ABSTRACT

Non-domesticated seasonally breeding ungulates exhibit marked seasonal changes in metabolic rate, voluntary food intake (VFI), pelage growth and moult and hormone secretion. It is not known whether these seasonal rhythms are regulated by the same central processes which control the onset and termination of the breeding season. Here we compare two closely related deer species which have significantly different mating and calving seasons. Seasonal changes in VFI, liveweight, coat growth, plasma prolactin and tri-iodothyronine (T₃), and the timing of the breeding season were examined over a 15-month period in six adult post-pubertal red and Père David's deer from January to April the following year. The timing of the seasonal changes in prolactin, T₃, VFI and coat growth were all significantly advanced by 56, 23, 60 and 54 days respectively in the Père David's deer. The times of onset and termination of the breeding season of Père David's deer were also significantly advanced by 90 days, but in both species, the breeding season was of similar duration (160 ± 5 (s.e.m.) days). Changes in liveweight of adult red deer could be explained by changes in VFI rather than efficiency of utilization. This was not the case in Père David's deer and may indicate seasonal changes in the efficiency of energy utilization. In order to establish whether these species differences develop with age, we undertook a second study in which seasonal changes in VFI, growth, plasma prolactin concentrations and the timing of the onset of the breeding season were recorded for ten red deer and six Père David's deer from 6 to 18 months of age. Both species exhibited a similar decline in VFI in the first autumn of life. Subsequently, the Père David's deer exhibited an advance in the timing of the seasonal peak in VFI and prolactin (21 and 66 days respectively); puberty occurred 3 months earlier than in red deer. The earlier breeding season of the Père David's deer was associated with a significant advance in a range of seasonal endocrine and physiological parameters. These species differences may develop with age. Our data indicate that seasonal patterns of metabolism and growth may be closely linked to those mechanisms which also regulate the onset and termination of the breeding season.

Journal of Endocrinology (1989) 122, 733–745

ABSTRACT

Seventeen red deer hinds were housed in individual pens and from 28 February until 11 November were injected each week with vehicle (group A; n = 6) or 5 (group B; n = 6) or 12·5 mg (group C; n = 5) of a long-acting formulation of bromocriptine. Liveweight and voluntary food intake (VFI) were recorded for each hind, and blood was collected for determination of progesterone, prolactin, tri-iodothyronine (T₃) and cortisol concentrations by radioimmunoassay. Treatment with the high dose of bromocriptine was associated with a significant (P <0·05) reduction in VFI, with the effect being greatest between March and July. There was no treatment effect on liveweight, but there was a significant (P <0·01) interaction between time and treatment due to the faster rate of weight gain in control animals at the beginning of the experiment. Changes in liveweight could be explained by changes in VFI rather than by changes in the efficiency of utilization of intake. Termination of the breeding season was significantly (P <0·01) delayed by 54 days in group C hinds. Growth of the summer coat and subsequent winter coats was delayed by 1 and 3 months respectively in group C hinds, and in groups B and C the duration that animals were in summer coat was increased by about 1 month. The seasonal increase in prolactin concentrations was seen in all groups, but levels were significantly (P <0·05) lower in group C hinds. Concentrations of T₃ and cortisol were not affected by bromocriptine.

J. Endocr. (1988) 119, 413–420

ABSTRACT

Three experiments were conducted in the period between July and November with non-lactating red deer hinds to describe the effects of treatment with melatonin during this period on voluntary food intake (VFI), the onset of the breeding season, coat changes and plasma concentrations of prolactin and tri-iodothyronine (T₃), and to examine whether prolactin mediated the observed effects.

In experiment 1, eight animals were treated orally each day with either 10 mg melatonin at 16.00 h or 10 mg melatonin at 16.00 h plus 10 mg domperidone (a dopamine antagonist) given twice daily for 120 days from July; eight animals were maintained as controls. In experiment 2, the same numbers of animals per treatment were used to compare treatments in which 10 mg melatonin or 20 mg bromocriptine (a dopamine agonist) were given orally each day at 16.00 h for 119 days from late June and compared with an untreated control group. In experiment 3, six animals were treated daily for 105 days from mid August with 5 mg domperidone given i.m. and compared with six control animals.

In experiments 1 and 2, the VFI of control animals reached a peak in late August and thereafter declined. Melatonin-treated animals showed a similar pattern but the peak in VFI was significantly (P<0·05) advanced by 2 weeks compared with controls, although the VFIs of both groups were similar in November. The mean date of onset of the breeding season of the melatonin-treated animals was advanced significantly (P < 0·05) by 23 days in both experiments and the coats of these animals had less undercoat and were pale coloured and patchy compared with the controls. The changes in VFI, coat and the onset of the breeding season were associated with the rapid decline in plasma prolactin concentration after the start of the melatonin treatment and significantly (P<0·01) lower plasma T₃ concentrations than those of control animals.

In experiments 1 and 3, plasma prolactin concentrations in animals treated with domperidone were higher than those of controls for periods of 2–3 weeks. These short-term increases in plasma prolactin concentration were not associated with changes in VFI, coat or onset of the breeding season compared with controls.

In experiment 2, the pattern of decline in plasma prolactin concentrations was the same in bromocriptine-treated animals as in the melatonin-treated animals; plasma T₃ concentrations were also similar in the two groups. The pattern of change in VFI over time in bromocriptine-treated animals was significantly (P<0·05) different from that of melatonin-treated animals and there was also a reduced amount and length of winter coat in the bromocriptine-treated animals. The mean date of onset of the breeding season in bromocriptine-treated animals was not significantly different from that of controls. It was concluded that a reduction in plasma prolactin concentration induced by bromocriptine produced different effects from that induced by melatonin treatment and that the effects of melatonin are unlikely to be induced through changes in contemporary plasma prolactin concentrations.

Journal of Endocrinology (1990) 125, 241–249

ABSTRACT

Plasma samples were obtained throughout pregnancy and pseudopregnancy from Sprague–Dawley (SD) rats and during pregnancy from rats of the Munich Wistar (MW) strain. The concentrations of progesterone, oestradiol, prolactin, plasma renin activity (PRA), aldosterone and corticosterone were measured by radioimmunoassay to establish hormonal profiles in the two strains of rat.

Circulating progesterone concentrations in both strains of rat were significantly higher during pregnancy than in virgin controls, except at term in the SD group. The hormonal pattern for pseudopregnancy was similar to that of the first half of pregnancy. Oestradiol concentrations were similar to, or lower than, those in virgin controls throughout pseudopregnancy and for the first 2 weeks of pregnancy in both strains of rat. Increased concentrations of steroid were seen only in the pregnant groups towards term. In SD rats, highest prolactin concentrations were apparent during the first half of pregnancy and pseudopregnancy, and at term in the pregnant group. Pregnant MW rats showed a different profile for this hormone, with low levels throughout pregnancy except at term. In all groups PRA rose to a peak at day 9 and decreased to day 16. Pregnant SD rats also showed a significant increase at term. Aldosterone concentrations were significantly increased at several stages of pregnancy in both strains of rat, particularly during the second half of gestation. Pseudopregnant animals showed a different hormone profile, with no significant changes until day 16 when lower concentrations were recorded. There was little variation in the circulating corticosterone concentration except in pregnant rats at term when levels fell.

These findings are discussed in relation to the known renal changes of pregnancy and pseudopregnancy.

J. Endocr. (1987) 113, 435–444