Practical 4 A-Physical and chemical evaluation of hay and silage samples
Silage Quality Properties of good silage
A. Physical properties
i. Acceptable aroma(slightly sweet odor of lactic acid with some ammonia odour)
ii. A pleasing taste/high palatability.
iii. A greenish yellow colour.
iv. Should not be mouldy, shiny or rottened.
B. Chemical properties
i. Must posses at least 35% dry matter content.
ii. The pH should be 4.0-4.5.
iii. Temperature – between 29.4-350C in the silo.
iv. Lactic acid -1.5-2.5%
Acetic acid -0.5-0.8%
Butyric acid -0.1 %
v. Ammonia Nitrogen should be 5-8% of total Nitrogen.
vi. 3% sugar content in herbage for ensiling.
vii. 55-70% digestibility
Properties of low quality silage
A. Physical properties
i. aroma– putrid or rancid odor –presence of butyric acid from Clostridium bacteria
vinegar odor – high level of acetic acid
A burnt odor — exposed to excessive heat.
iii. Very dark or brown due to excessive heat
iv. Presence of moulds
B. Chemical properties
i. dry matter content less than 35%
ii. pH more than 4.5.
iii. Temperature – more than 75 F
v. Ammonia Nitrogen more than 10 % of total Nitrogen.
vii. digestibility less than 55 %
The ensiled material should look similar to or slightly darker in color than the material before ensiling. If the color is very dark or brown, this indicates that excessive heating caused to the material to caramelize. Caramelization usually reduces protein digestibility. If molds are present in the material, this is an indication that insufficient lactic acid was produced.
Silage that has undergone normal fermenta- tion has the slightly sweet odor of lactic acid. There are also several odors that indicate issues with the fermentation process. If a putrid or rancid odor is detected, this indicates the presence of butyric acid from Clostridium bacteria. This odor usually is found in silages that are ensiled too wet or do not reach a pH below 5 due to insufficient lactic acid production. A vinegar odor usually indicates a high level of acetic acid and this will odor will discourage intake by livestock. A burnt odor indicates that the silage was
exposed to excessive heat.
Temperature is also an indication of poor fermentation. A temperature of more than 20⁰F above the air tempera-ture when the forage was ensiled indicates poor fermentation and excessive dry matter losses. Microbial activity usually raises temperature in the silage. The greater is the rate of micro-organisms in the temperature, the higher the temperature. As temperature increases, the rate of acidification in the silage is greater allowing for an earlier onset of fermentation. Higher temperatures encourage the growth of Clostridia (undesirable bacteria) which results in increased formation of butyric acid and ammonia. Silage temperature should not exceed 86 ⁰F. High temperature can also cause heat damage in the silage and reduce true protein digestibility from 90% to 30% or less.
Summary of common silage problems and possible causes. Download here
