In two experiments the growth, body composition and behaviour of steers and heifers kept in a building with natural day length only (average 9-7 h/day, treatment N) were compared with similar groups of animals kept in identical housing with the day length artificially extended to 16 h/day, (treatment L). The effects were recorded for 126 days in steers and 180 days in heifers, with both groups of animals being slaughtered in March when the two experiments ended. There were no effects over the entire experiment on the growth rate or food intake of either steers or heifers. The growth of the steers was reduced in the first 2 weeks after the lights were switched on but they gained more weight to compensate over the next 8 weeks. Over the whole experiment there was no treatment effect on food conversion ratio for either steers or heifers but it was reduced for steers on treatment L over the first 10 weeks. Steers in treatment N produced fatter carcasses than those on treatment L. Ultrasonic scanning of the heifers showed that those on treatment N deposited more fatty tissue between autumn and winter and less between winter and spring compared with those on treatment L.The behaviour of steers on treatment L did not vary over the experiment but steers on treatment N changed their behaviour with season. They slept for more time in winter and less in spring. Over the whole experiment steers on treatment L slept less and spent more time lying ruminating than those on treatment N but the total time spent lying was not affected by treatment. In contrast, the heifers on treatment L lay down for longer than those on treatment N, suggesting that the effect of supplementary light on lying time, which has been observed previously with dairy cows, is confined to female cattle. Heifers on treatment L started mounting each other earlier than heifers on treatment N and, like the steers, they spent less time sleeping It is concluded that extending the photoperiod for cattle in winter reduced body fatness in both steers and heifers and increased the time heifers spend lying down but that there were no major effects on growth rate or food intake.

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Two experiments were conducted to compare the response oflactating cows to supplementary light in their lying area during increasing and decreasing natural daylength. During decreasing daylength, supplementary light in the lying area increased the time cows spent lying down and considerably reduced calculated food intake, milk production, live weight and body condition, so that lights were installed in the feeding area for the last half of the experiment, which partially restored intake and live weight. Plasma cortisol concentrations and milk somatic cell counts were increased by supplementary light in decreasing daylength before, but not after, lights were installed in the feeding passage, suggesting that cows may have been stressed by the difficulties encountered during feeding in the dark. During increasing daylength supplementary light did not affect lying time, had less effect on food intake and no effect on milk production or live weight. There was a small reduction in plasma corticosteroid by the end of the experiment with supplementary light. It is concluded that providing supplementary light only in the lying area of dairy cows will have adverse effects on their production and welfare in decreasing, but not increasing daylength

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.