Sucking motivation and related problems in calves.

Since survival of the young mammals depends on sucking success, it is assumed that sucking motivation must be strong and that sucking deprivation would result in frustration which could have a negative impact on their welfare. This concern as well as that regarding cross-sucking between calves and intersucking between older animals has stimulated research on the motivation of calves for non-nutritive sucking. Non-nutritive sucking is elicited by the ingestion of milk, and the lactose concentration in milk, rather than that of fat or protein, is the main factor stimulating non-nutritive sucking. Every time a calf drinks milk, it is stimulated to suck and deprivation of sucking may interfere with digestive processes or satiety. To understand the behaviour of the calf during nutritive sucking, we examined the effects of milk flow on calves' sucking and butting an artificial feeding system. Slowing and stopping the flow rate stimulates butting and can lengthen the duration of sucking for the meal. It also stimulates the calf to switch teats when a second teat is available. These findings are well correlated to our observations of the calf suckling a cow in experimental manipulations. The duration of the meal is not correlated with milk intake, but it is influenced by milk availability and how hungry the calf is. Furthermore, calves will butt more often when there is less milk available in the dam's udder, presumably because milk flow is slower. Consequently, it is the occurrence of butting rather than sucking duration that would be a good indicator of milk intake when the calf is suckling the dam. Finally, we recommend a combination of slower milk flow and hay feeding and the provision of a non-nutritive artificial teat to reduce the occurrence of cross-sucking following a milk meal.