Enumeration of lactic acid bacteria on grass and the effects on silage fermentation of added bacteria
Moran, Joseph
(1990)
Enumeration of lactic acid bacteria on grass and the effects on silage fermentation of added bacteria.
Master of Science thesis, Dublin City University.
Initial studies on the methodology of enumerating lactic
acid bacteria (LAB) on grass and silage indicated that (a)
varying the homogenisation time in a stomacher from 1 to 7
minutes did not effect LAB numbers, (b) MRS and Rogosa
media gave similar LAB counts in silage and (c) anaerobic
incubation of plates led to higher counts of LAB from
silage compared to micro-aerophi1ic incubation, but
similar counts from grass. A survey of LAB numbers on
grass grown for silage showed pre- and post- harvest values
of 3.1 x 105 colony forming units (CFU)/g (range 1.40 x 104
CFU/g to 1.3 x 107 CFU/g.) and 3.3 x 105 CFU/g (range 1.6 x
104 CFU/g to 5.9 x 10° CFU/g) respectively. The numbers
recorded were not related to grass dry matter or water
soluble carbohydrate (WSC) content or to specific weather
conditions pre- harvest. From a random selection of
colonies, lactobacilli accounted for 64*, leuconostoc
25*, and streptococci 7* - of these 54* were identified as
homofermentative and 32* heterofermentative. Total LAB
were highest on dead material at the base of the crop (2.5
x 107 CFU/g), intermediate on the lower stem and
inflorescence and lowest on the leaf (6.0 x 104 CFU/g) and
upper stem (2.0 x 105 CFU/g). Counts of LAB differed
slightly across 6 grasses and one clover but were greater
than 10® CFU/g in all cases. LAB numbers on various parts
of a new harvester and mower ranged from 0 to 104 CFU/cm2.
After continuous use these values generally increased,
with 107/cm2 being recorded on the harvester chute. Where
unwilted grass with 4 x 105 CFU/g to 9 x 10s CFU/g was
ensiled in large scale farm silos, values of 5 x 108 CFU/g
to 1 x 109 CFU/g were found after 48 hours.