Can heat synchronization work for
BY LAURIE DOBROSKY
LiTI’X’Z Now that the longest
day of the year has come and gone,
farmers and livestock are being
subtly reminded the days are
getting shorter and the nights
cooler.
This annual phenomenon not
only triggers sheep throughout the
state to have “romantic' in
clinations, but it causes shepherds
to ponder their lot in life as they
“look forward’ to those cold nights
spent m the barn watching tor
lambs. These winter-vigil
reminiscences that last tor weeks
and sometimes months until all the
lambs arrive prompt each
shepherd to ask themselves it
there isn’t a better way?
The answer to those shepherds’
questions (and prayers) may be on
the horizon in the form ot hor
mones tor heat synchronization.
Researchers at various univer
sities and at laboratories ot private
sheep organizations have been
looking at a number ot possibilities
one in particular is
prostaglandin, known com
mercially as Lutalyse.
Used in common practice on beet
cattle and non-lactating dairy
cattle, Lutalyse is used to control
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the time ot the estrus cycle and
ovulation in reproductively cycling
cattle.
In cattle, its basic purposes are
to bring temales into heat and to
synchronize the estrus cycles in a
number ot animals so calving will
occur within a short interval.
Since Lutalyse works only in
cycling animals this presents a
major problem tor most sheep
producers where ewes don’t come
m heat every 21 days like cattle. In
nature, sheep are brought into
estrus cycles by a decrease m the
amount ot daylight. This occurs at
only one time ot year in late
summer and fall.
According to Penn State’s Clair
Engle, this would mean the
product could be used with good
results only during August and
September. Since the University
has done no controlled ex
perimentation on using
prostaglandins in sheep, his
conjectures are based on the ex
penences ot sheep producers who
have voluntarily tried the product
on their own.
There is one exception to this
rule, however Dorsets. This
breed ot sheep will cycle
throughout the year. So, on this
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particular breed, "Lutylase will
tunction the same as in cattle,”
states Engle.
‘“This material is not officially
cleared tor use in sheep,'' Engle
stresses. Howevei, he adds that, to
his knowledge, there are very tew
side ettects when used on sheep.
In discussing the potential use ot
a .product like Lutalyse, a
University of Pennsylvania
veterinarian working at New
Bolton Center, K.ennett Square,
commments how it could be a
management tool tor shepherds
wishing to have all the sheep in a
tlock lamb at approximately the
same time. This would reduce the
man-hours spent each year during
the lambing season, she says.
Because ot their close birth
dates, the lambs would have no
major size ditterence due to age.
This uniform group ot lambs has a
better chance ot finding a higher
priced market from volume
commission buyers than would an
assorted group ot ages, weights
and sizes.
For the shepherd who doesn’t
want to risk experimenting with a
hormone injection to bring sheep
into season, there are a number ot
management practices that can be
used to bring sheep into heat about
one month earlier.
According to the New Bolton vet,
artificial lighting will move the
season ahead. However, its
becoming an accepted practice
among sheep breeders is almost as
slow as the changing day length.
For those who are using this
concept, the sheep are kept in an
enclosed building sometime in
August and the amount of light is
regulated, making the sheep
believe it is fall.
'Developing breeds ot sheep
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that reproduce without breeding
restrictions, such as season, is
slow in development,” she stated.
An early introduction of a ram
with the ewe flock will start the
breeding season a month or so
earlier, too. Vasectomized rams
can be run directly with the ewes.
However fertile rams should be
separated trom the ewes by a
strong fences. Both will achieve
the desired effect.
““The use of other hormones,
such as progestogenes, will also
help advance the breeding season.
The length ot the luteal phase of
the estrus cycle will inhibit the
events associated with estrus and
ovulation until the corpus luteum
occurs. The removal of the
inhibiting effects of progesterone
is followed by estrus and
ovulation,” explains the
veterinarian.
There are several ways to ad
minister these hormones. The best
results have been obtained when 30
mg. ot Flourogestrone acetate is
administered by placing a vaginal
sponge m the canal and leaving it
tor 12-14 days. After removing the
sponge, an injection of 375-750
international units ot PMSG
(pregnant mare serum) is given to
the sheep.
There is some controversy over
the use of these sponges, however,
and it is advisable for all sheep
breeders to consult with their
veterinarians.
Flushing is another method that
helps to push the breeding season
forward along with helping to
increase fertility rates, according
to Engle. Flushing means giving
the ewes a higher energy ration
with more total volume ot feed.
According to Engle,“this
(Hushing) has the positive effect of
sheep
multiple births and early cycling of
the ewes.”
Or. Tom Yonkers, veterinarian
in charge of animal regulatory
services for the Upjohn Company,
joins Engle in stressing that
Lutalyse has not been approved for
use in sheep. At the present tune
there is no petition by the Upjohn
company to gam its approval, he
notes, even though there is an
increasing amount of interest m
the product for use in both sheep
and goats.
”In my opinion, Lutalyse is
probably sate for use in sheep,”
Dr. Yonkers states. However, he
qualified his opinion since it is only
based on practical experience, not
actual research data and has been
tested on only a small number of
animals.
Since Lutalyse has not been
approved for use in sheep, the
Company-can give no recom
mended dosages. Only ex
perimental data on dosages and
fertility can be given.
Citing The Sheep and Goat
Manual published by the Society
tor Thenogenology (a fancy word
for reproduction), the New Bolton
vet notes that a dosage of 8
milligrams of prostoglandin given
in two injections was administered
11 days apart m experiments done
on sheep. Ewes usually came into
estrus 53 hours after the first in
jection of the material.
Unlike cattle, where
prostoglandin can be used
throughout the year, the use and
effectiveness of the hormone in
sheep depends on the time of year.
Various studies have shown both
sides to the prostaglandin story
both positive and negative. Sheep
producers will have to consider
whether they are satisifed with
nature or want to help it along.
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