Studies on the reproduction of farmed fallow deer (Dama dama)

Abstract

The studies described in this thesis investigated physiological and behavioural aspects of reproduction in farmed fallow deer. The initial studies examined puberty. Pubertal development in fallow does (Section 2.1) was associated with a significant rise in mean serum progesterone levels between 10 and 15 months of age, which declined back to earlier prepubertal levels immediately before the onset of oestrous activity at 16 months of age. Almost all (55/56) pubertal does exhibited first oestrus at, or close to, 16 months of age and the mean date of this oestrus was not significantly different from that of first oestrus of the breeding season for older does. Prepubertal fallow bucks (Section 2.2) exhibited a markedly seasonal growth pattern, with entire bucks growing at a significantly greater rate than castrated bucks from 9 months of age. Both groups of bucks showed a progressive increase of serum testosterone and androstenedione levels from 12 months of age. However, while this increase was sustained until 16 months of age in the entire bucks, the castrated bucks exhibited a more transient and lower magnitude elevation of serum testosterone levels between 12 and 14 months of age. Castrated bucks failed to develop pedicles.

Other aspects of reproductive physiology were investigated in adult animals. First oestrus of fallow does (Section 3.1) was naturally synchronised within a 12 day period in late April to early May. Mean length (±sd) of the first oestrous cycle was 21.0±0.64 days, but mean cycle length increased significantly as the breeding season progressed.

The duration of the breeding season was 65-135 days (3-6 oestrous cycles) and was positively related to doe age. There was an indication that one or more short-lived luteal cycles from silent ovulations occurred before first oestrus and these may have helped to synchronise this oestrus. Some does appeared to have silent ovulations at the termination of the breeding season.

Hormonal changes around oestrus were investigated by hourly blood sampling of six fallow does (Section 3.2). The preovulatory luteinizing hormone (LH) surge was initiated an hour before the onset of oestrus and there was an indication of a small rise in progesterone secretion at the onset of oestrus. However, serum oestradiol-17β levels showed wide variation during the sampling period (46 hours) with only a slight tendency to rise at the onset of oestrus. Serum androstenedione levels exhibited a marked elevation (2x basal levels) immediately at the onset of oestrus and remained elevated for a further 6 hours. It is proposed that androstenedione may be influential in the expression of oestrous behaviour.

Conception rates, gestation lengths and live-weight/serum progesterone profiles during the gestating period were examined (Section 3.3). Over a 2 year period, 82.7% of does run with fertile bucks conceived at first oestrus matings and 96.0% conceived by second or third oestrus matings. There were no significant effects of fawn sex, doe age or sire on gestation length and the mean (±sd) overall length (n=88) was 234.2±2.7 days. In 1983, pregnant does (n=55) exhibited marked live-weight gains (+10 kg) during the third trimester of pregnancy, whereas non-pregnant does (n=14) showed only slight gains (+2 kg) over the same period. Pregnant does maintained high levels of serum progesterone (>5 ng/ml) during gestation, while non-pregnant does exhibited cyclical fluctuations of progesterone secretion during the breeding season (April to October) but low levels (<1.0 ng/ml) at the cessation of cyclic activity.

The annual cycles of live-weight, neck girth and serum testosterone levels of adult entire and prepubertally castrated fallow bucks were investigated in addition to the annual cycles of testis size and spermatozoal production of the entire bucks (Section 3.4). Entire bucks, which were always significantly heavier (14-18%) than the castrated bucks, exhibited marked live-weight changes, with most rapid live-weight gains occurring over spring and summer months (October to February) and marked live-weight losses during the rut period (April-May). Castrated bucks exhibited similar, but less pronounced, live-weight changes. Furthermore, pre- and post-rut changes in neck girth and serum testosterone levels observed in entire bucks were apparent to a lesser degree in castrated bucks. However, there was no evidence of testosterone secretion in adult castrated bucks. Testicular diameter measurements of entire bucks were poorly correlated with live-weight. The seasonal pattern of changes in testicular size was similar to that for neck girth, both presumably reflecting the observed pattern of testosterone secretion. While there was no significant seasonal variation in mean ejaculate volume (collected by electro-ejaculation), there was considerable variation in spermatozoal characteristics. Viable spermatozoa were absent during summer months (November to January). However, concentrations of viable spermatozoa increased progressively from about February, two months before the rut, and reached peak concentrations in September, four months after the rutting period.

Rutting behaviour of fallow bucks was observed in 1983 (Section 4.1). Groaning vocalisations occurred only during the period of first oestrus matings (~14 days) and there was a close association between the intensity of groaning activity on anyone day and the number of does exhibiting oestrus on that day. Over a 40 day period spanning the period of first oestrus matings, there were marked changes in primary activities. Of particular interest were the significant decrease in grazing activity immediately before and during the mating period and the associated significant increases in standing, walking, investigatory and agonistic activities. There was a 25% loss of buck live-weight associated with rutting activity.

Mating sequences of fallow deer were recorded on 21 occasions in 1983 (Section 4.2). Most does were observed to exhibit characteristic pre-oestrous behaviour, including fence pacing and aggression towards herd mates, between 12 and 24 hours before the onset of oestrus. Overt oestrus was always associated with fervent self-grooming (preening) behaviour by the doe and a marked change in receptivity towards the sexual advances of the buck. Courtship was characterised by repeated non-copulatory mounts by the buck (mean ±sd = 16.4±6.8 mounts including copulation), although the mean (±sd) interval from the first mount to copulation was only 14.8±10.4 minutes. The mount to service ratio was higher than reported for other cervid species, although the courtship interval was similar. Oestrus and courtship were apparently terminated at copulation.

The allocation of primary activities during the mating season was investigated in 1983 for 60 fallow does (Section 4.2). While there was significant circadian variation in group grazing, resting, standing and walking activities, there were only minor changes in group daily activity allocations during a 40 day period spanning the mating period.

Artificial manipulation of reproductive seasonality was investigated in a series of experiments. In the first experiment (Section 5.1) there was no apparent effect of the date of pre-rut buck introduction to mating groups on the onset of oestrus or the incidence of silent ovulations in does. In the second experiment (Section 5.2) fertile oestrus was induced, three weeks before that of control does, in 20/21 (95.2%) does each treated intravaginally with a progesterone CIDR (14 days) followed by an i.m. injection of 500 i.u. PMSG. Ovulation rates ranged from 1 to 4 but were inversely related to PMSG dose/kg live-weight. Non-ovulating, luteinized follicles were a feature of PMSG treatment, particularly at higher dose rates and only 3/21 (14.3%) does conceived at the induced oestrus. Non-conceiving does returned to oestrus 21-27 days later, with the length of the oestrous cycle being positively related to the relative mass of luteinized structures. Does with multiple corpora lutea had higher serum progesterone levels during the oestrous cycle than does with a single corpus luteum. There was an indication that induced does influenced the onset of oestrous activity in herd-mate controls.

In the third experiment (Section 5.3) fertile oestrus was induced, eight weeks before that of untreated does, in 6/13 (46.2%) does treated with progesterone CIDRs followed by the continuous infusion of GnRH (125 ng/h or 250 ng/h) via osmotic mini-pumps. However only one (16.7%) of these does conceived and produced a viable fawn. The remaining does returned to anoestrum until the onset of the natural breeding season.

In the fourth experiment (Section 5.4) daily oral administration of melatonin to entire fallow bucks during summer was successful in advancing temporarily some aspects of reproductive seasonality. In particular, treated bucks exhibited a transient phase of accelerated neck hypertrophy and earlier initiation of spermatozoal production.