Effekten av mjölkkors rang på ?antistresshormonet? oxytocin, mjölkavkastning, mjölkflöden och besökstider i mjölkningsenheten i ett automatiskt mjölkningssystem
The study was carried out at the Kungsängen Research Centre, Department of Animal Nutrition and Management, Swedish University of Agriculture Sciences, Uppsala.
The technical development in dairy production has resulted in a housing system where feeding and milking is done automatically without human contact, a so called automatic milking system. The motives for utilising an automatic milking system, is to increase the animal welfare and to decrease the need for manual labour. However, the system does involve a change for the animals, among the effects is the deprival or the diminishment of a chance for synchronous behaviour and the animals have to agree among themselves in which order they use the feeding stations and the milking unit itself. How and if this affects the animals well-being and production is yet to be solved. A possible way to form an opinion on this, is to study the animals ranking order along with hormone profiles and production.
The purpose of this work was to study the effect of low- vs. high rank among diary cows in an automatic milking system. Based on the knowledge that oxytocin has an effect on the anti-stress system, blood samples were collected to find out if the hormone profiles differ between the ranking groups during rest and milking. And, when knowing these levels of oxytocin, compare it to milk yield, milk composition and milk flow. Even the duration of the cows visits in the milking unit was noted throughout the study period.
The study was done in a heard with 56 Swedish red and white dairy cows that were housed in a stable with an automatic milking system. The data were collected during the period of December 1st 2001 until February 28th 2002. Twelve cows, the six highest and the six lowest in rank were selected for the experiment. Four cows of each rank were used when blood samples were collected both during milking and resting. The plasma was analysed for oxytocin using radioimmunoassay method. Milk yield, milk flow and milking time were registered every milking. Content of fat, protein and lactose, was registered once a week. The results were presented as means and standard deviation of mean to try to see if there was a pattern of difference between the two groups.
A trend indicated that the low ranked cows had a higher level of oxytocin than the high ranked cows both during resting and milking. The milk yield, lactose content, mean flow and peak flow were higher for the low ranked cows. The protein content was higher for the high ranked cows. There were no big differences in fat between the two groups. The low ranked cows visited the milking unit during a longer period than the high ranked.
The higher levels of oxytocin for the low ranked cows might be an indication that these cows are calmer and does not experience as much stress as the high ranked cows. If the rank has an impact on milk characteristics and on time spent in the milking unit is hard to say, but the stage of lactation is probably one factor that has a large impact on the result we got.