A Field Study of Histologic and Bacteriologic Characterization of Femoral Head Separation and Femoral Head Necrosis

Histologic and bacteriologic features for groups of average 31-day-old broilers manifesting with 3 gross categories of femoral head alterations were documented. Categories included simple femoral head separation (FHS), femoral head transitional changes (FHT), and femoral head necrosis (FHN). Groups having grossly normal femoral heads (NORM) and cull birds having gross signs of sepsis and FHN (Cull-FHN) were also included in the study. There was a 10% occurrence of positive bacterial cultures for all birds tested. Most positive cultures (33%) were found in the Cull-FHN group, while only a 12% occurrence was seen for the FHS group and no positives were present in the FHT or FHN groups. A 14% total occurrence of femoral bacterial chondronecrosis with osteomyelitis or simple osteomyelitis (BCO-O) was observed. A progressive increase in the prevalence of BCO-O was apparent between groups going from NORM (0%), FHS (4%), FHT (14%), FHN (13%), and reaching a maximum of 67% in the Cull-FHN group. Minimal to mild femoral head cartilage necrosis was present in 40% of normal broilers and 100% of the FHS, FHT and FHN groups, but at moderate severity in 20% of the Cull-FHN group. Thus, the majority of FHN cases were associated with aseptic cartilage necrosis rather than BCO-O. These findings suggest that aseptic cartilage necrosis may be as important as septic necrosis as a cause of gross femoral head disease. A 26% overall occurrence was seen for hip synovitis-arthritis, but group differences were not statistically significant. Synovitis was not seen in the NORM group, was present in some (12%) of the FHS group, but was observed at a high rate in both the FHN (43%) and the Cull-FHN (50%) groups. Morphometric measurements demonstrated that the area size of femoral fibrous cortical defects (or “cutback zones”) were generally larger for all gross categories relative to NORM, with a significant difference between NORM and FHS groups. This study underscores the multifactorial etiology of femoral head necrosis and the importance of conducting both histologic and bacteriologic evaluations where gross evidence of FHN or BCO occurs.