Sheep - AgRIS

12. Wool Production and quality
12.1 GreasyfleeceProduction
The greasy (unwashed) fleece weight is usually considered as a measure of the wool yield
of a sheep. Though the clean fleece yield is decisive form an economic point of view, but
phenotypic correlation between the greasy fleece kept under same enviornmetal conditions is
too high (around 0.9) thus the former can be considered satisfactory. A genetic correlation of
0.7 between the greasy and scoured is another measure. Fineness is measured as average fibre
diameter and recorded usually on a lanameter or a projection microscope. Such measurements
are made at constant temperature and humidity since wool is highly hygroscopic and the
diameter of the same fibre will change with the change in temperature and humidity. The
fineness and the length are the major factors contributing to the maufacturing quality. There is a
high correlation between the spinning count (number of spins of 560 yards in length which can
be spun from 1 lb. of scoured wool) and fibre fineness. In Indian wools, measure of medullated
fibres (as a percent of total fibres by weight of the total fibres) is also an important character.
Uniformity in fineness is usually considered interms of coefficient of variation of average fibre
diameter.
12.2 Factors affiecting wool production
Level of wool production and fleece structure may be affected by various climatic factors
and seasonal changes which can influence the shedding and regeneration of follicles, fiber
diameter and fiber length growth rate (Bhasin and Desai, 1965). In cold countries sheep is
shorn annually. In India it is normally shorn twice a year but in hot states they are shorn thrice a
year. Shearing even in warm climate results in change in the microclimate of sheep. Shearing in
a warm environment might stimulate wool growth or in cold conditions might bring about a
stress response from adrenal cortex. Injections of adrenocorticotrophic hormone (ACIN),
cortisone and the application of cortisone ointments depress wool growth.
12.2.1 Non Genetic
a) Humidity and Atmospheric temperature
It has been found that humidity differences of 25-30 percent and temperature differences of
upto 30°C had no effect. On the other hand there is a marked correlation between the rate of
wool growth and mean atmospheric temperature amongst maiden Corriedale ewes fed a
uniform maintenance diet throughtout the year.
b) Seasonal rhythm
The seasonal rhythm persists amongst Corridale ewes fed a ration of constant composition
at rates which maintained the effective body weights ofthe ewes constant. Marston (1955)
found five fold differences in the rate of wool production of fine wool sheep between lush
pastures of spring and the poor pasture of winter. The fundamental causes of the seasonal
rhythm of wool growth remains obscure.
c) Photoperiodicity
The ewes produced lesser wool in winter than in summer. Nutrition, pregnancy and
lactation can override or magnify the seasonal effect, but it canbe isolated and measured,
provided these factors, are adequately controlled. The photoperiodicity rhythm may be one
factor and it is probable that the seasonal rhythm in temperature may be another.
d) Hormones
Speculation of the mechanisms involved here is perhaps unwarranted at this stage though
the probable connection between hormone output and temperature and photoperiod rhythms
may be mentioned. Atmospheric temperature is known to affect the output of the thyroid. It has
been shown that thyroxin administration and deprivation influences wool growth.
The thyroid gland has a permissive effect on wool follicle development and wool growth.
Thyroidectomy reduces wool growth to about 40-50% of normal. Administration of thyroxine
to normal sheep stimulates wool growth. Dry ewes given a single 60-100 mg implant responded
by an increase in wool production by 15%.
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