title: Multivariate analysis to evaluate genetic groups and production traits of crossbred Holstein × Zebu cows.
abstract: The objective of this research was to try to unveil the relationship between production traits and genotypic proportions of crossbred dairy cattle using principal component analysis (PCA) and cluster analysis. The herd consists of crossbred animals of Holstein (H) and Zebu (Z) (Gir and Guzerat) in different genotypic proportions; the composition of which varies from 12.5 to 100.0 % of the genetic group H. For this study, 834 milk production records from 257 cows from the years 1997 to 2014 were analyzed. The animals were all managed at a farm located in northeastern Brazil. The variables in the PCA were total milk yield per lactation (MY), milk yield adjusted to 305 days (MY305), lactation length (LL), and proportion of H and Z breeding. This analysis reduced the size of the sample space from the original five variables to two principal components (PCs) that together explained 89.4 % of the total variation. MY, MY305, LL, and genotypic proportion of H all contributed positively to PC1. The genotypic proportion of Z contributed negatively, which established a contrast between H and Z. Further cluster analysis identified two distinct groups when considering production performance and genotype of the animals. The high-performance group was predominantly Holstein breeding, while the lower performing group consisted mostly of Zebu. Under the environmental and management conditions in which this research was conducted, the best performances for the traits considered were achieved from cows whose genotypic proportion was between 38.0 and 94.0 % Holstein breeding.
authors.affiliation: Centro de Ciências Agrárias, Universidade Federal de Alagoas, BR 104 Norte, Km 85, 57.100-000, Rio Largo, AL, Brazil. angelina.fraga@gmail.com.
authors.forename: Angelina Bossi
authors.initials: AB
authors.lastname: Fraga
authors.affiliation: Departamento de Estatística, Universidade Federal de Mato Grosso, 78.060-900, Cuiabá, MT, Brazil.
authors.forename: Fabiane
authors.initials: F
authors.lastname: de Lima Silva
authors.affiliation: Departamento de Estatística, Universidade Federal de Mato Grosso, 78.060-900, Cuiabá, MT, Brazil.
authors.forename: Kuang
authors.initials: K
authors.lastname: Hongyu
authors.affiliation: Centro de Ciências Agrárias, Universidade Federal de Alagoas, BR 104 Norte, Km 85, 57.100-000, Rio Largo, AL, Brazil.
authors.forename: Darlim
authors.initials: D
authors.lastname: Da Silva Santos
authors.affiliation: Animal Science, University of Wisconsin, 53.706, Madison, WI, USA.
authors.forename: Thomas Wayne
authors.initials: TW
authors.lastname: Murphy
authors.affiliation: Animal Science, University of Wisconsin, 53.706, Madison, WI, USA.
authors.forename: Fernando Brito
authors.initials: FB
authors.lastname: Lopes
mesh_terms: D000822:Animal Husbandry; D000818:Animals; D001938:Brazil; D001947:Breeding; D002417:Cattle / Q000235:genetics*; D003433:Crosses, Genetic; D005260:Female; D005838:Genotype; D007774:Lactation / Q000235:genetics* / Q000502:physiology; D015999:Multivariate Analysis; D010641:Phenotype; D013045:Species Specificity
keywords: Cluster analysis; Lactation length; Milk production; Principal component analysis