Resumo

VAN NIEKERK, D.J.; NESER, F.W.C.  e  VAN DER WESTHUIZEN, J.. An investigation into the possibility of a Genotype by Environmental interaction for milk production in the South African Jersey population. S. Afr. j. anim. sci. [online]. 2006, vol.36, n.5, pp.107-110. ISSN 2221-4062.

The possibility of a genotype by environment interaction for milk production in the South African Jersey population was investigated by grouping 37687 first lactation records completed between 1985 and 1999 into different production or environmental levels. The dataset consisted of 301 herds and 884 sires. Three different sets of criteria were used to group the animals. Firstly a cluster analysis was applied using different management, climatic and genetic factors. This analysis resulted into four different clusters. Secondly the herds were divided into four categories according to feeding systems and geographic location. All herds using a Total Mixed Ration (TMR) were placed in one group while the pasture herds form a second group. Herds that were situated in the warmer northern areas of South Africa (Limpopo and Northern KwaZulu-Natal) were placed into a third group and the herds in the Overberg area that did not have access to irrigation water formed a fourth group. Lastly the herds were divided into four groups according to production levels. A bivariate animal model was used to determine genetic correlation estimates for milk production between each group in the different scenarios. The correlations varied between 78% and 99%. The lowest correlation was between the warmer Northern areas and the Overberg area. The highest correlation was between Cluster 3 and Cluster 4 as well as between the low production group and the medium-low production group. The high genetic correlations indicate that no G x E existed for the different scenarios.

Palavras-chave : Cluster analysis; environmental factors; genetic correlations; milk production.

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