A 3 x 3 Latin square design was conducted with 3 trotters (mean weight 510 kg) fed concentrates supplemented with 5.0 kg wrap bale grass silage (WS), 7.0 kg mixed hay (H) or 6.0 kg barley straw (BS) daily. Amounts of concentrates were adjusted to cover maintenance energy requirements together with forage. Concentrates, WS, H and BS had 86, 80, 86, and 87% DM with 350, 560, 610 and 740 g NDF/kg DM, and 190, 350, 390 and 490 g ADF/kg DM, respectively. Forages and concentrates were fed twice daily, but during the 4 experimental days, the horses had access to one quarter of the daily forage ration for 60 minutes at 9 am, 11 am, 1 pm and 3 pm. Forages not eaten within each of the four meals were recorded and fed again at 4 pm. Eating behaviour was observed and jaw moments (JM) recorded from 7 am to 4 pm by measuring pressure oscillations (PO) in a tube filled with water positioned around the mouth. Effective time spent chewing (ECT) and the numbers of jaw movements (JM) were identified from the manual observations and JM with exclusion of small pauses without mastication. The number of JM, the effective chewing rate and the ECT values per kg forage DM, forage NDF and forage ADF differed significantly (P<0.01) between forages and between forages and concentrates (P<0.01). The mean ECT values ranged from 50±4.7 minutes per kg WS dry matter to 100±4.7 minutes per kg BS dry matter, and from 90± 6 minutes per kg WS NDF to 135±6 minutes per kg BS NDF. The highest chewing rate (1.45±0.06 Hz) was found during concentrate meals and the lowest during BS meals (1.20±0.05 Hz). The horses spent more time eating (min/kg NDF) forages compared with values reported from cattle eating forages, whereas the total ECT values of 90 to 135 minutes chewing time per kg NDF in horses range from 60 to 90% of the time dairy cows to spent masticating during eating plus ruminating.