Breeding Cashmere in Australian Goats
Following detailed research since 1980 into the inheritance of cashmere in Australian goats, we are now able to recommend breeding strategies to meet the varied objectives of cashmere producers. The research has been carried out at the North Coast Agricultural Institute, Wollongbar using goats derived from stock collected in the Cobar region of NSW. A large number of goats have been involved in these studies and the information reported here was derived from more than 2,200 fleece records.
The basic genetic parameters and selection strategies derived from them have been reported previously to meetings of goat breeders. See for example, the Proceedings of the 2nd International Cashmere Conference held in New Zealand in May 1987 and the Cashmere Goat Seminar held by the ACGA Region 27 in Orange in July 1988. Some of that information is repeated here for completeness but this paper will examine other topics including the genetic value of follicle density, fibre diameter variability and the effects of crossbreeding with Angoras on cashmere breeding.
NON-GENETIC FACTORS THAT AFFECT CASHMERE PRODUCTION
It is important that the effects of environmental factors on cashmere production and characteristics be examined so that a clear understanding can be gained of the relative importance of inheritance in the differences that are seen between animals. Of particular importance are age, sex and birth type and the overall environmental component of variation that remains after these have been allowed for.
Table 1 shows age and sex differences in the main components of down production and in skin follicle densities. A total of 2,224 records from 1,156 animals, all born and raised at Wollongbar, were used for the fleece study while skin data of 1,514 samples were available from 1,105 animals.
All goats became heavier and grew more down as they got older and there were large increases in down diameter. The average increase was almost one and a quarter um between first and second fleece and an average of a half um each fleece after that. With the normal variation between animals, this means that more than 60% of goats in a herd averaging 16.5um at the first fleece will not be growing cashmere by their fourth fleece (diameter greater than 18.5um). There are important implications here for the interpretation of measurements quoted on sale animals. Clearly the age at which the measurement is made must be known before the diameter has any meaning.
Secondary follicle density tended to decrease as animals became larger, either because they were older or because they were males. Secondary/primary ratio did not show this pattern because primary density also decreased. Note that skin data were not available for 4 year old goats.
Males were heavier and grew more down at each age than females, but their down diameter was no different. This too is important, because it is often stated that bucks can be 2 to 3 um stronger than females, yet have the same genetic value. Because of the importance of this finding, we examined the unanalysed data broken down into year and age subclasses, looking at the differences between sexes in each group. These are shown in Figure 1 and it is clear that there were no consistent difference between sexes and the random differences that did occur were not very great. Note that these results were obtained for a wide range of diameters and ages. Our results do not support the idea that males of the same genetic make-up have coarser down than females and breeders should be very wary about accepting it, especially if it is proposed by someone trying to sell a 19 or 20 um buck.
The repeatibilities of down weight, diameter and length were 0.50, 0.60 and 0.63. These measure the proportion of variation between animals that is permanent throughout their life. They are reasonably high and indicate that measurements made of the first full fleece give a good indication of lifetime relative productivity. The repeatibilities for secondary follicle density and S/P ratio were lower (0.35 and 0.30 respectively) indicating more temporary variation, probably caused by sampling problems with the small amount of skin taken from each animal.
INHERITANCE OF CASHMERE CHARACTERISTICS
The heritabilities and relationships among the main components of down production are given in Table 2. These show that the potential for cashmere production is strongly inherited but there are unfavourable genetic relationships between liveweight, diameter and down weight. There is however, a very strong relationship between down weight and length from which we have recommended that preliminary selection for down weight can be carried out by indirect selection on length.
Secondary follicle density and S/P density have much lower heritabilities and relatively weak correlations with the other characters. The implications for this are discussed further in a later section.
In 1985 we established high and low selection lines for down weight, down diameter and liveweight, in which selection was solely for increase or decrease in the character concerned. There were thus six selection groups and a randomly bred control line. Measurement were made on the fleeces of all progeny at both the first (9 months) and second (21 months) shearing. The trial was completed in 1992 and analyses of the divergencies between the high and low lines have yielded the realised, or actual, heritabilities for the three characters under selection. These realised heritabilities can be compared with the estimates (see Table 2) derived from the previous random breeding trial. The comparison is shown in Table 3.
The agreement is very good so we can have confidence that the genetic parameters for this herd can be used to construct selection indexes and breeding plans. The selection line data also confirmed the strong genetic correlation between down weight and diameter and it would seem unwise to assume lower values if there are financial penalties for the production of coarse down. The value of selection based on first fleece measurements at 9 months of age was also confirmed, with responses of equal or greater magnitude being carried through to the second fleece at 21 months of age.
Analyses of the reproductive performance of does in the selection lines gave heritability estimates for conception rate, kidding rate and multiple birth rate of 0.163, 0.210, and 0.510 respectively. This indicates that selection for multiple births would be more effective in raising lifetime production than selection against failure to kid. The genetic correlations between kidding rate, multiple birth rate and other production characters are shown in Table 4.
The strong positive genetic correlation between liveweight and the reproductive characters suggests that selection for liveweight will improve the reproductive rate. However, there are moderate negative genetic correlations between multiple birth rate and the fleece characters suggesting that selection for any of these will lead to a gradual decline in reproductive performance. Selection for reproductive performance would gradually reduce down production.
The development of efficient selection systems for improving down production is restricted by measurement problems. Full measurement of yield, and hence down weight, and diameter is very expensive, so with relatively low productivity per animal in the early years of a breeding program, breeders will seek to measure only a proportion of their bucks and they will not measure does. We have designed 2-stage selection systems for use in this situation but first it is necessary to examine the goals of breeders.
It is tempting for breeders to ask for programs that will maximise financial returns. However, it turns out that selection systems designed to do that using price levels of the past few years would result in steady increases in down diameter and reduced liveweight.
It is clear that these changes cannot be allowed in the long term so another strategy is needed. A system which holds diameter and liveweight constant while increasing down weight would suit many breeders while those already producing coarse cashmere (17um or more) may wish to reduce diameter to take advantage of the recently increased price margins for fine fibre.
A 2-stage index to hold diameter and liveweight constant is shown in Table 5. All does are selected on a combination of down length and liveweight using the index (f). Using the Stage I (m) index, the best 25% of males are reserved for measurement of yield and down diameter. The bucks required for breeding are then selected on the basis of all their records using the Stage II (m) index.
As an example, consider an 18 month old buck that had a liveweight of 27kg and down length of 96mm at his second fleece when the averages for all bucks born at the same time were 26.3kg and 56.6mm. The deviations for the mean are multiplied by the index weights for Stage I as follows:
Stage I Index = 0.7(0.101) + 39.5(0.322) = 12.8
As the buck was in the top 25% on the Stage I index, his fleece would be sampled and yield and diameter measured. From these, down weight and diameter were 263g and I 5.7um while the averages for the top 25% of bucks were: liveweight 26.8kg, down length 83.2mm, down weight 165.99, diameter 16.9um. The Stage II index weights are then multiplied by deviations from the means as follows:
Stage II Index =0.2(0.360) + 12.8(0.333) + 97.1(0.145) - 1 .2 (-9.450) =29.82
The top bucks on this Stage II index would then be selected for breeding provided they met any other important requirements. This particular buck was the top in his group on the second stage index whereas he was 8th on down weight and 10th on the first stage index.
There were 248 bucks in this group and their averages were: liveweight 26.3kg, down weight 121g and diameter 16.2um. The top 10 bucks on the Stage II index averaged 27.7kg, 238g and 1 6.2um for these characters. This shows that the 2-stage selection system has effectively controlled diameter and prevented a drop in liveweight while increasing down weight. There was some loss in potential weight improvement because the 10 highest down weights averaged 282g. However, this is the price that must be paid to control diameter and it is a fact of life whenever there are negative genetic associations between desirable characters.
The levels of improvement estimated in this table may appear to be low to some breeders. However, it should be pointed out that these are estimated for changes in the average production of the whole drop, not just the top animals, and such genetic changes accumulate.
REDUCING DIAMETER WITHIN A HERD
Many breeders are now finding that too many of their goats are producing coarse fibre and the average of their herd places it in the lowest cashmere price bracket. If a reduction in diameter is desired, some breeders will purchase finer bucks while others will prefer to breed finer animals within their own herd. For these breeders we have calculated 2-stage indexes for use with bucks assuming the same index is used for doe selection as above.
Table 6 gives 2 sets of indexes for different rates of reduction in diameter among the progeny of the selected animals. Note that it is difficult to make a major reduction in diameter in a short time without
causing a severe drop in down weight. In each case, 25% of the bucks are reserved for sampling and measurement after Stage I, however the indexes do not change greatly if different proportions are kept.
PROBLEMS CAUSED BY INACCURATE MEASUREMENTS
One of the greatest barriers to the genetic improvement of cashmere production is the expense and difficulty of measuring yield. Many samples of fleece do not dehair properly with current testing procedures so inaccurate estimates of yield may result. The AWTA warns growers on the measurement report when any sample is outside usual limits for yield but it is the breeder’s responsibility to carefully examine the results that are to be used for selection or sale. This section gives an example of a typical problem of this type and suggests ways that breeders can examine their results.
At the 1987 shearing of one of our selection lines, one buck supposedly produced 530g of down in its second full fleece. We were rather excited at the time but became suspicious when we saw that the next best 5 bucks produced 345, 320, 287, 277 and 277g of down and the mean of the whole unselected drop of 248 bucks was 121g. Thus our special buck was 409g or more than 6 standard deviations above the average and 185g, almost 3 standard deviations above the next best buck.
Now this sort of pattern just does not happen within populations bred from the same source. In fact, the statistical expectations are that less than I in 5,000 animals will be more than 3.5 standard deviation above the mean and only 1 in 10,000 above 4 standard deviations. Yet this buck was supposed to be 6 standard deviations above average. Clearly, there was likely to be a measurement error so we had the fleece re-tested. The test yield was reduced from 66.8% to 34.5% and the estimated weight of cashmere came down to 274g, well within the normal range for the group.
The strategies that we recommend breeders use to examine their test results are as follows:
The case used to illustrate this topic is not an isolated one and there may have been less extreme errors in the same group. This is not a criticism of the testing house but a recognition of the limitations of current procedures. Apart from the suggestions above about checking results and being careful about breeding from animals with suspicious records, equal care is needed in interpreting information presented in sale catalogues. There is a high probability that many of the impressive down weights we see advertised are simply a collection of measurement errors. The best safeguard against these is to look at the age of the animal, its down length and diameter, the down weights of other individual in the herd, and above all, the mean of the drop. If these cannot be provided you should discount the value of the record supplied.
VALUE OF FOLLICLE DENSITIES IN GENETIC IMPROVEMENT OF CASHMERE PRODUCTION
There has often been speculation on the importance of variation in follicle density in cashmere breeding. Density is certainly a component of down weight but the important thing is the extent to which differences between animals in down weight are determined by differences in density and whether or not this has a genetic basis. The parameters given in Table 2 are the first published figures that will allow this latter point to be investigated. However, they should be regarded as preliminary because there are many sampling difficulties in this work and final conclusions should await the analysis of further data.
We have examined the question of whether or not data on skin follicle densities can be used in selection to improve genetic gains in cashmere production. Selection index methods were used and expected genetic changes with and without density data were estimated. It was assumed that increased down weight was required with no change in diameter or Iiveweight. Table 7 shows the results of this study and indicated that neither secondary follicle density or secondary/primary ratio contribute to improve genetic gains over what is possible from selection based on fleece measurements.
POTENTIAL CHANGES IN VARIABILITY OF DOWN DIAMETER
It is often asked if genetic improvement in down weight will result in changes in variability of diameter and whether this needs to be considered as a separate character in a selection programme. It is well known that variability increases with increasing diameter and that crossbred animals produce fleeces with a large proportion of coarse down. However, the situation is not clear for breeding within a cashmere herd. We have examined the genetic parameters associated with the standard deviation of down diameter although we have reservations about this as an adequate measure of variability in view of the typical skewed distribution of diameter.
In our herd, the heritability of standard deviation of diameter was 0.30 and it had genetic correlations of 0.60 with down weight, 0.67 with diameter, 0.54 with length and -0.41 with liveweight. Phenotypic correlations were 0.31, 0.45, 0.21 and -0.13 respectively. Using these parameters we calculated expected changes in standard deviation that would follow selection for improved cashmere production in a typical herd.
If down diameter was not controlled, standard deviation of diameter would increase by 0.14 or 4.7% in the offspring of selected animals. If diameter and liveweight are restricted to zero change then the increase in standard deviation would be only 0.03 or 1.06%. It is apparent that there will be no serious undesirable changes in the variability of diameter in herds where selection aims to increase down weight and control diameter.
© 2000 A.C.G.A.