RELATIONSHIP BETWEEN NUMBERS OF ALPHA(2)-ADRENOCEPTORS AND BETA(2)-ADRENOCEPTORS ON BLOOD-CELLS OF BULLS AND MILKABILITY OF THEIR DAUGHTERS

Milk yield and milking time mere measured on one occasion for several daughters (n = 6-44) from 16 bulls at morning milkings. Blood from the bulls was collected, and platelets and mononuclear leucocytes were isolated. The alpha(2)-adrenoceptors on platelet membranes were identified by binding of [H-3]rauwolscine, whereas for the determination of beta(2)-adrenoceptors on intact mononuclear leucocytes, [H-3]CGP-12177 was used. It was found that mean milk flow rate was highly correlated (P < 0.001) with the alpha(2)-adrenoceptor densities on blood platelets. No correlation was found with the beta(2)-adrenoceptors on mononuclear leucocytes. It is concluded that estimation of the alpha(2)-adrenoceptors on blood platelets from bulls could eventually be used to investigate milking characteristics of cows, and might be useful in the future as a marker in genetic studies.