How to Stimulate Estrus in Sows
By following certain rules, it is possible to increase the rate of sows entering estrus within the first week after weaning.
Yevhen Kuzmenko, Consultant on Pig Breeding, LLC “Vitagro Nutrition”
The goal of any pig farm is to increase profitability, which depends on various factors. Improving the efficiency of the sow herd by reducing the number of non-productive sow days is one of the main factors affecting the farm’s profitability. Usually, the percentage of sows entering estrus within the first week after weaning does not exceed 87–90%. Our goal is to reach at least 90%, and ideally over 95%, with an average period from weaning to fertilization of 4–5 days.
To ensure the maximum number of sows return to estrus on the 4th–5th day after weaning, it is necessary to minimize the risks of failures and take good care of the sow immediately after farrowing. Typically, the main issue is the poor condition of the lactating sow, which requires a strategy of balanced feeding that takes into account the needs for micro- and macroelements and vitamins.
A crucial period after weaning is feeding; during this time, the sow should receive 12,500–14,500 kcal/head/day, which is approximately 4–5 kg of compound feed per day starting from the first day after weaning. The diet should be high in energy and low in fiber. The energy consumed by sows after weaning is one of the main factors for timely estrus onset. It also helps optimize ovulation and reduce the “weaning-to-fertilization” period. During the post-weaning to fertilization period, it is better to overfeed the sows than to underfeed them.
Another problem is infection or injury of the uterus due to farrowing assistance. Sows with healthy uteri return to fertility faster. To minimize the need for farrowing assistance, it is recommended to feed pregnant sows in a way that prevents them from becoming overweight. Up to the 84th day of pregnancy, they should consume 1.8 kg of compound feed per day, and from the 85th day to farrowing – 2.4–2.6 kg compound feed /day, depending on their body condition. If farrowing assistance is necessary, it should be provided by trained, qualified personnel following sanitary and hygienic requirements.
In the first days after weaning piglets, to achieve maximum effect, a boar should be used as a natural stimulator and a guarantee of quick estrus onset. Replacing one boar with another increases their activity. A boar sensing competition usually foams more and chomps, releasing important hormones from the oral cavity that stimulate estrus in sows.
The 4th–6th days are particularly important in this process. During this time, staff should be ready for insemination. The boar is placed in front of 4–6 sows (no more). A boar cart or partitions can be used. It is effective to use several boars simultaneously. After insemination, the boar can remain in front of the sows for up to 20 minutes.
An important factor in stimulating sows to enter estrus is the light regimen and illumination level. The duration of daylight should be 16 hours in the fertilization area and the area for replacement gilts. Illumination at sow eye level should be at least 150 lux, ideally 200 lux. To ensure the lighting level does not depend on human factors, it is better to install a time relay for automatic control.
The microclimate in the fertilization sector has a significant impact on sows entering estrus. Appropriate temperature, air quality with acceptable ammonia levels, and high oxygen content improve estrus onset and farrowing percentages.
Most of the sows that do not show signs of estrus immediately after weaning usually enter estrus by the 25th day. Sows with physiological or hormonal pathologies may not show signs of estrus and are therefore subject to culling.
The provided recommendations have practical confirmation. Based on my own experience and that of other specialists, I can assert that the main factor in stimulating sows to enter estrus is working with boars. In second place, I would put the level of illumination. Other factors should also not be neglected, as they significantly affect the efficiency of the sow herd.