INCREASED WINTER GROWTH IN MALE RED DEER CALVES UNDER AN EXTENDED PHOTOPERIOD

The growth of male red deer slows during the first winter of life befo re increasing again during spring. This study aimed to determine if th is period of slow growth could be minimized using artificial photoperi ods during autumn and winter (10 April (week 1) to II September (week 23), southern hemisphere). Four groups of deer (no. = 10) were housed indoors as follows. Two groups were placed on a winter solstice photop eriod (8.5 light (L) : 15.5 dark (D)) and given either a natural incre ase in photoperiod to 11.25L : 12.75D (WSH) or held on 8.5L : 15.5D fo r 7 weeks followed by an abrupt increase to 11.25L : 12.75D (WSH). One group was exposed to a summer solstice photoperiod of 16L : 8D (SS) a nd one group exposed to a natural photoperiodic pattern (IC). A fifth group of deer (no. = 10) tons maintained outside on a gravelled enclos ure under natural changes in photoperiod (OC). All groups were given a diet containing 160 g protein per kg and 11.0 MJ metabolizable energy per kg dry matter (DM) ad libitum. All animals were weighed weekly an d group food intake recorded daily. Metatarsal length was measured at weeks 3, 17 and 22 from the start of treatments. The major differences occurred between SS and the other groups. After a period of slower gr owth (weeks 1 to 5, SS = 88 g/day v, 168 g/day other groups, s.e.d. 31 .2, P < 0.05), SS grew more rapidly from week 10 TP < 0.01). As a resu lt, SS was heaviest from week 17 (P < 0.05) until the end of the exper iment (P < 0.01). The mean growth rate of SS animals from weeks 10 to 23 was 346 g/day compared with 173 g/day (s.e.d. 15.3; P < 0.001) for the other groups. Over the whole experiment, SS animals gained 42.3 kg live weight, compared with 31.1 kg for WSN, 26.6 kg for WSH, 25.1 kg for OC and 23.7 kg for IC (s.e.d. 2.08 kg, P < 0.01). The DM intake of SS from week 9 until the end of the experiment averaged 2.04 kg DM pe r head per day compared with 1.48 (s.e. 0.041) kg DM per head per day for the mean of the other groups. Metatarsal length increased more in SS than the other groups (P < 0.001) between weeks 3 and 17 and was lo ngest in SS at weeks 17 and 22 (P < 0.01). Exposure to a 16L:8D photop eriod during winter advanced the rapid growth of red deer calves norma lly associated with spring and summer. This response may be used to ad vance slaughter dates for venison production.