The study aimed to evaluate effects of maturity and conservation of primary growth grass/clover on apparent digestibility and rumen pH. Two batches of mixed ryegrass, red and white clover harvested in 2009 on May 9 and 25 were conserved as either silage or hay. The forages early silage (ES) and hay (EH), and late silage (LS) and hay (LH) had DM contents of 45, 84, 25 and 83%, and NDF contents of 32, 44, 42 and 50% of DM, respectively. Forages were fed as sole feed to four Jersey heifers of 435±30 kg BW in a 4×4 Latin square experiment. Feeding level was 90% of individual ad libitum intake, divided in two daily meals at 0800 and 1530 h. Potentially digestible NDF (DNDF) was determined after 288 h in situ. Apparent digestibility of OM and NDF was estimated using Cr3O2 as marker. Rumen fluid pH in the medial and ventral rumen was measured with 1 h intervals from 0730 to 1530 h. Data was analysed by Proc MIXED in SAS 9.2 with period, conservation, harvest time, and conservation × harvest time as fixed effects and heifer as random. Early compared to late harvest increased DM intake (DMI) (P<0.001), whereas DMI was unaffected by conservation. Daily DMI of ES, EH, LS, and LH averaged 8.7, 9.4, 7.2, and 7.2 kg, respectively. In early compared to late harvest, digestibilities were: OM 82% vs. 78 %; NDF 88% vs. 80% and DNDF 95% vs. 90% (P<0.01). Digestibility of OM was higher in silage (81%) than hay (80%, P<0.02), while NDF and DNDF digestibility were similar. Rumen pH ranged from 7.2 before feeding to 5.9 three h post feeding. Rumen pH was unaffected by type of conservation, but early compared to late harvest resulted in lower minimum and mean rumen pH (P<0.05). Results indicate that early harvest improves OM, NDF and DNDF digestibility and lowers rumen pH, and that ensiling improves OM digestibility without affecting rumen pH.