Interpretation and Use of Silage Fermentation Analysis Reports by Limin Kung and Randy Shaver Tables 1 and 2 provide the normal ranges for Introduction fermentation end products. Fermentation analyses have long been used in university and industry research trials to assess silage Table 1. Typical concentrations of common quality. These analyses are now available for fermentation end products in various legume evaluating silage quality on farms through and grass silages. commercial forage testing laboratories. Analyses Legume Legume Grass commonly included in silage fermentation reports are silage silage silage pH, lactic, acetic, propionic and butyric acids, End product (30-40%) 1 (45-55%) 1 (30-35%) 1 ammonia, and ethanol. The purpose of this Focus on pH 4.3-4.7 4.7-5.0 4.3-4.7 Forage is to answer the most frequently asked Lactic acid questions about the interpretation and use of these 7-8 2-4 6-10 reports. (%) Acetic acid 2-3 0.5-2.0 1-3 What do these reports tell us about (%) Propionic <0.5 <0.1 <0.1 the fermentation process and silage acid (%) Butyric acid quality? <0.5 0 0.5-1.0 (%) Collectively, data from a fermentation analysis can Ethanol (%) 0.2-1.0 0.5 0.5-1.0 tell us whether an excellent, average, or poor Ammonia-N fermentation has occurred. Based on these analyses, 10-15 <12 8-12 (% of CP) we can usually make some educated assumptions 1 Dry matter basis about the kinds of microorganisms that controlled the ensiling process. In many, but not all cases, the Table 2. Typical concentrations of common fermentation that a crop undergoes can be explained fermentation end products in corn silage and by various crop factors such as moisture content, high moisture corn. buffering capacity, and sugar content. However, Corn management factors such as silo packing speed, silage HM Corn silage pack density, type of additive used, chop End product (30-40%) 1 (70-75%) 1 length, silo management during storage, and silo pH 3.7-4.2 4.0-4.5 management during feed-out can affect fermentation analyses. In some cases fermentation analyses can Lactic acid (%) 4-7 0.5-2.0 qualitatively explain poor silage nutritive value or low intakes, but they cannot be used to balance diets Acetic acid (%) 1-3 <0.5 for cattle. Thus, they should always be used in Propionic acid (%) <0.1 <0.1 conjunction with other standard chemical analyses Butyric acid (%) 0 0 (i.e. ADF, NDF, CP, RDP/RUP, NEL, NDF digestion, etc.). Ethanol (%) 1-3 0.2-2.0 Ammonia-N (% of CP) 5-7 <10 Limin Kung, University of Delaware 1 Dry matter basis Randy Shaver, University of Wisconsin-Madison Focus on Forage - Vol 3: No. 13 Page 1 What does a high pH value tell us What does buffering capacity mean about the fermentation process and and what does it tell us about silage silage quality? quality? Buffering capacity measures to what degree a forage The pH of an ensiled sample is a measure of its sample will resist a change in pH. All forages have acidity, but is also affected by the buffering capacity different buffering capacities. Fresh forage with a of the crop. Two samples may have the same pH, but high buffering capacity will require more acid to different concentrations of acids. In general, legume reduce its pH than forage with a low buffering silages have a higher pH than corn or other grass capacity. In general, fresh legumes have a higher silages and take longer to ensile because of their buffering capacity than do fresh grasses or corn. higher buffering capacity. What does a low lactic acid Seldom do corn silages have a pH higher than 4.2. Such cases may be associated with extremely dry concentration tell us about the (>42% dry matter) silages that are overly mature or fermentation process and silage drought stricken. Because of its normally low pH (3.8), corn silage intake usually benefits from the quality? addition of sodium bicarbonate prior to feeding to Lactic acid should be the primary acid in good silage. neutralize its acidity. This acid is stronger than the other acids in silage Common reasons for legume silages having a pH (acetic, propionic, and butyric), and therefore is higher than 4.6 to 4.8 include: ensiling at <30% dry usually responsible for most of the drop in silage pH. matter (DM) which causes a clostridial fermentation, Further, fermentations that produce lactic acid result and ensiling at >45-50% DM, which restricts in the lowest losses of DM and energy from the crop fermentation. In the first example, a high pH due to during storage. clostridia is a definite indicator of an undesirable Some common reasons for low lactic acid content fermentation that has led to poor quality silage. include the following. However, in the second example, a high pH due to restricted fermentation is not always indicative of a q Restricted fermentation due to high DM poor fermentation or poor silage. But, silage from a content (especially legumes and grasses with restricted fermentation usually is unstable when > 50% DM). exposed to air because insufficient amounts of acid q Restricted fermentation due to cold weather. were produced to inhibit secondary microbial growth. q Sample taken after considerable aerobic exposure that has degraded lactic acid. Some common reasons for a high silage pH include q Silages high in butyric acid (Clostridial the following. silages) are usually low in lactic acid q Dry silage (> 50% DM) Lactic acid should be at least 65 to 70% of the total q Silage not fully fermented due to early silage acids in good silage. sampling time relative to harvest, cold weather during harvest, and slow or poor What does high acetic acid packing concentration tell us about the q Legume silages with extremely high ash fermentation process and silage contents (> 15% of DM) and (or) high protein content (> 23-24% CP) quality? q Silage with excess ammonia or urea Extremely wet silages (<25% DM), prolonged q Clostridial silages fermentations (due to high buffering capacity), loose packing, or slow silo filling can result in silages with q Spoiled or moldy silages high concentrations of acetic acid (>3 to 4% of DM). q Silages containing manure In such silages, energy and DM recovery are probably less than ideal. Silages treated with ammonia also tend to have higher concentrations of acetic acid than untreated silage, because the Focus on Forage - Vol 3: No. 13 Page 2 fermentation is prolonged by the addition of the Are there additives that can increase ammonia that raises pH. the propionic acid concentration of A new microbial inoculant (Lactobacillus buchneri) designed for improving the aerobic stability of silages silage? causes higher than normal concentrations of acetic acid in silages. However, production of acetic acid Biological additives that theoretically increase the from this organism should not be mistaken for a poor propionic acid concentration of silage usually contain fermentation and feeding treated silages with a high bacteria from the Propionibacteria family. However, concentration of acetic acid does not appear to cause research suggests that these organisms are usually negative effects on animal intake. unable to compete in normal silage environments and are thus, usually ineffective. What effect does silage with a high Chemical additives containing propionic acid are acetic acid concentration have on more effective at increasing the concentration of this animal performance? acid in silages. These additives can range markedly in their percentage of active ingredients but most mainstream products will increase the concentration The effect of high concentrations of acetic acid (>4- of propionic acid at ensiling from 0 to about 0.15 to 6% of DM) in silages fed to animals is unclear at this 0.30% (DM basis) if added at 2 to 4 lb per ton of wet time. In the past, some studies found that DM intake (~35% DM) silage. was depressed due to high acetic acid silage when fed to ruminants. However, the depressed intake due to What does a high butyric acid high acetic acid in the diet has not been consistent. There has been speculation that decreased intake may concentration tell us about the be actually due to unidentified negative factors fermentation process and silage associated with a poor fermentation and not to acetic acid itself. For example, in recent studies, animals quality? showed no indication of reduced intake when fed silages high in acetic acid due to inoculation with the A high concentration of butyric acid (>0.5% of DM) bacteria Lactobacillus buchneri for improved aerobic indicates that the silage has undergone clostridial stability. fermentation, which is one of the poorest fermentations. Silages high in butyric acid are If a producer has intake problems due to silages with usually low in nutritive value and have higher ADF excessively high acetic acid (>5-6% of DM), the and NDF levels because many of the soluble amount of that silage should be reduced in the TMR. nutrients have been degraded. Such silages may also Other alternatives for managing these silages include: be high in concentrations of soluble proteins and may aerating the silage for a day to volatilize the acetic contain small protein compounds called amines that acid, removing the silage and then gradually have sometimes shown to adversely affect animal reincorporating it back into the diet over a 2–3 week performance. period, and partially neutralizing the silage with sodium bicarbonate prior to feeding (about 0.5 to 1% What effect does silage with high addition on DM basis). butyric acid concentration have on What does silage acid concentration animal performance? tell us? High butyric acid has sometimes induced ketosis in Most silage contains very low concentrations of lactating cows and because the energy value of silage propionic acid (<0.2 to 0.3%) unless the silage is very is low, intake and production can suffer.