Empirical and theoretical evidence for herd size as a risk factor for swine diseases.

Herd size is frequently studied as a risk factor for swine diseases, yet the biological rationale for a reported association with herd size (whether positive or negative) is rarely adequately discussed in published epidemiological studies. Biologically plausible reasons for a positive association between herd size and disease include a greater risk of introduction of pathogens from outside the herd, greater risk of transmission of pathogens within and among herds when the herd is large, and effects of management and environmental factors that are related to herd size. However, compared with owners of small herds, owners of large herds might more frequently adopt management and housing practices that mitigate this theoretically increased risk.

Infectious and rearing-system related risk factors for chronic pleuritis in slaughter pigs.

Chronic pleuritis (CP) in Danish pigs for slaughter is by far the most frequent finding at the routine post-mortem meat inspection. An initial investigation published in 1990 demonstrated infectious and management-related risk factors. Serological testing for additional infectious agents, as well as the need to consider the effect of disease clustering at the herd level, required a re-analysis of the data.

No simple association between time elapsed from seroconversion until slaughter and the extent of lung lesions in Danish swine.

The association between the extent of pathological lung lesions at slaughter and the time elapsed from seroconversion to slaughter was examined in a longitudinal study including 830 pigs from eight herds. Pigs from an age of 3 weeks were bled every fourth week, and the sera were analyzed for the presence of antibodies to Mycoplasma hyopneumoniae and Actinobacillus pleuropneumoniae serotypes 2, 5, 6, 7 and 12. At slaughter, the extent of mycoplasma-like catharral pneumonia, chronic pleuritis (dorso-caudal and ventro-cranial), interlobular-scar retractions, acute pleuropneumonia and chronic pleuropneumonia was recorded.

No overall relationship between average daily weight gain and the serological response to Mycoplasma hyopneumoniae and Actinobacillus pleuropneumoniae in eight chronically infected Danish swine herds.

The association between the average daily weight gain (from approximately 4 to 20 weeks of age) and the serological responses to respiratory infections was examined in a longitudinal study including 825 pigs from eight chronically infected herds. Pigs were bled every 4th week (starting from approximately 4 weeks of age), and sera were analyzed for antibodies to Mycoplasma hyopneumoniae and Actinobacillus pleuropneumoniae serotypes 2, 5-7 and 12.Mixed analysis of covariance analyzed the relationship between the average daily weight gain and a categorical variable defining seroconversion as none, early or late as compared to the median time (estimated across herds) of seroconversion for the particular pathogen.

Microbiology and pathology of fibrinous pericarditis in Danish slaughter pigs.

The prevalence of fibrinous pericarditis detected at slaughter in Danish slaughter pigs is approximately 0.02%. The microbiology and pathology of this disorder was studied through 46 field cases collected at slaughter from May 1994 to August 1995.