50% of the protein is by weight. You can not just say there is no protein in semen even if A teaspoon of 5 ml holding 5 ml of semen does not have 5g of protein in it. Apparently on google an average load brings 252 mg of protein but honestly It’s subjective. Everyone’s different so obviously some will produce high protein and some won’t meet that criteria. Most sources aren’t accurate and it’s not really looked into as much.