Identification of SNPs located on BTA 6 and BTA 20 significantly associated with bovine respiratory disease in crossbred cattle.

The objective of the present study was to evaluate single nucleotide polymorphisms (SNPs) located in two quantitative trait locus (QTL) regions (BTA 6 and BTA 20) that are associated with bovine respiratory disease (BRD). A population of 323 crossbred steers sired by five purebred sire breeds during 2010-2013 (Angus, Braford, Braunvieh, Charolais, and Simmental) were evaluated for BRD susceptibility during the finishing process at a commercial feedlot. A total of 21 animals representing all sire breeds were affected with BRD at some time during the finishing process over the 4-year period. Although multiple sire breeds were evaluated in the present study, no sire breed effects were detected. A total of 82 SNPs were evaluated (58 on BTA 6 and 24 on BTA 20) in the present study for potential associations with BRD incidence. When evaluating the previously described QTL regions on BTA 6, three SNPs (rs42968895, rs42823614, and rs43448463) were significantly (P < 0.05) associated with BRD incidence. Another three SNPs (rs42477340, rs42512588, and rs42524468) were identified as significantly associated with BRD on the previously described BTA 6 QTL region. For both of these regions, animals inheriting different genotypes differed in BRD incidence during the finishing period. Although multiple SNPs were identified as being significantly associated with BRD incidence in the present study, these SNP associations should be validated in larger and more diverse populations.

On the origin of metabolic pathways.

The heterotrophic theory of the origin of life is the only proposal available with experimental support. This comes from the ease of prebiotic synthesis under strongly reducing conditions. The prebiotic synthesis of organic compounds by reduction of CO(2) to monomers used by the first organisms would also be considered an heterotrophic origin. Autotrophy means that the first organisms biosynthesized their cell constituents as well as assembling them. Prebiotic synthetic pathways are all different from the biosynthetic pathways of the last common ancestor (LCA). The steps leading to the origin of the metabolic pathways are closer to prebiotic chemistry than to those in the LCA. There may have been different biosynthetic routes between the prebiotic and the LCAs that played an early role in metabolism but have disappeared from extant organisms. The semienzymatic theory of the origin of metabolism proposed here is similar to the Horowitz hypothesis but includes the use of compounds leaking from preexisting pathways as well as prebiotic compounds from the environment.