Frank Møller Aarestrup
2. Consumption of Antimicrobial Agents for Food Animals
In modern food animal production antimicrobial agents are normally used in one of four different ways, i.e. i) therapy: treatment of infections in clinically affected animals, preferably based on a bacteriological diagnosis, ii) metaphylactics: treatment of clinically healthy animals belonging to the same flock or pen as animals showing clinical signs; In this way infections may be treated before they become clinically apparent and the entire treatment period may thereby be shortened. In fact, in view of the modern productions systems, such may often be the only effective approach to treat for instance large broiler flocks through water medication, iii) prophylactics: treatment of healthy animals in a period of stress (e.g. early weaning) to prevent disease; in such cases the use of antimicrobials is indicative for general management problems, and hence in most countries is either illegal or considered imprudent; and, finally, iv) growth promotion: the continuous inclusion of antimicrobials in animal feed to prevent (subclinical) infections and hence promote growth; such usage is under serious recent debate.
It is difficult to obtain good information about the consumption of antimicrobial agents for medical and growth promoting purposes. Exact figures are scarce and estimates are only available for a few countries. In the United States the consumption of antimicrobial agents increased tremendously from 1950 to 1978. In 1951, a total of 110 tonnes were produced for addition to animal feed and for other applications, whereas 580 tonnes were produced for purely medical use in humans and animals (Black 1984). In 1978, 5,580 tonnes were produced as feed additives, 6,080 tonnes for medical use in humans and animals: a 50-and 10-fold increase, respectively. British estimates on the 1996 situation mention Frank Møller Aarestrup
approximately 650 tonnes antimicrobials for animal therapy, and 100 tonnes for growth promotion (Harvey and Mason 1998). For humans approximately 470 tonnes were used in 1997 (Harvey and Mason 1998).
The pharmaceutical industry has estimated the world market for animal health products at 11 billion ECU in 1995. Therapeutic pharmaceuticals accounting for 44% (4.8 bill.) and feed additives for 41% (4.5 bill.) (FEDESA, 1997). Figures were not given for growth promoters and it is not known whether therapeutic pharmaceuticals include agents that are used for both therapy and growth promotion.
In a recent report the European Agency for the Evaluation of Medical Products (EMEA, 1999) estimated the amounts of antimicrobial agents used in 1997 for treatment and growth promotion of food animals in the different EU countries. The estimates for the production of animals from 1996 were also given. In Figure 1 the usage of antimicrobial agents to produce one kilogram of meat in the different EU-countries is given.
Although the validity of some of these data is difficult to assess, and in the realisation that in different countries differences in production systems exist, it is obvious that in the various countries there are major differences in the amounts of antimicrobial agents used to produce the same amount of meat. This provides room for major reductions in those countries that comparatively overdose antimicrobial agents.
Frank Møller Aarestrup
0 40 80 120 160 200
Aus tria
Belgiu m + L
ux. Denm
ark Finla
nd France
Germa ny
Gre ece
Ireland Italy
The Ne
the rlan
ds Portuga
l Spain
Sw ede
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United Kin gdo
m Usage in mg per kg meat produced
Therapy Growth promotion
Figure 1. Milligram of antimicrobial agents used in 1997 per kilogram of produced meat in the different countries in the European Union (source EMEA 1999).
Until recently, more antimicrobials were used as growth promoters than as therapeuticals (Aarestrup et al., 1998a; 1998b). Concerns, that such use of antibiotics might destroy their therapeutic efficacy because of increased resistance led in 1969 the Swann committee (Swann, 1969) to recommend antibiotics to be exclusively used for treatment of animal and human infections. This recommendation was only partly adopted by the European Union in their Guidelines for approval of antimicrobial growth promoters.
In 1995, the Danish authorities observed an increase in the use of antibiotics for treatment of animals. Furthermore, their use as growth promoters came under increased scrutiny.
Avoparcin was banned in Denmark because they select vancomycin resistant enterococci, and in view of the potential risk of resistance transmission to humans over the food chain.
In 1997, avoparcin was banned in all EU-countries.
In January 1998, virginiamycin was banned in Denmark because of cross-resistance to Synercid, a streptogramin used for human treatment. In December 1998, the European Commission decided to ban the use of bacitracin, spiramycin, tylosin and virginiamycin for growth promotion from the 1stof July 1999 onwards.
In Denmark the food animal industries have decided to voluntarily stop all use of antimicrobial growth promoters from the end of 1999, and for the last 2 years they have worked to achieve this goal. Consequently, the use of growth promoters has decreased significantly during 1998 and 1999.
Frank Møller Aarestrup
Table 1. Consumption of growth promoters in Denmark during 1990 through 1998.
Growth promoter 1990 1992 1994 1995 1996 1997 1998 1999 2000
Avilamycin 10 853 433 1,665 2,740 670 7 91
-Avoparcin1,3 13,718 17,210 24,117 5,690 - - - -
-Bacitracin3 3,983 5,657 13,689 7,910 8,399 8,544 3,945 63
-Carbadox3 850 7,221 10,012 1,181 1,985 4,153 1,803 293
-Flavomycin 494 1,299 77 48 18 93 6 665
-Monensin 2,381 3,700 4,755 5,007 4,741 3,08 935 0
-Olaquindox3 11,391 21,193 22,483 16,213 13,486 17,595 28,445 9,344
-Salinomycin 12 0 213 850 759 460 113 0
-Spiramycin3 0 0 95 507 15 3 0 0
-Tylosin3 42,632 26,980 37,111 52,275 68,350 62,009 13,148 1,827
-Virginiamycin2,3 3,837 15,537 2,801 2,590 5,055 10,644 892 -
-Total 79,308 99,650 115,786 93,936 105,548 107,179 49,294 12,283 0
1Banned in May 1995 in Denmark
2Banned in January 1998 in Denmark
3Approval suspended in EU in 1999
As stipulated by Danish regulations all sales of veterinary medicines must take place by prescription of a veterinarian. The use of antimicrobials increased between 1986 and 1994 (Table 2). This concurred with a simultaneous increase in the production of pigs in Denmark. However, this production increase alone could not explain the increase. The fluctuations in the total quantity of antimicrobials used were not associated with animal health problems. In the mid-1990s large amounts of tetracyclin were used as prophylactics.
In 1995, the regulations for delivery of therapeutic antibiotics to farmers and for sale of antimicrobial for therapy were changed, removing the economical incentive for veterinarians to sell antimicrobials to farmers. Consequently, the consumption decreased.
During 1996 and 1997, the total consumption of antimicrobial agents has increased.
However, this increase correlates rather well with the simultaneous increase that has taken place in the production of food animals. Following the total stop in using growth promoters for pigs at the end of 1999, an increase in the use of antimicrobial agents for therapy seems to have taken place. However, it is still too early to tell whether this holds true in the long run.
Concurrently with the institution of the ban on growth promoters, the Danish Veterinary Laboratory and the agricultural organisations have provided extensive information to farmers and veterinarians on how to react if they experience problems with diarrhoea or other diseases. This is a very important step to avoid problems with infections when one refrains from the use of antibiotic growth promoters.