The results of a study on two Merino studs in the Karoo clear up many of the mysteries surrounding selection programmes for fine wool. Roelof Bezuidenhout reports.
Farmers can grow finer wool without compromising other economically important traits, but should include these traits in their breeding objectives, or at least monitor them so that unwanted correlated changes can be picked up early. So says Willem Olivier, an animal breeding scientist at Grootfontein Agricultural Development Institute, who evaluated the effect of selection for decreased fibre diameter on production, as well as on subjective traits such as wool quality and overall conformation. “Fleece weight was emphasised during the 1950s and 1960s, so the proportion of fine wool (20 micron and finer) in the national clip dropped from 69% in 1951/55 to 4% in 1976/80,” says Willem “Then demand shifted and everyone wanted finer wool.”
The result was a huge price premium for finer wool types during the 1980s and 1990s. By 2005/06 the proportion of fine wool in the SA clip had increased to 24%, showing selection for decreased fibre diameter had become an important objective for many producers. “Sometimes it was even the only objective, irrespective of the effect on other production traits,” says Willem. “The better prices paid for finer wool types were the only goal, and farmers forgot how important it is to maintain a balance between the economically important traits, particularly in SA, where meat production contributes over 75% of Merino farmers’ income.” A study based on data collected on 5 820 ram and ewe hoggets at the Grootfontein Merino Stud from 1985 to 2003, and 6 127 ram and ewe hoggets from the Cradock Fine Wool Merino Stud from 1988 to 2004, found that these studs largely achieved their breeding objectives – increased body weight (BW) and staple length, maintaining clean fleece weight and decreasing average fibre diameter (MFD). This was despite unfavourable genetic correlations between MFD and the other traits, says Willem.
Traits bred concurrently
The secret was using estimated breeding values, which made it possible to select bigger and finer animals as replacement animals, increasing BW and decreasing MFD each generation. The hogget production traits analysis included body weight at 15 months, clean fleece weight, mean fibre diameter and staple length. The subjective traits, assessed on a scale from 1 to 50, were wool quality, variation over the fleece, staple formation, conformation of the front quarters and overall body conformation (CONF). Table 1 and Figure 1 show that the genetic trend for MFD was negative in the Cradock stud, and that MFD decreased only slightly from 1988 until 1996. This was because the animals were small with poor conformation; therefore, more emphasis was placed on BW than on MFD during the first few years. After 1997, when BW and CONF had improved, the Cradock stud placed more selection emphasis on MFD. In 1985 the Grootfontein stud began selection based on the breeding values of economically important traits. Table 1 and Figure 4 show fibre diameter steadily decreased over the 18-year period. This was achieved by placing more emphasis on fibre diameter from the start, as BW and CONF were satisfactory. But Willem cautions farmers to remember that unfavourable genetic correlations do exist between fibre diameter and other economically important traits, including BW, clean fleece weight and staple length. “Nonetheless, genetic changes in all the traits except staple formation and variation over the fleece were in the desired direction in both studs,” he explains. “Staple formation stayed constant at Cradock, but it decreased slightly at Grootfontein.” E-mail [email protected]. |fw
