Temperature requirements of pigs

Growth and food intake are highly dependent on temperature, particularly for piglets and weaners. This information looks at factors that affect pigs' temperature requirements.

Feed intake, feed conversion ratio (FCR) and growth are all affected by temperature. The thermoneutral zone is the range of temperatures over which pigs can maintain their normal body temperature without affecting their heat production.

The specific temperature required is determined by the cost of maintaining that temperature, measured against the benefits or penalties associated with changes in growth rate, feed intake and conversion efficiency.

Further details on the requirement to meet pigs' temperature needs can be found in the Code of practice for the welfare of pigs. 

Pigs' physiological needs will depend on their physical condition, for example health and weight, and their maturity.

It is important to note the following factors and the impact they have on temperature requirements.

Critical temperatures

• The lower critical temperature (LCT) is the minimum temperature that can be tolerated by pigs
• The upper critical temperature (UCT) is the maximum temperature that can be tolerated by pigs

When working out the LCT, it can be difficult to give an exact figure for a given group of pigs. It can be a matter of using anecdotal evidence, animal behaviour and experience to decide the optimal temperature.

The chance of a drop in performance caused by the estimated LCT being too low can be reduced by controlling the temperature at 2–3°C above that value.

Generally, as pigs age and gain weight, their tolerance to low temperatures increases while their tolerance to high temperatures decreases.

There is a step change at weaning where pigs' critical temperature increases for a short period. This is mainly due to a drop in feed intake caused by stressors such as a change in diet and separation from the sow.

Feeding levels vary based on the type of feeding system and the market for the finished pig.

Put simply, pigs that grow faster need to be kept cooler.

Animals that are unhealthy or stressed will require higher temperatures than those that are healthy and unstressed. Not unlike humans, pigs crave warmth when they are unwell.

The physical environment refers to external influences on the pig. This may include flooring, air speed, radiant effects and other animals.

Air temperature requirements are modified by these environmental factors.

Flooring

Many pigs are housed on slatted floors, which allow waste to fall through to slurry tanks or channels. Other housing systems often use straw for either the lying or dunging area, or both.

As a pig spends a significant amount of time lying down, the heat insulation property of the floor has an effect on the temperature tolerance of the animal. Therefore, straw-bedded animals often perform better at lower temperatures than those on slatted or solid floors.

Air speed, LCT and UCT

The LCT and the UCT values are affected by draughts (for pigs, a draught is defined as air moving faster than 0.15m/s).

A well-designed ventilation system subjects the pigs to low air speeds in winter to avoid chilling, and higher air speeds in summer to produce greater evaporative cooling and so raise the UCT.

These features are very important and can be achieved with the use of a fan ventilation system.

Radiant effects

At any given air temperature, the heat loss of the animal is not only affected by convective losses but by radiant effects.

For example, if the inside surface temperature of the surrounding building is low, then the net radiant heat transfer from the animal to the structure can make the animal feel colder – you’ll be aware of this effect if you sit close to a window on a cold day. This results in a higher LCT.

In well-insulated buildings, the temperature difference between the inside surface of the structure and the animal is not as great, therefore the heat loss of the animal is lower overall, giving a low LCT. Heating systems, which mainly rely on radiant output, can have an important effect on LCT. 

The classic example is the piglet in farrowing accommodation without boxed creeps. Although the air temperature may be at the LCT of the sow (typically 16°C), the radiant output from a pig lamp enables the piglet underneath it to remain above its own much higher LCT.

Stocking density

Pigs have a lower LCT when housed in groups than when penned individually. This is because their thermal interactions help to keep them warm.

The UCT is closely related to group size because in a given area, the ability of pigs to lie clear of each other drastically affects their ability to dissipate heat.

Supplementary heating is used to maintain temperature when there is a deficit of heat in a building or an area of a building.

If this happens, the temperature may fall below the LCT of the animals and energy from feed will be diverted from growth to maintenance. In extreme situations, especially with younger stock, low temperatures will have an effect on mortality rates.

In England, heating is normally only used for young pigs. With older pigs (finishers over 30 kg), the use of carefully controlled minimum ventilation rates and insulation in adequately stocked buildings will ensure that the recommended temperatures are achieved.

Major heating systems for pigs include creep heating for piglets and weaner accommodation. Piglets require heating from birth up to about three weeks of age. As well as promoting maximum growth during this period, its most important role is to reduce the mortality of the young animals, especially in the first few days after birth.

This is done in two ways:

• Heating helps to conserve the piglet's energy at a time when marginal changes in its own energy reserves can be the difference between life and death
• The incidence of overlying is reduced by the provision of a separate, safe, heated area away from the sow, which is an effective alternative to the warmth of her body

Work has been carried out to determine the value of providing extra heat at the tail and at the sides of the sow for the first few days after parturition.

In both scientific and commercial trials, such heating has been shown to have a significant effect on reducing piglet mortality. This is because it overcomes the disadvantage of the less-than-optimum piglet environment in the areas away from the creep.

The difference in energy cost between a basic heating system and a more extensive one might be a couple of pounds per farrowing, but this can be quickly recovered through only minor reductions in mortality.

When piglets are weaned from the sow under five weeks of age, heating is needed to maintain the correct temperatures for food utilisation. The trend towards earlier weaning has resulted in the use of more heating at the weaner stage. Housing systems vary greatly at this stage of production. Anything from fan-ventilated ‘walk -in’ rooms, to simple, naturally-ventilated ‘kennels’ can be found. Examples of heating systems include:

• Duct heaters
• Radiant heaters
• Underfloor heating

Pigs grow rapidly in weaner accommodation. Their heat output increases and their temperature requirement decreases. The result of this, as far as the heat balance of the building is concerned, is that the initial net heat requirement changes gradually to a net cooling (ventilation) requirement.

More information on heating sources, technologies and costings can be found in our controlled environment for livestock guide.

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