On the genomic regions associated with milk lactose in Fleckvieh cattle

Abstract

Lactose is a sugar uniquely found in mammals' milk and it is the major milk solid in bovines. Lactose yield (LY, kg/d) is responsible for milk volume, whereas lactose percentage (LP) is thought to be more related to epithelial integrity and thus to udder health. There is a paucity of studies that have investigated lactose at the genomic level in dairy cows. This paper aimed to improve our knowledge on LP and LY, providing new insights into the significant genomic regions affecting these traits. A genome-wide association study for LP and LY was carried out in Fleckvieh cattle by using bulls' deregressed estimated breeding values of first lactation as pseudo-phenotypes. Heritabilities of firstlactation test-day LP and LY estimated using linear animal models were 0.38 and 0.25, respectively. A total of 2,854 bulls genotyped with a 54K SNP chip were available for the genome-wide association study; a linear mixed model approach was adopted for the analysis. The significant SNP of LP were scattered across the whole genome, with signals on chromosomes 1, 2, 3, 7, 12, 16, 18, 19, 20, 28, and 29; the top 4 significant SNP explained 4.90% of the LP genetic variance. The signals were mostly in regions or genes with involvement in molecular intra-or extracellular transport; for example, CDH5, RASGEF1C, ABCA6, and SLC35F3. A significant region within chromosome 20 was previously shown to affect mastitis or somatic cell score in cattle. As regards LY, the significant SNP were concentrated in fewer regions (chromosomes 6 and 14), related to mastitis/somatic cell score, immune response, and transport mechanisms. The 5 most significant SNP for LY explained 8.45% of genetic variance and more than one-quarter of this value has to be attributed to the variant within ADGRB1. Significant peaks in target regions remained even after adjustment for the 2 most significant variants previously detected on BTA6 and BTA14. The present study is a prelude for deeper investigations into the biological role of lactose for milk secretion and volume determination, stressing the connection with genes regulating intra-or extracellular trafficking and immune and inflammatory responses in dairy cows. Also, these results improve the knowledge on the relationship between lactose and udder health; they support the idea that LP and its derived traits are potential candidates as indicators of udder health in breeding programs aimed to enhance cows' resistance to mastitis.

Environmental Factors and Genetic Parameters of Beef Traits in Fleckvieh Cattle Using Field and Station Testing

“…Analysis of meat yield from Fleckvieh cattle at fattening control station (FCS) stations was pursued by [3] and provided important guidance on analyses for meat traits in this breed. Fleckvieh is the fourth biggest population of dual-purpose cattle in the world and the focus of genetic improvement has been widely put on milk and fitness traits in recent years [4][5][6]. Genetic improvement for meat yield in dual-purpose cattle breeds was previously negatively affected by the lack of information for estimating meat yield breeding values.…”

Investigation of β‐hydroxybutyrate in early lactation of Simmental cows: Genetic parameters and genomic predictions

“…Particularly, the ANKH gene was associated with inorganic pyrophosphate transport regulator that helps to prevent the deposition of Ca and P in the bones (Sanchez et al., 2018 ). This gene was found to be highly expressed in the mammary gland compared to other 17 tissues in Holstein and Jersey cows (Kemper et al., 2015 ), and it was associated with lactose percentage in Holsteins, Jerseys (Lopdell et al., 2017 ) and in Fleckvieh cattle, which is closely related to Simmental (Costa, Schwarzenbacher, et al., 2019 ). Although intronic variants of ANKH were mainly reported to be associated with milk alpha‐lactalbumin in Montbéliarde (Sanchez et al., 2018 ), Normande and Holstein cattle (Sanchez et al., 2017 ; Zaalberg et al., 2020 ), this gene also explains a relatively large portion of the phenotypic variance in mineral content (Mg) and has effects on protein composition (Sanchez et al., 2019 ).…”

“…The effect of the ANKH gene on BHB milk content could be explained by the genetic correlation between the latter and other milk production traits (such as lactose and protein). This gene has been associated with lactose and protein in milk (Costa, Schwarzenbacher, et al., 2019 ; Lopdell et al., 2017 ; Sanchez et al., 2019 ). Fat‐to‐protein ratio and protein yield are indicators of dysmetabolism as well as BHB.…”

Genome-wide association study for genotype by lactation stage interaction of milk production traits in dairy cattle

“…Similar effects have not been reported previously for lactose content. A few GWAS have been performed for lactose content in dairy cattle (Lopdell et al, 2017;Wang and Bovenhuis, 2018;Costa et al, 2019a), but none considered changing genetic effects during lactation. Compared with other milk production traits, milk lactose content has the smallest coefficient of variation (Table 1).…”