The Butcher's Bill
I have charged you with resupplying my army with fresh beef. Take this coin and find a village with cattle to spare. You may accomplish this however you feel appropriate so long as you do not dishonor me..
Once you have taken this quest you'll be compensated with enough denars to buy the required cattle and be granted permission to leave the army. You can acquire the cattle in any manner that you see fit so long as you do not create a relation problem for your oathbound lord.
To turn the cattle in, you need to merely drive the herd towards the army. Once they are close enough they'll be added and the quest will credit you with completion. You can only drive one herd at a time for quest credit and may turn in smaller herds while the quest is active. Each will add up towards meeting the goal.