Hypothermia

Occurrence: Worldwide.
Age affected: Newborn (all ages).
Causes: Poor housing, lack of bedding, wet conditions, starvation.
Effects: Shivering, pallor, cold skin, lethargy, prone to infection, death.

Causes

Hypothermia occurs when pigs experience low environmental temperatures and cannot maintain their body temperature at 38.5-39°C (101.5-102.5°F). It is most serious in piglets aged 0-7 days, but can occur in pigs of any age and can even kill adults of particular breeds in certain circumstances. Piglets require environmental temperatures of 34°C or more for the single neonate, or 25-30°C or more for the piglet able to huddle in order to maintain body temperature. The piglet has no brown fat (used by mammals to generate heat quickly) so the piglet cannot use fat to generate heat in cold conditions. It must therefore use glucose and may be able to maintain both blood glucose levels and body temperatures if able take in sufficient milk from the sow. Any interruption of intake or too high a demand for energy (as in piglets with low body weights or very low temperatures and wet conditions) results in use of glycogen (animal starch) reserves from the liver. When these are exhausted, the piglet's body temperature begins to fall as does its blood glucose. In piglets aged 7 days and more, gluconeogenesis (the formation of glucose from proteins) can maintain the blood glucose level and prevent the reduction in body temperature. 

Mode of transmission

This condition is not transmissible, but will recur if pigs are kept in the same conditions.

Clinical signs

Piglets in low temperatures huddle under lights or against the sow, and older pigs huddle together. Single older pigs attempt to bury themselves in bedding if available. Piglets suffering from hypothermia, have an erect hair coat, they shiver and develop signs of hypoglycaemia such as uncertain gait, supporting themselves by placing their noses on the ground and spreading their hind limbs. More severely affected pigs rest on their abdomens but eventually fall on their sides and develop convulsions which are accompanied by slowing of the heart to 80 beats/minute, a decline in rectal temperature, shivering and dullness. Death normally occurs 24-36 hours after the commencement of the signs. Hypothermia in older pigs is less likely to lead to death, but in all cases there is an increase in appetite, less live weight gain per kg of feed, an increase in the length of the hair coat and a reduction in body condition and fat thickness. Chilling may lead to failure to show oestrus in sows and gilts, a decline in bodily condition which results in lower litter sizes and to bluish ears and extremities. Vietnamese pot-bellied pigs may die of hypothermia if maintained on high roughage diets and not protected from sudden cold.

Huddling behaviour of piglets and older animals suggests that chilling is occurring, and burial in bedding and their appearance (bluish extremities, erect hair coats) may support the presence of hypothermia. The presence of piglets with difficulty in standing, convulsing or in a coma may also suggest hypothermia. Examination of these animals will reveal low rectal temperatures (down to 35°C). There may be dead animals. Hypoglycaemia alone should be eliminated as a cause of the condition in piglets and disease considered as a cause of mortality.Confirmation comes from an analysis of the environmental temperature over 24 hour periods using maximum and minimum thermometers or other ambient temperature recorders installed at pig height. Minimum temperature requirements below which hypothermia may occur are shown in Table 1.

Postmortem lesions

The bodies of pigs which have died from hypothermia are often in poor condition, and in older pigs may be covered in long hair. There may be bluish discoloration of the extremities. Dead piglets are found to have empty stomachs, low plasma glucose levels and low liver glycogen levels as in hypoglycaemia.

Treatment and prevention

Hypoglycaemia treatments can also be useful for neonatal piglets with hypothermia. Affected animals should be given intraperitoneal injections of 15 ml of 5% glucose solution every 4-6 hours or oral glucose by stomach tube and kept at a minimum of 30-35°C (85-95°F). If the sow is unable to feed them, an artificial sow milk replacer should be given by stomach tube initially or they should be fostered onto another sow. Reduction in draughts and the provision or dry bedding and additional heating (either from heat lamps, from underfloor or from heat pads) will also improve their chances of survival. Orphaned or surplus piglets may be maintained in small groups in incubators. In all cases, the environmental temperature should be raised to the level appropriate to the age group. Where this cannot be done for the whole pen or house, dry bedding will improve the pig environment and a dry, bedded kennel area which excludes draughts will concentrate heat where required. Weaned pigs should be given more food or food of higher energy density until the effects of hypothermia on body condition are corrected.