Sampling procedure for the measurement of dissolved hydrogen and volatile fatty acids in the rumen of dairy cows1

Abstract

Dissolved hydrogen (dH) influences the pathways of VFA production and is a precursor of methane formation in the rumen. Measurements of dH in rumen fluid taken at the same time as measuring other rumen fermentation end products would improve our quantitative understanding of the role of dH as a controller of rumen fermentation. Sample collections though a rumen cannula and using oral stomach tubing were compared for measurements of dissolved gases and fermentation end products in the rumen fluid of 4 ruminally cannulated dairy cows fed a total mixed ration of corn silage and concentrate. Rumen fluid was collected at 0, 2.5, and 6 h after morning feeding through the cannula from cranial dorsal rumen, cranial ventral rumen, central rumen, caudal dorsal rumen, and caudal ventral rumen and in parallel by oral stomach tubing at 2 insertion depths of 180 cm (sampling the central rumen) and 200 cm (sampling the caudal dorsal rumen). The cranial dorsal rumen had the greatest pH and smallest VFA concentration among 5 sites sampled. Samples collected by oral stomach tubing had greater ( < 0.001) rumen pH and less ( < 0.001) dissolved methane (dCH) and lower VFA concentration than that collected through rumen cannula. The dH concentrations were positively correlated ( > 0.8) in rumen samples collected by the 2 sampling techniques, with a concordance correlation coefficient larger than 0.8 and scale shift being about 0.1 away from unity. The variations in the measurement of dH, dCH, pH, and VFA in samples collected by oral stomach tubing are most likely the result of saliva contamination. The time of sampling relative to feeding had significant influence ( < 0.01) on dissolved gases and fermentation end products, with the greatest concentrations of dH, dCH, and VFA measured 2.5 h after morning feeding. The dH was correlated positively ( > 0.58) with dCH and negatively ( < -0.65) with the estimated net H production relative to the amount of VFA produced. This indicated that greater dH enhanced rumen CH production and also led to fermentation pathways that produce less H, such as enhanced propionate and butyrate production. In summary, oral stomach tubing could be a feasible method to measure ruminal dH in intact animals, but caution should be taken to minimize saliva contamination. Measurements made using both techniques yield similar conclusions for the effects of dH on fermentation pathways and CH generation.

Technical note: Evaluation of the ororuminal FLORA sampling device for rumen fluid sampling in intact cattle

“…Shen et al (2012) observed a tendency for total VFA concentration to be lower in ororuminal samples compared with rumen cannula samples. Previous stud-ies have observed problems with saliva contamination in ororuminal samples and attribute observed differences from ruminal cannula samples to this contamination (Duffield et al, 2004;Wang et al, 2016). The positive and negative correlations between extent of saliva contamination and pH or total VFA (Table 3), respectively, observed in the current study indicate that saliva contamination caused the higher pH and lower VFA concentrations in FLORA samples.…”

“…However, the relative proportions of acetate, propionate, and butyrate were not affected by technique (P ≥ 0.44). Wang et al (2016) also observed pH to be higher, total VFA concentration to be lower, and VFA proportions not to differ in samples obtained via an ororuminal device compared with samples obtained through a rumen cannula. Shen et al (2012) observed a tendency for total VFA concentration to be lower in ororuminal samples compared with rumen cannula samples.…”

“…Samples of rumen fluid and recordings were obtained 6 h after feeding at 3 occasions, with 2-to 4-d intervals. We selected 6 h after feeding to represent a postprandial time point at which moderate fermentation activity could be expected (Storm and Kristensen, 2010;Wang et al, 2016), to avoid high fermentation activity amplifying differences. Rumen fluid samples were taken using 2 methods: (1) the ororuminal FLORA sampling device and (2) a suction strainer (#RT, Bar Diamond Inc.) inserted through the rumen cannula into the ventral ruminal sac and a 60-mL syringe for suction.…”

Diurnal Dynamics of Gaseous and Dissolved Metabolites and Microbiota Composition in the Bovine Rumen

“…Differences observed in results from the present study may be related to the ruminal site of sampling as the rumen is not a completely homogeneous environment. The cranial ventral sac, which was the sampling site in this study, is known to have a higher total VFA concentration, lower pH, and differ in its microbiota and activity compared to the central rumen sacs (Martin et al, 1999; Wang et al, 2016a). Another possible explanation is that the increased concentration of planktonic bacteria with linseed oil was caused by a decreased number of bacteria able to colonize the feed particles (Duval et al, 2004).…”

Effects of Antidesma thwaitesianum Muell. Arg. pomace as a source of plant secondary compounds on digestibility, rumen environment, hematology, and milk production in dairy cows

“…Ruminal fermentation products were affected by sampling time relative to feeding (Wang et al., ). Ruminal pH is one of the main fermentation variables directly affecting microbial growth, and consequently ruminal fermentation (Li, Penner, Hernandez‐Sanabria, Oba, & Guan, ).…”