The allometric relationship between mean fibre diameter of mohair and the fleece-free liveweight of Angora goats over their lifetime
B. A. McGregor A B F , K. L. Butler C and M. B. Ferguson D E
+ Author Affiliations
- Author Affiliations
A Centre for Material and Fibre Innovation, Deakin University, Geelong, Vic. 3220, Australia.
B Formerly Livestock Production Sciences, Future Farming Systems Research Division, Department of Primary Industries, Attwood, Vic. 3049, Australia.
C Biometrics Unit, Future Farming Systems Research Division, Department of Primary Industries, Werribee, Vic. 3030, Australia.
D Department of Agriculture and Food Western Australia, South Perth, WA 6151, Australia.
E Formerly, Livestock Production Sciences, Future Farming Systems Research Division, Department of Primary Industries, Hamilton, Vic. 3300, Australia.
F Corresponding author. Email: bruce.mcgregor@deakin.edu.au
Animal Production Science 52(1) 35-43 https://doi.org/10.1071/AN11086
Submitted: 26 May 2011 Accepted: 29 November 2011 Published: 4 January 2012
Abstract
As mean fibre diameter (MFD) is the primary determinant of mohair price we aimed to quantify the lifetime changes in mohair MFD as Angora goats aged and grew. Measurements were made over 12 shearing periods on a population of Angora goats representing the current range and diversity of genetic origins including South African, Texan and interbred admixtures of these and Australian sources. Records of sire, dam, birthweight, birth parity, liveweight, fleece growth and fleece quality were taken for does and castrated males (wethers) (n = 267 animals). Fleece-free liveweights (FFLwt) were determined for each goat at shearing time by subtracting the greasy fleece weight from the liveweight recorded immediately before shearing. A restricted maximum likelihood growth curve model was developed for relating MFD to FFLwt, age and other measurements. A simple way of describing the results is: MFD = κ (FFLwt)β E; where κ is a parameter that can vary in a systematic way with shearing(age), breed, weaning weight, sire, dam and individual; β is a parameter that is the same for nearly the whole study; and E are independent errors from a log-normal distribution. The analysis shows that 
= 0.34, with s.e. () = 0.021. Thus, mohair MFD was allometrically related to the cube root of FFLwt over the lifetime of Angora goats. However, the allometric proportionality constant differed in a systematic way with age at shearing, genetic strain, weaning weight, sire, dam and individual. For Texan-breed goats, MFD decreased as weaning weight increased (P = 0.00016). The findings indicate that management factors that affect liveweight and weaning weight have lifetime effects on mohair fibre diameter and therefore the value of mohair and the profitability of the mohair enterprise.
Additional keywords: age effects, genotype, mohair production, nutritional management, weaning management.
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