Last update: September 8, 2011 10:41:31 AM E-mail Print

 

ESTIMATION OF GENETIC PARAMETERS FOR PRODUCTION TRAITS OF A GENETIC FINE WOOL MERINO STUD

 

W.J. Olivier1# & A.C. Greyling2

1 Grootfontein Agricultural Development Institute, Private Bag X529, Middelburg (EC), 5900

2 Cradock Experimental Station, P.O. Box 284, Cradock, 5880

# E-mail: Willem Olivier

 


INTRODUCTION

There was a shift in the emphasis of wool production to the production of finer wool, rather than simply the amount of wool during the late 1980s and early 1990s. This was the due to the higher consumer demand for finer wool types that resulted in higher price premiums for finer wool. Subsequent to this, wool producers included fibre diameter into their selection programs in order to decrease the fibre diameter of their wool clip and obtain these higher wool prices. During this period the wool industry requested the then Department of Agriculture to initiate research projects with regard to the production of fine wool in South Africa.

 

In some instances, producers put all the emphasis on decreasing fibre diameter in their breeding plans, regardless of the effect that it might have on the production, reproduction and subjectively assessed wool and conformation traits. Olivier et al. (1999) stated that the objectively measured reproductive traits, body weight and wool production traits are the most important economically important traits for a wool sheep enterprise. Selection should therefore not only be based on one of these trait groups, but on all of them to ensure that production and reproduction will be at an optimum level. The aim of this study was therefore to quantify the relationships between body weight at different ages and wool production traits.

 

MATERIAL AND METHODS

The Cradock Fine Wool Merino Stud was established in 1988, as described by Olivier et al. (2006). The stud consisted of two groups, namely a fine wool strain and a strong wool strain. Ewes for the fine wool strain were bought from Merino farmers producing the finest clips throughout South Africa (Olivier et al., 1989). The ewes from the strong wool strain were selected from the then existing Merino flock at Cradock Experimental Station (Bezuidenhout et al., 1994). Four fine wool rams were imported from Australia to be used as sires during the first few years in both strains. Data collected on 6624 ram and ewe lambs born within the fine wool strain of this stud from 1988 to 2003 were used for the analysis of the body weights and wool production traits.

 

The body weights analysed included birth weight (BirthW), body weights at 42 days of age (BW42), weaning (WW), 6 months of age (BW6), 12 months of age (BW12) and 15 months of age (performance testing age; BW). The wool production traits included in the analyses were mean fibre diameter at 6 (MFD6) and 12 (MFD12) months of age and the following wool production traits at 15-month age: greasy fleece weight (GFW), clean fleece weight (CFW), mean fibre diameter (MFD), staple length (STL), clean yield (CY), number of crimps per 25 mm (Crimp), Duerden (Duer), standard deviation of fibre diameter (SDFD), coefficient of variation of fibre diameter (CVFD), pleat score (Pleats) and comfort factor (CF).

 

Several fixed effects and the interactions between these effects (year of birth, sex, rearing status and age of dam in years), as well as the age of the lambs, as a linear regression, were tested for significance. Only effects and interactions that had a significant effect (P<0.01) on a specific trait were included in the final operational model.

 

The least-squares means and standard errors for the body weights and wool production traits were obtained with the Proc GLM-procedure of SAS, and significance levels for the fixed effects were obtained with the PDIFF-option under the Proc GLM-procedure of SAS (SAS, 2006). The estimation of the genetic parameters and breeding values were done with ASREML (Gilmour et al., 2009). Log likelihood ratio tests were done to determine the most suitable model for the estimation of (co)variance components for each trait. The (co)variance components were estimated with univariate models and the correlations between the different traits were estimated using bivariate models.

 

The number of records, mean, standard deviation (SD) and coefficient of variation (CV) of the body weights and wool production traits are summarised in Tables 1 and 2 respectively.

 

Table 1. The number of records, mean, standard deviation (SD) and coefficient of variation (CV) of the body weights

Traits

Ram progeny

Ewe progeny

N

Mean

(kg)

SD

(kg)

CV

(%)

N

Mean

(kg)

SD

(kg)

CV

(%)

BirthW

3303

4.63

0.89

19.20

3321

4.38

0.85

19.38

BW42

3011

16.60

3.86

23.25

3085

15.66

3.52

22.48

WW

2962

27.87

5.37

19.27

3046

25.88

4.52

17.45

BW6

2873

37.82

6.81

18.02

2978

33.36

4.84

14.51

BW12

2728

65.00

8.81

13.56

2901

50.36

6.19

12.28

BW

2586

69.65

9.72

13.95

2815

53.41

7.06

13.22


 

Table 2. The number of records, mean, standard deviation (SD) and coefficient of variation (CV) of the fleece traits

Trait

Ram progeny

Ewe progeny

N

Mean

SD

CV

(%)

N

Mean

SD

CV

(%)

MFD6

2959

17.46

1.20

6.88

3046

17.80

1.24

6.95

MFD12

2707

19.08

1.58

8.29

2897

18.96

1.40

7.41

GFW

2585

7.09

1.47

20.74

2795

5.92

1.21

20.45

CFW

2585

4.71

1.04

22.14

2795

4.08

0.90

21.99

MFD

2587

19.40

1.55

8.02

2816

19.13

1.45

7.56

STPL

2587

104.09

16.29

15.65

2816

101.58

14.71

14.48

CY

2578

13.89

2.33

16.77

2813

14.33

2.34

16.36

Crimp

2578

99.63

9.62

9.66

2813

99.41

8.97

9.02

Duer

2587

66.59

6.50

9.77

2816

68.88

6.03

8.75

SDFD

2584

8.28

2.25

27.23

2814

7.72

2.01

25.97

CVFD

1792

3.26

0.41

12.46

1984

3.20

0.42

12.97

Pleats

1792

17.33

2.08

11.98

1984

17.10

2.13

12.47

CF

1794

99.38

1.01

1.02

1986

99.39

1.01

1.01

 

RESULTS AND DISCUSSION

The direct additive heritability (h2a), maternal heritability (h2m), genetic correlation between the animal effects (ram) and the dam permanent environmental effect (c2pe) are summarised in Tables 3 and 4 for the body weights and wool production traits respectively. It is evident from Table 3 that the direct additive heritability estimates ranged from 0.10 (WW) to 0.54 (BW) and the maternal heritability estimates ranged from 0.06 (BW) to 0.29 (BirthW). The covariance between the animal effects was negative and amounted to -0.47 for BirthW and -0.39 for BW42. The estimates for the pre-weaning body weights and weaning weight are in the same order as the values reported in the literature that ranged from 0.16 to 0.35 (Lewer et al., 1994; Wuliji et al., 2001; Safari et al., 2005), 0.14 to 0.29 (Mortimer & Atkins, 1995; Annalla & Serradilla, 1998; Safari et al., 2005), 0.11 to 0.17 (Annalla & Serradilla, 1998; Cloete et al., 1998; Safari et al., 2005) and -0.21 to -0.42 (Vaez Torshizi et al., 1996; Annalla & Serradilla, 1998; Safari et al., 2005) for h2a, h2m, c2pe and ram respectively.


Table 3. Direct additive heritability (h2a), maternal heritability (h2m), genetic correlation between the animal effects (ram) and the dam permanent environmental effect (c2pe) for body weights (± s.e.)

Trait

h2a

h2m

ram

c2pe

Birth weight

0.24 ± 0.05

0.29 ± 0.05

-0.47 ± 0.09

0.12 ± 0.03

42-day body weight

0.16 ± 0.04

0.21 ± 0.04

-0.39 ± 0.13

0.07 ± 0.02

Weaning weight

0.10 ± 0.03

0.17 ± 0.03

 

0.07 ± 0.02

6-month body weight

0.28 ± 0.04

0.14 ± 0.02

 

 

12-month body weight

0.51 ± 0.04

0.08 ± 0.02

 

 

15-month body weight

0.54 ± 0.04

0.06 ± 0.02

 

 

 

The h2a and h2m for the post weaning weights estimated in this study are within the range of estimates reported in the literature. The h2a estimates reported ranged from 0.13 to 0.55 (Brown et al., 2005; Safari et al., 2005, Van Wyk et al., 2008; Matebesi et al., 2009) and ranged from 0.04 to 0.15 for h2m (Vaez Torshizi et al., 1996; Ingham et al., 2003; Safari et al., 2005).

 

Table 4. Direct additive heritability (h2a), maternal heritability (h2m), genetic correlation between the animal effects (ram) and the dam permanent environmental effect (c2pe) for the wool production traits (± s.e.)

 Trait

h2a

h2m

ram

c2pe

6-month fibre diameter

0.34 ± 0.04

0.05 ± 0.02

 

 

12-month fibre diameter

0.79 ± 0.02

0.03 ± 0.01

 

 

Greasy fleece weight

0.63 ± 0.04

0.10 ± 0.02

 

 

Clean fleece weight

0.64 ± 0.03

0.12 ± 0.02

-0.32 ± 0.14

 

15-month fibre diameter

0.77 ± 0.03

0.03 ± 0.01

 

0.03 ± 0.01

Staple length

0.47 ± 0.03

 

 

 

Clean yield

0.71 ± 0.03

 

 

 

Number of crimps per 25 mm

0.52 ± 0.04

0.07 ± 0.02

 

 

Duerden

0.55 ± 0.03

 

 

 

Standard deviation of FD

0.72 ± 0.03

 

 

 

Coefficient of variation of FD

0.64 ± 0.04

 

 

 

Pleat score

0.67 ± 0.03

0.03 ± 0.01

 

 

Comfort factor

0.94 ± 0.02

 

 

 

 

The h2a estimated for fleece weight in this study is slightly higher than the values reported in the literature that ranged from 0.17 to 0.59 (Ponzoni et al., 1995; Safari et al., 2005; Van Wyk et al., 2008), while the h2m are in the same order as the values reported in the literature that ranged from 0.00 to 0.14 (Swan & Hickson, 1994; Lewis & Beatson, 1999; Safari et al., 2005). The h2a estimated for 6-month fibre diameter is lower than the values reported for fibre diameter at older ages, while the 12 and 16-month fibre diameter were similar to the higher values of the range reported in the literature (Snyman et al., 1995; Cloete et al., 2001; Cloete et al., 2002; Lee et al., 2002).

 

The h2a estimates for staple length, clean yield, number of crimps, Duerden, standard deviation of FD and coefficient of variation of FD are in the same order as the estimates reported in the literature (Ponzoni et al., 1995; Swan et al., 1995; Brash et al., 1997; Purvis & Swan, 1997; Cloete et al., 1998; Hill, 2001; Wuliji et al., 2001). The estimate reported in the literature for comfort factor was 0.55 (Notter et al., 2007), which is lower than the estimate of 0.94 obtained in this study. This might be the result of the fact that there was much less variation in comfort factor in this study when compared to the results reported in the literature. The average CF in this study was almost 100% (Table 2), which means that a large proportion of the animals of the Cradock fine wool Merino stud had no fibres coarser than 30 µm.

 

The genetic and phenotypic correlations among body weights and wool production traits are summarised in Tables 5, 6, 7 and 8. The genetic correlations between birth weight and pre-weaning weight are higher than the correlations between birth weight and post weaning body weights. These correlations are within the range of values reported in the literature (Lewer et al., 1994; Nasholm & Danell, 1996; Yazdi et al., 1997; Neser et al., 2001; Wuliji et al., 2001; Duguma et al., 2002; Safari et al., 2005). The genetic correlations among weaning weight and post weaning body weights ranged from 0.81 to 0.97 and are in the same order as the values reported in the literature (Brash et al., 1994b,c; Lewer et al., 1994; Al-Shorepy & Notter, 1996; Snyman et al., 1998; Safari et al., 2005).

 

Table 5. Genetic (above diagonal) and phenotypic (below diagonal) correlations among the body weights (± s.e.)

 

BirthW

BW42

WW

BW6

BW12

BW

BirthW

 

0.51 ± 0.11

0.41 ± 0.13

0.13 ± 0.11

0.17 ± 0.09

0.16 ± 0.09

BW42

0.49 ± 0.01

 

0.71 ±0.09

0.47 ± 0.11

0.64 ± 0.08

0.61 ± 0.08

WW

0.37 ± 0.02

0.78 ± 0.01

 

0.86 ± 0.05

0.86 ± 0.05

0.81 ± 0.06

BW6

0.32 ± 0.02

0.61 ± 0.01

0.79 ± 0.01

 

0.95 ± 0.02

0.89 ± 0.03

BW12

0.29 ± 0.02

0.50 ± 0.01

0.64 ± 0.01

0.82 ± 0.01

 

0.97 ± 0.01

BW

0.28 ± 0.02

0.46 ± 0.02

0.57 ± 0.01

0.73 ± 0.01

0.87 ± 0.01

 

 

 

Table 6. Genetic (above diagonal) and phenotypic (below diagonal) correlations among the wool traits (± s.e.)

 

MFD6

MFD12

GFW

CFW

MFD

STPL

CY

Crimp

Duer

SD

CV

Pleats

CF

MFD6

 

0.89 ± 0.04

-0.03 ± 0.08

-0.05 ± 0.08

0.84 ± 0.04

-0.03 ± 0.08

-0.02 ± 0.07

0.03 ± 0.09

0.63 ± 0.07

0.64 ± 0.08

-0.07 ± 0.09

-0.01 ± 0.08

-0.78 ± 0.06

MFD12

0.46 ± 0.02

 

0.19 ± 0.05

0.10 ± 0.05

0.98 ± 0.01

-0.03 ± 0.06

-0.10 ± 0.05

-0.00 ± 0.06

0.76 ± 0.03

0.51 ± 0.07

-0.29 ± 0.06

0.18 ± 0.05

-0.69 ± 0.06

GFW

0.07 ± 0.02

0.22 ± 0.02

 

0.85 ± 0.02

0.24 ± 0.06

0.31 ± 0.06

0.10 ± 0.05

-0.49 ± 0.06

-0.25 ± 0.06

0.35 ± 0.09

0.26 ± 0.07

0.54 ± 0.05

-0.26 ± 0.08

CFW

0.04 ± 0.02

0.13 ± 0.02

0.87 ± 0.01

 

0.10 ± 0.06

0.48 ± 0.05

0.60 ± 0.04

-0.61 ± 0.05

-0.43 ± 0.06

0.26 ± 0.10

0.18 ± 0.07

0.37 ± 0.05

-0.21 ± 0.07

MFD

0.43 ± 0.02

0.84 ± 0.01

0.23 ± 0.02

0.14 ± 0.02

 

-0.04 ± 0.07

-0.09 ± 0.06

-0.13 ± 0.07

0.73 ± 0.03

0.48 ± 0.08

-0.18 ± 0.07

0.20 ± 0.06

-0.71 ± 0.05

STPL

0.00 ± 0.02

-0.01 ± 0.02

0.21 ± 0.02

0.35 ± 0.02

0.00 ± 0.02

 

0.44 ± 0.05

-0.65 ± 0.05

-0.52 ± 0.05

0.04 ± 0.11

0.05 ± 0.07

-0.47 ± 0.05

0.03 ± 0.08

CY

-0.04 ± 0.02

-0.09 ± 0.02

0.03 ± 0.02

0.50 ± 0.02

-0.07 ± 0.02

0.33 ± 0.02

 

-0.48 ± 0.05

-0.42 ± 0.05

-0.11 ± 0.10

-0.08 ± 0.07

-0.10 ± 0.05

0.06 ± 0.07

Crimp

0.01 ± 0.02

0.01 ± 0.02

-0.27 ± 0.02

-0.36 ± 0.02

-0.05 ± 0.02

-0.28 ± 0.02

-0.29 ± 0.02

 

0.66 ± 0.04

-0.11 ± 0.11

-0.19  0.07

0.09 ± 0.07

0.13 ± 0.08

Duer

0.31 ± 0.02

0.59 ± 0.01

-0.04 ± 0.02

-0.17 ± 0.02

0.67 ± 0.01

-0.22 ± 0.02

-0.26 ± 0.02

0.70 ± 0.01

 

0.34 ± 0.10

-0.22 ± 0.07

0.14 ± 0.06

-0.36 ± 0.08

SD

0.36 ± 0.02

0.37 ± 0.03

0.19 ± 0.03

0.14 ± 0.03

0.38 ± 0.03

-0.03 ± 0.03

-0.07 ± 0.03

-0.10 ± 0.03

0.21 ± 0.03

 

0.85 ± 0.03

0.51 ± 0.08

-0.84 ± 0.03

CV

0.01 ± 0.02

-0.16 ± 0.03

0.10 ± 0.03

0.06 ± 0.03

-0.12 ± 0.03

-0.05 ± 0.03

-0.07 ± 0.03

-0.14 ± 0.02

-0.16 ± 0.03

0.88 ± 0.01

 

0.30 ± 0.07

-0.56 ± 0.06

Pleats

0.03 ± 0.02

017 ± 0.02

0.45 ± 0.02

0.32 ± 0.02

0.19 ± 0.02

-0.22 ± 0.02

-0.11 ± 0.02

0.05 ± 0.02

0.15 ± 0.02

0.26 ± 0.03

0.16 ± 0.03

 

-0.28 ± 0.08

CF

-0.43 ± 0.02

-0.51 ± 0.02

-0.19 ± 0.03

-0.14 ± 0.03

-0.52 ± 0.02

0.03 ± 0.03

0.05 ± 0.03

0.07 ± 0.03

-0.27 ± 0.03

-0.71 ± 0.02

-0.47 ± 0.02

-0.18 ± 0.03

 

 


Table 7. Genetic correlations between body weights and wool production traits (± s.e.)

 

MFD6

MFD12

GFW

CFW

MFD

STPL

CY

Crimp

Duer

SD

CV

Pleats

CF

BirthW

0.03 ± 0.11

0.04 ± 0.08

0.26 ± 0.08

0.28 ± 0.09

-0.03 ± 0.08

0.04 ± 0.08

0.18 ± 0.08

-0.09 ± 0.09

-0.15 ± 0.08

0.20 ± 0.12

0.17 ± 0.09

0.17 ± 0.09

-0.15 ± 0.10

BW42

0.27 ± 0.13

0.28 ± 0.10

025 ± 0.11

0.19 ± 0.11

0.24 ± 0.11

-0.01 ± 0.11

0.09 ± 0.10

0.05 ± 0.12

0.22 ± 0.10

0.17 ± 0.16

-0.01 ± 013

0.05 ± 0.12

0.06 ± 0.13

WW

0.41 ± 0.14

0.53 ± 0.10

0.09 ± 0.12

-0.04 ± 0.12

0.49 ±0.10

0.13 ± 0.14

-0.09 ± 0.11

-0.06 ± 0.13

0.27 ± 0.12

0.22 ± 0.17

-0.12 ± 0.13

-0.22 ± 0.12

-0.23 ± 0.14

BW6

0.34 ± 0.11

0.56 ± 0.07

0.02 ± 0.09

-0.06 ± 0.09

0.59 ± 0.07

0.19 ± 0.09

-0.04 ± 0.08

-0.05 ± 0.10

0.28 ± 0.09

0.07 ± 0.14

-0.38 ± 0.09

-0.36 ± 0.09

-0.25 ± 0.25

BW12

0.14 ± 0.09

0.34 ± 0.06

0.05 ± 0.07

0.01 ± 0.07

0.40 ± 0.06

0.19 ± 0.07

-0.02 ± 0.06

0.02 ± 0.08

0.23 ± 0.07

-0.03 ± 0.12

-0.30 ± 0.07

-0.37 ± 0.07

-0.18 ± 0.08

BW

0.12 ± 0.09

0.24 ± 0.06

-0.1 ± 0.07

-0.02 ± 0.07

0.28 ± 0.06

0.16 ± 0.06

0.01 ± 0.06

0.01 ± 0.07

0.14 ± 0.07

-0.07 ± 0.11

-0.28 ± 0.07

-0.39 ± 0.06

-0.07 ± 0.08

 

Table 8. Phenotypic correlations between body weights and wool production traits (± s.e.)

 

MFD6

MFD12

GFW

CFW

MFD

STPL

CY

Crimp

Duer

SD

CV

Pleats

CF

BirthW

-0.01 ± 0.02

-0.05 ± 0.02

0.32 ± 0.02

0.34 ± 0.02

-0.04 ± 0.02

0.02 ± 0.02

0.12 ± 0.02

-0.09 ± 0.02

-0.09 ± 0.02

0.09 ± 0.03

0.05 ± 0.02

0.14 ± 0.02

-0.02 ± 0.02

BW42

0.17 ± 0.02

0.04 ± 0.02

0.30 ± 0.02

0.30 ± 0.02

0.04 ± 0.02

0.01 ± 002

0.08 ± 0.02

-0.01 ± 0.02

0.04 ± 0.02

0.01 ± 0.02

-0.02 ± 0.02

0.11 ± 0.02

0.02 ± 0.02

WW

0.22 ± 0.02

0.13 ± 0.02

0.31 ± 0.02

0.28 ± 0.02

0.10 ± 0.02

0.04 ± 0.02

0.03 ± 0.02

-0.01 ± 0.02

0.07 ± 0.02

-0.01 ± 0.02

-0.07 ± 0.02

0.04 ± 0.02

-0.01 ± 0.02

BW6

0.18 ± 0.02

0.26 ± 0.02

0.35 ± 0.02

0.32 ± 0.02

0.23 ± 0.02

0.10 ± 0.02

0.02 ± 0.02

0.03 ± 0.02

016 ± 0.02

-0.05 ± 0.03

-0.21 ± 0.02

-0.03 ± 0.02

-0.06 ± 0.03

BW12

0.09 ± 0.02

0.27 ± 0.02

0.35 ± 0.02

0.32 ± 0.02

0.24 ± 0.02

0.12  + 0.02

0.02 ± 0.02

0.02 ± 0.02

0.17 ± 0.02

-0.06  ± 0.03

-0.23 ± 0.03

-0.07± 0.02

-0.07 ± 0.03

BW

0.06 ± 0.02

0.18 ± 0.02

0.27 ± 0.02

0.26 ± 0.02

0.19 ± 0.02

0.11 ± 0.02

0.03 ± 0.02

0.01 ± 0.02

0.13 ± 0.02

-0.08 ± 0.03

-0.21 ± 0.03

-0.09 ± 0.02

-0.02 ± 0.03

 

The genetic correlations between fleece weight and fibre diameter traits at performance testing age (MFD, SDFD and CVFD) are low to moderate positive. The corresponding values between fleece weight and number of crimps, Duerden and CF are moderate negative. These estimates are in the same order as the values reported in the literature (Swan et al., 1995; Hill, 2001; Brown et al., 2002; Safari et al., 2005; Matebesi et al., 2009). All of these relationships are unfavourable, which means that an increase in fleece weight would lead to coarser wool with a wider fibre diameter distribution and less crimps per 25 mm.

 

MFD is negatively correlated with number of crimps and CVFD, while SDFD and Duerden are positively correlated. This means that selection for decreased fibre diameter would result in fibres with less crimps and a wider fibre diameter distribution. These correlations between MFD, SDFD and CVFD are in the same order as the values reported in the literature (Swan et al., 1995; Brash et al., 1997; Hill, 2001; Brown et al., 2002; Cloete et al., 2002; Safari et al., 2005).

 

Decreasing the CVFD of animals will result in more uniform staples with a narrower fibre distribution. This will in turn result in an increase in staple strength (SS) because CVFD and SS is moderate to high negatively correlated (Swan et al., 1995; Greeff & Karlsson, 1998; Greeff & Karlsson, 1999, Hill, 2001; Wuliji et al., 2001). The unfavourable correlation between MFD and CVFD makes it imperative that the CVFD of animals is monitored or included in selection programs when selection for decreasing MFD is one of the main selection criteria. This will ensure that CVFD and SS are not subsequently adversely affected.

 

The genetic correlations between body weights at different ages and fleece weights ranged from -0.06 to 0.28 and decreased with age. The corresponding correlations reported in the literature are in the same order as the values obtained in this study (Lewer et al., 1994; Rose & Pepper, 1999; Snyman et al., 1998). Body weights at different ages, excluding birth weight, are moderately correlated with fibre diameter at different ages. The phenotypic correlations between the body weights, fleece weight and fibre diameters were low to moderate and ranged from -0.05 to 0.35.  These estimates are within the range of correlations reported in the literature for these relationships (Brash et al., 1994a; Lewer et al., 1994; Purvis & Swan, 1997; Cloete et al., 1998; Snyman et al., 1998; Safari et al., 2005).

 

CONCLUSION 

The results from this study correspond with the parameter estimates reported in the literature for body weights at different ages and wool production traits. The moderate to high heritability estimates of the economically important traits indicate that these traits can be included in selection programs to improve the production of Merino sheep and subsequently the profitability of a wool sheep enterprise.

 

Fibre diameter had the highest heritability of all the economically important traits and genetic progress will be at a faster rate than the other traits. Furthermore, fibre diameter is one of the traits that have the biggest influence on the wool price and on the profitability of a wool sheep enterprise. Due to this effect on the wool price and the possible genetic gain, much emphasis is placed on the selection for decreased fibre diameter. If this selection is done indiscriminately it can adversely affect the other economically important traits as a result of the unfavourable correlations between these traits. This means that decreasing fibre diameter can lead to a decrease in body and fleece weight, as well as short and less uniform staples with a lower staple strength. It is therefore of the utmost importance that all the economically important traits are included in the selection program, either to select on these traits or just for monitoring purposes. This will ensure that none of these traits and the profitability of the enterprise are adversely affected.

 

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Published

Grootfontein Agric 11 (2): 63-74