Oorsig/Review
either just use hybrid vigour in crossbreeding
systems or start developing a new breed for
intensive systems utilizing the best animals
existing in our local breeds?
8. Methods of selecting for fertility and fecundity
after the use of “modern synchronization
programs” and the use of hormones, also
needs a “re-look”. Now that we are not afraid
of raising multiple-birth lambs any more,
fecundity can be raised artificially by using
higher dosage rates of PMSG. As stated above,
we should maybe then put more emphasis on
repeatability of conception than on litter size
per se?
9. When selecting replacement ewes Magee and
Hogue used the same principles as with the
selection of flock sires, with some additional
traits:
- -
- -
They looked at “maternal-line selection”
primarily, as opposed to sire-line
selection. Once a “ram mother” was
identified, those genes were multiplied
in the flock predominantly via the rams.
This is in direct contrast to what I see
is being done on most SA farms where
things are being done the other way
around i.e. by selecting rams with little
emphasis on maternal lines!
They also noted that the season in which
a ewe lamb was born, had a significant
influence on her lifetime performance.
The majority of their replacement
lambs came from mature ewes who had
“proven themselves” and who lambed
down in spring. These lambs were then
mated for the first time at the age of 9
months to lamb down at 14 months of
age. Here in SA this will mean that the
majority of replacement ewes will come
from the November lambing period.
If they are then mated at the age of 9
months, that would be in August to
lamb down 5 months later in January.
We have the same principle that we find
in cattle where heifers calving for the first
time, or in this case young maiden ewes
who have lambed down for the first time,
have lower re-conception rates. The main
reason being that they are still growing
and therefore need additional food levels
for this, plus for production. By re-mating
during the “season of best conception”
i.e. during the autumn mating season in
20
April, we increase the chances of getting
better conception as well as better
fecundity in these ewes and thereby
an increase in “lifetime performance”!
- -
There is definitely “method in their
madness”! By using their records they
“fine-tuned” their overall performance!
Replacement ewe selection is therefore
also done on maternal performance but
season of birth, age at first mating as
well as the number of lambs born after
“natural synchronisation” with teaser
rams, are added…
(This paragraph contains a lot of “nuggets”
needing extra time to be “digested properly”!)
Que vadis (where to now)?
It is time to climb out of the box and to look back
into it – instead of just thinking outside the box!
We cannot keep on doing the things in the same
way as we have been doing and then expect a
different outcome…
If you still believe that a ewe should be raising her
own offspring and/or recommend to your clients
to go the “Intensive sheep farming route”, you
need not look any further – the STAR Management
Program is the way to go.
BUT – not the way Magee and Hogue originally
did it. I usually start with 5 x 21 day cycles giving
105 “high intensity days”. Ewes that “skip” rest
slightly longer and mostly conceive early in the
next cycle, after which they usually remain in the
STAR cycle.
A ewe that skips once after 2 x 219 day cycles still
lambs 3 times in 2 years - 219 + 219 + 292 = 730
÷ 2 = 365 days. 730 days equals 2 years…
It is now 2019 – implement new technology and
new approaches.
The sky is the limit!
References:
Hogue, D. (2019). STAR Management | Cornell Sheep
Program. [online] Blogs.cornell.edu. Available at:
http://blogs.cornell.edu/newsheep/management/
reproduction/star-management