- Influence of sex and age on wax and suint in wool of Merino sheep
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INFLUENCE OF SEX AND AGE ON WAX AND SUINT IN WOOL OF MERINO SHEEP
Sheep and Wool Research
Grootfontein College of Agriculture
Middelburg Cape 5900
Wool grease (wax) and suint are secretions from the sebaceous and sudoriferous (suint) glands within the skin, which mingle, forming "yolk" in the follicle shafts, and coat the developing fibre.
Apart from the fact that wool wax is considered essential for the well-being of the animal, it further proves to be associated with certain characteristics of the fleece.
Comparing greasy and non-greasy wool samples of the same quality, Winson (1929) noted that greasy samples were distinctly finer and more uniform in fineness, and that they showed less variation in size and shape of cross-section, as well as being more circular.
The penetration of liquids into the capillary cavities of the wool fibre were shown, by Speakman (according to Sutton, 1931), to influence the pliability and elasticity of the fibre, and that yolk functions in a similar manner. It was established by Truter & Woodford (1955) that the normal quantity of grease on the wool fibre, generally varying from below 15 percent to over 40 percent, had to be increased more than ten-fold before any real protection could be observed.
It is regarded as essential that the grease must have good fluidity to migrate along the fibre to the tip, cementing the fibres together and so keeping the fleece closed on the sheep (Le Roux, 1958; Louw, Swart & Mellet, 1963; Kruger, 1964).
Uys (1966) and Van Rensburg (1966) found no significant difference in grease content in large and small staples within a fleece. A fluid yolk evenly spread along the entire fibre or staple was considered more important since it also affects the substance and handle of wool (Venter, 1976).
A high wax content was also found to be a barrier to fleece rot (Hayman, 1953; Thornberry, Kowal & Atkins, 1980) and Dermatophilus Dermatonomus infection (Roberts, 1963). Resistant sheep had a higher wax content. The protective effect of suint, on the other hand, was found to be inconsistent.
Suint occurs in raw wool to an extent of 4 to 30 percent. It contains relatively large proportions of potassium salts, is water-soluble and has excellent emulsifying properties. It also imparts high wettability to a raw fleece. These factors are put to good use in wool scouring (Veldsman, 1965).
The pH of aqueous solutions may vary from acid to alkaline. Suint, which is highly alkaline, may have an adverse chemical effect upon the nature of the fibre substance. A positive correlation is generally found between suint content and the pH of the suint.
A high suint content in wool proved to protect the wool against weathering (Truter & Woodford, 1955; Venter, 1976). Fraser & Truter (1960), however, noted that wool showing bacterial discoloration had a high percentage of suint, which was highly alkaline (pH 10,0 - 10,5).
Story, Brook & Short (1963) showed that, in fleeces with different types of skin, suint was associated with the presence and size of sweat glands.
Whether suint content is an effect of major importance in the fleece is rendered questionable by the histological observation that only the primary fibres are equipped with accessory sudoriferous glands.
The ratio of suint to wax tends to be lower (alternatively a higher wax-suint ratio) in wool of sheep resistant to fleece rot (Hayman, 1953). The favourable between-flock association between fleece rot and suint to wax (or alternatively wax to suint) ratio is strongly considered as a selection criterion against fleece rot.
Strong wool strains tend to be more susceptible than fine wool strains. The skin of sheep of susceptible types proves to be hypersensitive to moisture. According to Fraser & Truter (1960), contact with water results in an oedematous reaction in which serum is exuded on to the fibres.
Nutrition has proved to influence wax and suint production. Daly & Carter (1955) pointed out that wax production was positively related to an increase in feed intake and negatively to a rise in atmospheric temperature. Suint production was positively related to both feed intake and fleece weight. Daly & Carter (1955) gave figures of 20 - 23 g of suint per 28 days (0,7 - 0,8 g/day) for fine wool Merinos on good rations and under cover. Story et al (1963) estimated the total daily suint production, assuming a whole body surface of 1 m2 for animals with normal sweat glands, in the range of 0,5 g per day - which is relatively similar to the afore-mentioned figures.
The feeding of ordinary maintenance rations, either high or low in protein, did not seem to have any influence upon the secretion of yolk (Bonsma & Starke, 1934).
Venter, Steenkamp & Edwards (1973), however, found that wool produced on a ration low in protein, but with adequate energy, had more wool wax than wool produced on a ration high in protein, but low in energy, or wool produced on a ration with sufficient protein and energy.
Venter, Cloete & Edwards (1969) compared sheep under different climatic and nutritional conditions on three sites differing in altitude, topography, geology, vegetation and veld types. The sheep receiving the same ad lib feeding of dry lucerne in pens on each different site showed no varying effects as far as wool wax, fluidity and suint content of the wool was concerned.
The wool of the sheep on the veld, particularly those on a higher altitude and whose grazing was deficient in protein during both the growing and dry season, had less suint with a lower pH than the sheep in pens.
It was evident that even sex and age had an effect on the secretion of wax and suint. Roberts (1963) noted a reduction in the wax content in wool of lambs from one month to 7/10 months. Rams also yielded more wax than ewes and wethers.
The influence of age and sex on various production characteristics of Merino sheep were shown by Venter (1966), Venter & Hugo (1969) and Venter (1970, 1981).
In order to study these changes, a number of lambs were kept under observation under favourable feeding conditions from birth till death. Half the ram lambs were castrated at the age of one month, so that the group consisted of rams, wethers and ewes. The ewes were not mated. Genetic influences could thus be studied.
Wool samples were taken from the mid-rib at the age of 6 months, 1 year, 1½ years and thereafter annually up to 7½ years.
Apart from the production characteristics and various fibre properties formerly discussed, the wool wax and suint content was also determined and expressed as a percentage of the clean dry wool.
The percentage of wool wax and suint, as well as the wax to suint ratio in the wool of the same group of ewes, wethers and rams at successive ages, is given in Table 1.
The change in the wax and suint for a number of individual animals within each sex group is graphically illustrated in Figures 1 and 2.
As previously stated by Venter (1966), the percentage of wool wax in the wool of ewes and wethers gradually increased with increasing age, confirming the observation noted by Roberts (1963). In the case of rams, a sharp increase was noted in the percentage of wool wax from 3½ years to 5½ years. Rams proved to be different from wethers and ewes, which followed relatively the same tendencies.
The decrease in the amount of wax for the period 6½ years to 7½ years may be attributed to the greater number of deaths among rams. During previous years the rams showed a noticeably higher wool wax content (possibly owing to hormonal imbalance).
From Table 1 and Figure 2 the percentage of suint in the wool of all three sex groups practically remained constant, with only slight variations over the 7½ year period. The change in wax to suint ratio for ewes, wethers and rams with increasing age is given in Table 1 and graphically illustrated in Figure 3. The similarity of the change in wool wax-suint ratio with increasing age with that of the change in wax content is striking. The relatively low percentage of suint in the wool of all three sex groups also remained practically constant over years, showing only a small variation within groups. This proves suint to be an insignificant factor in considering the wax-suint ratio as selection criterion against blow fly strikes. However, the marked variation in wool wax within groups, apparent from Figure 1, showed that selection for a high wax content may have more merit. Its effectiveness may be questionable before the age of 3½ years, where after a sharp increase particularly in the case of rams occurred.
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