Hindgut Plasticity in Wallabies Fed Hay either Unchopped or Ground and Pelleted: Fiber Is Not the Only Factor

Abstract

Phenotypic plasticity of the gastrointestinal tract is crucial for optimal food processing and nutrient balance in many vertebrate species. For mammalian herbivores, gut plasticity is typically correlated with the fiber content of forage; however, we show here that other factors such as ingesta particle size may effect profound phenotypic plasticity of the fermentative hind-gut in a medium-sized (10-kg body mass) marsupial herbivore, the red-necked wallaby (Macropus rufogriseus). When dietary fiber contents were comparable, red-necked wallabies that were fed a finely ground, pelleted hay for 60-72 d had hindguts that were some 28% heavier (empty wet mass) than those fed unchopped hay. The hindguts of pellet-fed wallabies contained more wet ingesta, which was also of a finer particle size, than those fed hay, indicating some separation of large-and small-particle fermentation between the foregut and the hindgut, respectively. Such a digestive strategy would benefit animals by allowing fermentation of a range of ingesta particle sizes that are expected for free-ranging animals faced with a spectrum of diet types and qualities. The heavier hindgut of pellet-fed wallabies was correlated with increased concentrations of short-chain fatty acids (SCFAs) in the fermentative hindgut (cecum and proximal colon) and particularly with increases in the molar proportions of n-butyric acid. The mechanisms facilitating gut plasticity in herbivorous mammals are uncertain, but we suggest that manipulating ingesta particle size rather than dietary fiber could provide a useful tool for evaluating causal explanations. In particular, altering ingesta particle size could help to distinguish possible direct processes (e.g., the favoring of smaller intestinal microbes and production of specific SCFAs) from indirect affects of feed structure (e.g., muscular hypertrophy to compensate for increased intakes and digesta bulk or the fermentation of mucus secreted to promote the flow of viscous, fine-particle material). ABSTRACT Phenotypic plasticity of the gastrointestinal tract is crucial for optimal food processing and nutrient balance in many vertebrate species. For mammalian herbivores, gut plasticity is typically correlated with the fiber content of forage; however, we show here that other factors such as ingesta particle size may effect profound phenotypic plasticity of the fermentative hindgut in a medium-sized (10-kg body mass) marsupial herbivore, the red-necked wallaby (Macropus rufogriseus). When dietary fiber contents were comparable, red-necked wallabies that were fed a finely ground, pelleted hay for 60-72 d had hindguts that were some 28% heavier (empty wet mass) than those fed unchopped hay. The hindguts of pellet-fed wallabies contained more wet ingesta, which was also of a finer particle size, than those fed hay, indicating some separation of large-and smallparticle fermentation between the foregut and the hindgut, respectively. Such a digestive strategy would benefit animals by allowing fermentation of a range of in...

Retention of different-sized particles and derived gut fill estimate in tammar wallabies (Macropus eugenii): Physiological and methodological considerations

“…The results of this study corroborate previous evidence (Langer et al 1980;Schwarm et al 2009b) that, in contrast to common expectations (Hume 1999, p. 240;Munn and Dawson 2006;Lentle et al 2007;Munn et al 2007), the forestomach of macropods does not appear to differentiate the passage of differently-sized particles. On the one hand, it has been suggested that, similar to the large intestine of rabbits, the macropod forestomach eliminates large particles faster than small particles (Hume 1999, p. 240).…”

“…In macropods, a differential passage of different sized particles has been suspected (Hume 1999). In tammar wallabies, the proportion of small particles in the forestomach decreases with time since feeding (Lentle et al 2007), and in both tammar wallabies and red-necked wallabies (Macropus rufogriseus), a finely-ground diet increased the material present in the caecum and colon, suggesting that fine particles pass through the forestomach quicker and accumulate in the hindgut Munn et al 2007). These findings could suggest a selective expulsion of fine particles from the macropod forestomach.…”

Function, size and form of the gastrointestinal tract of the collared Pecari tajacu (Linnaeus 1758) and white-lipped peccary Tayassu pecari (Link 1795)

“…The results for the pygmy hippos, babyrousa and wild boar are also given in Table 1. The large intestine wet content mass of the monogastric hindgut-fermenting suid, the wild boar, was (1968), Presbytis cristatus, leaf monkey, Pí (1973) and Kay et al (1976), Colobus polykomos, Western black and white colobus monkey, Hume (1977) and Munn et al (2009) Macropus rufogriseus, rednecked wallaby, Warner (1981) and Munn et al (2006) Macropus eugenii, Tammar wallaby, Dellow and Hume (1982) …”

Physiology in conservation translocations

“…Nutritional physiology encompasses more than a simple accounting of the foodstuffs that are available at a release site, and potentially considers a wide range of factors that are relevant to translocations. These factors include the phenotypic plasticity of the gastrointestinal system ( Starck, 1999a , b , 2005 ; Millán et al , 2003 ; O'Regan and Kitchener, 2005 ; Starck and Wang, 2005 ; Munn et al , 2006 , 2009 ), the impacts of gut pathogens ( Everest, 2007 ), microbes or other intestinal symbionts that are needed for healthy digestion ( Hooper and Gordon, 2001 ; Kohl and Dearing, 2012 ), and microbial ‘seeding’ of captive-reared animals, particularly herbivores, to aid digestion following release, and even foraging behaviours; all of these factors can ultimately affect survival and breeding success.…”