- Repeatabilities of and phenotypic correlations ...
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Repeatabilities of and phenotypic correlations between certain subjective and objective hair qualities of Angora goats
Agricultural College, Grootfontein
STYLE and character are important quality characteristics of mohair for which provision is not only made in the Board's evaluation system, but for which, in fact, a substantial premium is paid by the trade - this despite any valid proof of differences in ultimate textile qualities between mohair with good, versus mohair with less style and character! Further, it is argued, from a breeding and production viewpoint, that there is a relationship between good style and character and other economically important qualities. According to the present subjective selection procedure, much emphasis is indeed placed on style and character. It can be rightly asked if the strong emphasis placed on style and character is really justified, and to what extent these qualities are repeated in succeeding clips. An investigation was therefore made into the repeatability of the above two qualities, plus five other subjective hair qualities, as well as the phenotypic correlations between these subjective and four objective qualities. Because of their nature, it is difficult to evaluate subjective qualities accurately. Consequently an investigation was also made into the correlation between two judges, in order to establish how accurately the different qualities can be determined.
The investigation was carried out during 1990/91 on the Jansenville experimental farm's two Angora goat flocks, namely a fine hair flock and a control flock, a total of approximately 200 animals. Seven subjective qualities, namely style, character, evenness of the fleece, density of the fleece, facial cover, neck cover and kemp were independently evaluated by two judges on three occasions, namely just before the second shearing (10 months of age), the third shearing (14 months of age) and the fourth shearing (18 months of age). During and just after shearing, the body mass, fleece mass, fibre diameter and staple length of every animal was determined. The data was analysed in order to establish how the judges correlate for different qualities, what the repeatability of all the named qualities is among succeeding clips and the phenotypic correlations between the various qualities for the 18-month clip.
Correlation between judges
The correlations between the points awarded by the two judges for each quality was calculated separately for every clip -and are shown in Table 1.
From this it can be seen that, for all the qualities, except evenness of the fleece, positive correlations of 50 per cent or higher were estimated in most cases. This implies that the different qualities were evaluated in more or less the same way and that good and poorer animals were given the same evaluation by both judges.
Repeatabilities of the qualities between succeeding clips
The repeatabilities of the various qualities between the succeeding clips estimated by the two judges are shown in Table 2.
With the exception of style and evenness of the fleece, it appears that the repeatability of most of the qualities between 14 and 18 months of age are reasonably high. However, of fundamental importance is the low repeatability of some qualities between the first and third judging, in other words, between the ages of 10 to 18 months. The low repeatabilities for style of respective 4 per cent (judge A) and 15 per cent (judge B) respectively are particularly disturbing, because, during selection, most breeders placed great emphasis on this quality. A repeatability of, for example, 15 per cent for style (r = 0,15) means that the chances of a 10 month old goat holding the same ranking at the age of 18 months is only 2,25 per cent (r2 = 0,0225).
The repeatabilities for all the qualities are higher between the second and third judgings than between the first and third judgings, particularly with regard to style. This information indicates that the quality traits can be more accurately judged at a later age. Selection should therefore be postponed until as close as possible to mating time.
Phenotypic correlations between subjective and objective qualities
The phenotypic correlations between the judged subjective and objective qualities of the 18-month clip were then calculated for the two judges and are shown in Table 3.
With regard to the objective qualities, high positive correlations appear between all the qualities in these flocks, namely the larger goats produce more hair, longer staples and coarser fibres. With regard to the subjective qualities, the following general conclusions can be made from the phenotypic correlations. In both flocks the smaller goats produce less, finer hair, with a shorter staple length and better style and character. Their hair is more dense, they have less kemp and their faces and necks have a good, full cover. The bigger goats, on the other hand, are inclined to produce more hair with a longer staple length, a higher fibre diameter and poorer style and character. Their hair is less dense, they have more kemp and their faces and necks tend to be less well covered. As a result of the positive correlation between body mass, hair mass and fibre diameter, as well as the negative correlation between body mass and style and character that exist in these flocks, it will be difficult to breed a bigger goat with finer hair and good style and character, which is the aim of many farmers/breeders at present. From preliminary results it would appear that genetic correlations between these qualities are in reasonable agreement with these phenotypic correlations. These correlations imply that breeders, who want to increase body mass, keep hair mass constant and decrease fibre diameter, will only be able to effectively do this by means of measurement (performance testing of body mass and fibre diameter). This entails the accurate measurement and evaluation of the relative qualities at the proper time, and the incorporation of these qualities in a selection index in order to be able to accurately identify those goats, which will satisfy the selection goal.
Angora goat and mohair journal 34 (1) : 44-45