Abstract
Digesta retention patterns have been suggested to play a major role in ruminant diversification. Two major digestion types have been proposed, termed ‘cattle-type’ and ‘moose-type’, that broadly correspond to the feeding categories of grazers and intermediate feeders on the one, and browsers on the other hand.Wemeasured and calculated the mean retention time (MRT) of a solute and a particle (<2mm) marker in the gastrointestinal tract (GIT) and the reticulorumen (RR) of a small grazer, the Indian blackbuck (Antilope cervicapra, n = 5, body mass of 26 ± 4 kg) and an intermediate feeder, the nilgai (Boselaphus tragocamelus, n = 5, body mass of 168 ± 21 kg). MRTsolute and MRTparticle were 29 ± 4.1 h and 60 ± 6.6 h in blackbuck and 28 ± 2.5 h and 54±8.9 h in the nilgai for the GIT, and 14±1.7 h, 45±5.0 h, 19±2.0 h and 45±8.4 h for the RR, respectively. With a selectivity factor (SF, the ratio of MRTparticle to MRTsolute) in the RR of 3.2 ± 0.28 for blackbuck and 2.3 ± 0.36 for nilgai, both species are clearly in the category of ‘cattle-type’ ruminants. In particular, the high SFRR of blackbuck, in spite of its small body size, is remarkable, and leads to specific predictions on the RR anatomy of this species (such as a particularly large omasum), which can be tested in further studies. The adaptive value of a high SFRR is mainly considered as an increase in microbial productivity in the RR.
Hummel, Jürgen