Читать книгу Bovine Reproduction - Группа авторов - Страница 134

Evaluating semen quality is an integral part of a BBSE. Electroejaculation (EEJ) has been a reliable method of obtaining a semen sample for many years. Alternatives to EEJ include using an artificial vagina (AV), transrectal massage (TM) of the accessory sex glands, and aspiration of semen from the vagina of a cow following a recent natural service. Compared to these other techniques, EEJ is fast and efficient, eliminating the need for mount animals, animal training, and specialized laboratory and animal handling equipment. Nearly anyone can be trained to use an electroejaculator, and in recent years automated machines that use a preprogrammed series of electrical stimulation have been developed, enabling even the most inexperienced individual to operate with confidence. The one significant disadvantage of EEJ, however, is the widely held misperception that it is painful. Due to this its use has been forbidden in several countries. [3]

In the USA, EEJ is still widely used to collect semen from bulls for presale or prebreeding breeding soundness evaluations, but as is the case with many other previously accepted management practices, the potential discomfort of animals enduring these procedures is being increasingly scrutinized. At the core of the problem has been lack of widely disseminated critical knowledge to determine if EEJ is painful and to quantify the intensity of the pain. Certainly it was known that EEJ without anesthesia was painful for humans [4, 5]; therefore it must also be painful for bulls [3]. (Editor's note: see also [6].)

The first published report on the use of EEJ in domestic animals was in 1936 [7–9]. Rams were the first animals experimented with, and although attempts to electroejaculate most species of animals have been made, the technique has been most successful with rams and bulls [9]. Electroejaculators are designed to use AC or DC power and consist of a box containing a step‐down transformer to reduce the source current and a variable transformer to enable the electrical stimulation to be modified [10]. Electrical stimulation must be carried to the pelvic nerves; specifically, the pudendal nerve, located near the prostate over the pelvic urethra responsible for erection; and the hemorrhoidal nerves, located in the area of the ampullae and seminal vesicles responsible for ejaculation [9]. To accomplish this task, a solid rectal probe at least 30 cm long and at least 6 cm in diameter containing bipolar electrodes is used. Rectal probes on early models consisted of alternating, bipolar electrode strips or rings capable of providing electrical stimulation over their entire circumference. This design resulted in unnecessary stimulation of the muscles of the hindquarters reportedly causing undue discomfort and temporary paralysis in some animals [11]. This led to the development of finger‐electrodes in which bipolar rings were fitted to the index and middle fingers in such a way as to avoid them coming in contact with each other. This device enabled the operator to apply electrical stimulation specifically to the urethral muscles to cause erection, followed by stimulation of the seminal vesicles to achieve ejaculation [11]. A disadvantage of the finger‐electrode system was that two persons were needed to coordinate semen collection because the principal operator was unable to see if erection had occurred and when stimulation should be moved to the seminal vesicles [9].

Most probes in use today have three longitudinal electrodes. Probes with the electrodes divided into three segments have also been developed and are referred to as segmented probes. There are three caudal electrodes, three middle and two at the cranial end, and each segment can be activated as needed. Much like the finger‐electrodes, the intent of this probe design is to enable stimulation of specific areas with minimal stimulation of non‐target tissue [12]. The caudal segment is used to achieve erection and then the middle segment is used to achieve ejaculation. In some bulls, the activation of the cranial segment may be required to cause ejaculation [12]. The segmented probe is no longer popular due, at least in part, to its being complicated to use. In comparison with a conventional rectal probe it was shown that it was much easier to obtain full penile protrusion using the conventional probe, but ultimately both probe types were equally effective for obtaining semen emission. In a study comparing the pain response associated with the use of a conventional three‐electrode probe and the segmented probe for an equal number of stimulations, and with the segments activated according to the operator’s manual, no differences in cortisol or progesterone release were detected [13]. Weighted probes and probes with two longitudinal electrodes are now available. The intent of these design changes is to target the appropriate nerves with as little stimulation of surrounding tissue as possible. No critical studies have been done comparing weighted and two‐electrode probes to conventional (three‐electrode, no additional weight) probes; however, the clinical impressions of the author are that they are at least as effective as conventional probes yet appear to be more comfortable for the bull.

Electroejaculator probes are inserted into the rectum with the electrodes oriented ventrally and rotation of the probe is prevented by a U‐shaped tail cradle or yoke. The tail cradle helps to maintain the probe in the rectum, properly oriented with the electrodes down. Until the sequence of electrical stimulation is begun it is a good idea to hold the probe in place simply by pressing the tail into its relaxed position. Horizontal or vertically (upright) oriented yokes are available. Damage to the electrical cord connecting the probe to the electroejaculator is less likely with the upright yoke in the event that bull lies down during the collection procedure, whereas horizontal yokes invariably catch on the butt bar often at the electrical connection. Upright yokes are also easy to grasp, facilitating probe extraction. Figure 9.1 shows a Lane Pulsator V and the two‐electrode probe with upright yoke.

Figure 9.1 Lane Pulsator V and two‐electrode probe with vertical yoke.

Source: Courtesy of Lane Manufacturing, Inc.

Modern electroejaculators use a sine‐wave pulse at a frequency of 20–30 cycles per second [14, 15]. Other wave forms and frequencies have been tried but have been proven less effective [14]. The maximum voltage of a very common electroejaculator in use today, the Lane Pulsator IV (Lane Manufacturing, Denver, CO, USA), is 16 with a maximum current of 900 mA [12]. With this machine, ejaculation occurs with electrical impulses less than 8 or 9 V [12]; however, some bulls, usually older bulls, may require more electrical intensity to elicit ejaculation.