In sheep, the effects of a long day photoperiod can be mimicked by providing a ‘split night’ light stimulus during the dark phase of a short-day photoperiod. This study tested the hypothesis that a similar response to a split night photoperiod occurs in deer. From 6 May until 3 September 2003, three groups of weaner red deer stags (n = 10) were subjected to: natural daily photoperiods (short days, experiencing the normal seasonal pattern of daylight), a long day photoperiod (16L:8D, where L = h of light, D = h of darkness) or natural daily photoperiods with a period of 1 h of light (circa 370 lux) during the dark phase (split night). For the first 3 months, liveweight gain was similar in all groups (approx. 140 g/day). However, growth of long-day exposed animals began to exceed that of the other treatments so that after 6 August their mean liveweight was significantly (P < 0.01) greater than that of the other groups. From 26 June to 3 September mean liveweight gain was, 324 ± 28.3, 209 ± 23.9 and 186 ± 20.6 g/day for long day, split night and short day photoperiod groups, respectively. The long day group had the highest voluntary feed intake and appeared to initiate antler pedicle growth and testicular enlargement earlier than the other groups. Plasma prolactin concentration was elevated (P < 0.01) by the long day treatment (mean for long day group at 9 July = 33.4 ± 4.09 versus means of 6.9 ± 3.75 and 2.9 ± 0.99, ng/ml for split night and short day groups, respectively). These results show no stimulatory effect of the split night photoperiod on growth of red deer. It is concluded that some of the photoperiodic signals that can cause physiological changes in sheep are not effective in deer and, hence, there are differences in the underlying mechanisms of photoperiodism between these two species.
Proceedings of the New Zealand Society of Animal Production, Volume 64, Hamilton, 63-66, 2004
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