title: Differences in susceptibility to Mannheimia haemolytica-associated mastitis between two breeds of dairy sheep.
abstract: We used a Mannheimia haemolytica isolate to study differences in susceptibility to experimental mastitis between two breeds of dairy sheep. The isolate was deposited into the teat duct of Karagouniko (K, n=8) or Frisarta (F, n=8) ewes. The animals were monitored by means of clinical, bacteriological, cytological and pathological methods. K ewes did not develop any systemic or mammary clinical signs, whilst F ewes became ill and developed acute clinical mastitis 12 h later (P<0.001). Bacteria were isolated from 34/48 samples from K ewes and from 46/46 samples from F ewes. Positive California mastitis test (CMT) results were 17/24 samples from K ewes and 23/23 samples from F ewes; leucocytes were seen in Giemsa-stained films. Total pathology score summed over all group K ewes was 41 (maximum possible: 128); Man. haemolytica was isolated from 12/24 tissue samples. Total pathology score summed over all group F ewes was 93; Man. haemolytica was isolated from 24/24 tissue samples. Hyperplastic lymphoid nodules consisting of lymphocytes and plasma cells with germinal activity were characteristically present at the border between teat duct-teat cistern of group K ewes; no such structures were observed in teats of group F ewes. The results identified differences in susceptibility/resistance to a mastitis pathogen among animals of the two breeds. Defence mechanisms of the teat appeared to be inadequate against the invading organisms; as lymphoid nodules have been considered important defensive mechanisms of the ovine teat, their observed lack in Frisarta ewes might have predisposed them to development of mastitis.
authors: Veterinary Faculty, University of Thessaly, PO Box 199, 43100 Karditsa, Greece.
authors: Ilectra A
authors: IA
authors: Fragkou
authors: John
authors: J
authors: Skoufos
authors: Peter J
authors: PJ
authors: Cripps
authors: Ilias
authors: I
authors: Kyriazakis
authors: Nikos
authors: N
authors: Papaioannou
authors: Costas M
authors: CM
authors: Boscos
authors: Athina
authors: A
authors: Tzora
authors: George C
authors: GC
authors: Fthenakis
mesh_terms: D000818:Animals; D004198:Disease Susceptibility; D005260:Female; D007774:Lactation; D016978:Mannheimia haemolytica / Q000502:physiology*; D008413:Mastitis / Q000382:microbiology / Q000662:veterinary*; D016871:Pasteurellaceae Infections / Q000382:microbiology / Q000662:veterinary*; D012756:Sheep; D012757:Sheep Diseases / Q000145:classification* / Q000382:microbiology*; D013045:Species Specificity