The relationships between odd‐ and branched‐chain fatty acids to ruminal fermentation parameters and bacterial populations with different dietary ratios of forage and concentrate

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Keeney et al. (1962) indicated that bacterial odd‐ and branched‐chain fatty acids (OBCFAs) in the rumen might be used as a potential marker to quantify bacterial matter leaving the rumen. Recently, there has been some attention given to their presence in milk and their relation to rumen fermentation pattern (Vlaeminck et al., 2004), duodenal flow of microbes (Vlaeminck et al., 2005) and changes in feeding strategies (Dewhurst et al., 2000; Cabrita et al., 2003). Previous studies have focused more on variations in milk than in the rumen. Owing to the fact that odd‐ and branched‐chain fatty acids are usually generated from rumen micro‐organisms, and different bacteria strains had different OBCFA profiles (Vlaeminck et al., 2006b). Therefore, the relationships between the OBCFA and ruminal fermentation parameters as well as bacterial populations should be explored.
Vlaeminck et al. (2006a) analysed the effect of different dietary forage:concentrate ratios (F:C) on the fatty acid compositions of bacteria isolated from both ruminal and duodenal contents. The authors found a strong relationship between anteiso‐C15:0 and iso‐C17:0 with increasing F:C ratio. Other researchers have shown that the dietary F:C ratio influences the rumen bacterial populations (Latham et al., 1972; Tajima et al., 2001), volatile fatty acid (VFA) production and absorption (Lechartier and Peyraud, 2010; Benchaar et al., 2014) as well as changes in other fermentation parameters.
Analysis of the OBCFA profile in some predominant rumen bacteria showed that Ruminococcus flavefaciens (R. flavefaciens) and Fibrobacter succinogenes (F. succinogenes) were relatively enriched in odd‐chain iso‐fatty acids and Ruminococcus albus (R. albus) in even‐chain iso‐fatty acids (Vlaeminck et al., 2006b); these bacteria species are the predominant ruminal cellulolytic bacteria (Shi et al., 1997). Butyrivibrio fibrisolvens (B. fibrisolvens) had different fibrolytic ability (Gobius et al., 2002), and some strains had amylolytic ability (Klieve et al., 2003). Miyagawa (1982) suggested that the genus Butyrivibrio was a heterogeneous bacterial taxon through the OBCFA profile for Butyrivibrio strains. Eubacterium ruminantium (E. ruminantium) plays an important role in the rumen of animal fed forage rations (Bryant, 1959). Ifkovits and Ragheb (1968) analysed the OBCFA of E. ruminantium that includes more C15:0 and iso‐C15:0 than other OBCFAs. Selenomonas ruminantium (Selen. ruminantium) (Fernando et al., 2010) and Streptococcus bovis (Stre. bovis) (Klieve et al., 2003) are important for degradation of starch and lactate which are abundant in high‐grain diets. Vlaeminck et al. (2006b) summarized that the amylolytic bacteria showed high levels of linear odd‐chain fatty acids. However, little knowledge could be found on the relationships between OBCFA profile and bacterial population.
Consequently, the objectives of this study were to investigate the variations of OBCFA profile during ruminal fermentation in dairy cows fed rations with different F:C ratios and the relationships between OBCFA profile and ruminal fermentation parameters and bacterial populations were tested by real‐time PCR technique.
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