Читать книгу Bovine Reproduction - Группа авторов - Страница 197

The collection of semen for cryopreservation is a fairly simple and straightforward process, except for those with no experience. Therefore the procedures should only be administered by someone who is competent and experienced at handling bulls and very familiar with the collection process. Good facilities are paramount to a successful collection attempt, particularly when dealing with beef bulls that have primarily had pasture breeding experience. Collection of semen from bulls with an AV is not for the faint of heart. The procedure basically involves allowing the donor bull to mount or “jump” another steer, bull, or cow and diverting the penis laterally in order to introduce the extended penis into the AV. Usually, once bulls are familiar with the technique, they will readily mount and serve the AV. Training them to do this is an art, particularly when dealing with less docile mature beef bulls and bucking bulls.

CSS mandates guidelines to be followed for bull health and cleanliness. Steers are the most common mount animal unless the facility prefers the use of a phantom (dummy structure designed for supporting a mounting bull). Using cows as mount animals is discouraged because of the potential for penetration and contamination by the bull. Mount animals should have their hair closely clipped from the hindquarters, allowing for ease of cleaning and disinfection, which should be accomplished after every use. The process usually requires at least two people and preferably three. One person is assigned the mount animal, which is usually haltered or handled by nose ring. This person's responsibility is to position the mount animal for mounting and to assist in keeping it in position during collection. In large facilities there is also a bull handler who may have the bull haltered or tethered to control him during the mounting process. Most beef bulls in custom studs are free to mount the jump animal. Lastly, the semen collector manages the AV and is in charge of the entire collection area (Figure 12.4). It is this person who ensures the sample is properly identified and collected hygienically and is responsible for the safety and welfare of the team as well as the animals.

Figure 12.4 Collection area.

The procedure of semen collection is rather straightforward. Several bulls are usually penned separately along a “bull alley” facing the collection area. Mount animals are allowed to move along in front of the bulls in order to initiate some arousal. The bulls are allowed to observe other bulls mounting and being collected from this vantage point. It can be very evident that bulls in the bull gallery are aroused by the amount of vocalization that occurs as a bull is being collected.

Once it is time for a bull to be collected, he is allowed to leave his pen and enter the mount area. At this time, the mount handler will move the mount animal to prevent the bull from mounting. This may continue for several minutes until such a time as the semen collector is satisfied the bull is properly aroused. The semen collector may further determine that the bull needs to “false mount” to further his arousal and thus increase the quality and quantity of semen he produces. This is accomplished by the bull handler allowing the bull to mount but the semen handler diverting the penis away from the mount animal as the mount is withdrawn from under the bull. As discussed previously, when the semen collector believes the bull is properly stimulated, the bull is allowed to mount for collection (Figure 12.5). After collection the bull is either returned to housing or is placed back in the bull alley for another collection attempt.

Figure 12.5 Proper technique for collection of bull semen.

The preparation of the AV is important as the tactile sensation received by the bull is paramount to his semen production. It should simulate the natural breeding act as closely as possible. The AV is constricted, with a ridged tube that has a port allowing water to be added between the rigid structure and a latex liner. Within this liner another is placed to facilitate collection of the semen from the bull. This liner has a tapered end that allows the inclusion of a glass or plastic receptacle that will serve to hold the collected semen sample. Water added to the water jacket should be in the temperature range 40–60 °C and varies according to the preference of the bull; this has to be determined by the semen collector. Also, the amount of water within the jacket determines the rigidity of the liner, which can impact the bull's reaction to the AV. It is very important that a sterile non‐spermicidal lubricant be applied to the upper one‐third of the AV. This improves sensation and reduces the possibility of abrasive injury to the bull's penis.

For those bulls that are too fractious or are incapacitated and unable to jump a mount animal, the collector has the option to use an electroejaculator. Although it is discouraged in the semen production industry, it may be used when all else fails. Usually the bull will produce a slightly less concentrated ejaculate and with the potential for a somewhat higher abnormal sperm count. However, with proper stimulus (rectal massage of the ampulla and seminal vesicles) adequate semen may be collected for processing. Massage of the pelvic genitalia alone usually does not produce adequate semen product for processing and is discouraged in the industry.