Artificial insemination (AI) has a long-standing history in animal production, with the first recorded AI taking place in 1784. For many decades though, the high cost and inefficiencies associated with AI limited its use in cattle production. With the development of semen extending and cryopreservation techniques, estrous synchronization protocols and accurate sire data, AI has become more widely used in recent decades in both the beef and dairy industries. Aimed at propagating the genetics of valuable sires, AI (and the technologies that accompany it) facilitates the widespread use of these elite bulls.
Understanding the AI Process
The basic premise of AI is quite simple: use semen collected from elite bulls to breed cows by artificial means. Although simplistic in concept, the actual process requires training and considerable practice. Additionally, there are a host of auxiliary techniques that facilitate a successful AI program. Semen collection, extension and freezing as well as estrus detection and estrous synchronization are techniques that commonly accompany AI in contemporary breeding programs.
Semen is typically collected from AI bulls with the use of an artificial vagina (AV). A dummy or teaser animal is used to stimulate the bull’s interest in copulation. Once the bull mounts the teaser animal, a technician redirects the bull’s penis into the AV. The AV uses both thermal and mechanical stimulation to induce ejaculation, and the semen is collected in a collection tube attached to the end of the AV. Although the AV method is the preferred and most frequently used method, electroejaculation can also be used to collect semen.
As its name implies, electroejaculation stimulates ejaculation by delivering a series of short, low-voltage pulses of electrical current. A lubricated electorejaculator probe is inserted into the rectum of the bull so that the electrodes of the probe lie near the pelvic nerves involved in ejaculation. The probe is connected to the power source, which supplies electrical current to the probe. A manual rheostat on the power source is controlled by an experienced technician to deliver short, intermittent pulses of electricity with increasing voltage. These electrical currents stimulate the pelvic nerves to induce ejaculation and the ejaculate is collected in a collection tube by another technician.
After collection, the semen is evaluated under a microscope for quality characteristics such as sperm motility, morphology and concentration as well as for the presence of cells other than sperm cells. The technician uses these observations to make appropriate calculations and prepare the semen for freezing. Semen extender is added to protect the sperm cells during the freezing and thawing processes, provide an energy source for the sperm and prevent bacterial growth. The extended semen is then loaded into either ¼ or ½ cc plastic straws, sealed and frozen in a controlled-rate freezer. Once frozen, the semen straws are stored at -196oC in liquid nitrogen tanks. Freezing and storage in this manner allows the semen to be stored and easily transported once it is needed for AI.
Now that the semen is prepared and ready for use, how do we know when the right time is to breed the cows? When breeding cows by AI, the landmark indicator used to determine when to breed a cow is estrus, or heat. Estrus is about a 12 to18-hour period at the beginning of each estrous cycle when the cow is sexually receptive. Approximately 12 hours after the end of estrus is when ovulation occurs. The timing of these events has led to the development of the AM-PM strategy for breeding cattle. With this strategy, cows are observed for signs of estrus in the morning and in the evening. Those cows that exhibit estrus (i.e.: standing to be mounted by other cows) during the morning heat watch are bred by AI that same evening. Cows that exhibit estrus in the evening are bred by AI the following morning. By breeding 12 hours after estrus begins, the theory is that the sperm cells should have enough time to undergo capacitation (a process necessary for fertilization to occur) and travel to the oviduct to meet up with the oocyte by the time ovulation occurs.
Considering that the average cow’s estrous cycle is 21 days (18-24 day range) and that not all cows show heat at the same time, estrus detection for AI would need to be done twice daily for at least 21 days. Since most producers can’t afford to spend that much time heat watching, estrous synchronization becomes almost crucial when implementing an AI program. Estrous synchronization involves using exogenous hormones to manipulate the estrous cycle. By synchronizing their estrous cycles, a group of cows will come into estrus (or heat) at or around the same time. This can drastically shorten the window for estrus detection to a few days or even completely eliminate the need for watching heat when using timed-AI synchronization protocols.
Regardless of the strategy used to prepare cows for AI, when it’s time to inseminate, the technique is the same. The cow is first restrained and the semen is thawed in a 35-37oC water bath for approximately 45 seconds. The semen straw is removed from the water bath and dried thoroughly with a paper towel. The crimped end of the straw is cut prior to loading the straw into a warmed AI gun. The technician then rectally palpates the cow to locate and grasp the cervix. The AI gun is inserted vaginally and guided through the cervix. The semen is expelled from the gun and deposited in the uterine body, near the junction of the cervix and uterus.
Advantages of AI
Propagate elite bull genetics: One of the greatest motives for utilizing AI is to exploit the genetics of elite sires. Valuable bulls could once only breed at most 50 cows per year naturally, thus seriously handicapping their overall genetic impact. With AI, superior bulls can exert a significantly greater genetic influence by siring thousands of calves annually. It no longer takes an entire lifetime of calves to prove a bull’s “worth” either. The sheer number of calves produced from these sires can provide much quicker proof (through progeny testing) of their value as breeding animals. For exceptionally valuable bulls, frozen semen and AI allow them to continue siring calves even after their death.
More breeding options: Take a look through a semen company catalog and you will find a plethora of bulls available for AI. Today’s cattle producers have access to some of the most diverse and elite genetics in the industry. Genetics from curve-bender and high-indexing bulls that would be unavailable to producers with natural mating are attainable with AI. Producers can also individually select which bulls to breed to specific cows, creating more mating combinations than would be feasible with natural mating.
Improved economic gains: Semen purchased for AI typically costs much less than the outright purchase of a bull with comparable genetic merit. Once the costs of estrous synchronization and AI supplies as well as the additional labor required is considered, the up-front cost advantage may sway towards natural mating. However, the return on investment is often far and away greater for AI since the bulls used are typically industry leaders for economically important traits. The calves born from AI sires often outperform calves from natural mating and produce a higher return on investment. Additionally, if a single bull or bulls of a similar type are utilized in conjunction with estrous synchronization, the calf crop will frequently be more uniform, translating to more dollars at sale time.
Better resource management: Breeding cows by AI can help producers manage the calving season more efficiently. Since the breeding date(s) are known, the producer has a pretty good idea when to expect those cows to calve. When coupled with estrous synchronization, all cows (or large groups) can be bred by AI at or around the same time. Producers can use these strategies to create tighter calving groups so that labor resources can be concentrated during discrete timeframes when those groups are expected to calve. This can be particularly beneficial when breeding heifers that may require extra attention at calving.
Reduce late-calvers: For herds with defined calving seasons, late-calvers can be difficult to settle before the breeding season comes to a close, oftentimes resulting in open cows at preg check. Estrous synchronization and AI can be utilized to reduce the number of late-calvers in a herd by synchronizing all cows for AI breeding on or around the first day of the breeding season. By breeding more cows earlier, the proportion of cows that calve earlier is also increased. When using progestin-based estrous synchronization strategies, late-calvers can even be brought into estrus earlier than they would on their own, allowing them to become pregnant earlier in the breeding season.
Increase calf performance: Late-calving cows are not only hard to rebreed in a defined breeding season, but they often produce poorer performing calves. When a cow calves late in the season, her calf has fewer days to grow and is often lighter at weaning than calves born earlier. Using estrous synchronization strategies to get late-calvers bred earlier in the breeding season allows calves to be born earlier. With more time to grow from birth to weaning, overall calf performance can be improved.
Important Considerations for AI
Pregnancy rates: There are many factors that affect AI pregnancy rates, including (but not limited to) cow age, breed, postpartum status, health status and nutritional plane as well as sire fertility, inseminator skill and timing of the breeding. When AI is done in tandem with estrus detection, pregnancy rates of 60-90% are typical. When using estrous synchronization protocols for timed AI, pregnancy rates of 50-65% can be expected.
Increased management: Although there are many benefits of implementing an AI program, it is not feasible for every operation. Adequate facilities are needed for administering estrous synchronization products and to restrain cows for breeding. Additional labor and strict adherence to estrous synchronization protocols and/or good heat detection are necessary for a successful AI program. Skilled AI technicians are also essential to achieving acceptable pregnancy rates.