On the suitability of Illius and Gordon\'s model for simulating the intake and digestibility of roughage diets by ruminants

Abstract

________________________________________________________________________________ AbstractThe aim of this study was to evaluate the suitability of Illius and Gordon's simulation model for predicting the digestibility and intake of tropical roughages by ruminants. Data from seven suitable empirical studies (i.e. studies that reported all requisite data needed to run the model) in which tropical roughages were fed to ruminants were used. These seven studies had 235 intake and 70 digestibility measurements on goats, sheep and cattle. The coefficient of variation (cv)

Rate of Passage of Digesta in Ruminants; Are Goats Different?

“…Lechner-Doll et al [21] added that selective retention of particles is more pronounced in cattle than in sheep suggesting that the passage rate of large particles is greater in sheep than in cattle. Outflow rates of fine solid material are normally estimated by allometric procedures as an inverse function of body weight, which infers erroneously that the rate of passage in smaller ruminants is always greater than that in larger ruminants [1]. Parra [22] showed higher passage rates for smaller herbivores than larger herbivores with diet quality held constant.…”

“…This is partly due to limited information on the critical factors that affect intake, passage rates of digesta and rumen fill for goats. Nsahlai and Apaloo [1] examined the appropriateness of model in [2] to predict the intake in ruminants grazing on poor quality roughages in tropical regions and showed that the model, though structurally adequate, underestimated roughage intake, partly due to poor estimates of gut fill and rate of passage. Similarly, the authors [3][4][5] showed that the model of Illius and Gordon [2] overestimated retention time in browsing ruminants for particle sizes less than 2 mm.…”

“…Similarly, the authors [3][4][5] showed that the model of Illius and Gordon [2] overestimated retention time in browsing ruminants for particle sizes less than 2 mm. Nsahlai and Apaloo [1] pointed out that the model of Illius and Gordon [2] erroneously estimates rumen fill levels and passage rates as a function of body weight alone.…”

“…flow to a great extent [6]. Maximal rumen load for dry matter is determined by allometric procedures as a function of body weight [1,2]. However, a ruminant's fill capacity also depends on the volume of digesta that causes rumen distension and on rate of flow of digesta from and rates of degradation of digesta in the rumen [6,7].…”

“…However, a ruminant's fill capacity also depends on the volume of digesta that causes rumen distension and on rate of flow of digesta from and rates of degradation of digesta in the rumen [6,7]. As a result, criticism on determination of rumen fill based on body weight alone has been raised giving better models for rumen load based on body weight, mature body weight and dietary crude protein [1]. This fill capacity may also be determined practically by manually emptying the rumen at a time when full gut capacity is reached and weighing out digesta at that time [8] or slaughtering animals upon meal termination [9].…”