In modern bony fishes, or teleost fish, the general lack of leucocyte markers has greatly hampered investigations of the anatomy of the immune system and its reactions involved in inflammatory responses. We have previously reported the cloning and sequencing of the salmon CD3 complex, molecules that are specifically expressed in T cells. Here, we generate and validate sera recognizing a peptide sequence of the CD3e chain. Flow cytometry analysis revealed high numbers of CD3e + or T cells in the thymus, gill and intestine, whereas lower numbers were detected in the head kidney, spleen and peripheral blood leucocytes. Subsequent morphological analysis showed accumulations of T cells in the thymus and spleen and in the newly discovered gilllocated interbranchial lymphoid tissue. In the latter, the T cells are embedded in a meshwork of epithelial cells and in the spleen, they cluster in the white pulp surrounding ellipsoids. The anatomical organization of the salmonid thymic cortex and medulla seems to be composed of three layers consisting of a sub-epithelial medulla-like zone, an intermediate cortex-like zone and finally another cortex-like basal zone. Our study in the salmonid thymus reports a previously non-described tissue organization. In the intestinal tract, abundant T cells were found embedded in the epithelium. In non-lymphoid organs, the presence of T cells was limited. The results show that the interbranchial lymphoid tissue is quantitatively a very important site of T cell aggregation, strategically located to facilitate antigen encounter. The interbranchial lymphoid tissue has no resemblance to previously described lymphoid tissues.

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with a prevalence of 10% lameness reported by farmers who treat lame sheep bytrimming 19 affected feet. We tested the hypothesis that prompt treatment of sheep lame with naturally 20 developing FR or ID with parenteral and topical antibacterials reduces the prevalence and 21 incidence of lameness with these conditions compared with less frequent treatment by trimming 22 hoof horn and applying topical antibacterials. A further hypothesis was that reduction of ID and 23 FR would improve productivity. A lowland sheep flock with 700 ewes was used to test these 24 hypotheses in an 18-month within farm clinical trial with four groups of ewes: two intervention 25 and two control. The duration and severity of lameness was used to categorise sheep into three 26 weighted scores of lameness (WLS): never lame (WLS0), lame for a maximum of six days with 27 locomotion score 2 (WLS1) and lame for more than six days or a higher locomotion score 28 (WLS2). The intervention reduced the prevalence of lameness due to FR and ID in ewes and 29 lambs and the incidence of lameness in ewes. The WLS was significantly lower in sheep in the 30 intervention groups. Ewes with a higher WLS were subsequently significantly more likely to 31 have a body condition score (BCS) <2.5 and have lame lambs. Significantly more ewes lambed 32 and successfully reared more lambs that were ready for slaughter at a younger age in the 33 intervention versus control groups. There was an increase in the gross margin of £630 / 100 ewes 34 mated in the intervention group, including the cost of treatment of £150 / 100 ewes mated. We 35 conclude that prompt parenteral and topical antibacterial treatment of sheep lame with ID and FR 36 reduced the prevalence and incidence of these infectious conditions and led to improved health, 37 welfare and productivity. 38 -3 - Lameness is one of the greatest concerns for poor welfare in sheep (Goddard et al., 2006; 44 Fitzpatrick et al., 2006). It has been estimated to cost the UK industry £24 million / annum 45 (Nieuwhof and Bishop, 2005). More than 90% of farmers in the UK report lameness in their 46 sheep, with a farmer-estimated prevalence of 10% with more than 80% of lameness caused by 47 footrot (FR) and interdigital dermatitis (ID) (Grogono-Thomas and Johnston, 1997; Kaler and 48 Green, 2008a). In a study of 209 sheep farmers, those treating all sheep with FR with parenteral 49 antibacterials and foot sprays reported a significantly lower peak prevalence of FR of 2% 50 compared with the 9%reported by farmers who treated FR by paring the hoof horn and spraying 51 disinfectant on to the foot (Wassink et al., 2003). In addition, farmers who reported prompt 52 treatment of mildly lame sheep also reported a lower prevalence of lameness than those treating 53 groups of lame sheep (Kaler and Green, 2008). Further evidence for the benefits of parenteral 54 antibiotics comes from a prospective longitudinal study of 160 sheep on one farm where the 55 treatment of sheep with FR and ID with parenteral and topical antibacteria...

A postal survey of the techniques being used for the treatment and control of footrot in sheep flocks between November 1999 and October 2000 was conducted in England and Wales in November 2000. Of the 392 questionnaires circulated, 251 (64 per cent) were returned, and 209 of these were usable. Negative binomial regression analysis indicated that the isolation of bought-in sheep, and the separation and individual treatment of diseased sheep with parenteral antibiotics, foot trimming and topical foot sprays were associated with a significantly lower prevalence of footrot in a flock. In contrast, ewe flocks which were routinely foot trimmed more than once a year had a significantly higher prevalence of footrot. No evidence was found that footbathing a flock reduced the level of footrot, except on the 14 per cent of farms where the penning and race facilities for footbathing were reported by the farmer to be excellent. Vaccination had no significant beneficial effect on the level of footrot in a flock

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