Fluid and particle retention times in the black rhinocerosDiceros bicornis, a large hindgut-fermenting browser

Abstract

2005. Fluid and particle retention times in the black rhinoceros Diceros bicornis, a large hindgut-fermenting browser. Acta Theriologica 50: 367-376.The mean retention time (MRT) of ingesta in the gastrointestinal tract is one of the major determinants of herbivore digestive physiology. We examined MRTs of fluids and particles in the gastrointestinal tract of six adult captive black rhinoceroses Diceros bicornis on conventional zoo diets. Fluid MRT ranged from 25-45 h and averaged 31 h. Particle MRT ranged from 28-59 h and averaged 38 h. In the six animals, both fluid and particle MRT declined as relative dry matter intake (g/kg metabolic body mass) increased. Black rhinoceroses, which are large hindgut--fermenting browsers, retained ingesta for a shorter period relative to their body size than grazing equids or grazing rhinoceros species. Our findings support the hypothesis that browsing hindgut fermenters have relatively shorter MRTs than grazing hindgut fermenters.

The Nutrition of “Browsers”

“…In theory, it would not make sense for a browser to retain ingesta as long as a grazer does; compared with grass, browse does not yield relevant amounts of energy after a certain digestion time. Indeed, there have been numerous indications that browsing ruminants and browsing rhinos have shorter ingesta retention times than their grazing counterparts, 16,19 but for a comprehensive comparative evaluation, the existing database is still too small.…”

A comparison of faecal analysis with backtracking to determine the diet composition and species preference of the black rhinoceros (Diceros bicornis minor)

“…grasses), whereas for faecal analysis, some species might not be identified to species level. Faecal samples do not exactly mirror the diet composition in the vegetation types where they are found because of the movement of herbivores and the retention time for digesting the plant material (Anthony and Smith 1974;Prins et al 2006;Clauss et al 2005); this might also have influenced the results. Parker and Bernard (2006) concluded that direct observations tend to overestimate important food items, but faecal analysis integrates information over time and is therefore a more conservative and potentially accurate method.…”

“…Various authors suggested that the method of microhistological analyses of faeces has limitations to determine ungulate diet compositions, as differential digestion may result in differences between what is ingested and what is excreted (Leslie et al 1983;Mukhtar and Hansen 1983;Barker 1986). Shorter ingesta retention times and slow plant fermentation rates such as for grasses (Clauss et al 2005;Hummel et al 2006) might create a bias in the estimation of the diet composition. No correction for digestibility, however, was necessary as plant cuticle, which is used in this study for plant identification, is indigestible in any animal's guts (Stace 1965).…”

The relationship of food intake and ingesta passage predicts feeding ecology in two different megaherbivore groups

“…Such enormous ranges make the use of one “species‐specific value” seem dubious, and warrant explanation by other physiological measurements beyond body mass. Many authors have noted a negative correlation between food intake and MRT, not only in herbivorous species (Halse 1984, Wetherbee and Gruber 1990, Lechner‐Doll et al 1991, Fryxell et al 1994, Reid and Brooks 1994, McClelland et al 1999, Pearson et al 2001, Clauss et al 2004, Clauss et al 2005). Actually, the belief that relative dry matter intake (DMI, g kg −0.75 metabolic body mass day −1 ) is negatively correlated with MRT in the gastrointestinal tract is an integral part of digestion theory (Silby and Calow 1986).…”