Prepared by Jerry Kunesh, Food Animal Clinician, Iowa State University;
Palmer Anderson, Food Animal Clinician, Washington State University; Lew
Runnels, Food Animal Clinician, Purdue University; and Rand Larson, Veterinary
Practitioner, Alpha, Illinois. Edited by Gene P. Hettel, Communications
Specialist-Agriculture, Iowa State University
Therapeutic Selection in Swine
Antibiotics do not attack all disease-causing
organisms found in the pig. However, antibiotics or chemotherapeutic agents
[i.e. sulfonamides, Furox] may be prescribed by your veterinarian to control
concurrent or secondary bacterial infections that may intensify a viral
All drug preparations are approved
for specific disease control and for treatment dosages. These use instructions
appear on the product label, Use of any product for other than label approval
is an extra-label usage. In 1984, the Food and Drug Administration [FDA]
approved a policy that allows extra-label usage under the direction of
a veterinarian, The veterinarian must be familiar with the livestock operation,
be available for retreatment and, with the owner, be responsible for drug
residues which might occur because of the treatment. These regulations
are similar to use restrictions on prescription drugs. Feed additives are
under separate rules which do not allow extra-label or prescription usage.
The only legally acceptable usages of feed additives are the approved uses.
A feed mill or other third party cannot mix feed additives at other than
A variety of common swine diseases
use extra-label drug treatment programs. Coccidiosis is a diarrheal disease
of baby pigs caused by a protozoan [Isospora suis]. A variety of sulfonamides
and other drugs are used to treat this condition on an extra-label basis.
Each pig must be individually treated orally for about 3 days. The treatment
drugs are coccidiostats, which hold the total number of coccidia in the
gut down, but do not prevent infection or completely remove the infection.
Therefore, treatment must be continued
for several days to weeks to be effective. Because coccidiosis in piglets
generally occurs from 5 to 21 days of age, entire litters should be treated
several days before an anticipated outbreak. The parasitic life cycle is
so advanced by the time diarrhea develops that treatment may not give a
With all disease conditions, treatment
of sick animals should be started as early as possible to get the best
results. Most therapeutic agents are most effective on the rapidly multiplying
bacteria found early in the course of a disease.
When selecting a therapeutic agent
to treat a sick animal, a veterinarian should help diagnose a problem and
determine an appropriate drug, route of administration, and dosage. These
will vary depending on the disease condition and its severity. If response
to the initial drug is not good, further tests may be required to make
a rational drug selection. In some cases, this may include a laboratory
isolation of the disease-causing organism and performance of tests to determine
which drugs are most likely to be effective against the organism.
Medicating Drinking Water
When using therapeutics in treating
swine, medicating through the drinking water is an excellent and economical
treatment method because the most important diseases are infectious and
usually are herd problems, Water treatment offers the advantages of quick
action, the capability of providing therapeutic levels of medication at
economical rates, and lower labor requirements over individual treatment.
Water medication is preferred over
feed additives because when pigs are sick, they will usually stop eating
feed before they stop drinking water. This is particularly true for diseases
such as swine dysentery [bloody scours] and some pneumonias. Baby pigs
still nursing cannot be treated through water or feed and should be individually
treated. Also, severely sick pigs should be treated individually. They
require high levels of medication and may not be eating or drinking enough
to obtain the medication. ln some cases, both water and feed medication
for the entire group and individual treatment of the most severely ill
animals are required.
Reasons for Drug Failure
Drugs do not always work and there
may be several reasons why. One major reason is not maintaining the dosage
schedule long enough or not administering enough drugs in a treatment program,
It is very important to follow the correct dosages at the correct time
intervals. This is where a veterinarian's experience can provide valuable
guidance. In some cases, it can be the difference between successful treatment
The use of tetracyclines in feed demonstrates
a special problem. When given orally, tetracyclines may bind or be tied
up with certain compounds, particularly calcium and iron, so this causes
the drug to stay in the gut and not be absorbed to its fullest extent.
Therefore, excessive amounts of calcium and iron in the ration may be detrimental
to the tetracyclines being used. Similarly drugs may be chemically altered
when mixed with another injection product, possibly dropping effectiveness
Antibiotics and sulfonamides may be
rendered ineffective if bacteria become resistant to them after prolonged
usage. Such drugs should not be used indiscriminately or casually. Rotate
the use of treatment drugs or families of drugs to reduce specific resistance
General Rules for Selecting Drugs
If therapy is not working and a switch
to a different drug is considered, there are some general rules to keep
in mind about selecting drugs.
1.If an organism is resistant to one
of the tetracyclines, it will be resistant to all of the tetracyclines.
For example, if chlortetracycline foils, oxytetracycline probably will
not work either.
2.If an organism is resistant to one
sulfonamide, it will be resistant to all sulfonamides. For example, switching
from a short-acting sulfonamide to a longer-acting one may not work; or
switching from sulfamethazine to sulfathiazole may not work either.
3.Organisms resistant to gentamycin
will be resistant to neomycin and dihydrostreptomycin as well. Organisms
resistant to neomycin will be resistant to dihydrostreptomycin but may
or may not be resistant to gentamycin.
The antibiotics effective against gram
positive organisms do not generally carry cross resistance. Therefore,
if one is ineffective, change to another one to get a possible response.
Avoiding Violative Residues
When using drugs, there is always a
potential for violative residues, Some drugs are available only in oral
forms [bolus, tablet, etc.] because if given by injection, they leave residues
for long periods. Drugs failing into this Category will stay in the gastrointestinal
tract and effectively treat diarrheas or gut infections, but will not be
absorbed into the rest of the body. They may nave a low safety margin at
other locations in the animal's body, but are very safe in the gut. lf
injected, these drugs attach to cells in the body and stay for prolonged
periods--greatly increasing drug withdrawal times. An example of this type
of drug is neomycin.
The only way to be sure that residue
problems are avoided is to read the label carefully and use the drug according
to instructions. Labels may change as new data are collected.
To avoid violative residues follow
1.Read the instructions carefully.
2.Use the recommended dose.
3.Use the recommended route of administration.
4. Use the drug only in the animal
species for which it is approved.
5.Do not use the same drug in two different
dosage forms at the same time, i.e., oral and injectable. This may significantly
increase withdrawal times.
6.Select injection sites carefully.
Drugs are much more rapidly absorbed from muscle than from fat. Deposition
of drugs into fat may result not only in poor response to treatment, but
residues as well.
7.Keep accurate records. From these,
calculate withdrawal times for any and all drugs administered. Calculate
withdraws from the last day of treatment.
8.Never mix drugs that do not come
premixed. This may lead to ineffective treatment (mixing may destroy one
or more of the products mixed], prolonged drug residues, and adverse reactions
in the animals.
9.Never use drugs without withdrawal
information being provided.
10.Thoroughly clean all feed and water
handling equipment and scrape pens when removing swine from medicated feed
Careful selection and use of therapeutic agents for swine will increase
health in the herd, help reduce production costs, increase productivity,
and minimize the residues found in meat due to antibacterial drug usage.
Careless use can be expensive and cause harm to the producer.