Plasma levels of beta-endorphin in white-tailed deer: seasonal variation and the effect of thyroxine, GnRH, dexamethasone and ACTH administration

1. A distinct seasonal cycle of beta-endorphin (beta-E) was detected in plasma of four intact, male white-tailed deer. Peak levels (around 11 pg/ml) were observed in August and minimal concentrations (around 5 pg/ml) were detected in January and February. 2. The seasonal variation (which corresponds to intensity of antler growth) was more pronounced in the two mature bucks, as compared to the immature ones. 3. Intramuscular administration of synthetic thyroxine (in doses of 500, 750 and 1000 micrograms/deer) and GnRH (100 micrograms/deer) had generally no significant effect on the beta-E levels. 4. I.v. administration of dexamethasone (5 mg/deer) as well as i.m. injection ACTH (20 Int. Units/deer) significantly reduced beta-E levels.     

Does fluctuating asymmetry of antlers in white-tailed deer (Odocoileus virginianus) follow patterns predicted for sexually selected traits?

Secondary sexual characters have been hypothesized to signal male quality and should demonstrate a negative relationship between the size of the trait and degree of fluctuating asymmetry because they are costly to produce. We collected morphometric and antler data from 439 white-tailed deer (Odocoileus virginianus) in Oklahoma, USA, in order to determine whether measures of antler asymmetry follow the patterns predicted for sexually selected characters. Relative fluctuating asymmetry was negatively related to antler size for all deer and within age groups up to five and a half years of age. We did not detect an association between asymmetry and antler size among deer that were six and a half years or older. When categorizing deer by antler size, we found that deer with small antlers (< or = 33rd percentile) had greater levels of relative asymmetry than deer with large antlers (< or = 67th percentile). The relative asymmetry of antlers was negatively related to age and was greatest in deer that were one and a half years old. Relative asymmetry was also negatively related to carcass mass, inside spread, skull length and body length. These data suggest that asymmetry in the antlers of white-tailed deer may be a reliable signal of quality and, as such, may be important in maintaining honesty in intrasexual advertisements during the breeding season.     

Effect of antiandrogen cyproterone acetate on the development of the antler cycle in Southern pudu (Pudu puda)

The antler cycle of pudu is similar to other cervids, but unlike most boreal deer, male Southern pudu (Pudu puda) exhibits two seasonal peaks of LH and testosterone. In that respect, pudu is similar to roe deer. Whereas the antler cycle in some deer species, such as roe deer or white-tailed deer, is very sensitive to variation of testosterone, in other cervids, such as fallow deer or reindeer, a blockade of androgens with cyproterone acetate (CA) has little or no effect on the timing of the antler casting. In order to test the sensitivity of pudu antlers to variations of androgens, CA (administered 2x weekly at 50 mg/buck) was injected intramuscularly for 3 weeks in 5 adult male pudu, starting February 19 (late summer). Four other males of similar age served as controls. The experiment was performed at the University of Concepcion, Chile, latitude 36.6 degreeS. Blood samples were taken once a week between January 19 and April 3. In CA-treated bucks, the antlers were cast approximately 3 weeks after the initiation of CA treatment and a new antler growth began almost immediately. The antlers reached about 5 cm in length, before ceasing to grow at the end of April, when they became mineralized and were subsequently polished. CA had no effect on the already declining levels of LH. Plasma levels of testosterone in controls increased from February 15, whereas in CA-treated bucks remained depresses until March 21. It is concluded that similarly to white-tailed deer, the antler cycle of Southern pudu is very sensitive to manipulation of androgen levels.     

Testosterone and estradiol concentrations in serum, velvet skin, and growing antler bone of male white-tailed deer

The growth and mineralization of antlers correlate with the seasonal variation of serum androgens. Whereas seasonal levels of testosterone (T) in plasma are well established, steroid concentrations have not yet been determined in the tissues of growing antlers. Therefore, RIA was used to determine T and 17beta estradiol (E2) in serum, and three areas (tip, middle, and base) of the antler bone and the antler skin, called velvet. Blood and antler tissues of white-tailed deer (Odocoileus virginianus) were collected from May to August. The difference between levels of T and E2 among the sites was calculated using the square root transformation followed by a mixed model analysis with individual deer and an interaction of individual and year (individual(*)year) as a random factor. Concentrations of T in serum (799+/-82 pg/ml) were higher than T values in the velvet (589+/-58 pg/ml, P<0.01) and in the antler bone (538+/-58 pg/ml, P<0.001). Estradiol concentrations differed among antler tissues and serum (P<0.001) and between years (P<0.01). Estradiol concentrations in serum (25+/-25 pg/ml) were consistently lower than those in antler bone (208+/-11 pg/ml, P<0.001) and velvet (150+/-12 pg/ml, P<0.001). The E2:T ratio in serum was 1:10-60. The same ratio for the antler bone was only 1:2-3 and for the velvet 1:3.5. It is concluded that higher T and lower E2 concentrations found in plasma, as compared to antler bone or antler velvet, may indicate a partial metabolism of systemic androgens into estrogens xin the tissues of growing antlers.     

Correlates of variation in deer antler stiffness: age, mineral content, intra-antler location, habitat, and phylogeny

To test correlations between the stiffness of deer antler and aspects of cervid ecology, we measured the stiffness (in bending) of antler from white-tailed deer ( Odocoileus virginianus ) and compared our results to previous measurements from antlers of other cervid species. Stiffness of antler specimens did not correlate significantly with mineral content or the location within the antler from which specimens were taken in O. virginianus. However, antler stiffness in white-tailed deer decreased significantly between two- and three-year-old bucks, matching the time in O. virginianus life history when males shift from sparring with mostly larger individuals to sparring with mostly smaller individuals. Stiffer antlers may enable younger, smaller bucks to have a more effective lever through which their smaller muscular forces can be transmitted during sparring with older, larger bucks. The stiffnesses we measured for white-tailed deer antler are similar to values measured previously from other members of the odocoileine lineage, which are lower than those previously measured from the antlers of deer living in tropical habitats. However, confidence limits for maximum likelihood reconstructions of the ancestral stiffness of deer antler span the range of high stiffnesses found among tropical deer; furthermore, parsimony-based reconstructions of ancestral antler stiffness are equivocal. Thus, the high antler stiffnesses of tropical deer may reflect the retention of an ancestral condition, rather than adaptation to year-round antler use.     

Pineal influence on annual nuclear volume changes in ventromedial hypothalamic nucleus (VMH) neurons of the male Wistar rat

The ventromedial hypothalamic nucleus (VMH) regulates various autonomic, endocrine, and behavioral activities. These activities show annual changes, and the pineal gland is involved in their adjustment to environmental cues. Therefore, this study investigated whether the VMH belongs to the effector structures of the pineal gland. To abolish the rhythmic melatonin release, male Wistar rats were subjected to pinealectomy (PX) or ganglionectomy (sympathetic denervation of the pineal gland, GX) regularly at the beginning of any of the four seasons. Brains from animals of PX-, GX-, and sham-operated control groups were prepared 3 months later for measurement of the nuclear volume, which changes according to the general gene activity. At each of the four seasons, 2000 nuclei of VMH neurons stemming from 18 animals per group were measured to obtain both seasonal daily mean values and annual mean values,respectively, as well as to calculate annual curves of the nuclear volume using empirical regression and locally adjusted polynomial approximation. The major findings are the following. First,inactivation of the pineal function influences the nuclear activity of VMH neurons. (2) PX and GX mainly depress the nuclear activity, indicating that the pineal influence on the VMH may predominantly be a stimulatory one. Third, size and direction of the changes caused by PX and GX vary in a seasonally dependent manner. Fourth, the annual rhythm of the nuclear activity of the VMH is modified by PX and GX.To explain how the pineal effects on the VMH may be mediated, a possible inhibitory influence of the suprachiasmatic nucleus (SCN),which has been activated in the same animals following both PX and GX, is discussed. In conclusion, the results confirm that the nuclear activity of VMH neurons underlies pineal influences. This also indicates an involvement of the pineal gland in many VMH-regulated functions.(Chronobiology International,17(1),15-28, 2000)     

Influence of Landscape Composition and Structure on Antler Size of White-Tailed Deer

Abstract: Cause for spatial variation in phenotypic quality of white-tailed deer (Odocoileus virginianus) populations is of great interest to wildlife managers. Relating phenotypic variation of populations to large-scale land-use patterns may provide insight into why populations exhibit spatial variation and elucidate how management can influence population phenotype. We used an information-theoretic approach to relate average antler size of 203 deer populations to composition and structure of the habitat occupied by those populations. We used interspersion, edge, and diversity indices to represent habitat structure and percentage of area in vegetation types to represent habitat composition. Landscape composition was a better predictor of deer population antler size than was landscape structure. Percentages of the management unit in agriculture, pasture, and pine forest were variables commonly found in the region-specific set of best models. Model-averaged estimates of agriculture and pasture parameters were always positive and estimates of pine forest parameters were always negative, which suggests that land-use types that promote growth of early successional herbaceous plants will positively influence antler size and, most likely, body growth and reproduction of white-tailed deer populations. Conversely, our findings suggest landscapes dominated by pine forests did not provide optimal amounts of quality forages for white-tailed deer. Pine forest effects should be mitigated using a combination of increased harvest to lower deer density and silvicultural practices like thinning, prescribed burning, and selective herbicide applications that stimulate growth of high-quality forages beneath the forest canopy to improve deer phenotypic quality.     

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.     

PINEAL INFLUENCE ON ANNUAL NUCLEAR VOLUME CHANGES IN VENTROMEDIAL HYPOTHALAMIC NUCLEUS (VMH) NEURONS OF THE MALE WISTAR RAT

The ventromedial hypothalamic nucleus (VMH) regulates various autonomic, endocrine, and behavioral activities. These activities show annual changes, and the pineal gland is involved in their adjustment to environmental cues. Therefore, this study investigated whether the VMH belongs to the effector structures of the pineal gland. To abolish the rhythmic melatonin release, male Wistar rats were subjected to pinealectomy (PX) or ganglionectomy (sympathetic denervation of the pineal gland, GX) regularly at the beginning of any of the four seasons. Brains from animals of PX-, GX-, and sham-operated control groups were prepared 3 months later for measurement of the nuclear volume, which changes according to the general gene activity. At each of the four seasons, 2000 nuclei of VMH neurons stemming from 18 animals per group were measured to obtain both seasonal daily mean values and annual mean values,respectively, as well as to calculate annual curves of the nuclear volume using empirical regression and locally adjusted polynomial approximation. The major findings are the following. First,inactivation of the pineal function influences the nuclear activity of VMH neurons. (2) PX and GX mainly depress the nuclear activity, indicating that the pineal influence on the VMH may predominantly be a stimulatory one. Third, size and direction of the changes caused by PX and GX vary in a seasonally dependent manner. Fourth, the annual rhythm of the nuclear activity of the VMH is modified by PX and GX.To explain how the pineal effects on the VMH may be mediated, a possible inhibitory influence of the suprachiasmatic nucleus (SCN),which has been activated in the same animals following both PX and GX, is discussed. In conclusion, the results confirm that the nuclear activity of VMH neurons underlies pineal influences. This also indicates an involvement of the pineal gland in many VMH-regulated functions.(Chronobiology International,17(1),15–28, 2000)     

Effect of metabolic acidosis on white-tailed deer antler development

Metabolic acidosis can result when herbivores consume browse diets high in plant secondary compounds. One mechanism for buffering excess acid is the mobilization of calcium and other alkaline salts from the skeletal system. White-tailed deer (Odocoileus virginianus) and other cervids consuming browse during antler formation may use minerals essential for antler development as buffers, resulting in altered antler characteristics. Our research objectives were to examine the effects of metabolic acidosis on mineral metabolism, acid-base homeostasis, and antler development in white-tailed deer. Fifteen male white-tailed deer were assigned to one of three diets: 2% NH(4)Cl, 3% commercial tannic acid, or a basal ration without additive. Two feeding trials were completed on each deer to determine nutrient use. Urine pH and the percentage of urinary nitrogen excreted as NH+4 varied by diet. No significant diet or trial effects occurred for nitrogen, calcium, phosphorus, magnesium, or sodium use. Urinary calcium excretion varied between diets. No dietary differences were observed for antler characteristics. The NH(4)Cl diet induced metabolic acidosis but did not alter antler development in white-tailed deer. Skeletal mineral reserves and mineral intake appeared sufficient to buffer excess acids and support antler development.     

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 degrees 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.     

Concentrations of insulin-like growth factor-I in adult male white-tailed deer (Odocoileus virginianus): associations with serum testosterone, morphometrics and age during and after the breeding season

Our understanding of insulin-like growth factor-I (IGF-I) in cervids has been limited mostly to its effects on antler development in red deer (Cervus elaphus), roe deer (Capreolus capreolus), fallow deer (Dama dama), and pudu (Pudu puda). Although IGF-I has been found to play a critical role in reproductive function of other mammals, its role in reproduction of deer is unknown. The objectives of the present study were to determine if serum levels of IGF-I change during the breeding season, assess whether age influences serum IGF-I, compare levels of IGF-I measured during and following the breeding season, and determine if IGF-I is associated with body and antler characteristics in free-ranging adult, male white-tailed deer (Odocoileus virginianus). We collected serum and morphometric data from hunter-harvested and captured white-tailed deer to investigate these objectives. Mean level of serum IGF-I during the breeding season was 63.6 ng/ml and was greatest in deer between 2.5 and 5.5 years old (57.4-79.9 ng/ml). Levels of serum IGF-I decreased by approximately 40% as the breeding season progressed, but levels were less in deer following the breeding season (34.6 ng/ml). Both body and antler size were associated positively with IGF-I when controlling for age. Serum testosterone was also associated positively with IGF-I. Levels of serum testosterone during the breeding season generally increased with age from 4.82 (1.5 years old) to 18.79 ng/dl (5.5 years old), but decreased thereafter. These data suggest that IGF-I may be an important hormone in breeding, male white-tailed deer.     

White-Tailed Deer Antler Research: A Critique of Design and Analysis Methodology

ABSTRACT Debate within the popular and technical literature regarding predictability of antler size at maturity based on 1.5-year antler size in white-tailed deer (Odocoileus virginianus) has led to confusion and uncertainty within constituent groups. Koerth and Kroll (2008) provided measures of age-related antler development using recaptures of known-age males from 12 deer populations in southern Texas. Several design and analysis issues reduce the scope and validity of their conclusion that amount of growth in the first set of antlers was a poor predictor of antler growth at maturity. Although unstated, the statistical hypothesis they tested did not coincide with their specific conclusions. Using a simulation, we show that their methods were susceptible to measurement bias. Their results are applicable only to populations with similar culling and management programs. Additionally, we provide recommendations for future research projects that evaluate predictability of antler size at maturity based on antler size at younger ages.     

Major-histocompatibility-complex-associated variation in secondary sexual traits of white-tailed deer (Odocoileus virginianus): evidence for good-genes advertisement

Abstract Good-genes hypotheses predict that development of secondary sexual characters can be an honest advertisement of heritable male quality. We explored this hypothesis using a cervid model (adult, male white-tailed deer, Odocoileus virginianus ) to determine whether antler development could provide an honest signal of a male's genetic quality and condition to adversaries. We compared antler, morphometric, hormonal, and parasitic data collected from hunter-harvested deer to characteristics of the Mhc-DRB (Odvi) , the most widely studied gene of the major histocom-patibility complex (MHC) in Artiodactyla. We detected associations between genetic characteristics at Odvi-DRB and antler development and body mass, suggesting that antler development and body mass may be associated with pathogen resistance in deer and thus may be an honest signal of genetic quality. We also detected associations between Odvi-DRB characteristics and serum testosterone during the breeding season, suggesting that certain MHC characteristics may help deer cope with stresses related to breeding activity. In addition, we observed a negative relationship between degree of antler development and overall abundance of abomasal helminths. Our observations provide support for the hypothesis that antler development in white-tailed deer is an honest signal of quality.     

Growth hormone and cortisol levels in the annual cycle of white-tailed deer (Odocoileus virginianus).

The annual cycles of growth hormone and cortisol levels in white-tailed deer were followed. No significant difference was found in the average cortisol levels in a large group of animals during the year. In contrast to cortisol, growth hormone (GH) investigated by heterologous bovine GH radioimmunoassay, seems to have a distinct annual rhythm. High levels of GH in plasma were found between casting and the first week of antler growth with the peak of 23.1 ng/ml (estimated in bovine GH equivalents) in the middle of April. From the middle of June until the middle of November a plateau averaging 3 ng/ml was found. The relationships between very rapid growth of a bone tissue and the influence of GH and sex hormones are discussed.     

Effect of advancing births on testosterone until 2.5 years of age and puberty in Iberian red deer (Cervus elaphus hispanicus)

This study aimed to determine the age of attainment of puberty, as well as the pattern of reproductive seasonality in males of Iberian red deer and the relationship of these factors with antler development. A second aim was to examine the effect of the advance of births on the variables mentioned. Fourteen males of Iberian deer were used, five of them born 2.5 months before the others (early group). Male deer were blood sampled from birth until 2.5 years of age to assess the time course of plasma testosterone. The study also included measurements of testicular and neck circumference. As in most cervids, concentration of plasma testosterone was associated to the phases of antler development. Early development affected testosterone titres, since the most precocious males in antler growth also showed higher levels of testosterone during the first and second year of age. In the same way, results suggested that the advance of calving may result in puberty attainment in the first autumn of its life. However, this would require an advance of calving greater than the one we induced since puberty in the Iberian deer is usually attained during second autumn of life at 15-16 months of age. Finally, calving advance also affected antler development. Thus, two of the five males whose birth was advanced, showed two antler cycles in their first year of life.     

Juvenile-to-Adult Antler Development in White-Tailed Deer in South Texas

Abstract: Past studies using penned deer provide conflicting results on the age when reliable predictions about antler growth potential in white-tailed deer (Odocoileus virginianus) can be made. We captured wild whitetail males via aerial net gun on 12 ranches in 5 counties in south Texas, USA, from 1999 to 2007 to determine if a reliable juvenile-to-adult relationship in antler development existed. We individually marked and released captured animals at the trap site after we took antler and body measurements. We recaptured marked animals as possible in subsequent years or until we obtained final measurements after legal harvest. Amount of growth in the first set of antlers in whitetail males was a poor predictor of antler growth at maturity. By 4.5 years of age there were no differences (P > 0.05) in antler measurements regardless of the amount of development of the first set of antlers at 1.5 years. We concluded culling of yearling males based on number of antler points would have little positive effect on overall antler quality in future years.     

Habitat quality influences relative antler size and hunters’ selectivity in roe deer

Understanding factors affecting antler size, and the extent to which harvesting is selective for these traits, is important in order to address management strategies aimed to minimize the risk of negative evolutionary consequences. In an Alpine study area, we compared the phenotypic quality and the antler size of 2,725 male roe deer hunted in two regions differing for winter harshness and habitat quality, and evaluated whether the selective behaviour of recreational hunters was influenced by phenotypic quality and antler size. Antler length and antler circumference relative to both body mass and jaw length were larger in the region with more favourable climate and habitat conditions, indicating that here roe deer were able to allocate more resources to antler growth. The analysis of the temporal trends of harvest bags suggested that hunters did not select roe deer for their body mass or size, but instead for antler size. This resulted also in a preference for sub-adult and adult age classes, while yearlings were culled reluctantly, especially in the region where antlers were smaller. Our results indicate that environmental heterogeneity may influence the relative investment in antler growth. In this way, it may interact with the hunters’ preferences increasing the risk that recreational hunting of roe deer, which is a widespread practice in many European countries, might result in alteration of male age structure and possibly in directional artificial selection.     

Seasonal variations in red deer (Cervus elaphus) hematology related to antler growth and biometrics measurements

The aim of the study was to relate seasonal hematology changes with the rest of physiological variations suffered by red deer, such as antler and biometrics cycle, and to assess the relationship between hematology and the effort performed in antler development. Blood samples were taken from 21 male red deer every 4 weeks during 18 months. Samples were analyzed for the main hematological parameters. Simultaneously, biometrics measurements were taken, such as antler length, body weight, body condition score, testicular diameter (TD), and thoracic and neck girth. All the blood cell types (erythrocytes, leukocytes, and platelets) showed seasonal variations, increasing as antler cleaning approached, as did hematocrit and hemoglobin. The final size of antlers was negatively related to leukocyte count, nonlymphoid leukocyte count, red cell distribution width, mean corpuscular hemoglobin, mean platelet volume, and TD, whereas it was positively related to body condition during antler growth. Huge seasonal variations in some hematological values have been found to be related to changes in antler and biometrics measurements. Since these variations are even greater than the caused by deer handling, they should be taken into account when evaluating hematology in deer populations.     

Thyroxine levels and antler growth in white-tailed deer

1. Five normal male, 5 female, and 3 castrated fawns and 5 adult male white-tailed deer were housed in individual pens for one year to compare the relationships between thyroxine (T4) and other blood parameters and the antler cycle. 2. Biweekly serum samples were examined for T4 titers and levels of serum calcium (Ca), inorganic phosphorus (P), and alkaline phosphatase activity (AP). 3. Seasonal T4 changes were found in all deer groups, with elevated titers in the fall. Female fawns had overall lowered T4 levels. In male fawns and adult bucks, T4 seemed to play a synergistic role in antler initiation and growth. 4. Serum Ca levels remained constant throughout the year, but with lower levels in the female fawns. 5. Serum P levels were also constant seasonally, but with higher levels in the female fawns. There was no age effect on either Ca or P. 6. An age effect was evident on plasma alkaline phosphatase with lower activity in adult bucks. There was no sex effect on AP activity. 7. T4 might have an indirect association with the enzyme AP in Ca and P transport system in white-tailed deer.