The effect of level of forage and oil supplement on biohydrogenation intermediates and bacteria in continuous cultures
Introduction
Conjugated linoleic acids (CLA) are a mixture of geometric and positional isomers of linoleic acid (C18:2n6) with conjugated unsaturated double bonds. Isomers of CLA have been reported to have a wide range of beneficial effects, such as anti-carcinogenic, anti-atherogenic, anti-diabetic, and anti-obesity (Bauman et al., 2001). The major CLA isomer, c9t11, is synthesized either in the rumen as an intermediate in the biohydrogenation (BH) of C18:2n6 or in the tissues by Δ-9 desaturase from vaccenic acid (VA, t11 C18:1), an intermediate in ruminal BH of both C18:2n6 and linolenic acid (C18:3n3; Harfoot and Hazlewood, 1997). Piperova et al. (2002) reported that approximately 90% of c9t11 CLA appearing in milk fat is synthesized in the mammary gland. Although VA is usually the main trans C18:1 intermediate formed during the BH of C18:2n6 in the rumen (Harfoot and Hazlewood, 1997), under certain conditions, like low rumen pH, a shift in the BH pathway producing t10 C18:1 at a higher rate were reported (Loor et al., 2004, AbuGhazaleh and Jacobson, 2007, Fuentes et al., 2009). Such changes in fermenters trans C18:1 isomers profile may suggest a possible alteration in the microbial ecosystem and/or enzyme activities as a result of altering the proportion of concentrate in the diet.
The rumen ecosystem consist of a highly diverse collection of anaerobic microbes with the majority (70–80% of the microbial matter in the rumen) attached to feed particles in the digesta (McAllister et al., 1994). Rumen bacteria play the main role in lipid metabolism in the rumen (Harfoot and Hazlewood, 1997, Jenkins et al., 2008). More recent studies have identified Butyrivibrio fibrisolvens, Butyrivibrio hungatei, and Butyrivibrio proteoclasticus as the principal rumen bacteria in the BH of C18 unsaturated fatty acids (FA; Maia et al., 2007, Wallace et al., 2006). Harfoot and Hazlewood (1997) divided the rumen bacteria into two groups where Group A bacteria are responsible for the BH of C18 unsaturated FA to trans C18:1 and C18:2 isomers whereas Group B bacteria are involved in BH of trans C18:1 to C18:0. Accordingly, B. fibrisolvens and other cellulolytic bacteria (Ruminococcus albus and Ruminococcus flavifaciens) are categorized under Group A (Paillard et al., 2007b) while B. proteoclasticus are categorized under Group B (Wallace et al., 2006). Although the effects of diets on ruminal trans FA formation are well documented, little information is currently available about the effects of diets on rumen microbial ecology, particularly, bacterial species believed to be involved in the BH process. Therefore, the main objective of this study was to evaluate the effect of level of forage and oil supplement on rumen bacteria using continuous culture fermenters.
Section snippets
Experimental design
Four single-flow continuous culture apparatus, as described by Teather and Sauer (1988), were used in a 4 × 4 Latin square design with a 2 × 2 factorial arrangement over four consecutive periods of 10 days each. Each experimental period consisted of 9 days for adaptation, with the last day for sampling. Treatments used in this study were: high forage diet (700:300 g/kg (DM basis) forage to concentrate; HFC), high forage with oil supplement (HFO), low forage diet (300:700 g/kg (DM basis) forage to
Results
The nutrient compositions for the treatment diets are presented in Table 1. As expected, dietary acid detergent fiber (ADF) and neutral detergent fiber (NDF) content were greater (P<0.01) for the high than the low forage diets. Oleic acid and C18:2n6 content (mg/g of DM) were greater (P<0.01) with the low than the high forage diets while C18:3n3 content was greater (P<0.01) with the high than the low forage diets. Addition of oil supplement increased C18:1n9, C18:2n6 and C18:3n3 content in the
Discussion
Acetate concentration was greater with the high than the low forage diets consistent with previous reported effects of low forage diets and low rumen pH on rumen microbial fermentation (Rodríguez-Prado et al., 2004, Fuentes et al., 2009, Martinez et al., 2010). The lower intake of NDF with the high concentrate diets along with the inhibitory effects of low rumen pH on cellulolytic bacteria population (Martin et al., 2002) may explain the lower acetate concentration with the high concentrate
Conclusion
The concentrations of VA and c9t11 CLA were greater with the high forage diets while the concentrations of t10 C18:1 and t10c12 CLA were greater with the low forage diets and concentrations of these trans FA were further increased with oil supplementation. The DNA abundances of all tested strains were lower with the low forage diets indicating that these bacteria are sensitive to low rumen pH conditions. Oil supplementation, however, reduced the DNA abundance only for B. fibrisolvens, R.
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