Background

This agent is a fastidious intracellular bacterium, necessitating methods other than traditional bacterial culture to find an understanding of the true nature of the epidemiology and economics of Ileitis on pig farms. It was therefore only after novel PCR and serology methods were validated and applied widely as the veterinary vision of Ileitis as a perhaps occasional cause of diarrhoea and acute deaths, shifted to include that of a widespread, endemic and costly “background” disease, affecting over 90% of European pig farms.

The clinical signs in affected post-weaned animals can include diarrhoea, and reduced weight gains of varying degrees, due to distinctive pathological lesions in the lower bowel. In pigs older than 12 weeks, such as fattener or breeder pigs, more acute clinical signs can also occur, with the lesions accompanied by rapid onset of bleeding from the affected intestines, leading to bloody scours and sudden death. Subclinical infections are very common and may be defined as reduced production parameters (weight gain, feed conversion, uniformity etc) due to identifiable gut lesions of Ileitis, but without obvious diarrhoea or weight loss in affected pigs.

Oral medication of groups of pigs has been used commonly to control Lawsonia intracellularis via oral antibiotics such as tiamulin, lincomycin and tylosin. These antibiotics have been relatively successful in alleviating Ileitis in controlled experimental and field study situations and are approved by various regulatory authorities for that purpose. However, their use entails a cost burden and has also led to concerns about potential future development of transmissible drug resistance and spurred the development of a Lawsonia vaccine. We assessed that an oral vaccine may be effective, because the bacteria are taken up following oral infection by gut macrophages, then specific antibody and T-cell responses occur.

For intracellular bacterial pathogens, like Lawsonia intracellularis, live attenuated bacteria offer the most “natural” immunity and are widely considered the best form of vaccine approach (see Kroll et al. 2004). This paper summarises estimates of the economic impact of clinical and subclinical Ileitis. The costs of subclinical Ileitis can be difficult to explore and were analysed via data from challenge exposure studies of pigs with low or mild doses of Lawsonia intracellularis, which produced a subclinical Ileitis, compared to control pigs; also field studies of pigs with and without subclinical Ileitis.

Methods to analyze the incidence and costs of subclinical Ileitis

Subclinical Challenge Exposure Studies and Field Studies Analysis of a series of challenge exposure studies resulting in mild clinical and subclinical Ileitis was presented in a previous study (see McOrist et al. 1997). Subsequently, a study of groups of pigs given low or moderate doses of Lawsonia intracellularis via a similar challenge exposure model was reported (see Paradis et al. 2005) and analysed in the same manner. Field studies were analysed from both published reports of subclinical Ileitis (see Fourchon and Chouet 2000) and unpublished studies in the USA, German and Australian pig farms.

The general aim of these studies was to compare farms with subclinical Ileitis to farms with clinical Ileitis and/or case-control negative farms. A problem with these analyses is that it can be difficult to define these categories in the field and often requires diagnostics (such as serology) and field measures for feed conversion, weight gain and death losses. It is also vital that the various groups of farms are matched as closely as possible for factors such as pig genetics, other disease status, and type of diets. Studies were only included in this analysis if the control and subclinical Ileitis pigs were derived from the same genetic source and received feed from the same feed mill operations.

Biological observations and analysis – Several biological parameters were noted for each group of pigs in challenge exposure or field trials that resulted in case-controlled subclinical Ileitis, including weight gain, feed conversion ratio and mortality. Animals and their group feed consumption were usually weighed at least twice, to calculate each group’s average weight gain (kg/d) and feed conversion ratio (kg of feed consumed per kg of weight gain).

Economic observations and analysis for subclinical diseases

These biological values were converted into the suggested costs for clinical and subclinical Ileitis that come in several areas:

• The death or removal of a moribund fattener pig can be assessed in two ways.
  • the lost or opportunity market value at slaughter, minus the feed costs saved in the period between death and slaughter age.
  • the full costs of feed, housing and labour up to death or removal.
• The additional costs of death for breeding pigs will include the lost opportunity of future piglets and genetic improvements.
• A feed conversion problem due to Ileitis is usually assessed via the costs of the increased feed and housing costs per pig actually sold.
• A reduced weight gain in a grower pig can be assessed in two ways:
  • the cost of a reduced market weight, such as for a date-specific delivery contract.
  • the increased feed and facility costs for holding pigs longer, such as for a predetermined market weight contract.
• An increased variation in the weights of pigs sold can be assessed via an estimation of a standard matrix weight contract, which normally has penalties for light pigs. So for example, the costs for deviation from a premium rate for market pigs conforming to a range of 100–110 kg live weight.
• An increased back-fat depth due to the growth check suffered by pig with Ileitis can be assessed via an estimation of a standard back-fat depth matrix, which normally has penalties for over-fat pigs. So for example, the costs for deviation from a premium rate for market pigs conforming to 10 to 12 mm.
• The actual costs of medications and feed additives used on the farm, aimed at improving these production measures for Ileitis.
• Some indirect costs of a disease such as Ileitis come in the forms of veterinary and feed investigations, and the laboratory costs of disease diagnosis.

Surveys of the overall prevalence of Ileitis in most pig-raising regions now suggest that over 90 percent of European farms have some kind of active on-going infection, as noted by Sylvie Chouet et al (2003). On single-site, continuous-flow farms, infections typically start to build up in grower pigs at about 6 to 10 weeks of age, and remain active throughout the fattener and breeder pigs.

The cost for each economic parameter (market value, facility costs, labour costs and so on) and input were assessed from pig industry sources such as NPPC and BPEX and related commercial documents, such as the one by Tony Fowler (2005). The biologic data and other inputs were then processed to economic figures by a standard budgeting process (Excel Partial Budget), resulting in a format comparing affected and control pigs and the total extra costs of Ileitis.

Results of studies of economic costs of subclinical Ileitis

Chart 1: Differences in Feed Conversion Ratio and Average Daily Gain between challenged and non-challenged animals in three separate trials due to a subclinical Ileitis.

A summary of the biological data for a typical study comparing subclinical Ileitis with control pigs is shown in Chart 1, derived from a study by Marie-Ann Paradis et al (2005). In that study, specific groups of a total of 144 pigs developed subclinical cases of Ileitis after oral challenge with low doses of Lawsonia intracellularis and were compared to groups of healthy control pigs.

In summary, the results were that the average daily live-weight gain (ADG) is reduced by 37 to 42% and the feed intake required per kg of weight gain (FCR) is increased by 27 to 37% in the groups with subclinical Ileitis. Similar charts were prepared from all the other studies listed and analysed as described.

Analysis of these negative impacts on slaughter weight, feed conversion efficiency, space utilisation, and other morbidity effects as annotated above, were calculated to total at least € 3 per affected growing pig on a farm with subclinical Ileitis. A more exact calculation would depend on establishing an exact price for slaughter pigs, building pig spaces, labour, feed, contract specifications etc, for a particular farm or region. So for example, the costs of subclinical Ileitis may be much higher for a grow-out fattening farm with a tight slaughter weight or back-fat matrix contract that has steep “cliffs” or penalties for light-weight pigs or fatty pigs, delivered to the slaughterhouse.

Discussion of Economic costs of subclinical Ileitis

These estimates of the economic impact of clinical Ileitis and subclinical Ileitis (that is, pigs being infected and having some intestinal lesions, but without clear diarrhoea or weight loss), include the key impacts of sub-optimal weight gains and improper food utilisation, particularly the negative impact of Ileitis on digestion of in-feed amino acids in the pig. A study by Tim Rowan and Tom Alexander in 1982 showed the major reduction in amino acid uptake in Ileitis-affected pigs during a nutritional study.

The impact of Ileitis is sometimes felt first in breeding pig operations, Losses from deaths due to acute Ileitis in boars or breeding gilts represent a severe penalty in terms of lost breeding potential (future piglets, genetic improvements) as well the actual feed, housing and labour costs per pig lost. A common estimate is that each sow death loses the farmer around € 300. A further hidden side to the overall impact of endemic Ileitis has been its possible longer term effects on breeding herd performance, highlighted by Mauch and Bilkei (2005). That study presented evidence that breeding pigs with clinical infections can suffer lingering negative impacts on parameters such as the number of pigs born alive. This led to an estimated loss of up to another € 100 per affected breeding pig.

The total losses due to endemic subclinical Ileitis on most European farms could therefore regularly total € 3 or more per affected grower-fattener pig. So for example for a European farm producing say 5,500 fattener pigs per batch from 500 sows, with 30% percent of pigs with subclinical or clinical Ileitis in the grower-fattener period and suffering say 10 deaths per year in the breeding herd, could suffer costs from Ileitis of around € 37,000.

In contrast to many interventions that can add costs to production, use of vaccination for Ileitis actually allows for a level of cost reduction, as targeted feed medications can be removed or greatly reduced in vaccinated groups of pigs. This can have specific beneficial effects in marketing and prices obtained for this antibiotic-reduced pork. Japanese supermarket buyers routinely pay a 20% premium for imported pork from pigs kept free of antibiotics in the last 100 days before slaughter. European customers are also now routinely demanding premium pork from pigs with fewer antibiotics in their feed. Despite the short years since the elucidation of the cause of Ileitis, its endemic nature across Europe, its major economic impact and its variable time of onset persuasively indicate that a vaccine approach is the most logical for long lasting control. It is possible that successful vaccines for endemic intestinal diseases may provide innately more positive growth and feed utilisation impact than those for diseases in other body systems, such as the lungs. The rapid progress in understanding of the epidemiology of Ileitis with modern tools and a vaccine has led to an appreciation of its hitherto underestimated impact on a range of pig performance parameters.

Some references on the economics of Ileitis

Chouet, S., Prieto, C., Mieli, L., Veenhuizen, M.F., McOrist, S. (2003): Some patterns of exposure to Lawsonia intracellularis infection on European pig farms. Veterinary Record, 152, 14–17.
Fourchon A, Chouet S. (2000): Technical results of swine herds and serological results on pigs for Lawsonia intracellularis. Proc IPVS 16, p 62.
Fowler, A (2005): The cost of pig production in selected EU countries. MLC – BPEX, ISBN 1-904437-18-4.
Kroll, J.J, Roof, M.B., McOrist, S. (2004): Evaluation of protective immunity in pigs following oral administration of an avirulent live vaccine of Lawsonia intracellularis. American Journal of Veterinary Research, 65, in press.
Mauch, C-P, Bilkei, G. (2004): Reproductive performance of gilts following an outbreak of acute proliferative enteropathy due to Lawsonia intracellularis. Veterinary Journal 170, 128–131.
McOrist, S., Gebhart, C.J., Boid R, Barns SM. (1995): Characterization of Lawsonia intracellularis gen.nov., sp. nov., the obligately intracellular bacterium of porcine proliferative enteropathy. International Journal of Systematic Bacteriology 45, 820–825.
McOrist S, Smith SH, Green LJ. (1997): Estimate of direct financial losses due to porcine proliferative enteropathy. Veterinary Record 140, 579–581.
McOrist S. (2005): Defining the full costs of endemic porcine proliferative enteropathy. Veterinary Journal 170, 8–9.
Paradis, MA, McKay RI, Wilson JB, Vessie GH, Winkelman NL, Gebhart CJ. (2005): Subclinical Ileitis produced by sequential dilutions of Lawsonia intracellularis in a mucosal homogenate challenge model. Proc AASV 36, p189–192.
Rowan, TG, Alexander TJL. (1982): Amino-acid digestibility with signs of porcine intestinal adenomatosis. Veterinary Record 110, 306–307.
Veenhuizen MF, Elam TE, Soenksen N. (2002): Porcine proliferative enteropathy: diagnosis and impact. Compendium Continuing Education 24, S10–S15.

Further Information

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June 2006