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The release of oxytocin and milk ejection occurrence in response to teat stimulation are crucial for fast and complete milk removal during milking or suckling. The milk ejection reflex can be disturbed at central or peripheral level under different experimental and practical conditions. The central disturbance results in the lack or insufficient ejection of the alveolar milk into the cistern due to inhibited oxytocin release from pituitary into the blood circulation. The important role in the pathophysiological regulation of the inhibited release of oxytocin is played by an opioid system. Endogenous opioids have suppressive effects on oxytocin release under the normal conditions of milk removal. However under the conditions of disturbed milk ejection their role in dairy cows was not confirmed. Other possible mechanisms involved in the central inhibition of oxytocin release are discussed. In dairy cows as compared with rats the mechanisms involved in the regulation of oxytocin release at the central level remain unclear. The central inhibition of oxytocin release has often been observed in dairy practice during milking of primiparous cows after parturition, suckling by alien calf, calf removal before milking, milking of cows in the presence of own calf, relocation and milking in an unknown milking place. If sufficient released oxytocin cannot induce the transfer of milk from alveoli to cistern, peripheral mechanisms are involved. Peripheral mechanisms are related to the increased levels of catecholamines and/or activation sympathetic nervous system at the udder level. In conclusion, the release of oxytocin and milk ejection efficiency can be very easily suppressed by many factors. The effect of milking conditions on regulation of milk ejection has to be considered. Thus the physiological requirements of dairy cows have to be respected.

The aim of this trial was to clarify whether suckling after several weeks of only machine milking can affect the release of oxytocin, cortisol and prolactin in dairy cows. In total twelve Brown Swiss cows on their first to third lactation were used. Pre-experimental period: all cows were suckled three times daily (9.00, 14.00 and 20.00) and milked twice daily (7.00 and 17.30) in tie housing during the first 5 days postpartum. Afterwards the calves were separated and moved to another building. The cows were moved to loose housing and milked in the dairy parlour within the same stable. Experimental period: after four weeks of only machine milking twice daily, cows were relocated from the herd to the same place as they were housed and milked during their postpartum period. The cows were again suckled on day 3 and 4 after relocation at the same time as above. Oxytocin, cortisol and prolactin levels were evaluated during the first suckling on day 3 (9.00) and during suckling at the same time next day (4th suckling) after relocation. Oxytocin secretion was clearly inhibited in all cows during the first five minutes of suckling with tendency of slow increase during the next minutes of suckling (suckling lasted about 10 min) except for two primiparous cows showing an increase of oxytocin release from the first minute of suckling. The release of oxytocin in response to the 4th suckling significantly increased immediately after start of suckling. Both, cortisol and prolactin significantly increased in response to all sucklings. There were significantly higher prolactin and lower cortisol values during the first suckling as compared with the fourth suckling in primiparous but not in multiparous cows.

The goal of this study was to evaluate the dose dependent changes in common milk and blood parameters for udder health after an intramammary (IM) infusion of five different doses of lipopolysaccharide (LPS, 100, 50, 25, 12.5 and 6.25 μg, respectively). Ten Holstein Friesian cows randomly divided into five groups of 2 cows each were IM infused into one quarter with one LPS dose dissolved in 10 ml of saline. The contralateral quarter was infused with 10 ml saline (9 g/l). Milk samples were taken immediately before and 12, 24, 36, 48 and 60 hours after the treatment. All milk samples were analysed for somatic cell counts (SCC), lactose, sodium (Na), chloride (Cl) and electrical conductivity (EC). Two blood samples were taken immediately after milking for analysing leukocytes (WBC), polymorphonuclear neutrophils (PMN), Na and Cl. The SCC increased maximal at 12 hours after the LPS challenge and differed among LPS doses, as well as the area under curve from 0 to 36 hours (AUC 0-36 h). There were no significant differences among LPS doses in lactose levels for the regression at 12 hours and AUC 0-36 h. Lactose levels in milk from quarters receiving the lowest dose of LPS were lowest after 24 hours, whereas in all other groups lactose levels decreased maximal within the first 12 hours. The regression at 12 hours as well as the AUC 0-36 h showed significant changes for Cl levels but not for Na and EC, respectively. Amongst all groups EC increased maximal within 12 hours and peak EC showed dose dependent differences with highest values at the highest LPS dose. There were no dose differences in WBC. Blood electrolytes showed only tendentially dose dependent differences for blood Na in AUC 0-36 h. The results were possibly due to a great individual variance amongst all cows. In conclusion there are dose dependent differences in the response to LPS especially in milk parameters, which are likely caused by a greater tight junction damage by higher LPS doses. 100 μg LPS seems to be a threshold between low and high doses of LPS. All doses used in this study induced signs of mastitis but there might be a low dose of LPS with only an enhancing effect on mammary gland immune status without inducing mastitis symptoms. This needs to be investigated for developing new ways of mastitis prophylaxis.

The aim of this study was to test whether a more pronounced oxytocin release induced by naloxone during milking causes higher efficiency of milk removal. Eight pregnant multiparousHolsteincows from second to fifth lactation were used for this experiment. The experiment was carried out during three consecutive days, i.e. six milkings (three morning and three evening milkings). During first and third evening milking in cross over design (four and four animals) 250 mg of naloxone or 10 ml saline was injected 5 min before the start of udder preparation. During these milkings 2 IU of oxytocin was injected i.v. after stripping and the amount of milk obtained in response to oxytocin injection was measured. Pre-milking naloxone treatment increased the milking-related release of oxytocin, however, only in six of eight cows. The stimulatory effect of naloxone on oxytocin release in the mentioned six cows differed individually from 4 ng/l to 132 ng/l. Naloxone treatment did not influence milk yield before stripping and stripping milk yield. However, naloxone treatment significantly reduced the amount of milk obtained in response to oxytocin injection. Peak flow rate tended to be higher after naloxone treatment. In conclusion, oxytocin release seems to be very important for the evaluation of different milking routines and milk removal environment with respect to the welfare of dairy cows.

The objectives of our study were to describe the variation of quarter milk flow parameters and to determine the factors that affect these parameters the most. Additionally, repeatabilities (r2) of the quarter milk flow traits (duration of milk flow, time to reach peak flow, peak flow rate, and duration of milk flow in single phases - increase, plateau, decline and blind phase) were calculated. Repeatability of total milk yield and milk yield in single phases was calculated, too. The data from 39 Holstein cows, in their first to third lactation and free of clinical mastitis, were used for statistical analysis. A total of 1 656 curves of quarter milk flows were recorded during six consecutive days. At the last evening and morning milking samples of milk from each quarter were collected for determination of somatic cell count (SCC). Peak flow rate, quarter position, time of milking (morning and evening) and SCC significantly affected most of the measured traits. The highest r2 were for total milk yield and yield of plateau phase 0.53 and 0.50, resp. The lowest r2 were calculated for the duration of increase phase, and milk yield of the increase and blind phase 0.26, 0.12 and 0.21, resp. Peak flow rate, SCC, time of milking and front-rear position influenced the values of r2 of traits to various extent.