To get a raw deal or the short end of the stick. Derived from the behavior of barnyard pigs. The "runt" or weakest piglet is forced to nurse on the tit farthest back on the mother pig, which gives the least nourishment.
Not getting a fair share. Many female mammals have multiple rows of breasts, for example dogs. Typically the rear most pair of breasts is smaller and less developed than the rest. Hence a pup nursing from the rear most breast is likely to receive less milk than other nursing pups. Hind means rear most. Tit is slang for breast.
1.In the animal kingdom, the runt of the litter gets stuck with the tit closest to the ass of the animal. Which has the least amount of milk in it.Therefore the meaning has evolved into human terms as to get the shitty end of the stick, to get leftoversor to be the last in line.