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ICAR Technical Series no. 7 - Nitra Proc.

ICAR Technical Series no. 7 - Nitra Proc.

ICAR Technical Series no. 7 - Nitra Proc.

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Cog<strong>no</strong>me/iInhibition of oxytocin release duringrepeated milking in unfamiliarsurroundings: importance of opioids andadrenal cortex sensitivityJ. Macuhová 1 , V. Tancin 1,2 & R.M. Bruckmaier 11Institute of Physiology, WeihenstephanerBerg 3,D-85350 Freising, GermanyE-mail: macuhova@weihenstephan.de2Research Institute of Animal Production, Hlohovská 2,SK-949 92 <strong>Nitra</strong>, Slovak RepublicIn practical dairying, cows can be exposed to various emotionally stressfulsituations. Milking in unfamiliar surroundings can centrally suppress themilk ejection reflex accompanied by increased levels of cortisol andβ-endorphin (Bruckmaier et al. 1993). Endoge<strong>no</strong>us opioids inhibit OTsecretion in response to various stimuli in rats (Bicknell and Leng, 1982).Administration of the opioid antagonist naloxone abolished inhibition ofOT release in the rat (Pumford et al. 1991), but <strong>no</strong>t in cows during milkingin unfamiliar surroundings (Wellnitz et al.1997). Thus the importance ofthe opioid system in the central inhibition of oxytocin release duringmilking under stress conditions in dairy cows is still unclear.The response of the hypothalamic-pituitary-adrenal (HPA) axis to <strong>no</strong>velstimuli can characterise the individual sensitivity of animals to stress (vonBorell and Ladewig, 1992). Possible relationships between reaction ofindividual cows to <strong>no</strong>vel surroundings and sensitivity of the adrenal cortexto exoge<strong>no</strong>us ACTH could help to explain the mechanisms of centralinhibition of OT release.The aim of this study was to test if the opioid antagonist naloxone has abeneficial effect on <strong>no</strong>rmalisation of oxytocin (OT) release during repeatedmilking of cows in unfamiliar surroundings. Experiments were performedduring the usual evening milking time. One control milking withoutnaloxone treatment in all cows was performed in the familiar parlour. Forfour successive evening milkings cows were transported to and milked inthe operating theatre of the research station without (control group) orwith naloxone administration (1mg/kg BW) (naloxone group) beforemilking. After cessation of spontaneous milk flow, but <strong>no</strong>t before threemin of milking, vaginal stimulation was applied for 2 min. After milk<strong>ICAR</strong> <strong>Technical</strong> <strong>Series</strong> - No 7275

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