Geoff,

Thanks for the link to the article. It clears up a number of issues raised in this discussion.

There seems to be no question that ionophores perform an important antimicroboal function. It is not surprising that there is some debate over the recent Department of Agriculture ruling that ionophore use disqualifies a product from being advertised as "antibiotic free". Though clearly "antibiotic" in function, ionophores perform very differently than traditional antibiotics. Ionophores effect a change in ionization of the bacterial membrane, altering the bacteria, and uncoupling its ability to grow, resulting in cellular death .

Because of the specificity of the function of ionophores, and the fact that they remain in the digestive tract, and are not transferred to meat, they don't seem to pose any threat to humans by an increase in antibiotic resistance. However, the increase in E. coli colonization in some of the testing may explain why we seem to have a recent increase in the number of E. coli related meat recalls.

The article referred to ionophores as having been used for the treatment of the intestinal illness, coccidiosis, in poultry, but was primarily addressing their use with ruminants (cud chewing animals), specifically cattle. The digestive activity of ruminants begins with a fermentation process that depends on specific bacteria in the rumen. (One of the by-products of that fermentation process is methane, sometimes blamed for global warming.)

It seems that administration of ionophores reduces the concentration of rumenentary bacteria, and actually increases the efficiency of the digestive process. This results in greater feed conversion (increased nutrient uptake) and reduced ruminal gas (methane) production. For some reason, not fully explained in the article, animals with this increased feed conversion are not only less expensive to feed, but actually produce a better quality of meat.

There have been only three published trials where Agrastim was used with cattle. The first was specifically to determine if Agrastim could survive the fermentation process in the rumen, or would simply be digested without reaching the immune system. The test showed that Agrastim was able to survive in the rumen with only 15% degradation, and reached the Peyer's patch, "enhancing" the immune system.

The second test was performed with newborn calves, and greatly reduced the mortality rate on a farm with high levels of upper respiratory infections.

The third test showed Agrastim"s effectiveness in reducing infection in the udders of dairy cows, as evidenced by lower Somatic Cell Counts. (Somatic cells are blood protiens and white blood cells commonly associated with bacterial infections).

To my knowledge, there have been no trials with cattle, specifically designed to determine the effect of Agrastim on feed conversion, though Agrastim has significantly and consistently increased feed conversion in other species.

As one might imagine, there is a significant difference in the amount of feed consumed by a chicken or turkey, and that consumed by a beef cow. There is also a significant difference in the "grow-out" period. Any scientific test of Agrastim as a replacement for ionophores would have to measure changes in nutrient uptake, ruminal gas production and meat quality, as well as a reduction in specific bacteria in the rumen. Based on the amount of feed and the growth cycle of cattle, I suspect such a test could be very expensive ($200K-$300K) and time consuming (1-2 years).

I would not expect to see such a study any time soon, but would not be surprised to begin hearing of less scientific field trials that show increased feed conversion and improvement in overall health of beef cattle. We already know Agrastim reduces incidences of bacterial infection in dairy cattle. I imagine we could see similar results with beef cattle.

It is estimated that the use of Ionophores with beef cattle results in cost savings to the industry of 1 billion dollars, annually, through improved feed conversion. Similar results with Agrastim would certainly be newsworthy. The recommended dose of Agrastim for cattle is 2 grams/day. One herd of 10,000 beef cattle (not an unusal herd size) would consume 600 kilos a month.

Regards,

zties