Effects of Dominance Rank Changes, Age, and Body Weight on Plasma Corticoids of Mature Dairy Cattle

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Abstract
The purpose was to determine whether forced change in dominance rank affected total corticoids of plasma of dairy cattle. Nineteen cows in late lactation were assigned randomly to 1 of 2 lots. Restriction of manager space enhanced observations of dominance rank during feeding for three 1 h periods/wk over 6 wk. After 3 wk a group of the 5 highest ranking cows for each lot were combined into a new aggressive lot; 2 groups of subordinate cows formed a docile lot. Blood samples were from tail vein, and concentrations of total corticoids were determined by competitive protein binding. Changes of dominance rank varied from 0 to 8 places in the 10-cow assemblage after new lots were formed. Body weight was the most significant variable affecting dominance rank. There was no discernable relationship between total corticoids and dominance rank, body weight or age. The pattern of variation of total corticoids was similar for all groups during the first 3 wk period, but in the 2nd period docile and aggressive groups had dissimilar patterns. Interaction of group by week for total corticoids was significant; a cause and effect relationship could not be established. Total corticoids did not appear to be a valid or useful determinant of social stress.