Is there enough Omega 3 fatty acids in Horizon milk to make much difference or is just marketing ?
I’ve never had this kind; I drink Silk Coconut milk which markets that it has 50% more calcium than dairy milk. This was of interest - not the main reason for me starting on it - however, I saw it as a bonus either way.
To be sure with your Horizon milk, you might want to check the side panel of nutrition facts and ingredients.
I'd find a real food source that come naturally with DHA. i.e. Oily Fish.