Artificial insemination in beef cattle
Introduction
Many producers of purebred and commercial beef cattle can profitably utilize artificial insemination (AI) on virgin heifers or on the cow herd or both. Success with artificial insemination requires attention to detail in all areas of herd management. One of the most important factors affecting the success of the program is the manager's attitude. He or she must totally desire to make AI work and instill this commitment into each link in the chain of management decision. The weakest link sets the level of success of the operation. Should any aspect of management become subpar, AI conception rates will be reduced, most likely to the extent it will cancel many of the benefits the technique offers. Many managerial decisions relative to feeding, facilities, fences and corrals, equipment, sire selection, will be necessary. Both a sound health program and good nutrition are requirements of any breeding program but become an absolute essential ingredient for artificial insemination. In addition, more labor and skill are needed especially in the initial phases of the program.
Learning Artificial Insemination
Supervised instruction and guidance are essential because without adequate training, valuable AI equipment and semen could be seriously damaged. In order to ensure high fertility, frozen semen requires very special storage and handling techniques. Adequate training is also essential to minimize risk of injury to either a valuable animal or to yourself.
AI Training Schools are available from several semen suppliers. The objective of these schools is to teach the skills required to handle semen, inseminate cows, and manage a successful AI program. Three basic areas of instruction should be provided by AI Training Schools including:
1. Insemination technique, developing through live
animal practice, the ability to skillfully and accurately
place semen at the proper location within the repro
ductive tract using sanitary and correct techniques.
2. Semen handling, developing through practice, the
ability to properly handle, thaw and prepare semen
for insemination, according to the recommendations
of semen-producing organizations.
3. Reproductive management training in the importance of heat detection, herd health, and total herd management for the development and continued success of an AI program.
Heat Detection and Beef AI Programs
The most limiting factor in artificial insemination programs is the proper detection of cows or heifers in estrus. Estrus, or "heat", is that period of time that occurs every 18-24 days in sexually mature, nonpreg-nant female cattle when they are receptive to mounting activity by bulls or other cows. In beef cattle operations where artificial insemination is the means of breeding the females, the herdsman must recognize and interpret a cow's heat signals. Proper timing of the artificial insemination is necessary to accomplish a high percentage of conceptions in the cows that are bred artificially.
Considerable amounts of research have been conducted on the various factors contributing to the efficiency with which cows are detected in heat. When all is considered, one of the key factors is the skill of the human performing the heat detection. With an AI program, people assume the same responsibility as the bull for accurately detecting heat and the proper timing of insemination. Thus, the dilemma for the inseminator is determining which cows are in a "standing heat" and when that heat occurs.
A cow is fertile only when an egg has been released (or ovulated) from the ovary. This occurs about 10-14 hours after the period called "standing heat" ends. Because sperm need time in the cow's reproductive tract before they are capable of fertilizing the egg, insemination should be made several hours before ovulation. This means that for the highest fertility, cows or heifers should be inseminated in the latter two-thirds of heat or within a few hours after having gone out of heat. This represents approximately 12-18 hours after the cow first comes in "standing heat."
Timing of Artificial Insemination
Maximum fertility to artificial insemination occurs when cows are bred near the end of "standing heat." Ovulation occurs about 12 hours after the end of standing heat. The 12-hour lead time allows the sperm cells to go through a process known as capacitation by the time the egg is released. Fertility decreases slightly when cows are bred a few hours on either side of this target, and decreased markedly when breeding occurs more than 12 hours away from the end of "standing heat."
A guide that has proved to work well for timing AI is called the AM/PM rule (Table 2). At the end of the morning heat detection period, animals detected the prior evening are bred; at the end of the evening heat detection period, those observed that morning are bred. In some situations, AI must be employed once-a-day wherein all animals detected in the prior 24 hours are bred. Some studies show little decrease in fertility when this approach is used.
Using the AM/PM Rule
Semen Handling
The quality of frozen semen when it arrives at your farm or ranch is determined by the bull and organization that processed it. But once it arrives, it is up to you to take proper steps to ensure its viability.
Frozen bull semen can be stored indefinitely, if it is maintained constantly at very low temperatures. The critical temperature is approximately -112 degrees. Semen which is exposed to temperatures warmer than -112° F (even for a short time) and then returned to the storage tank may be damaged.
The extent of damage depends upon how long the semen is exposed to the elevated temperatures. Although it is easy to maintain frozen semen at a safe temperature, it is also easy to destroy it in a few moments of carelessness.
Tank Management
The semen storage tank is a large vacuum-sealed metal bottle with an extremely efficient insulation system. Because of the vacuum bottle construction, the temperature can remain at -320° F (liquid nitrogen temperature) as long as at least two inches of liquid nitrogen is present. Technical advances in design and construction have produced storage tanks with a liquid nitrogen holding time of six to nine months.
Although semen storage tanks are well constructed, they still are susceptible to damage from mishandling. Semen tanks should be kept in clean, dry, and well-ventilated areas. Avoid excessive movement of the tank. The inner chamber, which contains liquid nitrogen, is suspended from the outer shell by the neck tube. Any abnormal stress on the neck tube, caused by sudden jarring or an excessive swinging motion, can crack the tube. This results in vacuum loss from the outer chamber.
To increase holding time, keep the tank in a cool location away from direct sunlight. Avoiding drafts from furnaces and outside air also helps prevent excessive nitrogen evaporation. However, make sure there is sufficient ventilation in the room to prevent possible suffocation which can be caused by excessive nitrogen gas in the air you breathe.
Protect the tank from corrosion by keeping it elevated above concrete or wet floors. Use boards or pallets. Pick a location that is safe from children and vandals, but do not hide the tank; it must be placed where it can be seen daily and where it can be monitored routinely for nitrogen level.
Finally, always be watchful for a lid that is left off and for frost or sweat on the tank. Give particular attention to the neck and vacuum fitting. Frost indicates that the vacuum insulation has been lost, and liquid nitrogen has been or is evaporating rapidly. If you suspect this has happened, use a wooden yardstick to measure the amount of liquid in the tank. If the tank contains liquid nitrogen, the semen must be transferred to a good tank immediately. Should the tank be empty of liquid nitrogen it is doubtful that the semen is viable; it should be evaluated before it is used.
Retrieving Semen
In the typical farm semen tank, dangerous temperatures exist in the upper half of the neck tube. Exposure to these temperatures can occur when trying to locate a specific unit of semen or when transferring semen from tank to tank (Figure 1). Thermal injury to sperm is permanent and cannot be corrected by returning semen to liquid nitrogen.
In order to minimize thermal damage:
• Identify which canister contains the desired se
men. A semen inventory which keeps track of the
location of each bull prevents unnecessary search
ing.
• Remove the canister from its storage position to
the middle of the tank. Raise the canister just high
enough in the neck region to grasp the desired
cane of semen. Keep the canister tops no higher
than the frost line, or keep the tops of the canes no
higher than two to three inches from the tank's top.
• Grasp the desired cane, and immediately lower
the canister to the tank floor. Keep the cane as low
in the tank as possible while removing the unit of
semen. Use tweezers to remove the straw. If the
straw is located in the upper goblet, bend back the
top tab of the cane to a 45 degree angle. This will
keep the straw from bending or breaking. The
straw should be removed within 10 seconds from
the time the canister is raised into position.
• Immediately after the unit of semen is immersed in
water, return the cane to the canister by raising the
canister up over the cane. Return the canister to
its storage position.
• Any time it takes more than 8 to 10 seconds to
locate a particular cane, the canister should be
lowered back into the tank to cool completely.
Never return a unit of semen to the tank once it has
been removed from the cane.
During Insemination
One of the most frequent chances for semen damage is during transport to the cow. After thawing, the semen temperature must be maintained as close to 95 degrees as possible. Handling thawed semen and preparing the insemination rod should be done in a sheltered, heated area.
Proper steps for handling semen include:
1. While the semen is thawing, warm the insemination
rod by rubbing it briskly with a paper towel. In cold
weather, place the warm rod within clothing so it will
be close to the body and maintain warmth.
2. After the semen is thawed for the required time, dry
it thoroughly with a paper towel and protect it from
rapid cooling.
3. Adjust the air space in the straw to assure that no
semen is lost when the end of the straw is cut off. This
can be done by slightly flicking the wrist while holding
the straw at the crimp sealed end.
4. Transfer the straw to the rod and cut the tip of the
crimp-sealed end of the straw squarely and through
the air space. Only sharp scissors or a specially
designed straw cutter should be used. Make sure to
cut the straw "square" to achieve a good seal with the
sheath.
5. Wrap the assembled insemination rod in a clean, dry
paper towel, and tuck it within your clothing for
transportation to the cow. Do not place the rod in your
mouth or carry it uncovered in your hand.
6. Inseminate the cow within minutes after the semen
has been thawed. The period of time between re
moving the semen from the tank and depositing the
semen in the cow should not exceed 15 minutes.
Semen Transfer
When transferring semen between tanks, follow these tips:
1. Have the tanks side by side and as close as possible.
Fill the tanks with nitrogen before transfer, if possible.
2. Have the appropriate canister in each semen tank in
the center position.
3. Transfer the canes quickly (within three to five sec
onds). Never touch the units of semen with bare
fingers.
It is essential that frozen semen be handled and thawed carefully and properly in order to obtain anyone optimum results. It also is important to deal only with reputable, well-established AI organizations because their semen has been processed under standard, controlled conditions that are evaluated routinely.
Insemination Process
Although not part of the female genital tract, the rectum (terminal portion of the large intestine) is an important organ for you to become familiar with because your arm inside the cow will be working through this thin-walled tube. The rectum is 10 to 12 inches long and very stretchable. That is important because it is through the rectum that you will manipulate the cervix.
The anus serves as a valve between the rectum and the outside. It is made up of a circular (purse string) muscle located directly under the skin. It surrounds the very end of the rectum. Again, the anus is stretchable, hence, your hand and arm can easily slip into the rectum.
Circular muscle contractions move along the rectal wall toward the outside. When strong, these contractions may block your hand from moving forward and make it difficult to manipulate the genital organs through the rectal wall.
Semen Placement
The insemination process is quite straightforward. However, since relatively few sperm cells will be used, their placement is critical. The semen should be placed in the body of the uterus just in front of the cervix. You can recognize the proper site by the change in tissue consistency—from firm and hard in the cervix to soft and spongy in the uterus. To achieve the highest possible fertility rate, semen should be deposited at the very front end of the cervix. The internal (or front) end of the cervix is often called the anterior cervical os. To deposit semen at this location requires the use of a special device called Cassou pipette, or "AI gun." The recto-vaginal insemination process is used. The inseminator places his hand in the rectum and manipulates the reproductive tract so that the gun passes through the vagina, then it is manipulated through the cervical rings, and then held at the internal opening of the cervix for semen deposition. In adequately restrained cattle this will take 30 seconds to 2 minutes. At first, however, passing an insemination syringe might not be easy because you might encounter natural obstructions on your way to the target
الجمعة ديسمبر 19, 2008 6:44 pm
