Associations between behavioural indicators of "stress" in weaner pigs and respiratory lesions at slaughter.

The aim of the study was to investigate associations on the individual-pig level between eight behavioural indicators of 'stress' (defined in a very general sense), in seven to eight-week old piglets four weeks after weaning and the occurrence of atrophic rhinitis (AR) and chronic pleuritis (CP) at slaughter. The study was designed as a cohort study, including 512 pigs from two commercial farms. With one exception Actinobacillus pleuropneumoniae serotype 2 (App2) infection was not associated with any of the behaviour patterns observed. Using random-effects logistic regression, weak statistical associations, positive as well as negative, were found between the performance of several behaviour patterns and the two pathological lesions. This suggests the existence of biological associations between oral behaviour patterns in young pigs and the health status later in life. However, the results were not consistent between specific oral behaviour patterns or between the two herds indicating that the associations found are either due to chance or reflect the existence of herd-specific confounders. Therefore, results based on studies within only one herd should not be generalized to other herds without care. Behavioural observations on seven- to eight-week-old piglets on the basis of the present investigation cannot be recommended for use as early predictors of AR or CP at slaughter. Further studies are needed in order to elucidate causal relations between behaviour and health.

Application of enzyme-linked immunosorbent assay for the surveillance of Mycoplasma hyopneumoniae infection in pigs.

A monoclonal antibody-based blocking enzyme-linked immunosorbent assay (ELISA) was used for serological surveillance of Mycoplasma hyopneumoniae infection in pig herds. A follow-up study was conducted on "herd predictive values" previously reported for this ELISA. Of those herds giving positive results by this ELISA, 42% were subsequently found to be infected, while 100% of herds giving negative results were uninfected. Previous reports recorded positive and negative herd predictive values of 39% and 99.8%, respectively. Among naturally-infected animals, reaction in colostrum was more frequent than in serum, and this difference was most pronounced if the colostrum samples were obtained shortly before or after farrowing. Coughing was found to be the most reliable clinical indicator of infection, but surveillance through clinical herd inspections alone failed to detect 30% of infected herds. The time required for seroconversion following natural exposure to M. hyopneumoniae differed in two herds using different management systems: in one herd antibodies were first detected three weeks post-exposure, while in the other herd antibodies were not detected until five weeks after exposure.

Causes of mortality among sows in Danish pig herds.

The likely causes of sow mortality in Danish pig herds were investigated in a sample of 598 of the breeding animals delivered to a large rendering plant in the winter seasons of 1992 and 1993. In 263 cases information about the circumstances of the death or euthanasia and the herd characteristics were available, including the size of the herd, its health status, the age at weaning, the method of feeding and the use of straw for bedding. For these animals the distribution of likely causes of death or euthanasia was: leg weakness, 28.5 per cent; problems related to farrowing and late pregnancy, 20.9 per cent; disorders of the digestive system, 17.1 per cent; disorders of the urinary system, 13.1 per cent; physical injuries, 10.7 per cent; and other disorders, 9.5 per cent. For the other 335 sows the distribution of likely causes of death was: leg weakness, 16.1 per cent; problems related to farrowing and late pregnancy, 10.7 per cent; disorders of the digestive system, 21.2 per cent; disorders of the urinary system, 15.2 per cent; other disorders, 15.0 per cent; and unknown causes of death, 21.8 per cent. According to the official statistics from Danish rendering plants, more than 60,000 carcases of breeding pigs were processed during 1992, corresponding to a mortality rate of 5 to 6 per cent in the sow herds. The mortality rate appeared to increase with increasing herd size, and in herds with more than 100 sows the mortality rate was three times the mortality in herds with fewer than 50 sows. Compared with previous reports, the proportion of disorders involving the gastrointestinal system has increased during the past 20 years. Gastric dilation is particularly common, probably as a result of the intensification of pig production and the associated changes in management practises. The use of straw bedding was marginally significant (P = 0.06) and associated with a low frequency of gastrointestinal disorders.

An epidemiologic and economic study of respiratory diseases in two conventional Danish swine herds. I: Prevalence of respiratory lesions at slaughter and their effects on growth.

A total of 578 slaughter pigs from 2 Danish conventional farrow-to-finish operations (Herds A and B) were followed from an age of 14 days to slaughter. Pigs were weighted at 3 weeks intervals and at slaughter and an extended post mortem examination of the plucks was done. Comparison of growth rates in pigs with and without specific types of lesions by the t-test and those with multiple lesions with regression models demonstrated that Mycoplasma-like pneumonia, complicated pneumonia, anterio-ventral pleuritis, fissures and atrophic rhinitis significantly reduced mean daily gain and increased the time required to reach slaughter weight. The total impact of the lesions in Herd A was an estimated reduction in mean daily gain of 27 grams and a 2 day increase in the interval from 14 days of age until slaughter (MDG14). Decreases in MDG14 in Herd B were more substantial, 98 grams and 16.7 days. Reductions in mean daily gains during the interval from the fourth weighing until slaughter were 31 grams in Herd A and 137 grams in Herd B. Chronic dorso-caudal and parietal pleuritis, without other lesions present, had no significant adverse effects on growth rates in either herd. Interactions between lesions did not significantly alter the estimates. The R2 values obtained for the regression models showed that the presence, absence or extent of lesions at slaughter explained only 13-27% of the variations in growth rates in the 2 herds.

An epidemiologic and economic study of respiratory diseases in two conventional Danish swine herds. II: Associations between lesions present at slaughter and mean daily gains during specific intervals of the growth period.

A total of 578 slaughter pigs from 2 Danish conventional farrow-to-finish operations (Herds a and B) were followed from an age of 14 days to slaughter. Pigs were weighted at 3 weeks intervals and at slaughter and extended post mortem examination of the plucks was done. Regression models with second and third order interaction terms demonstrated that Mycoplasma-like pneumonia, complicated pneumonia, anterior-ventral pleuritis, pericarditis, fissures and atrophic rhinitis, separately and through interactions with other lesions, significantly reduced mean daily gains during specific intervals of the growth period in 2 conventional swine herds. It is likely that the periods of reduced growth reflect the times when the diseases were in the acute and early recovery stages. Maximum estimated reductions in daily gains associated with the combined lesions were 82 grams and 283 grams during the interval 120-140 days in Herds A and B, respectively. Although dorso-caudal pleuritis and parietal pleuritis had minor negative effects during 2 intervals neither had a significant adverse effect on total growth rate in either herd (Paisley et al. 1993). R2 values for the regression models were less than 0.27 showing that the lesions present at slaughter explained less than 27% of the variation in herd mean daily gains during any interval.