Genetic relationships among production and reproduction traits measured in a fine wool Merino stud

 

W.J. Olivier1,2#, S.W.P. Cloete2,3, M.A. Snyman1 & J.B. van Wyk4 

1Grootfontein Agricultural Development Institute, Private Bag X529, Middelburg (EC), 5900, South Africa

2Department of Animal Sciences, University of Stellenbosch, Matieland, 7602, South Africa

3Institute for Animal Production: Elsenburg, Private Bag X1, Elsenburg, 7607, South Africa

4 Department of Animal, Wildlife and Grassland Sciences, University of the Free State, Bloemfontein, 9300, South Africa

 

#Corresponding author: Willem Olivier

 

In some instances, producers put all the emphasis in their breeding plans on reducing fibre diameter, irrespective of the consequences for growth, wool weight, reproduction and subjective wool and conformation traits. Given the genetic relationship among reproduction, live weight and wool traits, it is clear that selection should consider all traits of importance to ensure that production and reproduction will be at an optimum level. It is important to have a good knowledge of the respective (co)variance components and accurate genetic parameters to design effective breeding programs. It is also important to understand the correlations and indirect responses that may accrue as based on different traits included in the selection program. Overall selection progress will be hampered if these relationships are not considered when breeding strategies are defined. The aim of this study was to quantify the genetic relationships among reproduction and objectively and subjectively measured wool and conformation traits, as well as the genetic progress achieved through selection. Data collected on a maximum of 8 368 ram and ewe progeny born within the Cradock fine wool Merino stud from 1988 to 2010 were used for the analysis of the body weight and wool characteristics. Reproduction data collected on 1 775 ewes born in this stud from 1988 to 2010, were used to analyse reproduction traits. The traits included in the analysis were body weight at 15 months of age (BW), clean fleece weight (FW), fibre diameter (FD), staple length (SL), staple strength (SS), wool quality (WQ) and overall body conformation (BC), as well as number of lambs weaned (LW) and total weight of lamb weaned (TW) over three lambing opportunities. The direct additive heritability for BW, FW, FD, SL, SS, LW, TW, WQ and BC were 0.49, 0.55, 0.63, 0.41, 0.26, 0.02, 0.02, 0.54 and 0.48 respectively. The corresponding maternal heritability for BW, FW, FD and BC were 0.05, 0.05, 0.02 and 0.05 respectively. The maternal permanent environmental effect for SS was 0.04 and the animal permanent environmental effect for LW and TW were 0.07 and 0.09 respectively. The genetic correlation (rg) between BW and FD was moderately and unfavourably (0.30). The rg estimates of FD with FW (0.24) and SS (0.51) were low to moderate and unfavourable (i.e. positive), while the rg between FW and SS (0.27) was moderately favourable. Number of lambs weaned and TW was highly correlated (0.91) and BW was also favourably correlated with LW (0.31) and TW (0.78), while FW and FD were unfavourably correlated to LW (-0.23; 0.56) and TW (-0.21; 0.59). The rg between SS and the reproduction traits were low positive (0.19; 0.15). The rg estimates of WQ with BC (0.02) and BW (-0.01) were non-significant, while FD (-0.45) and FW (0.28) was favourably correlated with WQ. The rg estimate of FD with BC (0.27) was moderately positive (i.e. unfavourable), while SS (0.35) was favourably correlated to the subjectively assessed conformation trait linked to size. Overall body conformation was favourably correlated to LW (035) and TW (0.77) while the corresponding rg with WQ were non-significant. It can be concluded from the results of this study that selection should be done holistically to ensure that the unfavourable correlations among the economically important traits are considered. Selection for FD or reproduction without monitoring the other economically important traits could have a detrimental effect on the sustainability of sheep production.

 

Published

Proceedings 47th SASAS congress, Pretoria