Microorganisms Very Often Responsible For

15. FEED MICROBIOLOGY

Microorganisms very often responsible for

-  decomposition of nutrients (proteins, lipids…)

-  production of undesirable metabolites (toxins, ammonium, acids..)

-  decline of sensory properties (colour, smelling, taste…)

Exceptions:

-  lactic acid bacteria in silage

-  microorganisms (esp. yeasts, some bacteria) as a sources of amino acids and vitamins

-  probiotics – living microbial feed supplement for improving gut microbial balance (Enterococcus, Lactobacillus), (see also chapter Animal Microbiology)

15.1. Epiphytic microflora

= microflora of green plant parts

·  important component of farm animal feed

·  approx. 105 – 108/g

·  composition:

-  proteolytic bacteria: decomposition of proteins, mostly Pseudomonas (60 – 90%)

-  spore forming bacteria incl. butyric bacteria: decomposition of saccharides, Bacillus, Clostridium, < 10%

-  micromycetes (fungi, moulds): decomposition of several nutrients, production of toxins and other undesirable metabolites, Mucor, Rhizopus, Aspergillus, Fusarium, Penicillium…., < 10% (very variable)

-  lactic acid bacteria: lactic acid fermentation of simple saccharides, Lactococcus, Lactobacillus, < 2%, usually the only positive group

15.2. Hay microflora

·  decreased level of water (to 12-16%) results in the changes of the microflora, which is based on epiphytic microflora

·  anabiosis of microorganisms (metabolism close to 0)

·  decreased total amount of microorganisms

·  increasing rate of spores (bacteria, Zygomycetes) and conidia (Deuteromycetes)

·  water entering stimulates physiological and microbial activities, often ~ 90% of nutrients is changed to heat, thermogenesis could result in burning of material (“self-burning”)

15.3. Feed mixture microflora

·  the lowest amount of microorganisms is preferable

·  no pathogens (Salmonella, enteropathogenic Escherichia coli…)

·  no toxinogenic fungi (Aspergillus, Fusarium…)

·  conditions for development – water, temperature, contamination…

·  our recommended levels:

-  total amount of bacteria < 105/g

-  micromycetes < 104/g

15.4. Silage microflora

Silage = plant material (maize…) conserved in anaerobic conditions through the metabolic activity of lactic acid bacteria (LAB)

·  3 basic conditions for good silage

-  anaerobic conditions (plants cutting, compacting…, closing)

-  fermentable sugar content (Zubrilin) – such level of fermentable sugars to reach after fermentation pH 4.2

-  acceptable level of lactic acid bacteria

·  Phase of silage processes

-  start phase (7 days) – intensive development of epiphytic microflora, firstly aerobes (consumption of O2), lately anaerobes – fermentation of sugars, LAB development starts - production of organic acids (mainly lactic, partly acetic),

-  phase of LAB: massive development of LAB and production of lactic acid, firstly development of cocoid forms of Lactococcus – quick growth rate, higher sensitivity to lactic acid; lately intensive development of lactobacilli

-  end phase (after 8 weeks): decreasing microbial activity and microorganisms number, silage acceptable for animal feeding

·  Main silage microorganisms (the same groups and characteristics as in epiphytic microflora):

-  LAB – the only positive group, preferable homofermentative LAB (Lactococcus lactis, Lactobacillus plantarum), optimal level > 90%,

-  Butyric acid bacteria (Clostridium), negative – use of saccharides, production of butyric acid; regulation - pH (< 4.9 resp. 4.5)

-  Micromycetes, negative - nutrients decomposition, toxins production; regulation – anaerobiosis

-  Proteolytic bacteria, negative - nutrients decomposition, regulation - pH (< 4.9 resp. 4.5)

Regulation of silage processes

-  Anaerobiosis – obligatory

-  inoculation with LAB = microflora composition improving in the beginning of silage processes, satisfactory sugar content is obligatory; Enterococcus, Lactobacillus

-  inoculation with other bacteria as a sources of enzymes (hydrolases) – decomposition of complex sugars for LAB; Bacillus, Aspergillus

-  combined preservatives – mixture of enzymes and LAB

-  sugar content improvement, mixture of plants with different content of sugars, molasses amendment

-  decreasing of pH with organic or inorganic acids

-  undesirable microorganisms regulation, chemical amendments decrease their number- salts of organic acids, earlier antibiotics (now banned)