Cow comfort: 14) Light

Light is an important environmental characteristic in dairy facilities. Proper lighting can improve cow performance and provide a safer and more pleasant work environment.


Dairy cows that are given 16 hours of light continuously each day (16L) will increase milk production from five to 16 percent (eight percent being typical) with feed intake up six percent and they will maintain reproductive performance, when compared to cows receiving 13.5 hours of light or less. This cow response to 16L is not immediate. A response can take two to four weeks or longer to develop, as long as nutrition and other management conditions are acceptable.

Summary of increased photoperiod on milk yield in lactating cows

 Summary of increased photoperiod on milk yield in lactating cows

Summary of 10 studies examining the effect of increased photoperiod on milk yield in lactating cows. Solid bars indicate the average daily milk yield (kg/d) of cows on natural photoperiod (range of 8 to 13.5 hr light/d; control), open bars indicate milk yield (kg/d) of cows exposed to extended photoperiod of 16 to 18 hr of light/d. Source: Dahl, G.E. & D. Petitclerc: Management of photoperiod in the dairy herd for improved production and health.

The best lighting system provides the required amount and quality of light at the least cost. Fluorescent or metal halide lamps that have a colour rendition index of 80 or more are recommended for use in the office and milk room. In stanchion or tied-up barns with relatively low mounting heights, fluorescent lamps are the most practical. The total installation and operating costs of the system must be considered when selecting a fixture type and lamp size. Make sure that all new fixtures and wiring conform to the special requirements of the electrical wiring regulations for livestock buildings and have all new work inspected.

The pineal gland in most mammals is controlled by the amount of light seen through the eyes each day. This includes both the intensity of light (amount) and the length of light exposure (duration). When activated by light, there is a “light signal” sent from the eyes to the hypothalamus and from there to the pineal gland (activating pineal secretion). This pineal secretion includes the substance melatonin. Increased amounts of light exposure actually decrease the amount of melatonin synthesis and release from the pineal gland. In all species studied, melatonin has been found to reach peak concentrations in darkness – in cerebral spinal fluid, blood and urine.


Why is melatonin important? Melatonin operates on the brain and has been shown to produce drowsiness in people. Feel a little tired and run down during the short days of winter? Again, higher levels of melatonin produced naturally by your system cause this effect. In seasonal animals (sheep, deer, etc.) these levels of melatonin actually shut down the reproductive function for the season. In an animal like the lactating dairy cow, short days (less light: more melatonin) do not shut down reproductive function, but they do have a negative effect on appetite and production levels.