THE EFFECT OF DIFFERENT STIMULI ON MILK EJECTION AND DIURESIS IN THE LACTATING COW

Abstract

SUMMARY The relation between milk ejection and antidiuretic response was studied on lactating cows using different stimuli. The stimuli, utilized to induce milk ejection, could be classified according to increasing effectiveness as follows: (1) showing the calf to the mother (visual stimulation); (2) washing the udder with water at 40° C in trained animals; (3) washing combined with visual stimulation; (4) suckling. Experimental conditions (hydration, bladder catheter) exerted a marked inhibiting effect in most animals on the milk-ejecting reflex induced by stimuli 1, 2 and 3. The reactions of domesticated cows under these circumstances are analogous to those of primitive breeds under normal conditions. Generally, the antidiuretic response seemed to be quantitatively correlated with the release of oxytocin. However, exceptions to this rule were observed. An antidiuretic response was obtained in cows after milk ejection unaccompanied by withdrawal of milk. The effect of known amounts of oxytocin on milk ejection was studied, and the dose-response curve was nearly a straight line when log dose was plotted against the volume of milk ejected. The slope of the curves, however, varied in different cows.