Additives to Improve Efficiency of Animal Production - Part II
As a note regarding FDA approval of drugs, FDA approval for any type
of compound classified as a drug is developing into a more extensive and
challenging process. As a result, a limited quantity of new compounds
is approved. In addition, approval may also be altered from the original
approval. In general, quantity of drugs approved for a specific specie
is associated with potential revenue generated by the approval and utilization
of the compound. The Feed Additive Compendium, published annually by Miller
Publishing Company, provides updated information on compounds approved
by the FDA.
Hormones are utilized to improve animal production. As only one of the
products is approved by the FDA as a feed additive, the discussion of
the various products will be brief. Hormones are chemical compounds produced
in a specific region and transported to another region in the animal body
to perform the compound's specific physiological function(s).
In the U.S., the only hormone product approved by the FDA as a feed additive
for beef cattle is melengestrol acetate (MGA). Table 9-2 on page 187 of
the text describes the approved use of melengestrol acetate. MGA is a
synthetic progesterone. MGA suppresses estrus and ovulation, therefore
improving gain and feed efficiency in feedlot heifers. Suppression of
estrus in heifers also maintains intake and performance of steers in the
feedlot.
Various hormone-based products are administered to improve animal production.
Products containing various combinations of estrogen, progesterone, and
testosterone are administered to growing and finishing ruminants to increase
growth rate, improve feed efficiency, and potentially reduce the deposition
of lipid on the animal. Frequently, products are administered via the
utilization of a subcutaneous implant. Bovine somatotropin is a product
used to increase feed efficiency and milk production in lactating dairy
cattle. Somatotropin, previously referred to as growth hormone, is a protein
hormone. Bovine somatotropin is administered via intramuscular injection.
Porcine somatotropin is administered to swine to increase growth rate
and leanness of animal.
Antibiotics are substances produced by living microorganisms (i.e. bacteria
and fungi) which have bacteriostatic or bactericidal properties on one
or more microorganism(s). In the U.S., the majority of production animals
receive at least one antibiotic in their lifetime. In regards to subtherapeutic
levels of antibiotics, for cattle the majority are fed to young and growing-finishing
animals. For poultry, the majority of broiler rations contain one or more
antibiotics and antibiotics may also be fed to layers. For swine, numerous
antibiotics are approved for subtherapeutic use. Antibiotics should not
be used as a substitute for appropriate sanitation and management.
Table 9-2 on pages 183-187 of the text provides information on antibiotics
approved by the FDA. The table provides the product name and approved
species and dosage, manufacturer claims, and required withdrawal period
for each of the antibiotics.
Antibiotics, as feed additives, are administered at low levels. Subtherapeutic
doses function to increase intake, growth rate, and/or feed efficiency
and aid in the control of infectious diseases. Subtherapeutic levels improve
the animal's ability to maintain optimal health and production, especially
during periods of distress. Response varies with factors such as species,
physiological state, and environmental conditions. Responses to subtherapeutic
levels of antibiotics are greatest for young, unhealthy, and/or stressed
animals.
The precise mechanism of antibiotics to improve feed efficiency and/or
growth has not been identified. The mechanism appears to be a function
of the effects of the antibiotics on the microorganisms of the GI tract.
Dependent on the specific antibiotic, the mechanism may be a combination
of one or more mechanisms. Proposed mechanisms include: 1) suppression
of microbes that cause subclinical disease; 2) reduction of microbial
growth-suppressants; 3) reduction of microbial destruction of nutrients;
4) stimulation of synthesis of nutrients; 5) reduction in thickness of
cell wall of the GI tract, therefore increasing absorption efficiency
of the GI tract and reducing protein and energy requirements of the animal;
and 6) inhibition of ability of microorganisms to stimulate an immune
response in the animal.
Subtherapeutic levels of antibiotics as feed additives are a controversial
issue. Subtherapeutic levels of antibiotics improve the efficiency of
animal production and therefore benefit the producer and the consumer.
The primary concern is extensive utilization of antibiotics promotes the
development of strains of bacteria resistant to antibiotics. Currently,
evidence does not support the use of subtherapeutic levels of antibiotics
in animal rations poses a human health risk.
Therapeutic doses are administered to control or treat various diseases
and control gastrointestinal parasites in animals. Specific examples of
uses of various therapeutic levels are to prevent or control disease associated
with transportation or adjustment to a new facility, anaplasmosis in cattle,
bacterial enteritis in swine, and respiratory diseases, diarrhea, fowl
cholera, and fowl typhoid in poultry. In general, administration of therapeutic
doses is for a short period of time. In general, higher doses are not
approved for extended use.
Chemotherapeutic agents are organic compounds with bacteriostatic or bactericidal
properties. Chemotherapeutics are similar to antibiotics. The chemotherapeutic
agents discussed are classified as drugs. Primarily, chemotherapeutics
control and/or treat disease. Various chemotherapeutic agents may also
be utilized to improve growth. Selection of chemotherapeutic is dependent
on the issue to address and objectives of production. Arsenicals, nitrofurans,
and sulfas are three classes of chemotherapeutic products. Table 9-2 on
page 185-186 of the text provides information on arsenicals, sulfas, and
nitrofurans.
Arsenicals are synthetic compounds containing arsenic. Various arsenicals
improve gain and efficiency in swine and poultry, control blackhead in
poultry, and prevent dysentery in swine. As arsenicals accumulate in body
tissues, all arsenicals have a five day or longer withdrawal period.
Sulfas are sulfur-containing compounds. Various sulfas function to prevent
bacterial enteritis in swine and coccidiosis and fowl cholera in poultry.
A primary problem with sulfa drugs is the presence of residues.
Nitrofurans are antibacterial compounds. For swine, various nitrofurans
improve growth and prevent bacterial enteritis and diarrhea. For poultry,
nitrofurans improve growth, feed efficiency and control coccidiosis, nonspecific
bacterial enteritis, and fowl typhoid.
Coccidiostats are compounds for the prevention and control of coccidiosis.
Coccidiostats are classified by the FDA as drugs. Various synthetic products,
antibiotics, as well as selected nitrofurans and sulfas are coccidiostats.
Table 9-2 on page 185 of the text describes various coccidiostats. Prevention
and control of coccidiosis is important for the animal industries, especially
the poultry, swine, cattle, and sheep industries.
Ionophores are additives that alter the population of rumen microorganisms,
resulting in an alteration of metabolism in the rumen. Ionophores were
named based on their mode of action; the compounds serve as carriers for
metal ions across cell membranes. In the U.S., the approved ionophores
are lasalocid (trade name, Bovatec) and monensin (trade name, Rumensin).
Ionophores are approved for beef cattle and dairy heifers. Ionophores
produce responses in growing and mature animals and in animals on high-forage
or high-concentrate rations. Ionophores are not approved for lactating
dairy cattle. Ionophores are also approved and used as a coccidiostat
for poultry, sheep, goats, and cattle. Ionophores are toxic to horses
and swine.
The following paragraph discusses the proposed mechanism ionophores utilize
to produce production responses in growing and mature cattle. As an additive
for cattle, ionophores improve feed efficiency and may also improve daily
gain. The mechanism suggests ionophores produce responses via an alteration
of the population of microorganisms in the rumen. As a result of differential
cell structures between gram positive and gram negative bacteria, ionophores
are able to inhibit the growth of gram positive bacteria and therefore
facilitate the growth of gram negative bacteria. The alteration of the
population of microorganisms produces a shift in the rumen metabolism
of carbohydrates from acetic acid to propionic acid. In comparison to
production of acetic acid, production of propionic acid is a more efficient
utilization of carbohydrates for energy. The primary products of metabolism
of carbohydrates by rumen microorganisms are acetic acid, propionic acid,
butyric acid, carbon dioxide, and methane. In the rumen, the various carbohydrates
are metabolized to glucose and glucose may be metabolized to produce the
various volatile fatty acids. High-roughage rations favor the production
of acetic acid and high-concentrate rations favor the production of propionic
acid. For the production of acetic acid, one glucose molecule is metabolized
to two acetic acid molecules, one carbon dioxide molecule, and one methane
molecule. As the ruminant is not able to use carbon dioxide and methane
for energy, only four carbons are available for absorption and metabolism
by the ruminant. In contrast, high-concentrate rations favor the production
of propionic acid. Each glucose molecule is metabolized to two propionic
acid molecules. Each propionic acid contains three carbons. The ruminant
retains all six carbons to be absorbed and metabolized.
In addition, ionophores also reduce the incidence of lactic acidosis and
aid in the control of feedlot bloat and acute pulmonary emphysema via
inhibition of the growth of Streptococcus bovis and/or Lactobacillus species.
Data also support ionophores decrease the degradation of protein in the
rumen resulting in an increase in rumen by-pass protein. Ionophores also
aid to control coccidiosis and face and horn flies.
Anthelmintics are additives fed to prevent and control parasitic organisms
within the animal. Anthelmintics control losses in productivity and profitability
resulting from parasitic organisms. The FDA classifies anthelmintics as
drugs. Anthelmintics may also be referred to as vermifuges or wormers.
Selection of the appropriate anthelmintic depends on accurate identification
of the specific parasite(s) in the animal, animal species and physiological
state, animal health, method of administration, side effects on the animal,
and the cost. It is recommended to establish a parasite control program
and schedule. An effective program may require the utilization of multiple
products in a rotation. Establishment of the program schedule requires
the consideration for the life-cycles of the various parasites. Anthelmintics
may be added to the ration or water as required by the established schedule.
Table 9-2 on page 186-187 of the text provides information regarding products
to control parasitic microorganisms.
Probiotics are substances with favorable microorganisms and/or ingredients
that enhance the growth of favorable microorganisms in the gastrointestinal
tract. Probiotics may contain the favorable microorganisms and/or products
facilitating the establishment of favorable microorganisms in the gastrointestinal
tract. The precise mechanism(s) of probiotics are unidentified and unproved.
Probiotics may also be referred to as direct-fed microbials. Probiotics
are alternatives to antibiotics.
Various probiotics are available. One common microorganism fed as a probiotic
is Lactobacillus acidophilus. Yeasts may also be added to the products.
Probiotics may be fed to monogastrics and ruminants. The optimal product
to feed depends on factors such as animal species, physiological state,
health, components of the ration, and objective of the probiotic. To be
effective, probiotics are required to be competitive with existing microorganisms
of the gastrointestinal tract. Probiotics are also required to survive
conditions of the gastrointestinal tract. Probiotics are most effective
for young animals and animals under distress. Probiotics are available
in liquid and dry form. Probiotics may be added to the ration, a liquid
supplement, or the water source. Efficacy of probiotics is variable.
|