Experiments were carried out to investigate the
effects of silage additives on ruminai metabolism. Three
experimental approaches were adopted; 1) in vivo
experiments using sheep; 2) in vitro experiments, and
3) infusion experiments in which silage additives were
directly infused into in vitro cultures.
In the first two experiments eleven grass
silages were used including materials treated with the
additives formic acid, acetic acid and formaldehyde, and
wilted silages. Both additive treatment and wilting
restricted fermentation and resulted in high residual
concentrations of water soluble carbohydrates and low
concentrations of protein degradation products.
The in vivo experiments showed that in all
cases restriction of in -silo fermentation increased
silage voluntary dry matter intake. Microbiological
analysis of rumen contents indicated that silage
composition influenced the microbial population of the
rumen. Numbers of proteolytic organisms were
positively correlated with ruminal ammonia concentration
and were depressed when formaldehyde- treated silages
were ingested. Silage intake influenced ruminai
microbial counts, particularly those of cellulolytic
Development of an in vitro apparatus (The
Rumenstat) was an important part of this work. The
literature relating to in vitro techniques was reviewed
and an apparatus for continuous culture at steady -state
was devised, employing established principles and a
number of innovations. With the in vitro apparatus,
cultures were maintained using the eleven experimental
silages as substrates.
The results with these cultures were in accord
with those in vivo and confirmed that ruminai characteristics were influenced by compositional differences between
the experimental silages, and not by the presence of
additives as such.
The effects of silage additives per se were
investigated in the third series of experiments. In vitro
cultures were infused with increasing concentrations of
formic acid, acetic acid, propionic acid and formaldehyde.
The organic acids depressed energy metabolism only at
concentrations higher than would result from the ingestion
of additive -treated silages. Formaldehyde caused a
general reduction in ruminal fermentation at low
concentrations. The implications of this work to the
future development of in vitro rumen technology and the
additive -treatment of silage are discussed.