INTRODUCTION In the modern ruminant industry, feeding regimes are gradually changing to diets containing a relatively high proportion of concentrate to meet the increasing energy requirements of intensively managed animals. Dietary fibre is an essential nutrient in feeds and useful for the maintenance of normal rumen function, which has been associated with adequate salivation, optimal pH for cellulolytic microorganisms and energy supply (Allen, 1997; Yang et al., 2001b; Beauchemin and Yang, 2005; Tafaj et al., 2005b). However, sufficient dietary NDF without a sufficient proportion of long particles could elicit metabolic disorders (Plaizier et al., 2008). The concept of physically effective fibre (peNDF) was developed to combine into a single measurement both the NDF concentration and the physical form of a feed (Armentano and Pereira, 1997; Mertens, 1997). Many studies carried out on the effect of peNDF in ruminants were on dairy cattle (Moon et al., 2004). Goats have different feeding behavior, level of intake and rate of eating from cattle and other ruminant species, but have hardly received equal attention (Reid et al., 1990; Lu et al., 2005). It has thus become imperative to systemically investigate the effect of different fibre particle sizes in the diet of goats.