Nutritional strategies to combat Salmonella in mono-gastric food animal production.

Nutritional strategies to minimize Salmonella in food animal production are one of the key components in producing safer food. The current European approach is to use a farm-to-fork strategy, where each sector must implement measures to minimize and reduce Salmonella contamination. In the pre-harvest phase, this means that all available tools need to be used such as implementation of biosecurity measures, control of Salmonella infections in animals at the farm as well as in transport and trade, optimal housing and management including cleaning, disinfection procedures as well as efforts to achieve Salmonella-free feed production. This paper describes some nutritional strategies that could be used in farm control programmes in the major mono-gastric food production animals: poultry and pigs. Initially, it is important to prevent the introduction of Salmonella onto the farm through Salmonella-contaminated feed and this risk is reduced through heat treatment and the use of organic acids and their salts and formaldehyde. Microbiological sampling and monitoring for Salmonella in the feed mills is required to minimize the introduction of Salmonella via feed onto the farm. In addition, feed withdrawal may create a stressful situation in animals, resulting in an increase in Salmonella shedding. Physical feed characteristics such as coarse-ground meal to pigs can delay gastric emptying, thereby increasing the acidity of the gut and thus reducing the possible prevalence of Salmonella. Coarse-ground grains and access to litter have also been shown to decrease Salmonella shedding in poultry. The feed can also modify the gastro-intestinal tract microflora and influence the immune system, which can minimize Salmonella colonization and shedding. Feed additives, such as organic acids, short- and medium-chain fatty acids, probiotics, including competitive exclusion cultures, prebiotics and certain specific carbohydrates, such as mannan-based compounds, egg proteins, essential oils and bacteriophages, have the potential to reduce Salmonella levels when added to the feed. These nutritional strategies could be evaluated and used in farm control programmes.

Salmonella contamination: a significant challenge to the global marketing of animal food products.

Salmonellosis is the most common food-borne bacterial disease in the world. Salmonella is a significant pathogen for food-producing animals and these animals are the primary source of salmonellosis. It is estimated that herd prevalence varies between 0% and 90%, depending on the animal species and region. The pathogen is spread by trade in animals and non-heated animal food products. The emergence of strains that are resistant to antimicrobials, often as a result of antimicrobial usage in animals, is a public health hazard of great concern. It is increasingly accepted that the prevalence of Salmonella in animal production must be decreased and, in the European Union, plans to achieve this are currently being implemented. In this paper, the authors propose various risk mitigation strategies. Successful control must focus on a range of preventive actions because there is no simple 'silver bullet' solution to reduce Salmonella contamination. The authors conclude that the key to controlling Salmonella is to follow the general rules that have been successfully applied to other infectious diseases.

The experience of reducing antibiotics used in animal production in the Nordic countries.

The Nordic countries (Denmark, Finland, Norway and Sweden) have a long tradition of infectious disease control in animal production. Special attention has also been paid to the use of antibiotics. This has resulted in a relatively low use of antibiotics and also relatively favourable status of antibiotic resistance. The current situation, interventions and achievements are summarised with special reference to Sweden which was probably the first country where stringent control and prudent use of antibiotics was put into practice. The use of antibiotics for growth-promoting purposes is highlighted.

The Swedish experience of the 1986 year ban of antimicrobial growth promoters, with special reference to animal health, disease prevention, productivity, and usage of antimicrobials.

In Sweden the use of antimicrobial growth promoters (AMGP) was banned in 1986. The experiences gained from that ban are presented. In production of slaughter pigs, specialized beef, and turkeys, no negative clinical effects were reported as a consequence of the ban. In broiler chicken production, expected problems with necrotic enteritis were prevented by a continuous use of antibiotics, largely to the same extent during the first 2 years after the ban. Following the implementation of results from experimental activities during that period, the general usage of antimicrobials could be stopped and expected problems with outbreaks of necrotic enteritis was prevented. In piglet production, significant clinical problems emerged that created a demand for antibiotic-medicated feed at therapeutic dosages. During the subsequent 4-year period, the use of antibiotics increased, involving up to 75% of the pigs. Thereafter, the use of antibiotics decreased because of improved management, and could be halved in 1993 followed by a gradual further decrease supported by the addition of zinc oxide to the feed. In 1998, compared to 1994, the total use of zinc decreased by 90%. In 1998/1999, only 5% of weaning piglet producing herds used antibiotic medicated feed and 17% used zinc. The AMGP ban has shown that under good production conditions it is possible to reach good and competitive production results for the rearing of poultry, calves, and pigs without the continuous use of AMGP. As a result of the ban and a focus on disease prevention and correct use of antimicrobials, the total use of antibacterial drugs to animals in Sweden decreased by approximately 55% during the last 13-year period, and a relatively low prevalence of antimicrobial resistance has been maintained.

The control of microbial diseases in animals: alternatives to the use of antibiotics.

In animal husbandry the control and prevention of infectious diseases is of basic economic importance. The introduction of antibiotics to treat bacterial infections almost 50 years ago led to a dramatic improvement in animal production. The emergence of antibiotic resistant strains demonstrates that the treatment of bacterial infections can not rely on the use of antibiotics without some critical consideration. Special attention has been paid to the use of antibiotics in animals including antimicrobial growth promoters because these can contribute to the problems with antibiotic resistance in humans. This has strongly emphasized the need to introduce disease preventive methods. A theory and methods for the prevention of diseases is presented that is based upon the effect on the target animal population of microbial exposure, defence and immunity to infections and combinations of these. It is emphasized that antibiotics should be an integral part of other disease preventive methods and used only when other methods have failed. They should not be included in the first line of action.

Vaccination and eradication programme against Aujeszky's disease in five Swedish pig herds with special reference to herd owner attitudes.

A vaccination eradication programme against Aujeszky's disease (AD), based on the use of gE-negative killed vaccine, was carried out between 1987 and 1992 in 5 Swedish weaner pig producing or farrow-to-finish herds, with 63 to 398 breeding animals. All breeding animals were tested at the start and the end of the programme. Seroprevalence to Aujeszky's disease virus (ADV) ranged between 47% and 100% in the herds at the first test. During the programme, all breeding animals were vaccinated simultaneously every 4 months and ADV-free replacement animals were vaccinated shortly after arrival and boostered within a month. In one herd only, a limited number of fatteners were vaccinated. The herds were declared free (gE-negative) 12 to 53 months after the start of the programme. When all seropositive breeding animals had been culled, the programme ended after 2 negative tests of the breeding animals. Seroconversion was limited in all herds but one, where initially no isolation unit was available for replacement animals. The attitude of the herd owners towards the programme and the special conditions prevailing in the herds are discussed. It is suggested that vaccination may promote risk behaviour of herd managers.

Patterns of seroconversion to Aujeszky's disease virus in unvaccinated chronically infected Swedish weaner pig-producing herds.

This study was carried out in nine unvaccinated Swedish weaner pig-producing herds, ranging in size from 20 to 134 breeding animals, which had experienced a previous outbreak of Aujeszky's disease (AD) and in which seropositive sows were still present. The objective was to quantify the seroconversion rate to Aujeszky's disease virus (ADV) in breeding animals and to find out whether unvaccinated herds could become free from ADV by using only seronegative animals for replacement. Serum samples were initially obtained from all adult pigs in the herds. Animals testing negative, as well as replacement animals, were subsequently tested every second or third month and the herds were followed for 10-28 months. The herd owners were advised to keep seropositive and seronegative animals separate whenever possible and to implement sanitary measures against the reintroduction of the virus into the herds. All herds experienced long consecutive periods (> or = 4 months, median 9 months) without seroconversion. Three herds became free from ADV during the serological study; in two of these herds no seroconversion was observed. In those seven herds where seroconversion occurred, between 9 and 86% of the susceptible pigs became infected. The reinfection was indicative of the reactivation of latent virus in all herds but two, where the reintroduction of the virus was most likely. The pattern of seroconversion was either sporadic, involving not more than three animals at a time, or epidemic, involving a large proportion of the susceptible animals in the herd. Severe clinical outbreaks hit the two largest herds and these only became ADV-free after the conclusion of the study when vaccine was used, which reduced the incidence of seroconversion to zero. The results from the present study show that it is possible for smaller herds to achieve freedom from ADV without any radical control methods, provided that only ADV-free replacement animals are used and the virus is not reintroduced. Moreover, the finding that long periods can elapse without transmission suggests that when infection is discovered in a herd, the risk of massive spread is not necessarily imminent.

Eradication of Aujeszky's disease virus from a Swedish pig herd using gI-/TK-vaccine.

An attenuated glycoprotein I-negative (gI-)/thymidine kinase-negative (TK-) constructed vaccine was used to eradicate Aujeszky's disease virus from a large farrow-to-finish herd in Sweden. The herd had had problems every year for seven years and two attempts to eradicate the virus without vaccination had failed. At the start of the vaccination programme 86 per cent of the 396 breeding animals were seropositive to the virus. In spite of evidence of virus circulation in the fattening units, no fatteners were vaccinated. The breeding stock was vaccinated every four months and monitored serologically. Seropositive sows and boars were culled at an economic rate. During the programme, four breeding animals seroconverted to gI. Another seven animals which seroconverted to gI were suspected to have been infected shortly before the first test and vaccination. When all the seropositive breeding animals had been culled, the fattening units were sampled and no seropositive animals were found. The herd was declared gI-negative 39 months after the start of the programme. Monitoring of the herd for another four years, until all the vaccinated animals had been culled, showed that the herd remained free from Aujeszky's disease virus.

Agricultural policy and social returns to eradication programs: the case of Aujeszky's disease in Sweden.

Economic-welfare analysis of animal disease prevention programs frequently ignore the constraints of the agricultural policy environment. Prevention programs affect producers, consumers and the government. The policy environment to a large extent determines the magnitude as well as the distribution of benefits of the program among these groups. The Swedish hog industry has been exposed to three major policy changes during the 1990-1995 period. These scenarios involve various degrees of government intervention in the agricultural sector including internal market deregulation and EU-membership. Aujeszky's disease is a virus disease with swine as the natural infection reservoir. Piglets are the most fragile and an outbreak of the disease results in symptoms such as shaking, cramps and convulsions with an increase in the mortality rate. Slaughter hogs suffer from coughing, fever and reduce their feed consumption. During the last 20-25 years the incidence of Aujeszky's disease (AD) has been increasing in Sweden. In 1989 an eradication program was undertaken. A model is developed to analyze social benefits of an eradication program given variations in agricultural policy. The model refers to the specifics of the AD-program implemented in Sweden. The expected benefits of the program are evaluated using a welfare-economic analysis applying cost-benefit analysis. Total benefits of the program are evaluated across herd and size categories and different regions. Data concerning the frequency of the virus among various categories of herds prior to enacting the program were used (Wahlström et al., 1990). In addition, data from an agricultural insurance company were used to estimate the conditional probability of an outbreak given that the herd is infected. Biological and technical parameter values were collected from a variety of sources. The results of the analysis indicate that the program is economically viable given a social rate of discount in the range of 3-5% without considering non-monetary aspects such as animal ethics. A scenario where the Swedish agricultural sector is deregulated provides the maximum benefits of the program. Consumers obtain about 50% of the benefits excluding program costs. The deregulation scenario would correspond closely to a case where a reformed Common Agricultural Policy (CAP) is applied across member countries. In the current case where Sweden is a member of the EU, the benefits are reduced mainly due to lower prices of inputs and pork.

Control of Salmonella enteritidis in Sweden.

The Swedish control of Salmonella, with special reference to Salmonella enteritidis, in poultry is described. The control is directed at all serotypes of Salmonella and imported grandparent chickens are controlled, which is considered to be the main reason why Sweden so far is not found to be involved in the worldwide spread of different phagetypes of S. enteritidis. However, this spread has initiated a more stringent control of Salmonella in layers as earlier existed in broilers. Since 1990, 90% of the layer flocks are voluntarily tested for Salmonella before slaughter by bacteriological examination of pooled faecal samples. If S. enteritidis is isolated the flock is destroyed. This test, and in addition two similar tests during the production are mandatory as of January 1st, 1994. The voluntary Salmonella control programme has also been extended to all of the layer parents and hatcheries since 1991. Only heat-treated feed is given to all layer chickens during the rearing period and its use is becoming gradually more common also during the production period. Since 1987, four layer flocks have been found to be infected by S. enteritidis phagetype 4 and one flock with phagetype 6. During 1970-1984, 90% of all flocks of broilers were voluntarily tested bacteriologically for Salmonella before slaughter, and since 1984 such a control is mandatory to all flocks. As a result of this and other controls, S. enteritidis has not been isolated from broilers since 1972. Based on a governmental regulation from 1961, introduced as a result of a large Salmonella epidemic in 1953, Sweden runs an active, official control of Salmonella (Wierup et al., 1992).(ABSTRACT TRUNCATED AT 250 WORDS)

Experience of a 10-year use of competitive exclusion treatment as part of the Salmonella control programme in Sweden.

In Sweden, competitive exclusion (CE) treatment has been used since 1981 as a part of the national control programme for Salmonella. According to the programme all broiler flocks are tested for Salmonella before slaughter thus providing an evaluation of CE treatment. The CE culture used is mainly for the two consecutive flocks raised in a unit after a Salmonella-infected flock has been identified. During the period 1981-1990 Ce culture has been given to 179 flocks, involving 3.82 million chickens. Only one of the treated flocks was found to be Salmonella-positive. A special study during a period when Salmonella was spread by contaminated feed demonstrated that CE treatment was effective in controlling Salmonella under field conditions. A likely contributory factor is that the hatcheries in Sweden can be claimed to be Salmonella-free. In addition, the control programme and related action, have led to a very low incidence of Salmonella in broiler chickens. A nationwide study carried out in 1990 demonstrated that less than 1% of broiler chickens was contaminated with Salmonella after slaughter.

Salmonella isolated from animals and feedstuffs in Sweden during 1983-1987.

This survey describes the frequency of Salmonella in animals and feedstuffs isolated in Sweden 1983-1987. Since 1949 National Veterinary Institute (NVI) has published such reports every fifth year. During the period of this report 760 outbreaks of Salmonella were reported in animals. This includes both domestic and wild animals. The corresponding figure for the previous period was 1266 outbreaks. 56 different serovariants were reported, 17 of these were new to Sweden. In cattle and swine there were a decrease of outbreaks. In poultry 86 outbreaks were reported, compared with 220 outbreaks during the previous five-year period. Swedish feed producing plants are checked both voluntary and compulsory, for the presence of Salmonella in raw materials, scrape and dust samples and compound feed. During 1983-1987 a total of 236 strains at Salmonella were isolated. This is the lowest incidence found during the last 15 years. All consignments of feedstuffs of animal origin intended for import to Sweden has to be examined for the presence of Salmonella. During 1983-1987 8.6% of the consignments were positive for Salmonella and were thus not allowed to be used in Sweden.

Vaccination and eradication programme against Aujeszky's disease in Sweden, based on a gI ELISA test.

A killed gI-negative vaccine combined with a gI enzyme-linked immunosorbent assay (ELISA) test was used for the first time in Sweden in an attempt to eradicate Aujeszky's disease from a weaner pig producing herd. The herd had experienced three severe outbreaks of the disease during a 10 year period and at the start of the programme 96 per cent of the herd's 104 breeding animals were seropositive to the Aujeszky's virus. In addition, there was serological evidence of active virus circulation among younger animals. During the programme, all breeding animals were vaccinated every sixth month and replacement animals were tested free of disease and vaccinated before entry into the herd. When the originally seropositive animals had been rotated out of the herd, all breeding animals and a sample of weaner pigs were tested twice at six weeks' interval. No seroconversions to gI had taken place and the herd was declared Aujeszky's disease-free, 22 months after the start of the programme.

Experimental infections of goats with Mycoplasma mycoides subspecies mycoides, LC type.

In five experiments 29 goats were infected experimentally by five different routes with a strain of Mycoplasma mycoides subspecies mycoides, LC type, isolated from a contagious caprine pleuropneumonia-like outbreak on a farm in northern Sweden. All the goats were colonised except those inoculated subcutaneously with small doses. In its pattern of pathogenicity this strain was similar to other experimentally tested strains except that peroral infection in kids produced no clinical signs. A 'contact' goat was also colonised but the clinical signs seen in it were probably due to a concomitant infection with Pasteurella haemolytica.

Epidemiological evaluation of the salmonella-controlling effect of a nationwide use of a competitive exclusion culture in poultry.

The purpose of the study was to evaluate the salmonella contamination-controlling effect of a nationwide use of a competitive exclusion culture in poultry. During a 5-yr period, a bacterial flora from caecum of adult birds was given to broiler chickens in order to control salmonella infection. The culture was given on 144 occasions to a total of 2.86 million chickens. The base for the evaluation was the compulsory and regular control for salmonella contamination conducted according to the salmonella control program applied to Sweden. Epidemiological evaluation, especially in relation to the use of the culture during a period when salmonella was spread from a feed factory, strongly supports the conclusion that the culture has a salmonella contamination-preventing effect under field conditions, as earlier had been found in laboratory studies. Questionnaires answered by producers did not indicate significant adverse effects of the treatment.

Animal consumption of antibiotics and chemotherapeutic drugs in Sweden during 1980, 1982 and 1984.

The total animal consumption of antibiotic and chemotherapeutic drugs in Sweden during 1980, 1982 and 1984 has been studied. The study also included coccidiostatic, antiparasitic and antimycotic drugs. The total animal consumption during the years mentioned was 66.1, 68.8 and 72.6 tons of active substance, respectively, and the amount of antibacterial drugs for therapy was 28.7 (43.4%), 29.1 (42.5%) and 34.1 (47.0%) tons, respectively. Tetracycline, penicillin, sulphonamide and aminoglycoside were the four major groups of antibiotics used for therapy of bacterial infections in animals. The consumption was related to the metabolic bodyweights of animals which were the potential consumers. A comparison was also made with the corresponding human consumption during 1980. The data on antibiotic consumption can be divided by county and compared to the animal population and disease situation in each county. This study thus offers a good base for further investigations on different aspects of the use of antibiotics.