Whole-crop cereals could find use as hay for ruminant feeding in semi-arid areas. This work was designed to study the relationships connecting a set of chemical-composition and physical parameters linked to in vitro digestibility with the organic matter digestibility (OMD) and dry matter intake (DMI) of a selection of whole-crop cereal hays. The in vivo characteristics of the four cereal hays (barley, oats, rye and triticale) were determined using six 4-year-old sheep wethers (51.5 ± 4.98 kg live weight) per hay. There were significant positive relationships between in vitro dry matter digestibility and OMD. Crude protein content (g kg−1 dry matter (DM)) was significantly correlated with OMD (r = 0.97; P inférieur à 0.05), and acid detergent fibre (g kg−1 DM) was negatively correlated with OMD (r = −0.97; P inférieur à 0.10). There was a significant negative relationship between bulk density of hays (g ml−1 fresh matter) and DMI (r = −0.96; P inférieur à 0.05) and the relationship between in vitro DM digestibility and intake was not significant (r = 0.67). These results suggest that bulk density may predict whole-crop cereal hay intake in sheep. Further research is needed to test this predictability over a wider range of feedstuffs.