While the effect of roughage chop length on decreasing the risk of acidosis in cattle is well established, there is limited information on the effect of roughage processing on intake and rumen parameters in sheep. Intake and rumen parameters were assessed in 10-month-old crossbred wethers (n ? 24, 48.4 kg ± 5.3) offered wheaten straw as finely chaffed (6 mm), coarsely chaffed (15-20 mm) or unprocessed (40 mm) lengths, along with barley grain. Animals were offered 300 g/head of barley grain on the first day of grain introduction, 450 g/head.day for Days 2-3, 550 g/head.day for Days 4-6, 650 g/head.day for Days 7-9 and 750 g/head on Day 10. Rumen fluid was collected 3 h post-feeding from each animal the day before grain introduction and on Days 1-3 of grain introduction. During Days 1-3 of grain introduction, roughage intake within 3 h of feed being offered was greater (P < 0.05) in sheep offered finely chaffed (0.20 kg ± 0.03) than those offered either coarsely chaffed (0.09 kg ± 0.03) or unprocessed (0.08 kg ± 0.03) straw. Rumen pH did not differ between treatments, but increased grain feeding significantly (P < 0.001) reduced pH. Sheep offered finely chaffed straw had a greater (P < 0.05) daily straw intake (0.59 kg ± 0.06) than sheep offered coarsely chaffed straw (0.37 kg ± 0.06), while sheep offered unprocessed straw had an intermediate intake (0.49 kg ± 0.06); sheep consumed all grain offered. Shorter straw particle lengths may have a role in reducing the risk of acidosis during grain introduction.