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Title: CATECHOLAMINE RESPONSE TO MANUAL TEAT STIMULATION OR MILKING IN LACAUNE ANDFRIESEN DAIRY SHEEP

Author
item LEFCOURT, ALAN - 1265-50-00
item PAUL, GEORG - TECHNISCHEN UNIVERSITAT
item MAYER1, HARALD - TECHNISCHEN UNIVERSITAT
item SCHAMS, DIETER - TECHNISCHEN UNIVERSITAT
item BRUCKMAIER, RUPERT - UNIVERSITAT BERN

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/23/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Increased sympathetic nervous activity, including peripheral release of catecholamines, has been hypothesized to inhibit milk removal in sheep and other species. This inhibition is most likely accomplished by blocking release of oxytocin from the pituitary gland, by blocking the effect of oxytocin on the mammary gland, or both. In an attempt to explain differences in the milk-ability of Lacaune and East Friesen sheep,catecholamine and oxytocin responses to milking and to manual teat stimulation were measured. Peripheral concentrations of epinephrine were determined to be low and not to be affected by milking or stimulation. Baseline concentrations of norepinephrine were much higher in Lacaune compared to Friesen sheep. For both breeds, when norepinephrine levels were elevated prior to or at the onset of milking or stimulation, oxytocin release was completely inhibited. This is the first direct evidence linking increased sympathetic activity with inhibition of release of oxytocin in a ruminant specie. However, milk-ability by bred was not related to peripheral norepinephrine levels. Despite higher basal norepinephrine concentrations, oxytocin levels following milking peaked at about 1.5 min for Lacaune compared to 4 min for Friesen sheep. Results from this study clearly show that basal concentrations of norepinephrine vary with breed of sheep, and provide the first direct evidence that increased sympathetic activity can result in central inhibition of the milk ejection reflex.

Technical Abstract: Increased sympathetic activity, including peripheral release of catecholamines, has been hypothesized to inhibit the milk ejection reflex by blocking the release of oxytocin, by blocking the effect of oxytocin at the mammary gland, or both. In an attempt to relate differences in the milk-ability of Lacaune and East Friesen sheep to degree of sympathetic arousal, catecholamine and oxytocin responses to milking and to manual teat stimulation followed by milking were determined. Peripheral concentrations of epinephrine, 67 +/- 6 pg/ml for Lacaune and 57 +/- 5 for Friesen sheep, were essentially constant. Mean concentrations of norepinephrine were 682 +/- 68 pg/ml for Lacaune and 250 +/- 54 for Friesen sheep. For both breeds, when norepinephrine levels were elevated prior to or at the onset of treatment, oxytocin release was completely inhibited. This is the first direct evidence that increased sympathetic activity can result in central inhibition of the milk ejection reflex. Milk-ability by bred was not related to peripheral norepinephrine levels. Despite higher basal norepinephrine concentrations, oxytocin levels following milking peaked at about 1.5 min for Lacaune compared to 4 min for Friesen sheep. Manual teat stimulation prior to milking enhanced the oxytocin response to milking for Lacaune sheep, and reduced the time to the oxytocin peak by about by 2 min for Friesen sheep when basal norepinephrine levels remained low.