Contemporary group alternatives for genetic evaluation of milk yield in small populations of dairy cattle
R. J. Pereira
A G , F. S. Schenkel B , R. V. Ventura B C , D. R. Ayres A , L. El Faro D , C. H. C. Machado E and L. G. Albuquerque F
A Grupo de Melhoramento Animal de Mato Grosso (GMAT), Instituto de Ciências Agrárias e Tecnológicas, Campus Universitário de Rondonópolis, Universidade Federal de Mato Grosso, CEP 78735-901, Rondonópolis, MT, Brazil.
B Centre for Genetic Improvement of Livestock, Animal and Poultry Science Department, University of Guelph, N1G 2W1, Guelph, Ontario, Canada.
C Beef Improvement Opportunities, Guelph, Ontario, Canada.
D Agência Paulista de Tecnologia dos Agronegócios, Instituto de Zootecnia, CEP 14160-900, Sertãozinho, SP, Brazil.
E Associação Brasileira dos Criadores de Zebu, CEP 38022-330, Uberaba, MG, Brazil.
F Faculdade de Ciências Agrárias e Veterinárias, Universidade Estadual Paulista Júlio de Mesquita Filho, CEP 14870‐000, Jaboticabal, SP, Brazil.
G Corresponding author. Email: rodjunper@gmail.com
Animal Production Science 59(6) 1022-1030 https://doi.org/10.1071/AN17551
Submitted: 7 August 2017 Accepted: 17 May 2018 Published: 10 July 2018
Abstract
In the present study, different random regression models, focussed on the nature of the effect of the contemporary group, fixed or random, were compared for genetic evaluation of test-day milk yield in dairy Gir breed, whose herds are characterised by relatively reduced numbers of cows. Cows were assigned to the same contemporary group if they were tested in the same herd, year and month. In one of the evaluated models, the contemporary group was investigated as a fixed effect and a clustering procedure was adopted to group herd-year subclasses in order to, at the end of the process, all contemporary groups contained at least three cows. The models were compared by the quality of fit, the accuracy of the predicted breeding values and their estimates of genetic parameters. The clustering procedure did not significantly improve the accuracy of predicted breeding values. Moreover, the fit to the data for this model was negatively affected. Therefore, this strategy should not be further implemented. The model including the herd-calving period effect and contemporary group treated as random effect showed similar characteristics to its equivalent, where the contemporary group was modelled as a fixed effect. However, the fit to the data for this model was slightly worse. Thus, the results suggest a random regression model including the herd-calving period effect and the fixed effect of contemporary group for the genetic evaluations of production traits in dairy Gir cattle. These findings could be extended to small dairy cattle populations whose herds are small-sized.
Additional keywords: animal breeding, dairy milk production, genetic correlation, genetic heritability.
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