Ionophores
We learn about ionophores as a treatment, I've seen em given in the field, and I've heard complaints about em by animal rights people. I know what ionophores are, but I don't know exactly how they work.
Ionophores are commonly used feed additives in production medicine and they protect against one of the most devastating illnesses I saw in late/heavy animals on a beef feedlot - the dreaded "bloat", also known as rumen acidosis. (We'd find em dead with little to no signs of illness - they marked a huge loss for the producer, and I imagine death by upset stomach toxins or respiratory compression is painful. Everyone involved wanted to prevent those deaths.) They're used in small ruminants and camelids (and for the same reason, though the disease isn't called bloat, it's called acidosis). They're also a current topic in the press and I've heard several lectures at veterinary conferences recently that bring them up as a hot topic in both the area of antibiotic resistance and animal rights (and the laws, constitutional amendments, propositions, and policy discussions that are the outgrowth of this discussion). I believe that they help. They work to prevent a devastating and painful disease from occurring at the high levels that it might otherwise, and the animals on them are healthier and don't walk around with persistently upset stomachs. In my opinion this is a good thing. I don't like to see animals in pain under any circumstances and I appreciate that we can give em something to modify their rumen bacterial function. Producers and consumers appreciate that the side benefit of their use is increased average daily gain and greater feed conversion/efficiency. Also, I appreciate that there's no question that they work. It's easier for me if there's a direct linear relationship between use of ionophores and decreased disease - being able to prevent disease is the ideal situation and this is, thankfully, one of those cases. So what I found was these two papers, one published and one by a student, and both answer my question: Ionophores reduce protein degradation in the rumen thus aiding in post ruminal digestion (Horton, 1992). Ionophores also increase production of the VFA propionate by modifying the microbial fermentation in the rumen (Gates et al, 1989). from http://animalscience.tamu.edu/ansc/beef/ANSC406/Prince,S.pdf So ionophores (which are in the antibiotic family, though not in the way that we give antibiotics for most diseases) somehow protect protein that is made by the rumen bacteria and protozoa from being broken down by different rumen bact/protozoa (allowing the animal to then "eat" this protein rather than loosing it), and then they increase volatile fatty acid propionate production by altering fermentation (these VFAs are what the animals are "eating" after their food has been fermented by bacteria and protozoa and proprionate is the best one for conversion to glucose, the body's preferred food source). That's an OK answer, but I'd like pathogenesis (which we may not know). The basic affect of ionophores is to alter the flow of cations across cell membranes (Kirk et al., 1989). This leads to a reduction in gram-positive bacteria (Oheme and Pickrell, 1999). Gram-positive bacteria are known as the cause of bloat and other digestive problems associated with high carbohydrate diets. Ah-ha! This is what I was looking for. So ionophores preferentially kill off G+ bacteria, which are the problem in acidosis. They have other effects (decreasing methane and ammonia losses, both desirable in my understanding). The second paper is published but including quotes would require re-typing those segments. It's conclusions are very similar to above, with more detail, with antibiotic resistance defense, and in more academic language. It is available and highly recommended, here: http://www.horizonpress.com/ciim/v/v4/05.pdf I won't address here the complaint about their use, period. I feel that given our production system as it stands, they're necessary and not using them would be painful and cruel for those animals. However, complaints about our current production systems are warranted, though the rebuttal is by now standard. I don't know of a way to decrease the use of high-concentrate diets except through governmental regulation and increased food prices for the consumer. While this is a fine solution in my mind (I lived in Sweden for 6mo and appreciated their high food prices directly!), there's no way to raise prices while remaining competitive and not-bankrupt without doing it across the whole agricultural industry. That's a huge undertaking. Pix.
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