Pregnancy Loss in Swine

Breeding failure vs. pregnancy failure

Breeding failure- never cycled, wasn't bred at right time, never conceived or lost before pregnancy recognition

Pregnancy failure - pregnant and lost some or all of litter after recognition

Return to estrus in breeding failure vs pregnancy failure

Breeding failure - regular return to estrus

Pregnancy failure - prolonged return to estrus

Estrus cycle length of the sow

21 days

Target conception and farrowing rates in swine

Conception rate ≥90%

Farrowing rate ≥88%

Primary causes of breeding failure

- management

- nutrition

- environment

- ovarian disorders

- uterine infection

Pregnancy failure is primarily caused by...

Infectious agents

The line between breeding failure and pregnancy failure is drawn at what crucial step?

Maternal recognition of pregnancy

In sows, how does maternal recognition of pregnancy occur?

- embryos enter the uterus around 48 hours after ovulation

- embryos migrate through both horns, secreting estrogen around day 10 and then again at days 14-18

- both estrogen secreting periods are required to maintain the CL

- minimum of 4 viable embryos must be present before the first signal

What defines regular vs irregular return to estrus?

Regular - occurs 17-24 days after breeding

Irregular - occurs after day 24 after breeding

What occurs in pseudopregnancy?

The CL persists without a viable litter - female neither returns nor farrows

Possible causes of pseudopregnancy

- embryonic loss after recognition

- exogenous estradiol given from around day 12 of the cycle

- zearalenone

If there is no conception, embryonic death, or < 4 embryos before day 10... what is the most likely cause and what will be the result (return to estrus, etc)

Regular return to estrus, 17-24 days after breeding

Non infectious cause - breeding timing, semen, ovulation failure, boar fertility, chronic endometritis, season

If there is significant embryonic death between the first and second estrogen signals... what is the most likely cause and what will be the result (return to estrus, etc)

Irregular return to estrus, after day 24 post breeding

Means pregnancy was established and then lost - could be infectious or non infectious

If there is conceptus death after the second estrogen signal but before day 35 of gestation... what is the most likely cause and what will be the result (return to estrus, etc)

Late return to estrus, complete resorption of fetus

Most likely infectious cause

If there is pregnancy loss after day 35... what is the most likely cause and what will be the result (return to estrus, etc)

Most likely infectious

Abortion, mummies, stillborns, pseudopregnancy, small litters at farrowing

Pregnancy is most accurately diagnosed with...

Real time B mode ultrasound (RTU)

RTU can detect pregnancy and fetal heartbeats on what days?

Pregnancy from day 20-21

Heartbeats from day 24

When does the fetal skeleton begin to ossify in swine?

Day 35

Gestation length in swine

114 days

When does the fetus become immunocompetent in gestation?

Days 65-70

Puberty occurs at what age in gilts?

180 days

4 reasons that a gilt won't cycle

- nutrition and body composition

- boar exposure

- season and heat

- disease and toxins

How does nutrition and body composition affect cycling in gilts?

If a gilt is in an energy deficit 17 days prior to breeding won't ovulate or will ovulate poor quality embryos

How does boar exposure affect gilts cycles?

They need male exposure to come into estrus

If a gilt is not pubertal within 28 days after exposure to a boar, what does this mean?

Less fertile, should be cull candidates

What in a boar allows gilts to start cycling?

Pheromones

How does season/heat contribute to gilt cycling?

- long days in summer and early autumn delay puberty

- high temps decrease feed intake

What are toxins that can affect gilt cycling?

Zearalenone

Sources of zearalenone

Wet corn that grows mold

How does zearalenone affect gilts/sows?

- hyperestrogenic

- causes false puberty in gilts

- suppresses GnRH

Sows should show estrus within how many days of weaning?

5 days

What type of vulvar discharge is pathological?

- fresh, bloody discharge

- purulent discharge several days after breeding

Stillborn vs mummified fetus

Stillborn - full term but die during parturition process

Mummified - die at some point during pregnancy

Pathogenesis of abortion

Cortisol released by sow/fetus -> PGF2a release -> luteolysis and pregnancy loss

The sow depends on the CL for the entire gestation

Infectious causes of abortion in swine

- PRRSV

- parvovirus

- leptospirosis

- influenza virus

Which abortion agents cause fetal/placental infection?

- PRRSV

- parvovirus

- lepto

Which abortion agent causes systemic maternal illness?

- influenza

Variably sized mummies alongside a few apparently normal live born piglets is highly indicative of...

PPV - maternal viremia

If infection occurs before day 10-12 of gestation, what is the result?

Conceptus is largely protected or embryo dies before recognition

Regular return to estrus

If infection occurs from day 12-35, what is the result?

Embryonic death and resorption

Irregular or late return if shoe litter is lost, small litters if only some embryos die

If infection occurs from day 35-70, what is the result?

Fetal death and mummification

Will see mummies at farrowing and of different sizes

If infection occurs after day 65-70, what is the result?

Immunocompetent fetus may clear the agent

Stillborn or weak born piglets result, or normal piglets born seropositive

Sow signs of PRRSV

- mild depression

- anorexia

- fever

Results of PRRSV in pigs

Abortion or infected fetuses with no repro disease

Sow signs of PPV

None

Parvovirus in pigs causes what?

Fetal mummification

Sow signs of PCV2

None

Result of PCV2

- late abortions

- stillbirths

- mummification

Sow signs of influenza A

- fever

- lethargy

- cough

- dyspnea

Important diagnostic feature of influenza A abortion

Cannot use fetuses, need sample from sow

Mechanism of abortion in pigs due to lepto

Placentitis

Signs of lepto in sows

- transient fever

- anorexia

Results of lepto in pigs

Normal fetuses aborted due to placentitis

Prevention of lepto and parvo

Vaccination

Why is immunity to lepto terrible but immunity to parvo is very good even though you can prevent both by vaccinating?

If a pig is exposed to parvo before pregnancy or when vaccinated, they develop lifelong immunity - doesn't happen with lepto so they need to be vaccinated frequently

Primary source of parvo

Other pigs - endemic

Primary source of lepto

Deer urine

How does influenza virus cause abortions?

Causes a very high fever and increase of TNF alpha

Sow will protect herself before fetuses while pregnant and will abort

Why can vaccines cause abortions?

Increasing immune system response and sow will abort fetuses to reserve energy to protect herself

Non-infectious causes of pregnancy failure

- zearalone

- carbon monoxide

- mycotoxins

- season, heat, stress

What are the ideal samples to submit after abortions?

All of fetus, placenta, and a sample of blood from mom