CHAPTER 97 Artificial Insemination in Swine: Boar Stud Management
Control of the introduction of pathogenic organisms into a boar stud operation cannot be overemphasized. Disease control not only is important for overall boar stud health and viability, but also is critical to minimizing the chance of disease transmission to other herds through the extended semen. Disease control consists of the following components: biosecurity, isolation, acclimatization, recovery, and monitoring.
Biosecurity should start with appropriate selection of stud and isolation site locations in order to physically assist in minimizing disease transmission between livestock facilities. Facility environment should be controlled to protect boars from the outside environment. Mandatory restrictions in the movement of animals, personnel, equipment, supplies, and sanitation protocols also are key components in a biosecurity program.
Selection of incoming boar source(s) should be dependent on health status equal to or better than that of the recipient boar stud group. Isolation procedures should be utilized on all boars before their introduction to the stud group to protect the recipient stud from the potential introduction of infectious agents that could cause economic distress. Isolation should be off site and away from any other pigs. Animal movement into and out of isolation should be handled in an all in–all out fashion. During isolation, boars should be monitored for signs of, or exposure to, disease through the strategic use of paired serologic tests and daily observation for coughing, sneezing, changes in consistency or amount of feces, decreased appetite or water consumption, skin lesions, lameness, or lethargy.
Acclimatization is used to prepare the replacement boars for the impending challenge of pathogens endemic to the recipient herd and to pathogens being controlled by the stud. Acclimatization starts immediately after isolation and consists of a controlled challenge to these select pathogens to stimulate but not overwhelm the immune system of the isolated boars. Exposure usually is provided through vaccination and direct exposure to young cull boars and their products. Clinical observation and serologic testing should be performed to confirm success of exposure.
The recovery phase is provided after acclimatization to allow the isolated boars time to build protective immunity to the controlled, exposed pathogens away from the resident herd. The recovery period also serves to reduce the risk of disease spread to the main stud from new boars still shedding pathogens. The length of time accorded to isolation, acclimatization, and recovery should be dictated by the pathogens that the boar stud operator is trying to control; in general, time periods range from 30 to 90 days.
Once the boar has been moved to the resident stud group, regular monitoring of the group should be performed. Monitoring is done through the use of serologic profiling (monthly or quarterly), daily observations of the resident boars, and temporal analysis of semen findings and stud production records.
Today’s boar stud facilities are designed to ensure animal well-being, personnel safety, and ease of movement and handling of boars. Alley width is limited, to allow a boar to freely move in the forward direction but not turn on the handler. To aid in moving the boar into and out of his stall, stalls usually incorporate both vertical entrance and exit gates. Pen partitions are of either solid or open panel design, with vertical bars on open panels to aid in deterring animals from climbing up the panel. For boar movement and cleaning ease, gates, partitions, and panels should be around 1.2 m in height, with a floor clearance of approximately 10 cm. To accommodate variation in boar size (due to their different ages and genetics), stalls of differing sizes usually are included within the same facility.
Nonslip flooring is used in the housing area. Both solid and slotted flooring, either alone or in combination, have been used in boar stud facilities. Solid flooring in the boar housing area requires the use of bedding (e.g., straw, wood shavings) to keep the area and animal dry. Slotted flooring, the most common type of flooring in modern swine facilities, incorporates space between cement slats that allows for the free passage of waste into a pit. Passage of urine and feces into a pit minimizes soiling of the animal and eliminates the need for bedding. From a hygienic standpoint, total slotted floors are preferable to either solid or a combined slotted/solid floor for housing boars.
Semen collection should be performed in a pen specifically designed for this task. Because personnel are operating close to the boar, the pen should be designed to allow multiple escape sites out of the pen if the boar becomes aggressive. Two or three of the perimeter walls should be constructed using a 5-cm-outer-diameter (OD) galvanized pipe. This pipe should be approximately 1 m in height and placed at 0.3-m intervals on center. The height and the space (approximately 0.25 m) between pipes should allow personnel to easily enter and exit the collection area without having to open or close gates but restrict the boar to the pen area. Collection pens should be 1.8 to 2.4 m in width and 2.4 to 2.75 m in length. A stable collection dummy (Fig. 97-1) should be placed in the collection pen. Added features of collection dummies may include capability for height adjustment and some type of support on the sides of the dummy that allow the boar to stabilize his front legs during mounting and thrusting. It is paramount that a nonslip surface be provided around the dummy so that the boar has secure footing during mounting and thrusting. It may be helpful to position the collection dummy in a corner of the pen or with one end against the wall so that the boar can easily be directed and maintained around the dummy. The pen and the collection dummy should be situated away from boars and other distractions that would divert the boar’s attention away from the collection dummy. Some stud operators design their facilities to include a pen—commonly called a “warm-up” pen—that is in close proximity to the semen collection pen. This pen is used to queue a boar so that he observes and hears the actions of another boar in the collection pen; these stimuli frequently help to excite the boar, so that when he is moved into the semen collection pen, reaction time to mount of the dummy sow is minimal, and semen collection can be accomplished more efficiently.
Traditionally, nutritional needs for boars were thought to be similar to those for gestating sows. The goal of these traditional programs was to provide boars with adequate caloric intake to meet their maintenance requirements, while minimizing weight gain. Under natural mating conditions, minimizing the weight gain of boars was critical to their length of usefulness in the herd, because gilts and sows have finite physical limitations on the amount of weight they can bear by the boar during the mating process. Once boars became too heavy, they were culled. This simple approach to defining boar feeding programs is still applicable for boars used under natural mating conditions. In today’s global swine industry, however, artificial insemination (AI) has taken over in many breeding programs. With this change, the traditional feeding strategy does not appear to meet the nutritional needs of an AI boar, for which productivity is measured through sperm production (i.e., number of extended semen doses/ejaculate) rather than servicing capabilities.
Much early work addressed the effects of restricted nutrient intake on boar reproductive performance. Restrictions or deficiencies in protein,1,2 energy,2 and certain vitamins and minerals3,4 have been shown to negatively affect boar reproductive performance. Conversely, overfeeding and excess body conditioning also can have a negative impact on boar reproduction. Ideally, adequate nutrition should be provided to active boars to meet their requirements for maintenance, growth, breeding activity, and sperm production. In general, feed intake is adequate in young (<16 months) boars if they show moderate (400 g/day) weight gains, and in mature boars if they show slight (200 g/day) weight gains. In practice, body condition scoring most often is used as an indicator of health and adequate feed intake. Depending on genetics and structural conformation, a body condition score of 3 to 3.5 (on a scale of 1 to 5) is a desirable target. To obtain a more objective assessment, backfat monitoring by means of B-mode ultrasonography also is being used to monitor boar body condition.
Feed constituents for boar diets vary widely and usually are dictated by local availability. Cost has become less important than with other swine diets because the boar ration is fed to only a small but valuable number of animals in a herd. A typical ration used in an AI boar stud operation contains approximately 3000 metabolizable energy (ME) kcal/kg, 16% to 18% crude protein (0.85% lysine), 4% fat, and 5% fiber.5 Generally, a boar will consume 1.5 to 3.0 kg of this ration on a daily basis. Daily allowances may be modified according to season and environmental conditions. Thermoneutrality for the boar is approximately 20° C.6 If temperatures fall below 20° C, the amount of feed provided to boars should be increased by 0.08 kg/day for every 1° C decrease. During periods of warmer ambient temperatures, it is not advisable to decrease feed amount, because this may lead to an unbalanced diet. Instead, energy density of the diet may be reduced to decrease body heat production but still maintain the ration’s balance. Nutritional supplements such as certain vitamins, minerals, and fatty acids have been advocated as aids for improving or maintaining boar semen quality and quantity under stressful environmental or nutritional conditions; further research is warranted.
On some farms it is not feasible to have a separate diet and storage area for the small number of AI boars housed on the property. To address this problem, supplements that contain high levels of certain nutrients are available that can be top-dressed onto feed used in gestation or lactation diets.
When the boar is introduced to the semen collection area, sufficient time should be allowed for the animal to investigate and become comfortable with the surroundings. Patience is required in training boars for semen collection using a mounting dummy. Prior exposure of naive boars to the semen collection process by allowing them to observe, in an adjacent pen, a boar having semen collected often can be helpful. After the boar identifies the stationary dummy, some animals will readily mount it and begin to thrust, whereas others may need to be gently directed toward the dummy. Once the boar shows interest in the dummy, he is quietly approached from the rear or side (behind the shoulder). During this time, sudden movements, loud noises, and moving into and out of the boar’s visual field should be avoided, to minimize the chance of startling the boar. To stimulate thrusting and exteriorization of the penis, the assistant gently reaches around and massages the boar’s prepuce. Once the penis is exteriorized, digital pressure is applied to the spiral-shaped glans penis. If properly stimulated, the boar will fully extend his penis. Once it is extended, thrusting will cease and ejaculation will commence.
Training periods should be limited to no more than a single 15-minute interval once daily. Daily training periods should be provided until semen collection is successful. After a successful event, reinforcement training of the semen collection process should be provided on at least 2 consecutive days before resting the boar or placement into a regular collection schedule.
Contamination should be minimized when semen is being collected for use in an AI breeding program7 (Box 97-1). Application of digital pressure to the penis using the gloved hand technique is the most popular method for collecting boar semen. Nonspermicidal gloves (e.g., vinyl, nitrile) should be used by the semen collector; some glove materials (e.g., latex) have been found to be spermicidal in this species.8 The semen collector should place two gloves on the collecting hand. After the boar has mounted the collection dummy and has commenced thrusting, the collector reaches underneath the boar and massages the sheath. Sheath massage will allow for evacuation of contaminant preputial fluids and aid in exteriorizing the penis. After the penis is exteriorized, the top glove is discarded. Holding the semen collection container (e.g., a prewarmed, insulated thermos or Styrofoam cup with a filter over the opening) in the free, ungloved hand, the collector then kneels down and grasps the boar’s corkscrew-shaped glans penis with the gloved hand. Constant pressure is applied to the glans penis with the fingers, so that the glans penis is “locked” in the hand; this grasp mimics the cervical lock that occurs during natural mating. Pressure applied elsewhere on the penis may elicit a negative response. If adequate pressure is applied, the boar will respond positively by fully extending his penis.
Data from Althouse GC, Kuster CE, Clark SG, et al: Field investigations of bacterial contaminants and their effects on extended porcine semen. Theriogenology 2000;53:1167–1176.