This depends on the breed. A Holstein can produce upwards of 30 gal. Per day, whereas a beef cow like that of a Hereford typically only produces 5 gal.
The average cow can produce between 8 and 35 gallons of milk per day.hubpages.com»
A cow gets milked twice a day and depending on the age, the size of the cow and the size of the utter determines the amt of milk a cow will produce, but typically 4 to 6 gallons a day. The heaviest milking breed of cow is the Holstein and they can produce from 10 to 20 gallons per day.hubpages.com»
The average cow produces approximately 54 pounds of milk per day or about 6 gallons.chacha.com»
A cow in a dairy can produce around 8 to 35litres of milk a day.wiki.answers.com»