relative length of cashmere and hair
McDonald, Queensland Department of Primary Industries, Animal Research
Institute, Yeerongpilly, Qld. 4105.
The length of cashmere fibres in goats compared to length of hair fibres is of interest for several reasons:
(i) Relative length of cashmere is one of the components of percentage yield of cashmere from total fleeces.
(ii) Where cashmere fibre length exceeds hair fibre length, cashmere fibre staples become curled in the tip.
(iii) Cashmere fibres which are longer than hair fibres are susceptible to UV light degradation, tip weathering, vegetable matter contamination and cotting.
The purpose of this review is to consider the nature of the relationship between cashmere and hair fibre length in terms of seasonal change, photoperiodic manipulation, breeding history and lactational status and history. These features will be discussed in relation to their influence on the characteristics of fibre length as outlined above.
The data were generated in experiments in which the following types of goats were used under different housing environments:
RESULTS AND DISCUSSION
The circannual changes in the length of cashmere and hair fibres of mature feral does under natural day length are shown in Figure 1. There are several features of these cycles which are worthy of comment. In the fleece growth cycle following lactation cashmere length reached a maximum of 40 mm while hair length reached 60 mm. At no stage during this cycle did cashmere length exceed hair length. In the second fleece growth cycle prior to which the does had not undergone pregnancy and lactation the length of cashmere and hair fibre reached a maximum of 60 and 55 mm respectively. Fibres were of equal length in May (50 mm). This time coincides with the recommended shearing time indicated by fleece metrology parameter mapping in the detailed results of this research.
The results suggest that after pregnancy and lactation in feral does, the length of cashmere fibres will not exceed that of hair fibres. Under favourable fleece growth conditions in the absence of pregnancy and lactation, cashmere length will exceed hair length by approximately 5 mm. Both situations have inherent problems since, in the former, cashmere production is reduced while in the latter, losses may accrue from cashmere fibres' being longer than hair fibres. Compromise action may be warranted, depending on the relative economic penalties. Shearing non-breeding feral goats in May will probably produce little fibre length differential.
Figure 1. Circannual changes in cashmere and hair fibre length of feral does under natural day length. The first growth cycle was preceded by pregnancy and lactation, whereas these events did not occur prior to the second cycle.
Cashmere length o- - - - o hair length
Circannual changes that occurred in fibre length whey mature feral does were exposed to continuous light are shown in Figure 2. This treatment induced three fleece growth cycles in 14 months. The maximum length of cashmere and hair fibres was 55 and 50 mm, 60 and 5C mm and 65 and 50 mm, at the first, second and third growth cycles respectively. Obviously, continuous light enhanced cashmere linear growth. The magnitude of this enhancement appeared to increase with the length of time that the goats were exposed to continuous light, as did the difference between the length of cashmere and hair fibres. Shearing in February (as indicated by previous fleece metrology parameter mapping) in the second fleece growth cycle, and October in the third cycle would have produced a fleece with cashmere and hair fibres of equal length.
Cashmere length o- - - - o hair length
The circannual changes in hair length under natural day length and continuous light as shown in Figure 3, provided some insight into the reason why cashmere length exceeds hair length following continuous light treatment. Generally, continuous light restricted hair length to 50 mm at each of the three growth cycles while hair length at the two growth cycles under natural day length was 60 and 55 mm.
Figure 3. Circannual changes in hair length of feral goats under natural day length and continuous light. Continuous light restricted hair length to 50 mm at each cycle compared to length of 60 and 55 mm at the first and second natural day length cycle respectively.
Natural day length o- - - - o Continuous light
Table 1 shows the relative fibre length of lactating and non-lactating feral does near the summer solstice. There is no difference between the groups and hair length exceeds cashmere length. This would be expected from the results of earlier studies on the cashmere growth cycle. Confirmation of the effect of lactation must await further measurements during the fleece growth phase.
1. Effect of lactational status on mean
The relative length of cashmere and hair fibres in the fleece of the wether progeny of selected sires is shown in Figures 4 and 5. Under natural daylength conditions (Figure 4), cashmere fibres were approximately 5 mm longer than hair fibres for most of the fleece growth cycle. Shearing in May (as indicated by previous fleece metrology parameter mapping) would produce the maximum fibre length differential in these goats. Shearing in February or March would result in relative length equality at the expense of cashmere production.
Shearing at this time would produce a mean cashmere fibre length of 30 mm which is below that required for woollen spinning (40-45 mm).
Figure 4. Changes in cashmere and hair length under natural day length in the wether progeny of selected bucks and feral does. Generally cashmere fibres were longer than hair.
Cashmere length o- - - - o hair length
Exposure to continuous light for three months accelerated cashmere fibre linear growth but did not affect hair growth (Figure 5). The maximum difference (20 mm) occurred at the end of the growth cycle in May when cashmere length was 65 mm and hair length 45 mm. As indicated for the wethers in natural light, earlier shearing in March or April would tend to produce a fleece with cashmere and hair fibres of equal length, to the detriment of cashmere production and result in mean cashmere length of only 35-45 mm.
Figure 5. Changes in cashmere and hair length under continuous light in the wether progeny of selected bucks and feral does. Continuous light increased the linear growth of cashmere but did not affect hair.
Cashmere length o- - - - o hair length
It should be emphasised that the foregoing observations indicating relative fibre length imbalance in these "bred-on" wethers need not be exclusively of genetic origin. This phenomenon may also result from the absence of the
physiological stress of pregnancy and lactation. Breeding does from the same source may exhibit a quite different fleece structure. If this is the case, then "bred-on" wethers may be showing fleece characteristics which are similar to those described for feral does in the absence of pregnancy and lactation. These wethers may not be genetically different from the feral goats but simply expressing a particular physiological state.
There is a strong positive genetic correlation between cashmere weight, diameter and length, indicating that selection for cashmere weight alone will increase fibre diameter and length (Restall et al. 1984). Since cashmere length is highly heritable, then the use of goats which have cashmere longer than hair in breeding programmes may exacerbate the problem of an undesirable cashmere/hair length relationship.
Table 2 shows the relative fibre length of the wether progeny of selected sires, measures when these wethers were located at different sites (one in a coastal region and the other at a similar latitude but some 100km west and at a higher altitude). There appears to be no effect of location, and at both sites hair length exceeds cashmere length. This would be expected at the summer solstice and any differences between sites must await further measurements later in the growth cycle.
Table 2. Effect of location on mean fibre length of wether progeny of selected sires.
a Measurement taken on 12 December.
b Some goats at both locations showed evidence of residual fleece casting.
The effect of the relationship between the length of cashmere and hair fibres on productivity and processing raises some important issues which must be considered in any attempts to increase per head production. Cashmere production as g per head per year - 1 could be increased by one, or a combination, of the following:
To increase production by unlimited increases in fibre diameter is not a realistic option. Increased skin area must be accompanied by maintenance of secondary follicle density if productivity is to be increased. This approach would require genetic manipulation of the goat, since current technology does not provide any obvious alternative methods of achieving it. Research into methods of increasing secondary follicle density by other than genetic processes has the potential to provide another solution to the problem.
Cashmere fibre length can be increased by genetic means and more than one fleece growth cycle can be induced in one year. If both of these propositions are accompanied by a relative diminution in hair length, and since cashmere length increases of genetic origin are associated with increased fibre diameter, then these two potentially useful methods of increasing productivity are of questionable value. They will remain so while ever there is the constraint that hair length must exceed cashmere length.
The suggestion that some genetically improved goats may produce a shearable fleece in which cashmere mean fibre length is greater than that of hair is of real concern. Goats with cashmere longer than hair give the impression that they are carrying more cashmere than those in which hair is longer. Thus, visual selection of apparently superior goats may also be selection for cashmere longer than hair.
Where cashmere length exceeds hair length, the use of coats may be an opportunity to reduce the problem of tip weathering. It would be important that coats reduced UV light degradation of long cashmere fibres. The use of this management option would depend on the economics of the exercise and its practicability.
It is worthwhile restating the enigma that now exists. Research designed to increase cashmere production has conscientiously addressed the need to maintain desirable cashmere fibre diameter and the difference between the fibre diameter distribution of cashmere and hair. However, it appears that, generally, increased cashmere production has been achieved by increases in cashmere fibre length and diameter. There is some evidence suggesting that the mechanisms controlling cashmere and hair linear growth are independent. The end result if the application of these findings would be a fleece in which cashmere is longer than hair. If this is an undesirable option, then increasing cashmere production by independently increasing cashmere linear growth henceforth becomes a definite research constraint. Thus increasing cashmere length to increase productivity has the potential to produce undesirable fleece characteristics which include increased diameter. As the options are reduced the probability of developing a practical method of increasing per head cashmere production becomes lower.
Geneticists, nutritionists, physiologists and fleece biologists must address the question of relative length of cashmere and hair fibres in future research. Processors should consider means by which this constraint may be moderated and growers must be aware of the potential problem when selecting goats for breeding.
If this situation is not readily resolved to the satisfaction of all sections of the industry, then an apparently retrograde approach may warrant consideration. The concept would contain four components:
CONCLUSIONS AND RECOMMENDATIONS
Restall, B.J., Pattie, W.A. and Winter, J.D. (1984). Proc. Aust. Assn. Anim. Breed. Genet. 4, 263.
© 1985 A.C.G.A.