Effect of rank, group size and number of group changes ante partum on the occurrence of milk ejection disorders in primiparous cows – a field study
Abstract. In the present study causes for the development of milk ejection disorders (MED) in primiparous cows of two herds were investigated. We hypothesised that MED are provoked by social problems within the herd that appear close to calving. Data were collected on 67 heifers of herd A and 60 heifers of herd B. In herd A, heifers were introduced into existing groups of cows 2–4 weeks prior to calving. They were kept in a group housing system with deep bedding. All animals were hornless. In herd B, heifers were kept separated from the cows from 2–4 weeks a.p. in a three-row cubicle barn. In contrast to herd A, all animals had horns. The animals´ reactions regarding the milking process and MED were analysed during the first four milkings p.p. We evaluated the correlation between social rank, group size and frequency of group changes in the antepartal period and the occurrence of MED.
12 % of the animals in herd A and 47 % of the animals in herd B showed MED. In herd A, lowranking heifers had significantly more often MED than higher-ranking heifers. A correlation between low rank, increasing strain due to rank order fights and increasing frequency of MED can be assumed here. In herd B, a correlation between stocking rate and frequency of MED could be observed.