No abstract

Starch from corn is less susceptible to equine small intestinal digestion than starch from oats, and starch that reaches the hindgut can be utilized by the microbiota. The objective of the current study was to examine the effects of starch source on equine fecal microbiota. Thirty horses were assigned to treatments: control (hay only), HC (high corn), HO (high oats), LC (low corn), LO (low oats), and LW (low pelleted wheat middlings). Horses received an all-forage diet (2 wk; d -14 to d -1) before the treatment diets (2 wk; d 1 to 14). Starch was introduced gradually so that horses received 50% of the assigned starch amount (high = 2 g starch/kg BW; low = 1 g starch/kg BW) by d 4 and 100% by d 11. Fecal samples were obtained at the end of the forage-only period (S0; d -2), and on d 6 (S1) and d 13 (S2) of the treatment period. Cellulolytics, lactobacilli, Group D Gram-positive cocci (GPC), lactate-utilizers and amylolytics were enumerated. Enumeration data were log transformed and analyzed by repeated measures ANOVA. There were sample day × treatment interactions (P < 0.0001) for all bacteria enumerated. Enumerations from control horses did not change during the sampling period (P > 0.05). All treatments except LO resulted in increased amylolytics and decreased cellulolytics, but the changes were larger in horses fed corn and wheat middlings (P < 0.05). Feeding oats resulted in increased lactobacilli and decreased GPC (P < 0.05), while corn had the opposite effects. LW had increased lactobacilli and GPC (P < 0.05). The predominant amylolytic isolates from HC, LC and LW on S2 were identified by 16S RNA gene sequencing as Enterococcus faecalis, but other species were found in oat fed horses. These results demonstrate that starch source can have a differential effect on the equine fecal microbiota.

BCA could serve as an effective mitigation strategy for rumen acidosis. Future research is needed to evaluate the effect of BCA on mitigating rumen acidosis in vivo.

Biochanin A (BCA) is an isoflavone produced by red clover (Trifloium pratense L.) that can inhibit hyper‐ammonia‐producing bacteria (HAB) to reduce deamination in the rumen and increase the feed amino acids available for gastric digestion. An ex vivo experiment was conducted to evaluate the effect of dried distiller's grains (DDG) and BCA (30 μg mL−1) on HAB in bovine rumen fluid. Following a 24‐h incubation, HAB and ammonia concentrations in the media increased with addition of DDG. However, DDG fermentations with BCA had 100‐fold fewer HAB and 37% less ammonia than DDG‐only fermentations. A grazing experiment was conducted with crossbred steers grazing a mixture of predominately endophyte‐free tall fescue [Lolium arundinaceum (Schreb.) Darbysh], Kentucky bluegrass (Poa pratense L.), and orchardgrass (Dactylis glomerata L.) in the early and late growing season. Average daily gains (ADG) were compared among treatments of pasture‐only control, daily feeding of 1.4 kg DDG steer−1, and daily feeding of 1.4 kg DDG plus BCA (6.3 g steer−1, representing ∼30% red clover diet). Averaged over the early and late growing seasons, feeding DDG (0.83 ± 0.05 kg d−1) increased ADG by 15% over the pasture‐only treatment (0.72 ± 0.03 kg d−1), but addition of BCA to the DDG (0.93 ± 0.04 kg d−1) provided an additive increase in ADG of 29% over the control treatment. Results of the ex vivo and grazing experiments provide evidence that BCA inhibits HAB in the rumen and that the reduced deamination in the rumen can enhance weight gain performance of steers.

Aims: The objective was to determine the effect of the isoflavone biochanin A (BCA) on rumen cellulolytic bacteria and consequent fermentative activity. Methods and Results: When bovine microbial rumen cell suspensions (n = 3) were incubated (24 h, 39°C) with ground hay, cellulolytic bacteria proliferated, short-chain fatty acids were produced and pH declined. BCA (30 lg ml À1 ) had no effect on the number of cellulolytic bacteria or pH, but increased acetate, propionate and total SCFA production. Addition of BCA improved total digestibility when cell suspensions (n = 3) were incubated (48 h, 39°C) with ground hay, Avicel, or filter paper. Fibrobacter succinogenes S85, Ruminococcus flavefaciens 8 and Ruminococcus albus 8 were directly inhibited by BCA. Synergistic antimicrobial activity was observed with BCA and heat killed cultures of cellulolytic bacteria, but the effects were species dependent. Conclusions: These results indicate that BCA improves fibre degradation by influencing cellulolytic bacteria competition and guild composition. Significance and Impact of the Study: BCA could serve as a feed additive to improve cellulosis when cattle are consuming high-fibre diets. Future research is needed to evaluate the effect of BCA on fibre degradation and utilization in vivo.