M. Clauss et M. Lechner-doll, Differences in selective reticulo-ruminal particle retention as a key factor in ruminant diversification, OECOLOGIA, 129(3), 2001, pp. 321-327
The measurement of passage rate is important for the concept of ruminant di
versification. While supporters of Hofmann's 1989 feeding type classificati
on claim that browsing ruminants have faster passage rates than grazing rum
inants, 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 "selectiv
ity factor", which is an expression of how much longer particles of a defin
ed size (<2 mm) are retained in the ruminant digestive tract than fluids. F
rom the limited data available, it seems that grazing ruminants display sel
ectivity factors between 1.56 and 3.80, whereas browsers have a much narrow
er range of 1.14-1.80. This suggests that browsers are not able to selectiv
ely retain particles as long as grazers. Intake of browsers, on the other h
and, may not be limited by physical fill of the forestomach to the same deg
ree as in grazers. This result can explain several observations on the dige
stive physiology of browsers, some of which have been linked to a rumen byp
ass mechanism. We propose that the ability for selective particle retention
is a key factor for understanding the physiological consequences of rumina
nt diversification.