Changes in the photoperiod or period of lighting that cows are exposed to over a 24-hour time period can increase milk production. Studies with milking cows have shown that a longer day length increases daily milk production by 5 lbs per cow. To achieve this response, milking cows need 16 hours of light followed by 8 hours of dark. When using artificial lighting sources, 20 footcandles of light must be supplied when measured at 3 feet from the stall bed or feedbunk.


With dry cows, recent studies have shown that short day lengths (8 hours light : 16 hour dark) increase milk production during the next lactation. This research helps explain why cows dry in the winter milk better than those dry during the summer. Thus, ideal lighting patterns are opposite for dry cows as compared to the milking herd.

Author:  Donna M. Amaral-Phillips