Previous studies have shown that bovine performance can be improved by manipulating photoperiod. This may be an acceptable alternative to the use of exogenous hormones but responses have been inconsistent. The objective of this trial was to determine the response of finishing cattle to extended photoperiod.

Sixty-four Hereford x Friesian steers and 48 Charolais x Friesian heifers were finished in consecutive years over the winter housing period under either natural daylength (Control) or daylength extended to 16 hours (16 hour). Lights were installed to provide 16 hour animals with 400 lux at animal eye level. A photocell and timeswitch combination ensured that lights were switched on if natural light levels were below this level between 04.00 and 20.00 GMT. Animals were penned in groups of eight and silage was weighed in daily to each pen. Animals were weighed fortnightly and feed conversion ratios calculated. Prolactin assays were carried out on blood samples taken monthly from 10 animals per treatment. Steer and heifer behaviour was monitored over 24 hours on three occasions.