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.

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.

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.

Dynamics of social behaviour at parturition in a gregarious ungulate.

Group living is the behavioural response that results when individuals assess the costs vs benefits of sociality, and these trade-offs vary across an animal's life. Here we quantitatively assess how periparturient condition (mother/non-mother) and births affect the dynamics of social interactions of a gregarious ungulate, and how such can help to explain evolutionary hypotheses of the mother-offspring bond. To achieve this we used data of the individual movement of a group of Scottish blackface sheep (Ovis aries) marked with GPS collars and properties of mathematical graphs (networks). Euclidean pair-wise distance between sheep were threshold at different percentiles to determine network links, and these thresholds have a profound effect on the connectivity of the resulting network. Births increased the average pair-wise distance between mothers, and between mothers and non-mothers, with less effect on the distance between non-mothers. Mothers occupied peripheral positions within the flock, more evident following births. Associations between individuals (i.e. network community change) were highly dynamic, though mothers were less likely to change community than non-mothers, especially after births. Births hampered individual communication within the flock (assessed via network closeness centrality), especially in mothers. Overall leadership (lead positioning relative to flock movement) was not associated to reproductive condition, and individual leadership rank was not affected by births. A ten minute GPS acquisition time was adequate to capture complex social dynamics in sheep movement. The results on mother's isolation behaviour support the hypotheses of selection for maternal imprint facilitation, reducing risks to nursing alien offspring, and group/multilevel selection on group formation.

The development of an intraruminal nylon bag technique using non-fistulated animals to assess the rumen degradability of dietary plant materials.

Although the conventional in situ ruminal degradability method is a relevant tool to describe the nutritional value of ruminant feeds, its need for rumen-fistulated animals may impose a restriction on its use when considering animal welfare issues and cost. The aim of the present work was to develop a ruminal degradability technique which avoids using surgically prepared animals. The concept was to orally dose a series of porous bags containing the test feeds at different times before slaughter, when the bags would be removed from the rumen for degradation measurement. Bags, smaller than those used in the conventional nylon bag technique, were made from woven nylon fabric, following two shape designs (rectangular flat shape, tetrahedral shape) and were fitted with one of three types of device for preventing their regurgitation. These bags were used in two experiments with individually housed non-pregnant, non-lactating sheep, as host animals for the in situ ruminal incubation of forage substrates. The bags were closed at the top edge by machine stitching and wrapped in tissue paper before oral dosing. Standard times for ruminal incubation of substrates in all of the tests were 4, 8, 16, 24, 48, 72 and 96 h before slaughter. The purpose of the first experiment was to compare the effectiveness of the three anti-regurgitation device designs, constructed from nylon cable ties ('Z-shaped', ARD1; 'double Z-shaped', ARD2; 'umbrella-shaped', ARD3), and to observe whether viable degradation curves could be generated using grass hay as the substrate. In the second experiment, three other substrates (perennial ryegrass, red clover and barley straw) were compared using flat and tetrahedral bags fitted with type ARD1 anti-regurgitation devices. Non-linear mixed-effect regression models were used to fit asymptotic exponential curves of the percentage dry matter loss of the four substrates against time of incubation in the reticulorumen, and the effect of type of anti-regurgitation device and the shape of nylon bag. All three devices were highly successful at preventing regurgitation with 93% to 100% of dosed bags being recovered in the reticulorumen at slaughter. Ruminal degradation data obtained for tested forages were in accordance with those expected from the conventional degradability technique using fistulated animals, with no significant differences in the asymptotic values of degradation curves between bag shape or anti-regurgitation device. The results of this research demonstrate the potential for using a small bag technique with intact sheep to characterise the in situ ruminal degradability of roughages.

Scaling methane emissions in ruminants and global estimates in wild populations.

Methane (CH4) emissions by human activities have more than doubled since the 1700s, and they contribute to global warming. One of the sources of CH4 is produced by incomplete oxidation of feed in the ruminant's gut. Domestic ruminants produce most of the emissions from animal sources, but emissions by wild ruminants have been poorly estimated. This study (i) scales CH4 against body mass in 503 experiments in ruminants fed herbage, and assesses the effect of different sources of variation, using published and new data; and (ii) it uses these models to produce global estimates of CH4 emissions from wild ruminants. The incorporation of phylogeny, diet and technique of measuring in to a model that scales log10 CH4gd-1 against log10 body mass (kg), reduces the slope, from 1.075 to 0.868, making it not significantly steeper than the scaling coefficient of metabolic requirements to body mass. Scaling models that include dry matter intake (DMI) and dietary fiber indicate that although both increase CH4, dietary fiber depresses CH4 as the levels of DMI increases. Cattle produces more CH4 per unit of DMI than red deer, sheep or goat, and there are no significant differences between CH4 produced by red deer and sheep. The average estimates of global emissions from wild ruminants calculated using different models are smaller (1.094-2.687Tgy-1) than those presented in the reports of the Intergovernmental Panel on Climate Change (15Tgyr-1). Potential causes to explain such discrepancy are the uncertainty on the world's wild ruminant population size, and the use of methane output from cattle, a high methane producer, as representative methane output of wild ruminants. The main limitation researchers' face in calculating accurate global CH4 emissions from wild ungulates is a lack of reliable information on their population sizes.

State-Space Modelling of the Drivers of Movement Behaviour in Sympatric Species.

Understanding animal movement behaviour is key to furthering our knowledge on intra- and inter-specific competition, group cohesion, energy expenditure, habitat use, the spread of zoonotic diseases or species management. We used a radial basis function surface approximation subject to minimum description length constraint to uncover the state-space dynamical systems from time series data. This approximation allowed us to infer structure from a mathematical model of the movement behaviour of sheep and red deer, and the effect of density, thermal stress and vegetation type. Animal movement was recorded using GPS collars deployed in sheep and deer grazing a large experimental plot in winter and summer. Information on the thermal stress to which animals were exposed was estimated using the power consumption of mechanical heated models and meteorological records of a network of stations in the plot. Thermal stress was higher in deer than in sheep, with less differences between species in summer. Deer travelled more distance than sheep, and both species travelled more in summer than in winter; deer travel distance showed less seasonal differences than sheep. Animal movement was better predicted in deer than in sheep and in winter than in summer; both species showed a swarming behaviour in group cohesion, stronger in deer. At shorter separation distances swarming repulsion was stronger between species than within species. At longer separation distances inter-specific attraction was weaker than intra-specific; there was a positive density-dependent effect on swarming, and stronger in deer than in sheep. There was not clear evidence which species attracted or repelled the other; attraction between deer at long separation distances was stronger when the model accounted for thermal stress, but in general the dynamic movement behaviour was hardly affected by the thermal stress. Vegetation type affected intra-species interactions but had little effect on inter-species interactions. Our modelling approach is useful in interpreting animal interactions, in order to unravel complex cooperative or competitive behaviours, and to the best of our knowledge is the first modelling attempt to make predictions of multi-species animal movement under different habitat mosaics and abiotic environmental conditions.

Wear Fast, Die Young: More Worn Teeth and Shorter Lives in Iberian Compared to Scottish Red Deer.

Teeth in Cervidae are permanent structures that are not replaceable or repairable; consequently their rate of wear, due to the grinding effect of food and dental attrition, affects their duration and can determine an animal's lifespan. Tooth wear is also a useful indicator of accumulative life energy investment in intake and mastication and their interactions with diet. Little is known regarding how natural and sexual selection operate on dental structures within a species in contrasting environments and how these relate to life history traits to explain differences in population rates of tooth wear and longevity. We hypothesised that populations under harsh environmental conditions should be selected for more hypsodont teeth while sexual selection may maintain similar sex differences within different populations. We investigated the patterns of tooth wear in males and females of Iberian red deer (Cervus elaphus hispanicus) in Southern Spain and Scottish red deer (C. e. scoticus) across Scotland, that occur in very different environments, using 10343 samples from legal hunting activities. We found higher rates of both incisor and molar wear in the Spanish compared to Scottish populations. However, Scottish red deer had larger incisors at emergence than Iberian red deer, whilst molars emerged at a similar size in both populations and sexes. Iberian and Scottish males had earlier tooth depletion than females, in support of a similar sexual selection process in both populations. However, whilst average lifespan for Iberian males was 4 years shorter than that for Iberian females and Scottish males, Scottish males only showed a reduction of 1 year in average lifespan with respect to Scottish females. More worn molars were associated with larger mandibles in both populations, suggesting that higher intake and/or greater investment in food comminution may have favoured increased body growth, before later loss of tooth efficiency due to severe wear. These results illustrate how independent selection in both subspecies, that diverged 11,700 years BP, has resulted in the evolution of different longevity, although sexual selection has maintained a similar pattern of relative sex differences in tooth depletion. This study opens interesting questions on optimal allocation in life history trade-offs and the independent evolution of allopatric populations.

Long-term density-dependent changes in habitat selection in red deer (Cervus elaphus).

Understanding how habitat selection changes with population density is a key concept in population regulation, community composition and managing impacts on biodiversity and ecosystem services. At low density, it is expected that individuals select habitats in terms of their preference, but as population density increases, the availability of resources per individual declines on preferred habitats, leading to competition which forces some individuals to exploit less preferred habitats. Using spatial information of Scottish red deer (Cervus elaphus) winter counts, carried out in 110 areas across Scotland between 1961 and 2004 (a total of 1,206,495 deer observations), we showed how winter habitat niche breadth in red deer has widened with increasing population density. Heather moorland and montane habitats were most and least preferred for deer, respectively. Increasing density favoured the selection of grassland, to the detriment of the selection of heather moorland. The selection of heather and grassland decreased when temperature increased, while the selection of montane and peatland habitats increased. These findings are important for understanding how habitat use, density and population are likely to be affected by weather, and allow us to predict habitat impacts by large mammal herbivory and climate.

Variable extent of sex-biased dispersal in a strongly polygynous mammal.

For mammals with a polygynous mating system, dispersal is expected to be male-biased. However, with the increase in empirical studies, discrepancies are arising between the expected and observed direction/extent of the bias in dispersal. In this study, we assessed sex-biased dispersal in red deer (Cervus elaphus) on 13 estates from the Scottish Highlands. A total of 568 adult individuals were genotyped at 21 microsatellite markers and sequenced for 821 bp of the mitochondrial control region. Estimates of population structure with mitochondrial sequences were eight times larger than that obtained with microsatellite data (F(st'-mtDNA) = 0.831; F(st'-micros) = 0.096) indicating overall male-biased dispersal in the study area. Comparisons of microsatellite data between the sexes indicated a predominance of male-biased dispersal in the study area but values of F(ST) and relatedness were only slighter larger for females. Individual-based spatial autocorrelation analysis generated a similar pattern of relatedness across geographical distances for both sexes, with differences only significant at two distance intervals (25-30 and 70-112 km). Patterns of relatedness differed between estates, male biased-dispersal was detected in eight estates but no sex-biased dispersal was found in the remaining five. Neither population density nor landscape cover was found to be associated with the patterns of relatedness found across the estates. Differences in management strategies that could influence age structure, sex ratio and dispersal behaviour are proposed as potential factors influencing the relatedness patterns observed. This study provides new insights on dispersal of a strongly polygynous mammal at geographical scales relevant for management and conservation.

Genetic diversity and population structure of Scottish Highland red deer (Cervus elaphus) populations: a mitochondrial survey.

The largest population of red deer (Cervus elaphus) in Europe is found in Scotland. However, human impacts through hunting and introduction of foreign deer stock have disturbed the population's genetics to an unknown extent. In this study, we analysed mitochondrial control region sequences of 625 individuals to assess signatures of human and natural historical influence on the genetic diversity and population structure of red deer in the Scottish Highlands. Genetic diversity was high with 74 haplotypes found in our study area (115 x 87 km). Phylogenetic analyses revealed that none of the individuals had introgressed mtDNA from foreign species or subspecies of deer and only suggested a very few localized red deer translocations among British localities. A haplotype network and population analyses indicated significant genetic structure (Phi(ST)=0.3452, F(ST)=0.2478), largely concordant with the geographical location of the populations. Mismatch distribution analysis and neutrality tests indicated a significant population expansion for one of the main haplogroups found in the study area, approximately dated c. 8200 or 16 400 years ago when applying a fast or slow mutation rate, respectively. Contrary to general belief, our results strongly suggest that native Scottish red deer mtDNA haplotypes have persisted in the Scottish Highlands and that the population retains a largely natural haplotype diversity and structure in our study area.

Does the Jarman-Bell principle at intra-specific level explain sexual segregation in polygynous ungulates? Sex differences in forage digestibility in Soay sheep.

The Jarman-Bell principle states that large-bodied mammalian herbivores can subsist on lower quality diets because of their lower metabolism requirement/gut capacity ratio. Two major hypotheses for sexual segregation (the behaviour in which animals of the same species aggregate by sex) base their foundations on extending this principle to the intraspecific level, despite the lack of experimental evidence to support this. The first proposes that the larger males can process fibre (low-quality diet) more efficiently than the smaller females, leading to sexual segregation by habitat partitioning due to selection of different food quality and/or quantity (sexual dimorphism-body size hypothesis). The second suggests that the longer time and extra rumination required to digest low-quality food will cause asynchrony of behaviour between males and females, which then leads to sexual segregation (activity budget hypothesis). To provide experimental evidence for the Jarman-Bell principle at the intraspecific level we carried out a set of digestibility trials in Soay sheep (Ovis aries) using grass hay as the diet to test whether sexual dimorphism in body mass can produce significant sexual differences in the efficiency of food digestion. Males were slightly more efficient in digesting forage than females that were at least 30% smaller than the males. Overall, there was a decrease in faecal output of 1 g/kg body mass in favour of males. These differences were not due to differences in food selection, passage rates or faecal particle size and it was not clear why males were more efficient in digesting forage. Although these results do not directly support arguments for either the sexual dimorphism-body size or activity budget hypotheses, they do indicate that the physiological argument upon which the Jarman-Bell principle is founded also operates at the intraspecific level and may be an important factor influencing sexual segregation.

Landscape features affect gene flow of Scottish Highland red deer (Cervus elaphus).

Landscape features have been shown to strongly influence dispersal and, consequently, the genetic population structure of organisms. Studies quantifying the effect of landscape features on gene flow of large mammals with high dispersal capabilities are rare and have mainly been focused at large geographical scales. In this study, we assessed the influence of several natural and human-made landscape features on red deer gene flow in the Scottish Highlands by analysing 695 individuals for 21 microsatellite markers. Despite the relatively small scale of the study area (115 x 87 km), significant population structure was found using F-statistics (F(ST) = 0.019) and the program structure, with major differentiation found between populations sampled on either side of the main geographical barrier (the Great Glen). To assess the effect of landscape features on red deer population structure, the ArcMap GIS was used to create cost-distance matrices for moving between populations, using a range of cost values for each of the landscape features under consideration. Landscape features were shown to significantly affect red deer gene flow as they explained a greater proportion of the genetic variation than the geographical distance between populations. Sea lochs were found to be the most important red deer gene flow barriers in our study area, followed by mountain slopes, roads and forests. Inland lochs and rivers were identified as landscape features that might facilitate gene flow of red deer. Additionally, we explored the effect of choosing arbitrary cell cost values to construct least cost-distance matrices and described a method for improving the selection of cell cost values for a particular landscape feature.

Voluntary intake and digestibility in horses: effect of forage quality with emphasis on individual variability.

Food intake is a key biological process in animals, as it determines the energy and nutrients available for the physiological and behavioural processes. In herbivores, the abundance, structure and quality of plant resources are known to influence intake strongly. In ruminants, as the forage quality declines, digestibility and total intake decline. Equids are believed to be adapted to consume high-fibre low-quality forages. As hindgut fermenters, it has been suggested that their response to a reduction in food quality is to increase intake to maintain rates of energy and nutrient absorption. All reviews of horse nutrition show that digestibility declines with forage quality; for intake, however, most studies have found no significant relationship with forage quality, and it has even been suggested that horses may eat less with declining forage quality similarly to ruminants. A weakness of these reviews is to combine data from different studies in meta-analyses without allowing the differences between animals and diets to be controlled for. In this study, we analysed a set of 45 trials where intake and digestibility were measured in 21 saddle horses. The dataset was analysed both at the group (to allow comparisons with the literature) and at the individual levels (to control for individual variability). As expected, dry matter digestibility declined with forage quality in both analyses. Intake declined slightly with increasing fibre contents at the group level, and there were no effects of crude protein or dry matter digestibility on intake. Overall, the analysis for individual horses showed a different pattern: intake increased as digestibility and crude protein declined, and increased with increasing fibre. Our analysis at the group level confirms previous reviews and shows that forage quality explains little of the variance in food intake in horses. For the first time, using mixed models, we show that the variable 'individual' clarifies the picture, as the horses showed different responses to a decrease in forage quality: some compensated for the low nutritional value of the forages by increasing intake, few others responded by decreasing intake with declining forage quality, but not enough to cause any deficit in their energy and protein supplies. On the whole, all the animals managed to meet their maintenance requirements. The individual variability may be a by-product of artificial selection for performance in competition in saddle horses.

The evolution of phylogenetic differences in the efficiency of digestion in ruminants.

This study investigates, for the first time (to our knowledge) for any animal group, the evolution of phylogenetic differences in fibre digestibility across a wide range of feeds that differ in potential fibre digestibility (fibre to lignin ratio) in ruminants. Data, collated from the literature, were analysed using a linear mixed model that allows for different sources of random variability, covariates and fixed effects, as well as controlling for phylogenetic relatedness. This approach overcomes the problem of defining boundaries to separate different ruminant feeding styles (browsers, mixed feeders and grazers) by using two covariates that describe the browser-grazer continuum (proportion of grass and proportion of browse in the natural diet of a species). The results indicate that closely related species are more likely to have similar values of fibre digestibility than species that are more distant in the phylogenetic tree. Body mass did not have any significant effect on fibre digestibility. Fibre digestibility is estimated to increase with the proportion of grass and to decrease with the proportion of browse in the natural diet that characterizes the species. We applied an evolutionary model to infer rates of evolution and ancestral states of fibre digestibility; the model indicates that the rate of evolution of fibre digestibility accelerated across time. We suggest that this could be caused by a combination of increasing competition among ruminant species and adaptation to diets rich in fibre, both related to climatically driven environmental changes in the past few million years.

The origins of sexual dimorphism in body size in ungulates.

Jarman (1974) proposed a series of relationships between habitat use, food dispersion, and social behavior and hypothesized a series of evolutionary steps leading to sexual dimorphism in body size through sexual selection in African antelope species. The hypothesis states that sexual size dimorphism evolved in a three-step process. Initially, ancestral monomorphic and monogamous ungulate species occupying closed habitats radiated into open grassland habitats. Polygynous mating systems then rapidly evolved in response to the aggregation of males and females, perhaps in relation to the clumped distribution of food resources in open habitats. Subsequently, size dimorphism evolved in those species occupying open habitats, but not in species that remained in closed habitats or retained monogamy. This hypothesis has played an important role in explaining the origins of sexual dimorphism in mammals. However, the temporal sequence of the events that Jarman proposed has never been demonstrated. Here we use a phylogeny of extant ungulate species, along with maximum-likelihood statistical techniques, to provide a test of Jarman's hypothesis.

Relationships between oral morphology and feeding style in the Ungulata: a phylogenetically controlled evaluation.

In ungulates it is argued that specialization in the consumption of a particular type of food (feeding style) is reflected in morphological adaptations of the organs involved in the selection, processing and digestion of food. We analysed the differences in size and morphology of some oral traits that have been functionally related to food-selection ability (muzzle width, incisor-arcade shape, incisor shape), prehension of food (incisor protrusion), food comminution (molar occlusal surface area, hypsodonty (high-crowned molars)) and intake rate (incisor breadth) between ungulate species with different feeding styles (browser, mixed feeder, grazer). Grazers were characterized by large-body-size species. After controlling only for body mass, we found that grazers had wider muzzles and incisors, more-protruding incisors and more-bulky and higher-crowned molars than did mixed feeders and browsers. When the analyses took into account both body mass and phylogeny, only body mass and two out of the three hypsodonty indexes used remained significantly different between feeding styles. Browsers were smaller, on average, than mixed feeders and grazers, whilst grazers and mixed feeders did not differ in size. Also, browsers had shorter and less-bulky molars than did mixed feeders and grazers; the latter two feeding styles did not differ from each other in any of the hypsodonty indexes. We conclude that the adaptation to different dietary types in most of the oral traits studied is subsumed by the effects of body mass and the sharing of common ancestors. We hypothesize that differences in the ability to exploit different food resources primarily result from differences in body mass between species, and also discuss why hypsodonty characterizes feeding styles.