PHOTOPERIODIC RHYTHM OF WOOL GROWTH AND ITS CONTRIBUTION TO SEASONAL WOOL PRODUCTION BY THE MERINO, POLWARTH, AND THEIR RECIPROCAL CROSSES IN SOUTHERN AUSTRALIA

Twelve wethers of each of the Merino and Polwarth breeds and their rec iprocal crosses were fed at 1 of 2 levels in individual pens for 14 mo nths. Periodic clean wool weight, yield, fibre diameter, and the coeff icient of variation (CV%) for fibre diameter were measured from midsid e patches harvested every 6 weeks. There was a significant effect of t ime of wool harvest on clean wool weight per cm2, yield, fibre diamete r (all P<0.01), and its CV% (P<0.05). A trough in wool production occu rred about August-September and a peak in January. The amplitude of th e 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, bu t 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 sta ple length from the tip there was no effect of genotype or level of fe eding. From comparison with published Tasmanian field data, the season al wool growth pattern of sheep at pasture appears similar to the phot operiodic rhythm but occurs about a month earlier. It was concluded th at the photoperiodic rhythm of wool production of Tasmanian Merino-bas ed breeds should not be a barrier to manipulation of wool quality (sta ple strength and fibre diameter) by nutritional management.