Oorsig/Review
percentages of in and around 434% in their
total flock of around 500 ewes, and an
adjusted lambing% of 535% after 3 lambings
in a group of MATURE Finnsheep (1982/3),
did the system not take off the way it should
have?
3. The third aspect was their synchronisation
program for natural mating - they
synchronised using teaser rams only. In
other words “no hormones” were used! We
can only speculate on what would have
happened had they used hormones, BUT,
there was also a method in this "madness"...
This is quite an important “nugget” –
when selecting for multiples, “hormone
produced” twins would in my mind not
be a heritable trait, whereas using a more
“natural stimulus” like this, might well be.
They also only used natural mating i.e. no
AI or laparoscopy! (I will discuss further at
a later stage or in another article, when we
look at the “principle of sperm competition”
as described by Themonier et al., from
Nouzilly, in France in the early 1970’s and its
effect on fecundity or multiple births). Group
mating increases both conception as well as
fecundity, but is not a heritable trait!
4. The other important consideration is that
they also selected strongly for “repeatability
of fecundity” as opposed to the “traditional
way of “us” (?) recommending using a ram
that is one of a twin or multiple at birth. To
become an ALL-STAR ewe and thereby a “ram
mother”, Dorsets had to have twins in at least
five successive STAR lambing oppotunities
and FINNS had to have triplets at least at each
given opportunity by 214 days post lambing
What did Magee and Hogue do that is/was (in my
opinion) far beyond the ordinary?
•
They worked out an excellent management
system which:
- - Produces lambs all year round based
on the same principles we use on dairy
farms to produce milk all year round.
- - Has 73 day “cycles” which gives 5 “feedlot
periods” in which lambs can be “rounded
off” and kraals have enough “rest time”
in between “lambing/feeding groups”.
- - Gives enough time in which a ewe can
raise her lambs herself and facilitate
early weaning
- - And gives enough recovery time for
“complete involution” to take place
before the next mating period.
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•
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They selected ewes according to different
reproductive measurements from those we
use as “standard practice”:
- - Repeatability of multiple births as
opposed to fecundity alone
- - Natural synchronisation with teasers,
not using any “hormones”
They identified “Ram Mothers” based on
“fertility performance” first, and then used
their sons and daughters to “multiply those
genes” into the flock!
After identifying the most “prolific ewes” and
their offspring, they started investigating
what made them “different”! In the rams
they found that these had less variation in
testicular circumference between spring and
autumn!
We know today that circumference alone
is not the best measurement of testicular
size and that testes volume is a much better
indicator.
We also know that there are other testicular
measurements like testicular growth from
days 90 to 180, with some adjustment for
live weight, which have been proven to be
effective. (Matos et al., 1992; Fossceco &
Notter,1995; Al-Shorepy & Notter, 1996).
I have started investigating variation in
testicular size during the mating period and
the recovery afterwards and I am excited
about what I have found thus far with the
“more fertile rams” seemingly having a
bigger drop in “testicular volume” during the
mating period as well as a quicker recovery
back to their original size (and even bigger)
thereafter. I believe that this definitely
warrants further investigation.
Our ultimate aim should be to find new ways
of identifying the most fertile animals sooner,
as well as to start applying methods that have
been proven to make a difference! I believe
that we have been missing this important
concept of measuring testes size variation
which Magee and Hogue applied many years
ago but possibly “failed to convey across
properly”! Instead of taking the “long route”,
we can save a lot of time by doing this from
the beginning and/or until we have enough
data a few years down the line.
The most important thing is that different
ways of measuring and selecting for
“fertility” were identified and applied by