Characteristics of Wool
The
Autumn Hills Woollens breeding strategy is to produce wool that results
in a superior spinning product. The emphasis of this narrative will
therefore be directed towards the understanding of the traits that
affect the breeding of fine to superfine wool sheep.
There is a
limit on how much the physical traits can vary within a species. When
traits stray too far from the norm as caused by new environmental
adaptations, a new species is created. The genetic latitude within a
species is limited and changing those parameters can be difficult. When
breeding for certain traits in wool sheep beneficial results are often
achieved through trade-offs, some desirable traits gained and some
sacrificed. Breeders since the beginning of time have been trying to
push against these trade-offs and try to create a new strain that has
the best characteristics of both strains.
Traits that are
important to the many of the producers of fine wool sheep are Fiber
Diameter (FD), Staple Length (SL), Coefficient of Variation (CV),
Standard Deviation (SD), Fiber Strength, Gross Fleece Weight (GFW) and
Yield, Type of Skin, Body Weight (BW), and Spinning Quality. Before
delving into these topics, I would strongly recommend an article that
is a free .pdf download from the CSIRO website in Australia, "A review
of the biology linking fibre diameter with fleece weight, liveweight,
and reproduction in Merino sheep" by N.R. Adams and P.B. Cronje
(http://www.publish.csiro.au/paper/AR02059.htm). This is one of the
best articles I have found on the web that discusses nearly all of the
problems associated with the breeding of fine wool sheep.
When
most people think of wearing a wool garment most react with an itching
reflex, me included. The fiber diameter in the Rambouillet and Merino
breeds vary between 11-26 microns. Most of the wool lies between the 17
and 24 micron range. A micron is one-millionth of a meter (39.37
inches). This may seem so small as to be invisible to the human eye,
but an untrained eye can easily see the difference between a 20 micron
fleece and a 30 micron fleece. A very important benchmark, which
defines the quality of fine wool, is "Prickle Factor". Simply put,
fibers that are 30 microns or greater in diameter can be felt by the
skin as prickly or itchy. One of the traits measured when you send a
sample of wool in to get tested is the percentage of fibers greater
than 30 microns. This percentage subtracted from 100% gives you the
Comfort Factor. The best Comfort Factor is 95% or greater, the closer
to 100% the better. The smaller the average diameter (FD) is, the
easier it is for the overall fleece to achieve a higher Comfort Factor
(i.e. the further away the average is below 30 microns, fewer fibers
will remain that exceed 30 microns).
Factors Affecting the Fiber Diameter (FD)
The
greatest factor influencing the fiber diameter is diet. Wool fiber is
greatly influenced by the amount of protein ingested by the sheep.
Scrubby desert brush and grasses have a very low protein content.
Alfalfa and fattening up grains (corn, c.o.b. etc.) have a high protein
content and can increase the fiber diameter by as much as 4 microns.
Fiber diameter is a highly heritable trait. It can still take several
years of selection for the average FD of a good size flock to be
lowered by 1 micron but only one season for diet to lower the FD
considerably more. A major problem that most commercial wool ranchers
face is that in order to make the operation a financial success, you
need to graze the sheep on what is available. This means that the early
spring grass is rich in protein and the fall grass is low in protein
resulting in a fiber that varies in diameter over its length. If the
feed supply varies greatly in protein content then the fiber can loose
strength or break easily in the thinner areas. This is where the next
two fiber traits become important.
Standard Deviation of the Mean (SD) and Coefficient of Variation (CV)
These
are terms that can make many non-mathematically people skip to the next
section. The Standard Deviation figure basically shows uniformity, the
lower the number the better. A low number SD (3.2 or less) will mean
that most of the fibers will be very close to the same diameter. Since
diet can so greatly affect fiber diameter, the SD will most likely stay
the same for the productive life of the animal as long as the type of
feed remains the same. A sheep fed on the same protein content feed
throughout the year should have a lower SD number. At first I couldn't
figure out why our sheep had so much lower SD numbers that many of the
flocks in Australia, which obviously had superior breeding. I finally
learned that because we feed alfalfa all year around, the fibers were
being nourished by a very consistent feed throughout the year. For the
Merino breed, it is recommended that the Standard Deviation not exceed
5 microns.
The Coefficient of Variation is simply the SD divided
by the fiber diameter and is expressed as a percent. In other words,
the CV relates the fiber diameter to the SD. This is important as a SD
of 5 microns for a fiber diameter of 30 m is a good trait but a SD of 5
for a finer staple of 17 microns would be quite undesirable. For the
Merino breed, it is recommended that the CV not exceed 20%. The CV also
has been shown to be very closely associated with fiber or staple
strength. Again, the lower number the better.
Crimp
A
recent touch test using 800 experienced spinners found that less crimp
made 23 micron wool feel softer. Conversely, an 18 micron wool felt
softer with more crimp. Also of note, women’s sense of touch was more
acute than men’s and sensitivity increased with age (FEMININE TOUCH
WINS SOFTNESS STAKES in Department of Agriculture, Western Australia -
Winter edition No 5 1999).
The term crimp may be summarized as a
trait that gives body to fine animal fiber so that it can be handled
and managed by human fingers more easily. The finer or narrower a group
of fibers becomes the harder it is for them to adhere to one another in
a non-greasy way, the straight fibers tend to slip by their adjacent
fellow fibers. The curl in a fine fiber (not too dissimilar looking
from curly human hair) allows each fiber to lock horns with adjacent
fibers and therefore through a series of steps be fashioned into a type
of fabric or garment. Fiber curvature and crimp are closely related
terms. Their detailed relatedness is a bit too technical (and harder to
grasp, myself included) to be discussed here. I believe that crimp can
be counted (per inch) and curvature is measured by hi-tech machines
looking at angles and rotation. For more detailed information see
OBJECTIVE MEASUREMENTS – MORE THAN PRETTY NUMBERS by Peter Sommerville
(1998)
http://www.awta.com.au/Publications/Research_Papers/Research_Index.htm.
Crimp
is an important fiber trait to Merino breeders in addition to fiber
fineness since the number of crimps per inch or centimeter affects the
fiber’s utility. Some of the folks that spin ultra-fine Alpaca (Suri)
and Angora Rabbit fiber, choose to blend it with crimpy Merino Wool to
increase its spinning performance.
Gross Fleece Weight (GFW), Yield and Fleece Rot
The
commercial wool producer can't experience much of a profit from his
wool if the fleece has little weight. This is why the Merino breed has
been bred for a heavy fleece.
The GFW for our pure merino and cross
ewes is 14 pounds (6.4 kgs.) and for our rams, 16 pounds (7.3 kgs.).
The GFW is the total sheared mass as it falls to the ground from the
shearers. From what I have been told by some very kind and
knowledgeable folks from Australia, this favorably compares to
commercial Merino flocks averages.
A heavy GFW is great but this
is not the whole story. What is important in most cases is how much the
fleece will weigh after going through the cleaning process. The great
Sire rams can have yield up to 82% (weight of clean/weight of
in-the-grease). What makes up the difference? Vegetable matter, dirt,
and skin produced grease, mainly the latter. At first one would think
that the higher the number the better, eh? Not necessarily. When I
first received many Drop Sire Reports (fiber statistics from top rams)
from a mentor in Australia I entered a lot of statistics into my
computer spreadsheet. We intend to move in five years from an area
which receives 6 inches (152mm) to an area in western Washington State
that receives up to 60 inches (1524mm) a year. I was trying to find out
what fiber characteristics are associated with low fleece rot
occurrence. I noticed that the rams that had a low yield (but high in
vegetable matter, dirt, and body grease) did indeed have a lower
incidence of fleece rot. I mentioned this to my Australian mentor and
she replied that yes, this is true. The high level of body grease is
referred to as "nourishment" and that it does retard the onset of
fleece rot in high rainfall areas. This "nourishment" is heritable but
moderately so. This is how I understand the problem: fleece rot is
similar to diaper rash, a bacterial infection affecting the surface of
the skin usually in a rain-soaked sheep. The rash oozes fluids that
stain the wool in irregular patterns of yellow making it undesirable
for marketing. What makes the situation worse are skin wrinkles which
retard the skin's ability to dry out. Nourishment either coats and
protects from the moisture, or perhaps there are antibiotic agents
present in the grease. There does however to be seem to be a strong
link between fine wool and fiber nourishment (low yield).
Type of Skin
Before
we had our latest crop of lambs I read an article by David Scobie of
the AgResearch, Lincoln, New Zealand (see link below) entitled,
"Wrinkles lower productivity". It discusses the pros and cons of
wrinkly skin. When our lambs arrived, I nearly panicked, 70% had a lot
of wrinkles. I immediately contacted some internet mentors, visited new
born lambs of the same breeding, and talked with the local University's
expert. On shearing day in mid-March locally, many sheep were sheared
that were Rambouillet as well as our Merinos. Many (perhaps 33%) of the
Rambouillet lambs had a fair amount of wrinkles and these lamb's dams
and sire did not have long staple or heavy fleeces.
For the last
couple of hundred years, people have been selecting for a heavier
fleece. This pretty much means more wool per square inch. The way that
this was achieved was by the development of skin wrinkles, effectively
increasing the surface area of the skin while keeping the same animal
underneath. Whether these breeders looked and planned for wrinkles to
appear or it just happened that the heavier fleeced animals slowly
developed wrinkles as their fleece weights increased is beyond my area
of understanding. From the article by Adams and Cronje mentioned above,
of the total protein that the sheep body uses for development and
maintenance, approximately 15% is allocated to skin development and
maintenance. Of this percentage, 20% is allocated for the production of
wool. In humans, a higher proportion of protein or muscle tissue is
usually accompanied by a lower fat content. In sheep, a similar thing
happens. The finer and heavier the fleece (also more follicles per
square inch) the less the fat content is in the skin. With less fat,
the skin can wrinkle easier. If more protein is allocated to the skin,
less goes for meat production. It is all linked to one another in a
give and take set of loosely defined genetic rules.
In the early
1970s, Dr. Jim Watts developed a breeding strategy known as SRS or Soft
Rolling Skin (http://www.severnparkmerinos.com.au/system/index.html).
He found that breeding sheep with soft rolling skin (also thin and
pliable) greatly increases the potential for increasing the quality of
wool, that is, heavier finer fleeces with a very long white lustrous
fibers. The fleece naturally groups into bundles rather than staples.
The skin is very pliable. A problem with heavily wrinkled skin that is
not soft and pliable is that the animal is not healthy; often smaller
in body size with a decrease in fleece quality (see David Scobie,
"Wrinkles lower productivity"). There is controversy in the Merino
countries down under over wrinkles. In our small flock, after shearing,
our new Merino ram (2 year old) did indeed have that SRS type skin.
Half of our wrinkly lambs grew out of their wrinkles. Our most wrinkled
one (harder wrinkles) is the smallest and tended to be somewhat sickly
as a very young lamb (the only one that received antibiotics). We will
understand a great deal more about this topic when we get this new lamb
crop's fleece tested at the end of the year. For more information on
this type of breeding system visit http://srswool.com/breedsys.htm.
Spinning Quality
For
the best spinning quality wool, the fiber staple should be at least 4
inches long and a courser fiber diameter is easier to handle (24 to 30
microns). However, with some practice the finest of wools can be
successfully spun producing superior garments (personal communication,
Dianne Seldomridge). This finer wool commands a far higher price in the
wool market.
Body Weight and the Trade-Offs
To
start this last section, I would like to quote a section in the Adams
and Cronje article, page 2, "for fine-to-medium wool bloodlines,
genotypes with 1 micron lower fibre diameter had on average 8-9% less
fleece weight and 4% less body weight".
It was very apparent at
the last few University of Reno's ram sales that the pure Merinos were
noticeably smaller than the Rambouillet/Merino crosses. Even in our
small flock, our smallest hogget (yearling) has the finest fleece. The
two year old that had the coarsest fleece (24.8) also had the heaviest
fleece of our entire flock (18 lbs./8.2 kgs.) even surpassing our two
rams (16 lbs./7.3 kgs.). We have a huge hogget black ram that was 150
pounds at 8 months of age. His fleece was 22.4 microns.
Like
many people trying to breed for a superior fleece, we don't want to
sacrifice our large bodied sheep. The SRS breeding strategy mentioned
above may hold out promise, time and fleece testing will tell.
Some
of the very superfine wool breeders in Australia are not concerned with
lengthening the staple. They are marketing their wool to Italian wool
mills that prefer a limit of 85 mm (3.3 in.). In the future, we will
select for narrow fiber diameter, staple length, fleece weight, body
size and, a minimum of skin wrinkles. An American expert in the wool
field recommended that I should to a large extent ignore the fiber
diameter as diet can account for a 5 micron difference and concentrate
on lowering the Standard Deviation and Coefficient of Variation
numbers. He also warned against getting too much nourishment as it
would yellow the fleece unnecessarily. Bright white fleece has a
definite market advantage.
I added this narrative to our website
to perhaps make it easier for fine wool enthusiasts to understand the
statistics used in more technical reports. It took me quite a while
pouring through Drop Sire Reports and bugging patient Merino experts
before I achieved a moderate understanding of the subject. If any
reader finds an error in this essay, please notify me at the email
address listed below.
Heterosis
From
what I have read from the Sheep L list and from the information I have
obtained from the internet this is how I understand Heterosis to work:
The
traits that the original ancestral breed of sheep exhibited were shaped
by millions of years of natural selection. These traits allowed the
species to thrive and adapt to an ever-changing environment. These
survival traits were programmed by genes that appear to work
synergistically with other genes whose functions are not readily
apparent to humans. When humans domesticated the wild sheep they
admired traits such as a better fleece or a faster weight gain ability.
When these animals were bred to others of the same species that also
shared similar characteristics, they were removed from Nature’s
influence and humans now controlled their future survival. Genes that
controlled human perceived non-desirable traits may also have
controlled fitness and hybrid vigor (Heterosis) and as a result, their
lack of influence adversely affected the hardiness of this earliest of
domesticated animal.
Fortunately, it appears that wild ancestral
sheep were domesticated by more than one group of humans each with a
different idea as to what desirable traits best suited their needs.
Most likely most of the genes that control Heterosis still exist within
the collective gene pool of the domestic breeds of sheep. Current
scientific research has not yet identified what genes work
synergistically with others to produce a superior offspring (plant or
animal). Trial and error appears to be the only available tried and
true method available for obtaining desired traits in offspring.
A
great hint to the way Nature created the ancestor to our domestic
animals is often revealed in the offspring that is produced by crossing
the breeds. It appears that the more crossing, the better the
offspring’s ability to thrive. Genes that had been separated for
hundreds if not for thousands of years when brought together again can
reintroduce the genetic tools needed for an increased level of hybrid
vigor and fitness. Often these crosses result in larger and more
vigorous lambs. This increased ability to survive in some crosses also
produces traits that may or may not be viewed by humans as desirable.
Most of the commercial flocks of sheep are composed of many breeds of
sheep that best produce the most desirable animal.
Conclusions
Whatever
two breeds of sheep one would breed, the crossed offspring is very
seldom larger than both of the parents. One primary purpose for
crossing sheep is to use a very large muscular ram on an existing flock
of smaller ewes that one may have established for wool (or other)
considerations. This is the fastest way to increase the average weight
of the new year’s lambs without getting a whole new set of ewes.
Crossing can produce a lamb that has better muscling and a better meat
to fat ratio but it will be smaller in body weight than the sire ram.
However, using a larger ram on a smaller ewe can cause problems.
Lambing difficulties increase. If the ewe has multiple lambs and if
they are from her own breed and therefore are small enough to lamb and
nurse successfully, then there should be no unusual problems. If a
larger ram from another breed covers this ewe then complications from
the birthing process can increase and the ewe’s nursing abilities can
get overtaxed. If she can only handle two of the three lambs (e.g.two
lambs total weight of 14 lbs. – 7 pounds each) when compared to raising
three smaller lambs with a combined weight of 15 pounds (5 lbs. each)
then we have a loss in productivity.
As far as picking the
breeds that would allow us to create an appropriate market lamb, we
have decided to choose a ewe that will produce a fast maturing and low
octane (i.e. gain weigh easily on low quality feed) market lamb. A
cross between a Border Leicester (BL) and a Bluefaced Leicester (BFL)
should meet this goal. The BFL and BL breeds were separated about a
hundred years ago so I am expecting a minor amount of crossbred vigor
in their cross. Both of these breeds do very well in damp climates and
can get fat on lower grade feed. No feeding of grains will be
necessary.
We first thought of getting a black-faced terminal
ram but due to their large size. We would however expect a higher
percentage of lambing difficulties. We settled on using a Dorper ram
as the final sire due to their extreme muscling, very easy weight gain
on low quality feed, and their progeny are smaller than the average at
birth but gain very quickly. They also have a very high resistance to
parasites. A high rate of hybrid vigor should allow the market lamb to
gain weight rapidly.