Last update: January 17, 2011 04:03:03 PM E-mail Print

 

REPEATABILITY OF OBJECTIVE AND SUBJECTIVE FLEECE TRAITS AND BODY WEIGHT

IN SOUTH AFRICAN ANGORA GOATS

 

M.A. Snyman1 & J.J. Olivier2

 

1 Grootfontein ADI, Private Bag X529, Middelburg (E.C.), 5900, South Africa

2 ARC-AII, Private Bag X529, Middelburg (E.C.), 5900, South Africa

 

 


 

INTRODUCTION

In South Africa, Angora rams are sold at 14 to 15 months of age with their full third fleece. Therefore rams have to be performance tested at 8 to 9 months of age at their second shearing. Performance testing of body weight, greasy fleece weight and mean fibre diameter is done. The question is asked whether testing at the relatively young age of 8 to 9 months is accurate enough to identify superior animals at that stage. Furthermore, during the selection process of both rams and ewes, a lot of emphasis is placed on traits such as softness of face and ears, fullness of face, neck and bellies & points, evenness of fleece and style and character. From observations in practice, it seems as though many of these traits have a low repeatability. Very little scientific information on the repeatability of objective traits for Angora goats are available (Yalcin, 1982) and none for South African Angora goats in particular. Furthermore, virtually no heritability and repeatability estimates for subjective fleece traits are available. The only estimates found are for kemp score and face cover score (Shelton & Bassett, 1970; Gifford et al., 1991). Consequently, a study was done to investigate the repeatability of body weight, greasy fleece weight and mean fibre diameter, as well as various subjective fleece traits of South African Angora goats.

 

MATERIAL AND METHODS

 

Data

Two data sets were used for analysis in this study. The first data set was collected on the 1991- and 1992-born ewes of eight stud breeders participating in the Angora goat performance testing scheme (AGPTS). For practical reasons, only data from ewes were available for data set I. Nine traits were assessed subjectively on a linear scale ranging from 1 to 50 at the second (9 to 10 months of age), third (15 to 16 months of age) and fourth shearing (21 to 22 months of age) of these ewes. The following traits were scored, namely softness of face and ears, fullness of face covering, extent of pigmentation in the face and on the ears, fullness of the neck, style, character, evenness of fleece (in terms of fibre diameter, length, style and character), presence of kemp and medullated fibres and fullness of belly and points. Furthermore, performance testing of body weight, greasy fleece weight and mean fibre diameter was done at each shearing. Prior to data analysis, greasy fleece weight was corrected to 180 days' hair growth. Pedigree information was obtained from the Angora Goat Stud Breeders' Society of South Africa.

 

Data set II comprised data collected on the fine hair and control flock progeny of the experimental flocks kept at the Jansenville Experimental Station (JEF). The same nine subjective traits were assessed on the 1992- to the 1995-born ram and ewe kids at the second (10 months of age), third (14 months of age) and fourth shearings (18 months of age). Performance testing data on body weight, greasy fleece weight and fibre diameter of the 1988- to the 1995-born kids were also available for each shearing. The number of records available after editing were 636 and 1107 for body weight, 645 and 1109 for fleece weight, 816 and 1107 for fibre diameter and 911 and 627 for the subjective traits in data sets I and II respectively.

 

Statistical analysis

 

Heritability and repeatability estimates were obtained by fitting repeatability animal models under the DFREML programme of Meyer (1993). For these analyses, fixed effects for flock, year of birth, birth status and sex (only for JEF) were included in the models. Models including both direct as well as maternal genetic effects were tested. Maternal effects only had a significant influence on body weight, and a maternal genetic effect was therefore included in the model fitted for body weight.

 

RESULTS AND DISCUSSION

Repeatability and heritability estimates for the various traits obtained with the two data sets are summarised in Table 1. Heritability estimates for subjective traits for JEF were higher than those obtained for AGPTS for all traits except for evenness of fleece and bellies & points. This could most probably be ascribed to the broader genetic basis of the JEF, compared to the Angora studs.

Negative P2-values were obtained for some traits, especially for JEF, which lead to repeatability estimates being lower than the corresponding heritabilities. This is probably due to the relatively small data sets used. Pigmentation and fibre diameter had the highest repeatability for AGPTS, while pigmentation and face cover had the highest repeatability for JEF.

At the third shearing, body weight and fibre diameter can be determined without shearing of the ram, but not fleece weight. Fleece weight also has the lowest repeatability of these three traits. Snyman et al., (1996) therefore proposed that fleece weight be left out of the selection index, as an increase in fleece weight is not desirable, due to a negative relationship between fleece weight per unit of body weight and reproduction performance (Herselman et al., 1998).

The subjective fleece traits on which a lot of emphasis is placed during selection, namely softness of face and ears, fullness of face, neck and bellies & points, evenness of fleece and style and character all had low repeatabilities compared to the economically important objective traits. The method of assessment of the subjective traits could possibly contribute to the lower estimates, as the consistency of the assessor was also incorporated into the estimate. To keep this factor as low as possible, only one assessor was used.

 

Table 1. Repeatability and heritability estimates (SE) for body weight and fleece traits in South African Angora goats

 

Repeatability Heritability

Trait

AGPTS

JEF

AGPTS

JEF

Body weight

0.53 (0.12)

0.63 (0.06)

0.34 (0.05)*

0.47 (0.01)

Fleece weight

0.41 (0.13)

0.27 (0.04)

0.22 (0.04)*

0.22 (0.04)

Fibre diameter

0.68 (0.14)

0.35 (0.03)

0.30 (0.05)*

0.29 (0.05)

Softness

0.32 (0.14)

0.31 (0.06)

0.07 (0.15)

0.33 (0.07)

Face cover

0.37 (0.11)

0.60 (0.07)

0.33 (0.12)

0.66 (0.11)

Pigmentation

0.62 (0.13)

0.62 (0.08)

0.43 (0.14)

0.49 (0.10)

Neck cover

0.26 (0.06)

0.39 (0.06)

0.13 (0.06)

0.33 (0.07)

Style

0.24 (0.06)

0.17 (0.05)

0.13 (0.06)

0.23 (0.06)

Character

0.35 (0.08)

0.39 (0.07)

0.14 (0.08)

0.34 (0.09)

Evenness

0.23 (0.09)

0.13 (0.04)

0.26 (0.10)

0.16 (0.05)

Kemp

0.29 (0.05)

0.25 (0.06)

0.01 (0.04)

0.32 (0.08)

Bellies & Points

0.22 (0.09)

0.12 (0.04)

0.30 (0.10)

0.30 (0.04)

 

AGPTS = Angora goat performance testing scheme; JEF = Jansenville experimental flocks

* = Heritabilities estimated on a larger data set (Snyman & Olivier, 1996)

 

 

CONCLUSION

The low repeatabilities estimated for the subjective fleece traits are a cause for concern, as stud breeders and ram buyers are placing relatively more emphasis on these traits than on the more economically important traits, such as body weight and fibre diameter. More accurate parameters should be estimated when more data become available. Those estimated in this study would have to suffice in the interim when recommendation for suitable breeding plans are made to breeders. A premium should also be placed on the estimation of genetic correlations between these subjective traits and body weight, fleece weight, fibre diameter and especially reproduction.

 

 

REFERENCES

 

Gifford, D.R., Ponzoni, R.W., Lampe, R.J. & Burr, J., 1991. Small Rum. Res. 4(3), 293

 

Herselman, M.J., Olivier, J.J. & Snyman, M.A., 1998. S. Afr. J. Anim. Sci (in press)

 

Meyer, K., 1993. DFREML : User notes, Ver. 2.1

 

Shelton, M. & Bassett, J.W., 1970. Texas Agricultural Station Research Report (PR-2750), 38

 

Snyman, M.A. & Olivier, J.J., 1996. Livest. Prod. Sci. 47(1), 1

 

Snyman, M.A., Olivier, J.J. & Wentzel, D., 1996. Angora goat and mohair journal, 38(1), 23

 

Yalcin, B.C., 1982. Proc. 3rd Int. Conf. Goat Prod. Disease, Tucson, Arizona, 269