The inclusion of low quantities of lipids in the diet of ruminants fed low quality forages has little effect on rumen function

Biohydrogenation within rumen fluid (RF) proceeds to varying degrees depending on retention time (RT) and type of basal diet, especially the profile of fatty acid (FA) being hydrogenised. The objective of this study was to examine the FA profile and the RT of liquid in the rumen of steers fed a low crude protein (CP) tropical grass (Chloris gayana hay, 38 g CP, 17 g crude lipid and 752 g neutral detergent fibre (aNDFom)/kg dry matter (DM)) supplemented with various lipids. Five rumen cannulated Bos indicus cross, five-year-old steers (799 ± 15 kg live weight (LW)) were allocated to a 5 × 5 Latin square design. The treatments were control, hay only, or the addition of 30 g/kg hay DM of lipid sources: Coconut (high lauric acid), cottonseed and soybean (high linoleic acid) or fish oil (high long chain FA (LCFA)). Retention time decreased with addition of soybean oil (14 h) but no differences between other treatments (mean 17 h). Coconut oil increased lauric and myristic acids in RF. There were no changes in total saturated FA (TSFA) in RF, with exception of a lower concentration for fish oil treatment. Addition of fish oil also decreased the concentration in RF of stearic and linolenic acid, but no differences to coconut and cottonseed treatments for linolenic acid. Fish oil also resulted in higher LCFA, linoleic and total unsaturated FA (TUFA), but no differences to soybean oil for the latter two acids. The conjugated linoleic acid (CLA) was only different in RF between cottonseed and fish oil treatments. Differences in FA profile of oils were only partially translated into the FA profile in RF of steers fed a tropical hay, without great changes in the proportion of CLA isomers observed.