What components of milk stimulate sucking in calves?

To examine the role of the various components of milk in stimulating non-nutritive sucking, 4-18 week-old male dairy calves (N = 10-15 in each experiment) were allowed to suck a dry teat after being given small quantities of milk or reconstituted milk and their sucking behaviour was observed. We varied the composition of milk or reconstituted milk by adding or removing four components: casein, whey protein, lactose and fat. Increasing concentration of lactose increased non-nutritive sucking but increasing the concentration of casein, whey protein and fat had no effect. Removing casein, whey protein and fat had no effect. Increasing the concentration of all milk components increased non-nutritive sucking but omitting lactose prevented this from occurring. Use of lactase (to break down lactose into glucose and galactose) did not affect non-nutritive sucking. Non-nutritive sucking can be enhanced by the taste of milk and the sugar components of milk are most effective in doing this. The protein and fat components appear to play little role.