Forages are usually inoculated with homofermentative and facultative heterofermentative lactic acid bacteria (LAB) to enhance lactic acid fermentation of forages, but effects of such inoculants on silage quality and the performance of dairy cows are unclear. Therefore, we conducted a meta-analysis to examine the effects of LAB inoculation on silage quality and preservation and the performance of dairy cows. A second objective was to examine the factors affecting the response to silage inoculation with LAB. The studies that met the selection criteria included 130 articles that examined the effects of LAB inoculation on silage quality and 31 articles that investigated dairy cow performance responses. The magnitude of the effect (effect size) was evaluated using raw mean differences (RMD) between inoculated and uninoculated treatments. Heterogeneity was explored by meta-regression and subgroup analysis using forage type, LAB species, LAB application rate, and silo scale (laboratory or farm-scale) as covariates for the silage quality response and forage type, LAB species, diet type [total mixed ration (TMR) or non-TMR], and the level of milk yield of the control cows as covariates for the performance responses. Inoculation with LAB (≥105 cfu/g as fed) markedly increased silage fermentation and dry matter recovery in temperate and tropical grasses, alfalfa, and other legumes. However, inoculation did not improve the fermentation of corn, sorghum, or sugarcane silages. Inoculation with LAB reduced clostridia and mold growth, butyric acid production, and ammonia-nitrogen in all silages, but it had no effect on aerobic stability. Silage inoculation (≥105 cfu/g as fed) increased milk yield and the response had low heterogeneity. However, inoculation had no effect on diet digestibility and feed efficiency. Inoculation with LAB improved the fermentation of grass and legume silages and the performance of dairy cows but did not affect the fermentation of corn, sorghum, and sugar cane silages or the aerobic stability of any silage. Further research is needed to elucidate how silage inoculated with homofermentative and facultative heterofermentative LAB improves the performance of dairy cows.

The forage lignocellulosic complex is one of the greatest limitations to utilization of the nutrients and energy in fiber. Consequently, several technologies have been developed to increase forage fiber utilization by dairy cows. Physical or mechanical processing techniques reduce forage particle size and gut fill and thereby increase intake. Such techniques increase the surface area for microbial colonization and may increase fiber utilization. Genetic technologies such as brown midrib mutants (BMR) with less lignin have been among the most repeatable and practical strategies to increase fiber utilization. Newer BMR corn hybrids are better yielding than the early hybrids and recent brachytic dwarf BMR sorghum hybrids avoid lodging problems of early hybrids. Several alkalis have been effective at increasing fiber digestibility. Among these, ammoniation has the added benefit of increasing the nitrogen concentration of the forage. However, few of these have been widely adopted due to the cost and the caustic nature of the chemicals. Urea treatment is more benign but requires sufficient urease and moisture for efficacy. Ammonia-fiber expansion technology uses high temperature, moisture, and pressure to degrade lignocellulose to a greater extent than ammoniation alone, but it occurs in reactors and is therefore not currently usable on farms. Biological technologies for increasing fiber utilization such as application of exogenous fibrolytic enzymes, live yeasts, and yeast culture have had equivocal effects on forage fiber digestion in individual studies, but recent meta-analyses indicate that their overall effects are positive. Nonhydrolytic expansin-like proteins act in synergy with fibrolytic enzymes to increase fiber digestion beyond that achieved by the enzyme alone due to their ability to expand cellulose microfibrils allowing greater enzyme penetration of the cell wall matrix. White-rot fungi are perhaps the biological agents with the greatest potential for lignocellulose deconstruction, but they require aerobic conditions and several strains degrade easily digestible carbohydrates. Less ruminant nutrition research has been conducted on brown rot fungi that deconstruct lignocellulose by generating highly destructive hydroxyl radicals via the Fenton reaction. More research is needed to increase the repeatability, efficacy, cost effectiveness, and on-farm applicability of technologies for increasing fiber utilization.

Inhibiting the growth of Escherichia coli O157:H7 (EC) in feeds may prevent the transmission or cycling of the pathogen on farms. The first objective of this study was to examine if addition of propionic acid or microbial inoculants would inhibit the growth of EC during ensiling, at silo opening, or after aerobic exposure. The second objective was to examine how additives affected the bacterial community composition in corn silage. Corn forage was harvested at approximately 35% dry matter, chopped to a theoretical length of cut of 10 mm, and ensiled after treatment with one of the following: (1) distilled water (control); (2) 1 × 105 cfu/g of EC (ECCH); (3) EC and 1 × 106 cfu/g of Lactobacillus plantarum (ECLP); (4) EC and 1 × 106 cfu/g of Lactobacillus buchneri (ECLB); and (5) EC and 2.2 g/kg (fresh weight basis) of propionic acid, containing 99.5% of the acid (ECA). Each treatment was ensiled in quadruplicate in laboratory silos for 0, 3, 7, and 120 d and analyzed for EC, pH, and organic acids. Samples from d 0 and 120 were also analyzed for chemical composition. Furthermore, samples from d 120 were analyzed for ammonia N, yeasts and molds, lactic acid bacteria, bacterial community composition, and aerobic stability. The pH of silages from all treatments decreased below 4 within 3 d of ensiling. Escherichia coli O157:H7 counts were below the detection limit in all silages after 7 d of ensiling. Treatment with L. buchneri and propionic acid resulted in fewer yeasts and greater aerobic stability compared with control, ECCH, and ECLP silages. Compared with the control, the diversity analysis revealed a less diverse bacterial community in the ECLP silage and greater abundance of Lactobacillus in the ECLP and ECA silages. The ECLB silage also contained greater abundance of Acinetobacter and Weissella than other silages. Subsamples of silages were reinoculated with 5 × 105 cfu/g of EC either immediately after silo opening or after 168 h of aerobic exposure, and EC were enumerated after 6 or 24 h, respectively. All silages reinoculated with EC immediately after silo opening (120 h) had similar low pH values (5.0) and EC counts (5.39 and 5.30 log cfu/g, respectively) 24 h later. However, those treated with L. buchneri or propionic acid had lower pH values (4.24 or 3.96, respectively) and lower EC counts (1.32 log cfu/g or none, respectively). During ensiling, EC was eliminated from all silages at pH below 4.0. During aerobic exposure, the growth of EC was reduced or prevented in silages that had been treated with L. buchneri or propionic acid at ensiling, respectively.

A meta-analysis of 158 peer-reviewed articles was conducted to examine effects of inoculation with Lactobacillus buchneri (LB)-based inoculants (LBB) that did or did not include homolactic or obligate heterolactic bacteria on silage fermentation and aerobic stability. A complementary meta-analysis of 12 articles examined LBB inoculation effects on dairy cow performance. Raw mean differences between inoculant and control treatment means weighted by inverse variance were compared with a hierarchical effects model that included robust variance estimation. Meta-regression and subgrouping analysis were used to identify effects of covariates including forage type, application rate (≤104, 105, 106, or ≥ 107 cfu/g as fed), bacteria type (LB vs. LB plus other bacteria), enzyme inclusion, ensiling duration, and silo type (laboratory or farm scale). Inoculation with LBB increased acetate (62%), 1, 2 propanediol (364%) and propionate (30%) concentration and aerobic stability (73.8%) and reduced lactate concentration (7.2%), yeast counts (7-fold) and mold counts (3-fold). Feeding inoculated silage did not affect milk yield, dry matter intake, and feed efficiency in lactating dairy cows. However, forage type, inoculant composition, and dose effects on silage quality measures were evident. Inoculation with LBB increased aerobic stability of all silages except tropical grasses. Adding obligate homolactic or facultative heterolactic bacteria to LB prevented the small increase in DM losses caused by LB alone. The 105 and 106 cfu/g rates were most effective at minimizing DM losses while aerobic stability was only increased with 105, 106, and ≥ 107 cfu/g rates. Inoculation with LBB increased acetate concentration, reduced yeast counts and improved aerobic stability but did not improve dairy cow performance.

The study was conducted to examine the effect of supplementing bentonite clay with or without a Saccharomyces cerevisiae fermentation product (SCFP; 19 g of NutriTek + 16 g of MetaShield, both from Diamond V, Cedar Rapids, IA) on the performance and health of dairy cows challenged with aflatoxin B1 (AFB1). Twenty-four lactating Holstein cows (64 ± 11 d in milk) were stratified by parity and milk production and randomly assigned to 1 of 4 treatment sequences. The experiment had a balanced 4 × 4 Latin square design with 6 replicate squares, four 33-d periods, and a 5-d washout interval between periods. Cows were fed a total mixed ration containing 36.1% corn silage, 8.3% alfalfa hay, and 55.6% concentrate (dry matter basis). Treatments were (1) control (no additives), (2) toxin (T; 1,725 µg of AFB1/head per day), (3) T + clay (CL; 200 g/head per day; top-dressed), and (4) CL+SCFP (CL+SCFP; 35 g/head per day; top-dressed). Cows were adapted to diets from d 1 to 25 (predosing period) and then orally dosed with AFB1 from d 26 to 30 (dosing period), and AFB1 was withdrawn from d 31 to 33 (withdrawal period). Milk samples were collected twice daily from d 21 to 33, and plasma was sampled on d 25 and 30 before the morning feeding. Transfer of ingested AFB1 into milk aflatoxin M1 (AFM1) was greater in T than in CL or CL+SCFP (1.65 vs. 1.01 and 0.94%, respectively) from d 26 to 30. The CL and CL+SCFP treatments reduced milk AFM1 concentration compared with T (0.45 and 0.40 vs. 0.75 µg/kg, respectively), and, unlike T, both CL and CL+SCFP lowered AFM1 concentrations below the US Food and Drug Administration action level (0.5 µg/kg). Milk yield tended to be greater during the dosing period in cows fed CL+SCFP compared with T (39.7 vs. 37.7 kg/d). Compared with that for T, plasma glutamic oxaloacetic transaminase concentration, indicative of aflatoxicosis and liver damage, was reduced by CL (85.9 vs. 95.2 U/L) and numerically reduced by CL+SCFP (87.9 vs. 95.2 U/L). Dietary CL and CL+SCFP reduced transfer of dietary AFB1 to milk and milk AFM1 concentration. Only CL prevented the increase in glutamic oxaloacetic transaminase concentration, and only CL+SCFP prevented the decrease in milk yield caused by AFB1 ingestion.

Subacute ruminal acidosis (SARA) is a metabolic disease of ruminants characterized by low pH, with significant impacts on rumen microbial activity, and animal productivity and health. Microbial changes during subacute ruminal acidosis have previously been analyzed using quantitative PCR and 16S rRNA sequencing, which do not reveal the actual activity of the rumen microbial population. Here, we report the functional activity of the rumen microbiota during subacute ruminal acidosis. Eight rumen-cannulated Holstein steers were assigned randomly to acidosis-inducing or control diet. Rumen fluid samples were taken at 0, 3, 6, and 9 h relative to feeding from both treatments on the challenge day. A metatranscriptome library was prepared from RNA extracted from the samples and the sequencing of the metatranscriptome library was performed on Illumina HiSeq4000 following a 2 × 150 bp index run. Cellulolytic ruminal bacteria including Fibrobacter succinogenes, Ruminococcus albus, and R. bicirculans were reduced by an induced acidotic challenge. Up to 68 functional genes were differentially expressed between the two treatments. Genes mapped to carbohydrate, amino acid, energy, vitamin and co-factor metabolism pathways, and bacterial biofilm formation pathways were enriched in beef cattle challenged with sub-acute acidosis. This study reveals transcriptionally active taxa and metabolic pathways of rumen microbiota during induced acidotic challenge.