Why were those who looked after milch cows not paid in milk and ghee?

The Superintendent of cattle should know about cattle looked after in return for a wage, tended with a tax and a fixed return, become useless and cast off, entered in the state herds by payment of a share, the total number of cattle in herds, cattle that are lost or have perished, and the total produce of milk and ghee. The cowherd, the buffalo-herdsman, the milker, the churner and the hunter should look after one hundred milch-cows, receiving a wage in cash; for if given a wage in milk and ghee, they might do harm to the calves. These are cattle looked after for a wage. One person should look after one hundred animals containing an equal number of aged cows, milch-cows, cows with young, cows with calf for the first time, and heifers. He should give eight varakas of ghee, one pana per animal and the hide with the mark, every year. This is tending with a tax and a fixed return. Herdsmen looking after one hundred animals divided into an equal number of cows that are diseased, that are crippled, that do not allow another person to milk them, that are difficult to milk and that kill their calves, should give a share appropriate to that class. These are cattle become useless and cast off.