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

McGregor, BA and Butler, KL 2016, Coarser wool is not a necessary consequence of sheep aging: allometric relationship between fibre diameter and fleece-free liveweight of Saxon Merino sheep, Animal, no. In Press, pp. 1-10, doi: 10.1017/S1751731116001038.

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Title Coarser wool is not a necessary consequence of sheep aging: allometric relationship between fibre diameter and fleece-free liveweight of Saxon Merino sheep
Author(s) McGregor, BAORCID iD for McGregor, BA
Butler, KL
Journal name Animal
Issue number In Press
Start page 1
End page 10
Total pages 10
Publisher Cambridge University Press
Place of publication Cambridge, Eng.
Publication date 2016-05-26
ISSN 1751-732X
Keyword(s) allometric coefficient
skin follicles
Summary 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 to 25.8) μm. A random coefficient restricted maximum likelihood (REML) regression mixed model was developed to relate the logarithm of MFD to the logarithm of FFLwt and other effects. The model can be written in the form of ${\rm MFD}\,{\equals}\,\rkappa \left( {{\rm GS,}\,{\rm A}{\rm ,}\,{\rm Segment}{\rm .Plot,}\,{\rm Segment,}\,{\rm ADG}} \right){\times}{\rm FFLwt}^{{\left( {\ralpha \left( {{\rm GS}} \right){\plus}\rbeta \left(\rm A \right){\plus}\rgamma \left( {{\rm Segment}{\rm .Plot}} \right)} \right)}} $ , where $\ralpha \left( {{\rm GS}} \right)\,{\equals}\,\;\left\{ {\matrix{\!\! {0.32\left( {{\rm SE}\,{\equals}\,{\rm 0}{\rm .038}} \right)\,{\rm when}\,{\rm sheep}\,{\rm are}\,{\rm grazed}\,{\rm alone}} \hfill \cr \!\!\!\!{0.49\left( {{\rm SE}\,{\equals}\,{\rm 0}{\rm .049}} \right)\,{\rm when}\,{\rm sheep}\,{\rm are}\,{\rm mixed}\,{\rm with}\,{\rm goats}} \hfill \cr } } \right.$ β(A) 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;
Language eng
DOI 10.1017/S1751731116001038
Field of Research 079999 Agricultural and Veterinary Sciences not elsewhere classified
06 Biological Sciences
07 Agricultural And Veterinary Sciences
Socio Economic Objective 970107 Expanding Knowledge in the Agricultural and Veterinary Sciences
HERDC Research category C1 Refereed article in a scholarly journal
ERA Research output type C Journal article
Copyright notice ©2016, Cambridge University Press
Free to Read? No
Free to Read Start Date 2016-11-01
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Document type: Journal Article
Collection: Institute for Frontier Materials
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Created: Thu, 09 Jun 2016, 10:59:15 EST

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