Effects of maternal age and offspring sex on milk yield, composition and calf growth of red deer (Cervus elaphus).

Differential maternal allocation theory states that mothers will invest more heavily in the offspring sex that will secure higher reproductive output. Senescence theory is concerned with the gradual deterioration of physiological function with age. We analysed the offspring sex-dependent response of calf growth and milk traits to mother age in an Iberian population of captive red deer (Cervus elaphus) using a 22 year time series longitudinal data set. Previous studies revealed that there was little evidence for the differential allocation theory on milk traits and that most studies lacked proper control for confounding factors. Our results indicated that (i) calf growth was offspring male-biased, negatively affected by mother age and positively influenced by mother weight and parity, and (ii) there was no support for differential allocation offspring sex-dependence in milk traits (yield, energy density, fat, protein and lactose content). Our findings suggest that maternal allocation responds to offspring energy requirements, which are mainly driven by offspring body weight, and contingent on mother age and weight and previous maternal reproductive effort.

Water sprinkling as a tool for heat abatement in farmed Iberian red deer: Effects on calf growth and behaviour.

Climatic models predict scenarios in which ambient temperature will continue increasing worldwide. Under these climatic conditions, fitness and animal welfare of many populations are expected to suffer, especially those that live in captive or semi-natural conditions, where opportunities of heat abatement are limited. We undertook an experimental design to assess the effect of heat abatement that water sprinkling might have on Iberian red deer calf growth and behaviour from birth to weaning (135 days). One group of ten mother-calf pairs lived on plots with water sprinkling (treatment) available during summer's hottest time of the day, while the control group (nine mother-calf pairs) occupied plots with no available water sprinkling. Treatment and control groups were fed ad libitum and swapped between plots every seven days to minimise any plot effect. Body weight was monitored weekly and individual behaviour was recorded once or twice a week at mid-day. We observed that calves had showers under the sprinklers and wallowed in mud puddles. The results clearly indicated that calves of the treatment group showed a significant increase in body weight at weaning in comparison with the control group, with no differences between sexes (treatment: male = 56.5 kg, female = 50.3 kg; control: male = 50.3 kg, female = 46.5 kg). Mother weight and mother age effects were negligible on calf body weight at weaning. The heavier the mother the faster was the rate of growth of its offspring, irrespective of calf sex. The model indicated that although males grew significantly slower than female calves in the control group, males grew faster than females when exposed to the treatment. Calves of the treatment group spent less time drinking, less time in the shade, similar time eating and more time in motion than calves of the control group. There were no behavioural differences between calf sexes of treatment and control groups. The results indicate the importance of providing animals with opportunities of heat abatement in hot environments to improve animal growth and welfare in farmed Iberian red deer.

Heat stress reduces growth rate of red deer calf: Climate warming implications.

Climate models agree in predicting scenarios of global warming. In endothermic species heat stress takes place when they are upper their thermal neutral zone. Any physiological or behavioural mechanism to mitigate heat stress is at the cost of diverting energy from other physiological functions, with negative repercussions for individual fitness. Tolerance to heat stress differs between species, age classes and sexes, those with the highest metabolic rates being the most sensitive to stressing thermal environments. This is especially important during the first months of life, when most growth takes place. Red deer (Cervus elaphus) is supposedly well adapted to a wide range of thermal environments, based on its worldwide distribution range, but little is known about the direct effect that heat stress may have on calf growth. We assessed the effect that heat stress, measured by heat stress indices and physical environment variables (air temperature, relative air humidity, wind speed and solar radiation), have on calf and mother body weights from calf´s birth to weaning. We used 9265 longitudinal weekly body weight records of calf and mother across 19 years in captive Iberian red deer. We hypothesised that (i) heat stress in hot environments has a negative effect on calf growth, especially in males, as they are more energetically demanding to produce than females; and that (ii) the body weight of the mother through lactation should be negatively affected by heat stress. Our results supported hypothesis (i) but not so clearly hypothesis (ii). By weaning (day 143) calves growing under low heat stress environment grew up to 1.2 kg heavier than those growing in high heat stress environment, and males were more affected by heat stress than females. The results have implications in animal welfare, geographical clines in body size and adaptation to climate change.

Short communication: Red deer (Cervus elaphus) colostrum during its transition to milk.

We studied changes in chemical composition, somatic cell count, and immunoglobulin G (IgG) and M (IgM) content in red deer (Cervus elaphus) colostrum during the transition to milk at different times after parturition (<5 h, 24 h, 48 h, 2 wk, and 4 wk). The production level was higher at 2 and 4 wk of lactation than during the first day after parturition, with intermediate values at 48 h postpartum. Fat content did not vary during the study period. However, total protein and casein contents were particularly high in the initial 5 h after parturition, decreasing to approximately 50% after 24 h postpartum. Conversely, lactose concentration was low in the beginning (<5 h), increasing gradually throughout the study. Similarly, dry matter dropped during the first 24 h and then remained constant throughout the study. Urea content decreased during the study, showing a slight recovery at 4 wk. Somatic cell count was higher during the first hours after parturition and gradually decreased throughout the study period. The IgG content was higher before 5 h postpartum than at 24 h postpartum. After 5 h, the level of IgG decreased progressively until it reached 0.18 mg/mL at 4 wk of lactation. We observed a similar pattern for IgM content, but it decreased more quickly than IgG and was not detected after 2 wk. In the case of deer, milk should be considered transitional from 24 to 48 h after parturition, and samples collected after 2 wk can be considered mature milk.

What do rates of deposition of dental cementum tell us? Functional and evolutionary hypotheses in red deer.

Cementum is a bone connective tissue that provides a flexible attachment for the tooth to the alveolar bone in many mammalian species. It does not undergo continuous remodelling, unlike non-dental bone, which combined with its growth pattern of seasonal layering makes this tissue uniquely suitable as a proxy for tracking changes in body repair investment throughout an animal´s life. We tested functional and sexual selection hypotheses on the rate of cementum deposition related to the highly polygynous mating strategy of red deer. We used a sample of 156 first lower molars from wild Scottish red deer of known age between 1 and 17 years old, approximately balanced by sex and age class. Cementum deposition on the inter-radicular pad increased with age at a constant average rate of 0.26 mm per year, with no significant differences between sexes. Cementum deposition was independent of (i) tooth wear, other than that associated with age, and (ii) enamel and dentine micro-hardness. The results partially supported the hypothesis that the main function of cementum is the repositioning of the tooth to maintain opposing teeth in occlusion. However, teeth that had more wear or males´ teeth that had faster rates of tooth wear than those of females did not present the expected higher rates of cementum deposition.

Antlers - Evolution, development, structure, composition, and biomechanics of an outstanding type of bone.

Antlers are bony appendages of deer that undergo periodic regeneration from the top of permanent outgrowths (the pedicles) of the frontal bones. Of the "less familiar" bone types whose study was advocated by John Currey to gain a better understanding of structure-function relationships of mineralized tissues and organs, antlers were of special interest to him. The present review summarizes our current knowledge about the evolution, development, structure, mineralization, and biomechanics of antlers and how their formation is affected by environmental factors like nutrition. Furthermore, the potential role of antlers as a model in bone biology and several fields of biomedicine as well as their use as a monitoring tool in environmental studies are discussed.

Meat quality of farmed red deer fed a balanced diet: effects of supplementation with copper bolus on different muscles.

Supplementation with copper (Cu) improves deer antler characteristics, but it could modify meat quality and increase its Cu content to levels potentially harmful for humans. Here, we studied the effects of Cu bolus supplementation by means on quality and composition of sternocephalicus (ST) and rectus abdominis (RA) muscles (n=13 for each one) from yearling male red deer fed with a balanced diet. Each intraruminal bolus, containing 3.4 g of Cu, was administered orally in the treatment group to compare with the control group. Meat traits studied were pH at 24 h postmortem (pH24), colour, chemical composition, cholesterol content, fatty acid (FA) composition, amino acid (AA) profile and mineral content. In addition, the effect of Cu supplementation on mineral composition of liver and serum (at 0 and 90 days of treatment) was analysed. No interactions between Cu supplementation and muscle were observed for any trait. Supplementation with Cu increased the protein content of meat (P<0.01). However, Cu content of meat, liver and serum was not modified by supplementation. In fact, Cu content of meat (1.20 and 1.34 mg/kg for Cu supplemented and control deer, respectively) was much lower in both groups than 5 mg/kg of fresh weight allowed legally for food of animal origin. However, bolus of Cu tended to increase the meat content of zinc and significantly increased (P<0.05) the hepatic contents of sodium and lead. Muscles studied had different composition and characteristics. The RA muscle had significantly higher protein content (P<0.001), monounsaturated FA content (P<0.05) and essential/non-essential AA ratio (P<0.01) but lower pH24 (P<0.01) and polyunsaturated FA content (P=0.001) than the ST muscle. In addition, RA muscle had 14.4% less cholesterol (P=0.001) than ST muscle. Also, mineral profile differed between muscles with higher content of iron, significantly higher (P<0.001) content of zinc and lower content of calcium, magnesium and phosphorus (P<0.05) for ST muscle compared with RA. Therefore, supplementation with Cu modified deer meat characteristics, but it did not increase its concentration to toxic levels, making it a safe practice from this perspective. Despite the lower content of polyunsaturated FA, quality was better for RA than for ST muscle based on its higher content of protein with more essential/non-essential AA ratio and lower pH24 and cholesterol content.

Effects of Mn supplementation in late-gestating and lactating red deer (Cervus elaphus hispanicus) on milk production, milk composition, and calf growth.

This study describes the effects of Mn supplementation of 20 late-gestating and lactating Iberian red deer (Cervus elaphus hispanicus) females (hinds) fed a balanced diet on milk production and milk composition over the lactation period. Body weight of their calves at birth and at weaning was also evaluated. In addition, the effect of lactation stage was studied. For these purposes, 2 groups of hinds, one composed by 12 individuals (experimental) and the other by 8 individuals (control) were compared. Experimental hinds were s.c. injected weekly with Mn (2 mg Mn/kg BW) from day 140 of gestation until the end of lactation (week 18; forced weaning by physical separation). Control hinds were injected with a physiological saline solution with the same volume and at the same frequency as the experimental group. Serum Mn content of hinds was assessed just before the first Mn injection and at week 10 of lactation to assess whether the injected Mn increased Mn concentrations in blood. No differences were observed for BW of calves at birth but calves whose mothers were injected with Mn tended (P = 0.07) to have greater gain of BW from birth to weaning in proportion of BW at birth compared to calves from control hinds. In addition, supplementation with Mn increased (P ≤ 0.05) daily milk production by 10.2%, milk fat content by 11.2%, and total fat yield by 17.8%. Also, milk from hinds supplemented with Mn had more Ca (P < 0.001) and P (P < 0.05) than milk from control hinds. Manganese supplementation did not influence Mn serum content when blood was analyzed at week 10 of lactation, but increased the Mn content of milk by 18.3% (P < 0.001). Lactation stage affected (P < 0.001) fat, protein, lactose, and DM. Their contents increased as lactation proceeded, and protein was substituted by fat. Therefore, results suggest that Mn supplementation of hinds is recommended, even when they are fed a balanced diet, to increase milk production and the content of fat, Ca, P, and Mn of milk.

Does Cu supplementation affect the mechanical and structural properties and mineral content of red deer antler bone tissue?

The main factors affecting the mechanical (and other) properties of bone, including antler, are the proportions of ash (especially Ca and P) and collagen content. However, some trace minerals may also play more important roles than would be expected, given their low levels in bone and antler. One such trace mineral is Cu. Here, we studied the effects of Cu supplementation on the mechanical and structural characteristics, and mineral content of antlers from yearling and adult (4 years of age) red deer fed a balanced diet. Deer (n=35) of different ages (21 yearlings and 14 adults) were studied. A total of 18 stags (11 yearlings and 7 adults) were injected with Cu (0.83 mg Cu/kg BW) every 42 days, whereas the remaining 17 (10 yearlings and 7 adults) were injected with physiological saline solution (control group). The Cu content of serum was analysed at the beginning of the trial and 84 days after the first injection to assess whether the injected Cu was mobilized in blood. Also, the mechanical and structural properties of antlers and the mineral content in their cortical walls were examined at three (yearlings) or four (adults) points along the antler beam. The effect of Cu supplementation was different in yearlings and adults. In yearlings, supplementation increased the Cu content of serum by 28%, but did not affect antler properties. However, in adults, Cu supplementation increased the Cu content of serum by 38% and tended to increase the cortical thickness of antlers (P=0.06). Therefore, we conclude that, even in animals receiving balanced diets, supplementation with Cu could increase antler cortical thickness in adult deer, although not in yearlings. This may improve the trophy value of antlers, as well as having potential implications for bones in elderly humans, should Cu supplementation have similar effects on bones as those observed in antlers.

Habituating to handling: factors affecting preorbital gland opening in red deer calves.

The preorbital gland plays not only an olfactory role in cervids but also a visual one. Opening this gland is an easy way for the calf to communicate with the mother, indicating hunger/satiety, stress, pain, fear, or excitement. This information can be also useful for farm operators to assess how fast the calves habituate to handling routines and to detect those calves that do not habituate and may suffer chronic stress in the future. Thirty-one calves were subjected to 2 consecutive experiments to clarify if observing preorbital gland opening is related to habituation to handling in red deer calves (Cervus elaphus). Calves were born in 3 different paddocks, handled as newborns (Exp. 1), and then subjected to the same routine handling but with different periodicity: every 1, 2, or 3 wk (Exp. 2). In Exp. 1, preorbital gland opening was recorded in newborns during an initial handling (including weighing, ear tagging, and sex determination). Preorbital gland opening occurred in 93% of calves during this procedure and was not affected by sex, time since birth, or birth weight. Experiment 2 consisted of measuring preorbital opening during the same routine handling (weighing, blood sampling, and rump touching to assess body condition) when calves were 1, 3, and 5 mo old. Binary logistic regression showed that gland opening was associated with habituation to handling, since at 1 and 3 mo the probability of opening the gland decreased with the number of handlings that a calf experienced before (P = 0.008 and P = 0.028, respectively). However, there were no further changes in preorbital gland opening rate in the 5-mo-old calves (P = 0.182). The significant influence of the number of previous handlings on the probability of opening the preorbital gland was confirmed through generalized linear model with repeated measures (P = 0.007). Preorbital gland opening decreased along the phases of the study. Nevertheless, we found a significant trend in individuals to keep similar opening patterns (intraclass correlation coefficient = 0.807, P < 0.001), which suggests that the more stressed individuals can be detected with this method. Therefore, we conclude that preorbital gland opening during routine handlings is related to the number of previous handlings, and thus it can be used as an indicator of lack of habituation to handling in farmed cervids.

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 2.15 µm/d). Lower MARs were recorded for later stages of primary osteon formation (1.56 µm/d) and for the smaller secondary osteons (0.89 µm/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.

Does nutrition affect bone porosity and mineral tissue distribution in deer antlers? The relationship between histology, mechanical properties and mineral composition.

It is well known that porosity has an inverse relationship with the mechanical properties of bones. We examined cortical and trabecular porosity of antlers, and mineral composition, thickness and mechanical properties in the cortical wall. Samples belonged to two deer populations: a captive population of an experimental farm having a high quality diet, and a free-ranging population feeding on plants of lower nutritive quality. As shown for minerals and mechanical properties in previous studies by our group, cortical and trabecular porosity increased from the base distally. Cortical porosity was always caused by the presence of incomplete primary osteons. Porosity increased along the length of the antler much more in deer with lower quality diet. Despite cortical porosity being inversely related to mechanical properties and positively with K, Zn and other minerals indicating physiological effort, it was these minerals and not porosity that statistically better explained variability in mechanical properties. Histochemistry showed that the reason for this is that Zn is located around incomplete osteons and also in complete osteons that were still mineralizing, whereas K is located in non-osteonal bone, which constitutes a greater proportion of bone where osteons are incompletely mineralized. This suggests that, K, Zn and other minerals indicate reduction in mechanical performance even with little porosity. If a similar process occurred in internal bones, K, Zn and other minerals in the bone may be an early indicator of decrease in mechanical properties and future osteoporosis. In conclusion, porosity is related to diet and physiological effort in deer.

Do drastic weather effects on diet influence changes in chemical composition, mechanical properties and structure in deer antlers?

We attempted to determine why after an exceptionally hard winter deer antlers fractured more often than usual. We assessed mechanical properties, structural variables and mineral composition of deer antlers grown in a game estate (LM) after freezing temperatures (late winter frosts, LWF), which resulted in high incidence of antler fractures despite being grown later in the year, and those grown after a standard winter (SW). Within each year, specimens from broken and intact antlers were assessed. LWF was associated with reduced impact energy (U) and somewhat reduced work to peak force (W), Young's modulus (E) and physical density, as well as cortical thickness. LWF was associated with considerably increased Si and reduced Na. In each year, broken antlers had lower Mn, P and physical density, and they had more Na and B than unbroken antlers. Because no such effect was found in farmed deer fed whole meal, and because freezing in plants usually produces an increase in Si content, which in turn reduces Mn, it is likely that LWF produced a diet rich in Si and low in Mn. Because antlers are grown transferring calcium phosphate from the own skeleton and Ca/P levels were slightly reduced, it seems likely that Mn reduction may have increased antler fractures. A comparison between farm deer and those in another game estate (LI) also shows a link between lower Mn content and lower W. Thus, small changes in minor bone minerals, probably induced by diet, may have marked effects in mechanical properties of bone.

Biometrics, testosterone, cortisol and antler growth cycle in Iberian red deer stags (Cervus elaphus hispanicus).

In this article, we aimed to describe the changes related to mating season in red deer, especially those related to antler growth, body condition score, testosterone and cortisol. Antler growth was studied in 17 Iberian red deer males, including body weight, antler length, biometric measures and testosterone and cortisol determination during 15 months. Body weight, body condition score, thoracic perimeter (TP), neck perimeter (NL) and testicular diameter (TD) showed the highest values immediately before mating season (autumn), decreased during it and remained constant at winter. Antler growth lasted 158 days and produced antlers with a final length of 80.8 +/- 2.0 cm. Testosterone and cortisol showed seasonal changes with maximum values at September and May, respectively. Final antler size was related positively to cranial longitude, TP, NL, TD and body weight at casting time. No relationship between weight loss during precedent mating season and current antler size was found, but spring recovery weight was positively related to final antler size. Final length was related to the descent in testosterone values during previous mating season and to body weight before it. Spring recovery weight was related to relative weight loss during previous mating season. These results suggest that there is no relationship between the reproductive effort performed during one season and the next year size of the antler. In contrast, antler size was positively related to spring recovery weight, in the sense that those deer that recover a higher percentage of body weight at the early stages of antler growth develop higher antlers.

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.

Effect of milk minerals on calf gains and sex differences in mineral composition of milk from Iberian red deer (Cervus elaphus hispanicus).

Milk mineral content has received little attention in studies focusing on milk nutrient effects on offspring growth. This study examines calf growth in Iberian deer and compares the influence of milk minerals, other nutrients, and lactation variables relevant for growth to discern the relative weight of each factor. In addition, because Iberian deer hinds are the first mammal found to produce different milk for sons and daughters, the present study examines whether there are also sex differences in milk mineral composition. Concentrations and yields of Ca, P, Mg, Na, K, Fe, and Zn in milk of 46 red deer hinds were monitored through 18 weeks of lactation. Calf growth was influenced by Ca and P percent, and total Fe production. Milk for males had a lower content in Ca and P, a greater content of K, and Mg, whereas no sex effects were found in Na, Fe, or Zn percentages. Higher percentages in Ca and P for daughters might constitute a compensatory response, as daily production was not biased towards females in Ca or P, whereas in the latter and all the other minerals daily production was greater for heavier calves, which are usually males. In conclusion, milk mineral content and production influence calf growth even after controlling for other important lactation variables and nutrients, and they show effects and interactions more complicated than expected.

Seasonal changes in plasma leptin concentration related to antler cycle in Iberian red deer stags.

The aim of this study is to describe the leptin cycle in male Iberian red deer (Cervus elaphus hispanicus) and relate it to antler and testosterone cycles. An additional aim is to assess the relationship between the plasma leptin concentration during antlers' growth and their final size. Therefore, blood from 21 Iberian red deer males was sampled monthly to analyse leptin and testosterone. At the same time the deer were weighed and their body condition was assessed. The length of antlers was measured every 2 weeks and, after casting, their final length and perimeters were taken. Leptin showed a seasonal cycle, with a peak in June that decreased as testosterone increased. Low values were observed in autumn, winter and early spring. The relationship observed between leptin and body mass or body condition score was different in spring, when plasma testosterone concentration is low, than in autumn, when testosterone increases. Leptin peak amplitude was positively related to final antler size. In conclusion, the relationship between leptin and body mass and body condition score changes through the year, possibly due to the influence of androgens and photoperiod. There was a positive relationship between plasma concentration of leptin during antler growth and final antler length.

Age-related body weight constraints on prenatal and milk provisioning in Iberian red deer (Cervus elaphus hispanicus) affect allocation of maternal resources.

Maternal phenotypic characteristics can influence key life history variables of their offspring through maternal effects. In this study, we examined how body size constraints on maternal weight in yearling and subadult compared to adult hinds (age class effects) affected prenatal (calf birth weight, calf to hind weight ratio) and postnatal (milk) provisioning of Iberian red deer calves. Age correlated with all prenatal and postnatal investment traits except calf gains, although correlations were weaker than those with maternal weight. Once the effect of linear increase in weight with age was removed from models, yearlings showed additional reductions in calf birth weight, calf gains, and milk provisioning. The low-calf birth weight might increase the risk of calf mortality during lactation, as this occurs primarily during the first day of life and is strongly related to birth weight. Yearlings showed a greater prenatal allocation of resources in terms of greater calf to hind weight ratio probably as an extra effort by yearling mothers to balance calf neonatal mortality. It might compensate young mothers to produce low-quality calves while still growing rather than waiting for the uncertain possibility of surviving to the next reproductive season.

Influence of physiological effort of growth and chemical composition on antler bone mechanical properties.

Antler is a good model to study bone biology both because it is accessible and because it grows and is shed every year. Previous studies have shown that chemical composition changes as the antler is grown, implying constraints in mineral availability and the physiological effort made to grow it. This study aimed at examining antler mechanical properties to assess whether they reflect physiological effort and whether they are associated with precise mineral bone composition rather than just ash content, which is usually the main factor affecting mechanical properties. We examined Young's modulus of elasticity (E), strength, and work to maximum load, as well as bone mineral composition, along the antler shaft. Then we compared trends between antlers from two populations: captive, well-fed, health-managed deer (n=15), and free-ranging deer with lower food quality and no health treatment (n=10). Greater E, strength and work were found for better fed and health managed deer. In addition, antler chemical composition of both populations differed in Na, Mg, K, Fe and Si, and marginally in Zn, but not in ash or Ca content. Significant and clear divergent trends in mechanical properties supporting greater physiological exhaustion in free-ranging deer were found for all mechanical variables. Detailed models showed that, in addition to ash content, independent factors extracted from principal component analyses on composition affected E and strength, but not work to maximum load. The results suggest that there is an association between bone chemical composition and mechanical properties independently of ash content.

Does chemical composition of antler bone reflect the physiological effort made to grow it?

In a previous study, antler bone chemical composition was found to differ between base and tip. If such variation is in part due to the physiological effort made to grow the antler, composition trends should differ between antlers from deer population differing in mineral or food availability, or body reserves. To assess this, we examined cortical thickness and bone composition along the antler shaft, and compared trends between antlers from two populations: captive, well-fed, health-managed deer (n=15), and free-ranging deer with lower food quality and no health treatment (n=10). Significant and clear divergent trends supporting greater physiological exhaustion in free-ranging deer and high or moderate predictive models were found for cortical thickness (R(2)=61.8%), content of Na (R(2)=68.6%), Mg (R(2)=56.3%), K (R(2)=40.0%), and Zn (34.6%); lower predictive power was found for protein (R(2)=25.6%) and ash content (R(2)=19.5%); and poor predictive power was found for Ca (R(2)=4.3%), Fe (R(2)=11.1%), and Si (R(2)=4.7%). A second part of the study assessed similar antler structures grown at the beginning (brow tine) and end (top tine) of antler growth within captive deer. Greater cortical thickness and ash content was found for brow tine, as well as a smaller protein, K and Mg content. In contrast, no difference was found for Ca, Na, Zn, Fe or Si. The results suggest that thickness and mineral composition reflect the physiological effort made to build antler bone.