SWINE

Metabolic bone disease and associated testing in finished pigs

Murray Hazlett, Martin Misener, Steve Ensley

Market hogs from a large finishing system that purchases feeder pigs from a 3,700 sow farrow-to-feeder pig farm

were having issues with increased losses associated with shipping, including pigs with fractures at loading and at

slaughter. The 3 pigs in the case came from 3 different barns - 2 were liquid fed and one was a wet/dry feed system. There was no clinical evidence of confounding disease issues.

When these pigs were submitted for autopsy, the ribs would tend to fold and crumple, rather than snap. Several areas of bone were examined histologically, with efforts aimed at the second rib (this is the sample of choice for a metabolic bone profile done in the veterinary diagnostic lab at Iowa State University). Histologically there was thinning of the cortex compared to control pigs (Fig. 1). Areas of fibrosis were present in the medulla and surrounding the cortical bone.

The 3 clinically affected pigs all had the lowest levels of bone ash (Table 1). The value for one of the control pigs was also below reference intervals (RI) but above that of affected pigs. Bone density was higher in affected pigs, perhaps because of replacement of fat with fibrous tissue. Bone ash calcium and phosphorus values were both higher than the control pigs but within RIs, likely a reflection of less bone, but the bone present had a higher percentage of mineral.

 It was suspected that the problem in these pigs was due to a reduced level of micronutrient inclusion for the last 6 weeks of the feeding period. The formulation was corrected and the problem resolved.

Submissions for bone ash testing can be done through the AHL, and we forward the specimen to the Iowa State Diagnostic Laboratory for analysis. Costs for a typical submission of 4 second ribs from 2 pigs (2 for histology and 2 for bone profiles) would cost ~$363 total (this varies with the Canadian/USD exchange rate).

Table 1. Results of bone profile testing (Iowa State Veterinary Diagnostic Laboratory).

Test	Reference interval	Affected pig A	Affected pig B	Affected pig C	Control pig A	Control pig B
Bone ash	58-62%	40	36	37	56	49
Bone density	1.4-1.5 g/mL	1.26	1.23	1.24	1.2	1.2
Bone ash calcium	32-39%	40.8	42.9	31.4	28.5	29.3
Bone ash phosphorus	13-22%	21.2	21.8	16.8	14.2	14.4

Figure 1 Control rib (left) showing normal cortical thickness and affected rib (right) showing
fibrous tissue proliferation (left arrow) surrounding a thin cortex (right arrow).