Enteric methane (CH4) emission is one of the major greenhouse gasses (GHGs) originating from cattle. Methane from ruminant animals originates primarily from microbial fermentation of feeds in the rumen. During this fermentation, microbes produce CO2 and hydrogen (H2), which are converted to CH4 by the microorganisms known as archaea.
The team outlined how iodoform is a halomethane that is considered to be neither ozone-depleting nor carcinogenic, and it is approved for use in the pharmaceutical industry with no upper tolerance level, but it is as yet not approved as a feed additive. “It has previously been observed that iodoform is a potent inhibitor of CH4 production in vitro. However, no studies have tested iodoform when fed to dairy cows.”
Their study, which was conducted at Aarhus University, AU Viborg - Research Centre Foulum, in Denmark, aimed to quantify potential of iodoform as an anti-methanogenic feed additive for dairy cows and investigate effects on feed intake, milk production, feed digestibility, rumen microbiome, and animal health indicators.
The experiment was conducted as a 4 × 4 Latin square design using four lactating rumen, duodenal, and ileal cannulated Danish Holstein dairy cows.
Four different doses of iodoform were evaluated: 0 mg per day, 320 mg per day, 640 mg per day, and 800 mg per day.
Iodoform was supplemented intra-ruminally twice daily. Each period consisted of seven days of adaptation, three days of digesta and blood sampling, and four-days of gas exchange measurements using respiration chambers.
Milk yield and dry matter intake (DMI) were recorded daily. Rumen samples were collected for microbial analyses and investigated for fermentation parameters. Blood was sampled and analyzed for metabolic and health status indicators.
DMI and milk production decreased linearly by maximum of 48% and 33%, respectively, with increasing doses, found the team.
Methane yield decreased by maximum of 66%, while up to 125-fold increases were observed in hydrogen yield with increasing doses of iodoform.
Total tract digestibility of dry matter (DM), organic matter (OM), crude protein (CP), carbon ©, neutral detergent fiber (NDF), and starch were unaffected by treatments, but large shifts, except for NDF, were observed for ruminal to small intestinal digestion of the nutrients, said the authors.
Some indicators of disturbed rumen microbial activity and fermentation dynamics were observed with increasing doses, but total number of ruminal bacteria was unaffected by treatment, while serum and plasma biomarkers did not indicate negative effects of iodoform on cow health, they added.
The team concluded that iodoform was a potent mitigator of CH4 emissions. However, DMI and milk production were negatively affected and associated with indications of depressed ruminal fermentation.
“Iodoform had a dramatic and dose-dependent suppressing effect on daily CH4 emission, yield, and intensity from dairy cows, most likely caused by a depression of metabolic activity of the methanogens.
“The theoretical excess of H2 resulting from the reduction of CH4 synthesis was only partially recovered as emitted H2 since alternative hydrogen-sink pathways were activated through upregulation of hydrogenotrophic bacteria and/or a change in microbiota towards a lower net H2 production.
“For all nutrients, except NDF, rumen digestibility was depressed, and the marked depressions in DMI might be ascribed to accumulation of H2 in rumen headspace or undesirable effects of iodoform on microbial fermentation, although total number of ruminal bacteria was unaffected by treatment.
“Due to a substantial shift from ruminal to small intestinal digestibility, overall digestibility for all nutrients was unaffected by iodoform.
“The supplemented doses of iodoform did not appear to have negative impacts on thyroid or liver function of the cows for the duration of the experiment, but there were several indications of a more negative energy and protein balance with increasing dose of iodoform, which contributed to explain why milk production was less negatively affected by iodoform than DMI.”
Future studies might reveal if depression of milk yield and feed intake can be avoided if iodoform is continuously administered by mixing it into a total mixed ration (TMR), said the scientists.