- Wool research in the Karoo Region. Part 2. 1950 - 1980
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WOOL RESEARCH IN THE KAROO REGION
PART 2 1950-1980
DR J.J. VENTER
Grootfontein College of Agriculture
In 1950 the wool research section was transferred from Onderstepoort to the Grootfontein College of Agriculture. This provided a closer link between wool research and nutritional and breeding work on the sheep itself.
The main object of wool research since 1950 was to improve the quality and production of wool in order to comply with the requirements of the manufacturer to ensure a continued use and demand for wool.
Research confined to wool was continued on quality aspects with special attention to factors affecting the handle of wool.
The effect of absorbed water on the dynamic bending modulus of fibres was investigated. It was evident that the change in compressibility with absorption of water may to some degree be directly attributed to the change in bending modulus of individual fibres and consequently has an effect on the handle and quality assessment.
A study of the resistance of crimped fibre to both extension and bending indicated that while the depth of crimp plays an important role in both cases, the crimp frequency has a great effect on the resistance to extension, but an almost negligible effect on the resistance to bending. These results indicate that the relationship between fineness and crimping will influence any process involving the extension and bending of crimped wool fibres, as for example in the case of felting. Differences in the handle of wool of the same diameter may be attributed to differences in the nature of their crimping.
As the South African wool grower puts great emphasis on the term "wool quality" or "handle", the physical properties of wool of good and poor quality from a two-way selection project for quality plus and quality minus wool were compared. From the results of this study it was clear that over-emphasizing softness of handle as a pre-requisite for good quality may not only cause the wool to become finer, but the wool will also become more under-crimped, flabby and lack substance and consequently be more liable to deeper weathering. A gradual decline in resistance to compression and an increase in felting propensity were noted as a consequence of purposeful selection for good quality.
The South African wool clip as a whole proved to differ markedly from the Duerden-relationship, being mainly finer than indicated by the crimps, i.e. under-crimped.
Both under-crimped and over-crimped wools have certain disadvantages in comparison with wool complying with the Duerden-standards.
Before finally recommending the selection and breeding of sheep producing wool complying-with the Duerden-standards, an investigation is being carried out on the physical properties of wool collected from sheep from different farming regions.
Age and sex
The effect of sex and age on the physical properties was studied in a group of rams, wethers and ewes. It was found that ram's wool has a higher fibre diameter than ewes and wethers under the same feeding conditions, suggesting that rams will tend to breed a slightly finer fleece than their own in their wether and ewe progeny.
Maximum fibre thickness, as well as wool production and body weight, was reached between the age of two to three years. Thereafter a gradual decrease in respect of all three parameters took place. The intensity of wool production, i.e. Clean Wool Weight (Bodyweight) 0.66, decreased by 8 to 10 per cent per year.
Lactation proved to influence the body weight of ewes and evidently also the body reserves. The influence of lactation on fibre diameter was only significant for the first eight weeks after parturition. No influence was established on the percentage of wool wax, suint and clean wool.
A study was made of the histology and morphology of the Merino skin and fleece. To assess the possibility of an earlier selection, which would have decided economic advantages, the differences in the degree of hairiness as demonstrated in the birth coat was taken as criterion for comparing Merino lambs from birth up to the age of two years. From the age of three months onwards, underlying fleece differences are obscured, because the hairs fall out and therefore the hairy born sheep cannot be distinguished from his woolly flock mates. There were no significant fleece differences between the different types at the adult stage. The current practice of selecting sheep at 18 months of age for wool production is still the most suitable method.
Relationship between fleece and fibre properties
A study of the interrelationship between fleece and fibre properties included both subjective assessment and objective measurement of these properties. Seventeen fleece attributes were assessed, while 25 fleece and fibre properties were measured.
The results gave a good indication of the factors involved in subjective assessment and also gave the correlations which exist between the various attributes and which consequently playa role in breeding. A poor relationship was found to exist between most of the wool characteristics, as assessed, and the corresponding objectively determined properties, such as fineness (spinning count), density, staple tip, substance, yolk, colour and bulkiness of the wool. This raises some doubt as to the efficacy of subjective evaluation as a criterion for selection.
Body weight, degree of skin development and percentage skin occupied by fibres were the most important determining components of the total wool production. The selection of large animals and more skinfolds to increase wool production is not recommended without reservation on account of the implications involved.
Nutrition and environment
Various studies have been carried out on the influence of nutrition, environment and climate (altitude) on wool properties. Nutritional effects were mainly responsible for the differences in production and physical and chemical properties of wool.
A low level of nutrition had no inhibiting effect on the development of wool follicles. A reduction in wool production must be ascribed to the production of thinner and shorter fibres, consequently affecting other properties of wool.
An investigation was made to determine the nutritional effect of different protein and energy levels on wool production, body weight and different properties of wool.
It was evident that, with an insufficient supply of protein, Merino sheep can suffer severe losses in wool production, while maintaining a good condition and even showing increases in body weight. A marked decrease in fibre diameter and fibre length and a corresponding increase in number of crimps per unit length were noted. The increase in crimp frequency was not sufficient to compensate for the decrease in diameter, with the result that the wool was severely under-crimped. The wool consequently had a higher feltability, indicating a more flabby wool.
Being a natural fibre, wool is subject to the influence of environmental factors. From the manufacturers point of view, a sound well-nourished wool, with a good tensile strength from base to tip, is the ideal wool, as it will give the least fibre waste and trouble during manufacturing and will result in a high quality fabric.
Research on the seasonal effects on weathering of wool, carried out at Grootfontein College of Agriculture, showed that the degree of weathering increased with an increase in daily temperature and hours of sunshine.
Also, when comparing eight-and twelve-month wool grown over different periods during the year, the results showed that long wool which was subjected to one or more of the hot summer months tended to open up, possibly owing to lack of staple formation, density (substance) or insufficient fluid yolk. Fine and undercrimped wool, as well as long wool, tended to be more severely and deeply weathered. To limit weathering to only the extreme tip portions, it is recommended that the time of shearing should be arranged so that the wool will be short during the hottest summer months, to prevent the wool from falling open.
Factors also found to influence the extent of damage on the sheep were the following:
The density and staple formation of the fleece were found to be primarily responsible for the protection of the wool on the sheep.
Wool containing high levels of yolk was not protected more effectively than that containing less yolk. A fluid wool wax from root to tip was associated with a decrease in the degree of weathering in the tip portion of the staple.
In order to limit weathering on the sheep, the effect of protection by means of sheep rugs and shade was investigated. From this study it was evident that the extreme tip portion becomes severely weathered soon after shearing. This can only be prevented by full-time rugging. Rugging for three or six months and even access to shade proved to have only a slight effect on weathering of the first centimetre of the tip. Deeper weathering, however, was significantly reduced by free access to shade and even better results were obtained by rugging for only the three hottest months.
Though sheep rugs may be considered as the most effective method of preventing weathering of wool, the provision of shade in camps, especially trees or open sheds, is recommended as the most practical method.
As the final degree of weathering in the fleece will to a large extent be determined by the season of growth and the time of shearing, the environment and adaptability of an animal to a particular climatic condition may also have an effect. The weathering in the Karoo and even more so in the Orange Free State was found to be significantly higher than in the Eastern Transvaal and Western Province mainly owing to the higher solar energy. The seasonal effect even differs from region to region.
So that a definite and generally acceptable shearing time applicable to the various farming regions in the Karoo can be decided upon, a study is now in progress with respect to the degree and intensity of weathering of wool produced in different climatic regions of the Karoo. This study will be extended to the other farming regions in the Republic.
Preliminary results obtained so far clearly show that the weathering of the tip even deeper into the staple is considerable. This shows that a large portion of the staple of a 90 millimetre (AM) wool becomes photochemically damaged by the sun.
Results so far collected confirm that the least weathering deeper into the staple occurs in wool shorn in October to early December, irrespective of the farming region.
Karoo Agric 2 (1), 9-12