Age affected: Newborn.
Causes: Prolonged farrowing; infections; mismanagement; malnutrition; poisoning.
Effects: Significant if >7% piglets born dead.
Stillbirth is the term given to the birth of a piglet which is found dead within the membranes after farrowing is complete. The pig may have died prior to farrowing, died during the process of birth, or died after birth but without clearing the membranes. Piglets removed at hysterectomy all survive, but some of those born naturally are born dead. Disease may cause the piglet to die shortly before farrowing, during the process and before clearing the membranes.
The diseases responsible include enterovirus, Mycoplasma suis infection (eperythrozoonosis), leptospirosis, mycotoxicosis (especially zearalenone), parvovirus, PRRS circovirus and toxoplasmosis. Carbon monoxide poisoning may also increase stillbirth rates dramatically. Many of the stillbirths which occur in normal litters result from delays in farrowing. These may result from the presence of a dead piglet or a mummy in front of the piglet concerned and the delay caused can deprive it of oxygen and kill it.
Similarly, destruction of the placenta before or during farrowing can lead to loss of oxygen and death unless the piglet is farrowed very fast. Oversized foetuses may delay parturition and are often born dead and uterine inertia may occur in older pigs, calcium deficient sows or those which have just passed a difficult piglet.
Mode of transmission
In many cases, this condition is spontaneous and results from conditions such as piglet oversize and uterine inertia which can occur in any sow at any time. The infectious causes usually result from infection of a non-immune pregnant sow or gilt and transmission is by the routes relevant to that disease. Management problems will recur particularly in circumstances where farrowings are not attended.
Stillborn pigs are found dead in the membranes behind the sow or delivered dead as a result of assistance at farrowing or following uterine inertia during prolonged farrowing.
Piglets found dead in the membranes behind a sow may be stillborn, but the point of death should be confirmed by post-mortem examination.
A history of uterine inertia or assistance at farrowing may explain the stillbirths. Piglets of older sows or those with large litters are most likely to be born dead in the other products of parturition, as mummified piglets frequently cause delay to the piglets which follow them. The cause of death may be congenital and the piglet may be malformed or so small as to be non-viable. Culture or demonstration of infectious agents may suggest a cause. Animals which have died from carbon monoxide poisoning are often cherry red.
Stillborn pigs have a fleshy cord, membrane on the skin and cartilaginous curled up tips to the toes. Those that died during without breathing have lungs which are non-expanded, resemble liver and sink in water.
Piglets which have died in the course of farrowing appear mature and fresh. Those that have breathed briefly have partially expanded lungs which float in water. In some cases, meconium pellets (the first faeces) have been breathed in during the process of birth and have blocked the airways. When death occurred in the uterus before birth, the membranes may already be discoloured, the skin yellowish not pink and the eyes may be beginning to sink in. Signs of immaturity such as closed eyes or lack or hair may be noted.
Congenital abnormalities are often obvious, but others, such as heart defects, may not be visible without detailed post-mortem inspection. The same may apply to piglets which have died from infections. There may be petechiae (blood flecks) on the skin or the white of the eye and haemorrhages in the body cavities. Straw-coloured fuid is often present around the heart and in the chest cavity of stillborn piglets and can be used to test for antibody to viruses and bacteria.
Treatment and prevention
Where uterine inertia is occurring (if no piglet has been born for 2 hours), remove foetuses manually as soon as possible until normal farrowing continues. Compromised piglets may be resuscitated by clearing the membranes from the mouth, using a sucker to clear airways, massaging the chest and swinging the piglet by the hind legs to stimulate breathing. If calcium deficiency in the sow is suspected, give calcium borogluconate into the ear vein and treat any other illness in the sow.
Where farrowing cannot be attended, confirm that the vulva of the sow is not pressed against the back of the farrowing crate and that there is a heat lamp at the tail of the sow to prevent chilling of the piglets. Prevention of stillbirths requires attendance at farrowing, careful attention to those sows known to have a high stillbirth rate, prompt intervention when uterine inertia occurs and culling of sows after the seventh litter. Where infectious disease is identified, it should be controlled by vaccination or prior exposure of the incoming gilts to the agent before service.