Antimicrobial use, meat inspection findings, and salivary biomarkers as porcine health-related indicators

Ill health in pigs may be difficult to notice and as pigs are typically group-houssed, infectious diseases can easily spread. Antimicrobials are commonly used to treat these diseases, which increases the development of antimicrobial-resistant bacterial strains, and threatens the efficacy of currently available antimicrobials. Therefore, it is necessary to lower the need to use antimicrobials in pigs. This could be achieved by investigating methods to improve porcine health, as well as methods that allow the detection of diseased pigs as early and as easily as possible. This dissertation is built upon three separate studies (I–III). In Study I, antimicrobial use (AMU) on nine commercial Finnish piglet-producing and fifteen finishing farms was investigated. Antimicrobial treatments of all age groups present on these farms during one year were obtained from the health classification register for pig farms in Finland (Sikava). Data on meat inspection (MI) findings during one year for sows and finisher pigs from Sikava was gathered, and the prevalence of MI findings was compared with overall AMU (as mg/PCU) and the treatment incidence (TI) of different disease categories in sows and finishing pigs. Furthermore, antimicrobial susceptibility testing of the indicator Escherichia coli (E. coli) bacteria isolated from pooled fecal samples, collected at the pen level from one unit on each farm, was conducted. Greater overall AMU (as mg/PCU) on piglet-producing farms compared to that on finishing farms, and the highest TI for piglets compared with sows and finishing pigs was expected. As expected, large between-farm variation was observed regarding all the parameters studied, and overall AMU (as mg/PCU) was higher on piglet-producing farms compared to finishing farms. When quantified as TI and in percentage terms, suckling piglets were most frequently treated with antimicrobials, followed by sows, weaned piglets, and finishing pigs. The surprisingly high AMU in sows warrants further investigation. Altogether, seven antimicrobial groups were used on the study farms, and penicillin was by far the most used antimicrobial, regardless of the age group. Antimicrobials belonging to the World Health Organization list of critically important antimicrobials for human medicine (CIA) were also used, mainly consisting of amoxicillin and lesser amounts of fluoroquinolones, tylosin, and long-acting tulathromycin. The majority of pigs were individually treated with injectable antimicrobials, whereas oral group treatments were administered only occasionally. Pleuritis was the most common MI finding recorded at slaughter, but was more prevalent in finishing pigs than in sows. Notably, the majority of the relationships between AMU and the prevalence of MI findings were negative, indicating that the greater the AMU, the fewer the MI findings. The occurrence of AMR on both farm types was similar. In general, resistance occurrence in E. coli indicator bacteria was low, and bacteria most often showed phenotypic resistance against tetracycline, sulfamethoxazole, trimethoprim, and ampicillin. Novel methods for pig health assessment include the determination of inflammatory and immune biomarkers from porcine saliva samples. In pigs, among the proposed salivary biomarkers are acute phase protein haptoglobin (Hp) and immune biomarkers adenosine deaminase (ADA) and immunoglobulin G (IgG). In Study II, we validated under experimental conditions whether salivary Hp and ADA are appropriate inflammatory biomarkers in growing pigs using a lipopolysaccharide (LPS) model. Sixteen healthy female growing pigs were randomly allocated to two groups that intravenously received either saline only or saline accompanied by LPS. Repeated saliva samples were collected from these pigs prior to injections, and four times during a 72-hour period after injections. As expected, the concentrations of Hp and ADA increased as a result of LPS administration, being indicative of an acute phase reaction (APR). The dynamics of both biomarkers followed a similar course, with a significant peak measured at four hours post-injection and then a rapid return close to the baseline in the LPS group between four and 24 hours post-injection. Moreover, there was a significant correlation between Hp and ADA responses at four hours post-injection in the LPS group. Study II confirmed that the studied biomarkers are indicative of systemic acute phase immune activation under experimental conditions in growing pigs. Some evidence suggests that salivary Hp and ADA concentrations in pigs are dependent on the production stage as well as the gender. However, longitudinal studies conducted under field conditions are scarce. Furthermore, the combination of several biomarkers may improve the diagnostic sensitivity. The objective in Study III, was therefore to investigate the dynamics of salivary Hp, ADA, and IgG, during a complete production cycle of commercial finishing pigs. Four Finnish piglet-producing farms and their respective four finishing farms were included in the study. Individual study pigs, including females and males, were selected at birth (n = 163) and followed until slaughter (n = 83). Saliva samples were collected four times, including the suckling, beginning and end of growing, and finishing stages. Finally, individual MI findings were obtained from the slaughterhouse, and the associations of biomarker concentrations in finishing pigs and MI findings were examined. Salivary concentrations of all the studied biomarkers differed significantly between production stages, always being highest in suckling piglets compared to later production stages. Some gender differences were found, with males more often having a numerically higher salivary biomarker concentration compared to females. Positive and significant relationships between the studied salivary biomarkers were found in other production stages apart from suckling piglets. The results indicate, and further confirm previous findings, that salivary biomarkers could be utilized for analytical purposes in pig disease diagnostics. No association was found between biomarker concentrations and MI findings, which could be related to the time that had elapsed between saliva sampling and slaughter, as well as to most of the reported MI findings being chronic. The present results indicated, that in the studied commercial pig farms, AMU was prudent and probably the good phenotypic bacterial resistance situation is the result of the rational AMU, which Finland has been working on for decades. Farm-level AMU that takes into account not only the amount but also treatment indications could be utilized in pig health care in the future. However, in order to evaluate the need to use antimicrobials in pigs, porcine health must be comprehensively monitored. Salivary biomarkers appear to be suitable for porcine health monitoring in farm circumstances, and especially in the detection of acute illness. However, they are not applicable for the selection of individual pigs to be treated or not due to their non-specificity. More knowledge about the normal variation in salivary biomarker concentrations is needed before their practical use in pigs.

Sikojen tarttuvia ja tulehduksellisia sairauksia hoidetaan yleisesti mikrobilääkkeillä, mikä lisää mikrobilääkkeille vastustuskykyisten bakteerikantojen kehittymistä. Sairauksien havaitsemista hankaloittaa ja tarttuvien tautien leviämistä edistää se, että sikoja kasvatetaan tyypillisesti ryhmäkarsinoissa. Näin ollen on tärkeää tunnistaa sikojen terveyteen liittyviä indikaattoreita, joiden avulla sikaryhmän sairaudet voitaisiin tunnistaa mahdollisimman varhaisessa vaiheessa ja mahdollisimman helposti. Syljen immunologisten biomarkkereiden mittaaminen on yksi ehdotetuista sikojen terveyttä koskevista indikaattoreista tilatasolla. Aikaisempien tutkimusten perusteella lupaaviksi sian biomarkkereiksi ovat osoittautuneet akuutin faasin proteiini haptoglobiini sekä immunologiset biomarkkerit adenosiinideaminaasi ja immunoglobuliini G. On viitteitä siitä, että sian syljen haptoglobiini- ja adenosiinideaminaasipitoisuudet riippuvat tuotantovaiheesta ja sukupuolesta. Tutkin väitöskirjassani mikrobilääkkeiden käyttöä ja lihantarkastuslöydöksiä suomalaisissa sikaloissa, sekä sian syljen biomarkkerien pitoisuuksia yksilötasolla. Lisäksi tutkin fenotyyppisen resistenssin esiintymistä sikojen ulosteesta eristetyillä indikaattori Escherichia coli -bakteereilla. Mikrobilääkkeiden käytössä havaittiin huomattavia eroja tilojen välillä, mikä oli odotettavissa. Suurimmalla osalla tiloista penisilliini oli käytetyin mikrobilääke, ja sitä käytettiin yksilöiden hoitoon, kun taas ryhmälääkitykset olivat harvinaisia. Keuhkokalvontulehdus oli yleisin lihantarkastuslöydös teurastuksen yhteydessä, ja useimmissa tapauksissa suurempi mikrobilääkkeiden käyttö oli yhteydessä lihantarkastuksessa todettujen löydösten vähäisempään esiintyvyyteen. Resistenssin esiintyminen oli yleisesti ottaen vähäistä. Toisessa väitöskirjan osatyössä vahvistettiin kokeellisissa olosuhteissa, että sekä syljen haptoglobiini- että adenosiinideaminaasipitoisuutta voidaan käyttää akuutin vaiheen immuunijärjestelmän aktivoitumisen indikaattorina. Viimeisessä väitöskirjani osatyössä tutkittiin syljen haptoglobiinin, adenosiinideaminaasin ja immunoglobuliini G:n dynamiikkaa tavanomaisissa tuotanto- olosuhteissa pidettyjen sikojen elinkaaren aikana. Kaikkien tutkittujen biomarkkereiden pitoisuudet erosivat merkittävästi tuotantovaiheiden välillä, ja ne olivat aina korkeimmat imevillä porsailla verrattuna myöhempiin tuotantovaiheisiin. Lukuun ottamatta imeviä porsaita, tutkittujen syljen biomarkkereiden välillä löydettiin positiivisia yhteyksiä. Löydös viittaa siihen, että biomarkkereiden käyttö paneelina yksittäisten biomarkkerien määrityksen sijasta voisi antaa kattavamman kuvan sikojen terveydentilasta. Yksikään lihasikojen biomarkkeripitoisuuksista ei ollut yhteydessä lihantarkastushavaintoihin, mikä saattaa liittyä siihen, että suurin osa ilmoitetuista lihantarkastushavainnoista liittyi kroonisiin sairauksiin. Yhteenvetona voidaan todeta, että tilatason mikrobilääkkeiden käyttö vaikuttaa olevan mikrobilääkesuositusten mukaista tutkituilla suomalaisilla sikatiloilla, ja hyvä indikaattoribakteerien resistenssitilanne on todennäköisesti seurausta tästä. Jotta mikrobilääkkeiden käyttötarvetta sioilla voidaan arvioida, on sikojen terveyttä kuitenkin seurattava monipuolisesti. Syljen biomarkkerit näyttäisivät soveltuvan sikojen terveyden seurantaan tavanomaisissa tuotanto-olosuhteissa ja erityisesti akuuttien sairauksien toteamiseksi. Niitä ei kuitenkaan vielä voida hyödyntää yksittäisten sikojen hoitopäätöksen tekemiseen, koska ne eivät ole kovinkaan spesifisiä. Tutkimuksen perusteella vaikuttaa siltä, että imevien porsaiden kohdalla biomarkkerit eivät ole järkevä vaihtoehto sairauksien havaitsemiseen tilatasolla ja vanhempien sikojen osalta syljen biomarkkeripitoisuuksien normaalista vaihtelusta tarvitaan lisää tietoa ennen kuin niitä voidaan hyödyntää käytännössä eläinlääkärin ja sikatilallisten työssä.

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