E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A contracted form of cattlegut, especially sheep. Another form is catling-gut, i.e. cattle-ing gut. In Gen. xxx. 40 we read that Jacob did separate his own flocks by themselves, and put them not unto Labans cattle [i.e. sheep]. Again, in xxxi. 9, Jacob said, God hath taken away the cattle [sheep and lambs] of your father, and given them to me; and verse 43 he says, These cattle [sheep and lambs] are my cattle.
Musical strings never, were made from the gut of a cat.