"Cows" can be a general term. (Do you suppose cowboys only ever dealt with female cattle?) The Oxford English Dictionary specifically recognises this sense of

"Cows" can be a general term. (Do you suppose cowboys only ever dealt with female cattle?) The Oxford English Dictionary specifically recognises this sense of "cows" (particularly in a U.S. context), complete with quotations that are very similar to the usage in this article: > c. plural. Cattle. U.S. > 1869 Overland Monthly Aug. 127/1 The ‘cow-whip’..is used only in driving the herd, which is often called ‘the cows’. > 1930 W. M. Raine & W. C. Barnes Cattle 60 Cows, as all cattle were called regardless of age and sex, were an investment which traveled on the hoof.