Introduction:
Artificial Insemination (AI) and embryo transfer (ET) is becoming more widespread in bovine
today than in previous years. Artificial insemination is the process of introducing live, prepared semen,
into the uterus, by means of a pipette and syringe, for purpose of fertilizing an ova, rather than natural
copulation. AI has several advantages over natural breeding including genetic improvement through the
use of superior sires, reduction of injury to the cow or the bull, and reduction of diseases in new born
calves, just to name a few. Embryo transfer is the transfer of multiple embryos (fertilized eggs) in female
cattle from one female (the donor) to several other females (the recipients), which carry them to term. ET
can allow superior females to increase their contribution to the cattle industry by having multiple calves in
one year. Artificial insemination and embryo transferring is quickly growing in the bovine industry today.
These two methods seem to be the best choice for reproduction in the cow for most cattle operations
because of their great advantages.
AI:
In order for a successful insemination to take place, it is crucial that the cows’ estrous cycles be
watched closely; the estrous cycle, or heat cycle, in cows occurs every eighteen to twenty-four days, and
usually lasts about twelve hours. The key for AI to work successfully in cattle is superovulation, or two
shots given eleven days apart, so that multiple eggs will be released as opposed to one or two, and for a
majority of a herd of cows to have synchronized estrous cycles. The best time to cover the cows is right
before they ovulate; this is generally right before the end of the heat cycle, or right at or right before the
twelfth hour of standing heat. At this point, maximum fertility is reached; if AI is carried out to soon or
after ovulation has begun, chances of pregnancy are decreased. Unlike the mare, cows that under go AI,
do not require a licensed veterinarian to perform the insemination; there are clinics all around the United
States that teach the insemination process in about five to six days. Once the correct time frame occurs,
insemination can occur. Semen from the bull will have already been collected, and frozen in a liquid
nitrogen tank. The liquid nitrogen tank must be kept at least -112o F, or colder to prevent the semen from
being destroyed or damaged before use. To freeze semen, there must be at least a fifty-five percent
motility rate, and forty million sperm are needed per straw. If the liquid nitrogen tank is kept at least the
minimum requirements for sperm to stay frozen without being damaged, frozen semen will never go bad.
Because not every cow is inseminated the first time, it is customary to order one and a half straws per
cow.
In order to obtain semen from the bull an artificial vagina (AV) or electroejaculation is used; most
commonly the AV is used to collect bulls. A normal average fertile bull can produce five to ten billion
sperm per ejaculation. For a higher conception rate, semen is extended with a dilutor before use. “An
extender is a solution that allows the semen from a donor to impregnate more females by making
insemination possible with fewer sperm” (Wikipedia). There are several different types of extenders that
each has their own specific handling methods. Two of these include egg yoke dilutors or pasteurized,
homogenized milk dilutors, and these seem to be the best methods of diluting sperm because of a higher
conception rate. As the extenders are added, the semen is also checked for quality, tested for various
diseases, and antibiotics may be added to prevent future health problems in the cow and calve. The semen
is then placed into straws for freezing.
In order to perform an AI, the semen must first be unfrozen; the semen is removed from the liquid
nitrogen tank and placed in water bath that is 95o F for forty-five seconds. Secondly, the perineal area
should be thoroughly cleaned with a surgical preparation scrub and the cow’s tail should be averted to
decrease the chances of bacteria getting into the vagina. Semen is then removed from the water bath and
injected into a pipette. Using a sterile lubricated gloved arm, the inseminator will introduce his arm into
the cow’s rectum. The inseminator will carefully guide the pipette into the vagina at an upward angle to
avoid placing the pipette into the bladder, and into the uterus of the cow. Once the pipette is inserted into
the uterus, the semen will be slowly injected at the front of the cervix. The pipette is then slowly retracted
from the cow’s vagina. After thirty days, ultrasound may be used to determine the actual pregnancy in the
cow.
Advantages of AI:
As previously mentioned, artificial insemination does not come without its advantages. AI has
many advantages over natural copulation. One of the mainstays being great distances between genetically
fit cows and genetically fit bulls; with the use of AI and frozen semen, this distance is no longer a
problem for breeders to heighten the genetic makeup of a calve. Because some cows can be overly
aggressive while during their estrus cycle, superior bulls have a higher risk of getting injured. With AI,
injury to the cow or the bull is completely ruled out. Another advantage to AI is the reduction of diseases;
because antibodies can be added to semen, disease rates remain relatively lower than that of natural
copulation. One other major reason AI is at a greater advantage than natural breeding is because more
cows can be bred with one ejaculation preventing overuse of the bull.
ET:
For a successful embryo transfer, several conditions must be met. First, both a donor cow and the
recipient cows should be in good physical condition and cycling regularly. The donor cow must also be
given a superovulation shot prior to transfer. In addition, the donor cow and recipient cow must be
synchronized in their estrus cycles, which are generally taken care of through the administration of drugs
used to keep all cows in a herd synchronized. Typically because multiple eggs have been released, the
donor cow will be inseminated twelve hours after the heat cycle has occurred, and then will be reinseminated possibly three to four more times in twelve hour increments. After seven days, the uterus is
flushed several times, and all embryos are ready to be transferred. If freezing the embryo for later use, the
embryo recovery must be done prior to six days because it will be too big for successful freezing at seven
days.
In order to recover an embryo from the donor cow, there are two methods that may be performed:
non-surgical and surgical. The surgical method however, is no longer used to recover embryos. The nonsurgical ET is performed much like the artificial insemination. A catheter is gently implanted into the
vagina, guided through the cervix and into one of the uterine horns where the embryos lie. Once the
catheter has reached one of the uterine horns, several milliliters of warmed sterile salt-buffered saline may
be induced into the horn in order to flush out the embryos. The fluid is then recovered in a collection
bottle, and the process is then repeated in the second uterine horn since the horn that produced the eggs is
unknown. Once the embryos have been recovered, they are found under a microscope, transferred into a
second solution where they can be held at room temperature for eight to twelve hours if necessary, and
then prepared for the transfer.
Transferring the embryos to recipient cows can also be carried out non-surgically. To carry out a
successful transfer, the embryo is placed in a straw and attached to an insemination gun. The pipette is
aided into the uterus, as previously explained, where the embryo is deposited slowly into the uterus.
Generally, five sufficient embryos can be expected from the donor cows, but it is often customary to set
up for eight transfers. The recipient cows must then be monitored closely to ensure they do not come back
into heat. Ultrasounds should be made on a twenty-day-old fetus, or thirteen days after the transfer to
insure a pregnancy. The key to a successful ET is considered to be the proper selection in recipient cows.
Advantages of ET:
Just as AI has its advantages, ET also can be quite rewarding. As previously mentioned, ET can
allow superior females to increase their genetic production. Secondly, older cows are capable of passing
on their genetic makeup despite the fact they are no longer able to carry a calf to term because of possible
uterine arterial hemorrhage. Injured cows are also capable of passing on their genetic makeup even
though they are not physically able to carry a calf. Finally, cows are able to produce more than one or two
calves per year with the ET, making ET a more sufficient way of reproduction.
Conclusion:
More and more cattle operations and cattle owners seem to be turning their reproduction needs to
artificial insemination and embryo transferring than ever before. With the widespread use of AI and ET,
more and more genetically balanced calves are being born in the bovine industry. With greater advances
in technology being discovered everyday, artificial insemination and embryo transfer is only the
beginning for the bovine industry, as we know it today.