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UNDERSTANDING HEAT (ESTRUS) IN SOW AND GILTS

October 1, 2015

 

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Understanding sow and gilt reproductive cycle is essential for a successful mating program, whether using artificial insemination (AI) or natural mating. Swine exhibit occasional sexual behaviour in certain period call estrus or “heat period” (or in Filipino, paglalandi). Investing time and skills in developing effective heat detection should be a top priority in every breeding farm. Heat period is the time when the sow or gilts manifested sexual behavior and is seen to be ready for mating. This heat period lasts to 2-3 days. However, the length of heat behavior among sows and gilts vary wherein the formers’ heat period usually last longer.

Ideally, the best time for breeding within the heat period happens during the time called standing heat — when the female stands rigidly and is receptive to the mounting of the boar. According to studies, ovulation occurs around 40 hours after the onset of standing heat. The released egg from the ovary didn’t last longer while Boar’s semen in the Sow’s body can stay alive up to 16 hours after mating. Knowing when the heat occur, detecting it and inseminating 12-24 hours after onset of standing heat will ensure high conception rates The optimum time for insemination is 12-24 hours before ovulation, or around 40 hours after the onset of standing heat (when the female shows signs of
heat). This proper timing of insemination will ensure high conception rates. If not impregnated the sows and gilts will go on heat again after 21 days.

Signs and Detection of Heat

In the day prior to the heat period, the sow and gilt may or may not show physical indication that heat is coming. The following are the signs when sows and gilts are showing heat: they always assume rigid stance (standing reflex) when pressure is applied in the lower back. The vulva of the pig nearing heat is swollen, red and discharges mucus. Other signs include: loss of appetite, restlessness, alertness, grunting and chomping of the jaws. The grunting and willingness of the sows and gilts to be mounted on is a definitive sign that they are in standing heat. If the signs are evident, there are two tests that are usually done to ensure the right time of mating or insemination. These are the Haunch Pressure Test and Riding Pressure Test, the former is done by using hand (both hands) pressure at the side of the lower back of the pig while the later is done by riding in the same back (see pictures below for details).

 

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When is the right time for mating?

The gilts may show signs of heat at the age of 6 months or earlier but they are not yet ready for gestation. Gilts are recommended to be mated or artifiially inseminated at the age of 8 months and weighing about 120 kg. This is to ensure that gilts will farrow at the age of one year and are ready to nourish their young.
On the other hand, sows will restart its heat period 3 days after weaning, and should be mated or AI after 12-24 hours of standing heat. Use the example guidelines for insemination shown in the table 1 below.

In general, the sows usually lose heat earlier compare to the gilts so mating should be done immediately. Pregnancy is usually detected by failure to return to heat after 21 days following mating. If mating is successful, gestation period will last for about 114 days. An easy way to remember is 3 moths (90 days), 3 weeks 21 (days), and 3 days. When plotting to the calendar, take note that there are months that are not exactly 30 days, for guidelines please refer to breeding calendar (table 2) below.

 

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Table 1. Guidelines in Breeding 

 

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Table 2. Guidelines for Breeding

 

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