What are the reasons for the persistently high return-to-estrus rate on pig farms?

The normal estrous cycle of pigs is 18-24 days. When a breeding sow is mated during estrus but does not become pregnant, this is called return to estrus. An increase in the return-to-estrus rate on a pig farm leads to a lower farrowing rate after mating, which in turn affects the farm's economic returns.

There are three main reasons for sows returning to estrus: first, the boar's semen quality is substandard; second, the timing of mating is inaccurate; third, the sow'sdisease-related and physiological return to estrus.

1. Regular return to estrus
 

Around 21 days or 42 days, indicating that estrus detection was accurate, but conception failed.

The possible causes of this phenomenon are: management stress factors within 30 days after insemination (excessive driving, vaccination, fighting after mixing groups, continuous high temperature in the barn, etc.); excessive backflow during insemination leading to fertilization failure; substandard semen quality; inaccurate timing of insemination, either too early or too late.

2. Irregular return to estrus

(1) Return to estrus within 20 days (usually at 18-19 days) may be caused by: inaccurate estrus detection; accurate estrus detection but failure to establish the sow's first pregnancy signal (about 9-12 days after insemination, when the fertilized egg reaches the uterus); occurrence of diseases causing high fever (especially swine fever and influenza); it may also be caused by mating too late.

(2) Return to estrus at 24-39 days mainly refers to embryonic loss caused by problems occurring 3-4 weeks after mating, which is a non-management factor.

Possible causes are: embryo resorption or pregnancy failure due to disease; individual differences in the sow's genotype; too short a lactation period, with the uterus not yet fully recovered.

(3) Non-pregnant return to estrus in mid-gestation (45-105 days), if no definite abortion is observed, is caused by oversights in pregnancy diagnosis; if obvious mid-term abortion is indeed observed, it may be infection caused by the most common pathogens - porcine parvovirus, Japanese encephalitis virus and influenza virus - and is especially likely to occur in the south and in early summer in the north.

(4) For abortion/premature birth at over 106 days, in addition to management factors, attention should be paid to whether there is porcine reproductive and respiratory syndrome virus infection.

II. Measures commonly taken to reduce return to estrus

To reduce the sow return-to-estrus rate, the following measures are commonly taken:
 

1. Provide qualified semen

Semen quality is one of the main factors affecting the conception rate. Without semen of good quality, it is unrealistic to try to improve the conception rate of sows. The physical properties of the semen (semen volume, color, odor, sperm density, motility, abnormality rate, etc.) should be checked to ensure the semen quality is qualified.

At the same time, before the high-temperature season arrives, adjust the heat prevention and cooling equipment and take measures such as adding anti-stress drugs and nutritional supplements to the drinking water, so as to reduce the impact of heat stress on boar semen quality.

2. Improve matingtechnique

3. Maintain good environmental hygiene in the pig barn

Clean the pig barn every day to reduce the breeding environment for pathogenic microorganisms, and disinfect regularly to ensure the pig barn environment is clean and hygienic.

To ensure the sow is in healthy body condition, preventive health care for sows must be done well. In particular, do a good job of vaccination against diseases that directly or indirectly affect sow pregnancy, such as swine fever vaccine (3 times/year), porcine reproductive and respiratory syndrome, porcine pseudorabies and porcine parvovirus.

Reduce the chance of bacterial infection, especially uterine inflammation caused by inadequate disinfection or rough handling during manual assistance at farrowing, artificial insemination and postpartum care. The presence of uterine inflammation makes return to estrus likely, and can even cause repeated breeding failure. Once uterine inflammation is found in a sow, it should be promptlytreated。

Because corn mycotoxins can easily cause false estrus in sows, the feed quality for sows must be guaranteed, ensuring the sow has healthy and suitable body condition to facilitate estrus and mating. For a period before and after mating, especially after mating, controlling the feed nutrition level for sows is a key factor in ensuring conception and the number of piglets born.

Generally, within one month after mating, feeding high-energy feed is prohibited, because excessive nutrient intake will lead to death of the fertilized egg and implantation failure. Appropriately supplement green fodder and add electrolytic multivitamins to make up for vitamin deficiencies. In the last 25 days of pregnancy, raise the nutrition level to ensure healthy fetal growth.