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INTRODUCTION

The 2017 summary report by the FDA on antibiotic use Antimicrobials Sold or Distributed for Use in Food-Producing Animals clearly demonstrated the effect of restrictions on the use of antibiotics in livestock for other than therapeutic purposes. An additional component was placing the onus on the Veterinary profession to prescribe and authorize antibiotics for livestock. The Report documents a reduction of 33 percent in sale and hence consumption of medically-important antibiotics for animal use between 2016 and 2017. A significant observation is that antibiotics used to produce chickens declined by 47 percent to represent 4.8 percent of livestock use in 2017 compared to 2016. Administration of antibiotics to turkeys declined 11 percent from 2016 to represent 12 percent of all livestock use.

The summary report issued by the FDA complies with Section 105 of the Animal Drug User Fee Act of 2008 (ADUFA) which requires drug manufacturers to report for each calendar year:-

• A listing of each antimicrobial active ingredient manufactured and distributed

• A description of each product sold by unit indicating dosage and concentration

• A listing of target animal species

• Differentiation between domestic use and exports. For practical purposes, more than 99 percent of antibiotics of human-health significance were used domestically.

  The regulation of antibiotics in livestock production is the subject to a series of Guidance Documents issued by the FDA. These include:-

• FDA Guidance Document #152, issued in October 2003 - This classified antibiotics according to critical importance for human medicine and proposed the VFD Rule including removal of medically-significant drugs from over-the-counter status.

• FDA Guidance Document #209, issued in April 2012 - This eliminated all growth promotion claims for antibiotic compounds. Ionophore anticoccidials and bacitracin in various forms were excluded as not being of human-health significance. This Guidance Document provided the framework for voluntary adoption of judicious use of medically- important antimicrobials based on a series of studies reviewed by the FDA extending from 1969 (the UK Swann Report) to a 2011 WHO report specifically dealing with emerging antibiotic resistance worldwide.

• FDA Guidance Document #213, issued in December 2013 - This effectively banned the use of antibiotics for growth promotion and placed antibiotics under veterinary supervision with specific criteria for issuing a VFD for feed or a prescription for water administration.

  RELEVANT STATISTICS

  The important conclusions from the 2017 FDA Summary Report comprise:-

• Tetracyclines are the most significant class of antibiotics used in livestock production representing 32 percent of the 10.9 million kg of active compound used in 2017 and 64 percent of the subtotal of medically-important antibiotics amounting to 5.6 million kg. Penicillins represented 12 percent and 6 percent respectively of medically important and total antibiotic use followed by macrolides at 8 percent and 4 percent respectively.

• Between 2016 and 2017 use of all medically-important antibiotics declined by 33 percent from 8.4 million kg of active compound. Ionophore anticoccidials are not medically-important but in the U.S. may be regarded as having an antibiotic activity on the intestinal biome, showed a 6 percent decline from 2016 to 2017 compared to an 18 percent increase over the years 2009 through 2017. Reduction may in part be due to adoption of anticoccidicals vaccines associated with production systems characterized as 'drug-free' relying on anticoccidial vaccines or complying with USDA Certified Organic rules.

• Among the antibiotic and chemotherapeutic compounds, sulfas declined by 26 percent and cephalosporins by 5 percent, penicillins by 18 percent, macrolides by 15 percent and aminoglycosides by 19 percent. Fluoroquinolones however increased by 24 percent albeit to a relatively low value of 22,904 kg.

• Between 2009 and 2017, antimicrobial drugs for food producing animals increased by 11.4 percent reflecting a 1.4 percent per annum increase, reflecting expansion in production volume to a total of 10.9 million kg of active compound. From 2016 to 2017, domestic use of all antibiotics for livestock decreased by 22 percent.

• Among the medically-important antimicrobial approved for use in food producing animals, chickens (principally broilers) fell 47 percent from 2016 to 2017 to a total of 268,047 kg. During the period 2016 to 2017, antibiotic use in turkeys declined by 11 percent to 670,831 kg. The egg-production sector uses virtually no antibiotics other than small quantities for pullets based on restrictions imposed by the FDA on administration to laying hens.

• The differential between antibiotic use in chickens and turkeys should be related to live mass produced. It is assumed that all 'chicken' antibiotic was used by the broiler industry. It is accepted that 8.5 billion broilers were produced in 2017 at a unit live weight of 2.8 kg. Based on the use of 268,047 kg of active antibiotic, use amounted to 0.01g per kg live mass. In the case of turkeys 244 million birds at a weighted live mass of 15 kg (allowing for tom and hen weighs and their respective production) were marketed. With 670,831 kg antibiotic uptake in the turkey sector, use amounted to 0.18 g per kg live mass. Effectively the turkey industry uses 18 times more antibiotic per unit of live mass than broilers. This reflects both the magnitude of disease challenge, pathogens involved and the training, experience and challenges faced by Veterinarians involved in turkey production.

• Among the major antibiotic and chemotherapeutic classes, tetracycline use in chickens declined from 2016 to 2017 by 46 percent but increased by 23 percent in turkeys. For penicillins, turkey use decreased by 20 percent with negligible use in either year for chickens. For macrolides, chicken use decreased by 87 percent but turkey use increased by 11 percent. For lincosamides, chicken use declined by 7 percent with negligible use in turkeys. For aminoglycosides, chicken use declined by 16 percent but in contrast turkey use increased by 8 percent.

• The report documented that 62 percent of antimicrobial drugs approved for use in food-producing animals were added to feed. This represented 3.43 metric tons of active ingredient compared to 30 percent in water or 1.66 metric tons among all species.

• In 2017 antibiotics were not used at sub-therapeutic levels to promote performance as mandated by Guidance Document #213.

• In 2017, considering all antimicrobials drugs approved for use in food-producing animals 5 percent was sold over-the-counter (271 metric tons). Of the remaining 95 percent, 32 percent was administered under Veterinary prescription and 63 percent under a VFD, comprising a total 5.6 million metric tons.

• For feed administration in all food-producing animals, sulfas declined by 72 percent between 2016 and 2017, tetracyclines by 45 percent and all other antibiotics by 26 percent. This suggests that the VFD imposing professional judgment and prudence, resulted in an effective reduction in use of antibiotics. The decline of the various antibiotic classes in water was less pronounced with sulfas lower by 23 percent and penicillins by 20 percent albeit from relatively small base volumes. The exception was the penicillin class amounting to 559 metric tons by the water route under prescription.

• For chickens, non-medically important antimicrobial drugs declined by 13 percent to 1.5 million metric tons and turkey use declined by 5 percent to 358 metric tons. The uptake in cattle declined by one percent to a total of 3.14 million metric tons.

• Of the non-medically important antibiotics administered to all food-producing species, 21 percent were for therapeutic indications, 2 percent for production and 77 percent was classified as the combined category of 'production and therapeutic'. This denotes that veterinarians are forced to make decisions relating to administration of antibiotics in what could be regarded as "gray area" reflecting a total 4.1 million metric tons of antibiotic consumed in 2017. Since ionophores are not medically important, the combined 'production and therapeutic' category in all probability includes this class and would not be related in any way to transmissible drug resistance.

  CONCLUSIONS

• The introduction of the VFD with concurrent elimination of OTC availability of antibiotics including those of human-health significance markedly reduced sales and hence administration to food-producing animals.

• Based on comparative species data, broilers and to a lesser extent turkeys have not contributed historically to the total use of antibiotics compared to ruminants and hogs.

• A disparity between antibiotic use in broilers and turkeys based on unit of live mass marketed is noteworthy and suggests that notwithstanding reductions in use of medically- important antibiotics, alternative modalities are required to reduce antibiotic use in this sector of the poultry industry.

• Despite the reduction in use of antibiotics in the broiler industry, USDA and commercial benchmark reporting systems have not indicated any increase in either mortality or condemnation or a reduction in live mass or feed conversion efficiency between 2016 and 2017. The question arises as to whether antibiotics were in fact over-used as contended by opponents of intensive livestock and poultry production. Requiring VFDs and prescriptions to authorize administration of antibiotics of human-health significance has clearly reduced antibiotic use in all sectors of the livestock industry but especially in poultry veterinary medicine where professional prudence is clearly evident. This is exemplified by the number of board-certified veterinarians now affiliated with production companies in both the broiler and turkey industries who exercise individual and collective judgment on use of antibiotics.

• The restrictions imposed by members of the National Restaurant Association, the National Chain Restaurants Association and the Food Marketing Institute concerning the use of antibiotics has complemented the activities of Veterinarians in restricting antibiotic use. Market factors are clearly driving the trend towards reduced use of antibiotics both for prophylactic and therapeutic purposes. The poultry industry in the U.S. led in displacing antibiotics for performance enhancement.

• The U.S. broiler and turkey industries can be proud of the transition from reliance on antibiotics to prudent use under accepted FDA and ethical principles.