Central and peripheral oxytocin profiles during milking in ewes

Abstract

The present work investigated the possible relationship between central and peripheral oxytocin (OT) release during milking in experimental ewes. Ten multiparous ewes were divided into four groups according to milk ejection stimuli: exclusive machine milking (EM), mixed-management milking and suckling, lambs separated during the night and reunited with their mother after morning milking (MMS); mixed-management with manual milking (MMM), and exclusive suckling (ES) lambs also separated during the night. Simultaneous sampling of cerebrospinal fluid (CSF) and blood was performed during milking. The means, standard deviations, variation coefficients, and minimum and maximum CSF and plasma OT concentrations were the following, respectively: 257.88 ± 265.90 pg/ml, 103.11%, and 11.70 and 1000.00 pg/ml. No statistically significant correlations were found between OT concentrations in the CSF and plasma samples (EM: -0.26; ES: -0.19; MMM: 0.05; MMS: 0.04). The OT concentration in CSF was not influenced by milk ejection stimuli, although plasma OT was higher in the MMM (679.80 ± 25.63) and MMS (591.82 ± 30.56) groups compared with the EM and ES groups. Additionally, plasma OT concentrations were higher in the OME group (381.04 ± 22.09) compared with the AE group (218.82 ± 27.04). In conclusion, no positive correlations were found between central and peripheral OT concentrations during milking and suckling. Plasma OT concentrations differed as a function of milking management and had consequences for both milk ejection and production. Plasma but not CSF oxytocin concentrations were influenced by different milk ejection stimuli.Keywords: Catheterization. Milk ejection. Cerebrospinal fluid. Sheep. Lactation. ResumoFoi investigada a possível relação entre as concentrações de ocitocina no líquido cefalorraquidiano e no soro em diferentes formas de ordenha em ovinos. Foram utilizadas dez ovelhas multíparas, divididas em quatro grupos de acordo com o estímulo para ejeção do leite: ordenha exclusivamente mecânica (EM), ordenha mista mecânica e mamada com os carneiros separados das mães durante a noite e reunidos a elas pela manhã para amamentação (MMS); ordenha mista com ordenha manual (MMS); apenas amamentação natural (ES). Foram coletadas amostras de fluido cerebroespinhal e de sangue, simultaneamente, durante as ordenhas. A média, o coeficiente de variação e os valores máximos e mínimos de ocitocina do plasma foram respectivamente 257,88 ± 265,90 pg/ml, 103,11%, e 11,70 e 1000,00 pg/ml. Não foram encontradas correlações entre as concentrações centrais e plasmáticas de ocitocina (EM: -0,26; ES: -0,19; MMM: 0,05; MMS: 0,04). Não foi evidenciada influência do tipo de estímulo para ejeção do leite nas concentrações centrais de ocitocina. Entretanto, as concentrações plasmáticas de ocitocina foram maiores nos grupos MMM (679,80 ± 25,63) e MMS (591,82 ± 30,56), quando comparadas às dos grupos EM e ES. Além disso, as concentrações plasmáticas de ocitocina foram maiores no grupo de OME (381,04 ± 22,09) em relação ao grupo AE (...