Читать книгу Bovine Reproduction - Группа авторов - Страница 135

Before attempting to electroejaculate a bull ensure that the electroejaculator is in good working order. Electrical cords and connections are most likely to be the cause if the electroejaculator unit is functioning and the probe is in place yet the bull is not responding to stimulation. Always turn the electroejaculator off before making even the slightest adjustments to trouble‐shoot electrical connections. A suddenly restored connection, even if the electrical intensity is relatively low, will unduly startle the bull. The rectal probe selected should be of sufficient diameter to enable full contact with the rectal mucosa, but not so large as to prevent its insertion. Usually, a probe with a diameter of 6.5–7.5 cm will suffice. Very large (>900 kg) or older animals may require a 9‐cm probe to ensure contact with the rectal mucosa [16]; 6‐ to 6.5‐cm yearling probes are available and are much easier to use on smaller bulls [17]. Bulls must be suitably restrained to prevent side–side and back–forth motion and should not be handled in such a way as to cause excitement. Overly excited animals tend to vocalize more during the procedure [18] and are more difficult to collect [16]. Cattle squeezes generally work very well for BBSE provided there is enough room for larger bulls to fit into them. Earlier models were designed mainly for use with cows and often are not long enough to accommodate a mature bull. A post, often referred to as a butt bar or kick post, placed horizontally across the chute immediately behind the bull will prevent the bull from moving backward or kicking the examiner. Ideally, the butt bar should be placed immediately behind the bull so that any kick action is softened, yet at a level that enables examination of the scrotum and testes. Modern hydraulic squeezes are the author's preferred system for examining bulls. Side–side pressure is infinitely variable and easy to apply, virtually eliminating any kicking. The side–side squeeze pressure and squeeze pressure on the neck must be relaxed prior to beginning the EEJ process. Failure to obtain a semen sample, bulls lying down in the chute, and poor quality ejaculates have all been caused by excessive squeeze pressure. Giving bulls room to move and to get their feet placed under them will go a long way toward shortening the duration of the EEJ procedure and yielding good quality samples.

A per rectum examination of the bull's ampullae, seminal vesicles, prostate, pelvic urethra, and inguinal rings should be conducted accompanied by a thorough clean‐out of feces from the rectum. Massage of the pelvic urethra and accessory sex organs lasting 30–60 seconds will provide sexual simulation for the bull and relaxation of the anal sphincter to enable insertion of the probe. An elbow to wrist, back and forth rectal massage with immediate insertion of the probe following arm removal works best, coupled with the smallest probe that is still effective for the size of bull being collected. The smaller yearling probes have proven effective in at least 9 out of 10 mature bulls when matched with well‐designed, late‐model electroejaculators. Lubrication of the probe with palpation sleeve lube or even water will facilitate insertion and enhance contact with the rectal mucosa [16].

Electroejaculators available today are similar in function with features that appeal to a variety of users. Advances in electrical circuitry and battery technology have been adopted by manufacturers, resulting in enhanced portability without the need for a constant electrical supply. Machines available today may be used to electroejaculate over 100 bulls on a single charge (Bob Green, Lane Manufacturing Inc., personal communication). A significant innovation has been preprogrammed, automated EEJ sequences that increase electrical voltage in a step‐wise fashion, bridging the gap between the art and science of collecting a bull. Manual control of voltage intensity is still available via a rheostat knob and step‐wise control buttons, allowing the operator to use the machine according to personal preferences. Experience is a great teacher when collecting semen from bulls using EEJ. Effective stimulation sequences vary with the breed, age, size, temperament, handling system, weather, and individual animal. For the novice a great deal can be learned by using the preprogrammed sequences, then try to emulate a sequence using the manual controls. Learn to watch the response of the bull not the indicator systems on the machine. The initial application of electrical stimulation must be applied carefully while observing the response of the bull. The operator should increase the electrical intensity just enough to cause a slight contraction of the muscles of the hind limb. Thereafter, with each successive stimulation the intensity of the voltage should be increased slightly and should last 1–2 seconds followed by ½−1 second of rest until erection, then ejaculation occurs [12, 16]. Some bulls are more difficult to collect than others for a variety of reasons. Common problems are inadequate contact between the probe and the rectal mucosa (excess feces, small probe, or a buildup of dried mucus or lube on the electrodes); insufficient voltage; bulls that have been recently used for breeding [16]; and excessive squeezing pressure on the neck or sides of the bull. Even when these potential problems are addressed, EEJ may still be unsuccessful with a small number of normal, fertile bulls.

Semen collection handles are useful for safely extending the operator's reach to obtain a sample. Disposable, single‐use, funnel‐shaped collection cones have largely replaced reusable latex rubber cones and are designed so that the wide end can be spread open inside the cylinder of the collection handle and held in place with a rubber ring on the outside of the cylinder. Commercially available semen vials or a urinalysis tube can be passed, bottom end first, through the collection cones and pulled snuggly through the smaller opening to make a tight seal near the opening of the vial (Figure 9.2). Bovine semen is sensitive to chilling, with the most noticeable effect being a rapid decline in sperm motility. Vials and collection cones should be kept in a warming area and only brought out just prior to use. Spare vials can be kept warm in a chest pocket or on a microscope warming stage. Warming jackets containing water can be fashioned from plastic bottles and attached to the collection handle using adhesive tape. Styrofoam coffee cups can also work well as a collection vial, with their insulating capability being an additional benefit when ambient temperatures are cool.

Figure 9.2 Semen collection handle, cone, and vial.

Numerous anesthetic protocols have been employed to evaluate and potentially reduce potential pain or anxiety associated with EEJ, but none of them can be considered to be viable alternatives to conventional EEJ. Caudal epidural anesthesia with 2% lidocaine appeared to be just as effective as conventional EEJ with lesser elevations in cortisol, but did not significantly affect heart rate change [13, 19]. The benefits did not appear to justify the time and effort expended administering the epidural. Xylazine, administered in an epidural or intravenously was effective for reducing pain, but because of associated ataxia and recumbency its use is not practical [12]. Intrarectal lidocaine reduced intrarectal smooth muscle contractions, but its effect is only superficial as heart rate change remained unchanged compared to conventional EEJ [3]. Although not all studies agree, the majority have shown that EEJ can be mildly painful [12] and stressful to bulls; however, heightened awareness and improvements in probe and electroejaculator technology coupled with careful, conscientious use have substantially decreased these concerns.

A mainstay in bull studs, the AV and a mount animal are very useful for collecting semen from trained animals, but are not practical for use with most beef bulls used for pasture breeding. Phantom cows, similar in design to the phantoms used for stallions, complete with an AV mounted within the frame were tested with untrained beef bulls. Not even the application of estrus cow urine sprinkled on the hides that covered the phantoms would entice the bulls to mount and serve [12]. Serving capacity tests are used to evaluate libido and the ability to mount and complete service [20–22]. These tests are conducted by introducing one or more bulls into a pen containing at least one cow restrained in stocks. Having cows in estrus may increase the sexual interest of some bulls [20]; however, willingness to stand to be mounted is a major cue used by breeding bulls that the female is ready to be mated. Therefore because they are restrained the cows used in these tests do not need to be in estrus. Although serving capacity tests are not considered to be reflective of true breeding behavior in juvenile bulls, most mature bulls will express sexual interest in and mount a restrained cow [20].

Early attempts to modify the serving capacity test to enable the collection of semen involved having a person deflect the bull's penis away from the cow and into an AV. Most untrained bulls were unwilling to mount with a person standing close by, so attempts were made to conceal the operator behind drapes while the bull mounted and semen was collected [12]. High libido bulls were undeterred by this system, but medium to low libido bulls seemed to be distracted by the drapes or the presence of humans behind the drapes and refused to serve. [12]. The next modification was to design an AV that could be fitted inside the cow's vagina, called the internal artificial vagina (IAV). The IAV consisted of a wire frame supporting a 7.5‐cm length of rubber tubing with a plastic specimen bag attached to the end placed closest to the cervix [23]. Once the bull had mounted the cow and completed service the IAV could be quickly removed and the semen sample recovered. Over a two‐year period, the IAV was compared to EEJ as a method of collecting semen from 165 range bulls. Fifty four and seventy percent of the bulls served the IAV in years one and two, respectively versus a 100% success rate when EEJ was used. Five percent of the bulls were found to be unable to serve cows due to physical abnormalities. Bulls that were unwilling to serve the IAV in year 2 were given a second opportunity, but the result remained the same. Over the subsequent breeding season, the breeding behavior of 15 of the bulls that did not serve the IAV was compared with 15 that did. Most of the bulls that would not serve the IAV were observed breeding cows but mounted less frequently than their counterparts [23]. The IAV proved useful for identifying bulls with physical abnormalities but was not a viable substitute for EEJ. Other concerns included the spread of venereal disease and the welfare of the restrained mount animals [12].

Transrectal massage of the seminal vesicles, ampullae, and pelvic urethra has been used as a method of obtaining a semen sample but is not as reliable as EEJ. In one experiment, TM was shown to be nearly as effective as EEJ for obtaining a semen sample [24], but the percentages of motile and live sperm were less than those of EEJ samples. This was attributed to the tendency of massaged bulls to dribble semen slowly, thereby exposing the sperm to cool temperatures for a longer period of time [24]. Two more experiments were conducted comparing TM with EEJ in infrequently handled, mature breeding bulls (range bulls) and yearling bulls. In an attempt to prevent chilling of the sperm, semen collection tubes were suspended in a 37 °C water jacket during the collection. Despite this effort, fewer motile and live sperm were recovered from TM samples in the range bulls, but there was no difference in percentages of motile sperm in the yearling bulls [25]. These differences were attributed to lack of penile protrusion during semen collection with TM – a problem that was particularly evident with the range bulls [25]. The differences in live and motile sperm percentages were not large, but these authors cautioned that poor semen sample quality and an inability to examine the penis could jeopardize the quality of a BBSE [25]. Transrectal massage of the seminal vesicles and ampullae can be useful following an unsuccessful attempt to electroejaculate a bull. In these cases, the maximum voltage has been reached but only preseminal fluid has been emitted. One useful trick is to rest the bull for at least 30 seconds and restart the collection at a much lower setting. If this quick fix fails, then the probe can be removed and TM may be effective.

Aspiration of semen from the vagina of a recently bred female is a last resort method of obtaining a sample as it is time consuming and requires a female in estrus that must be restrained to allow a sample to be obtained. A syringe and infusion pipette will facilitate the collection of mucus and semen from the anterior vagina.