. 'n Draer dier (heterosigoot) het een mutante geen en een normale geen. Indien so 'n dier in parings gebruik word kan 50% van die nageslag, net soos die ouers, draers vir die siekte wees, terwyl 25% "skoon" (dra geen mutante gene) kan wees terwyl 25% deur die siekte geaffkteer sal word en sal vrek.
Resultate is onder normale omstandigheide binne 7 werksdae na ontvangs beskikbaar.
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