A series of in vitro studies were performed to evaluate the effects of lauric acid (LA)-rich oils on rumen fermentation with a high-grain diet. Soy oil (SO) and palm oil (PO) as long-chain fatty acid triglycerides, palm kernel oil (PKO), coconut oil (CO), powdered coconut oil (pCO) and coconut oil calcium salt (COCa) as medium-chain LA-rich oils were used as tested additives. Rumen fluid from steers fed high-grain diet was incubated with ground corn with or without oil supplementation (2.0 g/L) for 6 h at 39°C to monitor rumen products. Methane production decreased, while hydrogen production increased on LA-rich oils except COCa. All the LA-rich oils increased total volatile fatty acids (VFA) production and molar proportion of propionate. Also, amylase activity in culture was higher when these oils were added. The most potent additives, pCO and free LA, were further tested to determine dose-response of rumen fermentation. Powdered coconut oil and LA altered rumen fermentation toward more propionate production by supplementation at 1.2 and 0.3 g/L, respectively. These results suggest that some LA-rich oils and free LA could be used for improving rumen fermentation under high-grain diet feeding conditions.

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The effects of being fed lauric acid on rumen characteristics were evaluated in a double 3 × 3 Latin square design using six Holstein steers with ruminal cannulas on a high grain diet. The steers were fed commercial concentrate (8.7 kg/day/steer) with one of three levels of lauric acid (0, 25 or 50 g/day/steer) and timothy hay (1.8 kg/day/steer). The feed intake and digestibility were determined. Ruminal fluid was collected at 3 h after feeding to determine chemical, physical and microbial parameters. An in vitro pure culture study was performed to determine the effects of lauric acid on Streptococcus bovis, a potent bloat‐ and acidosis‐promoting rumen bacterium. There were no differences in feed intake and digestibility among the treatments. The proportion of butyrate and the viscosity of the rumen fluid tended to be lowered (P < 0.08 and P < 0.09, respectively) and the stable ingesta volume increase was significantly decreased (P < 0.01) by the lauric acid feed. The abundance of protozoa and bacteria did not differ among the treatments. In the in vitro study, the growth of S. bovis was inhibited by the lauric acid (100 nmol/L) but it showed an adaptive growth to lauric acid in long‐term subculturing. The S. bovis that had adapted to lauric acid showed decreased viscosity and lactate production (P < 0.01) in culture with sucrose. These results indicate that supplemental lauric acid added to a high grain diet improves physical properties, possibly by altering the metabolic activity of S. bovis, and it may prevent the occurrence of feedlot bloat and acidosis in beef cattle.