The cow and the bear shall feed: This line also pairs domestic and wild animals. They share the same food. Normally cows are in the field and bears in the forest. But in the new kingdom they are all vegetarian and graze together, without the bears threatening the cows.
Their young shall lie down together: Their young refers to the young of the cow and bear. Good News Translation has “their calves and cubs.” They will lie down (sleep) in the same place.
And the lion shall eat straw like the ox: This line also occurs in 65.25. It means that the lion will not hunt and eat other animals. Instead it will eat straw and be a vegetarian like the domesticated ox. The Hebrew word for ox is a general term for “cattle” here. In cultures where cattle do not eat straw, “grass” may be used.
Translation examples for this verse are:
• Cows and bears will feed in the same place and their young ones sleep together; lions will eat straw like cattle.
• A cow and a bear will eat together and their young will sleep together. A lion will eat grass just like an ox does.
Quoted with permission from Ogden, Graham S. and Sterk, Jan. A Handbook on Isaiah. (UBS Helps for Translators). New York: UBS, 2011. For this and other handbooks for translators see here .

As everyone knows, cows do not eat straw. Academic translators who are not in touch with agriculture, have made this strange rendering survive. Grass, lucerne or something else. The German Gute Nachricht has “Häcksel,” cut herbs and vegetables. I heard someone explain that it refers to the remains of a threshing floor which includes all types of herbs, not only straw. This is something for an addition on this otherwise helpful website.
Very helpful. Thanks!