Age affected: Newborn, piglets pre-weaning.
Causes: Weakness from starvation or chilling or infection; leg weakness or illness of dam.
Effects: Injury or death.
The underlying reason for crushing and overlying is the disparity between the size of the piglet at birth (1.2 kg) and that of the sow (250 kg) and occurs particularly when the sow lies down to rest or to suckle the litter. Crushing results from failure of the piglet to avoid the sow or as a result of illness or behavioural problems in the sow which lead her to ignore the piglets. It occurs most frequently in systems of husbandry which do not fully protect the piglet from the sow or provide a separate lying environment. Reasons for piglet failure include: starvation leading to frequent testing of the udder and therefore exposure to the danger area; hypoglycaemia, resulting from starvation; splay leg, joint ill and other lamenesses; septicaemia resulting in fever and illness in the piglet; weakness at birth and chilling. Husbandry factors in crushing include inadequate separation of sow and litter, long straw bedding so piglets cannot escape, inadequate rail or crate design and low temperature. In temperate climates, farrowing room temperatures may be adequate during the day but drop sharply at night, so room temperatures should be checked during the night if overlying is a problem. Sow factors include: mastitis; general illness such as erysipelas which lead to reduction in sow milk supply; lameness which results in poor movement control; and behaviour as in inexperienced gilts.
Mode of transmission
This condition is, strictly, not transmissible, but occurs in successive litters where the husbandry and management conditions are not changed. Its occurrence where there is piglet or sow illness is merely one consequence of such diseases and is not transmissible.
Crushing may be detected by the sound of a squealing piglet. In all farrowing accommodation, squealing may be heard, signalling a trapped piglet. In normal circumstances, the sow responds and releases the animal. If it is not injured, it may then escape. More frequently, dead piglets are found beneath the sow or bearing injuries which suggest that crushing has taken place. If a squealing piglet can be identified, then it may be lame, have congenital tremor, splay leg or have reduced ability to escape for physical reasons. Where the piglet is not seen in life, at least one of the other piglets in the litter may be affected by causes of piglet failure. Starvation, diarrhoea, chilling, splay leg, congenital tremor and weakness often affect the whole litter. Illness in the sow, such as agalactia, may be obvious from direct inspection. The sow may not have eaten and may be depressed or fevered. Scratches from piglet tooth marks may be visible on the udder or there may be visible evidence of mastitis and agalactia. Lameness in the sow can be identified by inspection, but it is often necessary to get the sow to stand before this can be confirmed. Behavioural problems often occur in gilts and may take the form of savaging or simple poor management.
When crushing is heard or seen, it is easily identified. In most circumstances, dead piglets are found and crushing is presumed. It is important for production recording to confirm that crushing has genuinely taken place and that the sow did not lie on the already dead piglet. This can be done by inspection of the piglet for evidence of damage - feeling for broken bones, bruising, evidence of blood from the mouth or evidence that death took place as a result of some other cause, such as poor viability in newborn piglets. These have a covering of membrane, fleshy cords and intact cartilaginous tips to their toes if they have not walked. Expert post-mortem examination may be required to confirm that crushing took place. The predisposing cause may be determined by examination of the litter for clinical signs of illness such as splay leg, but veterinary post-mortem examination is usually required to identify predisposing causes in dead piglets. Husbandry factors such as chilling, pen design and the influence of unsuitable flooring/bedding can be determined by inspection. Examination of the sow for physical illness is straightforward and rests on the clinical signs, but detection of behavioural problems may require prolonged observation.
An important part of post mortem examination is inspection of the piglet for evidence of damage – feeling for broken bones, bruising, evidence of blood from the mouth or evidence that death took place as a result of some other cause, such as poor viability. Stillborn or poorly viable piglets have a covering of membrane, fleshy cords and intact cartilaginous tips to their toes if they have not walked. Dissection may confirm from unexpanded lungs that the piglet never breathed and that the death was a still birth. Crushed piglets frequently have internal bleeding, around broken bones and into the body cavities. Bleeding, blood clots (and bruising in slightly older animals) confirm that crushing has taken place, as none of these changes occur in piglets already dead.There may be evidence of starvation from an empty stomach and from body condition and fatal abnormalities may be seen to account for death. Conditions such as splayleg may be difficult to identify in crushed piglets, but there may be evidence of erosion of the perineum where the piglet has dragged itself along the floor. Evidence of illnesses such as neonatal diarrhoea, may indicate a predisposing cause.
It is important to remember that crushing of the skull in small piglets may result from unrecorded humane destruction.
Treatment and prevention
Living crushed piglets should be assessed for damage and supported until viable again or be killed humanely if unlikely to survive. Crushing can be prevented by correction of the underlying problem. Where the sow is ill (mastitis, erysipelas) and can be treated, the litter should be supported until she has recovered. When the problem cannot be resolved during the sucking period (lameness, serious illness), the litter may be fostered or reared artificially. Sows with behavioural problems could be tranquillised or prevented from crushing by physical means, such as crates, but should be culled if the problem persists.
Husbandry measures can prevent crushing. The most useful short term measure is the use of a blowaway unit which produces a current of air beneath the sow each time she stands up and prevents piglets from settling underneath her, where they may be crushed. Farrowing crates should be adjusted for the size of the sow. Poor crate design can be corrected, but only in the longer term. Farrowing pen lighting should be adjusted and warm creeps provided to separate piglets from the sow, particularly at farrowing. Attendance at farrowing may reduce crushing. Fine bedding, such as sawdust should be provided. Piglet problems can be corrected by managing splay leg, treating infections and providing supplementary feeding.