FIRST PUBLISHED JANUARY1985
Breeding plans using feral goats
Pattie, Reader in Animal Production,
This Goat Note concentrates on the derivation of selection objectives for feral goats with emphasis on cashmere production and liveweight growth. The objectives are based on the genetic and phenotypic parameters derived from the New South Wales Department of Agriculture's herd at Wollongbar, and in view of the restricted sample of sires used for those estimates, these objectives must be considered as preliminary at this stage.
The important characters affecting the value of cashmere and meat production are reasonably well defined. These are colour, weight of down, mean diameter, diameter distribution, liveweight and fertility. It is fortunate that the relative economic values of most of these can easily be calculated, but at present no genetic parameters are available for fertility or its relationships with the other important characters. As result the selection objectives given here do not include fertility. Similarly, fibre diameter distribution has not been included as no parameters are available and details of price penalties for undesirable distributions have not been established.
Coloured cashmere and white down from goats with coloured guard hair are heavily discounted. The effect of these price penalties will depend on the amount of cashmere produced and the proportion of coloured animals, and both of these factors vary considerably between herds. It is expected that individual breeders or their advisors will calculate the relative value of the white and coloured animals in their herds and compare the benefits to be gained from reducing the number of coloured animals with the value of expected genetic changes outlined here.
Selection indexes and Independent Culling Levels were calculated using an assumed population structure with typical production statistics. The genetic and phenotypic parameters above were combined with relative economic values based on prices current in May 1984. Several examples were examined covering a range of average diameters, breeding objectives, and measurement restrictions.
For calculating selection intensities and the numbers of fleeces and offspring produced by breeding stock the following details were assumed:
Several of the production characteristics are expressed more than once during each animal's life in the herd so the lifetime production of a breeding female was estimated from the following data:
(* Items used for calculating relative economic values)
Prices for the goat products used in calculating the production function were:
Combination of these prices with the lifetime production data gave the following relative economic values:
A. METHODS OF SELECTING REPLACEMENTS IN A FLOCK
1. Selection indexes
The following analyses showed similar expected changes in total value with the use of either down weight or down length*. As it is likely that most breeders will want to reduce measurement costs, the results obtained when using length as a measure of down weight are given here.
Table 1 shows three indexes with various combinations of length, diameter and liveweight and the expected changes that would follow one generation of selection with a selection differential of one standard deviation. These are the indexes that would give the maximum improvement in economic returns in each case.
Table 1. Selection indexes with length, diameter and liveweight.
*(Note that this is down length as measured in the method described in Goat Note No. E 11/1)
NOTE: Length of down is interchangeable with weight of down.
The table illustrates three ways of ranking the animals in a herd to select replacements. The three measurements that are required are down length, diameter and bodyweight. Therefore, in the first case, the index would be calculated by adding the length to .54 times the diameter and .29 times the bodyweight. In the second and third options only two measurements are required so that a breeder could choose to measure down length and diameter only, or down length and bodyweight only. In all cases, the diameter will rise by approximately .5 micron per generation and the bodyweight will fall. These responses result from the strong positive genetic correlation between down weight and down length (.9), and the negative genetic correlation between bodyweight and down weight (-.59).
These indexes show that maximum improvement in financial returns will follow selection that emphasises down weight (or length) while allowing diameter to increase and liveweight to fall. Little is lost if diameter or liveweight are omitted from the index but they will still change to almost the same extent.
Many breeders would consider these associated changes to be too extreme so it is of interest to examine indexes that aim to hold either diameter or liveweight constant. Table 2 presents several such indexes and the changes in each character and total value that would follow their use.
Table 2. Restricted Selection Indexes
NOTE: The table illustrates the negative selection pressure which must be applied to fibre diameter to hold it constant (options 1 and 3) and the positive selection for bodyweight to hold it constant (options 2 and 4).
It is clear that selection can be designed to prevent undesirable changes in diameter and liveweight but financial returns are halved in each case. Another analysis showed that if both are controlled then very little increase in down weight will occur.
Furthermore, before it would pay to control diameter, the price differential would have to exceed $20/um for goats producing an average of 90g of down, or production would have to exceed 200g per head at present prices.
2. Independent Culling Levels
It is often convenient for breeders to cull animals as records become available rather than wait for all records so that an index can be calculated. Independent Culling Levels are useful for this purpose and they become financially more efficient if some measurements that are very expensive are left until last when only a small number of animals remain as candidates for selection.
Three selection schemes are presented which will have the effect of (a) holding diameter constant, or allowing it to increase in the progeny of selected animals by (b) 0.2 um, or (c) 0.4 um. As it will normally be too expensive to measure fibre diameter among females, all selection among them is based on down length and liveweight. The latter is included to modify the severe decrease in body weight that is expected if no attention is given to it.
Initial cullings of 10 percent of females and 20 percent of males have been allowed to remove animals with deformities and coloured down that will still occur in some progeny of white parents. It is assumed that these faults are not related to down weight, length, diameter or liveweight.
(i) Female selection - for every 100 available
(ii) Male selection - for every 100 available
(iii) Expected changes in progeny
As with the selection indexes, the effect of holding down diameter constant, or even restricting its increase, is to markedly reduce the increase in down weight. Our analyses show that similar results are expected if down weight is used for selection instead of length. However, we consider that it is unwise to base all selection of males on indirect characters so we suggest that after a preliminary culling on length, yield measurements should be obtained and the remaining culling based on down weight and diameter.
B. INTRODUCTION OF MALES FROM AN OUTSIDE SOURCE
Value of purchased bucks
The expected genetic changes and values for genetic improvement given above are relevant to essentially closed breeding herds with bucks being selected from the offspring produced within the herd. It is also of interest to examine the value of commercial breeders of bucks purchased from studs or other breeders. Continued genetic improvement in these herds depends, solely on the improvement being made in the herd from which bucks are purchased but it is possible to lift the average level of the commercial herd by purchasing better bucks from the same source.
The value of purchasing better bucks has been examined using the genetic parameters, economic values and herd structures outlined above with the gene flow techniques of Hill (1974) and Brascamp (1978). Figure 1 shows the time scales that would be involved in recouping the additional costs of better bucks and the maximum value of the additional production obtained.
NOTE: Figure 1 illustrates the additional value of cashmere which may result from the purchase of a buck producing one standard deviation of cashmere above the average buck population. It shows how the benefit of such an animal will be distributed in the population. The immediate benefit is through the progeny of the buck (curve 1) - does and bucks, which will reflect his superior production. The increase in production in his progeny will be reflected for 6-8 years on average while he is used as a sire within the flock and his progeny reach producing age. The long term increase throughout the flock will be made through his daughters (curve 2) as they spread his genes when mated to other bucks. This effect will plateau out on average, after 18 years. The third curve shows the cumulative effect of introducing such an animal into the population and the added value of cashmere produced, (1984 prices). Thus, the vertical axis on the curve may be interpreted in 2 ways. Firstly as the extra value of cashmere produced and secondly as the additional purchase price over the cost of an average buck. If this is related to the horizontal axis the time taken to return this outlay may be calculated for the set of conditions given. It is important to realise that the time scale and value returned, relate to the set of parameters given: i.e. for a buck which is one standard deviation above the average of the population, where one standard deviation equals 40gms of cashmere. The principle illustrated is the important message in the graph.
It would seem that a commercial breeder could not afford to pay more than an extra $250 above the price for average bucks, for a buck that produced one standard deviation (approximately 40g) above average. It would take about eight years for this additional outlay to be returned.
The analyses on this Goat Note indicate that highest economic gains in the short term would be obtained by selecting for increased down weight allowing diameter to increase and liveweight to decrease. However if this policy is continued, down will be produced that cannot be sold as cashmere and problems may arise with small animals. Obviously, it will be difficult to make significant increases in down weight while controlling fibre diameter so satisfactory returns to breeders will depend on prices received for the different diameter grades. However, while price changes may make it more profitable to breed goats with finer down, such changes will not alter after the biological relationships and breeders will have to look to increases in stock numbers for greater down production unless breeding strategies are changed.
All of these predictions depend upon the breeding structures that are normally used and the average genetic parameters. However it is technically possible to make large changes to the breeding structure and there are animals in the population whose breeding results do not follow the average genetic parameters. Figure 2 shows the average down weights and diameters of progeny groups from individual sires. Clearly there are a few sires that produce offspring with desirable combinations of these characteristics but for normal breeding systems there are not enough of them and many others that fit the average trend have to be used.
However modern methods of A.I. and embryo transfer offer ways of using the desirable sires widely and this should allow much greater increases in per head production than have been estimated here. It should be noted that these sires could not be identified on the basis of their own production so that a progeny testing system would be needed for such a scheme to be effective. Further investigations of this possibility and the design of an appropriate system are needed but these will not be attempted until more data are available to check the accuracy of the estimates of heritabilities and genetic correlations.
Brascamp, E.W. (1978) "Methods on economic optimization of animal breeding plans".
Research Institute for Animal Husbandry, Zeist, The Netherlands.
Hill, W.G. (1974) Anim. Prod. 18, 117
Holst, RJ., Pym, R.A.E. and Nicholls, P.J. (1982). Proc. Aust. Soc. Anim. Prod. 14, 133
Pattie, W.A. and Restall, B.J. (1984). Proc. Aust. Assn. Anim. Breed. Genet. 4, 269
Restall, B.J. Pattie, W.A. and Winter, J.D. (1984).
Proc. Aust. Assn. Anim. Breed. Genet. 4,263.
(C) 1985 A.C.G.A.