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Antimicrobial Feed Additives for Swine--Past and Present and

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2021-02-16 22:49
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2021年2月16日发(作者:wasted)



Antimicrobial Feed Additives for Swine: Past,


Present and Future Trends



Livestock Update, February 2004



Allen Harper, Extension Animal Scientist


?


Swine, Tidewater AREC and


Mark Estienne, Swine Research Physiologist, Tidewater AREC



Background



Sub-therapeutic levels of antimicrobial feed additives have been used in


swine feeds since the 1950's for improved growth rate and feed efficiency


and to maintain pig performance in the presence of sub-clinical disease. The


most effective use is in the diets of weanling and young growing pigs but


responses are also obtained in finisher pigs and breeding swine. Over 15


years ago Zimmerman (1986) summarized the data from 239 separate


experiments and reported that average improvement response to


antimicrobial feed additives in starter pigs was 15% for growth rate and 6%


for feed efficiency. In older growing-finishing pigs the improvement was 4%


for growth rate and 2% for feed efficiency. It is believed that weanling and


starter pigs are more susceptible to stress and sub-clinical disease and


consequently show a greater response to growth promoting antimicrobial


products. Studies have also indicated that both starter and finisher pigs have


a greater response to antimicrobials under farm conditions than at swine


research facilities, possibly because the disease, sanitation and housing


stresses are typically greater at commercial farms than in research facilities.


The consistent effectiveness of antimicrobial feed additives has led to


extensive use in the swine feeding industry. Cromwell (2001) estimated that


80 to 90% of all starter pig feeds, 70 to 80% of all grower pig feeds, 50 to


60% of all finisher pig feeds and 40 to 50% of all sow feeds are fortified


with antimicrobial feed additives. There are 18 antimicrobial feed additive


products currently approved by the U.S. Food and Drug Administration for


use in swine diets (Table 1). General reviews on the use and effects of


antimicrobial feed additives for swine are available from Cromwell (2001)


and in Pork Industry Handbook fact sheet 31, Feed Additives for Swine


(Parker and co-workers, 1994).


Despite their effectiveness, continued use of antimicrobial growth promoters


faces a very uncertain future. In 1999, the European Union of agricultural


ministers banned the use of virginiamycin, spiramycin, tylosin phosphate


and zinc bacitracin (Smith, 1999). In addition, avoparcin, olaquindox and


carbadox are also not allowed for use as growth promoters in Europe. In this


country the U.S. Food and Drug Administration (FDA) and Centers for


Disease Control (CDC) have called for an extensive reevaluation of


continued use of antimicrobial feed additives (Smith, 1999, Elliott, 2001).


One concern associated with use of antimicrobial feed additives is the


potential for antimicrobial residues in meat products of treated animals. For


this reason certain antimicrobial feed additives have a legally required


pre- slaughter withdrawal period during which time the animals must not be


fed the product before shipping for slaughter (Table 2). Table 1.


Antimicrobial Agents Approved for use in Swine Feeds


a



Generic Name


Apramycin


Arsanilic acid


Bacitracin methylene


disalicylate


Bacitracin zinc


Bambermycins


Carbadox


Chlortetracycline


Lincomycin


Neomycin


Oxytetracycline


Penicillin


Roxarsone


Sulfamethazine


Sulfathiozole


Tiamulin


Tilmicosin


Tylosin


Virginiamycin


a


Classification


Example Trade Names


Antibiotic


Apralan


Chemotherapeutic


Pro-Gen 20%


Antibiotic


Antibiotic


Antibiotic


Antibiotic


Antibiotic


Antibiotic


Antibiotic


Antibiotic


BMD


Baciferm


Flavomycin, Gainpro


CTC, Pennchlor


Lincomix


Neomix,


Neo-terramycin


OXTC, Pennox


CSP-250, CSP-500


Chemotherapeutic


Mecadox


Chemotherapeutic


3-Nitro


Chemotherapeutic


Tylan 40 Sulfa-G


Chemotherapeutic


CSP-250, CSP-500


Antibiotic


Antibiotic


Antibiotic


Antibiotic


Denagard


Pulmotil 90


Tylan 40, Tylan 100


Stafac


Source: Feed Additive Compendium, 2004.


Table 2. Antimicrobial Feed Additives Requiring a Pre- slaughter


Withdrawal


a



Generic name


Apramycin


Carbadox


Neomycin


Example trade name


Pre- slaughter withdrawal (days)


Apralan


Mecadox


Neomix Ag 325


28


42


3


Terramycin



Oxytetracycline


10 - 50 grams/ton


0


10 mg/kg body weight


5


Oxytetracycline +




Neomycin sulfate


Neo-Terramycin 50/50


5


Roxarsone


Sulfamethazine


Sulfathiozole


3-Nitro 20


Tylan 40 Sulfa-G


CSP-250, CSP-500


Denagard


10 grams/ton


35 grams/ton


200 grams/ton


Pilmotil 18


5


15


7



0


2


7


7


Tiamulin


Tilmicosin


a


Source: Feed Additive Compendium, 2004.


An even greater concern among regulatory agencies and consumers is the


potential that regular use of antimicrobial feed additives may lead to the


development of resistant microbes that may compromise the effectiveness of


antibiotics in treating animal and human disease. But, there is considerable


debate as to whether the use of antimicrobial feed additives will lead to a


significant risk of inability to treat disease. For example, long-term studies


have shown that using feed grade antimicrobials on swine farms for


extended periods of time does lead to the development of resistant


organisms but that the growth promoting effects of the products continue to


be realized. Furthermore, within a herd in which antimicrobial use was


suspended for over 13 years, significant levels of resistant microbe strains


were still identified (Langlois and co- workers, 1986). Nevertheless the


impetus for banning antimicrobial feed additives in food animal production


is very strong. Such forces as consumer acceptance, export markets and


medical community directives are likely to force loss of some, if not all


antimicrobial feed additives for performance enhancement in food animals.


Can We Produce Pigs without Antimicrobial Feed Additives?



The simple (and absolutely correct) answer to this question is a definite yes.


There are currently a limited but growing number of small producers that


grow pigs without antimicrobial feed additives for


specialty markets. And more conventional producers are reducing the


quantity of antimicrobials being used. However, what is less apparent is


what producers have to give up in terms of pig productivity and efficiency if


antimicrobial feed additives are not used.


The issue has stimulated interest in alternatives to antimicrobial feed


additives. Included among potential alternatives are complex mannose


carbohydrates termed mannanoligosaccharides derived from the cell wall of


yeasts. There is evidence that dietary inclusion of mannanoligosaccharides


has immunomodulatory properties and may improve growth performance of


weanling pigs (Spring and Privulescu, 1999). So-called probiotics are a


second category of potential replacements for antimicrobial growth


promoters. Probiotics generally refer to viable microbial cultures that are


intended to increase the gastrointestinal population of beneficial microbes


while competitively excluding bacteria that may depress health or growth


performance (Cromwell, 2001).


At the Virginia Tech Tidewater AREC we assessed two commercially


available feed additives in 5-week nursery pig trials as potential alternatives


to traditional antimicrobial feed additives (Harper and Estienne, 2002). In


trial 1 a mannanoligosaccharide (Bio-Mos, Alltech Incorporated) was


evaluated with the antimicrobial feed additive carbadox (Mecadox, Phibro


Animal Health). Treatments included: 1) a control diet with no supplemental


feed additive; 2) a diet containing Bio-Mos (0.3% during wk 1 and 0.2% for


wk 2-5); 3) a diet containing carbadox (50 grams/ton); and, 4) a diet


containing both additives.


Results are summarized in Table 3. There were no main effects of Bio-Mos


supplementation and no interaction effects of Bio-Mos and carbadox in


combination (P > 0.40). The main effects of carbadox supplementation were


an 8 % increase in feed consumption and a 9 % improvement in growth rate


(P < 0.01).


In trial 2, a probiotic product (BioMate-2B, Chris Hansen Biosystems)


consisting of Bacillus licheniformis and subtilis was assessed. Treatments


included: 1) a control diet with no feed additive; 2) a diet containing


Bacillus additive (0.1%); 3) a diet containing carbadox (50 grams/ton); and,


4) a diet containing both additives.


Results are presented in Table 4. For the overall 5-wk trial there was no


Bacillus by carbadox interaction (P > 0.44) and no Bacillus main effect

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