South American camelids are ruminants in the strict sense of the word that is they chew a cud but there are some important differences especially in the digestive anatomy and physiology between camelids and true ruminants. The forestomach system of true ruminants like sheep, are three independent hollow organs (rumen, reticulum and omasum) with the attached glandular stomach (abomasum) (von Engelhardt and Breves, 2005; Loeffler and Gäbel, 2013). In contrast, camelids have only three distinct compartments (C1, C2 and C3) associated with the foregut and stomach (Vallenas et al., 1971). The first two compartments (C1 and C2) and the first four-fifths of the third compartment (C3) are representative of the reticulorumen and have the function of a fermentation chamber hosting a microbiological flora and fauna. The last fifth of the elongated tubular C3 is similar to the glandular stomach (abomasum) of true ruminants (Wang et al., 2000).
To digest the cellulose, fibre and dry matter (DM) of their feed, both species (true ruminants and South American camelids) are dependent on these microbiological flora and fauna in their foreguts and compartments (Van Saun, 2006; Gauly et al., 2011). Ruminating animals have developed a speciality for digesting feed rich in celluloses (von Engelhardt and Breves, 2005; Van Saun, 2006). The camelids flora exhibits a higher level of activity, which may be the reason to a greater digestive efficiency (San Martin, 1987; Dulphy et al., 1997; Sponheimer et al., 2003). Tichit and Genin (1997) found in an in sacco dry matter digestibility study that the digestibility was indeed higher in llamas than in sheep. Therefore, the best symbiotic relationship between microbial population and host animal is found in the South American camelids (Cebra et al., 2014). It can be concluded that a combination of greater degree of degradability coupled with an increased microbial yield provides llamas and alpacas with an increased advantage in dealing with coarse, low quality feed compared to other ruminants and herbivores (Van Saun, 2006).
Another difference between true ruminants and South American camelids is the size of their gastrointestinal tract and the particulate outflow rate. These camelids have smaller stomach compartments and a slower particulate outflow rate (San Martin, 1987). This slower outflow rate will lead to a longer retaining time of the food particles and in a longer fermentation time in the camelid foregut than in the ruminant one (Heller et al., 1986; Dulphy et al., 1994). The hydrolysis of cell wall components by certain microbial enzymes is working all in all slowly; hence, the time in which the ingesta is available for the microbes is very important for the efficiency of the digestion (von Engelhardt and Breves, 2005). Another outstanding anatomy feature of South American camelids is the specific upper lip. It is adjusted to select the better parts of the feed. Smaller than the lower lip it is divided by a median groove. Both lips are more mobile than the ones from other herbivores, what allows a high selective ability (Cebra et al., 2014).
All the differences in anatomy and physiology of the digestive tract between South American camelids and true ruminants may influence the DM-intake (DMI) and the selective behaviour of the different animals, which may require a different feeding approach for the camelids. more »