How do sow reproductive problems manifest at different stages?
Analysis of reproductive problems in sows at different stages
First, the sow is successfully inseminated, and the fertilized eggs move from the fallopian tube to each uterine horn, where they move freely until day 12. From day 12 to day 18, the zygotes automatically separate. Shortly after the embryos enter the uterus, they form amniotic sacs and implant on the uterine wall. After 21 days, all embryos have completed implantation. After 35 days of gestation, the piglet's whole-body organs are formed, and from then on the embryos continue to develop and the bones ossify. At around 70 days of gestation, the fetus can have an initial immune system and can resist invasion by some pathogenic bacteria. In the first 80 days of pregnancy, fetal weight gain is slow, and the weight gained is less than one third of the entire fetal weight at birth. In late pregnancy, that is, the 30 days before farrowing, is a period of faster fetal growth. During these 30 days, fetal weight gain accounts for more than two thirds of the birth weight of the fetus, until the sow farrows at around 114 days.
When we know the dynamic progression of sow gestation, and then note that mating of the sow is completed within 3 days according to the timing, this can provide a reliable basis for us to think about the deeper causes of diseases in sows at different periods.
We divide the sow reproductive process into five stages: return to estrus within 18 days, return to estrus at around 21 days, abortion at around 35 days, abortion at 45-70 days, and abortion after 70 days.
1. Analysis of causes of return to estrus within 18 days:
Case one: it indicates that the worker's estrus identification was inaccurate; this again includes two reasons: the worker's estrus identificationtechniqueis not up to standard, or the sow shows false estrus, or mycotoxin poisoning.
Case two: it indicates that the worker's estrus identification was accurate, but the insemination time was too late.
2. Analysis of causes of return to estrus at around 21 days:
This is normal return to estrus, indicating that estrus identification was correct, but conception failure occurred, including three major causes:
One, mating aspects: insemination time too early, or too much backflow, or unqualified semen, etc., causing insemination failure.
Two, management aspects: management stress factors after insemination (such as excessive driving, injection, mixing groups and fighting, continuous high temperature in the barn, etc.), causing loss of fertilized eggs and failure to reach the number of embryos required for establishment of pregnancy (generally considered to be at least 5).
Three, pathogen aspects: estrus identification was accurate, but because of diseases causing high fever (especially swine fever, foot-and-mouth disease, influenza, toxoplasmosis, etc.), the sow's first pregnancy signal (about 9-12 days after insemination, when the fertilized eggs reach the uterus) was not established.
3. Analysis of causes of abortion at around 35 days:
This type of abortion is mostly pathogen-infectious abortion, not a management factor. It is mainly a problem occurring 3-4 weeks after mating that causes loss of embryos.
This again includes two major causes:
One, embryonic resorption or pregnancy failure caused by disease, so symptoms may not be seen (pseudorabies virus, parvovirus), as well as leptospira combined with mycotoxins and toxoplasma infection.
Two, “too short a lactation period” or “uterine inflammatory damage”, the uterus failing to recover completely, etc.
4. Analysis of causes of abortion at around 45-70 days:
This type of abortion is the delivery of mummified embryos. The most common pathogens include Japanese encephalitis virus, parvovirus, pseudorabies virus, and toxoplasmosis, especially in early summer. Japanese encephalitis and fever in first-parity young sows can very easily cause abortion, especially when other pathogens (Mycoplasma, Salmonella) are co-infected.
5. Analysis of causes of abortion after 70 days:
Eperythrozoon, pseudorabies combined with toxoplasmosis (which can occur at any stage), and domestic pig farms should also pay attention to whether there are breeding sows (including boars) in the sporadic period of blue ear disease. Its characteristic is that the premature fetuses are relatively large, and stillbirths and mummies coexist.
When a sow gives birth to piglets, if mummified fetuses appear, the developmental age can be inferred from the length of fetal development, and then the pathogen can be analyzed according to the age at which the pathogen is prone to occur. Generally speaking, the relationship between fetal length and age at death is as follows: 2 cm/25 days of age, 2.7 cm/30 days of age, 4.6 cm/40 days of age, 8.9 cm/50 days of age, 13.5 cm/60 days of age, 17 cm/70 days of age, 20.7 cm/85 days of age, 27 cm/110 days of age. If weak piglets are delivered, based on the fact that at around 70 days of gestation the fetus can have an initial immune system and can resist invasion by some pathogenic bacteria, this indicates that this sow may have been infected with certain pathogens after 70 days of gestation, or experienced strong stress (injection of oil-based vaccine, etc.), thereby causing the appearance of weak fetuses.