Abstract
Until today, anti-microbial drugs have been the therapy of choice to combat bacterial diseases. Resistance against antibiotics is of growing concern in man and animals. Stress, caused by demanding environmental conditions, can reduce immune protection in the host, influencing the onset and outcome of infectious diseases. Therefore psychoneuro-immunological intervention may prove to be a successful approach to diminish the impact of diseases and antibiotics use. This study was designed to investigate the effect of social and environmental enrichment on the impact of disease, referred to as “disease susceptibility”, in pigs using a co-infection model of PRRSV and A. pleuropneumoniae. Twenty-eight pigs were raised in four pens under barren conditions and twenty-eight other pigs were raised in four pens under enriched conditions. In the enriched pens a combination of established social and environmental enrichment factors were introduced. Two pens of the barren (BH) and two pens of the enriched housed (EH) pigs were infected with PRRSV followed by A. pleuropneumoniae, the other two pens in each housing treatment served as control groups. We tested if differences in disease susceptibility in terms of pathological and clinical outcome were related to the different housing regimes and if this was reflected in differences in behavioural and immunological states of the animals. Enriched housed pigs showed a faster clearance of viral PRRSV RNA in blood serum (p = 0.014) and histologically 2.8 fold less interstitial pneumonia signs in the lungs (p = 0.014). More barren housed than enriched housed pigs developed lesions in the lungs (OR = 19.2, p = 0.048) and the lesions in the barren housed pigs showed a higher total pathologic tissue damage score (p<0.001) than those in enriched housed pigs. EH pigs showed less stress-related behaviour and differed immunologically and clinically from BH pigs. We conclude that enriched housing management reduces disease susceptibility to co-infection of PRRSV and A. pleuropneumoniae in pigs. Enrichment positively influences behavioural state, immunological response and clinical outcome in pigs.
Highlights
Psycho-social stress in man and animal alters disease susceptibility to infectious agents [1,2,3,4]
Post hoc analysis revealed that by housing (BH) pigs showed a 5.6 fold higher frequency of oral manipulation on the day before transport (Fig 1A)
Pen manipulation was affected by housing with higher frequencies for BH than for enriched housed (EH) pigs, and day (Fig 1D)
Summary
Psycho-social stress in man and animal alters disease susceptibility to infectious agents [1,2,3,4]. The adverse effects of stimulus-poor housing conditions and social stress on behaviour, (re)activity of the hypothalamic-pituitary-adrenal (HPA) axis and mood (pessimistic versus optimistic) are well established [6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]. In the current study we compared disease development following co-infection with porcine reproductive and respiratory syndrome virus (PRRSV) and A. pleuropneumoniae between pigs reared in environmentally and socially enriched pens and pigs reared in barren, stimulus-poor housing conditions. We hypothesized a reduced disease susceptibility to coinfection, as expressed by reduced clinical signs, in the enriched housed pigs
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