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Wed Feb 2 07:52:04 EST 2005
their ability to survive/thrive in their specific environment. Since we =
do our best (I hope we all do) to ensure the survival of all of our =
lambs it is hard to image natural selection working here. And, unless =
someone has an extreme and unique environmental factor at play, most =
(all?) of us breed for traits other than 'thriveability'. The only =
circumstance in which inbreeding could play a role in adaptations to a =
specific environment is if the flock is totally left to "fend for =
itself" "...
Reply: Absolutely...to a point. Selection for "thriveability" is a valid =
way to accomplish this under managed conditions. Ewes that have lambs =
that are less thrifty and show more parasitosis SHOULD be culled, for =
example. This will be a more gradual process than throwing 200 sheep =
into an environment that is heavily contaminated and seeing what is left =
at the end of the summer, but will work as long as resistance to =
parasites is not the primary selection criterion. More importantly, =
animals are adapted over time to the environment that they live in. =
According to Robert Johnson, who had the only Soay sheep flock in the =
country at one time, Soay sheep are extremely subject to the parasites =
in this area, despite being a primitive breed. At any rate, inbreeding =
is probably irrelevant to this group of sheep getting sick.
Mary Hansson says:..."Considering how hard we fight to NOT use animals =
with split eyelids, too-tight horns, or other PHENOTYPIC genetic flaws, =
it has been quite humbling to realize that the lead ram had multiple =
traits that should have had him culled prior to ever being used the =
first time by most of us today. The traits he carried PHENOTYPICALLY =
were rarely transferred to other individuals in the flock =
PHENOTYPICALLY. This tells me we do more messing up by selecting =
"registry" traits than by simply leaving the animals alone."
Reply: This goes to what I have said over and over ad nauseam. It is not =
so much that we mess up by selecting for "registry" traits as it is that =
these are superficial traits with pi...uh..poor/low heritability. Years =
of inbreeding here and only using rams with good horns has not changed =
the ratio of screwy horned animals. Since the amount of selection for =
each generation is limited, IF we insist on selecting for perfect horns =
and perfect fleeces we will have much less selection available for =
resistance to parasitosis and other factors. That does not mean we =
should not select for pretty things, just that we should (duh) consider =
the whole animal.=20
Linda says: "Your comment that the sheep seemed to go through alot of =
stress when being parted, even by see-through fences, and then get sick, =
is what led me to comment on a hardiness problem. Sheep should be able =
to handle some stress and should be able to adapt."
Reply: Very good points. Don't underestimate the effects of stress on =
critters. Even taking animals from a poorer environment to a better one =
can stress them enough to overload their systems if they are not used to =
NO change. This seems to be the case since the older ones have a worse =
time of it than the younger ones. Studies show that a moderate amount of =
stress increases immunity, but lots of stress decreases immunity. =
Perhaps we should all go out and slap our little dearies around =
occasionally.=20
Neal Grose
Harmony, NC
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<DIV><FONT face=3DArial size=3D2>Mary and all,</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>I wrote the first part of this before I =
drank=20
coffee this morning and the rest after others came in on the topic. I am =
going=20
to have to come see those guys soon....maybe on the way back from =
hauling culls=20
off to market!</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>Linebreeding is inbreeding done by =
someone who=20
thinks they are a professional. I have also heard it said that =
linebreeding is=20
inbreeding that works.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>We practice considerable inbreeding =
here. I have=20
yet to see any significant inbreeding repression. There may well be a =
good=20
reason for this. In the poultry industry, perfect=20
all-the-same chickens are the result of crossing strongly inbred =
SIB lines.=20
These inbred lines are created by intensive inbreeding of generations of =
siblings. [This is a much better way to handle "linebreeding" than =
crossing of=20
parent back to offspring...i.e., use the old bugger 'til he =
croaks.] In=20
poultry, defective chicks don't hatch. This is very effective at =
eliminating=20
adverse defective genes before they become established in the gene pool. =
Something very similar to this may have happened in Jacob sheep. The =
history of=20
Jacob sheep is one of isolation of breeding groups and inbreeding. When =
a=20
minimum amount of care is given to these animals, and heavy culling is=20
practiced, weak sheep are effectively eliminated from the group. The =
resulting=20
gene lines are more narrow, but stronger. This is only a good idea =
<EM>only=20
</EM>up to a point, but may be the reason we see relatively few genetic=20
deformities in Jacob sheep. </FONT></DIV>
<DIV>
<HR>
</DIV>
<DIV><FONT face=3DArial size=3D2>From Dan..."unless the shepherd is =
selecting parent=20
individuals based on their ability to survive/thrive in their specific=20
environment. Since we do our best (I hope we all do) to ensure the =
survival of <I>all</I> of our lambs it is hard to image natural =
selection=20
working here.<I> </I>And, unless someone has an extreme and unique =
environmental factor at play, most (all?) of us breed for traits other =
than=20
'thriveability'. The only circumstance in which inbreeding could =
play a=20
role in adaptations to a specific environment is if the flock is totally =
left to=20
"fend for itself" "...</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>Reply: Absolutely...to a point. =
Selection for=20
"thriveability" is a valid way to accomplish this under managed =
conditions. Ewes=20
that have lambs that are less thrifty and show more parasitosis SHOULD =
be=20
culled, for example. This will be a more gradual process than throwing =
200 sheep=20
into an environment that is heavily contaminated and seeing what is left =
at the=20
end of the summer, but will work as long as resistance to parasites is =
not the=20
<EM>primary</EM> selection criterion. More importantly, animals are =
adapted over=20
time to the environment that they live in. According to Robert Johnson, =
who had=20
the only Soay sheep flock in the country at one time, Soay =
sheep are=20
extremely subject to the parasites <EM>in this area,</EM> despite being =
a=20
primitive breed. At any rate, inbreeding is probably irrelevant to this =
group of=20
sheep getting sick.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>Mary Hansson says:..."<SPAN=20
class=3D010303214-28122002><FONT face=3DGoudy =
color=3D#0000ff>Considering how hard we=20
fight to NOT use animals with split eyelids, too-tight =
horns, or other=20
PHENOTYPIC genetic flaws, it has been quite humbling to realize that=20
the lead ram had multiple traits that should have had him culled =
prior to=20
ever being used the first time by most of us today. The traits he =
carried=20
PHENOTYPICALLY were rarely transferred to other individuals in the flock =
PHENOTYPICALLY. This tells me we do more messing up by selecting=20
"registry" traits than by simply leaving the animals=20
alone."</FONT></SPAN></FONT></DIV>
<DIV><FONT face=3DArial size=3D2>Reply: This goes to what I have said =
over and over=20
ad nauseam. It is not so much that we mess up by selecting for =
"registry" traits=20
as it is that these are superficial traits with pi...uh..poor/low =
heritability.=20
Years of inbreeding here and only using rams with good horns has not =
changed the=20
ratio of screwy horned animals. Since the amount of selection for =
each=20
generation is limited, IF we insist on selecting for perfect horns and =
perfect=20
fleeces we will have <EM>much less</EM> selection available for =
resistance to=20
parasitosis and other factors. That does not mean we should not select =
for=20
pretty things, just that we should (duh) consider the whole animal.=20
</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>Linda says: "<FONT face=3D"Times New =
Roman"=20
size=3D3>Your comment that the sheep seemed to go through alot of stress =
when=20
being parted, even by see-through fences, and then get sick, is =
what led=20
me to comment on a hardiness problem. Sheep should be able to =
handle some=20
stress and should be able to adapt."</FONT></FONT></DIV>
<DIV><FONT face=3DArial size=3D2>Reply: Very good points. Don't =
underestimate the=20
effects of stress on critters. Even taking animals from a poorer =
environment to=20
a better one can stress them enough to overload their systems if they =
are not=20
used to NO change. This seems to be the case since the older ones have a =
worse=20
time of it than the younger ones. Studies show that a moderate amount of =
stress increases immunity, but lots of stress decreases immunity. =
Perhaps=20
we should all go out and slap our little dearies around=20
occasionally. </FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>Neal Grose</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>Harmony, NC</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV> </DIV></BODY></HTML>
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