It symbolises wealth accumulated during those prosperous years mentioned above. The same is the interpretation if the skin, urine, droppings or any other filth of the stomach is seen. But whether such wealth is lawful or unlawful will depend on the odour of the urine, droppings or filth.
The same interpretation will be given if, instead of cows, the urine, droppings etc. of other animals are seen.
If the odour is overpowering it represents wealth that is totally unlawful. There is no good to be expected from such wealth.