Comparative chewing efficiency in mammalian herbivores

Abstract

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: 0.160.28). 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.

Evidence for a tradeoff between retention time and chewing efficiency in large mammalian herbivores

“…2a). The equids of our dataset represent the strategy of a particularly 263 sophisticated dental design (Jernvall et al 1996;Fritz et al 2009) that allows a high degree of 264 digesta particle size reduction (Fig. 1b) without a constraint on food intake.…”

“…The prerequisite for efficiently 255 increasing the time spent chewing per unit digesta is a sorting mechanism that separates 256 smaller from larger particles (Fritz et al 2009;Schwarm et al 2009). Rumination sets a 257 constraint on food intake, because it represents a relevant proportion of the activity budget 258 that can therefore not be used for feeding (Van Soest 1994).…”

“…Here, we use the most comprehensive dataset from one single trial on food intake, 83 digesta retention and digestive efficiency in large grazing mammals fed grass hay (Foose 84 1982), and add our own data on digesta particle size (from Fritz et al 2009) determined for 85 the same species by wet sieving analysis of faeces. We use conventional and phylogeny-based 86 methods to investigate the scaling of digestive traits with body mass and to test two 87 predictions.…”

“…Data were available for body mass (kg), relative organic matter intake (g/kg 0.75 /d), mean 105 retention time (MRT, h), and the apparent digestibility of organic matter and neutral detergent 106 fibre. Data on faecal (=digesta) particle size (mm) was gained from captive individuals of the 107 same species kept in European zoos (from Fritz et al 2009). 108…”

Giants on the landscape: modelling the abundance of megaherbivorous dinosaurs of the Morrison Formation (Late Jurassic, western USA)

“…Bjorndal et al 1990;Bjorndal 1997;Moore 1999;Ellis et al 2005;Hatt et al 2005;Clauss et al 2009;Fritz et al 2009). If so, this may have had a depressing effect on sauropod metabolic levels ) -perhaps even more than inferred for most ground sloths (Vizcaíno et al 2006).…”