General nutritional guidelines recommend reducing the consumption of fats originated from ruminant products. This is due to the ruminal biohydrogenation of unsaturated fatty acids (UFAs) which leads to the presence of unhealthy saturated or trans fats in ruminant products. Here, for the first time to our knowledge, we have focused on the main biochemical process which results in the saturation of UFAs. Rumen lipolytic activity (RLA) generates non-esterified fatty acids (NEFAs) in the rumen, which are a prerequisite for the biohydrogenation process to occur. We have examined different concentrations of pyridostigmine bromide (PB), of reversible cholinesterase inhibitor, in batch cultures containing 80 mg soybean oil, as a source of triglyceride. PB is the main active compound of an FDA approved drug for the treatment of myasthenia gravis and also pretreatment against nerve gas in humans. Our hypothesis was to evaluate PB as an inhibitor for RLA. In normal conditions, soon after triglycerides enter the rumen, they are hydrolyzed as a result and free fatty acids undergo the biohydrogenation process. Our results indicated that no significant (P > 0.01) reduction in linoleic acid (C18:2, ω6) after 6 h incubation was observed for cultures containing PB with concentrations above 0.052 g/dL. We concluded that PB has the potential to inhibit RLA in cultures after 6 h of incubation. Such findings suggest the potential of PB to be utilized in vivo as a feed additive to inhibit biohydrogenation of unsaturated fatty acids in the rumen. Practical applications: The biohydrogenation of health benefitial unsaturated fatty acids in the rumen cause ruminant products, such as milk and meat, to contain highly saturated fats. Inhibition of rumen microbial lipolytic activity in vivo could increase the flow of unsaturated fatty acids for absorption and therefore, would have the potential to improve fatty acid composition of ruminant milk and meat. This would also have benefits for the animal.

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