Oral fluids, meat juice, and processing fluids: non-invasive alternative diagnostic medium for disease monitoring in pigs

Abstract

The surveillance of infectious diseases represents a crucial aspect for the management of the herd health. This is of particular importance for the pig industry due to the high density and highly intensive nature of pig farms. In order to be effective and routinely usable, surveillance tools must be cost-effective and representative, collection of samples must be easy and the results must be reliable. Current pig disease surveillance relies primarily on monitoring humoral immunity via serum. However, blood sampling is costly and stressful for the animals. Recently, alternative diagnostic media such as oral fluid, meat juice, and processing fluids (oral fluid, OF; meat juice, MJ; processing fluids, PF) have been rapidly gaining interest. Relying on pig natural chewing behaviour and exploratory motivation, the collection of OF is easily carried out by hanging cotton ropes in pig pens. After being chewed by the animals, ropes are manually squeezed and the resultant oral fluid samples are collected in sterile tubes. In trained pigs, a rope hung for 30 minutes in a pen 25/28 pigs is representative for 75% of the animals housed in that pen. OF is used as a diagnostic matrix for the detection of pathogens and pathogen-specific antibodies. MJ defined as “drip fluid released from meat after freezing and thawing” is a sample type usually collected at the slaughter line. Meat samples for testing are tissue samples of roughly 3 cm, collected from diaphragmatic and neck muscles. After collection samples are stored at -20°C for at least 12 h and thawed in special containers to release the meat juice, which trickled into a collecting tube. MJ samples are mainly used in serological assays to monitor infectious diseases. PF are serosanguinous fluids recovered from piglet at the time of piglet castration and tail docking. Tissues are wrapped in a disposable gauze which allows fluids to pass through it and be collected in a clean bucket. To improve the yield of fluids, samples can be refrigerated. PF can be used for the detection of antigens and/or antibodies against a variety of pathogens. One of the major advantages of the PF and the OF specimens as well is due to the fact that can be collected at both the individual or group level (pooled samples). By using pooled samples, a large number of animals can be tested for a reduced cost, compared with the cumulative cost of individual testing. Optimization of commercial immunoassays is required to show the efficient application of alternative blood matrices. This review summarizes the main alternative biological matrices other than blood, focusing on the optimal conditions of their collection and their application for diseases monitoring in pig herds.