Pathological and bacteriological findings in sows, finisher pigs, and piglets, being culled for lameness

Lameness is a common pig disorder. In the herd, a recurring, consistent aetiology is often suspected based on the age of the pig and herd-specific predisposing factors. The aetiology may be difficult to establish especially in larger animals, since the primary pathogenesis is obscured by delayed diagnosis, chronic changes and sequelae, and thorough investigation usually requires culling and transport to a pathological laboratory for necropsy. Thus, treatments are mostly based on a tentative diagnosis, commonly including antibiotics to eliminate infectious agents. The study aimed to investigate the aetiology of lameness in various age-categories of pigs, compare the tentative clinical diagnosis with post mortem findings, and discuss the findings in relation to the adequacy of antibiotic treatment.

In total, 29 sows, 45 finisher pigs, and 130 suckling piglets diagnosed with lameness were included. In all age categories, arthritis was the most common finding (13 sows, 30 finisher pigs, and 126 piglets, i.e. 45, 67, and 97% of the respective category). 86% (n = 25) of the sows and 71% (n = 32) of the finisher pigs had been treated with antibiotics. Of the post mortal lesions assessed to have an infectious aetiology, 99% were interpreted as chronic and eight sows, two finisher pigs and one suckling piglet had fractures. In six samples from finisher pigs, the most common finding was beta-haemolytic streptococci. In the suckling pigs, 223 samples from affected joints and 37 samples from macroscopically unaffected joints were subject to cultivation. The most commonly found bacterial species were S. hyicus (n = 73 isolates) and S. dysgalactiae ssp. equisimilis (n = 58). 46 of 64 S. hyicus-isolates tested were resistant to penicillin, whereas all 44 isolates of S. dysgalactiae ssp. equisimilis tested were sensitive to penicillin.

In the majority of the cases, the findings at necropsy confirmed the clinical diagnosis. However, the rationale for antibiotic treatment must be questioned since 21 of 57 sows and finisher pigs (37%) treated with antibiotics were shown to suffer from lameness inflicted by non-infectious causes post mortem. Further, in all sows and finisher pigs, and in 83% (n = 104) of the suckling pigs with lesions being assessed to have an infectious aetiology at necropsy, the lesions were interpreted as being chronic. In piglets, S. dysgalactiae ssp. equisimilis or S. hyicus were isolated in 64% of the samples. A majority of these isolates were susceptible to penicillin, still rendering this a valid drug for treatment in acute cases of arthritis.