Epsilon Archive for Student Projects

Abstract

Mastitis is a major problem for cows all over the world. For decades selection against mastitis has been performed through direct and indirect selection. Favorable outcomes of reduced mastitis incidence include: Economic gains, reduced use of antibiotics as well as improved animal welfare. Lately, new immunogenetic methods have emerged and the era of genomic selection has arrived. The innate and adaptive immune response, the bovine MHC and epigenetics are all of great relevance in this endeavor to improve immune response (IR) in cattle. Regarding breed differences in IR, few studies have been carried out on this subject and several factors need to be examined.

The High Immune Response (HIR) technology is a patented method developed by the University of Guelph, it identifies so called high immune responders in the population. Another technique is Genome-wide association studies (GWAS), this method can be used to find the location of immune-related traits on the bovine genome. A few different GWAS will be accounted for. For example, GWAS searching for genome associations with natural antibodies (NAb) as well as for associations with antibody-mediated IR (AMIR) and cell-mediated IR (CMIR). Genomic selection (GS) is another modern technique in which estimated breeding values (EBV) are calculated based on single nucleotide polymorphisms (SNPs). This method requires a genotyped and phenotyped reference population and animals need only to be genotyped for the indicator markers to be assigned an EBV. This has reaped great success in increasing genetic gain as well as in decreasing generation intervals.

Can these emerging methods surpass the results of the previously favored ones? The advantages as well as disadvantages are discussed. The disadvantages with the previous methods of selection for breeding are due to the time required and high expenses. Advantages with the emerging ones are faster results and shorter generation intervals. However, does the long-term genetic gain of GS actually surpass the traditional methods? Also, when manipulating the immune system, balance between responses must be considered. Otherwise, adverse effects like autoimmunity might appear. Sources of bias to the studies presented are also briefly mentioned. In conclusion, the area is still far too new to draw any major conclusions. However, it is a promising subject and further studies are of interest. The purpose of this literature study is to bring clarity to the question of whether it is possible to improve the bovine immune response to mastitis using immunogenetics.