Pig Biology

Pigs need the right light levels so that they can identify each other, communicate and see pen features such as feeders. There is good evidence that pigs' eyes are not adapted for extremely bright light and that they may be better suited to dim levels of natural light. This knowledge is vital when deciding how to light your indoor or outdoor pig units.

While pigs need natural light to produce vitamin D3, a deficiency of vitamin D is not considered a problem in pig production, as vitamin D2 is provided in balanced pig diets.

Commercial lighting is unlikely to reach a level which pigs find aversive, however, high intensity lighting, e.g. spotlights, should be avoided. Pigs prefer to sleep in dim lighting/darkness, suggesting that lying areas of the pen should not be brightly lit in order to promote resting behaviour.

Colour Vision and Flicker Sensitivity

Evidence shows that pigs have poorer colour perception than humans and in particular a reduced sensitivity to the red end of the spectrum. There is little research into the effect of coloured lights on pig production. In cases where red light has been used, pigs respond as though in darkness.

There is currently little research into pigs' flicker sensitivity, but it is unlikely that pigs can see flicker from correctly functioning fluorescent tubes. (Tubes that are failing and have visible flicker to humans should be removed.)

Seasonality and Productivity

A pig's reproductive success can be seasonally-affected, with reduced reproduction during the summer months; the predominant reason for this being temperature-related.

Controlling day-length in pig units can affect reproductive behaviour and success. However, lighting only plays a minor part in this subject with the real impact coming from sire line traits.

Other important effects of seasonality:

Increasing day length (15–18 hours) increases piglet suckling

Increasing day length increases food intake in growers/finishers

24- hour light can increase stress levels and disruptive behaviour can reduce productivity (especially in young pigs).

Welfare

Twenty-four hour light can increase stress levels in pigs. Bright luminance can also result in eye damage and weight loss. Aside from these issues, generally, pig behaviour is affected very little by lighting factors and they are highly tolerant/adaptable to artificial lighting regimes.

Legislation

Currently, Defra states that pigs in buildings with no natural light should have at least 40 lux of additional light for a minimum period of eight hours per day. The original research on which this was based stated that 40 to 80 lux is sufficient to allow pigs to see objects, visual signs and distinguish between night and day. However, more recent work did not fully confirm this, as it was stated the light source (incandescent or fluorescent) will also effect how brightly the pig sees their environment. Fluorescent lighting is seen as nearly twice as bright as incandescent lighting using the same lux level.