s. P. ARORA

84 Pages·2014·1.99 MB·English

~~
MICROBIAL
; t
3J
IGESTION
IN RUMINANTS
s.
P. ARORA
I
MICROBIAL DIGESTION
IN
RUMINANTS
By
S. P. ARORA
M.Sc. Ph.D. (Illinois)
Head, Division of Dairy Cattle Nutrition and Physiology,
National Dairy Research Institute,
Karnal, Haryana
ICAR
INDIAN COUNCIL OF AGRICULTURAL RESEARCH
NEW DELHI
FIRST PRINTED: DECEMBER 1983
Chief Editor : P. L. JAISWAL
Editor : R. R. LOKESHW AR
Associate M. S. MEHDI
Chief Production Officer KRISHAN KUMAR
Production Associates: R. N. MANOCHA
: V. K. BAHL
Chief Artist : M. K. BARDHAN
Associates: D. HAZRA
R. M. MATHUR
Rs 11.50
Printed in India by S. N. Malhotra at Kapoor Art Press, A38/3, Mayapuri Industrial Area,
New Delhi 110064, and published by P. C. Bedi, Under-Secretary, for the Indian Council
of Agricultural Research, New Delhi 110 001
PREFACE
FROM time immemorial the contribution of ruminants in the service of
mankind has been valuable. Besides providing nutritious food ,from milk
and meat, they provide a renewable ~ource of energy and ,manure for
developing agricultural operations. In addition, the wool and halr produced
by them constitute a. valuable clothing material for protection against
inclement of w~ther in tb:e temperate and cold regions.
A remarkable attribute of ruminants is that for their own, maintenance
they do not normally'compete with human foods. They subsist mainly on
fibre-rich material unfit for direct consumption by humans and convert
them into nutrients of high biological value. This unique capacity of
ruminants characterizing specific physiological prOCesses of, digestion and
providing such metabolites as end-products, which could be used by the
host animal, has been ascribed to the presence of microbes in the rumen.
These peculiarities of ruminant digestion have, for some time, been
attracting tbe attentiotl of scientifk workers aJJ over tbe worJd, and tbe
application of these results has greatly helped in achieving increased pro
ductivity from cattle, buffaloes, sheep, goats and camels.
In this publication, prepared at the request of the Indian Council of
Agricultural Research, a concise account of the present knowledge of the
role of microbes in rumen digestion is presented. It is intended to be of
help to scientists, research scholars, teachers, field workers, and personnel
of the dairy and meat industry.
I take this opportunity to acknowledge the offer of the Indian Council
of Agricultural Research for inviting me to comllile information on this
important subject. I am grateful to Dr M. S. Swaminathan. formerly
Director-General, Dr O. P. Gautam, Director-G~neral, Dr B. K. Soni.
formerly Deputy Director-General (Animal Sciences), Dr D. Sundaresan.
Director, National Dairy Research Institute, Kamal, who all assisted in
the improvement of the manuscript of this bulletin. I express my deep
sense of gratitude to the Late Dr N. D. Kehar, the eminent Animal
Nutritionist, for offering very useful comments to improve the text of the
manuscript.
S. P. ARORA
CONTENTS
Preface iii
I Reticulo-Rumen: Histological and Physiological Development
II Feed Intake and Flow of Digesta in Ruminants 7
III Bacterial Fermentation of Carbohydrates 11
IV Protozoal Fermentation of Carbohydrates 30
V Fermentation of Dietary Proteins and Non-protein Nitrogenous
Substances 33
VI Influence of Minerals on Rumen Microbes 41
VII Digestion in Abomasum, Small Intestine and Large Intestine 45
VIII Rumen Dysfunctions and Detoxification Mechanisms 51
IX Techniques for Estimating Digestive Processes 55
References 60
CHAPTER I
RETICULO-RUMEN : HISTOLOGICAL AND
PHYSIOLOGICAL DEVELOPMENT
Development During Prenatal Period
RUMINANT foetus, like the monogastric foetus, uses carbohydrates as a
major source of energy. Glucose, fructose and amino acids are utilized
for growth during the prenatal period. Gene expression during this period
is further linked with the development of its own endocrine system which
secretes foetal hormones for the normal development of different tissues.
The ruminant foetus starts sucking amniotic fluid and thus has suckling
instinct when it is born. The liquid passes through the reticular groove
from the oesophagus and omasa! canal into the omasum (Bradley and
Mistretta, 1973). This mechanism continues to operate even after birth.
At birth, the abomasum of a calf weighs about half of the total stomach.
In the adult cattle and buffaloes rumen weighs about 80 per cent, reticulum
5 per cent, omasum 7 per cent and abomasum 7 per cent of the entire
stomach (Senger and Singh, 1969).
Development of Forestomach
After birth rumen, reticulum and omasum continue to develop till they
become functional. The transition phase in lambs starts at 3 weeks and
ends at 9 weeks of age (Edwards, 1970). In calves, this phase begins at
5 weeks and ends at about 12 weeks of age. It is a changing pattern of
carbohydrate metabolism, wherein carbohydrate utilization starts diminish
ing and gluconeogenesis process starts (Ballard et al., 1969). With the
development of rumen function, intestinal hexokinase activity decreases
along with drop in blood glucose levels (Jarrett et al., 1964).
Receptor Mechanisms
Out of the 4 major kinds of receptors, tension receptors are located with
contractile elements in the muscle layers in reticulum, rumen, cranial sac
and around reticular groove. They initiate primary cycle movements, sali
vation and'monitor rumen fill (Ash and Kay, 1959; Jggo and Leek, 1967;
Campling, 1970). The epithelial receptors are located in the reticulum,
rumen and cranial sac along the cranial and longitudinal ruminal pillars, and
have tendency to be stimulated by volatile fatty acids. They inhibit primary
cycle movements but stimulate parotid salivary secretion and satiety centre
in hypothalamus (BailIe and Mayer, 1969; Leek, 1973). When reticulum is
distended due t~ bloat, primary cycle movements are inhibi.t ed by reflex
,
2 MICROBIAL DIGESTION IN RUMINANTS
action (Kay alld Phillipson, 1,959). Tension receptors in abomasum tend
to slow down the primary cycle movements to reduce the outflow of reticulo
rumen ingesta. Mucosal receptors of abomasum are tonically active and
stimulate reticulo-ruminal primary cycle contractions (Bell and Grivel, 1975).
Gastric centres in brain are located in medulla to integrate vago-vagal
reflexes and exert influence on reticulo-ruminal motility (Harding and Leek,
1971 ).
Reticulo-rumen movements start even when the organ does not contain
solid feed. In the beginning the movements are irregular but later at about
57 days of age they are normal as double contractions (Benzie and Phillip
son, 1957).
Histo)ogy of Rumen Tissue
The epithelial lining of rumen is papillated, squamous, stratified, soft
keratinized and is coated with mucopolysaccharide (Lavker et aI., 1969).
The epithelium is non-glandular wij:h no secretory function but is well
adapted to digest coarse mass of digesta. The papilla has a basal layer
followed by stratus spinosa, stratus granulosa and the outermost layer
stratum corneum. Across the rumen wall there is a constant passage of
volatile fatty acids, which account for 60 per cent of digestible energy
intake (Bergman et ai., 1965; Orskov and McDonald, ]97]). The epithelial
lining contains mitochondria which help intracelluar transport and metabo
lism (Hyden and Sperber, 1965; Williams, 1965). On the outer side of the
basal cells, there are microvillus-like processes which facilitate passage of
absorbed fluids into the capillary bed through extensive vascular network.
The capillaries are lined with epithelial lining having pinocytotic vesicles
for absorption (Hyden and Sperber, 1965). In young ruminants receiving
only liquid diets rumen development is not normal The rumen walls are
smaller and thinner, and rumen papillae are not developed. When dry feed
is fed, rumen size, tissue growth and papillary development improve fast
(Blaxter, 1954; Brownlee, 1956; Warner et ai., 1956). Besides, papillary
bodies and paranuclear vacuoles which function to absorb solutes appear
in the mucosa later (Tamate et al., 1962; Senger and Singh, 1969; Parshad
and Arora, ]977).
Ultra-structure of rumen epithelia consists of basement membrane
between the epithelium and the connective tissue. Blood capiIlaries are
located below the basement membrane. At the junction of the basal cells
and the basement membrane there are numerous long slender cytoplasmic
finger-like processes. These are in-foldings of plasma membrane protruding
into the intercellular spaces. The intercellular spaces help in the absorptive
function of epithelium, and allow unrestricted diffusion of water and
solutes by increasing the cell surface through the epithelium to the basal
cells (Ash and Kay, 1959; Hyden and Sperber, ]965).
DEVELOPMENT OF RETICULO-RUMEN 3
The blood flow in the rumen increases with the absorption of volatile
fatty acids, effective in the order of butyrate, propionate and acetate
(Phillipson, 1959). A portion of volatile fatty acids is metabolized in the
rumen wall and the products stimulate the development of rumen papillae,
thus increasing the surface area for absorption. Butyrate is converted into
ketone bodies such as D (-) ~-hydroxybutyrate and aceto-acetate. As much
as 50 per cent of butyrate and 30 per cent of acetate of the total absorbed
quantity are metabolized in the rumen wall in cattle (Ramsey;and Davis,
1965). Propionate is also metabolized to a certain extent with the formation
of L-Iactate and pyruvate (Pennigton and Sutherland, 1956 ; Bergman and
Wolff, 1971; We~kes, 1972).
,
Rumen Contractions
The sequence of reticular and ruminal contractions after fast is a di
phasic contraction of reti.culum. In between, the contractions of anterior
dorsal sac of rumen start and later extend to the posterior dorsal sac.
During contractions in the dorsal sac, contractions also start in the ventral
sac of the anterior region and extend posteriorly. While the main ventral
sac contracts, the posterior ventral blind sac also contracts. -Total time
taken for these contractions varies from lIto 18 seconds in cattle and
sheep. The contractions are more prolonged and last 27-35 seconds when
the animals are fed. Eructation of gases occurs when dorsal ruminal con
tractions involve the anterior regions of dorsal sac, accompanied by a brief
contraction of abdominal muscles (Titchen and Reid, 1965). Rumen
movements are reflex responses under the control of central nervous system,
and stop when both vagus nerves are cut (Duncan, 1953; Singh et al., 1969).
The afferent and efferent cholinergic motor nerves control the smooth
muscles of rumen, reticulum and omasum (Comline and Titchen, 1951;
Dougherty et al., 1958). Roughage feed stimulates the frequency and
intensity, of rumen movements better than a concentrate mixture (Bhatta
charya and Mullick, 1963).
Functions of Different Compartments of Digestive Tract
Salil'ary glands,' Secretions of parotid; submaxillary and sublingual
glands are both mucus and serous types and constitute saliva. Salivary
secretion in ruminants is continuous and alkaline. It buffers the acid
products of microbial fermentation in the rumen. Further it is a lubricant
and surfactant, helping in the processes of mastication and rumination. It
provides certain electrolytes such as Na, K, Ca, Mg, P and urea for
enhancing the rate of microbial fermentation. In sheep and goats saliva is
secreted at the rate of 10-15 Iitres per day and in cattle at the rate of 75-100
litres. Secretion of saliva is affected by the physical nature of feed, dry matter
content, volume of the fluid in the gut and psychological stimulation.
4 MICROBIAL DIGESTION IN RUMINANTS
Ruminants fed large quantities of high fibre diets secrete enormous
quantity of saliva for lubrication and other functions (Balch, 1958; Bailey,
1961; Wilson and Tribe, 1963; Stacy and Warner, 1966). Lot of certain
salivary minerals and water are withdrawn from the blood plasma. This
leads to fall in plasma volume and a temporary rise in osmotic pressure of
rumen fluid (Ternouth, 1968; Blair-West and Brook, 1969; Christopherson
and Webster, 1972). Later osmotic pressure of the rumen fluid decreases
to match pre-feed values because the absorption rate of K, Na and volatile
fatty acids increases (Scott, 1967). Part increase in osmotic pressure of the
rumen fluid is also due to liberation of ammonia and formation of volatile
fatty acids.
Salivary flow in ruminants fed high energy cereal diets decreases
resulting in less buffering action in the rumen (Kay et al., 1969; Fell et al.,
1972). They also reported increased production of volatile fatty acids and
reduced salivary flow. This results in keratinized thickening of rumen
mucosa. Concomitantly there are aciduria and phosphaturia which can be
treated by infusing sodium bicarbonate into the rumen (Scott, 1972).
Reticulum: Reticulum (Fig. 1) is honey-comb like and pushes on solid,
ingested feed into the rumen and fluidy ingesta into the omasum. It assists
in rumination by allowing bolus to regurgitate into the mouth. The fer
mentation pattern in this organ is similar to that of rumen.
Rumen : Rumen is a big vat with different sacs to store and mix ingesta
for microbial fermentation. Extensive bacterial and protozoal actions on
dietary nutrients result in the liberation of end-products which are assimi
lable. The papillae are well developed resulting in increased surface area of
the rumen by seven times. Out of the total volatile fatty acids produced
85 per cent is absorbed through reticulo-rumen epithelium.
Omasum : Omasum, the third stomach, is studded with laminae which
increase the surface area. Small papillae over the surface increase further
the surface area by 28 per cent (Lauwers, 1973). The main functions of .
the omasum are to grind feed particles, absorb water along with sodium
and potassium (Hornicke, 1964; Bast, 1970), and absorb volatile fatty acids
from the ingesta flowing through the omasum (Gray et al., 1954; Badawy
et al., 1958; Johnston et at., 1961). Out of the total volatile fatty acids
formed in the reticula-rumen and omasum, only 10 per cent is absorbed in
the omasum (Leng, 1970a). Very little ammonia is absorbed, whereas
about 25 per cent sodium and 10 per cent potassium of the total that enters
the omasum are absorbed (McDonald, 1948; Dobson, 1959; Hyden, 1961;
Warner and Stacy, 1972). Omasa 1 epithelium secretes chloride ion whereas
rumen epithelia absorb it (Harrison, 1971). The water absorption property
of omasum is probably to prevent lowering of pH in the abomasum by
dilution. Magnesium and phosphorus have also been reported to be
absorbed in steers though not in sheep (Martens et al., 1978; Edrise and
DEVELOPMENT OF RETICULO-RUMEN 5
Fig. 1. Digestive system of a cow. A, Left side; B, right side.
Smith, 1979).
Abomasum: This is the first pface where chemical digestion of the food
starts due to the secretion of gastric juice. It also regulates the flow of
ingesta.
Small intestine: It is divided into duodenum, jejunum and ileum; it
regulates the flow of digesta into the large intestine by peristaltic move
ments. In the lumen, the pancreatic juice, intestinal juice and bile convert
dietary nutrients of end-products of microbial fermentation into suitable
manomers which are absorbed by active absorption or passive diffusion or
both. A number of proteolytic enzymes such as trypsinogen, chymotryp
sinogen, procarboxypeptidase, aminopeptidase in the intestinal lumen
hydrolyse proteins; intestinal lipases hydrolyse lipids; and amylases and
other disaccharidases act on sugars. In addition nudeosidases act on
nucleic acids. Enterokinase and gastrin are the enzymes involved in acti
vation of inactive enzymes or secretory processes.
Eating Behaviour of Ruminants
Feed intake provides one of the best indices of animal productivity. If
allowed free choice to eat on a good pasture, the cows would graze 540-720