Investing time and talent in developing effective heat detection methods should be a top priority on every sow farm. Gilt development aside, this activity drives the flow throughout the pork production system.

The pork industry is in dire need of stockmanship skills that will enhance heat detection and mating in the breeding herd. Conception rates of 75-85% are common, but rates of 90% or greater are ideal and achievable.

Granted, herd health, semen quality, housing, season, genetics, nutrition and body condition play a role. However, more often than not, it's the heat detection and breeding processes that lack quality control.

One reason many farms struggle with sow retention can be traced to a poor ability to detect and document estrus and complete successful mating. Too often, poor quality heat detection, stimulation and mating are reflected in the breeding herd records as reproductive failures, pregnancy check negative or low number born alive. Sows not accurately detected in estrus, and subsequently inseminated, are subject to a reduced farrowing rate and litter size.

Fortunately, this situation is correctable, and most likely a function of management capabilities, not a function of the pigs.

Sow Farm Example

Using a 1,200-sow farm example with a 5% farrowing rate improvement — which is easily achievable via higher quality heat detection and effective mating — results in a $34,200 annual savings (based on $1.50/non-productive day). By incorporating multiple controls, a difference of 10% (improving from 80% to 90%) would equate to an annual savings of $66,600.

The 1,200-sow farm requires a weekly average of 1-½ hours of heat detection and mating labor/day, creating a labor cost of $6,576 ($12/hr). If the additional caretaker time can produce a farrowing rate increase of 5%, the investment nets $27,624 ($34,200 annual savings minus $6,576 labor cost = $27,624).

To gain a better understanding of how to improve farrowing rate and sow retention through improved heat detection and mating, let's review the boar and female activities in the natural mating environment and rediscover what we are trying to emulate.

The Female

In the natural mating process, the gilt entering estrus may exhibit various signs of proestrus, the period immediately before estrus: redness and swelling of the vulva, off-feed, rooting or mounting penmates, vocalization, etc. The display of estrus is the result of hormonal activity associated with ovulation, which produces a period of sexual receptivity, or heat.

Upon standing heat, the female should have further signs consisting of erect or “perked” ears and a moist vulva, and exhibit a standing reflex or be “locked up” as a response to stimulation. The intense standing reflex is a result of the release of oxytocin, which causes surging contractions of the uterus and strong muscle rigidity.

The release of oxytocin generally lasts for 10-12 minutes. After this time, the rigidity of the standing response wanes. Estrus display typically lasts no more than 48 hours in gilts and 38-61 hours in sows. The minimal duration is 8 hours.

Sows returning to estrus three days after weaning will generally stand longer than those entering estrus later. Ovulation will occur from 36 to 42 hours after the onset of estrus.

The optimum time for insemination is within 24 hours prior to ovulation, or 2-24 hours after the first onset of estrus. While sows generally ovulate during the last half of their estrous period, gilts ovulate sooner. This implies that gilts should be mated immediately following detection of estrus, then 12 and 24 hours later, if still in standing heat.

The period of standing estrus is a basis for the timing of insemination. The timing of breeding in relation to ovulation affects both conception rate and litter size. Many factors (age/parity, season, body condition, feeding) affect the expression and length of estrus.

In a study of 55 farms, the average duration of estrus per farm ranged from 31 to 64 hours.

Thorough examination of return-to-estrus data in the reproductive records can identify weaknesses in the timing of insemination and post-breed heat checks, and help identify periods where heat detection is needed. These periods are commonly around the times gilts arrive or are exposed to boars, 21 and 42 days post-arrival, 3-8 days postweaning, and 21 and 42 days postmating.

In a system with optimal management, where the previous estrus date has been recorded, the date of the next estrus is also known. Boar exposure should start three days prior to Day 21 of the estrous cycle.

Ideally, estrus is detected twice daily in an attempt to accurately identify onset. The estrus detections should be performed 8 to 12 hours apart. Females should be segregated from boar contact for a minimum of one hour prior to estrus detection.

The heat check and response pattern of gilts, weaned sows, recycling sows and opportunity sows are different.

Opportunity or marginal sows are those that did not return to estrus after weaning, pregnancy checked negative or had a noticeable abortion, etc. These sows are finicky and may have reproductive tract damage or other diseases; although they may exhibit some behavioral indications of heat, they are often difficult to engage in firm, standing heat. Records have shown that these sows have a lower pregnancy rate. Best recommendations are to engage these sows in direct contact with boars and hand-mate or artificially inseminate (AI) immediately following signs of heat.

The most important heat check is not in preparation for breeding, but rather to detect the first and second estrus in the gilt pool. The gilt pool should be checked thoroughly once and preferably twice/day. In warm climates, this must be done in the morning hours. In the natural mating environment, more than 80% of matings will occur between 2 a.m. and 11 a.m.

Depending on selection criteria and the gilt development process, up to 10% of all gilts generally fail to show heat. Some don't cycle at all, while others cycle but may not show behavioral signs of estrus. This is often referred to as “blind heat.” Administration of PG600 or Matrix regimes (Intervet) can reduce the occurrence of blind heats as well as manage timing of the estrous cycle.

The Boar

In a natural mating environment, the boar is allowed free access to the female to perform stimulation and mating. With the advent of AI, larger facilities and biosecurity protocols, boar entry to the farm is minimized. Feed and housing costs and worker safety issues also decrease incentives to have supplement-ary boars on the farm.

So why are good teaser boars necessary? The boar's role first includes looking like and smelling like a boar. Their odor is a result of pheromones emitted by chomping and secreting saliva, carrier of the pheromone.

As the boar investigates the female, he noses her (nose-to-nose, nose-to-side and nose-to-vulva) in a noticeable pattern. Rooting, shoving and lifting by the boar occurs around the female with special emphasis in the flank. The androstenol pheromone triggers the female's release of oxytocin, resulting in surging contractions of the uterus and the intense standing period. Mounting attempts occur to test the standing response, and successful mounting and mating of the female ensue.

Combining individual elements of boar-associated stimuli (sight, sound, smell, touch) increases the number of females showing a standing response. Standing estrus will generally last longer at higher stimulus levels.

Each boar will have his own unique courting habits of stimulation, mounting and breeding. What makes a good boar can also make for a difficult boar. Aggressiveness and unpredictability often come with the high libido trait. Always respect the boar.

It is very critical that good heat- check boars are properly trained and are periodically allowed to mount and breed. If not vasectomized, they should be assisted in completing a natural service, possibly using cull sows. This will prevent boars from losing interest in females, maintain libido and reduce sexual frustration.

An Australian study reported a correlation between conception rate and the number of times the boar nosed the sides of the female per mating. The higher the level of boar stimuli that occurs during estrous detection, the greater is the chance of evoking a standing response.

A good teaser boar maintains the right size, weight, attitude and odor, and attracts sows. He is also one that trusts the caretaker and the caretaker trusts him. Good boars will also return to their respective quarters without a struggle.

There is tremendous variability in heat check performance, libido and associated characteristics of boars. Studies indicate that crossbred boars complete matings and require less time to mount than purebreds. This would indicate that crossbred boars tend to make better teaser boars by maintaining a higher libido.

From experience, the Chinese Meishan and Meishan hybrid boars tend to make good heat-detection boars due to their manageable weight and disposition and their capacity to “stink.” The effect of the saliva-bound pheromone and associated odor cannot be underestimated. In addition to stimulating standing heat, odor enhances oxytocin release and sperm transport within the uterus.

Type of Heat-Check Boar

Which is better for heat checking — a viable intact boar or a vasectomized boar?

What about the mechanized boar carts, tethers, aerosols, or no boar at all?

The manner of stimulating the standing heat response matters little across production systems. Appropriate schemes must be determined within the given farm. The sows' response greatly depends on their previous experiences with boar-associated stimuli. While no detection system will out-perform a team of active, rank boars, when properly implemented, many can deliver very similar success rates and will effectively meet farm production and financial goals as well as ease stockperson duties. The most important component is the stockperson's ability to observe and control timing of exposure and properly record the heat or breeding activity.

Any of these tools that inhibit the ability of the stockperson to effectively monitor standing responses and other signs of estrus, or interfere with the timing or duration of exposure, should be closely evaluated. Obviously, individual boar behavior and some barn designs limit utilization of the boar cart, tether or related devices. Allowing nose-to-nose contact is essential.

If heat-check boars don't smell, are reluctant or have low libido, there are options. They may be sprayed with aerosol boar odor or wiped with a stink stick. The stink stick, designed by Bruce Livingston, State Line Swine of Mahaska, KS, is created from rags attached to a 1-in. PVC pipe, recharged once or twice daily with saliva, preputial fluids and a small amount of urine from other boars.

Another option would be to have brief fenceline contact with a rival boar, which might create the necessary aggression and subsequent chomping and saliva production. Stockpersons must exercise caution and utilize only trustworthy boars for this activity.

Group Housing Challenges

For group housing situations, competition for the boar's attention can create struggles in heat detection. First, young boars or low-libido boars can become overwhelmed by sows and lose ambition to seek out estrus sows. These boars may even be ruined by continual exposure to overly aggressive sows.

To ensure coverage, a good guideline for heat checking group-housed females is a maximum 15:1 female-to-boar ratio. Second, in large sow groups, it becomes difficult for the stockperson to follow the boar and observe estrus sows that may be obscured by other non-cycling sows.

Effective methods of heat detection for group-housed sows involve monitoring the use of vasectomized boars working within the pen. Females should receive 15 minutes of boar exposure per heat detection period.

Where electronic sow identification (ID) is used, placement of an identification reader at a “sniffing hole” at a solid-partitioned boar pen (located at peripheral or between multiple sow pens) can monitor the number of times a sow ID appears to visit the boar over a specified time period. Should the sow reach the set threshold of visits in a day, automated marking of the potential estrus sow can occur at the boar station or an electronic feeding station.

The Surprise Effect

One method to reduce the occurrence of silent heat and increase strong behavioral presence of estrus is a practice referred to as a surprise effect. Popular in northern Europe, the concept involves continuous, 24-hour fenceline exposure to boars the first three days postweaning (Thursday — Saturday). Day 4 (Sunday) would have no contact (no sight, sound, smell).

On ensuing days, normal heat check and breeding activities are conducted twice daily. As an advocate of the surprise effect scheme, strong behavioral responses appear and a higher percentage of sows return to estrus within seven days postweaning. The percentage exhibiting standing heat on Day 5 is phenomenal, and an associated subsequent litter size advantage may be realized due to greater ovulation.

Simulating the Boar

Proper stimulation by the stockperson in preparation for artificial insemination should simulate the practices of the boar (See Figure 1 on page 14). While ideal boar exposure would involve physical contact where the boar is allowed to nudge, sniff and fully stimulate the female, consideration of time constraints and worker safety concerns has led to fenceline contact, which suffices.

With nose-to-nose fenceline boar contact, the stockperson should begin stimulation by applying pressure to the gilt's side and nudging a knee in the flank or aggressively rubbing the flank and udder. The rubbing of the udder and flank simulates the nosing actions of the boar. Progress to slight back pressure and press your fist to the vulval area. Move to firmer pressure and “thumbcheck” the vulva for a sticky, viscous secretion. To test the quality of the standing response, rub the flank and udder with one hand and push down firmly or bounce on the back with the other as if the weight of the boar were upon her. The standing response may also be elicited by actually sitting astride her (See Heat Detection poster, page 12, for visual aids to illustrate these steps).

Once the female becomes rigid in stance (“locked up”) with ears perked, etc., estrous documentation or insemination may begin.

Other Heat Detection Tools

There are a variety of practices available in the industry to aid heat detection in the absence of the boar.

Aerosol pheromones, stink sticks and hands-free AI tools like breeding saddles and belts have all met with relative success when properly implemented. However, one cannot omit the vital caretaker element and management of boar presence.

Studies show that the more boar-related stimuli provided by the stockperson, the greater the female response. Applying back pressure with boar presence yields twice as many sows in standing heat as back pressure alone.

When four levels of stimuli were studied (back pressure test by stockperson, presence of a boar, back pressure in the presence of a boar and back pressure in presence of multiple boars), 46% of females showed estrus response to back pressure alone, 56% to boar alone, 90% to boar with back pressure, and 97% to back pressure test in a mating pen surrounded by four boar pens.

Heat detection cannot be rushed. The breeder must dedicate time for heat detection with no other distractions or agenda items in mind. Heat detection should not be the last task of the day standing between the stockperson and going home.

Positive caretaker-sow interactions increase reproductive success. Handle boars, sows and gilts gently, calmly and quietly. This is productive for both the pig and stockperson. Not every stockperson is adept at working in the breeding area. The good breeder is keen to understanding normal behavior vs. abnormal behavior or appearance.

Be the Boar

Many systems work for heat detection, dependent on the barn arrangement, proximity of boar and female housing, physiological age and estrous history of the female, boar training, stockmanship skills and attitude. Accurate monitoring and recording is critical, as is having patience and observation skills. Remember, there is a $55.50/sow/year difference between conception rates of 80% and 90%.

It may appear an oversimplification, but we must be reminded to “be the boar.” Far too often, the heat detection and breeding tasks are rushed and the quality of mating (indicated by farrowing rate and liveborn pigs) decreases. A continual review of the original mating process is necessary.

While many farms can boast 85% or higher quarterly farrowing rates, success lies in consistently achieving targets. Maintaining a consistent breeding schedule, farrowing rate and number weaned results in stable pig flow, improved health and uniformity downstream and financial returns throughout the system.

The Female — Signs of Estrus

  • Swollen, reddened vulva (proestrus)
  • Vocalization/barking
  • Mounting penmates
  • Heightened activity level
  • Perked or twitching ears
  • Sticky, viscous secretion of vulva
  • Rigid back and legs; “locked up”

The Boar — Natural Mating

  • Nose-to-nose with female
  • Nudges female in side/flank
  • Noses female's vulva
  • Nudges and lifts female in flank
  • Attempts mounting
  • Mounts; feet drape sides

Stockperson — Simulating The Boar

  • Use fenceline boar contact.
  • Rub female's side and apply slight back pressure.
  • Fist pressure below vulva and check for vulvar moistening (“thumbcheck”).
  • Tug or lift the female's flank and rub underline.
  • Grip loins and increase back pressure to ensure standing reflex.
  • To AI, insert catheter while maintaining stimulatory activity.
  • May sit astride female and grip the sides with feet.

Eight Steps to Successful Heat Detection and Mating

Following are the main components to successful heat detection and subsequent mating:

  1. Get active

    Stockpersons must physically simulate the actions of the boar and have the right attitude and proficiency to do a thorough job. Repeatedly examine the activity in the natural mating process.

  2. Be patient and observant throughout the day

    Some females may not “lock up” until the boar has already passed by. Sows returning to estrus may be restless, off-feed and seeking attention.

  3. Control boar exposure

    Work to establish a heat detection routine in the barn. This involves sight, sound and smell. Timing is critical; too much unmonitored exposure is just as detrimental as too little exposure.

  4. Keep accurate records

    Record dates of gilt movement, mixing and exposure, hormonal treatment and withdrawal, signs of estrus, weaning or abortion. Note odd activities such as irritability, off-feed, vaginal discharges, etc.

  5. Have the correct attitude and skill

    The competent stockperson has the eyes to see, the mind to know how, and the attitude to do. Positive caretaker-sow interactions increase reproductive success.

  6. Reduce environmental and social stressors and provide adequate light

    Estrus can be delayed or difficult to recognize in dim environments and noisy surroundings associated with running augers, fans, pressure washers, other pigs, people or when sows are mixed or handled aggressively.

  7. Maintain optimum body condition

    This should be accomplished through feed and health management. Consider ad-lib feeding after weaning to allow sows to recover energy reserves.

  8. Train the boar

    To prevent sexual frustration and decreased libido, viable boars must periodically be allowed to mount and breed. To maintain pheromone secretion (odor) and interest in seeking sows, boars should be rotated every 15-20 minutes during heat checks.