Richard E. Muck

Storage Temperature Effects on Proteolysis in Alfalfa Silage

ABSTRACT FIRST and third cutting alfalfa was ensiled in mini-silos (100 ml centrifuge tubes) at 40 or 55% dry matter and incubated at 15, 25 or 35 °C for 40 days. In both trials and at both dry matter levels, the amount of proteolysis increased with storage temperature, averaging 10 percentage units as a fraction of total nitrogen between 15 and 35 °C. Increasing storage temperature also elevated ammonia concentrations between 15 and 25 °C but not between 25 and 35 °C. The results of this study indicated that temperature affected the rate of loss of protease activity during fermentation, based on simulations using the silage model of Pitt et al. (1985) as modified by Muck (1987). The experiments suggest that management practices that control or reduce silage temperature may be important in maximizing the amount of nitrogen in alfalfa which remains as true protein through ensiling.

FACTORS AFFECTING BUNKER SILO DENSITIES

High densities in bunker silos minimize losses and reduce storage costs; however, the guidelines to attain high densities are based on relatively little research. The objective of this study was to determine those practices or factors most correlated with bunker silo density. Density was measured in 175 bunker silos across Wisconsin using core samples collected at chest height (1.13 m, 3.70 ft, on average) across the feed-out face. Silo filling practices were surveyed and correlated with density. Most silages sampled were alfalfa or corn. Dry matter densities ranged from 106 to 434 kg/m 3 (6.6 to 27.1 lb/ft 3 ). The core densities were correlated with the height of silage above the core, indicating the effect of self-compaction. To adjust for this, all densities were corrected for the median depth below the surface (2.16 m or 7.09 ft) using the equations of Pitt (1983) for density with height for the center of tower silos. The adjusted dry matter densities were most strongly correlated with how thinly a load was spread (L), tractor weight (W), packing time per tonne as-fed (T), and dry matter content (D). These four factors were combined into a packing factor [W (TD)1/2 L –1 ] that explained 18.2% of the variation in dry matter density. Additional factors such as the use of dual wheels, etc. did not significantly improve the prediction of dry matter density. An equation was developed to predict average density in a bunker silo based on the packing factor plus crop height in the silo.

Silage microbiology and its control through additives

Ensiling is a method of preserving a moist crop. A moist crop can support the growth of a wide range of microorganisms, most of which will degrade the nutrient value to livestock. However, ensiling generally controls microbial activity by a combination of an anaerobic environment and a natural fermentation of sugars by lactic acid bacteria on the crop. This fermentation and the resulting low pH primarily suppress the growth of other anaerobic microorganisms. The fermentation can also inhibit yeasts, molds and aerobic bacteria, but the anaerobic environment is essential to preventing most of the spoilage microorganisms from growing. Inoculants have become the dominant additives for making silage. Homofermentative strains help guarantee a rapid suppression of anaerobic stains early in storage, increase dry matter recovery and have improved animal performance by means that we do not fully understand. Inoculants containing Lactobacillus buchneri, a heterofermentative species capable of fermenting lactic acid to acetic, are recent additives. The added acetic acid inhibits yeast and mold growth, increasing aerobic stability of silages at feeding.

Quantitative analysis of cellulose degradation and growth of cellulolytic bacteria in the rumen

Ruminant animals digest cellulose via a symbiotic relationship with ruminal microorganisms. Because feedstuffs only remain in the rumen for a short time, the rate of cellulose digestion must be very rapid. This speed is facilitated by rumination, a process that returns food to the mouth to be rechewed. By decreasing particle size, the cellulose surface area can be increased by up to 10(6)-fold. The amount of cellulose digested is then a function of two competing rates, namely the digestion rate (K(d)) and the rate of passage of solids from the rumen (K(p)). Estimation of bacterial growth on cellulose is complicated by several factors: (1) energy must be expended for maintenance and growth of the cells, (2) only adherent cells are capable of degrading cellulose and (3) adherent cells can provide nonadherent cells with cellodextrins. Additionally, when ruminants are fed large amounts of cereal grain along with fiber, ruminal pH can decrease to a point where cellulolytic bacteria no longer grow. A dynamic model based on STELLA software is presented. This model evaluates all of the major aspects of ruminal cellulose degradation: (1) ingestion, digestion and passage of feed particles, (2) maintenance and growth of cellulolytic bacteria and (3) pH effects.

Lessons from the cow: What the ruminant animal can teach us about consolidated bioprocessing of cellulosic biomass

Consolidated bioprocessing (CBP) of cellulosic biomass is a promising source of ethanol. This process uses anaerobic bacteria, their own cellulolytic enzymes and fermentation pathways that convert the products of cellulose hydrolysis to ethanol in a single reactor. However, the engineering and economics of the process remain questionable. The ruminal fermentation is a very highly developed natural cellulose-degrading system. We propose that breakthroughs developed by cattle and other ruminant animals in cellulosic biomass conversion can guide future improvements in engineered CBP systems. These breakthroughs include, among others, an elegant and effective physical pretreatment; operation at high solids loading under non-aseptic conditions; minimal nutrient requirements beyond the plant biomass itself; efficient fermentation of nearly all plant components; efficient recovery of primary fermentation end-products; and production of useful co-products. Ruminal fermentation does not produce significant amounts of ethanol, but it produces volatile fatty acids and methane at a rapid rate. Because these alternative products have a high energy content, efforts should be made to recover these products and convert them to other organic compounds, particularly transportation fuels.

HARVEST AND STORAGE OF TWO PERENNIAL GRASSES AS BIOMASS FEEDSTOCKS

Some perennial grasses, such as reed canarygrass (RCG) and switchgrass (SWG), have prolific yield and low inputs, making them attractive as biomass feedstocks. When harvested as biomass, these grasses are more mature and have much greater yield than when harvested as animal forage. Much is unknown about how harvest equipment performance and storage characteristics are affected by these crop conditions. The objective of this research was to determine the crop yield and drying rate, baling rate, bale density, and bale storage characteristics of these grasses harvested as biomass feedstocks. After the establishment year, the three-year average yield of RCG was 21% less than SWG (7.70 vs. 9.69 Mg DM ha -1 ) using a single-cutting system that occurred in August. When the crops were left standing over winter and harvested in the spring, DM yields were reduced by 17% and 26% for SWG and RCG, respectively. When crop yield was similar, switchgrass tended to dry faster than reed canarygrass. Drying rates of these grasses were faster than typically experienced with forage crops like alfalfa. Bale density averaged 163 kg DM m -3 with no significant differences between crops or type of wrap (twine or net). Dry bales stored outdoors for 9 to 11 months averaged 3.8%, 4.8%, 7.5%, 8.7%, and 14.9% DM loss for bales wrapped with plastic film, breathable film, net wrap, plastic twine, and sisal twine, respectively. Bales stored under cover averaged 3.0% DM loss. The chemical and physical properties of bales stored outdoors were spatially variable. Preservation by ensiling in a tube produced average DM losses of 1.1% at average moisture of 39.9% (w.b.).

The survival of silage inoculant lactic acid bacteria in rumen fluid.

Aims: To determine whether lactic acid bacteria (LAB) used in inoculants for silage can survive in rumen fluid (RF), and to identify those that survive best.

Optimizing on-farm pretreatment of perennial grasses for fuel ethanol production.

Switchgrass (Panicum virgatum L.) and reed canarygrass (Phalaris arundinacea L.) were pretreated under ambient temperature and pressure with sulfuric acid and calcium hydroxide in separate experiments. Chemical loadings from 0 to 100g (kg DM)(-1) and durations of anaerobic storage from 0 to 180days were investigated by way of a central composite design at two moisture contents (40% or 60% w.b.). Pretreated and untreated samples were fermented to ethanol by Saccharomyces cerevisiae D5A in the presence of a commercially available cellulase (Celluclast 1.5L) and beta-glucosidase (Novozyme 188). Xylose levels were also measured following fermentation because xylose is not metabolized by S. cerevisiae. After sulfuric acid pretreatment and anaerobic storage, conversion of cell wall glucose to ethanol for reed canarygrass ranged from 22% to 83% whereas switchgrass conversions ranged from 16% to 46%. Pretreatment duration had a positive effect on conversion but was mitigated with increased chemical loadings. Conversions after calcium hydroxide pretreatment and anaerobic storage ranged from 21% to 55% and 18% to 54% for reed canarygrass and switchgrass, respectively. The efficacy of lime pretreatment was found to be highly dependent on moisture content. Moreover, pretreatment duration was only found to be significant for reed canarygrass. Although significant levels of acetate and lactate were observed in the biomass after storage, S. cerevisiae was not found to be inhibited at a 10% solids loading.

EFFECTS OF CORN SILAGE INOCULANTS ON AEROBIC STABILITY

Aerobic stability of corn silage can be a major problem for farmers particularly in warm weather. Silage inoculants, while the most common type of silage additive, have not been effective at improving aerobic stability. This study investigated new and proposed inoculant products over three years on corn silage in mini-silos. Three new approaches were tested: enhanced homofermentative inoculants, a standard inoculant plus sodium benzoate, and heterofermentative lactic acid bacteria (Lactobacillus buchneri). These approaches were compared with untreated as well as four standard homofermentative lactic acid bacterial inoculants. The standard inoculants on average reduced aerobic stability 17 h relative to untreated silage. The best enhanced inoculant increased stability one year in three. The standard inoculant plus sodium benzoate increased stability but was only tested in one year. The L. buchneri inoculants improved stability consistently all three years except in one case where one of these products had low viability. Overall, the L. buchneri products appear to be most consistent at improving the aerobic stability of corn silage of those commercially available.

Lactic acid bacteria used in inoculants for silage as probiotics for ruminants.

Many studies have shown the beneficial effects on ruminant performance of feeding them with silages inoculated with lactic acid bacteria (LAB). These benefits might derive from probiotic effects. The purpose of the current study was to determine whether LAB included in inoculants for silage can survive in rumen fluid (RF), as the first step in studying their probiotic effects. Experiments were conducted in the United States and Israel with clarified (CRF) and strained RF (SRF) that were inoculated at 106–108 microorganisms/mL with and without glucose at 5 g/L. RF with no inoculants served as control. Ten commercial inoculants were used. The RF was incubated at 39°C and sampled in duplicates at 6, 12, 24, 48, 72, and 96 h for pH and LAB counts. The results indicate that with glucose the pH of the RF decreased during the incubation period. In the SRF, the pH of the inoculated samples was higher than that of the controls in most cases. This might be a clue to the mechanism by which LAB elicit the enhancement in animal performance. LAB counts revealed that the inoculants survived in the RF during the incubation period. The addition of glucose resulted in higher LAB counts.