ESTROUS SYNCHRONIZATION IN FARMED FALLOW DEER (DAMA-DAMA) - EFFECTS OF SEASON, TREATMENT DURATION AND THE MALE ON THE EFFICACY OF THE INTRAVAGINAL CIDR DEVICE

In three experiments conducted over successive breeding seasons we aim ed to determine the effects of season, treatment duration and the male on the incidence of oestrus, oestrous synchrony, ovulation and fertil ity in farmed fallow deer following treatment with an intravaginal pro gesterone device (CIDR-G). Stage of breeding season was studied in Exp eriment 1. Synchronisation involved device insertion for 14 days, with injections of prostaglandin analogue (PG) at insertion and 10 days la ter. Eighty mature does were divided into four equal groups that each received at least two repeated synchronisation treatments over a 9 wee k period. Treatment initiation was staggered between successive groups by 7 day intervals from March to May to span the rut. Untreated contr ol does (n=42) were mated to a crayon-harnessed buck to define the rut . Oestrus was recorded an 69% of occasions and ovulation on 80% among the treated does after device withdrawal. Oestrus was followed by ovul ation on 98% of occasions. Silent ovulations occurred most frequently early in the breeding season. An oestrous response was absent initiall y but increased to 89-100% after the onset of natural rutting. Mean in tervals to oestrous onset decreased, and oestrous synchrony improved p rogressively during the study, reflecting a pronounced seasonal effect . The effects of treatment duration on oestrous synchrony, ovulation a nd fertility were investigated in Experiment 2. Each of 80 mature does had a device inserted for 20, 17, 14, 11, or 8 days and with PG 48 h after insertion, Device withdrawal occurred synchronously on 6 May. Do es were inseminated by laparoscopy 70 h after device withdrawal. Oestr us was detected in 84% of does, but varied from more than 90% for trea tments of 14-20 days to 81% and 50% with the intervals of 11 days and 8 days, respectively (P< 0.001). Conception rates, assessed by rectal ultrasonography 45 days after artificial insemination, varied from 44% (17 days) to 80% (14 days) (P=0.10), with a significant interaction b etween the occurrence of oestrus and conception rate (P<0.05) manifest as improved conception rates amongst oestrous does receiving the 8 da y treatment. Plasma progesterone profiles indicated that all treated d oes ovulated, but some delayed responses with the shortest treatment i nterval were due to the presence of luteal tissue at device removal. T he effects of buck presence or absence on ovulation and fertility with in the breeding season were investigated in Experiment 3. Does were al located to one of three treatment groups (n=30, n=30 and n=28) which w ere run continuously in the presence of a vasectomised buck, or isolat ed from bucks until 10 days after AI, or completely isolated from buck s throughout the study. All does were synchronised with a device inser ted for 14 days and were inseminated laparoscopically as in Experiment 2. Differences in conception rate to AI, ranging from 43% (13/30) to 68% (19/28), were not significant. Analysis of plasma progesterone pro files indicated that all does ovulated following device withdrawal. Th ese studies have demonstrated marked effects of season and treatment d uration on the efficacy of the CIDR device to synchronise oestrus and ovulation in fallow deer. Furthermore, it is concluded that buck prese nce is not a prerequisite for an ovulatory response.