The effect of daily photoperiod on the wool growth of Merino rams subjected to unrestricted and restricted feeding regimes

Abstract

Twelve adult Merino rams were divided into two groups matched for body weight and previous fleece weights. One group was subjected to a reversed and accentuated rhythm of seasonal changes in day length. The second group received normal seasonal changes in day length (latitude 32¦s). There was no temperature control for either group. For eighteen months, these rams were fed a constant ration ad lib. Daily food intakes and wool growth from a tattooed mid-side patch were recorded. Although the periodic differences in wool growth were very highly significant (P<0.001), no well defined rhythm of wool growth was expressed. There was a highly significant treatment x period interaction (P<0.001). Examination of daily food intake values revealed very highly significant period interaction ; due to a positive relation between day length and food intake during part of the eighteen months. In each treatment group, 75 per cent of the period variation in wool growth could be accounted for by variations in food intake. During a further period of fifteen months, when all rams received the same quantity of a constant diet, there was a progressive loss of body weight which amounted to 18 per cent of the initial weight in each group. The wool growth responses of the two groups were similar, and there was no significant interaction term. The very highly significant period variation in wool growth was confined largely to the first three months following the decreased intake. It appears that temperature and day length have little direct effort on wool growth of Merino sheep. However, day length may influence wool growth indirectly through its effect on voluntary food intake.