2 January 1998

Light up your profits

Investing in lights for dairy

cows could produce an

economic return, according

to American research.

Jessica Buss reports

INCREASING the brightness and duration of lighting for dairy cows could increase profits by as much as £15 to £80 a cow.

This is the conclusion of the Farm Energy Centres Stephen Bettany, drawing on the findings of US research, completed by Alan Tucker, of Michigan State University.

Prof Tuckers research confirms the findings of UK research at Bangor University six years ago. But the US studies show that milk production responses to light can be economic when using efficient light sources, such as high pressure sodium lamps, and at half the level of light that was used at Bangor.

But it is critical that lighting is provided at 150-200 lux, according to Geoff Dahl of Maryland University, US. That is less than half the level of lighting – 400 lux – needed for a well lit office, says Mr Bettany. The 150-200 lux needed for cows must be provided for 16 to 18 hours a day.

"Milk yield stimulation is not triggered unless the light is on for 14-16 hours, so lighting for 18 hours is recommended to ensure a response," says Mr Bettany.

Yield lift

The result is an 8% to 16% increase in yield. Milk fat % may be maintained, but might decrease by up to 0.16%, he warns. It seems that the light increases hormone levels in cattle, including prolactin and progesterone, increasing yield gradually over a number of weeks.

This will result in an extra 1.44 litres a day from a cow yielding 18 litres, worth 30.24p when the milk price is 21p/litre. Increased light levels had no effect on protein and lactose %, or on oestrus cycles.

Cows meet the demand for extra production through increasing feed intake by 6%, and with a typical ration costing £2.33 a cow a day, the extra production adds 13.98p to feed costs, calculates Mr Bettany.

Lighting for 18 hours would cost 2.39p a cow a day and even in the worst scenario – when milk fat reduces by 0.16%, which would reduce any potential additional income by 5.6p a day – the minimum increase in profit due to extra production would be 8.27p a day, or £14.89 a cow over a 180-day winter.

But at the maximum response of 16% increase in yield and no fall in milk fat, the extra profit would be 44.11p a day, or £79.40 for a cow averaging 18 litres over a 180-day winter.

Investment repaid

Providing adequate lights would cost about £1600, when new lights needed fitting throughout a building for a 100-cow herd, so this investment would be repaid in between three months and a year, says Mr Bettany. His estimate is based on installing eight high pressure sodium lights. But he cautions that the lights must be placed correctly depending on the shape of the building, to provide the brightness of light without great variation in lux levels. But it is acceptable to have some darker areas because cows would spend little time in them, he explains. Up to 25% of the area can be below 150 lux.

He stresses that the design of light positions, height and strength of lamps is critical. To get this right would cost £150 for a single building when designed by the Farm Energy Centre. The same computer design programme is used to assess the light and spread already provided, at cow eye height. And FEC may find cheaper options for providing suitable light, by adding to the lighting in place either with high pressure sodium or more fluorescent fittings, adds Mr Bettany.

Low running costs

Fluorescent lighting has low running costs and could provide the light needed, but 32, double 1.8m (6ft) fluorescents only supply a similar amount of light to eight high pressure sodium lights. And the installation and wiring costs are also lower with high pressure sodium.

Ordinary bulbs and tungsten halogen lights, however, have high running costs compared with their light output, and are not economic to use. Low pressure sodium lamps provide a different type of light and are not recommended because their effect on dairy cows has not been tested. &#42

The correct lighting could increase milk yield by 8% to 16% in the winter, according to FECs Stephen Bettany.

Benefits and costs of 18

hours light (p a cow a day)




(+8% to 16%)30.2460.48


Fat (-0.16%)5.6-

Feed (+6%)13.9813.98




&#8226 Provide light for 18 hours day.

&#8226 An extra 8-16% milk production.

&#8226 Could be worth £15-£80 a cow.

The positioning and height of lamps will be critical to ensure the full milk production benefits, says Stephen Bettany (right), pictured with milk producer Chris Dickinson.


&#8226 High pressure sodium cheapest.

&#8226 Fluorescent expensive to fit.

&#8226 Provide 150 lux over 75% of area.

&#8226 Design, height, strength of lamps critical.