Adrenocortical response of jennies to milking stress

This is an observational study on the adaptive responses of circulating cortisol levels to milking stress evaluated in 34 mature lactating jennies (No = 16 non-milked; No = 18 milked), aged 4-18 years, in the 5th-6th month of pregnancy. The subjects not submitted to milking were divided in two groups on the basis of different times of basal blood sampling (group I: 08:00 a.m. and group II: 04:00 p.m.). These subjects were designated as control groups. The subjects submitted to milking were divided in two other groups on the basis of different times of blood sampling and the method of milking carried out, either at 08:00 a.m. (group III: hand milking) or at 04:00 p.m. (group IV: machine milking). These subjects were designated as observational groups.The median age of jennies ranged between 5 years for groups I and III and 11 years for groups II and IV.Blood samples were collected once a day from the jugular vein, in basal conditions, at 08:00 a.m. for groups I and III, and at 04:00 p.m. for groups II and IV; blood samples were also collected 5 and 15 min after milking in groups III and IV.RM-ANOVA showed a significant effect on the cortisol changes of hand milking only (P < .001). Compared to basal values, group III showed higher cortisol levels at 5 min (P < .05) and at 15 min (P < .01) after milking. Basal cortisol levels of group I were higher (P < .05) than group III; no significant differences for cortisol levels were found in group IV between basal and after machine milking. No differences were observed between group II and group IV.