Consequences of differing wool growth rates on staple strength of Merino wethers with divergent staple strengths

An experiment was conducted to determine the effects of dietary protein int ake after a period of weight loss on the wool components of staple strength for sheep with a history of low or high staple strength (18.0 vs 34 N/ktex ). After being fed to lose 15% of their liveweight over 10 weeks, sheep wit hin each staple strength group were assigned in equal numbers to either a l ow or high protein diet designed to re-gain initial liveweight in 8 weeks. Liveweight, feed intakes and the growth, fibre diameter and fibre length ch aracteristics of wool were measured at regular intervals. After the weight loss and growth regimes were imposed there was no differen ce in staple strength between the low and high staple strength groups (14.4 and 14.9 N/ktex , respectively). However, coefficient of variation (CV) of fibre diameter remained significantly different between staple strength gr oups. Wool growth rate at the time of diet change was the only significant component of wool growth and fibre measurements that was significantly corr elated with staple strength. Supplying a high protein diet after a period of weight loss increased wool growth. This changed the position of break along the staple and increased t he fibre diameter at the point of break from 13.0 to 13.9 mu m without affe cting staple strength. It also increased fibre diameter and mean fibre leng th growth rate. The low staple strength group had a significantly higher CV of fibre length than the high staple strength group. Fibre length growth r ate to fibre diameter ratio was stable over time in the high staple strengt h phenotype but declined with time in the low staple strength line. The results suggest that large weight losses will reduce the difference in staple strength between animals with a history of large difference in stapl e strength. Rate of wool growth after the point of break did not influence this staple strength outcome.