Agriculture Reference
In-Depth Information
h
o r m o n e
i
m P L a n t s
a n D
f
e e D
a
D D i t i v e s
f of r
i
m P r o v e D
g
r o w t h
a n D
b
e e f
L
e a n n e s s
Synthetic (melengestrol, MGA; trenbolone acetate, TBA; zeranol) and natural ste-
roid hormones (progesterone, estradiol, testosterone; all produced in significant
amounts throughout the life of every human) are used in beef cattle, and sometimes
in sheep, as a means of increasing growth rate, efficiency of feed utilization, and
increased lean tissue mass and carcass leanness. MGA is administered daily in the
feed, whereas each of the others is administered to an individual animal in a single
dose as a pellet implanted early in the finishing period so that the hormone release
is depleted long before animal slaughter, eliminating the possibility of tissue resi-
dues in the meat. More than 30 countries currently allow use of these hormones
in beef production, and even European scientific groups have deemed hormones
safe for use (Avery and Avery, 2007). Strict regulatory rules are enforced to ensure
safety. This procedure has provided an effective means of improving efficiency of
beef and lamb production.
f
e e D
a
D D i t i v e s
f of r
i
m P r o v e D
b
i o L o g i C a L
e
f f i C i e n C y
a n D
a
in i m a L
h
e a L t h
In addition to the nutrients contained in feedstuffs, many nonnutritive feed additives
are used to improve performance. Industrialized countries have their individual pro-
grams for approval, regulation, and enforcement of use. In the United States, the
Food and Drug Administration (FDA), Environmental Protection Administration
(EPA), and Food Safety and Inspection Service (FSIS) are among the administra-
tive agencies responsible for protecting the safety and efficacy of food and food
constituents for humans and for approving new feed additives for use in animals.
The European Union has similar programs, and parallel agencies in other countries
have similar responsibilities. The main broad groups of feed additives approved for
use in animal feeds are antibiotics, probiotics, enzymes, ionophores, and protein
anabolic agents.
Antibiotics
For more than 50 years of extensive use worldwide, antibiotics (antimicrobial agents)
have been added to livestock feeds at subtherapeutic levels to improve performance
(Hays, 2005; Cromwell, 2005). Antibiotics are still as effective as at the beginning
in increasing growth rate, efficiency of feed utilization, and decreasing mortality.
Development of microbial resistance to antibiotics in animals and humans being
treated with therapeutic levels (several times higher than the subtherapeutic levels
used in animal feeding) of antibiotics is a serious problem in human patients, espe-
cially those confined in hospitals. This has created concerns about the possible rela-
tionship between subtherapeutic antibiotics in animal agriculture and development
of antibiotic resistance to pathogens in humans. The existence of such a causal rela-
tionship has been difficult to establish given the complexity of the issue. A complete
ban on the use of antibiotics in animal feeds would increase the cost of food animal
production.
