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.

Seasonal variations in plant mineral content and free-choice minerals consumed by deer

The aim of this study was to assess the seasonal differences in mineral contents of plants often consumed by wild red deer located in a fenced game estate, south-eastern Spain. Forage plants were sampled throughout 1 year and analysed for macro and trace mineral concentrations. We also offered a cafeteria set of supplemented minerals to assess whether: (i) intake reflected seasonal reductions in plant content of specific minerals; or (ii) intake of mineral supplements responded to increased deer demand of minerals as a result of greater seasonal needs likely arising from lactation, antler growth or skeletal growth. Although no significant seasonal trend was found in mineral distributions of plants, our study suggested that concentrations of K, Mg, Mn, Na, P, Cu and Zn were usually low in plants available to, and consumed by, deer in the study area. In addition, Cu concentration was marginally deficient when compared with the published requirements for other subspecies of red deer. The cafeteria study showed that free-ranging deer had a strong preference for sodium compounds and zinc sulfate, a much weaker attraction to calcium iodate, and no intake in calcium phosphates, Mg and Fe. Consumption of supplemented minerals by deer was maximum in spring and summer and moderate during autumn and winter. Rather than increasing intake of minerals in response to their content in plants, deer may be responding to increased metabolic requirements during antler growth, late gestation and early lactation. Supplementation of mineral compounds is recommended, particularly in the spring–summer period, when the physiological activity is high.

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.

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.