Fleece and fibre measurements in angora goats and angora rabbits.

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Further information

The angora goat is primarily raised for textile fibre, known as mohair. Income from mohair is largely determined by the quantity and the quality of fibre produced by goats, that is, the weight of clean fibre, mean fibre diameter with fibre distribution and the rate of undesirable fibres (kemp and medullated fibres). Other fleece quality traits like staple length, style, character and lustre have a slight effect on the value of mohair.

Except for greasy fleece weight, that can be easily determine directly on the farm by the grower with a weighing machine, the other fibre characteristics which determined fibre quality need to be objectively measured in a laboratory. The main quality criteria are the clean fleece content, mean fibre diameter, fibre diameter distribution and kemp, and medullated fibre content.

The standard method used for wool and defined by the IWTO can be extended to mohair. It is the amount of wool or mohair base adjusted to a standard ash plus alcohol content of 2.27 % and brought finally to a regain (due to moisture content) of 17 %. The method required to determine the mohair base, that is the content of fibre free of all impurities (water, ash, grease or alcohol ether extract and vegetable matter), is achieved with the washing yield, determination of ash content, alcohol-extractable matter, and vegetable matter content. However, this method used for trade and industrial purpose is time consuming and expensive; Thus it cannot be used to determine clean fleece content of one animal. A derived methodology called "ITF-INRA washing yield method" has been developed in France. This method, using ultra sonic technology, is well correlated to IWTO standard method and accurate enough for determining clean fibre content of a fleece or a small fibre lot.

There are two main standard methods of obtaining information about the fibre diameter of a mohair or wool sample. The first method (IWTO E1/71E) establishes mean fibre diameter by using instruments such as an airflow apparatus of the constant flow or constant pressure type. This method is not recommended for medullated fibres. However, no information on fibre distribution is obtained with this method. The second method allows the calculation of mean fibre diameter and fibre distribution (standard deviation and coefficient of variation) using instruments, such as projection microscopes (IWTO B/66E) and OFDA (Optical Fibre Diameter Analyser). The latter apparatus allows to determine fibre distribution by observing up to several thousands of fibre within a few minutes and is becoming widely used. Another recently method, but not yet standardised, is based on the measurement of the area, shape and dimensions of the fibre cross section under a microscope with the help of a computerising image analysis system. This method is well correlated to the OFDA method and can also be used for determination of kemp and medullated fibre content (Allain & Thebault, 1995, Rasmussen, 1995).

Up to now, kemp and medullated fibre content are determined by observing and counting under a microscope a large quantity of individual fibres. This method is time consuming. There are other possible methods. The first is the cross-section method (Allain & Thebault, 1995, Rasmussen, 1995), that determined simultaneously mean fibre diameter, fibre distribution and medullated fibre content. The second is derived from OFDA apparatus, that have been modified to differentiate medullated fibres from non medullated fibres. It is based on fibre opacity (Brims, 1993; Peterson et al., 1994). However this method needs to be tested and improved.

The angora rabbit produces a very fine fibre (from 12 to 16 µm) without grease or any vegetable contamination that can be processed without any cleaning treatment by the textile industry. There are different kinds of fibres within the fleece: guard hair or bristle, that is a coarse and long fibre, an intermediate fibre and the down, a short and fine fibre. However, conversely to other fibre producing animals, all fibres are desirable. Furthermore, there are different grade of angora as the structure and the composition of the fleece vary over the body. Thus the main criteria determining the quantity and the quality of angora produced by angora rabbit are: total fleece weight, the weight of different angora grades making up the fleece, the fibre diameter, fibre length and the rate of each fibre type within the fleece.

Total fleece weight and the weight of each angora grade can be easily determined directly on the farm by the grower, with a weighing machine. Similarly, bristle length and down length within the fibre staple can be easily measured with a ruler, the French angora rabbit having a well structured fleece. However, other fleece and fibre characteristics, as well as fibre length in the German angora rabbit, need to be measured in a laboratory.

Up to now, an IWTO method (IWTO-8-89) is defined for determining fibre diameter and percentage of medullated fibre in wool and other animal fibres, by using a projection microscope. Nevertheless, this method is time consuming, not widely used for measuring fleece composition or fibre diameter in angora and not very precise, as most angora fibres are medullated and the fibre cross section shape is not circular. A recent method based on measurements of fibre cross section characteristics have been recently developed (Allain and Thebault, 1995). This method describes characteristics of the different fibre types of the angora rabbit fleece, determines the content of each fibre type and measures cross sections' characteristics by using a new histology technique, combined with microscopic image analysis and computer techniques. The new OFDA apparatus, that seems to be able to differentiate medullated fibres, could be an alternative for measuring fleece composition and diameter of each fibre type. However, this OFDA apparatus has to be tested for angora.

When the fibre staple is not well structured due to the harvest method by shearing, as it is very often in the German angora rabbit, the length of bristles and other angora fibres can be measured by determining bristle and height with a comb sorter.

Allain, D. and Thebault, R.G., 1995. A rapid method for measuring cross-section characteristic of animal fibres. In « Metrology and Identification of Speciality animal fibres », Eds. J.P. Laker & F.-J Wortmann, European Fine Fibre Network, Occasional Publication, 4:99-110.

IWTO-47-95, 1996. Measurement of the mean and distribution of fibre diameter of wool using an Optical Fibre Diameter Analyser (OFDA).

NF.G.07.060, 1968. Methodology to establish the length of bristles and other angora fibres with comb sorter.

Peterson, A.D., Gherardi, G.H. & Brims, M.A., 1994. The measurement of medullation in mohair using the Optical Fibre Diameter Analyser. Proceedings of the Australian Society of Animal Production, 20:363.

Rasmussen, P., 1995. Morphometric analysis of cross-sectional profiles of hair fibres applied to an objective fibre test. In « Metrology and Identification of Speciality animal fibres », Eds. J.P. Laker & F.-J Wortmann, European Fine Fibre Network, Occasional Publication, 4:87-98.