FIRST PUBLISHED JANUARY1985
Ranking on down production
AUTHOR: J.D. Winter, Agricultural Research Centre, Wollongbar, NSW.
Measurement of fleece characteristics of unselected feral goats and their progeny at Wollongbar Agricultural Research Centre has identified a practical method by which animals can be ranked on down production (by ranked, we mean place animals in order of highest to lowest down weight).
The components of fleece production in the fleece bearing animals have been divided into the following parameters. These are:
1. The size of the animal. Greater size and thus bodyweight will increase the surface area available to grow fleece. There is a standard formula which is used to equate bodyweight with surface area.
2. The density of the follicles producing the desired fleece. In the case of sheep, the density of primary plus secondary follicles are important. With the cashmere goat the density of the secondary follicles which grow cashmere will affect the total number of cashmere fibres. The other term used for follicle enumeration is S/P ratio or ratio of secondary to primary follicles. A high S/P ratio does not indicate on its own a superior fleece producer.
3. The diameter of the fibre. As the diameter increases so does the weight of fleece produced. Thus with two goats growing fleeces where all other components are constant, one that is 19 microns will have at least double the weight of fleece to the one which grows only a 13 micron fleece.
4. The length of the fibre. Doubling the length will automatically double the amount of fleece produced. Very high genetic variation for length has been identified indicating that it may be used as a selection tool. The high correlation between length and fibre diameter indicates that breeders using length as an indication of total fleece production will have to cull against increasing fibre diameter, as indicated in the Goat Note outlining breeding plans using the feral goat.
5. The specific gravity of the fibre which will contribute to the weight of an individual fibre. It is assumed constant within a type of fleece such as cashmere.
The following method outlines a systematic measurement of length to assess the ranking of animals in a herd on the basis of their down production. As a practical method it needs to be used in conjunction with the assessment of fibre diameter, due to the strong relationship between the two.
Development of the 'Method
The strong phenotypic (see Note 1) and genetic correlations between down weight and down length indicates that down length may be used as an indirect measure of down weight. This is not intended to replace the objective measurement of animals; however at the current cost of objective measurement we realise that many breeders may be unable to afford to measure all their stock. Using this indirect method, considerable cost savings can be made while still identifying animals with superior production characteristics.
Note 1. "Phenotype" is the word that explains the characteristics that are "seen" and measured on an animal. These phenotypic characters consist of the influence of inherited genes (or genotype) plus the influence of the environment (climate, food supply, etc.).
Thus the actual down growth is due to the genes inherited for length, diameter, etc. plus the effects of nutrition and external factors to give the realised length, diameter etc.
The relationship betwen the down length measurement and down weight (AWTA measurement) for the parent females and their male and female progeny are shown in the following diagrams. These show the phenotypic relationship between these two parameters; the genetic correlation is even stronger. (Or closer to the line drawn in the diagram).
Method of Length Measurement
The down length is measured on the live animal when down growth has ceased, and before shedding has begun. All animals in the drop should be managed similarly, and all should be measured if selections are to be made.
Using a short ruler (with the end flush with the zero measurement) or a dressmaker's tape measure, the longest length of down is measured at three body sites (A.B.C.) as shown in Diagram 4. The average of the three site measurements is calculated for each animal. Ranking the animals on the total length at the three sites or the average of the three sites will give the same order.
The reason for using these 3 sites is that it gives an average of length, taking into consideration the variability that occurs in the animal.
The choice of the actual site A may vary, as it represents the length of the cashmere on the neck region. Some animals have an area of long down that is larger or smaller near the site; the measurer must decide what length he will use, as a representative of the cover of the whole neck.
The method of measurement requires holding the end of the ruler or measure against the skin of the animal, carefully separating out a fair number of down fibres from the guard hair, and measuring the longest length of down in centimetres against the ruler. This procedure is illustrated in Diagram 5.
Diagram 5: Method of Down Length Measurement.
The length measurement generally varies from 1 centimetre up to 14 centimetres or longer. The heaviest down producers will tend to be those with the longest down. However, there are other factors that contribute to the down weight; such as diameter, number of fibres per unit of surface area, and total skin area of the animal.
© 1985 A.C.G.A.