Photoperiodic rhythm of wool growth and its contribution to seasonal wool production by the Merino, Polwarth, and their reciprocal crosses in southern Australia

Abstract

Twelve wethers of each of the Merino and Polwarth breeds and their reciprocal crosses were fed at1 of 2 levels in individual pens for 14 months. Periodic clean wool weight, yield, fibre diameter, and the coefficient of variation (CV%) for fibre diameter were measured from midside patches harvested every6 weeks.There was a significant effect of time of wool harvest on clean wool weight per cm2, yield, fibre diameter(all P<0.01), and its CV% (P<0.05). A trough in wool production occurred about August-September and a peak in January. The amplitude of the photoperiodic rhythm of wool growth (difference between maximum and minimum wool growth per cm2 per 42 days as a percentage of the average) was 40%. Yield also displayed a substantial photoperiodic rhythm, but that of fibre diameter was less pronounced. Mean staple strength was 32.3 N/ktex, the mean break occurring at a distance of 60% of the staple length from the tip; there was no effect of genotype or level of feeding. From comparison with published Tasmanian field data, the seasonal wool growth pattern of sheep at pasture appears similar to the photoperiodic rhythm but occurs about a month earlier. It was concluded that the photoperiodic rhythm of wool production of Tasmanian Merino-based breeds should not be a barrier to manipulation of wool quality (staple strength and fibre diameter) by nutritional management.