Formation of the Groove
The groove is formed by posture of the animal lifting its head to suckle. Calcium ions are obtained from the milk. A teat or teat-shaped experience aids the formation. The formation of the groove can be overridden, e.g. bucket feeding calves.
It is an unconditioned reflex when the animal is eager for milk. Water consumption does not usually initiate groove closure. The age when the rumen becomes fully functional and the oseophageal groove closes differs between ruminants; In calves 20 weeks, in lambs 8 weeks, in deer 16 weeks and in goats 12 weeks. It closes by reflex stimulation of the cranial laryngeal branch of the vagus nerve (CN X) (takes 2-5 seconds). With time it becomes a conditioned reflex. The closure consists of two movements, the lips of the groove become firmly opposed and shorten and the lips become inverted and twisted around the axis of the right lip of the groove, drawing the reticular mucosa over the right lip.
Function in the Adult Ruminant
The groove is stimulated in adult ruminants by ADH. The groove can also be closed in adult ruminants by the administration of drugs, e.g copper sulphate, which is of use to prevent drugs becoming diluted in the forechambers. Instead, it directs the drugs directly to the abomasum.
The floor of the groove is smooth and pale lined with stratified squamous epithelium.
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