Velvet Shedding Research Articles

Phenology of Antler Velvet Shedding in White-Tailed Deer (Odocoileus virginianus) from Central Nebraska

Phenology of Antler Velvet Shedding in White-Tailed Deer (Odocoileus virginianus) from Central Nebraska

Analysis of the male annual antler cycle, reproductive behavior and spotted fawn presence in the tropical white-tailed deer

The rutting season of the white-tailed deer (Odocoileus virginianus) is seasonal in North America, but in tropical latitudes it occurs year-round with peaks locally variable. Reproductive cycle of this species in Costa Rica is variable, clearly seasonal in San Lucas Island but continuous with two birth peaks in Palo Verde and Santa Rosa national parks in northwestern Costa Rica. In Hacienda y Refugio de Vida Silvestre Curú in the Nicoya Peninsula, a site south of these parks but in a different life zone, we observed males with hard antlers in 2015 but only from July to November. We therefore hypothesized that white-tailed deer have a continuous reproductive cycle during the year in Curú because the rainfall pattern is the same as in Palo Verde and Santa Rosa. We visited Curú every month and recorded the status of white-tailed deer antler growth: nubs, velvet, and hard, from January 2016 to December 2019. We also recorded other rut behaviors and the presence of spotted fawns. We recorded 1,134 observations of the status of antler growth, 13 observations on reproductive behavior and 133 observations of spotted fawns. The antler cycle was seasonal in the four years of study. Male antler casting took place from mid-November to mid-February and the growth of new antlers began in mid-December and lasted until mid-March. Velvet shedding occurred in April, May and June, and by July males had hard antlers. The rutting season lasted three months from mid-June to mid-August. Small spotted fawns were observed from the middle of the dry season to the beginning of the rainy season. All this highly contrasts with the reproduction pattern observed in Santa Rosa. Lack of seasonal variation in the photoperiod is likely an important factor that allows deer to reproduce throughout the year in these protected areas, but this variation does not exist in Curú either, where the species is seasonal. The reproductive patterns of white-tailed deer in Central and South America may have evolved in response to seasonal fluctuations in specific food availability, competition, or predation, all of which may be directly related to rainfall patterns. Greater knowledge of the link between rainfall patterns and food availability for deer would be of great help to further our understanding of factors driving the reproduction cycle of the White-tailed deer.

The consequences of living longer-Effects of an experimentally extended velvet antler phase on the histomorphology of antler bone in fallow deer (Dama dama).

Antlers are periodically regenerated paired cranial appendages of male deer (both sexes in reindeer) that constitute the fastest‐growing bones in the animal kingdom. The annual antler cycle of male deer is linked to testicular activity and largely controlled by seasonal fluctuations of testosterone concentrations in their blood. We studied the effects of an experimental doubling (to eight months) of the velvet antler phase, during which the antlers are covered by skin (velvet), on the histomorphology of antler bone in three adult fallow bucks. Extension of the velvet antler phase in the experimental animals had been caused by administration of the antiandrogen cyproterone acetate (CPA). The distal portions of the antlers from two of the CPA‐treated bucks exhibited partial sequestration of the antler cortex, with the separation plane typically located along the border between cortex and spongiosa. It is hypothesized that this was caused by cortical necrosis due to severe ischemia during later stages of the extended velvet antler phase. In places, new cancellous bone had been deposited on the resorption surface of the spongiosa, indicating a regeneration process. Normal fallow deer antlers (“controls”) from this and a previous study, that is, antlers with a timespan of about four months between onset of new antler growth and velvet shedding, exhibited no or only minor bone remodeling and still contained remnants of calcified cartilage in their distal portions. In contrast, the antlers of the three CPA‐treated bucks showed evidence (secondary osteons and resorption cavities) of marked bone remodeling along their entire length and lacked remnants of calcified cartilage. Our results underscore that the typical histological features of antler bone reflect its short‐lived nature. Antlers are not mechanically loaded during the velvet stage, and it is presently unclear what triggered remodeling activity in the antlers whose lifespan had been experimentally extended.

Thermography as a tool to monitor the velvet temperature and ossification stage of fallow deer (Dama dama) antlers under normal and modified photoperiodic conditions

An increase in testosterone levels affects the shedding of velvet which, in turn, influences the behaviour of farm-raised fallow deer bucks. Consequently, the welfare of the farmed animals can be considerably improved by controlling the timing of the velvet shedding period. The aim of this study was to analyse changes in the velvet temperature and the timing of the velvet shedding in farm-raised fallow deer bucks exposed to a modified photoperiod. A total of 28 bucks were examined. The experimental group was subjected to an experimentally modified photoperiod before the direct observations and measurements of the antler temperatures with a thermal imaging camera. The acquired thermograms were useful for analysing the stages and the rate of the antler growth and for predicting the timing of the velvet shedding. The introduction of a long-day photoperiod in spring affected the growth and ossification of the antlers as well as the velvet shedding. The optimal time for antler cutting can be planned based on the identified changes in the velvet temperature in different parts of the antler.

The Antler Cycle and Fecal Testosterone of Male Sambar Deer Rusa unicolor unicolor at the Horton Plains National Park in Sri Lanka.

This study is aimed at evaluating the relationship between endogenous testosterone levels and antler development in male sambar deer (Rusa unicolor unicolor) inhabiting the Horton Plains National Park, Sri Lanka. Seven antler growth stages of sambar were documented based on phenotypic observations for the first time in Sri Lanka as (a) cast, (b) growing 1—single spike, (c) growing 2—antler fork into a Y as the second tine appears, (d) growing 3—velvet begins to harden as the third tine appears, (e) growth completed—velvet shedding begins, (f) hard antler, and (g) casting. Fecal samples were collected every month for a period of eighteen months from male sambar deer in different stages of the antler growth cycle, feeding in the wet patana grasslands of the park, and the fecal testosterone level was estimated by radioimmunoassay. Ten animals were randomly selected from each antler stage for the experiment. The results disclose that the highest concentrations of testosterone were recorded in the hard antler stage. Velvet shedding was preceded by an increase in the testosterone level, and it is the sudden drop in the testosterone concentration which triggers the antler casting. The casting stage corresponded with the lowest mean testosterone concentration. Although the study was able to conclude a clear relationship between the fecal testosterone levels of the male sambar deer in the Horton Plains National Park and their antler stages, there is no clear seasonality for the antler cycle.

EARLY ONSET OF THE REPRODUCTIVE SEASON IN CAPTIVE WHITE-TAILED DEER ( ODOCOILEUS VIRGINIANUS VERAECRUCIS) IN EASTERN MEXICO.

The white-tailed deer ( Odocoileus virginianus) inhabits a wide latitudinal range in the Americas. Deer species dwelling throughout wide latitudinal ranges have developed subspecies with variations in their reproductive seasonality. In northern subspecies of white-tailed deer, such as those from Canada and the United States, the breeding season occurs from October through December. Odocoileus virginianus veraecrucis is a subspecies that inhabits eastern Mexico, and because its reproductive season has not been studied, it is believed to be similar to that from northern subspecies. The objective of the study was to determine the onset of the breeding season and the profile of fecal steroid hormone metabolites throughout the year in captive white-tailed deer subspecies veraecrucis in Mexico. Two groups of adult deer were included: 1) six does and one buck at a Wildlife Conservation Unit, and 2) five does and one buck at a zoo. From each group of deer, representative fecal samples were collected on a weekly basis for 1 yr for fecal analysis of progesterone and estradiol in the does, and testosterone in the bucks. Data on antler casting, parturitions, and velvet shedding were recorded. Progesterone was high during pregnancy and low throughout the parturition period. Estradiol fluctuated throughout the year. Testosterone was high during the rut and low after antler casting. Antlers were cast in March and velvet was shed in August at both sites. Parturitions started in February at the zoo and in April at the Wildlife Unit. In captive white-tailed deer subspecies veraecrucis the breeding season started in July, and therefore earlier than what has been reported for subspecies from northern latitudes.

Labeling studies on cortical bone formation in the antlers of red deer (Cervus elaphus)

The formation and mineralization process of antlers, which constitute the fastest growing bones in vertebrates, is still not fully understood. We used oxytetracycline injections to label different stages of bone formation in antlers of 14 red deer between days 28 and 156 of antler growth. Results show that initially a trabecular scaffold of woven bone is formed which largely replaces a pre-existing scaffold of mineralized cartilage. Lamellar bone is then deposited and from about day 70 onwards, primary osteons fill in the longitudinal tubes lined by the scaffold in a proximal to distal sequence. Mineral apposition rate (MAR) in early stages of primary osteon formation is very high (average 2.15μm/d). Lower MARs were recorded for later stages of primary osteon formation (1.56μm/d) and for the smaller secondary osteons (0.89μm/d). Results suggest a peak in mineral demand around day 100 when the extent of mineralizing surfaces is maximal. A few secondary osteons were formed in a process of antler modeling rather than remodeling, as it occurred simultaneously with formation of primary osteons. The degree of cortical porosity reflects a reduction in MAR during later stages of osteonal growth, whereas cortical thickness is determined earlier. Injections given when the antlers were largely or completely clean from velvet produced no labels in antler bone, strongly suggesting that antlers are dead after velvet shedding. The rapidity of antler mineralization and the short lifespan of antlers make them an extraordinary model to assess the effects of chemicals impairing or promoting bone mineralization.

Morphogenetic aspects of deer antler development

Deer antlers are unique mammalian appendages that have potential for application as a valuable model for biomedical research, such as organ regeneration, bone development and growth control. In this review we described the morphogenetic aspects of antler development, by summarizing relevant information accumulated over the course of our antler research in combine with other published papers. Antler development consists of two distinct phenomena: generation and regeneration. Generation starts with the initiation of a pair of pedicles, permanent bony protuberances on the skull of a male deer, when the animal approaches puberty; proceeds to transformation to antlers when the pedicles reach a species-specific height (around 5 cm in red deer); and terminates with total antler calcification and velvet (antler skin) shedding. Regeneration commences in the spring of the subsequent year with the initiation of new soft antlers growing from the pedicle stumps that remain following the casting of the previous hard antlers; proceeds to the elaboration of multi-branched antlers in summer; and ends up with total antler calcification and velvet shedding in autumn, resulting in the formation of hard bony antlers in winter. Therefore, this paper not only lays the foundation for further development of this valuable biomedical model, but also provides comprehensive background knowledge that will be of use to readers when reading the papers featured in this special issue.

The mechanical properties of red deer antler bone when used in fighting

We assessed the hydration state of antlers and its effect on antler mechanical properties compared with wet femur. Red deer antlers were removed from the head at various times, from a few days after velvet shedding till late in the season, and weighed weekly until after casting time. Antlers cut just after losing their velvet lost weight rapidly in the first few weeks, then settled down and changed weight very little, the latter changes correlating with air relative humidity. Antlers cut later showed little weight change at any time. The water content of cortical and trabecular parts of the contralateral antler was assessed after cutting. Most of the weight loss was from the cancellous, not the cortical, part of the antler. Wet and dry specimens from the antlers, and wet specimens from deer femora, were tested mechanically. Compared with wet bone, wet antler had a much lower modulus of elasticity and bending strength, but a higher work to fracture. Compared with wet bone, dry antler showed a somewhat lower Young's modulus, but a considerably higher bending strength and a much higher work to fracture. The impact energy absorption of dry antler was much greater than that of wet bone. In red deer, the antler is effectively dry during its use in fights, at least in southern Spain. In addition, dry antler, compared with ordinary bone, shows mechanical properties that suit it admirably for its fighting function.

Seasonal antler cycle in a herd of pampas deer ( Ozotoceros bezoarticus) in Uruguay

To describe the yearling antler cycle of pampas deer bucks ( Ozotoceros bezoarticus) 22 bucks and 72 antler cycles have been studied in a semi-captive population. Date of individual antler cast, first day on which the brow and the trez tine were observed, and day of the velvet shedding were registered. Time intervals (days) between first and second antler casts, between first antler cast and the brow tine observation, between brow and trez tines observation and from first antler cast to velvet shedding were calculated. The brow and the trez tine were first observed 22.8±0.6 and 45.9±0.9 days after the first antler cast. Velvet shedding was observed 103.3±2.1 days after the first antler cast. Both antlers casts were observed earlier in adult cycle bucks than in first antler bucks, although the interval between both casts was not different. The interval from the brow tine observation to the trez tine observation was shorter in first antler cycle bucks than in adults. As in other deer species, antler cycle was seasonal, but persistence of cycle-to-cycle antler growth well into adulthood is different from what occurs in most deer species.

Antlers as biomonitors of environmental pollution by lead and fluoride: A review

Antlers are periodically cast and re-grown cranial appendages of deer. Both endochondral and intramembranous ossification are involved in the formation of antler bone. After velvet shedding, antlers are completely bony structures which are referred to as hard antlers. Growing antlers accumulate substances with an affinity to mineralized tissues. Among these substances are lead and fluoride. Due to the seasonally limited life span of antlers, the concentrations of lead and fluoride in hard antlers reflect uptake by the forming bone during a defined, species-specific period of some months. Antlers can thus be viewed as “naturally standardized” environmental samples that are well suited as biomonitors of environmental pollution by bone-seeking contaminants. Because hard antlers are collected by hunters as trophies and kept in private or public collections, material for study can be obtained rather easily. So far, lead concentrations in hard antlers have been reported only from Europe, whereas data for fluoride are available from both Europe and North America. Some studies compared contaminant concentrations in antlers from different regions, while others analyzed time-trends in contaminant levels in antlers from a single region. Using the latter approach, a pronounced drop of lead concentrations during recent decades has been reported for antlers from various European countries. This indicates a marked decline of environmental lead levels that can be attributed mainly to the phase-out of leaded gasoline and, in addition, to a reduction of lead emissions also from stationary sources. In Germany, a corresponding drop has also been recorded for fluoride concentrations in antlers, which is attributed to a decline of fluoride emissions from stationary sources due to improved emission-control measures. There is some evidence that exposure to higher levels of fluoride may lead to an impaired antler mineralization. Using antlers as biomonitors has been shown to be an efficient method for assessing environmental pollution by lead and fluoride at low cost. Further studies using this now well established approach are therefore encouraged.

Relationship between dominance and antler cycle in white-tailed deerOdocoileus virginianus

We tested the hypothesis that there is a negative correlation between rank and order of casting antlers in white-tailed deerOdocoileus virginianus (Zimmermann, 1780) and that dominant individuals will start antler regrowth and velvet shedding earlier than subordinates. We assessed dominance relationship among 14 bucks (1.5 to 7.5 years-of-age) confined in a 0.6 ha enclosure and related hierarchal position to timing of antler casting, initiation of antler regrowth, and initiation of velvet shedding. During 66 observation sessions we recorded 2833 agonistic interactions. Bucks developed an unstable hierarchy with relatively frequent changes in rank, particularly in the upper half of the hierarchy. Antler casting dates were positively correlated with age and wins and losses of agonistic encounters; correlations with body mass approached significance. When age was eliminated as a confounding factor by partial correlation, no significant relationship between antler casting date and other characteristics occurred, except losses. When body mass was eliminated by partial correlation, the relationship between casting date and losses was more pronounced. Timing of antler regrowth was negatively correlated with age, body mass, rank and wins, while positively correlated with losses. The start of velvet shedding was negatively correlated with rank position. Our results are in apparent contrast with previous studies. However, our experimental group contained more individuals in a confined area than is typical for the species. Whitetails may be more susceptible to social stress in captivity than more gregarious species such as red deer, resulting in variable responses to rank position.

Seasonal changes in fecal testosterone concentrations and their relationship to the reproductive behavior, antler cycle and grouping patterns in free-ranging male Pampas deer ( Ozotoceros bezoarticus bezoarticus)

The purpose of this study was to validate noninvasive endocrine monitoring techniques for Pampas deer and to evaluate seasonal changes in testicular steroidogenic activity and their correlation to reproductive behavior, antler cycle and group size. Thus, fecal samples, behavioral data and observations of antler status were collected at monthly intervals during 1 year from free-ranging Pampas deer stags (three radio-collared individuals and 15 random individuals) living in Emas National Park, Brazil (18°S latitude). Fecal steroids were extracted using 80% methanol and steroid concentrations were quantified by a commercial enzyme immunoassay (EIA). Fecal testosterone concentrations peaked in December–January (summer), March (early autumn) and in August–September (winter–spring), with minimal values from April–July. Reproductive behavior had two peaks, the first in December–January, characterized by predominately anogenital sniffing, flehmen, urine sniffing, chasing and mounting behavior, and the second peak in July–September (behavior primarily related to gland marking). There were significant correlations between fecal testosterone and reproductive behavior ( r = 0.490), and between fecal testosterone and antler phases ( r = 0.239). Antler casting and regrowth occurred under low testosterone concentrations, whereas velvet shedding was associated with high concentrations of testosterone. We inferred that Pampas deer stags exhibited a seasonal cycle that modulated sexual behavior and the antler cycle, and we concluded that fecal steroid analysis was a practical and reliable non-invasive method for the evaluation of the endocrine status of free-ranging Pampas deer.

Cryptorchism, hypogonadism and antler malformations in black-tailed deer(Odocoileus hemionus sitkensis) of Kodiak island

Distinct antler malformations, (such as lack of points, distortion of antler forms, incomplete velvet shedding, casting above the coronet and a diagonal separation of cast antlers), were detected in Sitka deer(Odocoileus hemionus sitkensis) of the Kodiak Island (Alaska, USA). Many of these deer were also unilateral or bilateral cryptorchids and a few exhibited a moderate or severe separation of frontal skull bones. Radioimmunoassay analyses of serum revealed signs of hypogonadism: we found higher concentrations of LH (P=0.05) and lower concentrations of T (P=0.037) in bilateral cryptorchids as compared to intact bucks. There was no apparent impairment of spermatogenesis in the remaining testis of the unilateral cryptorchid deer. Unfortunately, no ectopic testes were so far recovered in cryptorchid deer. Surprisingly, only about half of deer with bilateral cryptorchism exhibited hypogonadic symptoms. In the other half of cryptorchid deer, the antlers appeared completely normal and the concentrations of LH or testosterone in the serum of several bucks were in the range of intact deer. It has been postulated that in some cryptorchid deer, ectopic testes can produce sufficient amount of testosterone, which prevents obvious antler and skull malformations, as well as reduces the compensatory elevation of LH. The possible causes of the hypogonadism resulting in cryptorchism and antler malformations are discussed.

New aspects of the regulation of antler development: reevaluation of old dogmas

New evidence supporting the hypothesis that antlers are display organs used as dispensers of pheromones, has resulted from morphological studies of the distribution and size of sebaceous glands in the velvet. These parameters correlate with the life-style of various investigated cervids. Recent hormonal studies seem to confirm that small, permissive amount of testosterone are required for the initiation and growth of antlers, whereas higher concentrations of testosterone are needed for velvet shedding and hardening of antlers. Testosterone (T) may not be the only hormone involved in the formation and calcification of antlers. The testosterone metabolites estrogen and dihydrotestosterone may be crucial for the formation of bone mantle and for the maintenance of viable tissues in the antler core after velvet shedding. The most profound discovery of antlerogenic research in the last decade was the finding that hard, calcified antlers are viable up to several months after velvet shedding Histological studies have revealed the presence of active osteoblasts and observation of rebuilding activity in hard antlers. In addition, the presence of viable blood supply in polished antlers was confirmed by the presence of fluorescent dye injected intravenously three months after velvet shedding.

Hard fallow deer antler: a living bone till antler casting?

Deer antlers are the only mammalian bone structures which regenerate completely every year. Once developed, antlers are cleaned of the velvet-like skin. Presently it is believed that due to velvet shedding the blood supply is interrupted in the solidifying antler bone. Histological examinations were made on different parts of fallow deer antlers investigated from the time of velvet shedding till the antler casting. The present study on hard (polished) antlers revealed living bone with regions presenting living osteocytes, active osteoblasts, osteoid seams and even early stages of trabecular microcallus formation, thus indicating to a continuous bone remodeling. A well developed vascular system was found despite the presence of hard antler bone. The pedicle bone exhibits a rich supply of capillaries and vessels connected to the spongy core of the main branch and the compact bone as well. There is evidence that hard fallow deer antlers possess a functioning vascular system that "keeps the antler moist" resulting in a high impact resistance when fights are most frequent. As late as 3 weeks prior to antler casting a large number of living cells were discovered within the antler core. As we have no doubt that parts of the polished fallow deer antler represent a living bone, we have concluded that a sufficient blood supply of the antler core is maintained almost till the time of antler casting by vessels passing through the antler base.

Territory Establishment and Antler Cycle in Male Roe Deer

AbstractTerritory establishment and antler cycle in male roe deer, Capreolus capreolus, were studied in two areas in south‐eastern Sweden during 1989–1993. Initial territorial behaviour was observed in early Mar., when overlap between male ranges decreased from 66 % to 0 % over a 3–6‐wk period, as determined from telemetry data. The decrease was associated with an increased number of agonistic interactions. Most territories were established at the end of Mar. to early Apr., with a tendency for males re‐establishing old territories to be first. In all years, territories were taken up 1–3 wk before males shed velvet from their antlers. The distance between geometric centres of neighbouring males in winter and after territory establishment increased from 164 to 364 m. Former territory holders moved the geometric centres of their winter range and subsequent territory a shorter distance than first‐year territorials, 129 and 267 m respectively. Territory defence ceased after the rut in late Aug., and the spatial relations between neighbours reverted to the situation before the territorial season. Neither velvet shedding nor antler casting was correlated with male age (yearlings excluded), which contradicts earlier statements. Neither were there any associations between timing of antler casting and subsequent velvet shedding, nor vice versa. Hence, a male casting antlers early one year derives no advantage by early shedding the next season. Furthermore, to be in hard antlers is not a prerequisite for territory take‐up, whereas antlers probably are necessary for maintaining the area throughout the season. Functional aspects on roe buck territoriality are also discussed.

The significance of male-male aggression for yearling dispersal in roe deer (Capreolus capreolus)

The significance of adult buck aggression as a proximate factor driving yearling male dispersal in roe deer, Capreolus Capreolus, was studied in Sweden during the dispersal season (April–June) in 1988–1991. In roe there is a well established positive correlation between yearling antler size and dispersal tendency. I tested the prediction that yearlings with large antlers will experience more agonism from adult bucks than those with smaller antlers. Additionally, I studied the relationship between antler size and level of sexual maturity, by recording date of velvet shedding, and sampling testes weights from culled yearlings during the breeding season. The amount of agonism experienced by yearlings was positively correlated with the size of their antlers during April and May, whereas in June no such relationship was found. Aggression towards all yearlings tended to increase as the season progressed. A positive correlation between antler size and testes weight was evident, and the larger the antlers of yearlings the earlier the velvet shedding occured. These results indicate: firstly, that adult buck agonism is an important proximate factor underlying yearling male dispersal; and secondly, that agonism is mainly directed towards the sexually most mature yearlings. This, in turn, suggests mate competition to be the ultimate cause of male-male agonism, and thus male dispersal in this species.

Effects of an antiandrogen treatment on morphological characters and physiological functions of male fallow deer (Dama dama L.).

From mid-April to late November, i.e., during antler growth phase and main breeding season, a group of four (later three) male fallow deer was treated with increasing doses of the antiandrogen cyproterone acetate (CA). Throughout the treatment period, plasma testosterone levels of the bucks were either undetectable or only slightly above the detection limit of 0.1 ng/ml. In marked contrast to controls, testicular volumes and neck girths of the CA treated bucks were basal during the application period, proving the strong antigonadotropic effect of CA (testicular volume) and the absence of androgen action at the normal target organs (neck girths), respectively. Antler growth in the CA treated bucks occurred during the normal time span for fallow deer and the antlers produced were of species specific shape. From this it is concluded that in fallow deer, onset, duration, and termination of antler growth are independent of androgen action. Velvet shedding in the CA treated bucks however did not occur at the normal time (late August/early September), but was postponed until late December/early January, i.e., about 5 weeks after the termination of CA application. Activity of alkaline phosphatase in the experimental animals increased during the antler growth phase, but was markedly lower than in controls. Maximum body weight in the CA treated bucks was reached already in June, i.e., about 3 months prior to controls. Furthermore, the rut associated, drastic decline in body weight observed in controls did not occur in the experimental animals.

Chronology of Antler Velvet Shedding in Captive Louisiana White-Tailed Deer

Little research has been conducted on the effects of photoperiod, birth date, or other factors on the antler cycle of white-tailed deer (Odocoileus virginianus) in the southeastern United States. Consequently, we studied the chronology of antler velvet shedding of 59 captive Louisiana whit-tailed bucks from 1986 to 1991 to test For effects of age, birth date, photoperiod, antler characteristics, and body mass. The age of bucks when they shed velvet from their first antler sets was negatively related to birth date (r 2 =0.82; P<0.001; age in days=582.42−0.78 [julian birth date])