Veterinary Research Communications, 27 Suppl. 1 (2003) 723–726 © 2003 Kluwer Academic Publishers. Printed in the Netherlands The Effect of Natural and Pharmacological Stressors on Sheep: Haematological, Biochemical and Granulocytic Functional Changes P. Sartorelli*, V. Spagnolo, S. Paltrinieri, A. Giordano and S. Comazzi Department of Animal Pathology, Hygiene and Public Health, Section of General Pathology and Parasitology, Faculty of Veterinary Medicine, University of Milan, Via Celoria, 10-20133 Milan, Italy *Correspondence: Dipartimento di Patologia Animale, Igiene e Sanita` Pubblica Veterinaria, Sezione di Patologia Generale e Parassitologia, Universita` degli Studi di Milano, Via Celoria, 10-20133, Milano, Italia E-mail: paola.sartorelli@unimi.it Keywords: biochemistry, granulocytes, haematology, pathophysiology, sheep, stress Abbreviations: ACTH, adrenocorticotropic hormone; ANOVA, analysis of variance; BHB, beta-hydro- xybutyrate; NEFA, non-esterified fatty acids; PCV, packed cell volume; PMNs, polymorphonuclear leukocytes INTRODUCTION Breeding animals are often exposed to different stressors that can affect their welfare and productivity either directly or indirectly through an increase of their susceptibility to infectious diseases. Stress may influence both the hypothalamus–pituitary–adrenal axis and the sym- pato–adreno–medullary axis, with consequences that depend on the type of stimulus, the species, the sex and on the individual considered. The present study was under- taken on a group of four ewes, in order to investigate the response to ‘natural stressors’ such as transport and isolation from the flock, in comparison with pharma- cologically-induced stress (1–24 ACTH). In particular we investigated the endocrine- metabolic response, haematological alterations and the main steps of PMNs func- tions. These parameters are considered to be the most indicative of a stress response. The results were compared with those obtained from the same animals under basal conditions, and after ACTH treatment which only stimulates the hypothalamus– pituitary–adrenal axis, in order to investigate the possible additional effects on the sympato–adreno–medullary axis due to acute natural stressors. MATERIALS AND METHODS The study was performed on blood samples (40 ml in tubes containing EDTA and 10 ml in tubes containing sodium heparin) collected from the jugular vein of four 723