Profils et taux de renouvellement en minéraux dans le pré-estomac de dromadaires pâturant en diverses saisons au Kenya

Les volumes et les taux de renouvellement du liquide des pré-estomacs ont été mesurés sur quatre dromadaires adultes fistulés entretenus sur pâturage dans les savanes arbustives à épineux du Kenya. Simultanément, les concentrations en minéraux et leur renouvellement ont été déterminés dans les compartiments C1 (rumen) et C2 (réseau). Les études ont été menées durant la saison humide et durant la saison sèche ; les comportements alimentaires ont été observés pour déterminer les régimes. Les volumes du liquide du pré-estomac n’étaient pas différents d’une saison à l’autre mais les taux de renouvellement du liquide étaient beaucoup plus bas en saison sèche. Les profils de concentration en minéraux Na, K, Ca, Mg et en phosphore inorganique variaient dans la journée selon les différents régimes alimentaires et probablement la production de salive. Le renouvellement journalier des cinq minéraux, dans les pré-estomacs a diminué durant la saison sèche

Comparative selective retention of particle size classes in the gastrointestinal tract of ponies and goats

There is a discrepancy in the literature on potential digesta separation mechanisms in horses, with both a selective retention of fine and of large particles postulated in different publications. To assess the net effect of such mechanisms, we fed ponies on a hay-only diet a pulse dose of whole (unchopped) marked hay together with a solute marker, collected faeces on a regular basis, measured marker concentrations in whole faeces and in their large (2.0-16 mm), medium (0.5-1.0 mm) and small (0.063-0.25 mm) particle fraction, and calculated the corresponding mean retention times (MRT). For comparison, the same experiment was performed in goats. In goats, as expected, MRTsolute (35 h) was significantly shorter than MRTparticle (51 h); only a very small fraction of particle marker was excreted as large particles (2%); and the MRT of these large particles was significantly shorter than that of small particles (with a relevant difference of 8.6 h), indicating that those few large particles that escape the rumen do so mostly soon after ingestion. In ponies, MRTsolute (24 h) did not differ from MRTparticle (24 h); a higher fraction of particle marker was excreted as large particles (5%); and the MRT of these large particles was longer than that of small particles (but with a non-relevant difference of less than 1 h). These results indicate that no relevant net separation of digesta phases occurs in horses, and that selective particle retention mechanisms in the large intestine are unlikely to represent important characteristics of the horse's digestive physiology

Methane emission by Camelids

Methane emissions from ruminant livestock have been intensively studied in order to reduce contribution to the greenhouse effect. Ruminants were found to produce more enteric methane than other mammalian herbivores. As camelids share some features of their digestive anatomy and physiology with ruminants, it has been proposed that they produce similar amounts of methane per unit of body mass. This is of special relevance for countrywide greenhouse gas budgets of countries that harbor large populations of camelids like Australia. However, hardly any quantitative methane emission measurements have been performed in camelids. In order to fill this gap, we carried out respiration chamber measurements with three camelid species (Vicugna pacos, Lama glama, Camelus bactrianus; n = 16 in total), all kept on a diet consisting of food produced from alfalfa only. The camelids produced less methane expressed on the basis of body mass (0.3260.11 L kg21 d21) when compared to literature data on domestic ruminants fed on roughage diets (0.5860.16 L kg21 d21). However, there was no significant difference between the two suborders when methane emission was expressed on the basis of digestible neutral detergent fiber intake (92.7633.9 L kg21 in camelids vs. 86.2612.1 L kg21 in ruminants). This implies that the pathways of methanogenesis forming part of the microbial digestion of fiber in the foregut are similar between the groups, and that the lower methane emission of camelids can be explained by their generally lower relative food intake. Our results suggest that the methane emission of Australia’s feral camels corresponds only to 1 to 2% of the methane amount produced by the countries’ domestic ruminants and that calculations of greenhouse gas budgets of countries with large camelid populations based on equations developed for ruminants are generally overestimating the actual levels

Differences in selective reticulo-ruminal particle retention as a key factor in ruminant diversification

The measurement of passage rate is important for the concept of ruminant diversification. While supporters of Hofmann's 1989 feeding type classification claim that browsing ruminants have faster passage rates than grazing ruminants, other researchers consider the passage rate to depend on body size alone. To date, no convincing comparison of ruminant passage rates has been put forward. For comparative purposes, we suggest the use of the "selectivity factor", which is an expression of how much longer particles of a defined size (<2 mm) are retained in the ruminant digestive tract than fluids. From the limited data available, it seems that grazing ruminants display selectivity factors between 1.56 and 3.80, whereas browsers have a much narrower range of 1.14-1.80. This suggests that browsers are not able to selectively retain particles as long as grazers. Intake of browsers, on the other hand, may not be limited by physical fill of the forestomach to the same degree as in grazers. This result can explain several observations on the digestive physiology of browsers, some of which have been linked to a rumen bypass mechanism. We propose that the ability for selective particle retention is a key factor for understanding the physiological consequences of ruminant diversification

Selektive Retention von Futterpartikeln verschiedener Groesse im Magen-Darmkanal von Kamelen im Vergleich mit Rindern und Schafen im Sudan

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