Introducing Breeding Stock into the Swine Herd

Dr. Micheal Sheridan Sheridan and Heuser Steinbach, Manitoba

The introduction of genetic material into a swine herd can have many implications for the health and productivity of the unit. Disease introduction is a primary concern. Destabilization of an existing health status without changing the disease profile is another. Finally, the impact of health problems in newly arrived animals, on their long term productivity and longevity in the herd must also be considered. This paper will focus on some of these concerns, and review changes in the methods used to introduce new animals to swine units.

There are many biosecurity procedures employed on swine farms to prevent disease introduction via vectors such as people, vehicles, or equipment. Live animals continue to represent the greatest risk as a source of disease however. Key practices such as purchasing stock from herds with intense biosecurity and health monitoring systems, single source purchases and well researched source changes will help protect the recipient herd. Disease can still be transferred unexpectedly though, if animals are incubating an early infection, but showing no signs of disease, or if they are carriers of an infection that is subclinical, and undetected in the source herd.

Disease patterns are changing in Western Canada, with diseases like Porcine Reproductive and Respiratory Syndrome (PRRS) or Transmissible Gastroenteritis (T.G.E.) spreading through regions and infecting even highly monitored seedstock herds.

There has also been a well publicized increase in swine operations in some areas, such that some seedstock herds have become compromised by new neighbours due to the potential for direct aerosol disease transmission to their herds. As regions become more densely populated with swine farms, area spread of disease through regions, though not fully understood, also impacts on previously isolated farms.

There have been two key changes implemented in the transfer of genetic material that have helped to reduce potential disease transfer. Artificial insemination allows the wider use of varied genetic material in a much safer manner than live boar inputs from several sources. Isolation units, used for live animal inputs, are becoming more important to protect farms from unexpected health changes in supply herds, or from contamination during transport.

An isolation unit is a facility, completely separated from the main barn, into which newly purchased breeding stock is placed for a period long enough to ensure they are not carrying specific diseases that would be damaging to the recipient herd. The duration of their isolation will be determined by the health status of the recipient herd, and by the incubation periods of the diseases of concern.

Isolation units are best located as far from the main barn as possible, without putting animals in the unit at risk from disease aerosols from neighbouring farms. The location must be manageable with respect to labour. For most farms, it will be a building detached from and located a minimum of 100 metres down wind of the main barn. Although a shower in and out policy is best, a clothing and footwear change and hand wash prior to entry is sufficient for most farms. Ideally, the barn would be serviced at the end of the day, and the caretakers involved would not re-enter the main barn that same day.

Isolation barns allow the purchaser time to ensure:

  • no new diseases have been detected on the source farm after purchase
  • no suspicious clinical signs of disease have occurred during the isolation period
  • any tests for disease detection can be delayed long enough to identify emerging infections

Table 1: Time to Detection Following Infection




7 – 14 days


7 – 14 days


varies with strain – 30 days

Mycoplasma hyopneumoniae

60 days or more

It is imperative that the isolation barn be run "all in all out" to avoid cross contamination of different groups. This poses a significant constraint on the flow of animals into the main herd, especially with long isolation periods, e.g. Mycoplasma hyopneumoniae. With a single isolation facility, new animals would be purchased every three months. Seedstock suppliers must be willing to supply a wide range of animal weights to accommodate the purchaser’s needs at the completion of the isolation period. The main herd must also be able to accommodate this large group of animals to allow for depopulation and refill of the isolation barn. Two or more isolation units would facilitate the flow of animals into the unit if protracted isolation periods are required.

Once animals are released from isolation, the next challenge is to acclimatize them to the health status of the recipient herd. Traditionally, breeding animals were delivered directly to the receiving herd and immediately exposed to all of the various infectious agents present. As long as the source herd and recipient herd have a similar health status, this method would have minimal impact.

There have been some significant changes in the industry over time which have made this introduction process more difficult:

  • Seedstock production units, which handle intermittent new populations of small to medium sized herds, are now faced with more frequent requests for larger populations, beyond the limits of their supply. These larger herds are forced to populate from two or more sources, resulting in the potential for a different combined health status than the supply herds. Future replacements from either of the original sources may not adapt well to this combined health status.
  • Seedstock herds are changing animal flow patterns. Traditionally seedstock suppliers were continuous flow, single site farrow to finish units. Animals sold had a consistent, predictable health status and stable immunity to that health status. As these units grow larger, flows change to multi-room or even multi-site grow out units. This has altered the general immunity of the animals sold and, more importantly, the predictability of that immunity has been compromised. These animals may become susceptible to infections that previously posed no risk.
  • Commercial herds are expanding, while changing their own flow patterns. Large influxes of young gilts and boars into previously stable herds can severely disrupt the health state not only of the incoming animals, but that of the original herd, which is now faced with a large number of sick, actively shedding animals.
  • As regions become more intensely populated with swine barns, diseases will spread through the herds in that area, changing the diseases that new arrivals must adapt to.
  • Disease prevention is also important as it relates to animal welfare and minimizing animal discomfort.
  • Newly arriving animals will eventually exit to the human food chain. By preventing disease in new arrivals we reduce the need for treatments within herds, thus reducing the risk of medication residues.

Unlike isolation, where an attempt is made to ensure specific diseases are not present, acclimatization represents the controlled exposure of new animals to the infectious agents on the farm. This can be done by natural exposure using pigs from specific areas of the recipient herd known to be shedding the infectious agents to which immunity is required. These animals must then be housed in close proximity to ensure adequate exposure of the new arrivals.

The acclimatization area should provide a separate air space within the barn. The animals received should be allowed a couple of weeks to rest after delivery and to adjust to the new feed and water, before seeder animals are placed. This form of immunization is unpredictable, and may not uniformly protect contact animals.

The use of vaccine is far more common for immunization against specific diseases. If used correctly, this can be a highly effective and more accurate means of immunization. The key to the success is knowing what diseases must be protected against, and using the correct vaccine in a proper and timely fashion. To be effective, the vaccination must occur far enough in advance of exposure to impart protection. It is important to note that not all vaccines will stimulate protection against their specific disease at the same rate. It must also be remembered that vaccines must not only protect against a specific disease, but also specific strains, e.g. Streptococcus suis, and Haemophilus parasuis. Killed vaccines require two doses fourteen to twenty-one days apart, and may take thirty to forty days to stimulate active protection. Exposure to the disease must then be delayed long enough for this protection to develop, or sickness will occur. Vaccines for diseases such as Mycoplasma Pneumonia, Glasser’s , and Strep. Suis are examples of killed products. PRRS vaccines at this time are live products, so single injection is sufficient if done correctly. Protective immunity still takes approximately thirty days to develop.

If adequate space and time are available, then on farm vaccination after arrival ensures the best results. In many cases, only a couple of weeks are available before exposure occurs, in which case, the suppliers may have to inject one or both doses of a vaccine to ensure protection. The recipient herd veterinarian, in conjunction with the supplier’s veterinarian can help work out the best immunization protocols for both parties.

It should be noted that isolation and acclimatization can be combined, when animals are held for prolonged periods before entry. This not only enhances the value of the isolation period, but more effectively ensures that larger groups entering the herd will not disrupt herd immunity and health stability.

The development and implementation of isolation and acclimatization programs for new breeding animals arriving on farm will become increasingly important. Proper strategies will enhance not only herd health stability, but also will help maximize the lifetime productivity of breeding stock. Though costly from an investment perspective, isolation is relatively straightforward and easy to understand from a technical perspective. Acclimatization, on the other hand, is a much more complex and perhaps more technically challenging concept. There is considerable information available on the housing, nutritional and development needs of the gilt which can be readily adapted as part of acclimatization procedures. There is, unfortunately, little information dealing with acclimatization and development of the boar. All to often the new boar is all but ignored until there are problems with libido or fertility. Management of the young boar through the isolation period is crucial to the animal’s future productivity and longevity. Many problems can arise at this early developmental phase of the breeding boar.

Figure 1: Libido vs Fertility

In order to understand some of the potential problems, a review of boar behaviour and reproduction is useful. As a young boar approaches sexual maturity, it’s physical, behavioural, and reproductive traits develop under the control of the region of the brain called the hypothalamus. The hypothalamus, through it’s action on the pituitary gland, causes the release of hormones that stimulate various reproductive organs to mature and create their own secondary effects. Two key functions, libido and sperm production, are under two different control mechanisms. It is a common misconception that libido and fertility are related, especially in the young boar. It is not uncommon for young boars to display a very active libido and aggressive mating behaviour. As Figure 1 demonstrates however, sperm maturation and thus fertility may lag significantly behind libido. It is important then that young boars be given time to develop fully, before being relied on to effectively mate gilts. Provision of a suitable training period whereby a boar learns it’s role without expectations of producing litters is important. This can be a difficult approach in start up populations where the pressure to start producing is intense. This likely explains the poor performance in the first few months of a start up population if boars have not been placed weeks before gilts arrive, or initial matings have not been delayed.

Training of young boar's must follow a planned program. Allowing one mating per week, in a pen with excellent footing, with a gilt in rigid standing heat, will enhance the development of proper mating behaviour. In this critcal development period, the prevention of injury, slippage, aggression by the gilt to be bred or rough handling by thr herdsman is imperative. Remember that reproductive behaviour is ultmately controlled by the brain, and traumma canhave a long term or even permanent impact on libido.

As boars mature, their semen volume and quality will improve. Between seven and nine months of age boar's should be allowed to breed once a per week.As the animal matures and the semen volume and quality increases, frequency of mating per week can be increase:

7 - 10 months 1 mating per week
9 - 12 months 2 matings per week
12 - 18 months 3 - 4 matings per week
over 18 months 5 - 6 matings per week

Overuse of boar' will result in decreased fertility. Figure 2 illustrates a cross section of a testicle. The sperm cells are produced in the seminiferous tubules, where they mature for approximatly 35 days. New cells are stimulated to begin to mature every few days, so semen production is an ongoing process with cells at various stages of development. It takes approximately 35 days for the sperm cells to develop within the testicle. During this time they are very susceptible to heat stress, and can be damaged by high environmental temperature and fever. Once they have completed their development in the testicle, the sperm cells transported to the epididymis, where they travel from the head, through the body and end up in the tail of the epididymis. Durinng this process the sperm cells mature further, and only become fertile in the tail portion, where they are stored untill the mating process. During transit through the epididymis the sperm cells are less susceptible to heat stress.

Illustrates a Cross Section of a Testicle

Heat Stress Effect on Fertility

The frequency of mating impacts on fertility, due to storage capacity and maturity of the sperm cells present in the tail of the epididymis. If boars are over used, immature sperm cells will be drawn from the body of the epididymis, thus reducing fertility. It will be necessary to rest the boar before fertility returns. The key is to under stand that two weeks rest is necessary, since sperm cells that would have been mature next week are gone.

Heat stress on boars can hav e a dramitic and long lasting impact on fertility. At the time of heat stress due to high environmental temperature or fever, sperm cells in the epidiymis are relatively resistant to damage. Any Impact from heat stress will not be reflected in semem quality for two or three weeks, until sperm cells present in the testicle at the time of the insult reach the tail of the epididymis. After that, there will be at least five to six weeks before normal sperm reappear, and fertility rebounds to normal. Figure 3 graphically illustrates a typical response to heat stress.

Any time your boar gets sick:, it is imperative that it's body temperature be monitored. Treatment to control fever is advised when rectal temperature rises above 40°C. Your veterinarian can review medication options for the treatment of fever in boars.

Hot weather, particularly early in the spring or summer, before boar's have acclimatizing the to heat, can be as damaging as fever. Close observation for signs of heat stress such as panting is key; adjustments to ventilation along with the use of drip coolers or misters must be prompt.

Attention to boar husbandry is offten overlooked. proper care and attention must begin at the time of or even pre-purchase while acclimatization and intoduction procedures are being planned. Ideally the boar' will be in the herd approximately twenty-four to thirty months and every effort must made to ensure it's comfort, health and safety.

Boar houseing :

  • clean dry draft free environment
  • individual pen
  • ensure adequate water nipple position and flow
  • full feed on arrival, ration levels adjusted to condition, size, and activity level
  • boar ration versus lactation or gestation
  • vaccination – same as gilts and sows – Parvo, Lepto, Erysipelas
  • parasite control – quarterly deworming; mange free

Take time when new boars arrive to socialize it to humans and other pigs. Remember that the relationship established will last two to two and a half years or more. Always respect boars, and never trust them regardless of their temperament. Boars with tusks can cut a your leg in seconds; the healing can take months.

Recommendations for boar longevity:

  • acclimatize well
  • keep vaccinations current
  • prevent injuries from pens, flooring, fighting
  • treat injuries promptly, particularly those of feet and legs
  • use foot boards (copper sulfate solution on carpet covered board)
  • trim tusks semi-annually
  • always protect yourself against potential injury
  • use "Slapshots" ® when injecting
  • use safety boards when handling boars
  • take prompt action whenever boars appear sick

Boars contribute significantly to sow herd fertility and productivity, and proper handling and development is important. The role of boars on farms is changing. Artificial Insemination (AI) is replacing natural matings at an ever increasing rate. Boars are becoming more valued for their estrus stimulation and detection roles than for their fertility per se. As more AI is used, the behavioural development of boars on farm will become more critical. In the interim, AI studs, both on farm and as stand alone businesses, will need to focus on boar development and boar management. It is evident from the problems encountered in these units, that more research into the nutritional, social and health needs of the boar is needed.