Last update: March 2, 2011 10:50:53 AM E-mail Print

RELATIONSHIP BETWEEN TYPE AND PRODUCTION TRAITS IN

SOUTH AFRICAN MERINO SHEEP

 

JJ Olivier1 , S W P Cloete2 & MA Snyman

1 Grootfontein Agricultural Development Institute, Private Bag X129, Middelburg 5900

2 Elsenburg Agricultural Development Institute, Private Bag X1, Elsenburg, 7607

 


 

INTRODUCTION

 

Type traits play a very important role during selection of Merino sheep and it is expected that they will remain to be important in selecting Merino sheep in future. Numerous studies, locally and abroad, have demonstrated the efficiency of selection for production traits. However, little is known about the relationship between production traits and type traits in the Merino.

 

The purpose of this paper is to give an indication of the relationships between production traits and type traits in the Merino stud industry and to determine whether selection for production will influence responses in type traits negatively.

  

MATERIALS AND METHODS

 

Data of the Grootfontein Merino stud (from 1985-1995) and the Tygerhoek Control flock (1989-1995) were used. Body weight was measured after shearing at 12-16 months of age. Clean fleece weights and staple lengths were corrected to a 365 days wool growth period, while fibre diameter, clean yield and crimp frequency were determined by the SA Fleece Testing Centre. The type traits were scored, per occasion, by two experienced sheep and wool classers. The traits were scored on a linear scale (1-50) as described by Olivier1. The more ideal type got the highest points. Exceptions were wool yolk and hocks, in which cases the intermediate value was considered as ideal. Conformation was not scored in the Tygerhoek flock but the straightness of the top line (straight 50 - very hollow 1) was scored in stead.

 

All the type traits had a skewness of >-2 and <2. The data were analysed by means of Harvey’s2 LSMLMW and MIXMDL programs. In both data sets, sire models were used to obtain the (co)variances. All known significant fixed effects were included in the mixed model. In both cases the interaction between year of birth and sex was also included. Sires with less than 10 progeny in Grootfontein stud and less than 5 progeny in the Tygerhoek flock were excluded from the analysis. Due to large standard errors of genetic correlations between the different traits, only phenotypic correlations are given.

 

 RESULTS

 

The numbers, means, standard deviations and heritabilities for type and production traits are presented in Table 1.

 

The similarity between the means and standard deviations as well as between the heritability estimates derived from the two data sources is remarkable. Exceptions were higher heritability estimates for wool quality and colour in the face/legs scores, which were higher in the Tygerhoek control flock. The reasons for this finding is probably the fact that no purposeful selection for these traits has been practised in the latter flock. The phenotypic variation in the scores for hocks was also higher in the Tygerhoek flock, probably for the same reason. In a typical Merino stud ( as represented by the Grootfontein stud) wool quality, variation in crimps over the fleece, colour (pigmentation) and hocks would have been emphasized as selection objectives over a long period.

 

The similarity between the results derived from the two data sets support the contention that the method of linear type scoring as defined, serves as a tool to differentiate the variation between animals in genetic and environmental components. It also appears to be robust, which facilitates application under different conditions by different classers.

From these results it is also evident that ample scope for selection exist in the various type traits in the Merino stud industry, should it be included in the selection objective.

 

 

Table 1. The means, standard deviations and heritability (standard error) estimates for the different traits as well as the number of progeny and sires for each data set.

 

Trait

Grootfontein Stud

Tygerhoek Control Flock

Number of progeny

3372

893

Number of sires

78

132

 

Mean (sd)

h² (se)

Mean (sd)

h² (se)

Body weight (kg)

56.2 ± 14.7

0.40 ± 0.07

47.8 ± 7.4

0.41 ± 0.11

Clean Fleece Weight (kg)

5.7 ± 1.5

0.36 ± 0.07

3.6 ± 0.6

0.36 ± 0.11

Fibre diameter (micron)

22.0 ± 1.6

0.44 ± 0.08

20.3 ± 1.4

0.47 ± 0.12

Staple length (mm)

10.5 ± 1.1

0.42 ± 0.07

10.0 ± 1.0

0.39 ± 0.11

Pleat score

9.4 ± 2.0

0.28 ± 0.06

9.5 ± 2.3

0.40 ± 0.11

Wool Quality

27.2 ± 5.9

0.34 ± 0.06

33.8 ± 7.9

0.57 ± 0.12

Variation in crimps over fleece

32.3 ± 6.2

0.14 ± 0.04

36.2 ± 7.3

0.41 ± 0.11

Wool yolk

24.6 ± 2.5

0.31 ± 0.06

24.7 ± 2.5

0.44 ± 0.12

Staple formation

28.5 ± 5.0

0.20 ± 0.04

28.3 ± 4.6

0.19 ± 0.10

Belly and points

26.2 ± 5.0

0.21 ± 0.05

29.7 ± 5.8

0.20 ± 0.10

Size of the head

29.1 ± 6.1

0.42 ± 0.07

25.5 ± 4.8

0.51 ± 0.12

Colour in face and legs

39.5 ± 7.0

0.14 ± 0.04

36.9 ± 8.4

0.43 ± 0.12

Front quarters

25.1 ± 5.6

0.28 ± 0.06

25.9 ± 6.7

0.27 ± 0.10

Pasterns

36.0 ± 5.8

0.07 ± 0.03

34.2 ± 6.4

0.20 ± 0.10

Hocks

23.3 ± 3.5

0.29 ± 0.06

26.9 ± 6.9

0.30 ± 0.11

Conformation

27.5 ± 5.8

0.28 ± 0.06

 

 

Top line

 

 

26.7 ± 5.9

0.25 ± 0.10

 

Moreover, the scoring system can be utilized to estimate change in conformation following selection on production traits. To investigate this, phenotypic correlations for the two data sets are presented in Table 2. The phenotypic correlations were generally low, ranging from -0.20 to 0.20 in most cases. Exceptions were the positive correlations of staple formation with both clean fleece weight and fibre diameter, of the size of the head with body weight and clean fleece weight, and of front quarters with body weight. In the Grootfontein stud, there was a high correlation between conformation and body weight. In general, all these correlations were favourable, except for the positive correlations of staple formation and under lines (belly and points) with fibre diameter.

  

CONCLUSION

 

The current breeding policy in the Merino stud industry is to increase body size, keep wool weight constant and decrease fibre diameter. The results obtained from this data suggest that selection for these traits will maintain or even improve the current standards in type traits achieved through selection over many years. There is thus no reason why a Merino stud breeder cannot switch from a policy where selection is based mainly on type traits to a selection policy based on production traits, while maintaining current standards in type traits. The method of scoring also suggest that genetic differences between animals for these traits can be utilized in a progeny testing scheme or as monitoring traits in a selection program based on production.

 

Table 2. Phenotypic correlations between production traits and type traits.

 

Type Traits

Flock

PRODUCTION TRAITS

 

 

Body weight

Clean fleece weight

Fibre diameter

Staple length

Pleat score

1

2

-0.09

-0.02

0.24

0.20

-0.009

-0.01

-0.15

-0.27

Wool Quality

1

2

0.06

-0.01

0.18

0.13

-0.06

-0.24

0.09

0.06

Variation over fleece

1

2

0.04

0.002

-0.005

-0.07

-0.09

-0.20

0.01

-0.06

Wool yolk

1

2

-0.07

0.02

0.15

0.20

-0.07

0.05

-0.17

-0.12

Staple formation

1

2

-0.14

0.04

0.36

0.19

0.33

0.29

0.15

0.05

Belly and points

1

2

0.12

0.09

0.33

0.20

0.19

0.25

0.23

0.10

Size of head

1

2

0.59

0.53

0.29

0.29

0.14

0.11

0.23

0.25

Colour in face/legs

1

2

0.005

-0.03

-0.02

-0.02

0.03

0.02

0.02

0.02

Fore quarters

1

2

0.45

0.28

0.15

0.15

0.15

0.13

0.23

0.09

Pasterns

1

2

0.005

0.001

-0.01

0.02

-0.02

-0.05

-0.009

-0.05

Hocks

12

0.13

0.28

-0.01

0.14

0.003

0.10

0.08

0.08

Conformation

Top line

1

2

0.53

0.12

0.23

-0.01

0.14

0.06

0.26

0.09

Flock 1 = Grootfontein Merino Stud Flock 2 = Tygerhoek Control Flock

 

 ACKNOWLEDGEMENTS

 

The authors acknowledge the contribution of all those involved in collecting of the data, both past and present, especially the sheep and wool experts who scored the animals.

 

LITERATURE

 

2 HARVEY, W.R., 1990. User’s guide for LSMLMW and MIXMDL PC-2 version, MIMEOGRAPH.

 

1 OLIVIER, J. J., DELPORT, G.J., ERASMUS, G.J. & EKSTEEN, T.J., 1989. Linear type scoring in Merino sheep. Karoo Agric., 3(9):1-4.

 

 

Published

Proceedings 35th SASAS congress, Nelspruit, 1-3 July