NUTRITION PIH-31
PURDUE UNIVERSITY. COOPERATIVE EXTENSION SERVICE.
WEST LAFAYETTE, INDIANA
Feed Additives for Swine
Authors
Gary Parker, University of Kentucky
Gary Cromwell, University of Kentucky
Virgil Hays, University of Kentucky
James McKean, Iowa State University
Reviewers
E. T. Kornegay, Virginia Polytechnic Inst. & State Univ.
George Meyerholz, USDA, Washington, D.C.
Dean Zimmerman, Iowa State University
Feed additives are nonnutritive compounds added to swine
diets for the purpose of enhancing animal performance. The major
ones used in swine diets are antibiotics, chemotherapeutics,
anthelmintics, probiotics, organic acids and copper sulfate. Of
these, antibiotics, chemotherapeutics, and anthelmintics are the
major feed additives used in swine feeds and have been exten-
sively used in the United States over the last 35 years.
Antibiotics and Chemotherapeutics
Antibiotics and chemotherapeutics are medications added to
swine feeds to improve health and performance. A list of com-
pounds and use levels that can be used for specific purposes such
as growth promotion, prevention of disease, and treatment of a
specific disease can be found by consulting the Feed Additive
Compendium (Miller Publishing Co, 12400 Whitewater Drive, Minne-
tonka, MN 55343, published annually). These medications, usages
and levels are determined by the Food and Drug Administration
(FDA). It is their responsibility to determine that products
intended for animal use are safe, effective, properly labeled,
and that food derived from treated animals is safe to eat.
Antibiotics are compounds produced by bacteria or molds that
inhibit the growth of other microorganisms. Chemotherapeutics are
chemically synthesized compounds that inhibit the growth of cer-
tain microorganisms. They may be used alone or in conjunction
with antibiotics for the purposes of enhancing growth and feed
efficiency, or for disease control in swine. It is generally
accepted that the beneficial effects of these compounds result
from alteration of the bacterial population within the animal's
digestive tract. The actual mechanism by which antibiotics and
chemotherapeutics exert the growth promoting effect has remained
an elusive unknown throughout the 35-year history of feeding
these compounds. A number of possible mechanisms have been sug-
gested:
(1) Metabolic Effect. The metabolic effect implies that
antibiotics directly influence the metabolic processes in the
animal. This is not a reasonable explanation, however, for those
antibiotics that are not absorbed from the intestinal tract.
(2) Nutritional Effect. Certain bacteria that inhabit the
intestinal tract synthesize vitamins and amino acids that are
essential to the host, while others compete with the animal for
essential nutrients. Shifts in bacterial populations due to the
feeding of antibiotics may result in a greater availability of
nutrients to the host animal. Antibiotics have been shown to
reduce the thickness of the intestinal wall, resulting in a
potential for greater absorption of nutrients. In addition, anti-
biotics reduce the total mass of the gut, so less nutrients are
wasted on these rapidly metabolized body tissues.
(3) Disease Control Effect. Antibiotics tend to suppress
those bacteria in the intestinal tract that cause subclinical or
nonspecific disease. These subclinical diseases prevent the
animal from performing to its maximum potential.
The response to antibiotics and chemotherapeutics seems to
be as large today as it was in earlier time periods1. Hays
(University of Kentucky, 1977) summarized many of the studies on
the value of antibiotics in swine diets from the period 1950-
1977, and Zimmerman (Iowa State University, 1986) surveyed the
literature on the effect of antibiotics on pig performance from
the time period 1978-1985. The data in Table 1 compare the aver-
age percentage improvements resulting from antibiotic usage in
the two time periods. The percentage improvements in rate of gain
and efficiency of feed utilization are similar for the two
periods. Antibiotics and chemotherapeutics remain the most con-
sistently effective feed additives for improving animal perfor-
mance.
There are many antibiotics, chemotherapeutics, and approved
combinations available for use in swine diets. The more common
additives and their withdrawal times are listed in Table 2.
Selection of a specific feed additive and the level necessary for
optimal response will vary depending on several factors: 1) the
stage of growth, with response being less as the pig increases in
age; 2) disease prevalence within the herd; 3) kind of additive;
and 4) the cleanliness and comfort of the environment.
____________________________________________________________________
|Table 1. Improvements in performance of pigs fed antimicrobials |
|during the years 1950-1985. |
| |
|_________________________________________________________________ |
| Improvement, % |
| _____________________________ |
| Years Periodsa Daily Gain Feed/Gain |
|_________________________________________________________________ |
|1950-1977b Starter 16.1 6.9 |
| Grower-Finisher 4.0 2.1 |
|1978-1985c Starter 15.0 6.5 |
| Grower-Finisher 3.6 2.4 |
|_________________________________________________________________ |
| |
|aStarter period from about 15 to 55 lb. and grower-finisher |
|from 55 to 200 lb. body weight. |
|bHays (1977); 15,689 pigs. |
|cZimmerman (1986); 10,083 pigs. |
|_________________________________________________________________ |
|Table 2. Withdrawal time for antibiotics & |
|chemotherapeutics in swine feeds.a |
| |
|______________________________________________________________ |
| Withdrawal time |
|Chemical name before slaughter |
|______________________________________________________________ |
|Bacitracin methylene disalicylate none |
|Bacitracin zinc none |
|Bambermycins none |
|Chlortetracycline none |
|Oxytetracycline noneb |
|Penicillin none |
|Tylosin none |
|Virginiamycin none |
|Apramycin 28 days |
|Arsanilic acid 5 days |
|Carbadox 70 days |
|Chlortetracycline/sulfamethazine/penicillin 15 days |
|Chlortetracycline/sulfathiazole/penicillin 7 days |
|Furazolidone 5 days |
|Furazolidone/oxytetracycline 5 days |
|Furazolidone/oxytetracycline/arsanilic acid 5 days |
|Lincomycin 6 days |
|Neomycin sulfate 20 days |
|Neomycin/oxytetracycline c |
|Nitrofurazone 5 days |
|Tiamulin 2 days |
|Tylosin/sulfamethazine 15 days |
|3-Nitro-4-hydroxyphenylarsonic acid 5 days |
|______________________________________________________________ |
| |
|aFeed Additive Compendium, 1989. |
|bAt 500 g/ton use level, withdraw 5 days before slaughter. |
|cWithdraw from feed 20 days befor slaughter when neomycin base |
|level is 140 g/ton and 5 days before slaughter when neomycin base |
|__________________________________________________________________|
Usage level of an additive or combination of additives must
comply with FDA approvals and the manufacturer's directions. The
FDA classifies additives into those that have a high degree of
human safety with no withdrawal time and those with a higher
potential risk for edible tissue residue. The latter have
specific withdrawal times before slaughter2 (Table 2). Producers
must responsibly use medications in their feeding program. They
must know the approved use levels and withdrawal periods of the
compounds they use. There is no extra-label usage (higher than
approved FDA levels or unapproved combinations) with feed addi-
tives.
Antibiotics and chemotherapeutics are not as commonly used
with breeding animals as in diets for growing pigs. Research has
shown antibiotics to be effective during certain critical stages
of the reproductive cycle, such as at the time of breeding. A
summary of nine research trials shows that a high level (0.5 to
1.0 gram/sow/day) of an absorbable antibiotic (such as one of the
tetracyclines) at the time of breeding improves conception rate
by 11% and improves litter size by .5 pigs/litter at the subse-
quent farrowing3 (Table 3). Generally, benefit from antibiotics
or chemotherapeutics in gestation diets is minimal unless the
disease level within the herd is quite high. Antimicrobial
agents are thought to be beneficial at farrowing and during early
lactation because the sow and her pigs are more vulnerable to
stress at this time. The data in Table 4 suggest that weaning
weights are increased by about 5% and pig survival increased
slightly when these agents are included in the prefarrowing and
lactation diet3.
____________________________________________________________________
| |
|Table 3. Effects of antibiotics at breeding on |
|reproductive performance of sows.a |
| |
|_________________________________________________________________ |
| Control Antibioticb |
|_________________________________________________________________ |
|Farrowing rate, %c 68.2 79.1 |
|Live pigs/litter 9.8 10.3 |
|_________________________________________________________________ |
| |
|aCromwell (1983); Data on 2,148 sows, 9 experiments, 1961-1985. |
|bIn most cases, .5-1.0 gram/sow/day prior to and after breeding. |
|cPercent of sows bred that farrowed. |
|_________________________________________________________________ |
|Table 4. Antimicrobial agents in the prefarrowing |
|and lactation diet for sows.a |
| |
|_________________________________________________________________ |
| Control Antimicrobialb |
|_________________________________________________________________ |
|Pigs born alive/litter 8.96 9.13 |
|Pigs weaned/litter 8.01 8.25 |
|Survival, % 89.4 90.4 |
|Weaning weight, lb. 8.78 9.20 |
|_________________________________________________________________ |
| |
|aCromwell (1983); Summary of 7 experiments, 787 litters. |
|bTetracyclines, chlortetracycline-sulfamethazine-penicillin, |
|tylosin or copper sulfate fed from 3-5 days prepartum through |
|__________________________________________________________________|
Anthelmintics
Swine are susceptible to infection with numerous species of
internal parasites (See PIH-44, Internal Parasites). These
parasites vary widely in structure, size, shape, habits, life
cycle, and extent of injury to swine. The pork producer has
available a wide array of anthelmintics (dewormers) that are very
effective in controlling several parasite species.
Some anthelmintics are more effective than others for cer-
tain species of worms. Producers should become aware of the
parasite spectrum and efficacy data of each anthelmintic. Anthel-
mintics may be added to swine feed for limited periods to kill
(purge) worm accumulation including worm eggs in
growing/finishing swine and the breeding herd. This type of
deworming program usually removes the immediate worm burden but
needs to be repeated (time period depends on specie of worm) for
improved control. Continuous feeding of some anthelmintic pro-
ducts will block development of parasites during the specified
feeding period. Currently, two dewormers on the market (pyrantel
tartrate and hygromycin) can be fed continuously in the diet.
These anthelmintics remove specific worm parasites, reduce the
immediate worm burden and help prevent the problem from recur-
ring. Withdrawal periods for the feed additive anthelmintics are
listed in Table 5.
Copper Sulfate
Elemental copper is a required nutrient for normal pig
growth and is routinely added to swine diets at the rate of 6 to
11 ppm to meet this requirement.
Copper sulfate possesses antibacterial properties and is an
effective growth promotant when fed at levels of 125 to 250 ppm
of copper (1 to 2 pounds of copper sulfate/ton of feed) in the
diet4,5. The addition of 250 ppm copper to swine diets improved
performance of weanling pigs and growing-finishing swine in tri-
als conducted at the University of Kentucky (Table 6). In young
pigs, the combination of copper and antibiotics gave a greater
growth response than the feeding of copper or antibiotics alone6
(Table 7).
Copper sulfate, when fed in excess of 250 to 500 ppm for an
extended period of time, may be toxic. The severity of the toxi-
city is directly related to the level fed, and is increased if
the diets are low in zinc and iron, and if the copper is fed for
a
Table 5. Withdrawal time for anthelmintics in swine feeds.a
_________________________________________________________________
Withdrawal time
Chemical name before slaughter
_________________________________________________________________
Dichlorvos none
Fenbendazole none
Piperazine none
Hygromycin B 15 days
Levamisole Hydrochloride 3 days
Pyrantel Tartrate 1 day
Thiabendazole 30 days
_________________________________________________________________
a Feed Additive Compendium (1989).
Reference to products in this publication is not intended to be
an endorsement to the exclusion of others which may be similar.
Persons using such products assume responsibility for their use
in accordance with current directions of the manufacturer.
Table 6. Effect of copper sulfate on performance of weanling and
growing-finishing pigs.
_________________________________________________________________
Copper, ppma Improvement
_________________________________________________________________
Growth Stage 0 250 %
_________________________________________________________________
Starting period (15 to 30 lb.)b
Daily gain, lb. .51 .62 21.6
Feed/gain 2.04 1.86 9.7
Growing period (40 to 123 lb.)c
Daily gain, lb. 1.47 1.56 6.1
Feed/gain 2.80 2.70 3.7
Growing-finishing period (40 to 205 lb.)c
Daily gain, lb. 1.56 1.63 4.2
Feed/gain 3.18 3.10 2.5
_________________________________________________________________
a Does not include copper in trace mineral mix.
b Cromwell et al., 1983. Summary of 12, 28-day experiments with
482 pigs weaned at 28 days of age, 44 replications of 4-8
pigs/pen, conducted at the University of Kentucky from 1978 to
1983.
c Cromwell et al., 1981. Summary of 18 experiments, 84
replications of four pigs per treatment, conducted at the
University of Kentucky from 1970-80.
long period of time. Therefore, producers should check with their
feed manufacturer about the level of copper sulfate, iron, and
zinc present in commercial feed before indiscriminately adding
additional copper sulfate to feed. Drawbacks to copper sulfate
supplementation include increased corrosion of galvanized metal
and decreased bacterial degradation of manure in lagoons.
Probiotics
Probiotics are mixtures of bacteria, yeasts or other
microorganisms that may be fed to pigs with the intention of
establishing a population of desirable microflora within the
intestine. The most common microorganisms included in probiotic
products are Lactobacillus species, Bacillus subtilis and Strep-
tococcus faecium and yeast (Saccharomyces cerevisiae). These
organisms, through competitive inhibition, favor the development
of desirable health promoting microorganisms that theoretically
improve weight gain and feed efficiency. To be effective, the
bacteria should be established as normal inhabitants of the
intestinal tract of healthy animals. They must also be able to
survive passage through the stomach and establish themselves in
the small intestine where digestion and absorption occur. They
should be acid and bile tolerant if they are to survive in the
digestive system.
It has also been suggested that the beneficial actions of
probiotics include7: (1) change the enteric flora and reduction
of E. coli; (2) synthesis of lactate with subsequent reduction in
intestinal pH; (3) adhesion to or colonization in the digestive
tract; (4) production of antibiotic substances; (5) reduction of
toxic amines and ammonia levels in the gastrointestinal tract and
blood.
There is speculation that probiotics may have some negative
effects on pig performance, which may be caused by: nutrient com-
petition; a decrease in carbohydrate utilization; and an increase
in the transit rate of the digesta.
Although probiotics have been commercialized and used exten-
sively for at least 30 years, the documented evidence of their
therapeutic and nutritional value is still quite variable. Some
of the possible reasons for the variability of results are: via-
bility of microbial cultures related to storage method; strain
differences; dose level and frequency of feeding the culture;
drug interactions; and lack of systematic investigation by
researchers.
Previously, research information on probiotics was not
required to substantiate therapeutic or growth promotional
claims. However, on June 2, 1988 FDA published a compliance
statement on direct fed microbial products. Under the new guide-
lines, a direct-fed microbial product that is labeled/promoted
with any therapeutic or growth promotional claims is a new animal
drug and requires a completed new animal drug application (NADA)
before the product can be sold with therapeutic or growth claims.
The intent of this regulation was to minimize misleading or
deceptive advertising for therapeutic and growth promoting claims
by microbial products in the market place.
Organic Acids
There are several organic acid compounds available for use
in feeds. Fumaric and citric acid are the most common. Both have
been shown to improve gain and feed efficiency in weanling pigs.
The exact mode of action is not known, but has been rationalized
from several positions:
(1) Acidification of the diet may decrease stomach pH and
increase pepsin activity (required for protein digestion).
(2) A reduced stomach pH may decrease the rate of stomach
emptying, thus increasing protein digestion time in the stomach.
(3) A reduction in stomach pH may reduce the proliferation
of coliforms and other pathogens in the upper gastrointestinal
tract.
Research data have shown the effects of organic acid addi-
tions to diets on performance to be quite variable. This varia-
bility may be attributed to: 1) age of pigs; 2) the amount of
milk by-products in the diet; and, 3) the presence or absence of
antibiotics. At the present time, the optimal inclusion rate and
economic benefits of organic acids in weanling pig diets have not
been established.
Other Additives
Flavors are sometimes added to diets to enhance the aroma or
taste of the feed. Most of the research suggests that they are
of limited benefit unless one is attempting to mask feed that has
off-odors or off-flavors.
Enzymes are sometimes included in feeds for the purpose of
assisting in the digestive process. Most research indicates very
little benefit from enzyme supplementation. An exception is the
enzyme, beta-glucanase, which has been shown in certain instances
to benefit the utilization of barleys that are high in beta-
glucans, a complex carbohydrate that interferes with the pig's
ability to efficiently utilize barley.
Antioxidants are often included in feeds that are high in
fat. They help to prevent the feed from becoming rancid, espe-
cially in hot weather.
Pellet binders are occasionally added by feed manufacturers
to feeds prior to pelleting. Their purpose is to increase the
cohesiveness of the pellets.
Proper Use of Feed Additives by Producers
Producers should follow directions for feed additive usage
as provided by the manufacturer (See PIH-86, Management to
Prevent Drug Residue Problems in Pork). Thoughtful use of these
compounds to maximize profits, while preventing residues and
reducing consumer concern, is important.
Antimicrobial additive claims and approved usage levels in
feed are regulated by the FDA. USDA-FSIS (Food Safety Inspection
Service) is actively initiating more rigid swine identification
and residue-monitoring controls of pork carcasses at packing
plants. Every pork producer must take precautions to abide by FDA
required preslaughter withdrawal times for feed additives and
other medications. To disregard these regulations could result in
a sizable monetary loss to individual producers from condemna-
tions due to tissue residue and to the pork industry from with-
drawal of approval for certain effective feed additives.
In using medicated feeds (antibiotics, chemotherapeutics,
and anthelmintics) the producer should:
1. Read the tag to assure that this is an appropriate addi-
tive for the stage of production and is being used for approved
reasons.
2. Comply with the proper withdrawal times to avoid residues
thereby ensuring safe, wholesome pork. All approved drugs have
been tested for tissue clearance and length of withdrawal time is
based on research data and approved by regulatory agencies.
3. Prevent drugs and medicated feed from contaminating other
medicated or nonmedicated feeds through mixers and feed handling
equipment.
4. Avoid giving additional medications to animals on medi-
cated feed without professional advice. One compound may inter-
fere with the effectiveness or clearance rate of another drug.
5. Use only those medicated feeds approved for swine and
only for the appropriate purpose and stage of production.
Table 7. Effects of single and combined
additions of copper and antibiotics on
performance of weanling pigs.a
___________________________________________
Additive
None CopperbAntibioticcBoth
___________________________________________
Daily gain, lb. .46 .57 .55 .62
Feed/gain 1.98 1.87 1.81 1.75
Survival, % 95 100 93 98
___________________________________________
a Two trials involving 256 pigs from 4-8
weeks of age (15 to 30 lb.)
b 250 ppm copper as copper sulfate.
c 55 ppm chlortetracycline in one
experiment, 27 ppm of virginiamycin in a
second experiment.
Summary
The majority of feed additives available to producers are
antibiotics, chemotherapeutics, anthelmintics, organic acids, and
probiotics and to a lesser extent, flavors, enzymes, antioxidants
and pellet binders. Current research has shown that antibiotics,
chemotherapeutics and copper sulfate provide the most consistent
improvements in growth rate and feed efficiency.
Producers should obtain professional help to develop a
specific feed additive program to maximize returns. Short-term
switching from one additive to another should be avoided unless
made in response to a new disease problem. A well planned program
can help prevent management errors associated with withdrawal
times and make it easier to execute specific disease prevention
and treatment programs. One should always practice good feeding,
sanitation, and disease control management techniques. Don't
expect to buy management in a bag of medicated feed. Seek and
utilize the services of a practicing veterinarian and animal
nutritionist.
Federally approved feed additives are thoroughly tested and
proven to increase animal performance. Approved antibiotics and
chemotherapeutics or combinations are recommended for growth pro-
motion in each stage of the growth period and, for the improve-
ment of breeding and lactation performance in sows.
References:
1 Zimmerman, D. R. 1986. Role of subtherapeutic levels of antimi-
crobials in pigs. J. Anim. Sci. 62 (Suppl. 3): 17.
2 Feed Additive Compendium, 1989. Miller Publishing Co., 12400
Whitewater Drive, Minnetonka, MN 55343.
3 Cromwell, G. L. 1983. Antibiotics for growth promotion in swine.
Animal Nutrition and Health. July/August 1983.
4 Braude, R. 1975. Proc. Copper in Farming Symposium. Copper
Development Association. London.
5 Cromwell, G. L., et. al. 1981. Efficacy of copper as a growth
promotant and its interrelation with sulfur and antibiotics for
swine. Proc. Distillers Feed Conference, Cincinnati, Ohio.
6 Stahly, T.S. et.al. 1980. J. of Animal Science 51:1347.
7 Pollman, D.S. 1985. Feed ModifiersWhat Are They? Guelph Pork
Symposium.
8 Hays, V. W. 1977. Effectiveness of feed additive usage of anti-
bacterial agents in swine and poultry production. Office of
Technical Assessment, U.S. Congress, Washington, D.C.
9 Cromwell, G.L. et al. 1983. High levels of copper as a growth
stimulant in starter diets for weanling pigs. Kentucky Swine
Research Report No 274, 1983.
REV 4/89 (5M)
______________________________________________
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