Short communication: Time-dependent genetic parameters and single-step genome-wide association analyses for predicted milk fatty acid composition in Ayrshire and Jersey dairy cattle

摘要

Milk fat content and fatty acid (FA) compositionhave great economic value to the dairy industry asthey are directly associated with taste and chemicalphysicalcharacteristics of milk and dairy products.In addition, consumers’ choices are not only based onthe nutritional aspects of food, but also on productsknown to promote better health. Milk FA compositionis also related to the metabolic status and physiologicalstages of cows and thus can also be used as indicator forother novel traits of interest (e.g., metabolic diseasesand methane yield). Genetic selection is a promisingalternative to manipulate milk FA composition. In thisstudy, we aimed to (1) estimate time-dependent geneticparameters for 5 milk FA groups (i.e., short-chain,medium-chain, long-chain, saturated, and unsaturated)predicted based on milk mid-infrared spectroscopy, forCanadian Ayrshire and Jersey breeds, and (2) conducta time-dependent, single-step genome-wide associationstudy to identify genomic regions, candidate genes,and metabolic pathways associated with milk FA. Weanalyzed 31,709 test-day records of 9,648 Ayrshire cowsfrom 268 herds, and 34,341 records of 11,479 Jerseycows from 883 herds. The genomic database containeda total of 2,330 Ayrshire and 1,019 Jersey animals. Theaverage daily heritability ranged from 0.18 (long-chainFA) to 0.34 (medium-chain FA) in Ayrshire, and from0.25 (long-chain and unsaturated FA) to 0.52 (mediumchainand saturated FA) in Jersey. Important genomicregions were identified in Bos taurus autosomes BTA3,BTA5, BTA12, BTA13, BTA14, BTA16, BTA18,BTA20, and BTA21. The proportion of the varianceexplained by 20 adjacent SNP ranged from 0.71% (saturatedFA) to 1.11% (long-chain FA) in Ayrshire, andfrom 0.70% (unsaturated FA) to 3.09% (medium-chainFA) in Jersey cattle. Important candidate genes andpathways were also identified, such as the PTK2 andTRAPPC9 genes, associated with milk fat percentage,and HMGCS, FGF10, and C6 genes, associated withfertility traits and immune response. Our findings onthe genetic parameters and candidate genes contributeto a better understanding of the genetic architectureof milk FA composition in Ayrshire and Jersey dairycattle.