Use of gene marker technology for livestock improvement

Early animal breeders practised selective breeding by identifying what they considered worthwhile characteristics and sought a means of increasing the frequency of such desirable qualities in future generations. This has resulted to the present day specialised breeds of livestock like the Belgian Blue well known for its lean meat, the Holstein-Friesian noted for its milk-production, Superfine Merino for good quality wool and the Japanese Wagyu renowned for its highly marbled beef. For many farm animals, conventional breeding has already achieved high producing animals, but it seems increases in productivity by this means have peaked and are at the sedentary plateau phase. World population on the other hand is on the increase and so is the demand for animal products. Selective breeding cannot keep up with the pace of population growth because it is a painfully slow process and can take many years (especially in cattle with long gestation periods and generation intervals) to establish the desired phenotypic changes. However, the advent of DNA marker technology and its application to animal breeding programmes now provides a fast-tracking of selective breeding and livestock improvement. A genetic marker for a trait is a DNA segment which is associated with, and hence segregates in a predictable pattern, as the trait. Genetic markers facilitate the "tagging" of individual genes or small chromosome segments containing genes, which influence the trait of interest. Availability of large numbers of such markers has enhanced the detection of major genes influencing quantitative traits. The method involves screening the genome for genes with a large effect on traits of economic importance through a procedure known as linkage analysis The process of selection for a particular trait using genetic markers is called marker assisted selection (MAS). MAS can accelerate the rate of genetic progress by increasing accuracy-of selection and by reducing the generation interval. About 50% additional genetic gain can be obtained if the marker explains 20% of the additive genetic variance and the economic trait has a heritability of 0.2. This paper discusses the use of gene marker technology for the improvement of economic traits in beef cattle, sheep and pigs covering aspects of the Ryanodine receptor (Halothane) gene in pigs, Myostatin (double muscling) gene in cattle, Callipyge gene in sheep, TG5 (marbling) gene in cattle and the use of DNA profiling for parentage testing, carcass traceability, worm parasite resistance testing in sheep and the identification of the Inverdale gene for prolificacy in sheep. The paper will conclude with our current collaborative research in SNP Markers for healthy omega-3 fatty acids in crossbred prime lambs at the University of Tasmania