Last update: December 8, 2010 01:50:42 PM E-mail Print

 

THE EFFECT OF FEEDING STRESS ON THE WOOL PRODUCTION

OF STRONG AND FINE WOOL MERINO SHEEP

 

W.J. Olivier1# and J.J. Olivier2


1 Grootfontein ADI, Private Bag X529, Middelburg E.C. 5900

2 ARC: LBD (Animal Production), Private Bag X5013, Stellenbosch, 7590

#Corresponding author: E-mail: Willem Olivier

 


INTRODUCTION

The demand for fine wool during the late 1980’s has lead to an increase in the number of flocks in South Africa where one of the main breeding objectives was to decrease fibre diameter. Most of these flocks are kept under extensive farming conditions in the semi-arid and arid areas of South Africa. Seasonal droughts occur regularly in these areas, subjecting these animals to nutritional stress.

It is widely known that several wool quality factors such as fibre diameter, fibre length and tensile strength are influenced by the amount of nutrients available to the wool follicles. The amount of wool is in turn influenced by, among others, fibre diameter and fibre length (Reis & Sahlu, 1994). Several researchers have indicated that the effect of nutrition on wool production is mainly expressed through fibre length and diameter (Nichols, 1933; Galpin, 1948; Stewart et al., 1961; Sumner & Wickham, 1969). It is also well known that nutritional stress of ewes during pregnancy will result in less and stronger wool being produced by their progeny. Kelly et al. (1996), for example, found a significant (P<0.05) difference in the fibre diameter of cloned embryos of which the receiver ewes have been fed two different diets. Hunter et al. (1990) reported that stress factors, such as nutrition and lambing, decreased fibre diameter by 30% on average, sometimes by up to 10mm.

 

Some South African wool producers have a perception that sheep with the genetic potential to produce fine wool are affected more by stress related factors than those producing strong wool. Furthermore, it is believed that the production loss of the fine wool animals will be permanent, while that of strong wool animals is only temporary. The objective of this study was, therefore, to investigate the effect of short term nutritional stress after weaning on the short and medium term wool production and characteristics of fine vs. strong wool Merino sheep.

 

MATERIAL AND METHODS

Eighty wethers from the Grootfontein Merino flock were used for this study, 40 from a genetic line producing fine wool and 40 from a line producing strong wool. The lambs from each line were allocated  randomly into two groups  of approximately the same body weight and mean fibre diameter, viz. two treatment and two control groups.The study was carried out in two phases. During the first phase the animals were kept in pens for a period of 15 weeks and received two quality diets ad libitum. The treatment groups received a diet of low nutritive value and the control groups one of high nutritive value. The energy content of the control diet was increased due to the fact that there was no differences in body weight between the respective treatment and control groups. The composition and estimated nutritive value of the different diets are presented in Table 1.

 

During the second phase, the animals were kept as one group for a period of 18 months on natural pastures at Grootfontein Agricultural Development Institute (GADI) near Middelburg (31°28'S, 25°1'E) in the north-eastern Karoo region of South Africa. GADI is located in the False Upper Karoo (Veld type 36, Acocks, 1988) and has an annual rainfall of 360mm.

 

The animals were weighed weekly during the first phase and monthly during the second phase. The animals were shorn at the commencement of the first phase and at the end of the first phase and every six months thereafter for a period of 18 months. At each shearing,  individual fleece weights were recorded and mid rib fleece samples were taken from each animal for analysis. The samples were used to determine the clean yield (CY), clean fleece weight (CFW), mean fibre diameter (MFD), staple length (STPL), number of crimps per 25mm (Crimps), diviation from the Duerden standard (Duer), coefficient of variation (CV), comfort factor (CF, percentage of fibres below 30 µm) and tensile strength (TS). The tensile strength could not be measured for the first two shearings as the staple length of the samples were shorter than 50 mm, which is the minimum boundary for the measurement of tensile strength. The fleece weight and staple length of the first and second shearings were corrected to a wool growth of 180 days.

 

Table 1. The composition of the two different diets and their nutritive value

 

Low nutritional value

(Treatment group)

High nutritional value (Control group)

First 4 weeks

After 4 weeks

Ingredients

 

 

 

Maize (%)

 

 

17.5

Lucerne (%)

47.5

95.0

77.5

Maize stover (%)

47.5

 

 

Molasses meal (%)

5.0

5.0

5.0

Crude Protein (g/kg)

95.0

145.0

134.0

Energy (TDN; g/kg)

540.0

555.0

604.0

Ca (g/kg)

6.4

12.0

9.6

P (g/kg)

2.7

2.0

2.1

 

A skin biopsy on the midrib of each animal was taken just prior to each shearing for the second (at the end of the first phase) and third (six months after the end of the first phase) shearings. These biopsies were used to determine the primary and secondary follicle ratio (SP Ratio) of each animal, using an image analyzer (analysis 3.2 Auto; Soft Imaging System, Münster, Germany).

 

To determine if there was a difference in the number of fibres between the respective treatment and control groups the  number of fibres per animal (Fib)was calculated, using the following equation:

    CFW

Fib =     ____________

Sg*π*r2*l

where;

Fib    = the number of fibres per animal,

CFW = clean fleece weight (kg),

Sg    = the specific gravity of wool (1.31gcm-3),

r      = the radius of the fibre (cm),

l       = the length of the fibre (cm).

 

Least-squares means (LSM) and standard errors (± s.e.) for body weight and wool traits were obtained with the Proc GLM-procedure of SAS and the significance levels between the treatment and control groups of each flock were obtained with the PDIFF-option under the Proc GLM-procedure of SAS (Littell et al., 2002). The fixed effects that were tested for significance for the different traits were age of the dam in years (Dage), flock x group (fine wool or strong wool; control or treatment; FG) and rearing status (combination of birth and weaning status; RS). For each trait the effect of age of the animals (linear regression; Age) was also tested for significance.  The effect of GFW and MFD of the first shearing on subsequent fleece weights and MFD were tested for inclusion as linear regressions. Only the effects that had a significant effect on a specific trait were included in the final model, except for flock x group, which needed to be included in all of the models, regardless of the significance level in order to obtain the LSM for the respective groups and flocks.

 

RESULTS AND DISCUSSION

The body weights at the commencement of the first phase, at the end of the first phase and at the end of the second phase are summarized in Table 2, while the changes in body weights, recorded during the first and second phases of this study are depicted in Figures 1 and 2 respectively. From Figure 1 it is evident that the change in the diet of the control groups resulted in a marked increase in the body weights of the control groups after week 8, when the animals were well adapted to their new diet. Body weights of the treatment groups remained constant for the duration of the first phase. There was a significant difference of more thant 12 kg in body weight between the treatment and control groups of the two flocks at the end of the first phase (Table 2 and Figure 1). After the animals were moved to the veld, there was a marked increase in the growth rate of the treatment groups compared to their respective control groups (Figure 2). No significant differences in body weight were observed between the respective treatment and control groups at the end of the second phase (Table 2).

 

Table 2. The initial body weight, body weight at the end of the first phase and body weight at the end of the study (± s.e.)

Body weight  (kg)

Fine wool Treatment

(n)#

Fine wool Control

(n)

Strong wool Treatment

(n)

Strong wool Control

(n)

Start of first phase

22.21 ± 0.73

(20)

23.56 ± 0.68

(20)

23.74 ± 0.70

(20)

24.06 ± 0.66

(20)

End of first phase

22.74 a ± 1.03

(16)

34.71 a ± 1.06

(15)

23.21 b ± 0.97

(18)

36.99 b ± 1.00

(17)

End of project

68.33 ±1.93

(15)

72.09 ± 2.07

(13)

69.03 ±1.87

(16)

74.23 ± 1.93

(15)

a,b - values with the same superscript differed significantly (P<0.05), a = fine wool, b = strong wool

# - Number of animals in each group; s.e. – standard error

Figure 1. The growth curves of the respective fine and strong wool groups recorded during the first phase of the study (weekly body weights)

 

Figure 2. The growth curves of the respective fine and strong wool groups recorded during the second phase of the study (monthly body weights)

 

The GFW, CFW, MFD, STPL and CY for the respective shearings are summarized in Table 3. At the commencement of the study there were no significant differences between the treatment and control groups of each flock with regard to any of the wool traits. Nutritional stress had a significant effect on wool production of the treatment groups compared to the respective control groups. Wool production of the fine wool treatment group was affected more negatively than that of the strong wool treatment group. This is illustrated by the fact that the fine wool treatment group animals produced 42% less wool than their control group animals, while the strong wool treatment group animals produced only 29% less wool than their control group animals. Six months after the stress period ended (3rd shearing), the differences (P<0.05) in wool production between the respective fine wool and strong wool groups had decreased to 29% and 23% respectively. At the end of the study, the treatment group animals produced the same amount of wool than their respective control group animals.

 

At the end of the stress period, the fine wool treatment group produced 0.64 mm finer (P<0.01) wool compared to their control group. At the same stage there was no difference between the strong wool groups’ MFD. This is a further indication that fine wool sheep are affected more negatively by nutritional stress than strong wool sheep. The significant differences in MFD between the fine and strong wool groups six months after the stress phase had ended, suggest that animals that were subjected to nutritional stress will take some time to recover fully from the stress.

 

At the end of the first phase, both treatment groups had higher (P<0.01) CY’s than their respective control groups. This might be due to the fact that better feeding conditions increased the production of wool yolk (Ryder & Stephenson, 1968).

 

The wool characteristics and the primary to secondary follicle ratio (SP ratio) analyzed in this study are summarized in Table 4. From this table it is evident that nutritional stress did not have an influence on these traits. The exceptions are the higher number of crimps per 25 mm of the strong wool treatment group compared to their control group (2nd shearing), as well as the higher CV of the strong wool treatment group (3rd shearing). The differences in Duerden at the 3rd shearing are more likely the effect of the differences in MFD, as there were no differences in the number of crimps at that stage. It is evident from these tables that nutritional stress did not have an effect on these traits from the 3rd to 5th and the 2nd and 3rd shearings respectively.

 

Table 3. The wool production traits (± s.e.) of the four groups

 

Fine wool

Treatment

Fine wool

Control

Strong wool

Treatment

Strong wool

Control

Greasy fleece weight (kg)

 

 

 

 

1st shearing *

1.76 ± 0.08

1.81 ± 0.08

1.81 ± 0.08

1.95 ± 0.06

2nd shearing *

1.24a ± 0.09

2.27a ± 0.08

1.53b ± 0.08

2.31b ± 0.08

3rd shearing

2.00 a ± 0.10

2.75 a ± 0.10

2.47 b ± 0.10

3.12 b ± 0.10

4th shearing

2.97 ± 0.17

3.25 ± 0.18

3.99 ± 0.17

4.29 ± 0.17

5th shearing

3.83 ± 0.15

3.87 ± 0.16

4.79 ± 0.15

4.69 ± 0.15

Clean fleece weight (kg)

 

 

 

 

1st shearing *

1.31 ± 0.06

1.34 ± 0.06

1.37 ± 0.06

1.46 ± 0.06

2nd shearing *

1.00 a ± 0.07

1.74 a ± 0.07

1.25 b ± 0.06

1.77 b ± 0.06

3rd shearing

1.47 a ± 0.08

2.07 a ± 0.08

1.84 b ± 0.08

2.38 b ± 0.08

4th shearing

2.30 ± 0.15

2.51 ± 0.15

3.29 ± 0.15

3.48 ± 0.15

5th shearing

2.79 ± 0.13

2.77 ± 0.14

3.65 ± 0.12

3.52 ± 0.13

Mean fibre diameter (μm)

 

 

 

 

1st shearing

15.83 ± 0.18

16.01 ± 0.18

18.40 ± 0.18

18.30 ± 0.18

2nd shearing

16.43 a  ± 0.27

17.07 a  ± 0.24

17.64 ± 0.23

17.86 ± 0.23

3rd shearing

16.81 a ± 0.34

18.21 a ± 0.34

18.60 b ± 0.33

20.12 b ± 0.31

4th shearing

20.02 ± 0.40

20.28 ± 0.40

22.82 ± 0.39

23.66 ± 0.37

5th shearing

20.48 ± 0.45

20.25 ± 0.39

23.14 ± 0.43

23.09 ± 0.40

Staple length (mm)

 

 

 

 

1st shearing *

51.34 ± 1.99

51.85 ± 2.04

54.16 ± 2.04

51.11 ± 2.04

2nd shearing *

51.71 ± 2.19

55.07 ± 2.11

48.00 ± 1.99

52.58 ± 1.99

3rd shearing

48.69 a ± 1.66

55.36 a ± 1.78

52.31 ± 1.66

53.44 ± 1.66

4th shearing

53.19 ± 1.70

52.36 ± 1.81

52.00 ± 1.70

53.56 ±1.70

5th shearing

57.73 ± 1.38

56.15 ± 1.48

55.94 ± 1.34

55.00 ± 1.34

Clean yield (%)

 

 

 

 

1st shearing

74.34 ± 1.02

73.00 ± 0.99

75.32 ± 1.02

75.86 ± 1.04

2nd shearing

80.51 a ± 0.89

76.45 a ± 0.86

81.44 b ± 0.81

76.63 b ± 0.81

3rd shearing

73.36 ± 0.83

75.16 ± 0.88

74.43 ± 0.83

75.77 ± 0.83

4th shearing

77.96 ± 1.05

77.39 ± 0.54

82.24 ± 1.05

81.05 ± 1.05

5th shearing

72.99 ± 1.08

71.65 ± 1.16

76.14 ± 1.04

75.08 ± 1.04

a,b - Values with the same superscript differed significantly (P<0.05), a = fine wool, b = strong wool

* - Corrected to 6 month wool growth; s.e. – standard error

 

The differences in MFD and STPL between the respective groups within each flock were relatively small or even non-significant, whereas the differences in the fleece weights were relatively large and significant. Therefore, it is evident that the small differences in the two most important factors that influence the amount of wool growth, namely MFD and STPL, did not account for the loss of wool production. The reason for the differences in wool production could be due to differences in the activity of the wool follicles, since there were also no significant differences between the S:P ratios in both flocks.

 

The estimated number of follicles per animal could be used as am indication of the activity of the follicles. The LSM of the number of fibres per animal for each shearing are summarized and depicted in Table 5. It is clear from this table that there were no significant differences at the commencement of the first phase between the number of fibres of the respective fine wool and strong wool groups. Furthermore, it is clear that the fine wool sheep had significantly more fibres than the strong wool animals at the commencement of the study.

Table 4. The wool characteristics (± s.e.) and the primary to secondary follicle ration (S:P ratio ±SE) of the four groups

 

Fine wool Treatment

Fine wool Control

Strong wool Treatment

Strong wool Control

CF (%)

 

 

 

 

1st shearing

99.81 ± 0.13

99.78 ± 0.13

98.92 ± 0.13

99.05 ±0.13

2nd shearing

99.92 ± 0.16

99.86 ± 0.15

99.04 ± 0.14

99.09 ± 0.14

3rd shearing

99.87 ± 0.31

99.67 ± 0.33

98.65 ± 0.31

97.79 ± 0.31

4th shearing

99.69 ± 1.03

99.49 ± 1.10

92.18 ± 1.03

90.69 ± 1.03

5th shearing

98.18 ± 0.85

98.42 ± 0.92

92.39 ± 0.82

93.01 ± 0.82

No. of Crimps per 25mm (n)

 

 

 

 

1st shearing

12.49 a ± 0.36

14.66 a ±0.38

10.34 ±0.37

11.42 ± 0.38

2nd shearing

14.72 ± 0.48

15.01 ± 0.43

12.41 b ± 0.43

10.78 b ± 0.41

3rd shearing

15.86 ± 0.45

16.46 ± 0.48

11.88 ± 0.45

11.81 ± 0.45

4th shearing

15.69 ± 0.51

16.27 ± 0.54

9.96 ± 0.51

9.88 ± 0.51

5th shearing

15.39 ± 0.48

14.46 ± 0.51

9.45 ± 0.46

10.64 ± 0.46

CV (%)

 

 

 

 

1st shearing

22.87 ± 0.43

22.31 ± 0.43

24.16 ± 0.43

24.07 ± 0.44

2nd shearing

21.09 ± 0.53

20.85 ± 0.52

23.59 ± 0.48

23.31 ± 0.48

3rd shearing

19.51 ± 0.49

18.35 ± 0.52

22.34 b ± 0.49

19.78 b ± 0.49

4th shearing

16.69 ± 0.43

16.91 ± 0.46

19.26 ± 0.43

18.38 ± 0.43

5th shearing

17.83 ± 0.60

17.52 ± 0.63

20.76  ± 0.56

19.34  ± 0.56

Duerden

 

 

 

 

1st shearing

77.96 a ± 1.38

84.56 a ± 1.46

83.97 ± 1.41

87.17 ± 1.47

2nd shearing

83.50 ± 1.82

88.27 ± 1.63

89.27 ± 1.63

84.94 ± 1.53

3rd shearing

89.50 a ± 1.76

98.71 a ± 1.88

91.81 b ± 1.76

98.38 b ± 1.76

4th shearing

104.56 ± 2.38

108.07 ± 2.54

105.88 ± 2.38

108.38 ± 2.38

5th shearing

108.67 ± 1.91

105.46 ± 2.06

102.31 ± 1.85

106.69 ± 1.85

Tensile strength (n/Ktex)

 

 

 

 

3rd shearing

61.55 ± 2.55

61.38 ± 2.34

63.60 ± 2.18

61.71 ± 2.26

4th shearing

59.15 ± 1.86

63.17 ± 1.94

65.31 ± 1.86

64.64 ± 1.80

5th shearing

59.67 ± 2.61

61.00 ± 3.05

66.69 ± 2.53

68.50 ± 2.53

SP Ratio

 

 

 

 

2nd shearing

26.47 ± 1.90

31.14 ± 2.20

26.37 ± 1.70

26.86 ± 2.33

3rd shearing

23.98 ± 1.97

28.28 ± 1.97

21.60 ± 1.82

28.18 ± 1.97

a,b - Values with the same superscript differed significantly (P<0.05), a = fine wool, b = strong wool

s.e. – standard error

 

The only significant differences between the respective groups of each flock were evident at the end of the stress phase with the second shearing. The number of fibres per animal of the fine wool treatment group decreased sharply during the stress phase, while  that of the respective control group remained almost constant during the stress phase (Table 5). Furthermore, when the LSM  of the fine wool groups are compared to that of the strong wool groups it is evident that the situation was reversed, where the value of the treatment groups remain constant and the number of fibres per animal of the strong wool control group increased. However, there were no significant differences in the number of fibres per animal throughout the second stage (Table 5). This suggests that the follicles of the fine wool treatment group shed their fibres and became inactive for the duration of the stress period, but started to produce fibres again after the stress factor was removed, i.e. when the feeding conditions improved. With regard to the stressed animals in the strong wool group, the stress period stopped the normal increase and development of follicles until the feeding conditions was improved.

 

It is a well documented that wool follicles can become inactive or shed their fibres as a result of stress factors, such as feeding stress (Lang, 1945; Lindner & Ferguson, 1956; Lyne, 1964; Chapman & Bassett, 1970; Thwaites, 1972; Schlink et al., 1992; Schlink & Dollin, 1995; Hynd  et al., 1997;  Thompson et al., 1998). Furthermore, Thompson et al. (1998) reported that the incidence of fibre shedding is higher in young, growing animals as a result of their low reserves of fat and protein that limit their ability to buffer against seasonal fluctuations in the availability of nutrients.

Table 5. The number of fibres (± s.e.) per animal of the four groups (±SE)

 

Fine wool Treatment

Fine wool Control

Strong wool Treatment

Strong wool Control

1st shearing

105.27 *106 ±

6.41 * 106

105.21 * 106 ±

6.43 * 106

73.51 * 106 ±

6.41 * 106

83.69 * 106 ±

6.60 * 106

2nd shearing

64.95 * 106a ±

6.24 * 106

104.75 * 106a ± 5.56 * 106

72.56 * 106b ±

5.61 * 106

93.40 * 106b ±

5.34 * 106

3rd shearing

104.71 * 106 ±

5.26 * 106

117.05 * 106 ±

5.62 * 106

93.95 * 108 ±

5.26 * 106

107.81 * 108 ±

5.25 * 106

4th shearing

110.81 * 106 ±

7.70 * 106

124.02 * 106 ±

8.23 * 106

112.67 * 108 ±

7.70 * 106

112.81 * 108 ±

7.70 * 106

5th shearing

112.05 * 106 ±

6.82 * 106

121.51 * 106 ±

7.32 * 106

118.78 * 108 ±

6.60 * 106

121.06 * 108 ±

6.60 * 106

a,b - Values with the same superscript differed significantly (P<0.05), a = fine wool, b = strong wool

s.e. – standard error

 

The results from this study suggest that the wool follicles of the stressed animals in both the fine and strong wool flocks became inactive and that some follicles had shed their fibres. However, the inactivity of the follicles was not permanent, since at the end of the second phase there were no differences in the amount of wool and the number of follicles produced by the control and treatment groups. Allden (1968) also reported that stress at an early age caused by poor nutrition for a short period did not have a negative affect on the ability of Merino lambs to produce wool.

 

CONCLUSION

From the results of this study it is evident that in the long term nutritional stress at an early age did not affect the body weight of young growing lambs negatively.  The results furthermore indicated that wool production of the fine wool sheep was affected more negatively during the stress period than that of the strong wool sheep. However, this negative effect was only of temporary, because the difference in the amount of wool produced between the control and treatment groups decreased after the stress was removed. At the end of the experiment the fine wool sheep from both experimental groups produced the same amount of wool, while the stressed animals in the strong wool group produced 3% more wool than the unstressed group.

The results from this study suggest that the wool follicles of the animals of the treatment groups of both the fine and strong wool flocks became inactive and that some follicles shed their fibres. However, a most important factor is that the inactivity of the follicles was not permanent, and at the end of the second phase there were no differences in the amount of wool produced by the stressed and unstressed groups.

It could be concluded that early nutritional stress did not have a permanent detrimental effect on the wool production potential of fine and strong wool sheep. 

 

ACKNOWLEDGEMENTS

The authors want to express their gratitude to Cape Wools South Africa for funding the project, the Provincial Veterinary Laboratory at Middelburg, Eastern Cape, for the preparation of the histological slides and the Elsenburg Agricultural Development Institute for the analyses of the histological slides.

 

REFERENCES

Acocks, J.P.H., 1988. Veld types of South Africa. 3rd Ed., Botanical Research Institute, Dept. of Agric. and Water Supply.

Allden, W.G., 1968. Undernutrition of the Merino sheep and its sequelae. II. The influence of finite periods of arrested growth on the subsequent wool growth, fleece development and utilization of feed for wool production of lambs. Aust. J. Agric. Res.19, 639-648.

Chapman, R.E. & Bassett J.M., 1970. The effects of prolonged administration of cortisol on the skin of sheep on different planes of nutrition. J. Endocrinology. 48, 649-663.

Galpin, N., 1948. A Study of wool growth. II Mean fibre thickness, density of fibre population, the area of skin covered by fibre and the mean fibre length. J. Agric. Sci. 38, 303-314.

Hunter, L., Van Wyk, J.B., De Wet, P.J., Grobbelaar, P.D., Pretorius, P.S., Morris, J. de V. & Leeuner, Williena, 1990. The effect of nutritional and lambing stress on wool fibre and processing characteristics. Wool Tech. Sheep Breed. (Sep., 1990 / Oct., 1990 & Dec., 1990 / Jan., 1991), 89-91d.

Hynd, P.I., Hughes, A., Earl, C.R. & Penno, N.M., 1997. Seasonal changes in the morphology of wool follicles in Finewool and Strongwool Merino strains at different stocking rates in southern Australia. Austr. J. Agric. Res. 48, 1089-1097.

Kelly, R.W., Macleod, I., Hynd, P. & Greeff, J., 1996. Nutrition during fetal life alters annual wool production and quality in young Merino sheep. Aus. J. Exp. Agric. 36, 259-267.

Lang, W.R., 1945.  Growth in tender wool. J. Text. Inst. 36, T243-252.

Lindner,  H.R. & Ferguson, K.A., 1956. Influence of the adrenal cortex on wool growth and its relation to break and tenderness of the fleece. Nature (London). 177, 188-189.

Littell, R.C., Freud, R.J. & Struop, W.W., 2002. SAS-system for linear models, 4th Ed. SAS Institute. Inc. Cary, NC.

Lyne, A.G., 1964. Effect of adverse nutrition on the skin and wool follicles in Merino sheep. Austr. J. Agric. Res. 15, 788-801.

Nichols, J.E., 1933. Fibre growth phases in a sample of Australian Merino wool. J. Text. Inst. 24, T333-T340.

Reis, P.J. & Sahlu, T., 1994. The nutritional control of the growth and properties of mohair and wool fibres: A comparative review. J. Anim. Sci. 72, 1899-1907.

Ryder, M.L. & Stephenson S.K., 1968. Wool Growth. 11. Fleece variation owing to nutritional change. Academic Press. 562-592.

Schlink, A.C. & Dollin, A.E., 1995. Abnormal shedding contributes to the reduced staple strength of tender wool in Western Australian Merinos. Wool Tech. Sheep Breed. 43, 268-84.

Schlink, A.C., Masters, D.G. & Dollin, A.E., 1992. Effects of animo acids on fibre shedding in reproducing ewes. Proc. Nutrition Soc. Australia. 17, 80.

Stewart, A.M., Moir, R.J.& Schinckel, P.G., 1961. Seasonal fluctuations in wool growth in south western Australia. Aust. J. Exp. Agric.1, 85-91.

Sumner, R.M.W. & Wickham, G.A., 1969. Some effects of an increased stocking level on wool growth. Proc. New Zealand Soc. Anim. Prod. 29, 208-217.

Thompson, A.N., Schlink, A.C., Peterson, A.D. & Hynd, P.I., 1998. Follicle abnormalities and fibre shedding in Merino weaners fed different levels of nutrition. Aust. J. Agric. Res. 49, 1173-1179.

Thwaites, C.J., 1972. The effects of short-term undernutrition and adrenocortical stimulation on wool growth. Austr. J. Biological Sci. 32, 317-327.

 

Published

Karoo Agric 7 (1), 39-46