Forage fermentation patterns and their implications for herbivore ingesta retention times

Abstract

Summary1. Differences in digestive physiology between browsing and grazing ruminant feeding types have been discussed extensively. The potentially underlying differences in fermentative behaviour of forage plants have received much less attention. 2. In this study, different groups of temperate forage plants (grasses, browse leaves and twigs, herbs and legumes) were compared in their chemical composition and fermentative behaviour. They were evaluated via an in vitro fermentation system (modified Hohenheim gas test), and relevant fermentation parameters such as maximal gas production and relative gas production rate were calculated. 3. Grasses generally had a higher NDF (neutral detergent fibre = total cell wall) content than browse leaves, herbs and legumes, while browse leaf cell wall was more lignified than that of herbs, legumes and grass. 4. With respect to fermentation parameters, grass had the highest maximal gas production, followed by herbs and legumes, and the lowest maximal gas production in browse leaves and twigs. Relative gas production rate was highest in herbs and legumes, while that of grass and browse was lower. As expected, browse twigs had the lowest nutritional value. 5. Dicot material reached given setpoints of absolute gas production rate like 1·0 or 0·5 mL gas/(200 mg dry matter × h) faster than grass material. Based on these results, a longer passage time of food particles seems to be adaptive for grazing ruminants, as over a wide range of fermentation times, absolute gas production rate is higher in grass compared with dicots. Especially for browse leaves, a higher intake level should be expected to balance energy requirements of animals relying on this forage type.

The digestive morphophysiology of wild, free-living, giraffes

“…Although it is generally accepted that the fermentation rate of browse is faster than it is of grass (du Toit and Yetman 2005; Hummel et al, 2006) because of the differences in insoluble fibre content, the rate of VFA production from DM in giraffes is similar to that of other wild ruminants including grazers Gordon and Illius, 1994). Reduction in particle size by rumination in giraffes to increase digestibility occupies a relatively short part of their day: they allocate a disproportionate time to feeding compared to rumination (du Toit and Yetman 2005), which implies that the size of the particles that enter the rumen stimulate the rumination reflex relatively infrequently.…”

The Morphophysiological Adaptations of Browsing and Grazing Mammals

“…Grass should yield more energy from fermentation per unit forage (Codron et al 2007a), which explains why both in vivo and in vitro overall digestibility (generally measured as digestibility after fermentation times >24 h) are often found to be higher in grass than in woody browse (Wofford and Holechek 1982;Wilman and Riley 1993;Van Wieren 1996b;Hummel et al 2006). However, the evidence is equivocal, as some other references give higher digestibilities for woody browse than for grass (Short et al 1974;Blair et al 1977;Holechek et al 2004).…”

“…Grass contains more fibre, and a greater proportion of this fibre is cellulose, while browse has less total but more lignified fibre (Short et al 1974;Oldemeyer et al 1977;Owen-Smith 1982;McDowell et al 1983; Cork and Foley 1991;Robbins 1993; Van Wieren 1996b;Iason and Van Wieren 1999;Holechek et al 2004;Hummel et al 2006; Codron et al 2007a). These differences are more pronounced if C4 grasses are compared to browse (Caswell et al 1973).…”

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

“…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).…”