Is there a specific weakness in staple strength around the break of season?
Authors: Adams N. R. , Masters D. G. , Schlink A. C. , Mata G. , O'Dea T. 
Published: September 2002

In a Mediterranean climate the weak point of the staple normally occurs at the
break of season in autumn, but it is not clear whether the staple simply
breaks at the minimum fibre diameter or whether there is a specific weakness
at this time. Three hypotheses were tested to determine if specific
environmental effects on staple strength could be detected under field
conditions. First, environmental stresses associated with rainfall and low
temperature, resulting in a sudden disruption of warm summer–autumn
conditions and lack of feed, may cause follicle shutdown. Second, the sudden
decline in feed available following the rain event and the response of sheep
to chase the green pick rather than eat the available dry feed may reduce the
flow of nutrients to wool. Third, the slow adaptation by rumen microorganisms
to changes in the diet from dry to green pasture may result in a further
reduction of nutrients available to the wool follicle. We compared a group of
sheep managed to minimise nutrient intake fluctuations at the break of season
with a group grazing under normal farm practice and tested the hypothesis that
a specific lowering of staple strength is associated with the break of season.
On 2 April (3 days after the first rains of the season), 120, 18-month-old
Merino wethers were allocated to 2 groups, paddock and yard. The paddock group
comprised sheep following normal farm practice. The yard group was confined to
yards and fed to maintain liveweight, to determine whether the break in the
staple was associated with the rainfall event or with the subsequent changes
in feed intake. These animals were left off feed for 4 days beginning 24
April. Within each group, 2 separate treatments were imposed. The paddock
group was split, and half were moved into covered pens inside a shearing shed
on 15 May, a few days before a second major rainfall event, to examine
directly stresses associated with rainfall. The sheep from the yard group were
kept as a single mob until 3 June, when they were split into 2 groups, sudden
and gradual, in relation to their release onto green pasture, to examine the
effect of adaptation time to green feed on the flow of nutrients to wool and
staple strength. The sudden group was released onto green pasture, while the
gradual group was given access to the pasture for increasing periods over the
next week.
The point of break was delayed by moving sheep into yards after the initial
rainfall, suggesting that the rain event per se was not the direct cause of
the break in the staple in this experiment. Furthermore, protecting the
paddock sheep against the second major rainfall event by shedding half of them
did not affect staple strength. The point of break in the staple in the yard
group occurred after an accidental 4-day feed deprivation period. This
indicates that even short periods of liveweight loss from feed deprivation due
to poor or inattentive management when sheep are in low nutritional condition
at this time of the year may precipitate the point of break. The rate of
release onto green feed after yarding did not significantly affect staple
strength and we conclude this was not an important factor. We conclude that
neither stress associated with rainfall nor adaptation of ruminal
microorganisms to the change in feed weakened the wool.