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Swine Reproduction
Illinois Livestock Trail
The techniques for success, and the pitfalls for failure in detection of estrus in the breeding herd.
by R. Knox

The procedures for detecting estrus in pigs are well known and for the most part are relatively straightforward. Yet, what is often very simple can become complicated by the realities of daily production at the farm. These realities often change the optimum conditions and the use of best procedures and ultimately alter the success of detecting the signs of estrus in the female pig. For example, management of labor, facilities, and the animals, can either improve or greatly reduce the efficiency of estrous detection. While the symptoms of estrus vary for each female, the response to the human backpressure test in the presence of a boar use the response of females to various stimuli within a typically short period of time to identify tan female in standing heat. Those symptoms are a female that previously would not stand rigid in the presence of a boar the previous day or time period, now "locks" to boar stimuli and the back pressure test and remains quiet. She may or may not have erect ears depending upon the bred.

Young gilts are by far more difficult to deal with than with mature sows. With gilts, the objective is to eliminate fear from the detection procedures, maximize the daily routine, provide powerful stimuli, and to elicit the behavioral expression of estrus in response to the stimuli. In gilts, failure to detect is a common problem but false identification of heat also occurs due to allowance of the symptoms of estrus such as vulvular swelling and other symptoms to be used as markers for estrus. In sows, false and missed heats may also be true but their causes may be far different. Sows are much calmer and less prone to fear of humans. They are also commonly housed in stalls. These two factors, often lead to technicians identifying a sow in heat when in fact she is not. Proper application of the stimuli at the correct intensity can help to eliminate these problems. Further, failure to detect sows in heat is often a result from lack of proper stimulus and these may become even more important when sows are housed in stalls. Technicians must physically apply the stimuli even if this means getting in the stall with the female. Many choose not to do this because of the time and effort required.

Labor scenarios differ between farms, and different systems will have different requirements for persons needed to effectively control the boar to expose each female while application of physical back pressure is performed. In some farms one person may suffice while in others 2 to 3 people may be needed. Often, labor shortages, emergencies or other circumstances reduce the number of people assigned to this task and results in reduced boar control and boar and human stimuli applied to each female. In either case, the chances for failure to detect estrus increases. Technicians must know that the best way to detect estrus is to physically apply back pressure to an animal and note its positive or negative reaction for standing rigid. This response must be the primary determinant as other signs are not valid indicators for estrus and not all animals show the same rigidity response just to the presence of a boar with fenceline or the physical presence without other stimuli rubbing and backpressure application. Technicians are responsible for placing the boar in close proximity to the head of the female for ~ two minutes or until the female is rigid, whichever comes first. The duration of the exposure period is important as the female must have time to detect and react to the array of visual, olfactory, sound and tactile stimuli that are provided to her by the boar and the human. This time period is important as the female usually requires some time to acclimate to the presence of the technician in her space. During this time she realizes that the human is not a danger or cause for fear and will express the symptoms of estrus. Fearful animals are usually very nervous and regardless of reproductive stage, may fail to allow full estrus symptoms to be expressed.

Animal housing conditions, which will include stalls or pens, number per pen, boar to female ratio, lighting and sound, air speed and temperature, and time of day, and physical or fenceline method of boar exposure can either improve or reduce the effectiveness of the technique. For sows or gilts, stalls or pens can work well. Excessive riding in pen situations can alter the accuracy of the technicians for detection of estrus. Young gilts are sometime more difficult to detect in stalls as they often times require more intense boar stimuli to elicit a response. Number of females in a pen should allow adequate exposure rates to the boar during the timeline for the contact. If there are too many females in a pen, opportunities for female:male contact and receiving boar stimuli become limiting. Since sight and sound and smell of the boar are powerful stimuli for estrus detection, factors such as low lighting, noisy barns, and fast air speed or high gas levels may all limit the reception of these stimuli by the female. Avoid detection at the hot times of the day, after animals are tired from moving or exertion, and late in the day. Animals tend to respond best in the early to mid morning. Physical or fenceline exposure can work well. Fenceline exposure is straightforward and should occur by moving the boar down a row of stalls or pens one at a time. Then a technician applies side rubbing and back pressure after a minute or so to detect signs. This effort is performed for only a small number of females within the immediate area of fenceline contact with the boar at a time. A more powerful detection effect can be used if the females are moved to a pen or alleyway adjacent to the boar's pen or within his pen itself. Another popular option in loose or pen housing is to walk a boar physically with the female and note their response. This can work quite well, but it is worthy to note that boar do not detect females in heat as much as females in heat seek out boars and therefore it is important to control the boar to female ratio in pens. Also, many boars commonly used for detection of estrus, do not show excessive libido, and may not attempt to stimulate females with physical rubbing or mounting so it is still important for technicians to apply stimuli to females. Always remember that unintentional boar exposure, boars housed too close, and the interval from last boar exposure, can all influence whether a female will express estrus symptoms when she really is in estrus. This is known as a refractory period and is the period that a female will not stand for a boar when she is in heat. Females in heat do not stand continuously but will stand for a 15-30 minute period in the presence of a boar but then will refuse to stand for a period of time. In summary, accurate detection of estrus depend upon remembering the basics and recognizing the pitfalls so that sources of errors can be eliminated.

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