Effect of pH and level of concentrate in the diet on the production of biohydrogenation intermediates in a dual-flow continuous culture

Abstract

Milk fat depression in cows fed high-grain diets has been related to an increase in the concentration of trans-10 C 18:1 and trans-10,cis-12 conjugated linoleic acid (CLA) in milk. These fatty acids (FA) are produced as a result of the alteration in rumen biohydrogenation of dietary unsaturated FA. Because a reduction in ruminal pH is usually observed when high-concentrate diets are fed, the main cause that determines the alteration in the biohydrogenation pathways is not clear. The effect of pH (6.4 vs. 5.6) and dietary forage to concentrate ratios (F:C; 70:30 F:C vs. 30:70 F:C) on rumen microbial fermentation, effluent FA profile, and DNA concentration of bacteria involved in lipolysis and biohydrogenation processes were investigated in a continuous culture trial. The dual-flow continuous culture consisted of 2 periods of 8 d (5 d for adaptation and 3 d for sampling), with a 2 × 2 factorial arrangement of treatments. Samples from solid and liquid mixed effluents were taken for determination of total N, ammonia-N, and volatile fatty acid concentrations, and the remainder of the sample was lyophilized. Dry samples were analyzed for dry matter, ash, neutral and acid detergent fiber, FA, and purine contents. The pH 5.6 reduced organic matter and fiber digestibility, ammonia-N concentration and flow, and crude protein degradation, and increased nonammonia and dietary N flows. The pH 5.6 decreased the flow of C 18:0 , trans-11 C 18:1 and cis-9, trans-11 CLA, and increased the flow of trans-10 C 18:1 , C 18:2n-6 , C 18:3n-3 , trans-11,cis-15 C 18:2 and trans-10,cis-12 CLA in the 1 h after feeding effluent. The pH 5.6 reduced Anaerovibrio lipolytica (32.7 vs. 72.1 pg/10 ng of total DNA) and Butyrivibrio fibrisolvens vaccenic acid subgroup (588 vs. 1,394 pg/10 ng of total DNA) DNA concentrations. The high-concentrate diet increased organic matter and fiber digestibility, nonammonia and bacterial N flows, and reduced ammonia-N concentration and flow. The high-concentrate diet reduced trans-11 C 18:1 and trans-10 C 18:1 , and increased C 18:2n-6 , C 18:3n-3 and trans-10,cis-12 CLA proportions in the 1 h after feeding effluent. The increase observed in trans-10,cis-12 CLA proportion in the 1 h after feeding effluent due to the high-concentrate diet was smaller that that observed at pH 5.6. Results indicate that the pH is the main cause of the accumulation of trans-10 C 18:1 and trans-10, cis-12 CLA in the effluent, but the trans-10,cis-12 CLA proportion can be also affected by high levels of concentrate in the diet.

Prediction of enteric methane emissions from Holstein dairy cows fed various forage sources

“…Importantly, shifts in ruminal bacteria and BH intermediates (i.e. elevations in the concentration of milk trans10-18:1 at the expense of trans11-18:1) are caused by low ruminal pH (Qiu et al, 2004;Fuentes et al, 2009), or by a direct toxic effect of PUFA on bacteria (Bauman and Griinari, 2001;Maia et al, 2007). In agreement with previous studies (Chilliard et al, 2009;Mohammed et al, 2011), trans10-18:1 was negatively associated with CH 4 in the present study, whereas trans11-18:1 was not correlated (Table 3).…”

The Effects of Subacute Ruminal Acidosis on Milk Fatty Acid Profile in Dairy Cattle

“…In this study the trans-10 isomers were associated with a decline in milk fat (%) from 3.89 to 3.25 (Steele et al, 2012). During acidosis, these FA are a result of intermediates from a secondary biohydrogenation pathway of C18:2 n-6 (Fuentes et al, 2009). An increase in ruminally derived trans-10 isomer is closely linked with milk fat depression, (Bauman and Griinari, 2003).…”

“…Baumgard et al (2000) detected a relationship in milk fat depression and increases in trans-10 cis-12 and C18:1 trans-10. In addition Fuentes et al (2009), also demonstrated that a pH of 5.6 decreased the trans-11 C18:1 and cis-9, trans-11 CLA; and increased the concentration of trans-10 C18:1, trans-10 cis 15 C18:2 and trans-10, cis-12 CLA. These studies indicate that the biohydrogenation intermediated FA in milk could be indicators the presence of SARA, as they are closely linked to rumen pH.…”

Fat source and dietary forage-to-concentrate ratio influences milk fatty-acid composition in lactating cows

“…Both the composition and amount of concentrates in the diet influences the extent of lipolysis and BH in the rumen (Palmquist et al, 2005). At least part of the influence of higher concentrate supplementation on ruminal lipid metabolism is thought to be mediated via decreases in rumen pH (Fuentes et al, 2009) and alterations in microbial communities (Weimer et al, 2010). In the present investigation, increases in the F : C ratio of diets containing SFO resulted in higher milk fat 4:0 to 12:0 concentrations, without altering milk 14:0 and 16:0 content.…”