A milk or other dairy product, capable of minimising the onset of disease such as coronary heart disease or enhancing the immune response is derived from animals which are substantially free of the .beta.-casein A.sup.1 allele. Bulk milk can be produced by testing for and culling cows who test positive for the .beta.-casein A.sup.1 allele, or by producing immunoglobulins and other immune response proteins, in cow's milk from animals not possessing the .beta.-casein A.sup.1 allele, or other commercial, milk producing animals, to this allele, to counteract the immunosuppressant substances present that are produced from it, in commercial milking cows such as Holsteins, together with its blending with non-treated milk or the recovery of such immunoproteins.