ARTIFICIAL INSEMINATION
Artificial insemination is a technique by which semen is introduced artificially into the body of the uterus at the time of heat in an attempt to cause pregnancy. The major advantages of artificial insemination may be summarized as follows:
- It provides the opportunity to choose sires that are proven to transmit desirable traits to the next generation;
- It eliminates the cost and danger of maintaining a bull on the farm;
- It minimizes the risk of spreading sexually transmitted diseases and genetic defects (e.g., mule foot);
- It has cumulative beneficial effects over the years.
Use of artificial insemination makes it necessary to develop a system to identify cows and record dates of heats and inseminations. Accurate recording is necessary to develop good reproductive management on the farm and it provides the data for breeding associations to keep accurate herd books.
NATURAL SERVICE
The use of bulls for natural service remains widespread even in areas where artificial insemination has proven to be very effective. Many farmers believe that pregnancy rates are higher when a bull is used than when artificial insemination is used. However, when heat detection is accurate and the insemination is properly performed, artificial insemination and natural service give similar breeding success. Continued use of natural service may seem to be a paradox considering the genetic advantages of artificial insemination. However, there are three situations when the use of natural service may be indicated:
- When personnel are unwilling or inadequately trained to perform the tasks associated with heat detection and the technique of artificial insemination, leading to extremely poor pregnancy rates;
- When long term genetic gain is of minor importance;
- When local conditions do not provide the infrastructure necessary for successful artificial insemination (access to semen, liquid nitrogen storage tanks, telephones, etc.).
Farmers with bulls on the farm should never forget that bulls have caused many fatal accidents.
They represent a real danger (especially when believed to be safe) and must be handled firmly (with no signs of fear) and with extreme caution. In addition, bulls may spread sexually transmitted diseases (vibriosis and trichomoniasis). Infected cows may become infertile for up to four months; or, if they conceive, early embryonic death (a form of abortion) may occur.
TIMING OF SERVICE OR INSEMINATION
Artificial insemination or natural service lead to a pregnancy only if the spermatozoa are “at the right place at the right time.” The egg is released from the ovary about 10 to 14 hours after the end of heat and can only survive unfertilized for six to 12 hours. In contrast, the spermatozoa may live up to 24 hours in the reproductive tract of a cow.
A common recommendation for the best timing of artificial insemination is the “morning-evening” rule: cows observed in heat in the morning are inseminated the same evening, and cows observed in heat in the afternoon are inseminated the next morning. In the case of natural service, the cow and the bull may be allowed to mate starting a few hours after the cow accepts mounting until the cow refuses to be mounted (Figure 3).
CAUSES OF LOW CONCEPTION RATES
More than 90% of the cows in a herd should require fewer than three services to conceive. Possible causes of low conception rates (less than 50%) may fall into different categories:
1) Problems related to heat detection:
- Not servicing a cow that is in heat;
- Servicing a cow that is not in heat;
- Improper timing of service;
- Misidentification of cows leading to errors in records;
2) Problems related to natural service or artificial insemination:
- A bull with a low fertility;
- Improper insemination techniques;
3) Cow factors:
- Infection of the reproductive tract;
- Hormonal disorders;
- Obstructed oviducts;
- Anatomical defects;
- Early embryonic death (cow becomes pregnant, but the pregnancy is not maintained);
4) Problems related to nutrition (see Dairy: “Reproduction and Nutrition”).
