Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 2015
Digesta flow plays an important role in ruminant digestive physiology. We measured the mean reten... more Digesta flow plays an important role in ruminant digestive physiology. We measured the mean retention time (MRT) of a solute and a particle marker in the gastrointestinal tract (GIT) and the reticulorumen (RR) of five gazelles and one dikdik species. Species-specific differences were independent from body mass (BM) or food intake. Comparative evaluations (including up to 31 other ruminant species) indicate that MRT GIT relate positively to BM, and are less related to feeding type (the percentage of grass in the natural diet, %grass) than MRT RR. The MRT particle RR is related to BM and (as a trend) %grass, matching a higher RR capacity with increasing BM in grazers compared to browsers. MRT solute RR is neither linked to BM nor to %grass but shows a consistent phylogenetic signal. Selectivity factors (SF; MRT particle /MRT solute , proxies for the degree of digesta washing) are positively related to %grass, with a threshold effect, where species with N 20% grass have higher SF. These findings suggest that in different ruminant taxa, morphophysiological adaptations controlling MRT solute RR evolved to achieve a similar SF RR in relation to a %grass threshold. A high SF could facilitate an increased microbial yield from the forestomach. Reasons for variation in SF above the %grass threshold might represent important drivers of ruminant diversification and await closer investigation.
Chewing efficiency has been associated with fitness in mammals, yet little is known about the beh... more Chewing efficiency has been associated with fitness in mammals, yet little is known about the behavioral, ecological, and morphological factors that influence chewing efficiency in wild animals. Although research has established that dental wear and food material properties independently affect chewing efficiency, few studies have addressed the interaction among these factors. We examined chewing efficiency, measured as mean fecal particle size, as a function of seasonal shifts in diet (and corresponding changes in food fracture toughness) in a single breeding population of a grazing primate, the gelada monkey, at Guassa, Ethiopia. We also measured dental topographic traits (slope, angularity, and relief index) and relative two- and three-dimensional shearing crest lengths in a cross-sectional wear series of gelada molars. Chewing efficiency decreased during the dry season, a pattern corresponding to the consumption of foods with higher fracture toughness. Older individuals experien...
Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 2015
In herbivore ecophysiology, comparative chewing efficiency has only recently received increased a... more In herbivore ecophysiology, comparative chewing efficiency has only recently received increased attention. This measure is best assessed on un-processed forage-only diets; corresponding comparative datasets are missing. We measured a faecal mean particle size (MPS [mm]) in 14 large herbivore species (body mass (M) range 60-4000 kg; 8 ruminants and 6 hindgut fermenters) fed a consistent grass hay diet, in which intake, digesta mean retention times (MRT [h]) and digestive efficiency (as digestibility of faecal fibre measured by 96 h cumulative in vitro gas production GP96h [ml per 200 mg faecal fibre], and metabolic faecal nitrogen MFN [% organic faecal matter]) had been quantified simultaneously. MPS was generally lower in ruminants than in hindgut fermenters and increased with M in the total dataset, but was nearly constant among closely related taxa (e.g. within ruminants, within equids) irrespective of M. MPS (but not MRT) was significantly correlated to GP96h, whereas MRT (but not MPS) was significantly correlated to MFN, suggesting different effects of these factors on different aspects of digestibility. Combinations of measures including MPS mostly explained digestibility better than other combinations. The phylogenetic signal λ, which was mostly 1 when linking any single measure to digestibility, was estimated 0 in models that linked digestive efficiency to combinations of measures. These results support the intuitive concept that species diversification in large herbivores is tightly related to digestive physiology, and that chewing efficiency as measured by faecal particle size is an integral aspect of this scenario.
Data from captive animals indicated that browsing (BR) ruminants have larger fecal particles-indi... more Data from captive animals indicated that browsing (BR) ruminants have larger fecal particles-indicative of lesser chewing efficiency-than grazers (GR). To answer whether this reflects fundamental differences between the animal groups, or different reactions of basically similar organisms to diets fed in captivity, we compared mean fecal particle size (MPS) in a GR and a BR ruminant (aurox Bos primigenius taurus, giraffe Giraffa camelopardalis) and a GR and a BR hindgut fermenter (Przewalski's horse Equus ferus przewalskii, lowland tapir Tapirus terrestris), both from captivity and from the wild. As would be expected owing to a proportion of finely ground, pelleted feeds in captive diets, MPS was smaller in captive than free-ranging GR. In contrast, MPS was drastically higher in captive than in free-ranging BR of either digestion type. Thus, the difference in MPS between GR and BR was much more pronounced among captive than free-ranging animals. The results indicate that BR teeth have adapted to their natural diet so that in the wild, they achieve a particle size reduction similar to that of GR. However, although GR teeth seem equally adapted to food ingested in captivity, the BR teeth seem less well suited to efficiently chew captive diets. In the case of ruminants, less efficient particle size reduction could contribute to potential clinical problems like "rumen blockage" and bezoar formation. Comparisons of MPS between free-ranging and captive animals might offer indications for the physical suitability of zoo diets.
To date, no studies have investigated the predictive validity of variables from the initial exami... more To date, no studies have investigated the predictive validity of variables from the initial examination to identify patients with neck pain who are likely to benefit from thoracic spine thrust manipulation. The purpose of this study was to develop a clinical prediction rule (CPR) to identify patients with neck pain who are likely to experience early success from thoracic spine thrust manipulation.
Although the relevance of particle size reduction in herbivore digestion is widely appreciated, f... more Although the relevance of particle size reduction in herbivore digestion is widely appreciated, few studies have investigated digesta particle size across species in relation to body mass or digestive strategy. We investigated faecal particle size, which reflects the size of ingesta particles after both mastication and specialized processes such as rumination. Particle size was measured by wet sieving samples from more than 700 captive individuals representing 193 mammalian species. Using phylogenetic generalized least squares, faecal particle size scaled to body mass with an exponent of 0.22 (95% confidence interval: 0.16Á0.28). In comparisons among different digestive strategies, we found that (1) equids had smaller faecal particles than other hindgut fermenters, (2) non-ruminant foregut fermenters and hindgut fermenters had similar-sized faecal particles (not significantly different), and (3) ruminants had finer faecal particles than non-ruminants. These results confirm that the relationship between chewing efficiency and body mass is modified by morphological adaptations in dental design and physiological adaptations to chewing, such as rumination. This allometric relationship should be considered when investigating the effect of body size on digestive physiology, and digestion studies should include a measure of faecal particle size.
Mammalian Biology - Zeitschrift für Säugetierkunde, 2013
Herbivores that digest plant material in the fore-stomach can be divided in ruminants and non-rum... more Herbivores that digest plant material in the fore-stomach can be divided in ruminants and non-ruminants. This study describes the distribution of feed particles (and inorganic material) and dry matter (DM) in the digestive tract of non-ruminant foregut fermenters. Results from passage trials led us to hypothesize that specific particle-sorting mechanisms, as observed in ruminants, are unlikely in non-ruminants. Therefore, no systematic particle size distribution effects (indicative of a sorting mechanism) should be evident in the fore-stomachs of these animals, but differences in fluid and particle retention suggest that differences in fluid concentration (measured as DM) could occur in the foregut of macropods and hippos. The gut content of eleven Bennett's wallabies (Macropus rufogriseus), six collared peccaries (Pecari tajacu), three pygmy hippos (Hexaprotodon liberiensis), two common hippos (Hippopotamus amphibius) and one twotoed sloth (Choloepus didactylus) were analyzed with an emphasis on the fore-stomach. The ventral and dorsal regions in sacciform compartments, and peripheral and central regions in tubular compartments, were examined. Results were not uniform across the species studied. A potential sedimentation mechanism was observed firstly by the accumulation of sand in the fore-stomach of the peccary and sloth, and secondly by the lower DM content in peripheral versus central and ventral versus dorsal regions of the fore-stomach of the wallabies and common hippos, respectively. However, pair-comparisons for different gut regions of wallabies and peccaries yielded no differences in mean particle size between forestomach regions. To conclude, some digesta fractionation does occur in the fore-stomach of the studied groups of non-ruminants, but not in a uniform manner, which in turn is in accordance with morphological dissimilarities of their respective foregut structures. The absence of systematic fractionation effects in non-ruminant foregut fermenters emphasizes the innovative character of the sorting mechanism in ruminants.
Journal of Experimental Zoology Part A: Ecological Genetics and Physiology, 2010
A major difference between reptile and mammalian herbivores is that the former do not masticate t... more A major difference between reptile and mammalian herbivores is that the former do not masticate their food. Actually, food particle size reduction by chewing is usually considered one of the adaptations facilitating the higher metabolic rates of mammals. However, quantitative comparisons of ingesta particle size between the clades have, to our knowledge, not been performed so far. We measured mean fecal particle size (MPS) in 79 captive individuals of 14 reptile herbivore species (tortoises, lizards, and Corucia zebrata) by wet sieving and compared the results with a mammalian dataset. MPS increased with body mass in both clades, but at a significantly higher level in reptiles. Limited evidence in free-ranging and captive individuals of Testudo hermanni indicates that in reptiles, the ability to crop food and food particle size significantly influence fecal particle size. The opportunistic observation of a drastic particle size difference between stomach and intestinal contents corroborates findings that in reptiles, in contrast to terrestrial mammals, significant ingesta particle size reduction does occur in the gastrointestinal tract, most likely owing to microbial action during very long ingesta retention. Whether behavioral adaptations to controlling ingesta particle size, such as deliberate small bite sizes, are adaptive strategies in reptiles remains to be investigated.
The isthmus at the caecocolical junction in domestic equids is well described. Like another isthm... more The isthmus at the caecocolical junction in domestic equids is well described. Like another isthmus between the ansa proximalis coli (the colonic fermentation chamber or 'large colon') and the colon transversum (the distal or 'small' colon), this spot represents not only a potential anatomical feature contributing to particle ingesta retention but also an explicit predilection site for intestinal obstructions. The question whether this anatomical feature also occurs in wild equids is therefore of both physiological and medical interest but has not been addressed so far. In this paper, we report dissections of the large intestine of a domestic pony (Equus caballus f. dom.), a Przewalski horse (Equus przewalski) and a plains zebra (Equus burchelli). The intestinal tract section of all three animals were similar in length; each species displayed the caecocolical isthmus as well as the abrupt narrowing of the intestinal tract between the 'large' and the 'small' colon. Graphical descriptions of wild equid gastrointestinal anatomy should include these features.
Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 2011
Morphological characteristics of the forestomach, as well as reports of a natural diet that mostl... more Morphological characteristics of the forestomach, as well as reports of a natural diet that mostly excludes monocots, suggest that dikdiks (Madoqua spp.), among smallest extant ruminants, should have a 'moosetype' forestomach physiology characterised by a low degree of selective particle retention. We tested this assumption in a series of feeding experiments with 12 adult Phillip's dikdiks (Madoqua saltiana phillipsi) on three different intake levels per animal, using cobalt-EDTA as a solute marker and a 'conventional' chromiummordanted fibre (b2 mm; mean particle size 0.63 mm) marker for the particle phase. Body mass had no influence on retention measurements, whereas food intake level clearly had. Drinking water intake was not related to the retention of the solute marker. In contrast to our expectations, the particle marker was retained distinctively longer than the solute marker. Comparisons with results in larger ruminants and with faecal particle sizes measured in dikdiks suggested that in these small animals, the chosen particle marker was above the critical size threshold, above which particle delay in the forestomach is not only due to selective particle retention (as compared to fluids), but additionally due to the ruminal particle sorting mechanism that retains particles above this threshold longer than particles below this threshold. A second study with a similar marker of a lower mean particle size (0.17 mm, which is below the faecal particle size reported for dikdiks) resulted in particle and fluid retention patterns similar to those documented in other 'moose-type' ruminants. Nevertheless, even this smaller particle marker yielded retention times that were longer than those predicted by allometric equations based on quarter-power scaling, providing further support for observations that small ruminants generally achieve longer retention times and higher digestive efficiencies than expected based on their body size.
Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 2009
2009. Evidence for a tradeoff between retention time and chewing efficiency in large mammalian he... more 2009. Evidence for a tradeoff between retention time and chewing efficiency in large mammalian herbivores. Comparative Biochemistry and Physiology -Part A: Molecular & Integrative Physiology 154(3): 376-382. Published Version
Particle size reduction is a primary means of improving efficiency in herbivores. The mode of foo... more Particle size reduction is a primary means of improving efficiency in herbivores. The mode of food particle size reduction is one of the main differences between herbivorous birds (gizzard) and mammals (teeth). For a quantitative comparison of the efficiency of food comminution, we investigated mean fecal particle sizes (MPS) in 14 herbivorous bird species and compared these with a data set of 111 non-ruminant herbivorous mammal species. In general MPS increased with body mass, but there was no significant difference between birds and mammals, suggesting a comparable efficiency of food processing by gizzards and chewing teeth. The results lead to the intriguing question of why gizzard systems have evolved comparatively rarely among amniote herbivores. Advantages linked to one of the two food comminution systems must, however, be sought in different effects other than size reduction itself. In paleoecological scenarios, the evolution of ‘‘dental batteries,’’ for example in ornithopod dinosaurs, should be considered an advantage compared to absence of mastication, but not compared to gizzard-based herbivory.
Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 2015
Digesta flow plays an important role in ruminant digestive physiology. We measured the mean reten... more Digesta flow plays an important role in ruminant digestive physiology. We measured the mean retention time (MRT) of a solute and a particle marker in the gastrointestinal tract (GIT) and the reticulorumen (RR) of five gazelles and one dikdik species. Species-specific differences were independent from body mass (BM) or food intake. Comparative evaluations (including up to 31 other ruminant species) indicate that MRT GIT relate positively to BM, and are less related to feeding type (the percentage of grass in the natural diet, %grass) than MRT RR. The MRT particle RR is related to BM and (as a trend) %grass, matching a higher RR capacity with increasing BM in grazers compared to browsers. MRT solute RR is neither linked to BM nor to %grass but shows a consistent phylogenetic signal. Selectivity factors (SF; MRT particle /MRT solute , proxies for the degree of digesta washing) are positively related to %grass, with a threshold effect, where species with N 20% grass have higher SF. These findings suggest that in different ruminant taxa, morphophysiological adaptations controlling MRT solute RR evolved to achieve a similar SF RR in relation to a %grass threshold. A high SF could facilitate an increased microbial yield from the forestomach. Reasons for variation in SF above the %grass threshold might represent important drivers of ruminant diversification and await closer investigation.
Chewing efficiency has been associated with fitness in mammals, yet little is known about the beh... more Chewing efficiency has been associated with fitness in mammals, yet little is known about the behavioral, ecological, and morphological factors that influence chewing efficiency in wild animals. Although research has established that dental wear and food material properties independently affect chewing efficiency, few studies have addressed the interaction among these factors. We examined chewing efficiency, measured as mean fecal particle size, as a function of seasonal shifts in diet (and corresponding changes in food fracture toughness) in a single breeding population of a grazing primate, the gelada monkey, at Guassa, Ethiopia. We also measured dental topographic traits (slope, angularity, and relief index) and relative two- and three-dimensional shearing crest lengths in a cross-sectional wear series of gelada molars. Chewing efficiency decreased during the dry season, a pattern corresponding to the consumption of foods with higher fracture toughness. Older individuals experien...
Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 2015
In herbivore ecophysiology, comparative chewing efficiency has only recently received increased a... more In herbivore ecophysiology, comparative chewing efficiency has only recently received increased attention. This measure is best assessed on un-processed forage-only diets; corresponding comparative datasets are missing. We measured a faecal mean particle size (MPS [mm]) in 14 large herbivore species (body mass (M) range 60-4000 kg; 8 ruminants and 6 hindgut fermenters) fed a consistent grass hay diet, in which intake, digesta mean retention times (MRT [h]) and digestive efficiency (as digestibility of faecal fibre measured by 96 h cumulative in vitro gas production GP96h [ml per 200 mg faecal fibre], and metabolic faecal nitrogen MFN [% organic faecal matter]) had been quantified simultaneously. MPS was generally lower in ruminants than in hindgut fermenters and increased with M in the total dataset, but was nearly constant among closely related taxa (e.g. within ruminants, within equids) irrespective of M. MPS (but not MRT) was significantly correlated to GP96h, whereas MRT (but not MPS) was significantly correlated to MFN, suggesting different effects of these factors on different aspects of digestibility. Combinations of measures including MPS mostly explained digestibility better than other combinations. The phylogenetic signal λ, which was mostly 1 when linking any single measure to digestibility, was estimated 0 in models that linked digestive efficiency to combinations of measures. These results support the intuitive concept that species diversification in large herbivores is tightly related to digestive physiology, and that chewing efficiency as measured by faecal particle size is an integral aspect of this scenario.
Data from captive animals indicated that browsing (BR) ruminants have larger fecal particles-indi... more Data from captive animals indicated that browsing (BR) ruminants have larger fecal particles-indicative of lesser chewing efficiency-than grazers (GR). To answer whether this reflects fundamental differences between the animal groups, or different reactions of basically similar organisms to diets fed in captivity, we compared mean fecal particle size (MPS) in a GR and a BR ruminant (aurox Bos primigenius taurus, giraffe Giraffa camelopardalis) and a GR and a BR hindgut fermenter (Przewalski's horse Equus ferus przewalskii, lowland tapir Tapirus terrestris), both from captivity and from the wild. As would be expected owing to a proportion of finely ground, pelleted feeds in captive diets, MPS was smaller in captive than free-ranging GR. In contrast, MPS was drastically higher in captive than in free-ranging BR of either digestion type. Thus, the difference in MPS between GR and BR was much more pronounced among captive than free-ranging animals. The results indicate that BR teeth have adapted to their natural diet so that in the wild, they achieve a particle size reduction similar to that of GR. However, although GR teeth seem equally adapted to food ingested in captivity, the BR teeth seem less well suited to efficiently chew captive diets. In the case of ruminants, less efficient particle size reduction could contribute to potential clinical problems like "rumen blockage" and bezoar formation. Comparisons of MPS between free-ranging and captive animals might offer indications for the physical suitability of zoo diets.
To date, no studies have investigated the predictive validity of variables from the initial exami... more To date, no studies have investigated the predictive validity of variables from the initial examination to identify patients with neck pain who are likely to benefit from thoracic spine thrust manipulation. The purpose of this study was to develop a clinical prediction rule (CPR) to identify patients with neck pain who are likely to experience early success from thoracic spine thrust manipulation.
Although the relevance of particle size reduction in herbivore digestion is widely appreciated, f... more Although the relevance of particle size reduction in herbivore digestion is widely appreciated, few studies have investigated digesta particle size across species in relation to body mass or digestive strategy. We investigated faecal particle size, which reflects the size of ingesta particles after both mastication and specialized processes such as rumination. Particle size was measured by wet sieving samples from more than 700 captive individuals representing 193 mammalian species. Using phylogenetic generalized least squares, faecal particle size scaled to body mass with an exponent of 0.22 (95% confidence interval: 0.16Á0.28). In comparisons among different digestive strategies, we found that (1) equids had smaller faecal particles than other hindgut fermenters, (2) non-ruminant foregut fermenters and hindgut fermenters had similar-sized faecal particles (not significantly different), and (3) ruminants had finer faecal particles than non-ruminants. These results confirm that the relationship between chewing efficiency and body mass is modified by morphological adaptations in dental design and physiological adaptations to chewing, such as rumination. This allometric relationship should be considered when investigating the effect of body size on digestive physiology, and digestion studies should include a measure of faecal particle size.
Mammalian Biology - Zeitschrift für Säugetierkunde, 2013
Herbivores that digest plant material in the fore-stomach can be divided in ruminants and non-rum... more Herbivores that digest plant material in the fore-stomach can be divided in ruminants and non-ruminants. This study describes the distribution of feed particles (and inorganic material) and dry matter (DM) in the digestive tract of non-ruminant foregut fermenters. Results from passage trials led us to hypothesize that specific particle-sorting mechanisms, as observed in ruminants, are unlikely in non-ruminants. Therefore, no systematic particle size distribution effects (indicative of a sorting mechanism) should be evident in the fore-stomachs of these animals, but differences in fluid and particle retention suggest that differences in fluid concentration (measured as DM) could occur in the foregut of macropods and hippos. The gut content of eleven Bennett's wallabies (Macropus rufogriseus), six collared peccaries (Pecari tajacu), three pygmy hippos (Hexaprotodon liberiensis), two common hippos (Hippopotamus amphibius) and one twotoed sloth (Choloepus didactylus) were analyzed with an emphasis on the fore-stomach. The ventral and dorsal regions in sacciform compartments, and peripheral and central regions in tubular compartments, were examined. Results were not uniform across the species studied. A potential sedimentation mechanism was observed firstly by the accumulation of sand in the fore-stomach of the peccary and sloth, and secondly by the lower DM content in peripheral versus central and ventral versus dorsal regions of the fore-stomach of the wallabies and common hippos, respectively. However, pair-comparisons for different gut regions of wallabies and peccaries yielded no differences in mean particle size between forestomach regions. To conclude, some digesta fractionation does occur in the fore-stomach of the studied groups of non-ruminants, but not in a uniform manner, which in turn is in accordance with morphological dissimilarities of their respective foregut structures. The absence of systematic fractionation effects in non-ruminant foregut fermenters emphasizes the innovative character of the sorting mechanism in ruminants.
Journal of Experimental Zoology Part A: Ecological Genetics and Physiology, 2010
A major difference between reptile and mammalian herbivores is that the former do not masticate t... more A major difference between reptile and mammalian herbivores is that the former do not masticate their food. Actually, food particle size reduction by chewing is usually considered one of the adaptations facilitating the higher metabolic rates of mammals. However, quantitative comparisons of ingesta particle size between the clades have, to our knowledge, not been performed so far. We measured mean fecal particle size (MPS) in 79 captive individuals of 14 reptile herbivore species (tortoises, lizards, and Corucia zebrata) by wet sieving and compared the results with a mammalian dataset. MPS increased with body mass in both clades, but at a significantly higher level in reptiles. Limited evidence in free-ranging and captive individuals of Testudo hermanni indicates that in reptiles, the ability to crop food and food particle size significantly influence fecal particle size. The opportunistic observation of a drastic particle size difference between stomach and intestinal contents corroborates findings that in reptiles, in contrast to terrestrial mammals, significant ingesta particle size reduction does occur in the gastrointestinal tract, most likely owing to microbial action during very long ingesta retention. Whether behavioral adaptations to controlling ingesta particle size, such as deliberate small bite sizes, are adaptive strategies in reptiles remains to be investigated.
The isthmus at the caecocolical junction in domestic equids is well described. Like another isthm... more The isthmus at the caecocolical junction in domestic equids is well described. Like another isthmus between the ansa proximalis coli (the colonic fermentation chamber or 'large colon') and the colon transversum (the distal or 'small' colon), this spot represents not only a potential anatomical feature contributing to particle ingesta retention but also an explicit predilection site for intestinal obstructions. The question whether this anatomical feature also occurs in wild equids is therefore of both physiological and medical interest but has not been addressed so far. In this paper, we report dissections of the large intestine of a domestic pony (Equus caballus f. dom.), a Przewalski horse (Equus przewalski) and a plains zebra (Equus burchelli). The intestinal tract section of all three animals were similar in length; each species displayed the caecocolical isthmus as well as the abrupt narrowing of the intestinal tract between the 'large' and the 'small' colon. Graphical descriptions of wild equid gastrointestinal anatomy should include these features.
Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 2011
Morphological characteristics of the forestomach, as well as reports of a natural diet that mostl... more Morphological characteristics of the forestomach, as well as reports of a natural diet that mostly excludes monocots, suggest that dikdiks (Madoqua spp.), among smallest extant ruminants, should have a 'moosetype' forestomach physiology characterised by a low degree of selective particle retention. We tested this assumption in a series of feeding experiments with 12 adult Phillip's dikdiks (Madoqua saltiana phillipsi) on three different intake levels per animal, using cobalt-EDTA as a solute marker and a 'conventional' chromiummordanted fibre (b2 mm; mean particle size 0.63 mm) marker for the particle phase. Body mass had no influence on retention measurements, whereas food intake level clearly had. Drinking water intake was not related to the retention of the solute marker. In contrast to our expectations, the particle marker was retained distinctively longer than the solute marker. Comparisons with results in larger ruminants and with faecal particle sizes measured in dikdiks suggested that in these small animals, the chosen particle marker was above the critical size threshold, above which particle delay in the forestomach is not only due to selective particle retention (as compared to fluids), but additionally due to the ruminal particle sorting mechanism that retains particles above this threshold longer than particles below this threshold. A second study with a similar marker of a lower mean particle size (0.17 mm, which is below the faecal particle size reported for dikdiks) resulted in particle and fluid retention patterns similar to those documented in other 'moose-type' ruminants. Nevertheless, even this smaller particle marker yielded retention times that were longer than those predicted by allometric equations based on quarter-power scaling, providing further support for observations that small ruminants generally achieve longer retention times and higher digestive efficiencies than expected based on their body size.
Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 2009
2009. Evidence for a tradeoff between retention time and chewing efficiency in large mammalian he... more 2009. Evidence for a tradeoff between retention time and chewing efficiency in large mammalian herbivores. Comparative Biochemistry and Physiology -Part A: Molecular & Integrative Physiology 154(3): 376-382. Published Version
Particle size reduction is a primary means of improving efficiency in herbivores. The mode of foo... more Particle size reduction is a primary means of improving efficiency in herbivores. The mode of food particle size reduction is one of the main differences between herbivorous birds (gizzard) and mammals (teeth). For a quantitative comparison of the efficiency of food comminution, we investigated mean fecal particle sizes (MPS) in 14 herbivorous bird species and compared these with a data set of 111 non-ruminant herbivorous mammal species. In general MPS increased with body mass, but there was no significant difference between birds and mammals, suggesting a comparable efficiency of food processing by gizzards and chewing teeth. The results lead to the intriguing question of why gizzard systems have evolved comparatively rarely among amniote herbivores. Advantages linked to one of the two food comminution systems must, however, be sought in different effects other than size reduction itself. In paleoecological scenarios, the evolution of ‘‘dental batteries,’’ for example in ornithopod dinosaurs, should be considered an advantage compared to absence of mastication, but not compared to gizzard-based herbivory.
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Papers by Julia Fritz