Measuring hair and blood cortisol in sheep and dairy cattle using RIA and ELISA assay: a comparison

초록

Cortisol hormone shows distinct circadian rhythmicity in humans and animals. In this study, preliminary cortisol assessments were conducted using wool samples from ewes (nine ewes) exploiting both RIA and ELISA assays. Afterwards, eighteen high production (milk = 38 +/- 1.5 kg d(-1)) lactating Holstein cows (2nd parity) and 12 growing heifers (10-12 mo of age, BW = 200 +/- 35 kg) were employed in this experiment. Higher (P = 0.04) serum cortisol and subsequently significantly higher (P = 0.001) hair cortisol levels were observed in lactating cows compared with heifers. Both RIA and ELISA (intra- and inter-assay coefficients of variations were 1.11 and 10.61, respectively) assays were used and the accuracy was approximately 0.0031 mu g/dL similar to the wool cortisol assessment. Apart from the limitations of using RIA assay, using ELISA for the hair/wool cortisol analysis provided more reliable data output and less errors. In addition, application of ELISA is more environmental-friendly. Lower cortisol values were observed in both hair and plasma of Holstein heifers than those of lactating cows concluding that lactating cows are more vulnerable to thermal stress than growing heifers.

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