all technical hunting clothing should be wash before use to get the best results, sometimes yarm and fabrics has some waste
that limit breathability. In Oncahuntingwear blog you can find post about this question.
I use a sport wash and have used wool specific soap. I prefer the sport wash or a free and clear detergent. Always wash my merino separately and air / hang dry.
I always wash mine before wearing. A lot of merino clothing is manufactured overseas. Before shipping they dip/coat the clothing in a substance to prevent damage (insects, etc) during the boat ride. I'm sure an animal can smell this. I know i can.
After buying merino I usually run it once with NikWax Wool Wash. After that I use Dead Down Wind's scentless detergent.
I run an empty hot water load through the washer to rinse any residual Tide left in there, wash my merino (and all hunting cloths) in cold water with Sport Wash, merino is hang dried non-merino tumble on low with Fresh Earth dryer sheets. All goes in to plastic storage container after.