Last update: November 24, 2010 12:15:30 PM E-mail Print


P G Marais, & J A Roux*


Grootfontein Agricultural College, Middelburg, 5900 Eastern Cape South Africa

* Department of Agriculture, Eastern Cape, Cradock. 5880. South Africa.


A large number of digestibility studies have been undertaken comparing sheep and goats. Contrasting results concerning interspecies differences for in vitro digestibility, were observed. Where grasses were the main component of the pasture consumed, the in vitro digestibility of dry matter and organic matter ingested by sheep was on average 3.5 percentage units higher than those of goats. Where, shrub and tree leaves accounted for the larger part of the diet the in vitro digestibility of the forage grazed by goats was on average 7.0 percentage units higher than those of sheep. The aim of this study was to widen the range of observations from poor to good quality diets, the hypothesis is that there are interspecies differences in apparent digestibility of nutrients. Four groups of experimental animals, Merino wethers, Dorper wethers, castrated Angora goats and castrated Boer goats were used. Six animals per group had permanent ruminal cannulae (22mm). They were kept individually in conventional metabolism crates. These animals were used to determine the nutrients= digestibility of four different diets, viz: 100% lucerne (100% diet), 75% lucerne and 25% wheat straw (75%diet), 50% lucerne and 50% wheat straw (50% diet) and 25% lucerne and 75% wheat straw (25%diet). The following parameters were determined: chemical composition of diets, rumen environment (pH; NH3-N)... in vivo apparent digestibility of energy, protein and fibre fractions, effective degradation (in situ), degradation and passage rate of solid ingesta. On the 75%, 50% and 25% diet the apparent digestibility differ significantly between the Merino and Boer goat. On the 50% diet, the pH of rumen fluid was lower (P<0.05) in goats than in sheep. The rumen NH3 concentration was lower in goats than in sheep(P<0.05). Regarding intake/Wkg0.75 between breeds, the number of significant differences was fewer between the Merino and the Angora goat than between the Dorper and Boer goat. It seems thus possible to group fibre-producing animals and non-fibre-producing animals into two distinct groups.