Agriculture Reference
In-Depth Information
triglycerides that in turn are composed of free fatty acids,
mainly palmitic, linoleic, and linolenic. Diets often contain
oilseeds that consist primarily (65-80%) of triglycerides
that contain the free fatty acids palmitic, oleic, and linoleic.
Reticulo-rumen microbes rapidly hydrolyze dietary lipids
and synthesize their own body lipids. They hydrolyze tri-
glycerides to form glycerol and respective fatty acids and
galactolipids to galactose. Glycerol and galactose are fer-
mented to VFA. The majority of fatty acids is neutralized
with calcium and adheres to the surface of bacteria or feed
particles (McAllen et al., 1983). Unsaturated fatty acids
are saturated, and the positions of the remaining double
bonds are distributed along the chains. Hydroxylation of
fatty acids and production of keto acids also occurs. Trans
fatty acids are more stable, have higher melting points, and
are diffi cult to hydrogenate, resulting in higher concentra-
tions than their counterpart cis acids. Saturated fatty acids
are not degraded further but pass to the abomasum as
calcium salts. Because unsaturated fatty acids are largely
hydrogenated within the rumen, the supply of fatty acids
available for absorption from the small intestine (SI), are
largely saturated. This contributes to the more saturated
nature and higher melting point of tallow (ruminant fat).
Biosynthesis of microbial fats in the reticulo-rumen can
involve formation of odd and branched chain fatty acids.
Fatty acids with 15 carbons and branches are found in
microbial lipids.
Metabolism of lipids in the anaerobic environment of
the reticulo-rumen is quite limited. Diets with more than
7% of DM as fat may reduce methanogenic and cellulo-
lytic fermentations. Although unsaturated fatty acids do
not compete directly with methane production, they serve
as a separate sink for excess hydrogen and indirectly
reduce methane production. Ionophores added to the diet
similarly inhibit hydrogen transport, increase the preva-
lence of propionate, and may inhibit lipid hydrolysis in the
rumen.
reduce copper availability. A cofactor for tyrosinase,
copper is needed for melanin (pigment) formation and the
normal crimp in wool, so a defi ciency can reduce hair
coloration and cause wool to become straight and steely.
Rumen microbes are benefi cial through partially hydrolyz-
ing oxalates and phytates to increase mineral bioavailabil-
ity from plants and in addition can detoxify many plant
metabolites that are toxic for nonruminants.
R
UMEN
P
ROTOZOA
AND
F
UNGI
Two main groups of ciliate protozoa are found in the
rumen. The entodiniomorphid protozoa engulf particles
and together with attached or internal bacteria can hydro-
lyze some structural carbohydrates (cellulose and hemicel-
lulose). Bacteria associated with protozoa may contribute
as much as one-third of the total rumen cellulolytic
activity. The holotrichs prefer nonstructural carbohydrate
such as starches and sugars. Entodiniomorph protozoa
also consume and digest bacteria as substrate and use
bacterial amino acids for producing protozoal protein. The
end-products of protozoal fermentation in the reticulo-
rumen include organic acids, CO
2
, ammonia, and hydro-
gen. The extent to which protozoa can digest fi ber and
synthesize amino acids is unclear because ruminal bacteria
always are so closely associated with protozoa so that
cultures of ruminal protozoa free of bacteria have never
been grown.
Although protozoa are not necessary for rumen fermen-
tation, their role in balancing the fermentation process in
the ruminants must not be underestimated. Protozoa engulf
starches and sugars to retard rapid fermentation and
thereby reduce the prevalence of lactic acidosis. Engulfed
starches and sugars can pass to the abomasum and intes-
tines digestion by the host. These are favorable functions
of protozoa. Major rumen protozoa are listed in Figure 8.1.
Anaerobic fungi also are present in the rumen, but their
contribution to the ruminal microbial mass is quite small,
and their turnover rate is slow and similar to that of pro-
tozoa. Fungi usually are associated with slowly passed
forage particles. Fungi prefer lignifi ed coarse cell walls
as a substrate, and contribute to VFA, gases, traces of
ethanol, and lactate in the rumen. Their contribution to the
rumen digestion is not yet fully understood.
O
THER
F
ERMENTATION
P
RODUCTS
Microbes in the reticulo-rumen synthesize the B-vitamins
provided an adequate amount of cobalt for B
12
synthesis,
and an adequate supply of sulfur is available for synthesis
of biotin and thiamin. For synthesis of sulfur-containing
amino acids (methionine, cystine), sulfur also is required.
This can become critical for fi ber production because
wool and mohair are rich in cystine and cysteine, amino
acids that contain sulfur. By complexing with sulfur
and reducing its availability, molybdenum and copper
can reduce sulfur availability and induce a defi ciency.
Conversely, excess sulfur complexing with copper can
T
HE
F
AT E
OF
F
ERMENTATION
E
ND
- P
RODUCTS
The main end-products of carbohydrate fermentation are
acetic, propionic, and butyric acids. Fermentation of
protein also yields these VFA plus valeric acid and
branched chain VFA and ammonia. Branched chain
VFA defi ciencies for microbial protein synthesis would
