Jamieson, Fausset and Brown on Genesis 41:19

19. behold, seven other kine ... poor and ill-favoured--The cow being the emblem of fruitfulness, the different years of plenty and of famine were aptly represented by the different condition of those kine--the plenty, by the cattle feeding on the richest fodder; and the dearth, by the lean and famishing kine, which the pangs of hunger drove to act contrary to their nature.