The effects of inoculation of Mannheimia haemolytica into the teat of lactating ewes

Abstract

-The objectives of the work described in this paper were: (i) to study the outcome of challenging ewes with Mannheimia haemolytica, at different sites of their teats, (ii) to compare the effects of two different isolates of the organism and (iii) to describe the features of the resulting lesions. Thirty-two ewes were used in the study and allocated into one of two groups (A or B, n = 16); they were challenged with one of two isolates of M. haemolytica, respectively, strain ES26L of known pathogenicity or strain VSM08L from the teat duct of a healthy ewe. Each group was further divided into four equal subgroups: the ewes in the A1/B1 subgroups were intramammarily challenged; one teat of the ewes in the A2/B2 subgroups was immersed into a broth-culture of the organisms; one teat of the ewes in the A3/B3 subgroups was inoculated 2 mm-deep, whilst one teat of the ewes in the A4/B4 subgroups was inoculated 6 mm-deep. The animals were monitored clinically, bacteriologically and cytologically before and after challenge; one animal in each subgroup was euthanised 2, 4, 7 and 11 days after challenge. All ewes in the A1/B1 subgroups developed clinical mastitis, whilst of the other animals, only one ewe in each of the A4/B4 subgroups did. Neither of the two strains used was associated with more positive bacteriological or CMT results; the A2/B2 subgroups were associated with less positive results than the A3/B3 and A4/B4 subgroups. In some ewes of the A2/B2 subgroups, mild leucocytic infiltration in the teat was evident; in the ewes of the A3/B3 subgroups, leucocytic infiltration (neutrophils, lymphocytes, plasma cells) was seen, as well as a lymphoid hyperplasia at the border between the teat duct and teat cistern; in ewes of the A4/B4 subgroups, intense subepithelial leucocytic infiltration was the salient feature. No differences were found in the severity of lesions between the two strains used or the three treatments carried out. Although strain VSM08L had been isolated from the teat duct of a healthy ewe, it caused mastitis when inoculated intramammarily; although strain ES26L is of known pathogenicity for the mammary gland, it did not cause clinical mastitis when deposited 2 mm-deep into the teat. These findings point to a protective role of the teat of ewes, which appear to limit bacterial penetration from the teat duct or cistern to the mammary gland. The lymphoid tissue, at the border between the teat duct -teat cistern, may play a significant protective role.

The bacterial flora in the teat duct of ewes can protect against and can cause mastitis

“…in the duct were inoculated with an isolate of M. haemolytica (strain VSM08L). This strain had been isolated in Greece and was found to cause mastitis in ewes when inoculated directly into the gland cistern, whilst deposition into the duct or the cistern of clinically healthy teats resulted in subclinical mastitis [36].…”

“…For selection of the ewes three, 2-day interval, examinations and samplings were carried out. Initially, a thorough clinical examination was carried out; special attention was paid to their mammary glands and teats, which were examined as described before [17,36]. A sterile plastic fine catheter 2 mm long was inserted into the teat and moved from the left to the right, in order to sample the mucosa [37].…”

“…Ewes were examined again and samples were collected as above, on the day of inoculation (D0), which was carried out as described by Mavrogianni et al [36]. The ewes in A1, B1, C1 and D were challenged 2 mm deep into the teat by means of a sterile plastic fine catheter (Abbocath; Abbott Laboratories Inc., Abbott Park, IL, USA) 20 G. In the other teat of these ewes, 0.2 mL of sterile PBS was injected 2 mm deep into the teat.…”

“…The ewes were euthanised on the timepoints detailed in Table I. Dissection of the mammary glands and the teats started immediately; it was carried out as described before [11,36]. In A1, B1, C1, D and H group ewes, an electronic cutimeter was used to measure 2 mm from the teat orifice, in order to determine the precise site within the teat, where the inoculum had been deposited.…”

“…The significance of the ovine teat as a defence mechanism against intramammary infections has been established [36]. Clinically healthy teats provide a substantial * Corresponding author: gcf@vet.uth.gr protection against Mannheimia haemolytica intramammary infection.…”