Coarser wool is not a necessary consequence of sheep aging: allometric relationship between fibre diameter and fleece-free liveweight of Saxon Merino sheep

Abstract

The mean fibre diameter (MFD) of wool is the primary determinant of price, processing performance and textile quality. This study determines the primary influences on MFD as Saxon Merino sheep age, by allometrically relating MFD to fleece-free liveweight (FFLwt). In total, 79 sheep were grazed in combinations of three stocking rates and two grazing systems (GS: sheep only; mixed with Angora goats) and studied over 3 years. Measurements were made over 14 consecutive periods (Segments), including segments of FFLwt gain or FFLwt loss. Using shearing and liveweight records and dye-bands on wool, the FFLwt and average daily gain (ADG) of each sheep were determined for each segment. The mean and range in key measurements were as follows: FFLwt, 40.1 (23.1 to 64.1) kg; MFD, 18.8 (12.7 is a random animal effect, γ(Segment.Plot) a random effect associated with Segment.plot combinations, and κ a constant that depends on GS, random animal effects, random Segment.plot combination effects, Segment and ADG. Thus, MFD was allometrically related to the cube root of FFLwt over seasons and years for sheep, but to the square root of FFLwt for sheep grazed with goats. The result for sheep grazed alone accords with a primary response being that the allocation of nutrients towards the cross-sectional growth of wool follicles is proportional to the changes in the skin surface area arising from changes in the size of the sheep. The proportionality constant varied systematically with ADG, and in sheep only grazing, was about 5 when sheep lost 100 g/day and about 6 when sheep gained 100 g/day. The proportionality constant did not systematically change with chronological age. The variation in the allometric coefficient between individual sheep indicates that some sheep were more sensitive to changes in FFLwt than other sheep. Key practical implications include the following: (a) the reporting of systematic increases in MFD with age is likely to be a consequence of allowing sheep to increase in size during shearing intervals as they age; (b) comparisons of MFD between sheep are more likely to have a biological basis when standardised to a common FFLwt and not just to a common age; (c) wool quality (MFD, staple strength) are most likely to be optimised in management systems that maintain constant FFLwt of adult sheep within and between years.Keywords: allometric coefficient, sheep, scaling, wool, skin follicles ImplicationsResponses in mean fibre diameter (MFD) of Merino wool to changes in fleece-free liveweight (FFLwt) were in accord with the primary response of MFD being proportional to the changes in the skin surface area arising from changes in animal size. However, this response can change with individual sheep and nutritional environment. Comparisons of MFD between sheep are more likely to have a biological basis when standardised to a common FFLwt than when standardised to a common age. Wool quality (MFD and staple strength) will be optimised in management systems that maintain constant FFLwt of adult sheep within and between years...

Effects of Age, Body Region and Mineral Contents on the Fleece Characteristics of Central Anatolian Merino Sheep

“…In Karacabey Merino sheep, Atav et al [9] reported that the mean of wool diameter as 28.67 µm which is higher than our result. However, the study conducted on Saxon Merino sheep and Anatolian Merino sheep (i.e., Central Anatolian Merino), the fibre diameters were found respectively, as 18.8 µm and 20.08 µm which is significantly lower than our study [37,38].…”

Productivity and Reproductive Performance of Mixed-Age Ewes across 20 Years of Selection for Ultrafine Wool in Uruguay

“…Adult ewe wool traits are key determinants of Merino flock income [38,39]. Wool micron accounts for 80% of the fleece value, with finer wool obtaining the highest prices [40][41][42]. During the FMP period (1999-2010), ewe FD decreased by approximately 3 µm, from 19 to 16 µm, which is comparable with previously reported reductions in FD in yearling lambs of the same flock [24].…”

Se and I status in pregnant ewes from a pastoral system and the effect of supplementation with Se and I or only Se on wool quality of lambs

“…A possible explanation for this result could be that the adopted supplementation was too late in the gestational moment, decreasing the effect on the overall parameters studied. However, McGregor and Butler (2016) showed that the diameter of fibre wool in Merino is an allometric property and that it is affected by the live weight of the sheep. Consequently, it is highly probable that as the live weight and the live weight gain of lambs with different treatments was the same over the first year of life, a difference in the diameter of fibre wool could not be expected.…”