title: Short communication: Recursive model approach to traits defined as ratios: Genetic parameters and breeding values.
abstract: A novel method for analysis of ratio traits (Y2/Y1) is proposed. Utilizing a recursive modeling approach, a proxy for Y2/Y1can be postulated as Y2- λ × Y1(i.e., Y2adjusted for the effect of Y1), where λ is a structural parameter describing an effect of change in phenotype of Y2caused by the phenotype of Y1. Estimates of parameters (direct effect parameters) for the recursive model Y1→ Y2can be derived from parameters of an equivalent 2-trait mixed effects model for Y1and Y2, using linear (location) and quadratic (dispersion) transformations. The method is illustrated with an application for milk fat (protein) content, calculated as a ratio of fat (protein) and milk yields (kg), in the context of genetic parameters estimation and genetic evaluation via the Canadian test-day model for production traits. Results indicated the potential usefulness of the proposed approach for analysis of any Y2/Y1(or Y2adjusted for the effect of Y1) type of trait utilizing standard multiple-trait modeling techniques for Y1and Y2.
authors.affiliation: Canadian Dairy Network, Guelph, Ontario, Canada, N1K 1E5; Centre for Genetic Improvement of Livestock, Department of Animal Biosciences, University of Guelph, Guelph, Ontario, Canada, N1G 2W1. Electronic address: jjamrozi@uoguelph.ca.
authors.forename: J
authors.initials: J
authors.lastname: Jamrozik
authors.affiliation: Canadian Dairy Network, Guelph, Ontario, Canada, N1K 1E5.
authors.forename: J
authors.initials: J
authors.lastname: Johnston
authors.affiliation: Canadian Dairy Network, Guelph, Ontario, Canada, N1K 1E5.
authors.forename: P G
authors.initials: PG
authors.lastname: Sullivan
authors.affiliation: Canadian Dairy Network, Guelph, Ontario, Canada, N1K 1E5; Centre for Genetic Improvement of Livestock, Department of Animal Biosciences, University of Guelph, Guelph, Ontario, Canada, N1G 2W1.
authors.forename: F
authors.initials: F
authors.lastname: Miglior
mesh_terms: D000818:Animals; D001947:Breeding; D002170:Canada; D008892:Milk; D010641:Phenotype; D017476:Receptors, Neuropeptide Y
chemical_list: D017476:Receptors, Neuropeptide Y
keywords: genetic parameters; ratio traits; recursive model