Abstract

In 1986, antimicrobial growth promoters (AMGP) were banned in Sweden. All antimicrobials were classified as veterinary medicines and were made available only by veterinary prescription. In the production of slaughter pigs, eggs and specialized beef and turkeys, no negative clinical or economic effects were reported as a consequence of the ban. However, broiler chicken and piglet production faced problems. During the first two years after the ban, antibiotics were used in broiler production largely to the same extent as they had been used before the ban, mainly to prevent outbreaks of necrotic enteritis. Following implementation results of experimental activities, this usage was discontinued and expected problems with outbreaks of necrotic enteritis were prevented. In piglet production, significant clinical problems created a demand for antibiotic-medicated feed at therapeutic dosages. Four years after the ban this use involved 75 % of the weaner pigs. Thereafter, this use decreased by 50% in 1993 and continued to decrease through a general use of zinc oxide as additive to the feed. In 1995, only 11 % of weaning piglets were treated with antibiotic medicated feed. A currently ongoing program aims at a further decrease in the use of antimicrobials. It is possible to reach good and competitive production results for rearing of poultry, calves and pigs without the continuous use of AMGP. As a result of the ban and efforts to focus on correct use of antimicrobials, the total use of antibacterial drugs for animals has decreased by approximately 55% during the last 13 years.

Top of Page

Introduction

Organised control of infectious diseases in animal production has a long tradition in Sweden. These controls in different ways lead to a decreased demand of antimicrobials. This paper is limited to the clinical experiences gained when, in 1986, the use of antimicrobials for growth promoting purposes (AMGP) was banned and were only allowed, as for other antibiotics, to be used after veterinary prescription in therapeutic doses. The total pattern of the consumption of antibiotic drugs before and after the ban is presented. In a separate paper at this conference, the actions taken to prepare and motivate producers and practitioners for the change in use pattern of antibiotics and to introduce disease preventive measures needed because of the ban is presented.

Top of Page

Broiler Production

AMGP (nitrovin) started to be used in the 1970s. Its use almost completely eliminated existing problems with necrotic enteritis caused by toxin from Clostridium perfringens. However, some sporadic outbreaks of the disease occurred and it was evident that those were related to the type of AMGP and/or coccidiostat used. Nitrovin was gradually replaced by avoparcin and later on by virginiamycin.

As a consequence of the upcoming ban, different studies were undertaken to find ways to control necrotic enteritis in the absence of AMGP. It was concluded that many factors such as the construction and climate of stables, hygiene, management and feed can contribute to the outbreak of necrotic enteritis (Elwinger et al. 1992, 1993, 1996).

The results gained were summarised as follows (Engström, 1989):

• additions of enzymes acting on carbohydrates and the addition of certain probiotics to develop an adequate intestinal bacterial flora reduced the incidence of necrotic enteritis.
• dietary levels of protein were reduced and amino acids were added which also resulted in improved stable hygiene and animal health.
• feeding of whole wheat did not influence the prevalence of Clostridium perfringens but stimulated the skeletal muscle activity and reduced moisture in animal bedding.
• coccidiostats of the ionophore type used to prevent coccidiosis also protect against certain gut infections.

The results and experiences gained were continuously implemented. The most important change was to reduce the protein content in the feed and to have a composition richer in fibre and supplemented with enzymes. Cases of necrotic enteritis can today often be related to overriding the recommended level of protein in the feed. The feeding regimens employed were developed through close collaboration between the feed industry and the farmers.

In connection with the ban on AMGP, strong emphasis was also placed on improving animal environment because many diseases including necrotic enteritis have a multifactorial background. Notably airflow was inadequate in several units, which affected animal health negatively.

It was strongly felt by the parties concerned that the ban was implemented too quickly and enough time to adjust to the new situation was not given. This created initial difficulties, reflected in about 90% of broiler chickens being continuously treated with virginamycin at a dose of 20 ppm during the first year of the ban and in 1987 the corresponding treatment frequency was 100%. Prior to the ban virginamycin was dosed at 10 ppm.

During 1987 an alternative to the prophylactic virginamycin was introduced. This involved a two-day treatment with phenoxy methyl penicillin in drinking water in cases of outbreaks and in the beginning of 1988 that treatment had largely replaced the use of virginamycin. The amount of active ingredient of antibiotics used for treatment of necrotic enteritis subsequently decreased from about two tons of virginamycin in 1987 to 100 kg of phenoxy methyl penicillin in 1988 (Wierup et al. 1989). Since1995, the amount of antibiotics to prevent or cure outbreaks of necrotic enteritis is practically negligible, and today on those very rare occasions when outbreaks of the disease occur tylosin is used.

It should be noted that coccidiostats of the ionophore type now used have antibacterial effects and act prophylactically against necrotic enteritis and may improve growth rate. However, despite this, the sanitary situation of broiler chicken rearing in Sweden today would not have been reached without the above-mentioned enforcement.

Top of Page

Turkey Production

The situation for turkey production units was similar to that for broiler chicken production units. Before 1986 the AMGP were used solely as a prophylactic agent against necrotic enteritis and not as a growth promoter. The ban did not result in noticeable clinical problems or reduced growth rate.

Top of Page

Egg Production

Before the ban no AMGP were used in egg production. The use of zinc bacitracin had been discussed since it was used to improve production in other countries. In the egg production sector the ban in 1986 did not influence production. Neither are the animals treated with coccidiostats during the egg production period but problems with coccidiosis can be seen during the growing stage and are then concentrated to farms where the level of animal hygiene is not satisfactory. When laying hens are transported from a rearing unit to a producing unit they are sometimes given coccidiostats (amprolium). The availability of vaccine against coccidiosis has reduced the need of coccidiostats in floor-raising of laying hens.

Top of Page

Pig Production

Before 1986 practically all piglets were given the AMGP's, olaquindox or mecadox (50 ppm), from the start until they were delivered to the finishing units at an age of 10-12 weeks. Thereafter as finishing pigs they were given AMGP (avoparcin or virginamycin) until slaughter at the age of about 7 months.

The ban on AMGP did not create obvious clinical problems for growing/finishing pigs that in 1984, consumed 7.8 tons of active ingredient of virginamacin. Since 1997 the mean daily weight gain is above 850 grams and not known to be larger in countries where AMGP is used.

For piglet production, significant problems initially emerged as a consequence of the removal of olaquindox that was used for weaning piglets. Robertsson & Lundeheim (1994) studied the incidence of disease, mortality and growth rate in piglets from 220 producing units during 1986 and compared it with 1985. The study showed that the post-weaning mortality in the first year after the ban was significantly higher, about 1.5 percentage units compared with 1985. Similarly, the age at 25 kg increased by 5-6 days. Pre-weaning mortality and the number of piglets produced per sow and year, however, did not show significant differences between 1986 and 1985. An extended rearing period after the ban is also obvious from the National Pig Record by which the age of pigs tested at 30 kg increased by about two days from 1986 and onwards.

Despite the lack of alternative strategies at the time when the ban was introduced, the pig sector, in contrast to the broiler chicken sector, did not continue to use antibiotics on prescription. The use of olaquindox to weaning pigs was reduced by 82% (amount of active ingredient per pig produced) from 1985 to 1986 and by 33% from 1985 to 1987. Thereafter, however, more antibiotics were prescribed and the total amount used during the subsequent years, 1988 and 1989, was 5 and 6%, respectively, higher than in 1985 (Björnerot et al. 1996). Considering that the dosage prescribed from 1986 was about three times higher than the AMGP dosage employed previously, a smaller fraction of weaning pigs was treated with olaquindox after the ban or 12% in 1986, 55% in 1987, 75% in 1988 and 76% in 1989. Thereafter the use was continuously reduced during a four-year period and in 1993 it was 35%. From 1993-94 a further reduction occurred supported by the introduction of zinc oxide (See below)and in 1995 the proportion of pigs treated with olaquindox was 12%. During the period studied the annual production was approximately 4 million pigs.

In a study from 1994, Holmgren & Lundeheim, analysed the result from 55 piglet-producing herds in the western part of Sweden and concluded that the prescription of medicated feed to weaning pigs was clinically motivated and followed the recommended guidelines . From that study it is also obvious that the need for medicated feed differs markedly between herds and that these differences could be ascribed to housing and management systems. The production results were strongly related to the degree of segregated rearing systems and to the level of hygiene. In herds rearing post-weaning pigs on deep litter bedding both segregation and degree of hygiene was better and the use of antibiotic three to four times lower than in herds with pigs in traditional post-weaning pens. The study also underlines the differences by preventing weaning diarrhoea in units that lack or have limited facilities to arrange satisfactory sectioning and hygiene. Clinical problems emerging in the different herds could further seldom be prevented through single prophylactic environmental or rearing adjustments. In many cases, more thorough changes in production planning and in housing were needed.

After the ban on AMGP, numerous measures have been undertaken and are continuously being undertaken to optimise the rearing and production system and to employ available techniques concerning sectioning and age grouping and planned production. The ban also created a development towards new rearing systems. The weaning of piglets on deep litterbeds in large groups is one example and the so called birth to slaughter system which is based on production in the same pen from birth to slaughter is another (Olsson 1996). The adjustment of old buildings and pens to the new production system is expensive and before such an adjustment is done antibiotics are used to combat weaning diarrhoea in exposed herds. Holmgren and Lundeheim (1994) also found that the use of antibiotics prevented low production results in such herds.

Efforts have also been undertaken to adjust pig feed to the new situation. The most prominent changes have been lowering of the protein content, use of the protein content, use of water soluble fibers and supplementation with acids(Göransson et al 1995).The antisecretory factor to prevent liquid penetration to the gut induced by enterotoxin has also been used as preventive measures (Göransson et al 1993).

Since the end of 1993 zinc oxide has been used to prevent weaning diarrhoea as previously was employed in other countries in Europe since. Since 1992 it is permitted in Sweden to feed pigs starting two weeks before weaning with a feed containing 2000 ppm of zinc oxide. Zinc oxide was found to have a preventive effect on weaning diarrhoea equal to the effect reached when using olaquindox (Holmgren 1994). The use of zinc became widespread but due to actions taken (described separately) the usage has from 1994 to 1998 decreased by approximately 90 % (Odensvik et al 1999).In a separate study during 1998- 1999 of 350 herds in different parts of the country it was found that 17 % used zinc and 5% antibiotics to weaner pigs (Löfstedt and Holmgren, 1999).

In summary it is evident that the best production result can be gained without the continuous use of AMGP. However, all pig-producing herds do not have optimum conditions for production. This is reflected in the fact that certain production results seen before the ban of AMGP still have not been reached. The available data from production control data from herds used for evaluation of the ban in 1985-86 have also been evaluated for 1997. A comparison of the average values for 1997 with those for the first year after the ban (1986-1987) reveals post-weaning mortality to have decreased by 1-2 percentage units and the age at 25 kg to be reduced by 3.5- 4.5 days. The losses in these production parameters seen after the ban have thus not yet been fully recovered on a national bases. However, the progressive producers report better production results than before the ban of AMGP.

Top of Page

Specialized Beef Production

Already in the 1960s and -70s different antibiotics were used as AGP in concentrate and milk replacers for calves. The antibiotics used in low doses (50ppm) in the 1970s were bacitracin, manganbacitracin, zincbacitracin, flavomycin, oleandomycin and spiramycin. The purpose was to improve growth rate of the animals. The effect was, however, often doubtful and documented improvements in animal growth were only sometimes seen in repeated experiments (e.g. Wierup et al. 1975). The use of AGP in specialized beef production had more or less come to an end before the ban in 1986. Negative clinical or other effects as a consequence of the ban have not been reported. None of the AGP used in calves today are used as therapeutics.

Top of Page

Use of Antibacterial Drugs

The total usage of antibacterial drugs to animals in Sweden prior to and after the ban against use of antibiotic growth promoters has been studied in detail (Wierup et al 1987, Wierup et al 1989, Björnerot et al 1996, Odensvik and Greko 1998 and Odensvik 1999).In Table 1 the data since 1980 is presented. In contrast to previously presented data up to 1995, in this summary procaine has been excluded from the amount of procaine penicillin and data on the total consumption have been changed accordingly.

The total use of antibacterial drugs from 1980 to 1984 increased from 41.3 to 50.6 tonnes of active ingredient and decreased by 49% (24,8 tonnes) from 1984 compared with 1986 when veterinary prescriptions for all use of antibiotics were introduced. The distribution of antibacterial drugs from the feed factory decreased by 70% (from 31,. to 9.5 tonnes) during the same period. During the following years the total use of antibiotics increased but was then, during 1988 to 1994, stable at approximately 30 tonnes of active ingredient per year, a level approximately 35% below the level before the new legislation was introduced. The consumption then further decreased to 20.6 and 19.3 tonnes of active ingredient during 1996 and 1998 respectively. This means that the total use of antibacterial drugs in animal production has decreased by approximately 55% compared with the usage before the legislation concerning the use of growth-promoting antibiotics was introduced. This decrease is also at least of that magnitude when calculations is measured by dose units instead of weight of active substance of the antimicrobials (Greko 1998). In Table 2 is also presented the sales of antimicrobials divided into formulations intended for treatment of individual animals and for group treatment.

Top of Page

Summary

In production of slaughter pigs, specialized beef and turkeys no negative clinical effects were reported as a consequence of the ban on AMGP. Neither was egg production affected since no AMGPs were used in the feed during the production period. However, broiler chicken production and piglet production faced problems. In broiler production, antibiotics were used largely to the same extent during the first two years after the ban as before, mainly to prevent outbreaks of necrotic enteritis. Following implementation results of experimental activities this usage could be stopped and expected problems with outbreaks of necrotic enteritis was prevented.

In piglet production significant clinical problems emerged which created a demand for antibiotic-medicated feed at therapeutic dosages. During the subsequent four-year period the use of antibiotics increased, involving up to 75 % of the pigs . Thereafter the use of antibiotics decreased and could be halved in 1993 and thereafter a gradual further decrease occurred supported by the addition of zinc oxide to the feed. In 1998 the total use of zinc has decreased by 90 % since 1994 and in 1998/9 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 rearing of both poultry, calves and pigs without the continuous use of AMGP. In fact, the total use of antibacterial drugs to animals has decreased by approximately 55% during the last 13-year period due to the new legislation and efforts to focus on correct use of antibiotics in animal production. Today, this quite dramatic change has not negatively influenced the animal health status or productivity, with the exception of piglet production.

Table 1. Total quantity of antibacterial substances (kg active substance) for treatment of animals based on sales statistics from Apoteket AB (National Corporation of Pharmacies) (Based on Wierup et al, 1987, Björnerot et al 1996 Odensvik and Greko, 1998 and Odensvik 1999)