Mbh 13.73.1d

If a Vaisya, possessed of similar accomplishments, were to make a gift of a single cow, that cow would be equal to five hundred kine (in respect of the merit she would produce). If a Sudra endued with humility were to make a gift of a cow, such a cow would be equal to a hundred and twenty-five kine (in respect of the merit it would produce). Devoted to penances and truth, proficient (in the scriptures and all acts) through dutiful services rendered to his preceptor, endued with forgiveness of disposition, engaged in the worship of the deities, possessed of a tranquil soul, pure (in body and mind), enlightened, observant of all duties, and freed from every kind of egotism, that man who makes a gift of a cow unto a Brahmana, certainly attains to great merit through that act of his, viz., the gift, according to proper rites, of a cow yielding copious milk. Hence, one, with singleness of devotion, observant of truth and engaged in humbly serving one's preceptor, should always make gifts of kine.[360] Hear, O Sakra, what the merit is of that person, who, duly studying the Vedas, shows reverence for kine, who always becomes glad at sight of kine, and who, since his birth has always bowed his head unto kine. The merit that becomes one's by performing the Rajasuya sacrifice, the merit that becomes one's by making gifts of heaps of gold, that high merit is acquired by a person who shows such reverence for kine. Righteous Rishis and high-souled persons crowned with success have said so. Devoted to truth, possessed of a tranquil soul, free from cupidity, always truthful in speech, and behaving with reverence towards kine with the steadiness of a vow, the man, who, for a whole year before himself taking any food, regularly presents some food to kine, wins the merit, by such an act, of the gift of a thousand kine. That man, who takes only one meal a day and who gives away the entire quantity of his other meal unto kine.