Accurate genetic parameters are vital for genetic prediction, selection on breeding values and creation of selection objectives. Consequently, records for birth weight (BW), 200 (WW), 400 (YW) and 600 (FW) day weight were analyzed to obtain heritability estimates. These records originated from Limousin herds with performance data on the South African Limousin Cattle Breedersâ€™ Societyâ€™s database for the period 1980 to 2006. The dataset consisted of 26533 BW, 9756 WW, 6558 YW and 3329 FW records. Log likelihood ratio tests were used to indicate the most suitable model for each trait. Models tested included a herd-year-season by sire interaction (HYSxS) and permanent maternal environmental effect as additional random factors. Single trait analyses yielded direct heritability estimates of 0.09 and 0.19 for BW and WW, respectively while corresponding maternal heritability estimates were 0.05 and 0.12. A strong negative association was found between direct and maternal effects with a genetic correlation of â€“0.64 and â€“0.70 for BW and WW, respectively. Direct heritability estimates for YW and FW were 0.16 and 0.24, respectively. Direct genetic correlations of BW with YW and FW were 0.37 and 0.33, respectively. Direct genetic correlations of WW with YW and FW were 0.99 and 0.93, respectively while the correlation between YW and FW was 0.92. Heritability estimates indicate that genetic progress of the above traits will be slower than might be envisaged by some authors, due to lower direct estimates. The strong negative relationship between direct and maternal effects needs to be deliberated when defining selection objectives.
"Experientia docet" - Experience is the best teacher