M. Marounek et al., THE EFFECT OF VIRGINIAMYCIN ON RUMEN FERM ENTATION IN-VITRO AFTER ADAPTATION OF INOCULUM DONORS, Veterinarni medicina, 40(5), 1995, pp. 129-132
Virginiamycin is an antibiotic active against grampositive bacteria in
the alimentary tract, which is also suitable for supplementation of d
iets of growing and finishing ruminants. The aim of this work was to s
pecify the effect of virginiamycin on some parameters of rumen ferment
ation in vitro with inoculi taken from wethers adapted or non-adapted
to the virginiamycin intake. Incubations were performed anaerobically
at 39 degrees C in serum bottles closed with Bunsen valves. Virginiamy
cin was added at 0 or 10 mg/l to the rumen fluid diluted with McDougal
l buffer. Virginiamycin significantly decreased production and utiliza
tion of lactic acid, production of methane and decomposition of casein
when rumen fluid was taken from non-adapted wethers. Most of its effe
cts disappeared when rumen fluid was sampled from wethers adapted to t
he virginiamycin intake (100 mg per head daily for 2 months). Adaptati
on of wethers to virginiamycin was further confirmed by analyses of th
e rumen fluid which was used for inoculation of in vitro cultures. Mol
ar percentages of acetate, propionate, butyrate and valerate were the
same before and after the adaptation. Therefore it can be concluded th
at the effects of virginiamycin on rumen parameters are not stable and
its addition to ruminant diets cannot be recommended, with exception
of the milk nutrition period. In the last experiment the stability of
virginiamycin in the rumen fluid of adapted wethers was investigated.
The rumen fluid was diluted with buffer containing glucose and virgini
amycin (10 mg/l, final cone.) and incubated in the LF2 fermenter at pH
= 6.5. Samples taken at 0, 3, 6 and 9 h were centrifuged and cell-fre
e supernatant was added to the MRS nutrient broth inoculated with Baci
llus stearothermophilus 794B. Inoculated cultures of this indicator or
ganism were incubated overnight. It was found that the antibiotic acti
vity was stable within 9h incubation interval and, thus, a resistance
mechanism other than the direct inactivation of virginiamycin existed
in virginiamycin-adapted wethers.