Hair samples, including the follicles, provide genetic material for commercial DNA-based analysis in beef and dairy cattle. Similar cattle, same environmental conditions, same vaccine protocols, same exposure to pathogens, and yet some get sick while some do not. Veterinarians have long observed that genetic differences must account for some of the variation in disease resistance or susceptibility in cattle, but the complexity of disease and immune response make development of selection tools much more difficult than for traits such as birthweight or coat color.
The emergence of genomics technology, however, opens up possibilities for more incorporation of health into selection strategies and development of more targeted vaccines, management and treatments based on genetic backgrounds.
DNA technology in livestock production has come a long way over the past decade, and ongoing research promises continued advancements and opportunities for veterinarians to further serve their dairy and beef clients.
Feedyard cattle exhibit a wide range of resistance or susceptibility to respiratory disease, and the imprecise nature of most field diagnosis complicates the process of quantifying the role of genetics. Geneticist Matt Spangler, PhD, at the University of Nebraska, says in the immediate term, marker-assisted selection has been most useful in selecting for or against simple traits such as horned versus polled, hair color and genetic defects.
Parentage is another simple, but often overlooked, application of DNA technology with a great deal of value, particularly for evaluating bull performance in beef herds where producers use multiple bulls in breeding pastures.
Next , Spangler says, the technology has advanced to the level of providing genomic predictions for more complex traits already described by phenotype-based measurements such as expected progeny difference (EPD) and predicted transmitting ability (PTA). These include traits such as growth, milk production, longevity, fertility, somatic-cell count, calving ease and carcass merit. Breed associations and milk recording agencies have collected phenotypic data for these traits on large numbers of cattle, which facilitates testing and validation of the genomic markers. By combining genomic predictions with an established EPD or PTA, breeders can offer an enhanced, more accurate prediction, particularly for young animals that lack progeny data.
The development process for genomic-enhanced predictions becomes more difficult when dealing with traits for which there are no conventional EPDs or PTAs, such as feed efficiency or susceptibility to specific diseases.