Conditions stimulating neutral detergent fiber degradation by dosing branched-chain volatile fatty acids. II: Relation with solid passage rate and pH on neutral detergent fiber degradation and microbial function in continuous culture

Abstract

To support improving genetic potential for increased milk production, intake of digestible carbohydrate must also increase to provide digestible energy and microbial protein synthesis. We hypothesized that the provision of exogenous branched-chain volatile fatty acids (BCVFA) would improve both neutral detergent fiber (NDF) degradability and efficiency of microbial protein synthesis. However, BCVFA should be more beneficial with increasing efficiency of bacterial protein synthesis associated with increasing passage rate (k p ). We also hypothesized that decreasing pH would increase the need for isobutyrate over 2-methylbutyrate. To study these effects independent from other sources of variation in vivo, we evaluated continuous cultures without (control) versus with BCVFA (0 vs. 2 mmol/d each of isobutyrate, isovalerate, and 2-methylbutyrate), low versus high k p of the particulate phase (2.5 vs. 5.0%/h), and high versus low pH (ranging from 6.3 to 6.8 diurnally vs. 5.7 to 6.2) in a 2 × 2 × 2 factorial arrangement of treatments. Diets were 50% forage pellets and 50% grain pellets administered twice daily. Without an interaction, NDF degradability tended to increase from 29.7 to 35.0% for main effects of control compared with BCVFA treatments. Provision of BCVFA increased methanogenesis, presumably resulting from improved NDF degradability. Decreasing pH decreased methane production. Total volatile fatty acid (VFA) and acetate production were decreased with increasing k p , even though true organic matter degradability and bacterial nitrogen flow were not affected by treatments. Decreas-ing pH decreased acetate but increased propionate and valerate production, probably resulting from a shift in bacterial taxa and associated VFA stoichiometry. Decreasing pH decreased isobutyrate and isovalerate production while increasing 2-methylbutyrate production on a net basis (subtracting doses). Supplementing BCVFA improved NDF degradability in continuous cultures administered moderate (15.4%) crude protein diets (excluding urea in buffer) without major interactions with culture pH and k p .

The Effects of Incremental Doses of Aflatoxin B1 on In Vitro Ruminal Nutrient Digestibility and Fermentation Profile of a Lactating Dairy Cow Diet in a Dual-Flow Continuous Culture System

“…Microbial efficiency of 17.5 g [ 23 ] and 18.4 g of microbial N flow/kg of digested OM [ 24 ] observed in previous studies using similar continuous culture fermenter system with comparable liquid and solid passage rates are in agreement with values observed in this study. In contrast, others reported 34.6 and 22.7 g of microbial N flow/kg of OM truly digested [ 25 , 26 ], respectively. In these studies, a buffer containing 0.1 g/L of urea was used, while the passage rate was 7 and 10%/h [ 25 , 26 ], respectively; however, in the present experiment, the buffer contained 0.4 g/L of urea and the system passage rate was 11%/h.…”

“…In contrast, others reported 34.6 and 22.7 g of microbial N flow/kg of OM truly digested [ 25 , 26 ], respectively. In these studies, a buffer containing 0.1 g/L of urea was used, while the passage rate was 7 and 10%/h [ 25 , 26 ], respectively; however, in the present experiment, the buffer contained 0.4 g/L of urea and the system passage rate was 11%/h. Hence, variability in microbial efficiency between studies may be attributed to the differences in buffer solution and passage rates used.…”

Effects of milk, milk replacer, and milk replacer plus ethoxyquin on the growth performance, weaning stress, and the fecal microbiota of Holstein dairy calves

“…Moreover, previous studies demonstrated that isoacids could increase the number of cellulolytic bacteria ( fibrobacter succinogenes, Ruminococcus flavefaciens , and so on) (Bryant and Doetsch, 1954 ; Dehority et al, 1967 ). Some in vitro studies have shown that isoacids can accelerate the degradation of DM and NDF (Soofi et al, 1982 ; Roman-Garcia et al, 2021 ). They tended to increase the proportion of isoacids, further suggesting that milk replacer and milk replacer plus ethoxyquin might influence the degradation and usage of feedstuffs.…”

Effects of Barley Starch Level in Diet on Fermentation and Microflora in Rumen of Hu Sheep

“…The branched fatty acids (isobutyric, isovaleric, etc.) are the growth factors of cellulolytic bacteria in the rumen [ 36 , 37 ]. In the current study, the molar proportions of isobutyrate and isovalerate in the rumen in the 33 BS group were higher than those in the 100 BS group, which may promote the proliferation of Fibrobacter succinogenes and Ruminococcus flavefaciens .…”