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 (≥10 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 (≥10 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 first objective of this study was to examine effects of adding Escherichia coli O157:H7 with or without chemical or microbial additives on the bacterial diversity and composition of alfalfa silage. The second objective was to examine associations between the relative abundance of known and unknown bacterial species and indices of silage fermentation quality. Alfalfa forage was harvested at 54% dry matter, chopped to a theoretical length of cut of 19 mm, and ensiled in quadruplicate in laboratory silos for 100 d after the following treatments were applied: (1) distilled water (control); (2) 1 × 10 cfu/g of E. coli O157:H7 (EC); (3) EC and 1 × 10 cfu/g of Lactobacillus plantarum (EC+LP); (4) EC and 1 × 10 cfu/g of Lactobacillus buchneri (EC+LB); and (5) EC and 0.22% propionic acid (EC+PA). After 100 d of ensiling, the silage samples were analyzed for bacterial diversity and composition via the Illumina MiSeq platform (Illumina Inc., San Diego, CA) and chemically characterized. Overall, Firmicutes (74.1 ± 4.86%) was the most predominant phylum followed by Proteobacteria (20.4 ± 3.80%). Relative to the control, adding E. coli O157:H7 alone at ensiling did not affect bacterial diversity or composition but adding EC+LP or EC+LB reduced the Shannon index, a measure of diversity (3.21 vs. 2.63 or 2.80, respectively). The relative abundance of Firmicutes (69.2 and 68.8%) was reduced, whereas that of Proteobacteria (24.0 and 24.9%) was increased by EC+LP and EC+PA treatments, relative to those of the control (79.5 and 16.5%) and EC+LB (77.4 and 18.5%) silages, respectively. Compared with the control, treatment with EC+LP increased the relative abundance of Lactobacillus, Sphingomonas, Pantoea, Pseudomonas, and Erwinia by 426, 157, 200, 194, and 163%, respectively, but reduced those of Pediococcus, Weissella, and Methylobacterium by 5,436, 763, and 250%, respectively. Relative abundance of Weissella (9.19%) and Methylobacterium (0.94%) were also reduced in the EC+LB silage compared with the control (29.7 and 1.50%, respectively). Application of propionic acid did not affect the relative abundance of Lactobacillus, Weissella, or Pediococcus. Lactate concentration correlated positively (r = 0.56) with relative abundance of Lactobacillus and negatively (r = -0.41) with relative abundance of Pediococcus. Negative correlations were detected between ammonia-N concentration and relative abundance of Sphingomonas (r = -0.51), Pantoea (r = -0.46), Pseudomonas (r = -0.45), and Stenotrophomonas (r = -0.38). Silage pH was negatively correlated with relative abundance of Lactobacillus (r = -0.59), Sphingomonas (r = -0.66), Pantoea (r = -0.69), Pseudomonas (r = -0.69), and Stenotrophomonas (r = -0.50). Future studies should aim to speciate, culture, and determine the functions of the unknown bacteria detected in this study to elucidate their roles in silage fermentation.

Ensiled forage, particularly corn silage, is an important component of dairy cow diets worldwide. Forages can be contaminated with several mycotoxins in the field pre-harvest, during storage, or after ensiling during feed-out. Exposure to dietary mycotoxins adversely affects the performance and health of livestock and can compromise human health. Several studies and surveys indicate that ruminants are often exposed to mycotoxins such as aflatoxins, trichothecenes, ochratoxin A, fumonisins, zearalenone, and many other fungal secondary metabolites, via the silage they ingest. Problems associated with mycotoxins in silage can be minimized by preventing fungal growth before and after ensiling. Proper silage management is essential to reduce mycotoxin contamination of dairy cow feeds, and certain mold-inhibiting chemical additives or microbial inoculants can also reduce the contamination levels. Several sequestering agents also can be added to diets to reduce mycotoxin levels, but their efficacy varies with the type and level of mycotoxin contamination. This article gives an overview of the types, prevalence, and levels of mycotoxin contamination in ensiled forages in different countries, and describes their adverse effects on health of ruminants, and effective prevention and mitigation strategies for dairy cow diets. Future research priorities discussed include research efforts to develop silage additives or rumen microbial innocula that degrade mycotoxins.

Silage may contain several agents that are potentially hazardous to animal health, the safety of milk or other animal food products, or both. This paper reviews published literature about microbial hazards, plant toxins, and chemical hazards. Microbial hazards include Clostridium botulinum, Bacillus cereus, Listeria monocytogenes, Shiga toxin-producing Escherichia coli, Mycobacterium bovis, and various mold species. High concentrations of C. botulinum in silage have been associated with cattle botulism. A high initial concentration of C. botulinum spores in forage in combination with poor silage fermentation conditions can promote the growth of C. botulinum in silage. The elevated pH level that is generally associated with aerobic deterioration of silage is a major factor influencing concentrations of L. monocytogenes, Shiga toxin-producing E. coli, and molds in silage and may also encourage survival and growth of M. bovis, the bacterium that causes bovine tuberculosis. Soil is a major source of B. cereus spores in silage; growth of this bacterium in silage appears to be limited. Hazards from plant toxins include pyrrolizidine, tropane and tropolone alkaloids, phytoestrogens, prussic acid, and mimosine, compounds that exist naturally in certain plant species that may contaminate forages at harvesting. Another group of toxins belonging to this category are ergot alkaloids, which are produced by endophytic fungal species in forages such as tall fescue grass, sorghum, and ryegrass. Varying effects of ensiling on the degradation of these plant toxins have been reported. Chemical hazards include nitrate, nitrite, and toxic oxide gases of nitrogen produced from nitrate and high levels of butyric acid, biogenic amines, and ammonia. Chemical and microbiological hazards are associated with poorly fermented silages, which can be avoided by using proper silage-making practices and creating conditions that promote a rapid and sufficient reduction of the silage pH and prevent aerobic deterioration.

Silage is one of the main ingredients in dairy cattle diets and it is an important source of nutrients, particularly energy and digestible fiber. Unlike properly made and managed silage, poorly made or contaminated silage can also be a source of pathogenic bacteria that may decrease dairy cow performance, reduce the safety and quality dairy products, and compromise animal and human health. Some of the pathogenic bacteria that are frequently or occasionally associated with silage are enterobacteria, Listeria, Bacillus spp., Clostridium spp., and Salmonella. The symptoms caused by these bacteria in dairy cows vary from mild diarrhea and reduced feed intake by Clostridium spp. to death and abortion by Listeria. Contamination of food products with pathogenic bacteria can cause losses of millions of dollars due to recalls of unsafe foods and decreases in the shelf life of dairy products. The presence of pathogenic bacteria in silage is usually due to contamination or poor management during the fermentation, aerobic exposure, or feed-out stages. Silage additives and inoculants can improve the safety of silage as well as the fermentation, nutrient recovery, quality, and shelf life. This review summarizes the literature on the main foodborne pathogens that occasionally infest silage and how additives can improve silage safety.

This study examined whether adding 3 mycotoxin-sequestering agents to diets contaminated with aflatoxin B1 (AFB1) would reduce milk aflatoxin M1 (AFM1) concentration, and improve the performance and alter immune status of dairy cows. Fifteen lactating dairy cows were used in an experiment with an incomplete crossover design including four 28-d periods. Treatments included a control diet (C), a toxin diet (T; 1,725µg of AFB1/head per day; 75µg/kg), and diets containing the toxin and 20g/head per day of a proprietary mixture of Saccharomyces cerevisiae fermentation product containing a low (SEQ1) or high (SEQ2) dose of a chlorophyll-based additive, or a low dose of the chlorophyll-based additive and sodium bentonite clay (SEQ3). Sequestering agents were top-dressed on the total mixed ration (TMR) daily in each period, and AFB1 was dosed orally in gelatin capsules before the TMR was fed on d 21 to 25. Milk was sampled twice daily on d 20 to 28 and plasma was sampled on d 20 and 25. Sequestering agents did not affect milk AFM1 concentration during the toxin-dosing period. However, after AFB1 was withdrawn, the sequestering agents reduced the time required (24 vs. 48h) to reduce the milk AFM1 concentration below the Food and Drug Administration action level of 0.5µg/kg. Feeding T instead of C tended to reduce milk and fat-corrected milk yields, but feeding SEQ1 prevented these effects. Red blood cell count and hemoglobin concentration were reduced by feeding T instead of C, but not by feeding SEQ1, SEQ2, or SEQ3. The mean fluorescence intensity of antibody staining for 2 leukocyte adhesion molecules, L-selectin (CD62L) and β-integrin (CD18), tended to be greatest when SEQ1 and SEQ3 were fed. Plasma acid-soluble protein concentration was decreased by feeding SEQ1, SEQ2, and SEQ3 instead of T. Sequestering agents had no effect on milk AFM1 concentration, but they reduced the time required to reduce milk AFM1 concentration to a safe level after withdrawal of AFB1 from the diet. Only SEQ1 prevented the adverse effects of AFB1 on milk and fat-corrected milk yields.

This study was conducted to examine effects of the dose and viability of supplemental Saccharomyces cerevisiae on the ruminal fermentation and bacteria population and the performance of lactating dairy cows. Four ruminally cannulated lactating cows averaging 284±18d in milk were assigned to 4 treatments arranged in a 4×4 Latin square design with four 21-d periods. Cows were fed a total mixed ration containing 41.7% corn silage, 12.1% brewer's grains, and 46.2% concentrate on a dry matter basis. The diet was supplemented with no yeast (control) or with a low dose of live yeast (5.7×10 cfu/cow per day; LLY), a high dose of live yeast (6.0×10 cfu/cow per day; HLY), or a high dose of killed yeast (6.0×10 cfu/cow per day; HDY). Microbial diversity was examined by high-throughput Illumina MiSeq sequencing (Illumina Inc., San Diego, CA) of the V4 region of the 16S rRNA gene. The relative abundance of select ruminal bacteria was also quantified by quantitative PCR (qPCR). Adding LLY to the diet increased the relative abundance of some ruminal cellulolytic bacteria (Ruminococcus and Fibrobacter succinogenes) and amylolytic bacteria (Ruminobacter, Bifidobacterium, and Selenomonas ruminantium). Adding live instead of killed yeast increased the relative abundance of Ruminococcus and F. succinogenes; adding HDY increased the relative abundance of Ruminobacter, Bifidobacterium, Streptococcus bovis, and Selenomonas ruminantium. The most dominant (≥1% of total sequences) bacteria that responded to LLY addition whose functions are among the least understood in relation to the mode of action of yeast include Paraprevotellaceae, CF231, Treponema, and Lachnospiraceae. Future studies should aim to speciate, culture, and examine the function of these bacteria to better understand their roles in the mode of action of yeast. A relatively precise relationship was detected between the relative abundance of F. succinogenes (R=0.67) from qPCR and MiSeq sequencing, but weak relationships were detected for Megasphaera elsdenii, Ruminococcus flavefaciens, and S. ruminantium (R≤0.19).

This study examined effects of the dose and viability of supplemented Saccharomyces cerevisiae yeast strain YE1496 on ruminal fermentation and performance of lactating dairy cows. A second objective was to examine correlations between ruminal bacteria abundance and performance measures. Four ruminally cannulated lactating cows (284 ± 18 days in milk) were assigned randomly to 1 of 4 treatment sequences in a 4 × 4 Latin square experimental design using four 21-d experimental periods. Cows were fed a nonacidotic total mixed ration comprising 22.5% starch (minimum ruminal pH >5.8), 41.7% corn silage, 7.60% wet brewers grain, and 50.7% concentrate on a dry matter (DM) basis. The diet was supplemented with no yeast (control), a low (5.7 × 10 cfu/d; LLY) or high (6.0 × 10 cfu/d; HLY) dose of live yeast, or a high dose of killed yeast (6.0 × 10 cfu/d; killed by heating at 80°C for 1.5 h; HDY). Milk production and composition were measured twice daily from d 11 to 21 of each period, and rumen fluid samples were collected on d 21. In vivo digestibility was measured using chromic oxide as a marker. Pearson correlation analysis was used to assess whether animal performance parameters were correlated with relative abundance (RA) of ruminal bacteria. Supplemental LLY increased yields (kg/d) of milk (29.6 vs. 31.7) and milk protein (0.95 vs. 1.03), tended to increase milk fat yield (1.10 vs. 1.17) and ruminal acetate:propionate ratio (1.92 vs. 2.21), and increased in vivo apparent digestibility (%) of DM (64.5 vs. 69.1), neutral detergent fiber (NDF; 45.0 vs. 54.5), and ADF (53.1 vs. 60.9) compared with the control. Feeding HLY had no effects on milk yield compared with the control (30.0 vs. 29.6 kg/d). Feeding HDY tended to increase in vivo digestibility (%) of NDF (45.0 vs. 50.7), ADF (53.1 vs. 57.7), and the ruminal concentration of lactate (0.78 vs. 2.82 mM) but did not affect milk yield compared with the control. Dry matter and NDF digestibility correlated negatively with RA of unclassified Lachnospiraceae in both solid (r = -0.50 and -0.52, respectively) and liquid (r = -0.56 and -0.57, respectively) fractions, whereas milk yield correlated positively with RA of Lachnospiraceae [Ruminococcus] (an incompletely classified genus; r = 0.43) in the solid ruminal fraction. Supplemental LLY, HLY, or HDY increased or tended to increase DM, NDF, and ADF digestibility, but only LLY increased yields of milk, milk fat, and milk protein.