The potential use of delactose whey permeate (delac) as an energy supplement for cattle offered low quality roughage was investigated. Young steers (initial liveweight 267 kg) were fed delac at 0, 0.25, 0.5 or 0.75% of liveweight. The steers had ad libitum access to oaten straw and were fed a protein supplement (cottonseed meal) at 1.33 kg/head once daily with the delac. Total intakes increased with increasing levels of delac. During the first half of the experiment, cattle offered delac had higher intakes than those not offered delac, but intake did not differ between delac supplemented groups. Furthermore, liveweight gain did not differ between groups. In the second half of the experiment, intake and liveweight gain increased with increasing level of delac in the diet. Intake of oaten straw over the whole experiment was greater with 0.25% delac than with no delac, but declined at higher levels of delac as animals substituted delac for straw in the diet. A storage study, conducted over 6 weeks, indicated a higher rate of microbial spoilage in delac with a lower solids content, however pH remained low. Calculations, based on the actual liveweight, liveweight gain and feed intake results, indicate that delac has a metabolisable energy content of about 11 MJ/kg DM. These results indicate that delac has potential as an energy supplement for cattle on low quality roughage diets and could be used on commercial farms if composition (especially solids content) is consistent and storage issues are addressed. Further investigations into the use of delac, in combination with low cost nitrogen supplements such as urea, are also recommended.