Possible impact of the “yellow card” antimicrobial scheme on meat inspection lesions in Danish finisher pigs

Abstract

In 2010, the “yellow card scheme” which was adopted by the Danish Veterinary and Food Administration imposed restrictions on pig farmers who used more antimicrobials than twice the average.

To study the potential impact on pig health, we looked into antimicrobial consumption and vaccine use data from the monitoring programme Vetstat, covering all treatments conducted on Danish pigs between January 2010 and July 2011. The decrease in antimicrobial consumption was pronounced for all age groups (sows/piglets, weaners and finishers) treated for either gastro-intestinal or respiratory disease. Evaluated over 12 months, use of vaccines increased in general: PCV2-related infections (+31%), gastro-intestinal disease (27%), respiratory infections (21%) whereas use of vaccines against other infections remained almost constant (−18%).

Data from meat inspection of finisher pigs from before and after introduction of the scheme were compared. This included 1.7 million finisher pigs originating from 2765 pig farms, slaughtered on one large Danish abattoir and covered the first 9 weeks in 2010 and 2011, respectively. Nine lesions of chronic nature and infectious origin and the code “condemned” were selected. The prevalence of these lesions was calculated. Logistic regression models with year and week as explanatory variables were used to identify whether the prevalence of a lesion changed from 2010 to 2011. Possible clustering due to correlation within herds and between weekly shipments of animals originating from the same herd was taken into account in the models.

The most common lesion seen was chronic pleuritis (∼23%) while the other lesions occurred less-commonly (<1%). For osteomyelitis, pleuritis, chronic arthritis and condemnation, no differences were observed between the 2 years. The prevalence of chronic peritonitis (OR = 1.5), umbilical hernia (OR = 1.2) and chronic enteritis (OR = 1.2) were statistically higher in 2011 compared to 2010, whereas it was lower for tail bite infection (OR = 0.6), chronic pericarditis (OR = 0.6), and chronic pneumonia (OR = 0.7) (P < 0.001). Moreover, in the condemned carcasses, chronic pneumonia plummeted as a lesion found in 2011 compared to 2010 (OR = 0.07, P < 0.0001). Our results indicate that marked reduction in use of antimicrobials is associated with a short-term increase in the prevalence of specific lesions found during meat inspection and higher coverage of vaccines against respiratory diseases might impact the prevalence of chronic pneumonia positively. Other factors that impact on pig health were not included in the study. Moreover, effect of productivity was not evaluated.

Introduction

Discussion about prudent use of antimicrobials in animal production is on-going. There is concern about the development of bacteria that are resistant to the antimicrobials commonly used to cure infections in both humans and livestock. However, it might be speculated that animal health might deteriorate if diseased animals are not treated, hereby jeopardising animal welfare.

In Denmark, much attention is on the consumption of antimicrobials in pigs, because pigs account for 79% of the total consumption of antimicrobials in livestock (DANMAP, 2010). This reflects that pig production is the predominant animal production in Denmark involving production of 28 million finisher pigs annually. The amounts of antimicrobials used per livestock unit are low in Denmark compared to other countries with a similar pig production (European Medicines Agency, 2011). This is the result of actions taken over the years to mitigate the risk related to antimicrobial resistance. Among others, use of antimicrobials for livestock is by prescription only, and all prescriptions are filed into a database called Vetstat (http://www.uk.foedevarestyrelsen.dk/AnimalHealth/Veterinary_drugs/forside.htm). The veterinary practitioner cannot make a profit on sales of antimicrobials, but will make the prescriptions at the level of species and the age group, and this will be recorded into the database. For pigs the age groups are (1) sows and piglets, (2) weaners, and (3) finisher pigs. Moreover, the indication is given (e.g. gastro-intestinal or respiratory disorder) and the type of antimicrobial substance (Stege et al., 2003).

In 1995, prophylactic use involving routine treatments of the majority of pigs in a herd for a given disease became illegal, and treatment was only allowed in diseased animals or animals in a well-defined incubation period (metaphylaxis) (Order (DK) 303/1995 – Anon., 1995 – later revised by Order (DK) 910/2006 – Anon., 2006). During 2010 and 2011, compliance with this prohibition was checked at the pig practitioners by representatives from the Danish Veterinary and Food Administration. Among others focus was on avoiding routine treatment of neonatal umbilical infections in pigs. However, according to pig practitioners, metaphylactic treatment of umbilical infections is often indicated – and therefore used – in neonatal pigs, among others for prevention of a later development of umbilical hernia and peritonitis.

Despite of the actions taken, the consumption increased between 2008 and first half of 2010. This led to a public debate about the use of antimicrobials in Danish pigs. As a reaction to this debate, two further reductive actions were implemented in July 2010. The first action consisted of a voluntary ban on use of cephalosporins in Danish swine herds for a 2-year period, adopted by the Danish pig industry. The voluntary ban on use of cephalosporins in pigs is unique in the world. As long as other effective antimicrobials for treatment of infections are available on the market, banning cephalosporins should in principle not reduce the possibility to treat diseased pigs.

The second action consisted of a so-called yellow card antimicrobial scheme adopted by the Danish government. According to this scheme, restrictions are imposed on farmers who use more than twice the average consumption of antimicrobials in one of the three age groups. By the end of 2010, this corresponded to approximately 10% of the pig farmers. The consumption in pigs is evaluated as animal daily doses (ADD) prescribed per 100 animals evaluated over the last 9 months by age group. Permit limits by December 2011 for a yellow card in ADD per 100 animal days depended on the age group and were 5.2 ADD for sows and piglets, 28 ADD for weaners, and 8 ADD for finishers. An example of a yellow card evaluation (in Danish) can be found here: http://www.foedevarestyrelsen.dk/SiteCollectionDocuments/25_PDF_word_filer%20til%20download/05kontor/Kort_Laesevejledning_VetstatGultkort.pdf.

In July 2010, farmers with an antimicrobial use close to these limits received a warning letter from the Danish Veterinary and Food Administration which stated that unless actions were taken to reduce the antimicrobial use, the producer would receive a yellow card by December 2010. A yellow card would result in requirement for various measures such as restrictions on oral medication usage and supervision from the authorities, and all at the expense of the farmer. The new policy was communicated directly to the farmers and their organisations as well as to the entire population through the general media such as television and newspapers. A decrease in the national antimicrobial consumption was seen in pigs; 13% during the last half-year of 2010 compared to the same half-year in 2009. The consumption in January–February 2011 was 25% lower compared to January–February 2010 (Andreasen et al., 2011). No other changes occurred with respect to antimicrobial policies apart from the voluntary ban on use of cephalosporins in pigs, the warning letter and the yellow cards sent out from December 2010 and onwards.

The recent introduction of the yellow card scheme in Denmark might be viewed as a large experiment – and from this it might be possible to learn what impact a marked decrease in use of antimicrobials will have on pig health. Therefore, it was decided to study the impact of the decrease in the use of antimicrobials on the health of the pigs. Meat inspection data were used to describe the health of pigs.