title: Stress enhanced reduction in peripheral blood lymphocyte numbers in dairy cows during endotoxin-induced mastitis.
abstract: Two groups of Holstein dairy cows, which showed either high- (HC; n = 8) or low (LC; n = 10) plasma cortisol concentrations in response to a psychological stressor (novel-environment test) in their first lactation, were used 1 year later for studying the effects of psychological stress on various aspects of the host defence during endotoxin-induced mastitis. Social isolation was used as a stressor; endotoxin was used to activate the host defence. HC-cows appeared to be more stressed by the experimental procedure than LC-cows. One hour after having been isolated, rectal temperature increased (+0.59 degrees C) in HC- but not in LC-cows. Handling, related to the intra-mammary administration of endotoxin, induced a higher increase in cortisol concentration in HC- than in LC-cows 1 h after injection. In addition, HC-cows vocalised significantly more frequently (595 +/- 222) than LC-cows (81 +/- 24) between 1.5 and 9.5 h after isolation. Between 3 and 5.5 h after endotoxin-treatment, cortisol concentrations increased profoundly in both LC- and HC-cows and peaked at 24.6 +/- 3.8 and 22.8 +/- 3.1 ng ml(-1), respectively. The rise in plasma cortisol concentration was associated with a decrease in the number of circulating lymphocytes between 0 and 8 h post injection (PI). Between 8 and 10 h PI, the number of circulating lymphocytes in HC-cows further decreased (40%) to 1.58x10(6) cells ml(-1) and remained so until 21 h PI. This was not the case with the LC-cows. The results show that a differing sensitivity of dairy cows to environmental stressors is associated with a significant difference in the number of circulating leukocytes following intra-mammary administration of endotoxin during a period of social isolation. The results further suggest that, apart from adrenocortical hormones, other factors related to general stress-responsiveness modulate the number of peripheral lymphocytes in dairy cows during endotoxin-induced mastitis. During environmental stress, these factors may enhance endotoxin-induced reduction in circulating lymphocyte numbers, particularly in cows that are sensitive to environmental stressors. As to the clinical relevance of these differences in stress responsiveness, no differences between LC- and HC-cows were found in disease incidence nor in duration of a disease episode during both the 1st and 2nd lactation. In the 2nd lactation. HC-cows tended to produce less milk than LC-cows.
authors.affiliation: Institute for Animal Science and Health (ID-DLO), Lelystad, The Netherlands. h.hopster@id.dlo.nl
authors.forename: H
authors.initials: H
authors.lastname: Hopster
authors.forename: J T
authors.initials: JT
authors.lastname: van der Werf
authors.forename: H J
authors.initials: HJ
authors.lastname: Blokhuis
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D001831:Body Temperature; D002417:Cattle; D004731:Endotoxins; D005260:Female; D006339:Heart Rate; D006799:Housing, Animal; D006854:Hydrocortisone / Q000097:blood; D015994:Incidence; D018655:Lymphocyte Count / Q000662:veterinary*; D008414:Mastitis, Bovine / Q000139:chemically induced* / Q000453:epidemiology / Q000276:immunology*; D008892:Milk / Q000737:chemistry; D012934:Social Isolation; D013312:Stress, Physiological / Q000276:immunology / Q000662:veterinary*; D015032:Zinc / Q000097:blood
chemical_list: D004731:Endotoxins; D015032:Zinc; D006854:Hydrocortisone