Garlic reduces effect of Actinobacillus pleuropneumoniae infection in pigs

Lung diseases in pigs are among the most important health problem in pig husbandry, and generally treated with antimicrobials. To reduce the amount of antimicrobials used in pigs, we tested the preventive effects of freeze dried garlic added to feed on an infection with Actinobacilluspleuropneumoniae (APP). Thirty male pigs of about seven weeks of age were aerosol challenged with APP serotype 2. Fifteen pigs received 5% (w/w) garlic added to their diet (Garlic group), from two days prior to infection until four days after infection. The others received the a standard diet (Control group). There was no difference in the number of pigs with symptoms of lung diseases. 48 hours after infection, the number of white blood cells had significantly increased in the Control group but not in the Garlic group. In the Control group a positive correlation (p<0.001) was found between the occurrence of clinical respiratory disease signs and pathological findings. This correlation was not found in the Garlic group (p=0.15). We conclude that feeding high concentrations of freeze dried garlic does not prevent an APP infection, however, it affects the course and reduces the severity of an APP infection Introduction The development of antibiotic resistance possibly due to the use of antibiotics in animal production has resulted in a growing public concern (Rijsman et al., 2010). Organic farms aim to produce animal products without the help of antibiotics, mainly through preventive and stress reducing measures, but also by using alternative curative treatments. Lung diseases, endoand ectoparasites and diarrhoea are the main health problems in Dutch organic pig herds. Actinobacilluspleuropneumoniae (APP) is a lung disease which is prevented by vaccination or treated with antibiotics (Van der Meulenet al., 2006). Dutch organic pig farmers are looking for alternatives to reduce the use of antibiotics and prevent APP. Garlic is a possible immunostimulant and has an anti-microbial activity (Sohnet al., 2009; Harjaiet al., 2010; Liu et al., 2010). Volatile sulphurous compounds are essentially responsible for the garlic smell of the exhaled air, and allyl methyl sulphide (AMS) is one of the most stable decomposition products of garlic in the body. AMS can exert antibacterial effects in the lungs (Hell and Kruse, 2007; Kyung and Lee, 2001). In vitro tests with AMS showed an antibacterial effect against APP serotype 9: it impaired the in vitro growth rate by 8% (unpublished data). The present study aims to test the preventive effect in vivo of freeze dried garlic added to feed on an infection with APP. Material and Methods Thirty male pigs of about seven weeks of age were aerosol challenged with APP serotype 2 (reference strain 1536) in a stainless steel incubator. Aerosols were introduced with an AeronebTM Pro micropump nebulizer (Aerogen Ltd., Galway, Ireland). 5 ml of the inoculum containing 1x109cfu/ml was completely dispersed within 30 minutes. Fifteen pigs received a 5% (w/w) garlic constituent of EnteroguardTM (Orffa Additives, The Netherlands) added to their diet (Garlic group), from two days prior to infection until four days after infection. The others received a standard diet (Control group). Body temperature, appetite, and behaviour of all pigs were monitored daily. White blood cells (WBC) were counted three days before the exposure and at day one and three after exposure. At four days after exposure the pigs were euthanized. Gross pathology findings were recorded, tissue samples were taken and lymph nodes were histologically and bacteriologically examined. AMS was measured in blood sampled from the pigs at the day just before the exposure and at day four after exposure. The analysis of variance was applied to test the effects of the garlic diet on WBC count at days 1 and 2 after inoculation. Differences of lung weights between the two groups were analysed by using a two tailed Mann-Whitney U test.