Lighting

Cows are susceptible to photoperiodic manipulation. Perception of light suppresses the secretion of melatonin by the pineal gland, whilst darkness enhances its secretion. The change in melatonin secretion affects day length dependent, seasonal physiological functions of animals.

Lactating Cows

Long-day lighting aims to deliver a constant, 16- to 18-hour period of light, and a 6- to 8-hour period of darkness (18 light: 6 dark) for lactating cows. Long days are associated with increased prolactin secretion, reduced prolactin receptor expression, and increased circulating levels of IGF-1, all of which result in an increase in milk production of ~5 lb/day (2.3 kg/day) without any change in components when compared to 12 light:12 dark. The increase in milk yield precedes an increase in dry matter intake (DMI), thus an increase in DMI of ~2 lb/day (0.91 kg/day) must be allowed for when feed is delivered.

For three times a day milking herds, milking intervals must allow for a minimum of 6 hours of uninterrupted darkness between two of the milkings.

Target light intensity for long-day lighting is 15 to 20 foot-candles (162 to 215 lux) of uniform illumination at a level of 3 feet (0.9 m) above the stall surface. The milk production response requires consistent light intensities at the cows’ eye of 15 foot-candles (162 lux). However, 20 foot-candles (215 lux) has been recommended because as bulbs age and collect dust and dirt over time, the light intensity decreases. Lights should be cleaned on a routine basis to have maximum effect.

For low ceiling buildings, LED or fluorescent lighting is preferred while for higher ceilings, LED or metal halide lamps may be a better choice. Spacing between the lamps is typically 1.5 times the mounting height.

For cow movement and observation during the ‘dark’, dim red lights (~15 watts) at 20- to 30-foot (6.1 to 9.1 m) intervals may be used as this will not be perceived by the cow as ‘light’.

The timing of turning the lights on and off must also be consistent each day, so having timers is essential. On exceptionally bright days, a photo sensor can be used to turn some lights off to avoid using more energy than needed.

Dry Cows

In contrast to lactating cows, dry cows are responsive to short-day lighting which results in ~7 lb/day (3.2 kg/day) greater production once the cow begins to lactate. The response is associated with greater expression of prolactin receptor mRNA at the mammary gland, which is associated with greater mammary development during the dry period, resulting in higher milk yield during lactation. Improved immune function has also been recognized.

Implementing a photoperiod of 6 light: 18 dark in practice has been difficult to achieve on farms, but cross ventilated and other large mechanically ventilated barns have better ability to keep dry cows under darkness.