Last update: November 19, 2010 10:38:08 AM E-mail Print

 

Effect of season on fible diameter

 

M.A. Snyman1 & N.M. Kritzinger2


1 Grootfontein Agricultural Development Institute, P/Bag X529, Middelburg (EC), 5900, South Africa

2 Cape Mohair and Wool, P.O. Box 3314, Port Elizabeth, 6056, South Africa 

 


Introduction

Fibre diameter is the single most important price-determining variable of mohair and is of critical importance in determining the textile qualities and final manufacturing applications of mohair. Age of the Angora goat largely determines the quality and quantity of mohair produced, and the fineness of the fleece is to a large extent determined by the age of the goat at the time of shearing.

There is substantial variation in fibre diameter over the fleece of individual Angora goats, with mohair from the neck usually stronger than that from the rest of the fleece. Fibre diameter also varies considerably within a staple, as well as along the length of individual fibres.

Another aspect that has an influence on the price of mohair is the season of production. For instance, higher prices are paid for summer than for winter kid mohair. The reason for this remains a controversial issue in the mohair industry in South Africa.

The aim of this study was to determine the variation in mean fibre diameter and its associated traits of various age groups within South African Angora goat flocks and to investigate the effect of season on the fibre diameter profile.

 

Data recorded

Data were recorded on mohair from adult ewes (21590 records), young goats (10923 records) and kids (11019 records) from 10 Angora goat producers from the summer 2000 until the winter 2004 shearing seasons. Within two weeks prior to shearing, each goat received a numbered ear tag and individual mid-side samples were taken for micron testing. The following fibre diameter traits were determined with OFDA-procedures: fibre diameter (MFD; µm), coefficient of variation of fibre diameter (CV_MFD; %), standard deviation of fibre diameter (SD_MFD; µm), spinning/effective fineness (SF_MFD; µm) and standard deviation of fibre diameter along the length of the staple (SD_ALONG; µm).

Spinning, or effective fineness is a function of the mean fibre diameter (FD) and coefficient of variation of fibre diameter (CV, expressed as a percentage), as follows:

SF_MFD = FD √ (1 + 0.0005 x CV2)

This formula takes into account the fact that fibres with a wider range of diameters behave as if they had a higher mean diameter during processing.

 

Results and discussion

The percentage of the overall variation in the fibre diameter traits accounted for by producer and season, are summarized in Table 1.  From Table 1 it can be seen that more of the overall variation in the fibre diameter traits could be declared through the effect of producer than through the different seasons per se. Much of the variation in the traits investigated could be attributed to the interaction of producer x season.

 

Table 1. The percentage of the overall variation in the fibre diameter traits accounted for by producer and season

Trait

Producer (%)

Season (%)

Producer x Season (%)

Adults

MFD

17.3

1.0

27.3

SD_MFD

20.3

0.0

29.6

CV_MFD

8.4

0.2

18.4

SF_MFD

30.2

10.8

38.8

SD_ALONG

5.4

0.4

6.5

Young goats

MFD

15.6

11.3

40.1

SD_MFD

23.7

6.8

50.0

CV_MFD

17.3

1.0

33.3

SF_MFD

8.2

8.7

30.9

SD_ALONG

13.6

5.4

21.6

Kids

MFD

19.4

45.1

57.6

SD_MFD

5.8

7.0

47.2

CV_MFD

15.2

5.8

47.9

SF_MFD

4.3

37.9

59.5

SD_ALONG

4.4

2.1

8.8

 

Season accounted for more of the variation in fibre diameter traits of kid and young goat mohair, than for adult mohair. This is due to an age effect, which is confounded with the season effect, as the first shearing of kids comprised the summer clip, while their second shearing comprised the winter clip. The same applied for young goats, where the winter clip is usually from relatively older goats.

Means for fibre diameter traits of summer and winter adult ewe mohair, young goat mohair and kid mohair are presented in Table 2. The frequency distributions of MFD of summer and winter adult ewe mohair, young goat mohair and kid mohair are depicted in Figures 1 to 3 respectively, while those for CV_MFD are depicted in Figures 4 to 6.

 

Table 2. MEANS (±SE) of fibre diameter traits of summer and winter adult ewe, young goat and kid mohair

Age / Season

MFD (µm)

SD_MFD (µm)

CV_MFD (%)

SF_MFD (µm)

SD_ALONG (µm)

Adult mohair

Summer

33.56±0.04 a

8.13±0.02

24.15±0.04 c

32.03±0.06 d

1.48±0.01

Winter

34.37±0.04 a

8.14±0.02

23.74±0.04 c

34.93±0.09 d

1.43±0.02

Young goat mohair

Summer

27.30±0.03 a

6.07±0.01 b

22.21±0.04 c

28.00±0.07 d

1.39±0.01 e

Winter

29.69±0.05 a

6.82±0.02 b

23.07±0.07 c

29.84±0.11 d

1.64±0.01 e

Kid mohair

Summer

20.55±0.03a

5.70±0.02a

27.68±0.06a

21.06±0.04 d

1.34±0.01 e

Winter

24.66±0.03a

6.31±0.01a

25.67±0.05a

25.58±0.04 d

1.19±0.01 e

a, b, c, d, e   Trait values with the same superscript differ (P<0.001) between seasons within age groups

 

MFD of adult mohair differed among producers, ranging from 29.2 µm to 37.9 µm on average. Overall, for all producers, summer adult mohair (33.56±0.04 µm) had a lower MFD than winter adult mohair (34.37±0.04). The same applied for SF_MFD. However, the difference of 0.8 µm in MFD between summer and winter adult mohair is less than the normal variation in MFD within the same season, which ranged from 22 to 52 µm for summer and from 20 to 49 µm for winter adult mohair (Figure 1).

There was no difference in SD_MFD between summer and winter adult mohair in the pooled data set, although differences were recorded for individual producers (Table 2). CV_MFD of the pooled data set for adult mohair was higher in summer (24.15±0.04 %) than in winter (23.74±0.04 %) adult mohair. SD_ALONG did not differ between the seasons. Differences that occurred at some producers could be ascribed to different management practices and feeding conditions.

The mohair produced by adult ewes during the summer season, usually includes mohair produced during pregnancy and lactation. Those produced during the winter season, includes mohair produced during the dry period and early pregnancy. Reproduction generally suppresses the rate of mohair growth and the demands of lactation are quantitatively more pronounced than those of pregnancy.  During late pregnancy and lactation it is often physically impossible for a ewe to ingest sufficient low quality roughage on normal veld grazing to meet her nutritional requirements for maintenance, production and lactation.  Under such conditions, body weight and mohair production, especially fibre diameter and length, will suffer. Nonetheless, very little differences were recorded in fibre diameter traits between the summer and winter clips for adult mohair (Table 2, Figures 1 and 4). Therefore, processing properties of adult mohair should not be influenced by season of production per se.

It is evident from Table 2 and Figure 2 that summer young goat mohair had a lower MFD than winter young goat mohair. As mentioned earlier, this could most probably be ascribed to an age effect. SD_MFD and CV_MFD of young goat mohair in the pooled data set were lower for summer than winter mohair, although season differences at the various producers varied. There was also less variation in MFD along the length of the staple in summer compared to winter young goat mohair.

Summer kid mohair had a lower MFD and SF_MFD than winter kid mohair at all producers (Table 2 and Figure 3). As in the case of young goat mohair, differences between summer and winter kid mohair could be ascribed largely to an age effect. SD_MFD was lower for the summer than for winter kid mohair. CV_MFD was generally higher in summer than winter kid mohair (Table 2 and Figure 6). This could be due to the possible presence of birth coat fibres in the first fleece. Variation in MFD along the length of the staple was also higher in summer kid mohair. The first shearing of the kids (summer clip), includes mohair grown over periods of different feeding regimes, i.e. milk, then first roughage and then only roughage diets and the weaning period. All of these contributed to the higher variation in MFD among the length of the staple, compared to the second (winter) clip, which is more even in terms of MFD.

The recorded differences in fibre diameter traits between the summer and winter mohair of kids could contribute to the price difference between summer and winter kid mohair.

 

Conclusions

From the above results and discussions the following can be concluded:



Acknowledgements

This project was funded by Mohair South Africa. The authors appreciate the cooperation of the Angora goat producers who participated in the project.

 

Figure 1. Frequency distribution of fibre diameter of summer and winter adult mohair


 

Figure 2. Frequency distribution of fibre diameter of summer and winter young goat mohair


 

Figure 3. Frequency distribution of fibre diameter of summer and winter kid mohair


 

Figure 4. Frequency distribution of CV of fibre diameter of summer and winter adult mohair

 

 

Figure 5. Frequency distribution of CV of fibre diameter of summer and winter young goat mohair

 

Figure 6. Frequency distribution of CV of fibre diameter of summer and winter kid mohair