Genome-Wide Association for Fat Percentage in Buffaloes

Genome-wide association is a very promising tool to identify genes with major effect in a specific trait. Identifying these genes, we are able to better understand the physiology behind the trait as well as to prospect major genes for fine-mapping. The aim of the study was to do genome-wide association for fat percentage in dairy buffaloes. A total of 452 buffaloes (57 sires and 395 dams) were genotyped using the 90K Axiom ® Buffalo Genotyping (Affymetrix). The associations were done with the deregressed breeding values. The most important genes identified were genes related to the carbohydrate metabolism (KCTD8, FOXP4, LOC782855) and one gene related to lipid metabolism (ESRRG) were identified. The KCTD8 gene interacts with genes that act in the insulin secretion and glucagon liberation pathways, participating in the glucose absorption, FOXO4 gene down-regulates gluconeogenesis and up-regulates glycolysis  and LOC782855 (RPS26) was related to diabetes in humans. The association of ESRRG to fat production in the present GWAS could be expected, since this gene regulates other adipogenic genes. In cattle, ESRRG was also considered a key regulator of puberty in a multi-trait analyses that included fat deposition traits. Most of the top genes associated with fat percentage and fat production integrate the carbohydrate metabolism and not the lipid metabolism as in cattle. This fact could suggest some differences between buffalo and cattle fat production in milk. On average, buffaloes have higher contents of milk fat than cattle. In buffaloes the percentage of milk fat ranges from 6.7% to 12.0% while in cattle it ranges from 3.1% to 4.5% The difference in milk fat might be explained by a more efficient acetate metabolism to produce lipids in buffaloes, as the results suggest. Some hypothesis of buffalo lipid physiology were presented as well as good candidate genes for fat percentage.