sugars), lactose fermenting organisms will in- 
crease so rapidly that they will become domi- 
nant and upset the normal microbial balance. 
So much lactic acid will be produced that the 
pH of the rumen will drop, and the animal 
may die of acid indigestion. Injection of acid 
has been used occasionally to defaunate ani- 
mals (Warner 1961), with a loss or decrease of 
cellulolytic bacteria as well. 
The administration of antibiotics such as oxy- 
tetracycline, chlortetracycline, and penicillin 
into the rumen could seriously affect many bac- 
teria (Munch-Petersen and Armstrong 1958; 
Bryant et al. 1961). Some species may decrease 
in numbers only temporarily, while others may 
disappear completely (Maki and Foster 1951). 
In ruminant nutrition, especially when dealing 
with wild ruminants, we will encounter not 
only manmade antibiotics but also a number of 
natural antibiotics. Most of these natural an- 
timicrobial agents will not influence the popu- 
lation of the rumen under normal dietary re- 
gime. These substances might be important, 
however, in determining the amounts of food 
the animal will consume voluntarily or under 
starvation conditions when only the plant spe- 
cies containing these substances is available 
(Dietz et al. 1962). An example of these antimi- 
crobial substances are the volatile oils which 
are present in varying amounts in a number of 
wildlife foods such as sagebrush, juniper, pine, 
etc. These volatile oils have been known to in- 
hibit and kill a number of rumen micro-organ- 
isms (Nagy et al. 1964; Nagy and Tengerdy 
1968 ; Oh, et al. 1967). The recent work of Long- 
hurst and his coworkers (Longhurst et al. 
1968; Oh et al. 1967; Oh et al. 1968) indicates 
that plant species containing substances with 
the most effective antibacterial action are the 
least palatable to deer. 
Our in vitro experiments (Nagy and Ten- 
gerdy 1968) on the action of volatile oils of 
sagebrush on deer rumen bacteria suggest that 
deer could consume sagebrush with its volatile 
oils without harm if their diet also contains 
other substances. If only sagebrush is con- 
sumed for prolonged periods, our results indi- 
cate that the antibacterial substances in the 
sagebrush will interfere with proper microbial 
digestion and consequently with normal energy 
ow. 
Different growth rates of micro-organisms 
will also influence the numbers of micro-organ- 
isms and thus the balance of bacterial species 
at any given time. There are no data available 
on the diurnal changes in the concentration of 
rumen micro-organisms of wild ruminants. 
Data gathered on domestic ruminants suggest, 
however, that frequency of feeding and not 
time of day of feeding will influence the con- 
centration of micro-organisms in the rumen. 
Some phenomenal changes in the numbers of 
protozoa and bacteria can be observed after 
feeding. The holotrich protozoa, such as the 
dasytrichs, can show a spectacular, thirtyfold 
increase (equivalent to five generations) 
within 7 hours after feeding (Warner 1965). 
Another factor influencing the environmen- 
tal conditions and thus the balance of mi- 
crobial species in the rumen is the different 
rate at which micro-organisms are removed 
from the rumen. Under a normal regular die- 
tary regime, this factor will not influence the 
total number of microbial species in the 
rumen; it will only influence the numbers of 
organisms at any given time. Under starvation 
conditions, which we can encounter with domes- 
tic range animals as well as with our wild 
ruminants during the winter months, removal 
of micro-organisms from the rumen might be a 
very important factor to consider. Starvation, 
even for only 2 days, can eliminate at least 
temporarily some species of micro-organisms 
from the rumen, resulting in lower digestion 
rates of sugars and cellulose. In some cases, 8 
to 4 days of starvation can cause complete loss 
of an organism from the rumen, and a new 
source of infection is needed to reestablish the 
species (Meiske et al. 1958). Rumen protozoa, 
probably because of their slow rate of repro- 
duction, are more susceptible to decrease in 
numbers than bacteria. Loss of certain micro- 
organisms can occur even under prolonged un- 
dernutrition. Which organisms will disappear 
will probably depend on available nutrients in 
the rumen, rate of reproduction of the organ- 
ism, and the rate of removal of the organism 
from the rumen. 
The importance of loss of functional rumen 
micro-organisms is often overlooked. We mono- 
gastrics can eat even after prolonged starva- 
tion. Our digestive juices will be present 1 day 
or 1 week after the digestion of the last food. 
The ruminant has to depend, as a first step in 
digesting food, on a functional microbial popu- 
lation in the rumen. If this functional mi- 
crobial population is lost for some reason such 
as starvation, acid indigestion, or excessive in- 
take of antimicrobial substances, ruminants 
often stop taking in food. If food is taken, no 
regular digestion can occur in the absence of 
functional rumen micro-organisms. In either 
case, the animal is doomed. 
FOOD INTAKE AND MICRO-ORGANISMS 
Another important (and, by us, neglected) 
difference between monogastrics and rumi- 
nants is the regulation of food intake. This 
also can lead to semistarvation or starvation. 
Regulation of food intake by monogastrics will 
depend mainly on the rate at which gastric 
juices are able to handle food constituents. 
161 
