Ian D. Corson

Effects of testosterone on pedicle formation and its transformation to antler in castrated male, freemartin and normal female red deer (Cervus elaphus).

Pedicles and antlers are male deer secondary sexual characters. As such, development of these structures is under the control of androgen hormones. Pedicle growth is caused by increasing and elevated plasma testosterone (T) levels, whereas first antler transformation from a fully formed pedicle occurs when the T levels are decreasing. Castration prior to pedicle initiation abrogates future pedicle and antler formation. Female deer also have the potential to develop pedicles and antlers, but they do not normally express this phenotype due to lack of sufficient androgen stimulation. Previous studies have shown that female white-tailed deer could be readily induced to grow pedicles as well as antlers by singular administration of exogenous androgens (EA), but in red deer (Cervus elaphus) singular or irregular EA treatment could only stimulate castrated male, normal or ovariectomised females to grow pedicles, but not antlers. The present study was set out to test whether these EA-induced pedicles in red deer failed to give rise to antlers was because they were constitutively incapable of doing so, or because the plasma T profile naturally exhibited in intact stags was not achieved by the androgen treatment used in these previous studies. Eight castrated red deer stag calves, 3 freemartins (females which were born co-twin to males), and 3 normal female red deer were used in the present study and treated with EA, either as biweekly injections for the castrates or as implants for freemartin and females until the late stage of pedicle growth. Blood sampling was carried out biweekly for the analyses of plasma T and IGF1 concentration. The results showed that the natural plasma T profile in the experimental deer was successfully mimicked through regular EA treatment and subsequent withdrawal at late pedicle growth stage. All castrated males, 2 out of 3 freemartin, and 1 out of 3 normal female red deer formed not only pedicles, but also antlers. Based on these results, we conclude that EA-induced pedicles at least in red deer of the genus Cervus, like those in the genus Odocoileus, are constitutively capable of giving rise to antlers, if they are of sufficient height.

Effect of diet energy density and season on voluntary dry-matter and energy intake in male red deer.

Food intake and growth of red deer is lower in winter than in spring and this reduces the efficiency of venison production. Rumen capacity is also lower during winter and this may contribute to the reduced food intake and therefore growth. In the present study, we investigated the ability of deer to regulate food intake during winter and spring by feeding diets of differing energy densities. Six groups of eight male red deer calves were housed indoors in separate pens. Each group was given, ad libitum , a pelleted diet of a different energy density (8·5, 9·0, 9·5, 10·0, 10·5 and 11·0 MJ metabolizable energy (ME) per kg dry matter (DM) for groups 1 to 6 respectively) but the same amount of protein (156 g/kg DM). Food intake of each group was recorded every 2nd day and animals were weighed every 6 days from 17 May to 9 December. For seasonal comparisons, winter was defined as 24 May to 31 August and spring as 1 September to 9 December. There was no difference ( P > 0·05) between the mean live weights of the groups at any time during the study. Live-weight gain (LWG) reached a minimum on 4 July and was lower in winter than spring (161 v. 308 g/day, s.e.d. = 10·0, P P 0·75 per day) and ME intake (MJ ME per kg M 0·75 per day) decreased until 16 July and increased thereafter. Mean DM intake was lower in winter than spring (83·5 v. 97·2 g/kg M 0·75 per day, s.e.d. = 2·05, P P P P > 0·005) and was lower in winter than spring (0·82 v. 0·95 MJ/kg M 0·75 per day, s.e.d. = 0·25, P m ) across groups and seasons was calculated to be 0·45 (s.e. 0·22) MJ ME per kg M 0·75 and the energy requirement for LWG (ME f ) was 53 (s.e. 8·5) MJ/kg LWG. ME f was related ( P In summary, deer consuming diets with a wide range of energy densities, altered their DM intake, resulting in similar energy intakes and growth rates on all diets. Animals seemed less able to achieve this compensation in winter compared with spring when food intake increased to support the natural rise in growth rate at that time. These results indicate that deer have target growth rates and/or energy intakes that change with season, and are defended by adjusting food intake.

The effect of housing and food restriction during winter on growth of male red deer calves

Low winter growth is a characteristic of male red deer and is caused, in part by a combination of reduced appetite and higher energy expenditure due to cold weather. This study aimed to determine whether housing during winter would reduce energy expenditure and increase the growth rate of male red deer calves. An additional aim was to investigate whether food restriction in winter would be compensated for by increased spring growth. In each of two consecutive years, 80 calves were randomly allocated to eight groups (no. = 10) comprising two replicates of four treatments during winter. Groups were housed inside (I) or outside (O) and given food either ad libitum (AL) or restricted (R) to maintain live weight. Winter treatments (southern hemisphere) ran from 22 May to 25 August (year 1) and from 5 June to 5 September (year 2). During these periods, animals were weighed weekly and group food intake recorded daily. At the end of winter animals were moved outside onto pasture and weighed monthly until the end of spring (27 November, year 1 and 7 December, year 2). In year 2 weighing continued during summer, until 4 April. The animals were slaughtered on 28 November and 18 January (year 1) and 5 April (year 2). The effect of housing on live-weight gain (LWG) and dry-matter intake (DM1) in AL groups was not significant in either year. However in R groups, O had a higher DMI than I in both years (P In conclusion, housing calves given food ad libitum during winter did not reduce DMI or increase growth rate. When normal growth rates were prevented by restricting food intake, housing lowered DMI requirement, although such a situation is unlikely to be a useful farm management practice as recovery from the growth check was slow. Annual variations in climate may determine both the food savings made by housing and the extent of compensatory growth of food-restricted animals in spring.

Effect of feeding supplements on the intake and live-weight gain of male red deer given silage during winter

The live-weight gain (LWG) of young male red deer in New Zealand naturally slows during winter and feeding diets of mainly silage appears to exacerbate this effect. We aimed to quantify the effect of feeding silage on intake and LWG during winter and the ability to improve LWG by feeding supplements, mainly in the form of barley. Seven groups of eight deer were maintained outside in gravelled enclosures and offered silage ad libitum for 94 days during winter. Six groups were given supplements (950 g barley with 50 g rapeseed meal per kg to make all diets isonitrogenous) at rates of proportionately 0·2, 0·4, 0·5, 0·6, 0·7 and 0·9 of the metabolizable energy (ME) intake of the group given only silage (0). The study also examined the effect of the winter treatments on subsequent LWG to slaughter weight whilst grazing on pasture during spring and into summer (102 days). Increasing supplement intake resulted in a decrease in silage dry matter (DM) and ME intake ( P P P P This study has confirmed that the LWG of young male deer is low during winter when given only silage and that feeding supplements increases total ME intake and LWG. The reduced LWG due to silage feeding was not compensated for on pasture during spring and summer, thus delaying the time to reach slaughter weight by approximately 1 month. High proportions of silage in the diet appear unsuitable for young male deer if the aim is to achieve rapid LWG during winter.

Photoperiodic requirements for rapid growth in young male red deer

Winter growth of young male red deer can be increased by exposure to 16 h of light (L) and 8 h of dark (D) per day (16L: 8D). This study tested the duration of photoperiod required for this growth response, determined if the time to reach slaughter weight can be reduced and monitored plasma IGF-1, prolactin and reproductive development. Fifty male calves were allocated to five equal groups. Four groups were housed indoors and for 33 weeks from the winter solstice (22 June, southern hemisphere) until 11 February were placed under either 16L: 8D (16L), 13·25L: 10·75D (13L), 10·751:13·25D (111) or 8L: 16D (8L) photoperiods. The fifth group of deer (OC) remained outside in a gravelled enclosure. All groups were given a pelleted diet ad libitum. Group food intake was recorded daily, individual live weight was measured weekly and testes diameter and blood samples taken at weekly or 2-week intervals. Plasma prolactin concentrations in 16L increased within 4 weeks of treatment and were different ( P P P v. 38·5 for 13L, 35·7 for 11L, 37·0 for 8L and 37·4 for OC; s.e.d. 3·76). Food intake was positively related to growth rate in a similar way among the inside groups ( P P P P P This study confirmed that 16L: 8D stimulates rapid growth of young male red deer during winter for sufficient time to achieve an earlier slaughter date. The live-weight advantage was lost by late summer however. The increased growth rate was mediated by food intake and associated with increases in IGF-1 and prolactin and earlier reproductive development. Photoperiods of 13 h of light per day or less did not stimulate growth and increases in IGF-1 and prolactin were of a lower amplitude than under 16L: 8D.

Antler Growth Patterns in Young Red Deer Stags

Stages of the antler cycle were recorded for up to 16 red deer stags (Cervus elaphus) as 2-, 3- and 4-year-olds. Antler dimensions were recorded at weekly intervals for five stags over 2 successive years; the pattern of growth in antler length and estimated volume were analyzed for these stags using the generalized logistic growth curve. The results show marked effects of age on the date of casting and the period in velvet, and indicate the appropriateness of the generalized logistic growth curve in analysing antler growth patterns. At the completion of growth, the main beam made up approximately 71% of the total volume, the brow tine 7%, the trez tine 8%, and the royal tines 14%.

Prolactin does not enhance glucose-stimulated insulin release in red deer stags

Red deer stags have a seasonal pattern of insulin secretion that is characterized by both elevated basal and glucose-stimulated insulin release in summer compared with winter. Since the seasonal timing of this pattern is similar to that of prolactin and growth rate, the objectives of this study were: first, to determine whether prolactin is associated with the enhanced secretion of insulin during the summer growth period, and second, to determine whether a chronic reduction in plasma prolactin levels would alter body composition. Prolactin was suppressed in plasma using a long-acting form of the dopamine agonist bromocriptine (parlodel LA), which was administered at one of four doses (0-0.3 mg/kg) to each of four groups of castrate stags. Bromocriptine was administered during two 6-wk periods; the first in winter and the second in summer. During the sixth wk of each period, each animal was given three IVGTT at the following glucose doses (10 mg/kg, 70 mg/kg, and 200 mg/kg). Two d later, ovine prolactin was administered to each animal (0.08 mg/kg) and a single IVGTT (70 mg/kg) was given 2 hr later. Body composition was determined by the tritriated water dilution method at the beginning and end of each 6-wk treatment. Chronic suppression of prolactin during winter or summer did not significantly alter the amount of insulin released after each IVGTT, nor did it significantly alter body composition. Furthermore, acute administration of prolactin did not significantly enhance the release of insulin following an IVGTT, during winter or summer treatment periods. It is concluded that elevated levels of prolactin in summer do not enhance the release of insulin to glucose in red deer. Furthermore, a reduction in growth rate following a reduction in plasma prolactin is not associated with a change in body composition.

Changes in Live Weight and the Reproductive Tract of Farmed Red Deer Stags from 6 to 27 Months of Age

Groups of farmed red deer stags (n = 49) were weighed and slaughtered, and the reproductive tracts dissected, at 2- or 3-month intervals from age 6 to 27 months. The penis, testes, epididymides, seminal vesicles, ampullae, and prostate gland were weighed separately, and testes sections were examined using light microscopy. At 6 months of age reproductive tracts were immature. The seminiferous tubules were mostly solid and contained spermatogonia only. At 9 months the testes had doubled in size, and spermatocytes were seen indicating that spermatogenesis had begun; at 12 months, elongated spermatids were present. A dramatic increase in the weight of the reproductive tract occurred between 12 and 15 months of age at which time the seminiferous tubules were mature and fully active. This was coincident with the timing of the seasonal rut in older stags. Over winter, from 15 to 21 months of age, weight of the reproductive tracts decreased, and live weights fell slightly. Live weights began to increase again at 24 months of age, and this was associated with the resumption of reproductive tract development. At the time of the second rut in March (27 months of age), the testes and accessory glands attained their greatest weights recorded. Live weights at slaughter increased during spring and summer and fell in autumn. We conclude that reproductive development of farmed red deer stags from 6 to 27 months of age consists of two phases of growth which occur during spring and early summer each year. The first phase includes the onset of spermatogenesis indicating that puberty occurs between 9 and 15 months of age. After puberty is attained, the stags exhibit a decline in reproductive state over winter followed by recrudescence in spring, similar to the reproductive cycle of adult stags.