Post-mortem Examinations:

Birds were selected for post-mortem examination to include both natural mortality on the day of the visit (though it was not possible to identify house of origin for these) and birds selected from each of the houses on the basis that they were showing the signs described above. Most of these birds were examined on-farm, though 6 were culled and returned intact to the laboratory to facilitate bacteriological examination

Gross Pathology.
A detailed breakdown of the lesions encountered in each of the 22 birds subjected to post-mortem examination is shown in Table 2. As expected from the signs seen in live birds the most common findings were inflammatory lesions affecting the tissues of the head and joints and other synovial structures (tendon sheaths and sternal bursa).
The head lesions were much more acute in males. Many birds had severely swollen and cyanotic wattles (though the cyanosis disappeared some hours after death). On cutting the wattles a dramatic layered lesion was revealed with alternating pus and oedema forming patterns. The impression was that the inflammatory reaction was attempting, unsuccessfully, to wall off the infection. In one bird the wattle lesions were more chronic with associated scarring and resolution of the lesions (but also extending into the sub-mandibular area). In the females the sub-cutaneous lesions tended to spread out from the area of the eyes, though they did extend into the right wattle in a few birds.
Table 2. Summary of the post-mortem findings when the birds were 25 weeks old.

...............................Sex---> M M M M M M     F F F F F F F F F F F F F F F F F M F All %
Birds Examined                                                   6 16 22  
Head Lesions                                                          
...Facial Oedema X   X X X X                     X       X X X X X 5 4 9 40.9
...Inflamed Wattle X   X X X X                                 X X   5 2 7 31.8
...Facial s/c pus/inflammation                                         X X X X X   5 5 22.7
...Inter-mandibular pus           X                                       1   1 4.5
...Head Haematoma (infected)                         X                         1   1 4.5
Joint and synovial lesions                                                          
...Sternal Bursitis X X                   X X     X                   2 3 5 22.7
...Hock arthritis/tenosynovitis   X               X X                             1 2 3 13.6
...Foot arthritis                   X X X                               3 13.6
Ovarian Lesions                                                          
...Out of lay                   X X X X X X X X X X       X X X 11   11 68.6
...Ovarian Congestion                                 X                 1   1 6.3
Other Lesions                                                          
...Nephrosis                                   X X             2   2 9.1
...Peritonitis   X                                   X           1 1 2 9.1
...Cannibalism at vent                                         X X         2 2 9.1

Figure 4. A post-mortem specimen from one of the affected males with the wattle cut to show its thickness and the patterns of pus and haemorrhagic oedema within.

Case 1 Fig. 4 Gross lesion in wattle of male

Figure 5. An affected female with pus visible in cuts above and below the eye and at the base of the wattle.

Case 1 Fig.5 - Gross Lesions under skin of the head of a pullet

The articular and synovial lesions consisted of thickening of the lining membranes of the affected structures with accumulation of variable amounts of pale-coloured pus in their lumen. In most birds this pus was solid.

Most of the females examined had little development of follicles in the ovary. Of those which did, 2 birds from house 2 had died as a result of cannibalism (vent-pecking). This finding was consistent with the observations made, particularly in house 2, that cannibalism was a greater problem than normal. Another incidental finding was nephrosis in 2 birds, suggesting that one of the effects of the disease might be reduced mobility and water consumption in some of the affected birds.