Seasonal variations in the dimensions of individual Romney wool fibres determined by a rapid autoradiographic technique

Abstract

A technique for radio-labelling short regions of growing wool fibres was modified by using intradermal injections of 3H-cystine and a rapid detection method. This technique allowed emergence times and dimensional changes of individual wool fibres to be rapidly and precisely monitored. Seasonal changes in fibre dimensions were determined for five sheep on maintenance nutritional levels following monthly injections over 12 months. Fibre diameter and length-growth varied seasonally, maximum and mimimum values occurring in summer and winter respectively. However, the amplitude and timing of each of these cycles differed between sheep and between fibres from individual sheep. As a consequence, the seasonal cycle in wool production (i.e., fibre volume) may be brought about by different combinations of fibre diameter and length-growth changes. Monthly diameter and length-growth measurements were often poorly correlated, suggesting that the cellular/physiological mechanisms determining these parameters in the follicle are complex.

Seasonal variation in fibre diameter and length in wool of grazing Merino sheep with low or high staple strength

“…At the break of season, liveweight and wool production changes were closely matched and within the time frame for responses recorded from a base diet with protein and amino acid supplementation regimes (Reis et al 1973;Reis and Tunks 1978;Hynd and Allden 1985). Grazing Merino wethers had a large and statistically significant variation in L : D ratio, in line with that recorded for Romney sheep (Woods and Orwin 1988). Purser (1980) suggested that L : D ratio varied over the year for Merino sheep grazing in a Mediterranean environment, based on divergences in the relationship between clean wool growth and fibre diameter.…”

“…Black (1987), in an analysis of unpublished data of D. J. Cottle, similarly found L : D ratio varied with nutritional status that altered wool growth but found that L : D 2 was constant. In both this grazing study and Woods and Orwin (1988) L : D 2 had significant variation with time when sheep were exposed to the full seasonal grazing environment.…”

“…The reports showing a consistency of L : D ratio have been pen-based experiments. Woods and Orwin (1988) in a grazing study with Romney sheep reported significant seasonal fluctuations in the L : D ratio and Hynd (1989) found a significant change in L : D ratio with nutritional status in penned Merino and Corriedale sheep but found that L : D 2 was constant. Black (1987), in an analysis of unpublished data of D. J. Cottle, similarly found L : D ratio varied with nutritional status that altered wool growth but found that L : D 2 was constant.…”

“…Other reports have shown changes to L : D ratios and suggested that L : D 2 is constant and a better descriptor of the relationship between length and fibre diameter (Black 1987;Cottle 1987;Hynd 1989). In grazing Romney sheep, significant seasonality was found in both L : D and L : D 2 (Woods and Orwin 1988), as well as a poor correlation between monthly fibre diameter and length measurements. A number of environmental, nutritional and hormonal factors have been shown to influence L : D ratio in Merino sheep and the impact of possible L : D ratio changes on staple strength has not been resolved (Hynd and Schlink 1992).…”

Genetics of fibre production and fleece characteristics in small ruminants, Angora rabbit and South American camelids

“…The amplitude is less pronounced in modern Merino sheep than in Angora goats and most other sheep breeds (Margolena, 1974;Ryder, 1978). The seasonal cycle in fibre growth is associated with concomitant changes in fibre length, growth rate, mean fibre diameter and mean fibre volume (Woods and Orwin, 1988). This seasonal cycle of fibre growth, and occasional fleece shedding, in modern SC breeds, therefore appears to be a vestige of the moulting cycle of primitive and DC breeds (Ryder, 1978).…”