to Genetic Improvement
the Ideal Ewe
Therapy for A.I.
Shepherd Instructions and Requirments for AIing
A MEANS TO IMPROVE GENETICS
Martin R. Dally
Animal Science Department
University of California - Hopland Field Station
many years artificial insemination of sheep was thought
to be impractical, mainly due to the difficulty of detecting
estrus and controlling the ewe's estrus cycle. The inability
to freeze ram semen was another factor that limited a wider
use of AI. However, today with the use of progestogen and
PMSG the synchronization of the ewe's estrus cycle is possible.
In addition, ram semen can now readily be frozen which opens
the door for interstate as well as international movement
of semen. Even with these technological breakthroughs the
conception rate of artificially inseminated ewes was relatively
low and therefore was not practical for the commercial producer.
The main reason for the low conception rate is that semen
could only be placed at the opening of the cervix or slightly
inside the cervix. The anatomical structure of the ewe's
cervix makes the penetration of the cervix nearly impossible.
Cervical AI conception rates using fresh or frozen semen
are approximately 55% and 25% respectively. If semen could
be deposited in the uterus as is the case with cattle, the
conception rate would improve to the point where AI of sheep
would be practical on a commercial basis.
In 1982, Australian researchers
developed a laparoscopic insemination procedure that revolutionized
the sheep AI technique. Conception rates using frozen semen
range from 50% to 80% when a skilled technician uses a laparoscopic
insemination technique to place the semen directly into
the ewe's uterus. Laparoscopic AI conducted at the University
of California's Hopland Field Station, using frozen semen,
has routinely resulted in a 70% or higher conception rate.
Individual rams have consistently produced 85% conception
rates. Conception rates can vary greatly depending on semen
quality, breed of sheep, management, time of year, and the
technician's skill. An additional advantage of laparoscopic
insemination, also referred to as intrauterine insemination,
is that lower numbers of sperm are required per insemination.
SEMEN AND SYNCHRONIZATION
The number of spermatozoa needed
for laparoscopic insemination is about one-third of that
required for cervical insemination using frozen/thawed semen.
A suitable ejaculation is diluted and processed into 50
to 90 1/4cc French straws for laparoscopic insemination.
One straw is required per ewe inseminated and contains between
40-60 million spermatozoa post thawing. If frozen pellets
are used, approximately 22 pellets can be made per ejaculation,
each containing enough semen to laparoscopicly inseminate
3 ewes. Straws and pellets are stored in liquid nitrogen
at -196C (-385F). Prior to insemination, the straws are
thawed in a waterbath at 37-38C (98.6-100.4F) for 2-3 minutes.
Fresh ram semen can be used but insemination should take
place within 10 hours of collection.
The laparoscopic insemination procedure
is a minor surgical method by which semen is placed in the
uterine horns. Prior to surgery, the ewe's estrus cycle
should be synchronized by the use of hormone therapy. This
normally involved inserting a pessary impregnated with progestogens
into the ewe's vagina and leaving it there for 12-14 days.
During that period the progestogen is slowly absorbed through
the vaginal wall into the ewe's blood stream. The increased
level of progesterone inhibits follicle development and
prevents the ewe from coming into estrus. Once the pessary
is removed, the progesterone level drops off and follicles
develop. At the time of pessary removal, PMSG is given to
tighten up the degree of synchronization. Normally, 400
international units of PMSG are given. If insemination is
to take place at the peak of the natural breeding season
and the ewes are in excellent condition the level of PMSG
may be reduced to 300 IU. If too much PMSG is administered,
the ovulation rate will be too high resulting in an excessive
number of multiple births. Insemination should take place
56-66 hours after pessary withdrawal.
PREP AND PROCEDURE
Twenty-four hours before surgery
both feed and water should be withheld from the ewes. This
reduces the contents of the rumen and bladder. A full rumen
and/or bladder may hinder locating the uterus and increase
the chance of puncturing these organs during surgery.
The ewe is placed on her back in
a laparoscopy cradle and the posterior abdominal region
in the area of the pubis is surgically prepared by removing
the wool and disinfecting the skin. The ewe is given an
injection of local anesthetic approximately 5 inches anterior
of the udder and 2 inches on either side of the midline.
The cradle is then placed in it's surgical position with
the posterior of the ewe lifted to an approximate 40 degree
angle. Two very small incisions are made in the skin at
the site where the anesthetic was injected to facilitate
puncturing the abdominal wall with a trocar. The muscles
of the abdominal wall are not cut - the muscle fibers are
separated and once the cannula is removed at the completion
of the laparoscopy, the fibers return to their normal position
in relation to each other. Once the abdominal wall is punctured,
the trocars are removed from the cannulas and an endoscope
and a manipulating probe are placed through the cannulas
into the abdominal cavity.
An endoscope is a special telescope
with a fiberoptic light, which permits the technician to
view the ewe's reproductive tract. A small amount of carbon
dioxide is used in the abdominal cavity to help isolate
the uterus from the other organs. The carbon dioxide also
has a mild anesthetic effect on the ewe. A manipulating
probe is used to bring the uterus into the proper position
for insemination. In some cases this is not necessary, as
the uterus is already in the proper position. The less the
reproductive tract is manipulated, the better the conception
rate. Once the uterus is in the correct position, the probe
is removed and replace by the inseminating gun containing
The technician then punctures the
uterine horn half way between the uterine bifurcation and
the utero-tubal junction as seen in the graphic. The semen
is injected directly into the lumen of the uterus, and the
same procedure is repeated on the other uterine horn. The
inseminating needle that enters the uterine wall is extremely
fine, having an outside diameter of 0.04mm. The insemination
procedure takes only 2-5 minutes. Once both horns have been
inseminated, the cannulas are removed and a topical antibacterial
spray is applied on the two small incisions. In some cases,
bleeding may occur which is due to the perforation of surface
blood vessels. If excessive bleeding takes place, michel
wound clips or staples may be used to close the wound. Experience
shows that very little suturing is required. The ewe is
removed from the cradle and allowed to walk, under her own
power, to a holding pen. Ewes normally start eating within
minutes of being place in the holding pen. The incidence
of infection because of this minor surgery is extremely
CLICK HERE FOR SLIDE SHOW
OF A.I. PROCEDURE
The genetic gains that AI can offer
sheep producers are almost unlimited. Semen from superior
domestic and international rams is now available, and straws
may be purchased for as little as $15 to as much as $135
depending on the breed and quality of ram. The cost of hormone
therapy and insemination will vary based on the number of
FOR THE SHEEP PRODUCER
AI is the gateway to the use of
top sires, both domestic and international. It offers progressive
producers the opportunity to make previously unimagined
genetic gains in a very short period of time. Rapid genetic
gains can be made especially in wool quality and quantity
due to their high to moderately high heritability estimates.
In selecting a sire one should consider the progeny's ability
to adapt to the environment. The possibility of negative
effects on economically important traits is particularly
important when exotic breeds are being considered.
Chemineau P., Y. Cagie, Y. Guerin,
P. Orgeur, and J.C. Vallet. 1991. Training Manual on Artificial
Insemination in Sheep and Goats. FAO Animal Production and
Health Paper 83. Rome.
Evans, G. and W.M.C. Maxwell.
1987. Salamon's Artificial Insemination of Sheep and Goats.
*Reprinted from "Wool Production School;" Hopland
Field Station Publication 103
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