2,4 - D Amine Herbicide is labeled to be used on pasture and rangeland. It would be best to keep animals out for at least 24 hours after applying.
Per the 2,4 - D Amine Herbicide product label for annual broadleaf weeds in pastures you would use 1 quart per acre. For biennial and perennieal weeds you would use 1-2 quarts per acre. The amount of water is not set and is however much water it takes you to cover the acre but usually 100 gallons per the label.