No Antibiotics, Just Ionophores
In the late 1940s and early 1950s it was found that feeding small amounts of antibiotics to chickens, pigs, and beef cattle improved their growth and performance while helping compensate for less sanitary and crowded conditions. Soon scientists began suggesting the non-therapeutic use of antibiotics at levels just high enough to control a host animals bacterial population, but too low to wipe them out, was encouraging resistant bacteria.
An excellent discussion by Gary Stix published in the April 2006 issue of Scientific American explains genetic mutation as it relates to antibiotics. The heavy use of antibiotics in both human medicine and animal agriculture has been allowing various bacteria to develop resistances. The excessive use of antibiotics in human medicine is well known and understood, but not so well known is that many of the antibiotics used for animals are also used in human medicine, and the volume used on animals is massive. Some USDA members say 70 percent of all US antibiotics are used non therapeutically on animals.
An Environmental Defense study claims 26.5 million pounds of antibiotics are used in the United States each year as animal feed additives, but that 13.5 million pounds of those antibiotics are excreted. The USDA's Agricultural Research Service (ARS) in the February 13, 2006, issue of Feedstuffs said, "The trouble is that when animals excrete unmetabolized antibiotics and other pharmaceuticals in their waste, the compounds may linger in the environment. This so-called 'pharmaceutical pollution' can encourage bacteria to mutate and form strains that are resistant to current antibiotics," and bacteria, once inside the human body, can easily transfer their antibiotic resistance to other bacteria.
Once the warning light came on for the use of antibiotics in livestock feed the agricultural establishment searched for an approach to circumnavigate the problem. So, now ionophores enter the antibiotic discussion. The livestock industry, especially the chicken industry, in conjunction with several large food companies said they would require suppliers to phase out antibiotics in their feeding protocols. However, they gave a pass to a class of antibiotics called ionophores. This happened because the ionophores are among the shrinking list of antibiotics not considered medically important to human medicine by the World Health Organization (WHО).
Recently modified data from the Sustainable Agricultural Systems Laboratory at Beltsville, Maryland examined the use of composting animal waste on the persistence of ionophores. Since ionophores are not used in human medicine the land application of ionophore containing manure does not pose a potential threat to public health by influencing the development of antibiotic resistance in human pathogens. However, ionophores inhibit the activity of many bacteria and eukaryotic cells. Therefore, these compounds pose a serious threat to soil microbiological life. As the agricultural establishment discusses soil health and the need for healthy soil microbiology to reduce the need for chemical fertility, the addition of ionophores to the soil environment works against that result. Therefore, this research was undertaken to reduce the effect of the ionophores on the environment.
Although reported half-lives for ionophores in soils are short (2 to 4 days) they have been detected in surface water and ground water. Treatment (composting) of ionophore containing manure prior to land application is one possible way of reducing the amount of these compounds that is released into the environment.
However, the results of a USDA composting study showed that procedures needed to reduce ionophores in livestock waste were not physically (time and temperature) practical or did not accomplish any reduction of the volume of the ionophores.
Since Growers Mineral, Corp. was established we have noticed that very heavy application rates of manure can create soil microbiological problems. With the usage of antibiotics (ionophores) beginning in the 1940's can we conclude that ionophores have created the soil microbiological damage to the soil environment that we have observed? We have no scientific data to back this idea. However, in the cases where field production problems occurred with heavy manure applications; the use of high calcium (Ca) lime with a reduction in manure volume helped to reduce the field production problems. In many cases a manure rate reduction of 50% with an addition of 1 to 2 tons per acre of high Ca limestone helped alleviate the soil's production issues. So we believe that reducing the manure toxicity to the symbiotic soil microbes in the soil environment helped to bring back the health of the soil.
This is an excerpt from the Winter Growers Solution (2026) written by Jim Halbeisen, Director of Research.
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