THE EFFECT OF SUPPLEMENTARY LIGHT DURING WINTER ON THE GROWTH, BODY-COMPOSITION AND BEHAVIOR OF STEERS AND HEIFERS

In two experiments the growth, body composition and behaviour of steer s and heifers kept in a building with natural day length only (average 9.7 h/day, treatment N) weve 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 st eers and 180 days in heifers, with both groups of animals being slaugh tered in March when the two experiments ended. There were no effects o ver 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 move weight t o compensate over the next 8 weeks. Over the whole experiment there wa s no treatment effect on food conversion ratio for either steers or he ifers but it was reduced for steers on treatment L over the first 10 w eeks. Steers in treatment N produced fatter carcasses than those on tr eatment L. Ultrasonic scanning of the heifers showed that those on tre atment N deposited more fatty tissue between autumn and winter and les s between winter and spring compared with those on treatment L. The be haviour of steers on treatment L did not vary over the experiment but steers on treatment N changed their behaviour with season. They slept for move time in winter and less in spring. Over the whole experiment steers ob treatment L slept less and spent move time lying ruminating than those on treatment N but the total time spent lying was not affec ted by treatment. In contrast, the heifers on treatment L lay down for longer than those on treatment N, suggesting that the effect of suppl ementary light on lying time, which has been observed previously with dairy cows, is confined to female cattle. Heifers on treatment L start ed mounting each other earlier than heifers on treatment N and, like t he steers, they spent less time sleeping It is concluded that extendin g the photoperiod for cattle in winter reduced body fatness in both st eers and heifers and increased the time heifers spend lying down but t hat there were no major effects on growth rate or food intake.