The objective of this study was to determine the environmental and genetic factors influencing mature cow weight (MCW) trait in Tswana cattle breed. Analyses of environmental and genetic effects for mature cow weight trait were performed using 19301 records of Tswana cows born between 1996 and 2010 from 610 dams and 137 sires in 54 contemporaries. Mature cow weight trait was analysed using repeatability model. The significant environmental effects for MCW were selection line, cow age and contemporary group. Heritability estimate for mature cow weight traits was 0.26±0.03. Genetic correlations between growth traits and MCW ranged from 0.15±0.17 between BWT and MCW to 0.84±0.19 between YWT and MCW. Phenotypic correlations between growth traits and MCW ranged from 0.15±0.04 between BWT and MCW to 0.31±0.03 between EWT and MCW. The existence of significant genetic variability and moderate repeatability in MCW trait coupled with high genetic correlation between this trait and early growth traits suggest that caution should be exercised when selecting for growth traits to avoid undesirable resultant change in mature cow weight trait.

Keywords: Selection, cow weight, genetic correlations, Heritability, repeatability model