Mbh 13.71.2e

He, who gives unto a Brahmana a bull well-broken and capable of bearing burdens, possessed of strength and young in years, disinclined to do any mischief, large-sized and endued with energy, enjoys those regions, that are reserved for givers of kine. He is regarded as a proper person for receiving a cow in gift who is known to be mild towards kine, who takes kine for his refuge, who is grateful, and who has no means of subsistence assigned unto him. When an old man becomes ill, or when a Brahmana intends to perform a sacrifice, or when one wishes to till for agriculture, or when one gets a son through the efficacy of a Homa performed for the purpose, or for the use of one's preceptor, or for the sustenance of a child (born in the usual way), one should give away a beloved cow. Even these are the considerations that are applauded (in the matter of making gifts of kine) in respect of place and time. The kine that deserve to be given away are those that yield copious measures of milk, or those that are well-known (for their docility and other virtues), or those that have been purchased for a price, or those that have been acquired as honoraria for learning, or those that have been obtained in exchange by offering other living creatures (such as sheep and goats, etc.), or those that have been won by prowess of arms, or those that have been gained as marriage-dower (from fathers-in-law and other relations of the wife)."