Increasing levels of two different fish oils lower ruminal biohydrogenation of eicosapentaenoic and docosahexaenoic acid in vitro

Abstract

Ruminal biohydrogenation of dietary n-3 fatty acids limits any attempt to increase their contents in products of ruminants. The aim of the study was to determine whether total lipolysis, re- lease rate of eicosapentaenoic (EPA) and docosahexaenoic acids (DHA) from triacylglycerols (TG), their biohydrogenation and their accumulation as unesterified fatty acids was affected by the fish oil type (FOa; FOb), inclusion level (12.5, 25, 50, 75, 100 and 125 mg per incubation flask) and incuba- tion time (24 h; 48 h). The two fish oils which differed in EPA (FOa: 18.7%; FOb: 5.8%) and DHA (FOa: 11.7%; FOb: 7.6%) concentrations were incubated using a batch culture technique. Total lipolysis of fish oil decreased with increasing oil level at 24 h (P < 0.001). By contrast, at 48 h total lipolysis tended to be higher at 25 compared to 12.5 mg but remained constant (FOa: 74%; FOb: 81%) with inclusion levels above 25 mg. Although EPA and DHA proportions were markedly higher in FOa, release rates were similar for the two fish oils. Rates of EPA and DHA released from TG of both oils decreased with increasing levels (P < 0.001) and were higher at 48 h (P < 0.001). Biohydrogenation of EPA and DHA were lower with FOa and increasing inclusion levels (P < 0.001). Concurrently, the accumulation of unesterified EPA and DHA was more pronounced in FOa and increasing inclusion levels (P = 0.06). Compared to 24 h, 48 h of incubation enhanced the biohydrogenation of EPA and DHA (P < 0.001) and also increased their accumulation in the unesterified form (P < 0.001). In conclusion, the release and the biohydrogenation of EPA and DHA primarily depended on the amount of supplied oils and the accumulated unesterified fatty acids, respectively.