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Anim Biosci > Volume 34(4); 2021 > Article
Animal Breeding and Genetics
Animal Bioscience 2021;34(4): 499-505.
DOI: https://doi.org/10.5713/ajas.20.0031    Published online May 12, 2020.
Genotype by environment interaction for somatic cell score in Holstein cattle of southern Brazil via reaction norms
Henrique Alberto Mulim1  , Luis Fernando Batista Pinto2  , Altair Antônio Valloto3  , Victor Breno Pedrosa1,* 
1Department of Animal Science, State University of Ponta Grossa, Ponta Grossa, PR, 84030-900, Brazil
2Department of Animal Science, Federal University of Bahia, Salvador, BA, 40170-115, Brazil
3Paraná Holstein Breeders Association, APCBRH, Curitiba, PR, 81200-404, Brazil
Correspondence:  Victor Breno Pedrosa, Tel: +55-42-32203081, Fax: +55-42-32203072, Email: vbpedrosa@uepg.br
Received: 15 January 2020   • Revised: 18 March 2020   • Accepted: 20 April 2020
The objective of this study was to evaluate the genetic behavior of a population of Holstein cattle in response to the variation of environmental temperature by analyzing the effects of genotype by environment interaction (GEI) through reaction norms for the somatic cell score (SCS).
Data was collected for 67,206 primiparous cows from the database of the Paraná Holstein Breeders Association in Brazil, with the aim of evaluating the temperature effect, considered as an environmental variable, distinguished under six gradients, with the variation range found being 17°C to 19.5°C, over the region. A reaction norm model was adopted utilizing the fourth order under the Legendre polynomials, using the mixed models of analysis by the restricted maximum likelihood method by the WOMBAT software. Additionally, the genetic behavior of the 15 most representative bulls was assessed, in response to the changes in the temperature gradient.
A mean score of 2.66 and a heritability variation from 0.17 to 0.23 was found in the regional temperature increase. The correlation between the environmental gradients proved to be higher than 0.80. Distinctive genetic behaviors were observed according to the increase in regional temperature, with an observed increase of up to 0.258 in the breeding values of some animals, as well as a reduction in the breeding of up to 0.793, with occasional reclassifications being observed as the temperature increased.
Non-relevant GEI for SCS were observed in Holstein cattle herds of southern Brazil. Thus, the inclusion of the temperature effect in the model of genetic evaluation of SCS for the southern Brazilian Holstein breed is not required.
Keywords: Dairy Cattle; Environmental Effects; Genetic Evaluation; Mastitis; Somatic Cell Count

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