Effects of supplemental lauric acid-rich oils in high-grain diet on in vitro rumen fermentation.

摘要

A series of studies were performed to evaluate the effects of lauric acid (LA)-rich oils on rumen fermentation of 2 steers under a high-grain diet. Soyabean 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 2 steers fed with high-grain diet was incubated with ground corn with or without oil supplementation (2.0 g/litre) for 6 h at 39 degrees C to monitor rumen products. Methane production decreased, while hydrogen production increased on LA-rich oils except COCa. All the LA-rich oils increased the total volatile fatty acids (VFA) production and molar proportion of propionate. Rumen pH, proportions of acetate, butyrate and iso-valerate concentration decreased, while ammonia and lactate concentration and propionate proportions increased after oil supplementation. Protozoal count decreased with PKO, CO and pCO supplementation. The amylase activity in culture was higher when these oils were added. The most potent additives, pCO and free LA, were further tested to determine its dose-response on rumen fermentation. pCO and LA increased propionate production at 1.2 and 0.3 g/litre supplementation, respectively. Rumen pH decreased with pCO supplementation, while VFA and ammonia production increased at 1.2 and 0.6-1.2 pCO supplementation, respectively. Acetate decreased at 0.9-1.2 g/litre pCO supplementation, while propionate increased at 1.2 g/litre only. Total gas production remained the same with pCO supplementation. Results of LA supplementation were similar to those of pCO supplementation. However, free LA had a lower supplementation level to significantly decrease rumen pH, acetate portion, protozoal number and total gas production, and increase ammonia, propionate portion and VFA. It is concluded that LA-rich oils and free LA are able to reduce methane and increase VFA, especially propionate, in a culture with ground corn. However, it is necessary to clarify the details of the actions of the oils on rumen microbes, especially the long-term effects on in vivo rumen fermentation and animal performance on a high grain diet..