Identifying biomarkers of sheep welfare using a metabolic discrepancy model.

The welfare of an animal is largely determined by the transient state within them that relates to what they experience. We evaluated candidate biomarkers of mental state and experience from human biomedicine as possible welfare biomarkers for sheep using a metabolic energy discrepancy model. The metabolic status of female Merino sheep was altered over three periods to induce changes in their experience and coping capacity. The first group was fed at maintenance for all periods (n = 11); the second group was fed above maintenance in period 1, at maintenance in period 2, and below maintenance in period 3 (n = 12); and the third group was fed below maintenance in period 1, at maintenance in period 2, and above maintenance in period 3 (n = 11). An isolation box test was used at the start and end of each feed period to assess the coping capacity of each sheep. Our results indicated that two of the five candidate biomarkers, insulin-like growth factor 1 and thiol oxidation, were associated with positive and negative experiences in the sheep, respectively. Future research should validate these biomarkers in sheep with other testing paradigms and in other ruminant species.