This quest has other problems too as time of posting:
When I found the first potion I talked to the cows, but did not give them the potion (I was like I want to cure both of them). Later I got the other too, so went back. When I spoke with them again, they were still in the state there is only one potion, so they have to choose... but I only have option to give THEM the potion. This gave me only half the XP and did fail to close the quest. (The log also gets bugged, saying repeatedly that we only had potion for one cows.)
There is a solution suggested to drop one potion while speaking, and then select to give them + drink it, this will close the quest for 75% of the XP.
A good solution is that you drop one potion before speaking, and transform one of them. Then pick up other potion and transform other, which closes the quest with full XP gain (which is 2x13450XP). (The log also properly states that both were saved, unlike in my original case.)