The effect of daylength on the growth of lambs 4. Daylength extension to 20h under practical conditions

Abstract

ABSTRACT1. Four experiments were performed to study the effects on the growth of lambs of extending natural daylength to 20 h with dim artificial light, under management conditions similar to those on commercial farms.2. Thirty-six female lambs aged 6 months were given a concentrate ration at a restricted level in groups of nine; there was significantly faster live-weight gain in the two groups that received extra light but no effect on carcass weight or linear measurements.3. Forty-eight castrated male lambs were fed either ad libitum or at a restricted level on a concentrate diet; half were given additional light. Feeding ad libitum gave faster growth than restricted feeding but there were no significant effects of daylength.4. One hundred and fourteen lambs of mixed sex were offered silage ad libitum plus one of three concentrate supplements at an average of 0·25 kg per head per day. Half were exposed to 20·h daylength from mid-October until slaughter in mid-January. There were no effects of light treatment on growth or carcass weights.5. The fourth experiment was a repeat of the third and again there were no effects of extended daylength.6. It is concluded that this method of controlling daylength is not appropriate for commercial use.