Quality of the trophies in game ruminants: from the study of mechanical and structural properties, to the mineral composition and characterization of the trophy
- Autores: Jamil Cappelli
- Directores de la Tesis: Andrés José García Díaz (dir. tes.), Laureano Gallego Martínez (codir. tes.), Tomás Landete Castillejos (codir. tes.)
- Lectura: En la Universidad de Castilla-La Mancha ( España ) en 2019
- Idioma: español
- Tribunal Calificador de la Tesis: Jose Angel Gomez Nieto (presid.), Francisco Javier Pérez-Barbería (secret.), Aurora Monzón Capapé (voc.)
- Programa de doctorado: Programa de Doctorado en Ciencias Agrarias y Ambientales por la Universidad de Castilla-La Mancha
- Materias:
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- Resumen
Nowadays, hunting plays a very important role in the conservation of biodiversity; and is considered a good tool to preserve the biological heritage and an important source of sustainable economic growth. Thus, hunting is a recreational activity which generates wealth and employments in depressed rural context. Moreover, the hunting sector seems to have a large turnover of money and it represents an important sector in the boundary of agrarian and wildlife related industry of European states. The Spanish example showed that the hunting sector employs more than 186,000 people and suppose a 0.3% of the GDP of Spain, and according to some estimates, a turnover equal to of 6,475 M€ that has a fiscal return of 614 M€. Moreover, the hunting permissions were 851,894 with an economic value of 20,5 M€; and only the red deer as species moves about 25,6 M€. Other authors estimate that in Spain, game estates have an economic impact which would range between 665 and 2,600 M€ (estimated based on USA study for economic impact for deer farm and per animal, respectively). In Spain the hunting estates are approximately 3,000, with an average surface of 1,000 ha, and the estimated total number of red deer is almost 650,000. As a matter of fact, European ungulate species represent an immense potential resource, not only in terms of biodiversity but also in economic terms. Economic estimates, based on economic impact per animal and per farm in USA study, assess an impact of 1120 M€ at the level of the EU farming industry (with 280,000 deer farmed in 10,000 farms, FEDFA data). At the present, trophy is the main objective of big game with a secondary use of meat (the economic estimation is 45 M€ for meat). In the commercial market, larger antlered males are more valuable to private landowners, and one of the most used criteria for selecting animals for future trophies is the length of the trophy's beam. Following these lines in the deer production, already in the past, our research group carried out various studies on wild and bred populations of red deer. The aim was to understand the effects of management and the effects of environmental factors on animal growth and the growth of their antlers. For this reason, a study protocol was developed using as parameters the quality of the trophy, intended as a tool for analysing the quality of a deer or, more generally, a herd of deer. This protocol provides for the study of the mechanical and structural characteristics of the trophy, as well as its mineral content. In this thesis we will examine these concepts in different subspecies of red deer, and moreover, for the first time, we will use this method of study on other species that play an important role in the world of hunting and wildlife production, at international level.
This thesis is focused on 4 studies completed on distinct species of ungulates included between Bovidae and Cervidae. The species included are: the red deer (with two subspecies: Cervus elaphus hispanicus and Cervus elaphus corsicanus), the roe deer (Capreolus capreolus) with two populations subject to different diets and habitats, and finally an African bovid (Taurotragus oryx), which it has considerable importance in the hunting world as well as for the production of meat on farms, especially in New Zeland, USA and South Africa; the latter country, only in the northern regions, has farms with about 30,000 animals. These species and subspecies have a strong faunistic-hunting interest; moreover, some of them are under the protection and management programs, in order to improve the coexistence between man and ungulates. The main aims of this thesis are the characterization of the trophies and the analysis of their quality; for this reason the mechanical properties (Young’s Modulus of elasticity= E; Bending Strength= BS; Work under the curve= W; Impact energy= U), structural characteristics of the bone tissue of the antlers and the mineral content were analysed, to determine: 1) the relationship between mineral composition, mechanical properties and function and type of growth (continuos or seasonal) of the Cervidae and Bovidae cranial appendages; 2) interspecific common patterns of differences; 3) the relationship between composition and mechanical properties in a wide frame of different species.
In the first research work, for the first time, the morphological characteristics and the mechanical and structural properties and the mineral content of the Sardinian deer's antlers were described (Chapter 5.1). This subspecies of the red deer is distributed on the islands of Sardinia and Corsica, and currently the population is increasing (4270 animals); since in the past they suffered from excessive hunting pressure, this subspecies is currently protected by Italian and European law. However, the protection status of the species is causing problems of interaction between the deer and the anthropic activities present in the area. For this reason, probably in a future it will be necessary to carry out a population management even through the controlled use of selective hunting. Given that this study is the first to assess the characteristics of the antlers of this species, initially the external morphological characteristics of the trophy were assessed, using antlers of 35 adult deer and 26 subadults. The antlers were collected within a protected area where the Sardinian deer is widely distributed ("Sette Fratelli" forest complex). The differences between subadults and adults were easily distinguishable: the adult trophy was heavier, wider and with more tines. Compared to other European populations, the Sardinian deer had a trophy with a lower weight and fewer tines (only 20% of the antler have three tines, while in red deer of the Italian peninsula three-tined trophies appear in more than 40% of cases). Compared to the Spanish deer, the Sardinian deer presented lower values for weight (-65%), length (-26%), burr perimeter (-30%) and length of the first tine (-45%). Subsequently, 12 antlers of adult deer were analysed in more depth, selected according to the morphology that characterizes the typical trophy of an adult Sardinian deer. On this set of antlers, the mechanical tests, the analysis of the internal structure and thet of the mineral profile were made; using cortical bone samples from 4 different positions along the vertical axis of trophy. The results showed that the bone tissue of the Sardinian deer has lower values for the average thickness of the cortical tissue, for the mechanical properties as stiffness (E) and work to fracture (W) and for the ash content; this was probably due to a lower quality diet that is reflected in a bone tissue with non-optimal characteristics compared to other sub-species of cervids. Even the mineral content turned out to be different compared to the Spanish deer. Probably the Sardinian deer follows the theory of the "phenotypic maintenance model", where phenotypic plasticity is driven through efficient growth models under the effect of restrictive ecological factors (as can be a Mediterranean environment). Moreover, the Sardinian deer may be subject to the effect of insular dwarfism, in which a species is smaller than other populations of the same species distributed on land. Finally, the discussion of this article also commented on the positive consequences of a selection hunt for this sub-species of deer, once its limit of spread on the island was reached, thus favouring also the economic growth of areas natural marginal.
Following the aim to compare different species, the second research (Chapter 5.2) concerned, for the first time, the study of two different roe deer populations subject to different habitat and management conditions. Sets of antlers from an extensive open-breeding farm near Prague (Czech Republic) and antlers from a closed-breeding farm of Murcia (Spain) were analysed. The animals of the Czech Republic lived in a vast area with mixed forest-cultivated cover; food supplementation was present only in a few cases, and the natural vegetation was covered by snow during the period of growth of the antlers for this species (winter). In contrast, the population of Iberian roe deer was managed more carefully, with a diet that provided food supplements throughout the year and a vegetative cover also continuous throughout the year. Therefore, the objective of this scientific study was to study differences in trophy characteristics (structural-mechanical qualities and mineral content of cortical bone tissue); in order to observe the effects of a very different management of two populations of the same species that lived in a very different habitat. A secondary aim was to compare the effects of an optimal/poor diet in the roe deer with similar studies in the antlers of red deer. From each analysed antler, samples were extracted from two different positions, along the trophy beam (at the base and near the upper tip). The results showed that the Czech’s antler set showed lower values for the size of the trophy: such as the length of the beam (-20%), the weight of the trophy (-130%), and therefore, lower score for the trophies (-24.3%). In contrast, the structural properties (cortical bone width = CBD% and cortical bone area = CBA%) are significantly higher in the Czech population. The two populations have different mechanical properties: the Spanish roe deer had a greater W and U (+19% and +72%, respectively), while the Czech roe deer offset its deficiencies with a greater cortical area and higher mechanical values for BS (+16%) and E (+12%). The mineral profile showed non-homogeneous differences: the roe deer of the Czech Republic had a higher value for ash content, Ca, K, P, Cr, Li, Sr and Zn; while the Spanish roe deer had higher values for Na, Mn, Tl and for the Ca/P ratio. In addition to the origin, the sampling position also has an effect on the observed variables; through the GLM it was possible to observe that for the values of the mechanical properties there was a variability of 27% for E, 36% for BS, 38% for W, 49% for U; for the structure the models explained a 55% of the CBDcm variability. For minerals, only Zinc was affected by the position (48% variability in GLM models); this mineral was also 25% higher in the antlers of the Czech Republic, perhaps due to a greater physiological stress during the growth of their trophy. In relation to the differences in the mineral profile between the two sampling positions, and the relationship with the physiological stress of the growth of the antler, there were no significant differences for both studied populations, probably because the roe deer's antlers is small, considering the body mass of this species. Since the group of Spanish animals was bred in optimal conditions with mineral supplements and continuous vegetative cover, while the Czech group grew in a poorer habitat, we concluded that these results support the hypothesis that a rich diet is reflected in the growth of the antlers, and that the antler can be considered an indicator of the quality of the environmental conditions.
In the third scientific study (Chapter 5.3) we aimed at comparing the previous studies and others in antlers with a similar study in the horn of a bovid, thus, for the first time, the bone nucleus belonging to the horn of the Common Eland was characterized, as example of bovid horn. The trophy of these African bovids has a spiral shape, with an evident thickening that, like a helix, rises from the base to the tip. Moreover, as characteristic for the bovid family, its trophy consists of a bony core (which remains moist), an outer keratin case and a membranous tissue interposed between these two components. In this case, samples of the core bone tissue were made in 4 sequential positions, starting from the base and climbing the vertical axis of the horn. Eight bony cores of different animals raised in an experimental breeding farm in Prague were used. The main objective was to observe the mechanical differences and the mineral content along the vertical axis of the horn, and for this, for each position, two bony bars were extracted for the mechanical tests and subsequent tests on mineral content, ash and bone density. Moreover, in the first position, at the base of the horn, the differences in the mechanical yields between the central standard bone and the bone tissue forming part of the characteristic spiral of the horn were studied. The results showed that the density and ash content decreased, from the base to the tip of the horn (-32% and -36%, respectively). Also, the mechanical properties achieved a similar decreasing gradient, but only the impact energy showed significant differences (U= -48%). This strong difference between horn areas was due to the different mechanical function and the characteristics of the material and microstructure. For the mineral profile, there are differences depending on the observed mineral: the concentrations of some of these significantly increased, rising from the base to the tip (Se= +4%, Cu= +84%, K= +16%), while other minerals decreased (Mg= -33%, Mn= -31%). This species, as in red deer, showed a similar dynamic of minerals: the content of Ca and Na decreased in the proximal-distal direction, while K showed an increase. Furthermore, our results followed the "gradient due to differential fighting stress within the horn" hypothesis; where the most stressed region of the horn (the one subject to bear more deformations) is that next to the skull of the animal; and this would explain why this region is best designed to support mechanical stress during thrusts and twists, in males fight. The mechanical and mineral profile variables, observed between the standard bone and the spiral horn region, showed no great differences, only some mechanical properties were weaker in the spiral bone tissue (W= -300%, BS= -153%, U= -118%). The most plausible explanation was that the weaker properties of the spiral region serve to deflect the transverse mechanical stresses suffered by the bone tissue during torsional collisions and pushes, with other males of the species. Moreover, another hypothesis was that a larger surface of the spiral could avoid slippage/rotation of the horny keratin sheath with respect to the internal bone nucleus, in the composite structure of the horns in Bovidae.
Finally, the fourth scientific study (Chapter 6.1), is part of a miscellaneous study, although in the line of this thesis, because it showed the effects in the diet of supplementation of an interesting mineral, manganese, in deer antler composition and mechanics. The study followed the steps already marked in previous studies of our group, in which it was possible to observe how the mineral content and the quality of the food are reflected on the composition and mechanical properties of the bone tissue of the antlers of adult and young Iberian deer (yearlings). This study confirmed the hypothesis that manganese supplementation also play an important role in the development of the antlers (a previous study assessed effects of Mn deficiency). The role of the Manganese was studied through a supplementation by injections of 4% Gluconate of Manganese. Nineteen adult and ten yearling animals were used, which were distributed between the control group and the group subjected to weekly injections; the experiment lasted from January to mid-August (the period of antler growth). A balanced diet was the same for all individuals, so the manganese supplementation may show effects on the growth of antlers of well-fed animal. The antlers, once cleaned and fully grown, were cut in September, and samples were taken in four positions along the main beam for adults and two positions for the young deer (base and tip of these smaller antlers). The results showed that young deer, compared to adults, have lower values for mechanical yields, structural features (less than the average thickness of cortical bone) and mineral content of bone tissue; in both groups the level of Mn increased in the groups of treated animals (2.5 times in the young and 2.3 times in the adults). The yearlings did not show significant results in the mineral content (only for Fe and Mn) between the control and the treated group, probably because these animals were subject to the strong constraint of the effort of their growth. Consistent with this hypothesis, there was a minor influence of supplementation in the rest of characteristics of the antlers (mechanical properties and structure). The treated adult deer, in contrast, showed that body weight increased by 10% less than the control group during the trial. In addition, treated adults showed higher content of Ca (+8%), P (+10%), Na (+14%), K (+47%), Se (+142%) and Cu (+29%); while Si was the only one decreasing. Regarding mechanical properties, adults showed a significant increase of +11.8% in U. To study the effects of animal weight and Mn supplementation, GLMs were used: it was observed that supplementation has an effect on Co, K, Mn, Se and Si; while only the weight of the animal has effect on the CBD, on antler’s length, the density of the bone, E, BS and on the content of the Zn. The difference between the base and the tip of the antlers, which shows the effort of the animal for the growth of the trophy, showed no significant differences in the mineral profile (only for the content of the Mn); in the distal position an increase of 16% of the W was observed, only for treated animals, after having checked for the effect of the weight of the animals. The results obtained in this study were very similar to a previous study carried out by our own group, assessing antlers grown in two years differing strongly in late winter frost (February). Thus, decrease in the content of ash, Ca, P, Na, Co, Se and an increase in Si content was observed in antler set grown by deer feeding on plants during exceptional frosts. The study concluded that a general antler breakage due to reduced cortical thickness, add change in mineral composition in the year of late winter frosts was actually caused by a reduction in Mn content in the plants, likely similar to Mn deficiency in deer diet. That is exactly the opposite to Mn supplementation, which resulted in logical opposite effects in the antler characteristics (Mn hypothesized deficiency vs. current Mn supplementation). In conclusion, it can be said that the characterization of the trophies through the study of the mechanical properties, the structural characteristics and the mineral profile of the bone tissue of the trophies themselves can be an excellent tool for the management of both wild and bred populations. Moreover, with the studies carried out in this thesis, it is shown that this method of study can also be applied to Bovidae or other species of Cervidae.
