Effects of repeated jugular puncture on plasma cortisol concentrations in loose-housed dairy cows

In three experiments, the effects of venipuncture on plasma cortisol concen trations were studied in loose-housed dairy cows. In Exp. 1, two blood samp les were collected 18 min apart on three alternate days from 20 dairy cows for studying their adrenocortical response to a single venipuncture, To fur ther evaluate the effect of cows anticipating venipuncture, in Exp. 2, 15 d airy cows were sequentially venipunctured once daily on 12 successive days in a randomized order in groups of five, starting 15 min apart. In Exp. 3, 10 primiparous cows were used on three altercate days to study habituation to serial sampling (i.e., collection of five blood samples by venipuncture, 15 min apart). In cows accustomed to handling, jugular puncture did not af fect cortisol concentrations in plasma collected 18 min later. Average dail y cortisol concentrations varied between 2.07 +/- .38 and 3.81 +/- .56 ng/m L in the first (t = 0) and between 1.43 +/- .15 and 2.61 +/- .72 ng/mL in t he second (t = 18) blood samples. Likewise, when cows were sampled sequenti ally once a day, the order of sampling between and within groups did not in fluence (P > .05) plasma cortisol concentrations. In contrast, primiparous dairy cows that were less used to being handled showed an average increase in cortisol concentrations when five samples were collected by venipuncture 15 min apart. During successive sampling sessions,however, the cows did no t decrease or increase plasma cortisol concentrations in response to repeat ed serial sampling at the group level (P > .05). Between individuals, the m aximum effect of repeated venipuncture on cortisol concentrations (4.5 to 2 2.6 ng/mL), the time at which the effect reached its maximum (30 to 60 min) , and the consistency of the response pattern over successive series varied largely. The results of this study show that in cows that were accustomed to handling and to being restrained, baseline cortisol concentrations can b e measured in single blood samples that are collected by jugular puncture w ithin 1 min after first approaching the cow. When successive blood samples need to be collected within 15 to 20 min, jugular puncture may induce an in crease in cortisol concentration, which seems to depend on the handling exp erience of the animals and on individual differences.