FROM FEED TO MILK: UNDERSTANDING RUMEN FUNCTION
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
EXTENSION CIRCULAR 422 FROM FEED TO MILK: UNDERSTANDING RUMEN FUNCTION
CONTENTS
Part I: Background in Basic Nutrition of Dairy Cattle ........................... 1
Rumen physiology ................................................................................................................ 1
Rumination and saliva production ..................................................................................... 3
Function of the rumen ........................................................................................................... 3
Rumen microbiology ............................................................................................................. 4
Microbial digestion in the rumen ........................................................................................ 6
Carbohydrates ................................................................................................................ 6
Protein ............................................................................................................................. 8
Lipids ............................................................................................................................... 8
Vitamins .......................................................................................................................... 8
Basic nutritional concepts behind feeding dairy cattle .................................................... 8
Dry matter intake and its effect on the cow ..................................................................... 11
Part II: Feed and Feed Nutrients for Dairy Cattle .............................. 13
Carbohydrates ...................................................................................................................... 13
Fats ......................................................................................................................................... 15
Protein ................................................................................................................................... 17
Energy ................................................................................................................................... 21
Minerals ................................................................................................................................ 23
Vitamins ................................................................................................................................ 25
Water ...................................................................................................................................... 26
List of Figures
Figure 1. Summary of digestion and absorption in the ruminant. ............................................ 2
Figure 2. Ruminal fermentation as a consequence of adaptation due to pH regulation. .......... 6
Figure 3. Feed, nutrient flow from the rumen, and milk components. ..................................... 6
List of Tables .......................................................... Inside back cover
Prepared by Virginia Ishler, extension assistant in the Department of Dairy and Animal
Science; Jud Heinrichs, professor of dairy and animal science; and Gabriella Varga, associate
professor of animal science.
Development of this publication was made possible through a grant from Church & Dwight Co.,
Inc., manufacturers of ARM & HAMMER® feed ingredients.TABLES
Table 1. Rate of passage of feed for dry cows and lactating cows. ................................ 1
Table 2. Effect of ration on eating rate and on saliva production. ................................. 3
Table 3. Chemical composition of saliva from cattle. ....................................................... 3
Table 4. Typcial composition of rumen gases. ................................................................... 4
Table 5. Grouping of rumen bacterial species according to the type
of substrates fermented. ........................................................................................ 5
Table 6. Effect of forage to concentrate ratio on the volatile fatty acid
proportions in the lactating cow. .......................................................................... 7
Table 7. Estimated rumen fermentation characteristics. .................................................. 7
Table 8. Feed ingredient sources that are utilized by ruminants. .................................. 8
Table 9. Eating, rumination behavior, rumen pH, volatile fatty acids (VFA’s),
average milk yield, and milk composition as influenced by particle
size of the ration. ..................................................................................................... 9
Table 10. Differences in extent of ruminal digestion of starches as affected
by source and processing. ................................................................................... 10
Table 11. Target scores for stages of lactation using the 5-point
body condition scale. ............................................................................................ 11
Table 12. Classification of concentrate ingredients. ......................................................... 13
Table 13. Carbohydrate fractions for some common forages and
feed ingredients. ................................................................................................... 14
Table 14. Fiber partition in various forages. ...................................................................... 15
Table 15. Guidelines for forage neutral detergent fiber (NDF) and
forage dry matter intakes. ................................................................................... 15
Table 16. Guide to carbohydrate composition in rations for
high-producing dairy cows. ................................................................................ 15
Table 17. Fatty acid profile of various commodity and specialty fat sources. .............. 16
Table 18. Crude protein and protein fractions in various forages and
feed ingredients. ................................................................................................... 17
Table 19. Average distribution of protein and nitrogen fractions in
some feedstuffs. .................................................................................................... 18
Table 20. List of the essential and nonessential amino acids. ......................................... 19
Table 21. The essential amino acid profiles of milk, ruminal bacteria, and feeds. ...... 19
Table 22. Guide to protein composition in rations for high-producing
dairy cows. ............................................................................................................. 20
Table 23. Regression equations for estimating energy values of various feeds. .......... 20
Table 24. Calculation of cattle NEM and NEG values. .................................................... 21
Table 25. Summarization of minerals in the dairy ration. ............................................... 22
Table 26. Guide to mineral composition in rations for high-producing cows. ............ 24
Table 27. Summarization of fat-soluble vitamins in the dairy ration. ........................... 25
Table 28. Guide to vitamin composition in rations for high-producing
dairy cows. ............................................................................................................. 25
Table 29. Water intake needs by various age groups of dairy cattle,
drinking water only. ............................................................................................. 26
Table 30. Interpretation of a water analysis report. .......................................................... 27PART I: BACKGROUND IN BASIC NUTRITION OF DAIRY CATTLE
Feed costs represent 45 to 60 percent of muscular organ. The rumen develops The presence of food in the aboma
the total cost of producing milk. anatomically in size, structure, and sum stimulates hydrochloric acid
The key to maximizing dairy farm microbial activity as the calf’s diet is production. Hydrochloric acid converts
profitability is to maintain nutrient levels changed from liquid milk or replacer to pepsinogen to pepsin, which breaks
while carefully managing feed costs. dry feed or silages. In the mature down protein to shorter molecular chain
When optimal nutrition is achieved, cows ruminant, the rumen nearly fills the compounds such as peptides and amino
will produce better quality and larger entire left side of the abdominal cavity. acids for further digestion and absorp
quantities of milk. Overall health should The rumen is a fermentation vat that tion in the small intestine. The true
improve, resulting in cost savings in can hold 40 to 60 gallons of material and stomach has a low pH of 2 to 4, due
veterinary fees, breeding, and treatment is the site of microbial activity. An largely to this acid production. Some fat
with drugs. estimated 150 billion microorganisms per digestion also occurs in the true stomach.
A basic understanding of animal teaspoon are present in its contents. They Digesta flowing from the abomasum
nutrition as it applies to dairy cattle is consist of bacteria, protozoa, and fungi. to the small intestines is composed of
essential to good herd management. Bacteria require a warm, moist, oxygen- small particles suspended in liquid
Proper feeding of the dairy cow is free environment for optimum growth. digesta. There is little sorting of particu
complicated and requires a combination This type of environment is naturally late matter, and the flow of liquid and
of scientific knowledge, creativity, and maintained in the rumen with a tempera particles is rather similar. As digesta
good management skills to balance the ture range of 100 to 108oF. If cows are fed passes through the small intestine, the
needs of the rumen microorganisms and a proper balance of forages and grain, the pH increases at a relatively slow rate.
the needs of the animal. pH should range between 5.8 and 6.4, This has important implications for
which allows the growth of many species enzymatic activity in the intestine
Rumen physiology of bacteria. because enzymes secreted by the
What makes ruminant animals unique is The omasum is sometimes referred pancreas and intestinal mucosa generally
their four stomach compartments: the to as the “manyplies” because of its have a pH optimum which is neutral to
reticulum, the rumen, the omasum, and many layers of muscular tissue. In the slightly alkaline.
the abomasum. The reticulum and the omasum, the particle size of digesta is
rumen are often discussed together reduced, and any excess water is Table 1. Rate of passage of feed for dry cows
because they are adjoining compart removed before the digesta enters the and lactating cows.
ments. The reticulum is actually the abomasum. The omasum can contain up ITEM DRY COWSa MILK COWSa
largest of the various sacs of the rumen. to 4 gallons of digesta. Body weight, lb 1541 1381
Digestion of feedstuffs by microorgan The fourth compartment is the
Dry matter intake, lb/day 23.8 43.5
isms takes place in both stomach abomasum or “true stomach,” where
Milk production, lb/day — 53.6
compartments. acids and enzymes further digest the
cow’s digesta. It is the first true glandular Ruminal mean retention
The reticulum, often called “the
time, hr
blind pouch,” is the first stomach portion of the gastrointestinal tract where
Grain 25.6 19.4
compartment. If the cow consumes metal the stomach walls secrete enzymes. It Hay 30.0 30.3
or other large indigestible items, the functions very similarly to the stomach of Total mean retention time
honeycomb structure of the stomach wall many simple stomached animals such as in the digestive tract, hr
acts as a sieve and prohibits any hard the pig. This stomach compartment can Grain 47.0 39.2
ware from moving further into the hold approximately 5 gallons of material. Hay 55.3 50.7
digestive tract. Feed that enters the The time that digesta remains in the Source: Adapted from Hartnell, G. F. and L. D.
reticulum is later regurgitated and abomasum is very short compared to the Satter. 1979. Determination of rumen fill,
remasticated as part of the cud. The retention time of feeds in the rumen. The retention time and ruminal turnover rates of
reticulum can contain up to 2.5 gallons of turnover rate of feedstuffs in the rumen ingesta at different stages of lactation in dairy
and total retention time in the digestive cows. J. Anim. Sci. 48:381.
undigested feed and feed being digested
a Means reported in this table were taken from
(digesta). tract, for lactating and dry cows, are
four dry cows and four lactating cows.
The rumen is a large, hollow shown in Table 1.2 FROM FEED TO MILK: UNDERSTANDING RUMEN FUNCTION
Bile salts, which are synthesized in In adult ruminants fed high forage Protein reaching the small intestine
the liver from cholesterol, aid in main diets, virtually all of the soluble sugars as of the ruminant is derived from three
taining this alkaline pH in the small well as most of the starch in feeds are sources: (a) dietary protein that has
intestine. They also act as emulsifiers that fermented by the rumen microbial escaped breakdown by rumen microbes;
separate fat globules and give lipase population. However, animals fed high (b) protein contained in bacterial and
enzymes more surface area upon which grain diets at high intake levels may have protozoal cells that flow out of the
to act. Both the biliary and the pancreatic as much as 50 percent of the dietary rumen; and (c) endogenous proteins
secretions neutralize the gastric acids and starch escape ruminal fermentation and contained in sloughed cells and secre
provide enzymes for hydrolysis of be presented in the lower tract for tions into the abomasum and intestine.
starches, proteins, and lipids. The small digestion. In these circumstances, Pancreatic and intestinal proteases break
intestine is the main absorption site for substantial amounts of glucose may be down these forms of protein so the amino
these breakdown products (Figure 1). absorbed from the small intestine. acids and peptides can be absorbed in the
small intestine.
Figure 1. Summary of digestion and absorption in the ruminant.
DIGESTIVE ORGAN FEED CONSTITUENT
Nonprotein nitrogen
MOUTH (NPN) Feed proteins Fats Carbohydrates
NPN Feed proteins Fats Cellulose Starches
RETICULUM Hemicellulose Sugars
B B B B B B
Bacterial protein B Glucose
RUMEN (contains essential Volatile fatty acids
amino acids) (VFA's)
OMASUM VFA's
Bacterial Feed
ABOMASUM OR TRUE STOMACH protein protein
Peptides
Starches
Peptides Fats Sugars
SMALL INTESTINE
Amino acids Fatty acids Glucose
and
Glycerol
KEY: = some absorbed = main site of absorption B = bacterial actionPART I: BACKGROUND IN BASIC NUTRITION OF DAIRY CATTLE 3
Lipids arriving in the small intestine Saliva neutralizes the acids produced Rumination may be significantly
are primarily esterified fatty acids and during fermentation and helps to reduced, for example, by feeding high
phospholipids. Triglycerides that escape maintain an ideal environment for amounts of concentrates and finely
ruminal breakdown and esterified fatty bacteria growth. chopped forages. High moisture feeds
acids of microbial origin are readily Production of saliva can be encour such as pasture or silage can reduce
hydrolyzed by pancreatic lipase to aged by controlling the ruminant’s diet. saliva produced per pound of dry matter
release free fatty acids. These are The more a cow chews, the more saliva it intake by 50 percent. Grains or pelleted
absorbed by the intestinal mucosal cells. produces. The amount of time a cow feeds can reduce the flow to 20 percent of
Any material that has not been spends chewing is influenced by feeding that on a long-hay diet. Saliva production
utilized in the digestive tract to this point management practices and the nature of can drop dramatically if the cow does not
enters the large intestine. Absorption of the diet. The order in which feed ingredi receive adequate effective fiber, which is
water, minerals, nitrogen, and volatile ents are fed, the particle size of the feeds, defined as a combination of forage
fatty acids occurs in the large intestine. the number of times during the day cows particle size and forage neutral detergent
The homostatic functions of the large are fed, and the type of feed consumed fiber intake.
intestine involve electrolyte balance, can all directly affect saliva production.
some microbial fermentation, and Long hay stimulates the greatest amount Function of the rumen
temporary storage for excreta. Any of chewing, rumination, and saliva The rumen through its strong muscula
products that have not been digested will production. Feeding forages high in cell ture allows mixing and churning of
pass out through the feces. Fecal material wall content or neutral detergent fiber digesta. The movement of the rumen
contains undigested feed, metabolic fecal would tend to increase rumination time. mixes the contents, promoting turnover
nitrogen, and undigested fat and and accessibility of the coarser forage
bacteria. particles for regurgitation, cud chewing,
Table 2. Effect of ration on eating rate and on size reduction, and microbial digestion.
Rumination and saliva production saliva production. Fine forage particles, dense concentrate
A ruminant animal has the ability to EATING RATE SALIVARY PRODUCTION particles, and materials which have
POUNDS OF TEASPOONS/POUND
ingest feed rapidly and to complete the FEED FEED/MIN OF FEED
become hydrated tend to congregate near
chewing at a later time. This process is Pelleted .79 1.0
the bottom. Particles tend to move out
known as rumination. The steps involved from the rumen as they are reduced in
Fresh grass .62 1.5
are regurgitation of the feed, remasti size through cud chewing and microbial
Silage .55 2.0
cation or rechewing, resalivation, and action. The microbes also pass from the
reswallowing of rumen digesta. The Dried grass .18 5.0 rumen for possible digestion in the lower
process of rumination reduces the Hay .15 6.0 gastrointestinal tract.
particle size of feeds, which enhances Source: Bailey, C. B.1958. The role of secretion of The structuring and composition of
microbial function and allows for mixed saliva in the cow. In: Proceedings of the rumen contents is influenced by diet.
easier passage out of the stomach Nutrition Society, p. xiii. Since the dairy cow consumes such a
compartments. varied selection of feedstuffs and feed
The regurgitated material is called a particle sizes, rumen contents do not
“bolus” or “cud” and consists primarily have a uniform composition, and as a
Table 3. Chemical composition of saliva from
of chewed material coated with saliva. cattle. result there is stratification of feed
Saliva is a major secretion into the particles. Long-hay diets produce
ELEMENT mEq/la
digestive tract, and its production is contents with a large, less dense, floating
Sodium 126
directly related to the amount of time a layer beneath the gas dome with rela
cow spends eating and ruminating Potassium 6 tively liquid contents and suspended
(Table 2). Production of saliva in a Phosphate 26 fiber beneath. Denser material sinks to
mature ruminant can exceed 47.5 gallons Chloride 7 the bottom of the rumen. The floating
per day when cows chew six to eight Bicarbonate 126 mat is composed of the more recently
hours per day. ingested forage. In diets where forage
Source: Bailey, C. B. and C. C. Balch. 1961. Saliva
Saliva is rich in mineral ions, secretion and its relation to feeding in cattle.
particle size is fine and forage neutral
particularly sodium, phosphate, and British Journal of Nutrition 15:371. detergent fiber is low, the floating mat is
bicarbonate, which serve as buffering a mEq/l is milliequivalents per liter. diminished, but this occurs to a much
agents in the digestive system (Table 3). greater extent when high levels of4 FROM FEED TO MILK: UNDERSTANDING RUMEN FUNCTION
pelleted grain or concentrates are fed. period of two to three weeks is usually responsible for regulating the overall
The rumen contents with these types of needed. fermentation in the rumen. They remove
diets are generally more viscous. The development of the ruminal hydrogen gas by reducing carbon dioxide
The function of the rumen as a papillae is related to the production of with hydrogen gas to form methane.
fermentation vat and the presence of certain acids from the fermentation of Producing methane keeps the hydrogen
certain bacteria promote the develop feeds. Increasing the proportions of concentration in the rumen low, which
ment of gases. These gases are found in butyric and propionic acids, as seen with allows methanogenic bacteria to promote
the upper part of the rumen with carbon high grain rations, increases blood flow the growth of other bacterial species and
dioxide and methane making up the to the ruminal epithelium, which provides for a more efficient fermenta
largest portion (Table 4). The proportion stimulates vascular budding and tion. The effective removal of hydrogen
of these gases is dependent on rumen epithelial cell proliferation. Papillae by these methanogenic species encour
ecology and fermentation balance. either grow in size and number or ages hydrogen-producing species to
Ordinarily, the proportion of carbon shorten in size, depending on the diet produce more hydrogen and thus alter
dioxide is two to three times that of and the fermentation acids produced. their metabolism towards higher yielding
methane, although a large quantity of pathways. These higher yielding
carbon dioxide is reduced to methane. Rumen microbiology pathways result in the synthesis of more
Approximately 132 to 264 gallons of gas The objective of feeding dairy cattle microbial cells, which increases available
produced by fermentation are belched nutritionally balanced diets is to provide protein to the ruminant.
each day. The eructation of gases via a rumen environment that maximizes The protozoa in the rumen number
belching is important in bloat prevention. microbial production and growth. When about 105 to 106 cells/gram of rumen
designing rations for ruminants, the contents and are influenced by feeding
needs of both the animal and the rumen practices. Higher numbers of protozoa
microorganisms must be considered. In are generally found in the rumen when
Table 4. Typical composition of rumen gases.
order to optimize animal performance, diets of high digestibility are fed.
COMPONENT AVERAGE PERCENT
compromises in feeding the microbes or Different types of diets seem to encour
Hydrogen 0.2 age different protozoal genera. Some
the cow may occur.
Oxygen 0.5 The microbial population in the protozoa numbers are higher when diets
Nitrogen 7.0 rumen consists of bacteria, protozoa, and contain large amounts of soluble sugars
Methane 26.8 fungi. The majority of the concentration and other types predominate with high
Carbon dioxide 65.5 is as bacteria, which can number 1010 to starch diets.
1011 cells/gram of rumen contents. The protozoa actively ingest bacteria
Source: Sniffen, C. J. and H. H. Herdt. The
Bacteria can be grouped according to as a source of protein. They also appear
Veterinary Clinics of North America: Food Animal
Practice, Vol 7, No 2. Philadelphia, Pa.: W. B. their three main shapes (cocci, rods, and to be a stabilizing factor for fermentation
Saunders Company, 1991. spirilla), according to their size (generally end products. Protozoa, like bacteria and
from 0.3 to 50 µm), and according to their fungi, contribute to fiber digestion. While
different structures. They can also be the protozoa are an integral part of the
grouped according to the type of microbial population and have a marked
The mucosal surface of the rumen is substrate fermented and are categorized effect on the fermentation, their benefit to
characterized by ruminal papillae, the into eight distinct groups of rumen the ruminant is still controversial.
organs of absorption. Papillae distribution, bacteria (Table 5). These species of The anaerobic fungi are the most
size, and number are closely related to bacteria degrade or utilize products such recently recognized group of rumen
forage to concentrate ratio, feeding habits, as cellulose, hemicellulose, starch, sugars, microbes. When animals are fed a high
forage availability, and digestibility. intermediate acids, protein, and lipids forage diet, rumen fungi may contribute
If a ruminant’s diet is significantly and produce methane. An expanded up to 8 percent of the microbial mass.
altered, as in moving from a high forage classification could include pectin While it is still unclear whether these
diet to a high grain diet or a dry cow utilizers and ammonia producers. Most fungi are functionally significant, they
ration to a lactating cow diet, this change species of bacteria are capable of ferment have been shown to degrade cellulose
should be implemented gradually to ing more than one substrate. and xylans, indicating some role in fiber
allow ruminal papillae time to adapt to The methane-producing bacteria are digestion.
nutritional changes. An adaptation a special class of microorganismsPART I: BACKGROUND IN BASIC NUTRITION OF DAIRY CATTLE 5
Consideration of microbial repro
Table 5. Grouping of rumen bacterial species according to the type of substrates fermented.
duction rate is essential when making
Major Cellulolytic Species Major Lipid-utilizing Species dietary changes in any ruminant. Major
Bacteroides succinogenes Anaerovibrio lipolytica changes in the diet require a period of
Ruminococcus flavefaciens Butyrivibrio fibrisolvens transition to allow for shifts in the
Ruminococcus albus Treponema bryantii populations of different microbial
Butyrivibrio fibrisolvens Eubacterium sp. species. This adaptation may take several
Fusocillus sp.
Major Pectinolytic Species Micrococcus sp.
days. One of the most common problems
Butyrivibrio fibrisolvens encountered in nutrition management is
Bacteroides ruminicola Major Hemicellulolytic Species sudden changes in the ruminant’s diet to
Lachnospira multiparus Butyrivibrio fibrisolvens include large amounts of readily ferment
Succinivibrio dextrinosolvens Bacteroides ruminicola
able carbohydrates. Feeding diets of this
Treponema bryantii Ruminococcus sp.
Streptococcus bovis type results in a succession of changes in
Major Amylolytic Species the rumen microbial population during
Major Ureolytic Species Bacteroides amylophilus the adaptation period, specifically in
Succinivibrio dextrinosolvens Streptococcus bovis those bacteria which produce and
Selenomonas sp. Succinimonas amylolytica
Bacteroides ruminicola Bacteroides ruminicola
utilize lactate.
Ruminococcus bromii In this type of scenario, the acid-
Butyrivibrio sp. Major Methane-producing Species sensitive lactate utilizers are replaced by
Treponema sp. Methanobrevibacter ruminantium acid-tolerant lactate utilizers. Lactic
Methanobacterium formicicum
acidosis arises from this abrupt shift to a
Major Sugar-utilizing Species Methanomicrobium mobile
Treponema bryantii high concentrate diet and keeps the
Lactobacillus vitulinus Major Acid-utilizing Species effective lactate-utilizing species from
Lactobacillus ruminus Megasphaera elsdenii increasing in sufficient numbers to
Selenomonas ruminantium prevent the accumulation of lactate. This
Major Proteolytic Species
Bacteroides amylophilus Major Ammonia-producing Species results in decreasing the rumen pH to a
Bacteroides ruminicola Bacteroides ruminicola very acidic level, less than 5.5.
Butyrivibrio fibrisolvens Megasphera elsdenii Rumen pH is one of the most
Streptococcus bovis Selenomonas ruminantium variable factors which can influence the
microbial population and the levels of
Source: Church, D. C., ed. The Ruminant Animal: Digestive Physiology and Nutrition. volatile fatty acids produced (Figure 2).
Englewood Cliffs, N.J.: Prentice Hall, 1988. The rumen pH at which certain functions
are optimized can differ. There are two
basic groups of bacteria which function at
There are three interconnecting Microbial attachment in the rumen various pH’s. The fiber digesters are most
environments in which the microbes are has numerous implications in the active at a pH of 6.2 to 6.8. Cellulolytic
located in the rumen. The first is the liquid ruminant. In order for bacteria to bacteria and methanogenic bacteria can
phase, where free-living microbial groups maintain their numbers in the rumen, it be reduced when the pH begins to fall
in the rumen fluid feed on soluble is necessary that their reproduction time below 6.0. The starch digesters prefer a
carbohydrates and protein. This portion be shorter than the turnover rate of the more acidic environment, a pH of 5.2 to
makes up 25 percent of the microbial rumen digesta. Since the passage rate of 6.0. Certain species of protozoa can be
mass. Next is the solid phase, where the the particulate phase is much slower than greatly depressed with a pH under 5.5. To
microbial groups associated with or that of the liquid phase in the rumen, accommodate all these needs, normal
attached to food particles digest insoluble slower-growing species attach to particle feeding practices should maintain a pH
polysaccharides, such as starch and fiber, matter and are thereby prevented from range between 5.8 to 6.4.
as well as the less soluble proteins. This being washed out of the rumen. The diet
can make up as much as 70 percent of the fed to the dairy cow influences the
microbial mass. In the last phase, 5 number and relative proportions of the
percent of the microbes attach to the different microbial species in the rumen.
rumen epithelium cells or to the protozoa.6 FROM FEED TO MILK: UNDERSTANDING RUMEN FUNCTION
Microbial digestion in the rumen Figure 2. Ruminal fermentation as a consequence of adaptation due to pH regulation.
The rumen provides a site where the
rumen microorganisms can digest Mol %
carbohydrates, proteins, and fiber. 70–
Through this digestion process, energy or
60– Lactic
volatile fatty acids (VFA’s) and microbial acid
protein that can be utilized by the animal 50– Active Active
are produced (Figure 3). cellulolytic amylolytic
40– flora flora Propionic
acid
Carbohydrates 30–
When carbohydrates, both structural Acetic
20– acid
(neutral detergent fiber) and non-
structural (sugars and starches), undergo 10–
microbial fermentation, they produce
VFA’s. The primary VFA’s in descending 7 6 5 Rumen pH
order of abundance are acetic, propionic,
butyric, isobutyric, valeric, isovaleric, Kaufman, W., H. Hagemeister, and G. Durksen. Adaptation to changes in dietary composition level and
and traces of various other acids. The frequency of feeding. In: Digestive Physiology and Metabolism in Ruminants, ed. Y. Ruckebusch and P.
VFA’s can provide up to 80 percent of the Thivend. Westport, Ct.: AVI Publishing, 1980, p. 587.
energy needs of the animal.
Acetic acid can constitute 50 to 60
percent of the total VFA’s. It predomi- Figure 3. Feed, nutrient flow from the rumen, and milk components.
nates in a high forage diet. Acetate is
used for fatty acid synthesis and is the Crude Sugar, Fermentable Fat
FEED protein starch fiber
main precursor for lipogenesis in adipose
tissue. Some acetate is also used for
muscle metabolism and body fat. DIP
Production of adequate levels of acetate
in the rumen is essential to maintain UIP Microbial growth and fermentation
adequate quantities of milk fat.
Acetic acid levels can drop if there is
Microbial protein
a lack of effective fiber in the ration. This
can also occur when feeding a heavy
concentrate diet or a diet high in heat- Amino Propionic Acetic, Fatty
NUTRIENTS acids (glucose) butyric acids
treated starch as in pelleting, steam
crimping, or steam flaking. High intakes
of oil can also depress acetic acid. Milk Milk Milk
MILK
Propionic acid can make up 18 to 20 COMPONENTS protein lactose fat
percent of the total VFA’s. It reaches its
highest concentration in a high grain diet. Source: Sniffen, C. J. and H. H. Herdt. The Veterinary Clinics of North America: Food Animal Practice,
Propionic acid provides energy through Vol 7, No 2. Philadelphia, Pa.: W. B. Saunders, 1991.
conversion to blood glucose in the liver. Note: UIP = undegradable intake protein; DIP = degradable intake protein.
It is also used in lactose or milk sugar
synthesis.
Butyric acid provides energy to the used for fatty acid synthesis in adipose ruminal VFA proportions are fairly stable
rumen wall and makes up 12 to 18 and mammary gland tissues. among diets with varying forage to
percent of the total VFA’s. It is largely The proportion of VFA’s are greatly concentrate ratios. However, the ruminal
converted to ketones during absorption influenced by diet and the status of the proportions of VFA’s are largely pH
through the rumen epithelium. B-hydro- methanogenic population in the rumen. dependent.
xybutric acid (B-HBA) accounts for more Despite wide swings in the microbial In general, as the forage to concen
than 80 percent of the ketones. B-HBA is population and differences in feed intake, trate ratio decreases, the acetate toPART I: BACKGROUND IN BASIC NUTRITION OF DAIRY CATTLE 7
propionate ratio also decreases (Table 6). Table 6. Effect of forage to concentrate ratio on the volatile fatty acid proportions in the
As cellulose and hemicellulose levels lactating cow.
increase relative to soluble carbohydrate MOLAR RATIOS, %
and starch levels, the acetate to propi- FORAGE TO CONCENTRATE RATIO ACETATE PROPIONATE BUTYRATE
onate ratio also tends to increase. 100:00 71.4 16.0 7.9
However, VFA production from a given
75:25 68.2 18.1 8.0
substrate such as cellulose or starch
50:50 65.3 18.4 10.4
varies with diet composition (Table 7).
Although cellulose and hemicellulose are 40:60 59.8 25.9 10.2
usually digested simultaneously in 20:80 53.6 30.6 10.7
forages, the end-products produced may Source: Physiology of Digestion and Metabolism in the Ruminant, ed. A.T. Phillipson. Newcastle-upon
vary depending on diet. Tyne, England: Oriel Press, 1970, p. 422.
The vast majority of VFA’s are
passively absorbed through the rumen
wall. This continuous removal of VFA by
absorption from the reticulo-rumen is Table 7. Estimated rumen fermentation characteristics.
important for maintaining a stable PROPORTION OF CARBOHYDRATE CONVERTED TO b
ruminal pH. Removal of acid products is SUBSTRATE DIET a ACETATE PROPIONATE BUTYRATE
also important for the continued growth Soluble carbohydrate c F 0.69 0.20 0.10
of cellulolytic organisms. VFA’s that C 0.45 0.21 0.30
remain in the digesta flow from the
rumen to the lower tract and are ab- Starch F 0.59 0.14 0.20
sorbed by the omasum and abomasum. C 0.40 0.30 0.20
Rate of VFA absorption from the
rumen is influenced by the chain length Hemicellulose F 0.57 0.18 0.21
of individual acids and ruminal pH.
C 0.56 0.26 0.11
Increasing the chain length of the acid
results in increased absorption rates in Cellulose F 0.66 0.09 0.23
the following order: butyrate greater than
C 0.79 0.06 0.06
propionate greater than acetate. Lower
pH and the resultant increases in the Source: Murphy, M. R., R. L. Baldwin, and L. J. Koong. 1982. Estimation of stoichiometric parameters for
proportion of the acids in the rumen rumen fermentation of roughage and concentrate diets. J. Animal Sci. 55:411-421.
aF codes forage diets; C codes diets containing more than 50 percent of a cereal-based concentrate diet.
favor more rapid absorption.
b Ratios do not add up to 100 because the isoacids are not taken into account.
The net absorption of VFA’s reaching
the blood is dependent on the concentra c Soluble carbohydrate fraction includes organic acids and pectin in this analysis.
tion in the rumen and the quantity used Note: The acetate to propionate ratio resulting from fermentation of hemicellulose in a high forage diet
by the rumen wall. The rates of utiliza was 3.2, but only 2.2 when fermented in a high grain diet. The acetate to propionate ratio from cellulose
tion by the rumen wall are for butyrate fermentation also varied with diet, 13.1 for a forage diet and 7.3 for a grain diet, both being much higher
→ propionate → acetate. As a result of than that produced by hemicellulose.
the higher concentration in the rumen
and the low rate of utilization by the
rumen wall, acetate enters the blood in directly through the rumen wall. Lactic drates. Problems arise when large
the greatest quantity, followed by acid does not accumulate to any large amounts of starch or cereal concentrates
propionate. Very little butyrate enters the extent in dairy cattle that have been fed are fed. Total lactate in severe cases may
blood due to the lesser amount in the nutritionally sound rations that are comprise 50 to 90 percent of the total
rumen and greater amount metabolized managed properly. If gradual introduc rumen acids. The absorption of large
by the rumen wall. tion of grains is practiced, the lactate- amounts of lactic acid across the rumen
Lactic acid is important when starch utilizing bacteria will develop and permit wall to the blood produces systemic
is a part of the diet and is itself fermented only a transient increase in lactic acid acidosis and results in animals going
to acetate, propionate, and butyrate. accumulation following ingestion of a off feed, developing laminitis, and
Lactate, when present, is absorbed diet high in readily fermentable carbohy performing poorly overall.8 FROM FEED TO MILK: UNDERSTANDING RUMEN FUNCTION
Protein result from the degradation of protein the surfaces of bacteria and feed par
Another critical function of the rumen and can be used as nitrogen sources by ticles. The rumen microbes cannot use
microbes is synthesis of microbial the rumen microbes. fatty acids as an energy source, and their
protein. The biological value of microbial The ruminant animal relies upon use is restricted to cell incorporation and
protein is 66 to 87 percent. Dietary microbial crude protein synthesized in synthetic purposes. Following the
protein may be improved or reduced in the rumen and dietary protein which breakdown of lipids, the microbes are
biological value by rumen microbes, escapes digestion in the rumen for its responsible for biohydrogenation, or the
depending on the quality of protein fed. supply of amino acids. Microbial protein addition of hydrogen to fatty acids with
Most ruminal bacteria can use is very high in quality, rivaling animal double bonds. An example would be the
ammonia nitrogen as a source of nitro protein and exceeding most vegetable microbial hydrogenation of oleic acid to
gen. Some species of bacteria require proteins in essential amino acid content. stearic acid.
additional nitrogen compounds such as However, the rumen microbes cannot
intact protein or carbon chains of certain produce all the essential amino acids Vitamins
amino acids for most efficient or rapid required for animal growth and high The rumen also functions in synthesizing
growth. levels of milk production. B-complex vitamins and vitamin K. This
Ammonia is derived in the rumen The amino acids are absorbed and makes the dairy cow less dependent on
through microbial degradation of dietary utilized in the small intestine. Most dietary sources. If cobalt intake is
protein and dietary nonprotein nitrogen, amino acids are used in the synthesis of adequate, then vitamin B12 is generally
from hydrolysis of recycled urea to the body proteins, such as muscle and milk not lacking. Additional supplementation
rumen, and from degradation of micro proteins. Some amino acids, especially of niacin or vitamin B12 may show a
bial crude protein. Rumen ammonia those from protein reserves in the body production response, though sometimes
disappears from the rumen in different tissue, may be used to maintain blood only in high-producing cows under
ways, such as incorporation of the glucose levels and meet energy needs. stress.
nitrogen by the microbes, absorption
through the rumen wall, and flushing to Lipids Basic nutritional concepts behind
the omasum. Rumen microbes rapidly and extensively feeding dairy cattle
Ammonia not taken up by the modify dietary lipids. Hydrolysis in the Ruminants are excellent recyclers. They
microbes is absorbed directly through the rumen proceeds rapidly after ingestion. consume fibrous feeds and waste by-
rumen wall. The rate of absorption is The microbial metabolism of galacto products that are not suitable for
dependent on the pH of the rumen lipids (found in plant leaves) and consumption by humans and single-
environment and the concentration of triglycerides (found in seeds) starts with stomached animals and convert them
ammonia. Absorption is rapid at a pH of their hydrolysis. The glycerol and into nutritious feeds like meat and milk.
6.5 or higher. It declines to nearly zero at galactose portions are readily fermented Table 8 lists feed sources that are utilized
a pH of 4.5. Ammonia absorption to VFA’s. Liberated fatty acids are by the ruminant.
increases as ruminal concentration neutralized at rumen pH and adhere to
increases. Indications of ammonia
toxicity include ruminal ammonia
concentration above 100 mg/dl, ruminal Table 8. Feed ingredient sources that are utilized by ruminants.
pH above 8, and blood plasma ammonia FORAGE CROP FOOD-PROCESSING FIBER-PROCESSING PROTEIN ANIMAL
CROPS WASTES WASTES WASTES SUBSTITUTES WASTES
concentrations above 2 mg/dl.
Substitution of dietary nonprotein Legumes Straw Corn factory Wood fines Urea Blood meal
nitrogen, such as urea, for protein from Grasses Cornstalks Apple pomace Paper Anhydrous- Meat meal
plant and animal sources can reduce ammonia
Corn silage Pea vines Beet pulp Cardboard Bone meal
costs of protein supplementation. Urea is Small grain Bean vines Brewers grain Cottonseed hulls Feather meal
degraded by the microbes into ammonia,
Sorghum Distillers grain Fish meal
which can be used for microbial synthesis sudan
Soyhulls
resulting in microbial protein. The
microbes can also utilize nonprotein Oil meals
nitrogen in ensiled feeds and other Bakery waste
feedstuffs. During the ensiling process, Mill by-products
ammonia, amines, amides, and nitratesPART I: BACKGROUND IN BASIC NUTRITION OF DAIRY CATTLE 9
Land that is not suitable for growing Table 9. Eating, rumination behavior, rumen pH, volatile fatty acids (VFA’s), average milk yield, and
food crops for human consumption can milk composition as influenced by particle size of the ration.
be utilized to grow forage for ruminants. RATION
Perennial and annual forages, such as ITEM FINE MEDIUM COARSE
alfalfa and corn silage, are low-cost and
Eating, min./24 hr 195.3 204.4 204.7
land-effective sources of nutrients.
In order for the ruminant to utilize Ruminating, min./24 hr 374.4 a 466.3 b 530.7 c
these various sources of feedstuffs, Total chewing time, min./24 hr 569.7a 670.7 b 735.4 c
certain basic rules for nutrition must be
followed to ensure optimum perfor pH 5.3 a 5.9 b 6.0 b
mance. The main concepts are related to VFA, molar %
feed particle size, the structural and
Acetic 58.33 c 61.24 d 61.82 d
nonstructural carbohydrate fractions, and
the protein fractions supplied from the Propionic 22.34 c 20.16 c, d 19.46 d
various feeds.
Adequate effective fiber is necessary Actual milk, lb/day 69.3 70.6 68.4
for proper rumen function. Rations fed 4% FCM, lb/day 60.5 a 66.6 b, c 64.9 a, c
with insufficient forage particle length Milk fat, % 3.0 a 3.6 b, c 3.8c
result in cows spending less time
Milk protein, % 3.0 3.0 3.1
chewing, which decreases the volume of
saliva produced and leads to inadequate Source: Grant et al. 1990. Milk fat depression in dairy cows: Role of silage particle size. J. Dairy Sci.
buffering and lower rumen pH. 73:183442.
When rumen pH falls below 6.0, the Note: Rations formulated on 55:45 silage to concentrate basis consisting of alfalfa silage, high moisture
growth of the cellulolytic organisms can corn, and a mineral vitamin supplement. A field chopper with knives adjusted to a 3/16-inch theoretical
be reduced, allowing for an increase in cut length and fitted with a 3-inch recutter screen chopped the fine silage. A 3/8-inch theoretical cut
the propionate-producing microbes. This length yielded coarsely chopped silage. A 1:1 mixture (dry weight) of the two silages provided the
intermediate particle length in the medium ration.
can cause a decrease in the acetate to
a, b, c, d Means within rows with unlike superscripts differ significantly.
propionate ratio and potentially result in
a lower milk fat percentage.
Particle size is important, especially
for forage utilization and maintenance of faster, less time is available for microbes NDF and on the nonstructural
a good fiber mat in the rumen. A fiber to digest the feeds. carbohydrates.
mat is essential to assure adequate In addition to the forage particle The digestibility of the fiber will
growth and microbe activity and results length, the fiber content in the diet is vary depending on the source. For
in an increase of VFA’s, especially acetate, important. Fiber is necessary to provide example, fiber in some by-product
and microbial protein yield. Table 9 adequate amounts of complex carbohy ingredients may be more digestible and
illustrates the influence particle size can drates to slow digestibility and control more quickly digested than forage with
have on rumen function and production the acidity in the rumen. Acid detergent the same fiber content. Fiber in low-
parameters. fiber and neutral detergent fiber (ADF, quality forage may not be adequately
Feeding a ration with reduced forage NDF) are the main fiber fractions that are digested. However, forages that are too
particle size will increase dry matter used in ration formulation. For high- immature may be lacking adequate fiber
intake, decrease digestibility, and result producing, early lactation animals, and may be digested too rapidly.
in lower rumen solid retention time. recommendations are 18 to 20 percent of The manner in which grains are
Rations that have a smaller initial forage ADF and 28 to 30 percent of NDF in the prepared can have a substantial effect on
particle size will enter the rumen at an total ration dry matter. The level of both the rumen environment and the
even smaller size after initial chewing forage NDF and the forage particle cow. The particle size of the grains, such
and swallowing, and therefore leave the length in the diet play an important role as fine ground, coarse, rolled, or steam
rumen at a faster rate. The result is an in determining effective fiber in the diet. flaked, can affect the digestibility of the
increase in the rumen turnover rate However, not all fiber is of equal value in grain and the total ration. The finer the
allowing for an increase in dry matter the ration. See Carbohydrates (p. 13) for grind of a cereal grain, the more exposed
intake, but because the rate of passage is more in-depth information on forage the endosperm of the grain, which allows10 FROM FEED TO MILK: UNDERSTANDING RUMEN FUNCTION
for easier attack by rumen microbes.
Table 10. Differences in extent of ruminal digestion of starches as affected by source and processing.
The type of heat processing influences
PERCENTAGE DIGESTION IN THE RUMEN
availability of the starch (Table 10). This
is associated with the gelatinization and PROCESSING OATS WHEAT BARLEY CORN MILO
rupture of the starch granules as seen, for Ensiled, high moisture
(fine grind) 99 99 98 85 —
example, in steam flaking. The method of
grain processing, the amount of concen Steam flaked
(thin flake) 99 98 97 86 84
trate fed, and the level of nonstructural
carbohydrates (NSC) in the total ration Ensiled, high moisture
(coarse rolled) — — — 82 80
dry matter have a tremendous influence
on animal performance. Dry, fine grind 94 93 91 78 72
There needs to be a balance between Dry, medium grind 89 88 87 74 68
the cell wall (NDF) and the cell contents Dry, coarse grind 79 78 77 65 61
(NSC) to maximize production as well as
Dry, whole — — — 60 —
maintain the health of the animal.
Effective fiber is needed in the diet to Source: H. H. Van Horn and C. J. Wilcox, ed. 1992. Nonstructural and structural carbohydrates.
provide a fiber mat and to slow down the In: Large Dairy Herd Management. Management Services, American Dairy Science Association,
Champaign, Ill., p 222.
availability of the carbohydrates to avoid
low rumen pH. The NSC or sugars and
starches are necessary to provide readily
available energy for the rumen microbes of high energy feeds, and feeding formulating rations. The rumen microbes
and the animal. Balancing rations too far concentrates more than twice daily. are sensitive to both excessive and
in one direction or the other can be Buffers can aid in controlling rumen deficient levels of protein, ammonia,
detrimental to the dairy cow. pH. Sodium bicarbonate is the mostly urea, and the type and level of fat in the
The main objective in balancing NDF widely used dietary buffer. Rations ration. Mineral levels, especially calcium,
and NSC is to control rumen pH. The which benefit the most from buffers are phosphorus, sulfur, magnesium, copper,
optimum range in pH is 5.8 to 6.4 for rations containing a large percentage of zinc, and cobalt, can cause problems
synthesis of microbial protein and corn silage and/or high moisture corn, when either too high or too low.
B-complex vitamins. This pH range and low fiber forages. Abnormally fermented material may
may be somewhat higher or lower for In addition to a good balance alter the VFA’s and lactic acid in the
short periods of time throughout the day, between the carbohydrate fractions, there rumen. This is more apt to occur if pH or
especially in conventional feeding needs to be a balance between rumen moisture contents of the material are out
systems. Ruminal pH normally degradable and rumen bypass protein to of the optimum range. Using feed spoiled
fluctuates less when cows are fed a total meet the amino acid needs of high- by mold, putrefaction, and mycotoxins
mixed ration. producing cows. Bypass or undegradable may decrease production and may
There are various ways to control the intake protein (UIP) should range from increase the incidence of displaced
pH, such as providing adequate effective 35 to 40 percent for early lactation and abomasum.
fiber and providing a balance of protein high milk production (over 80 pounds of Water can have an effect on the
nitrogen, concentrate, fiber, and minerals milk per day). Paying close attention to rumen microorganisms especially when
in the rumen. Much of the final outcome the amino acid profile of bypass sources there is heavy bacterial or metal contami
of daily rumen pH level and fluctuation of protein will help supply the essential nation or high mineral concentrations
is determined by the feeding system and amino acids in the diet. However, such as chloride. Water that is extremely
feeding management practice. In balancing for UIP alone is not recom acidic or alkaline can also create prob
conventional feeding systems (those mended. Adequate degradable protein is lems. It may be necessary to send water
where grain and forage are fed sepa necessary so there are sufficient ammonia samples out for analysis to check for
rately), implementing a feeding strategy levels in the rumen to meet the nitrogen abnormalities, especially when rations on
is essential to eliminate the peaks and needs of the microbes. paper appear balanced but cows are not
valleys in rumen pH. Some common In order for the ruminant to function responding accordingly.
recommendations are feeding hay prior properly, the nutritionist must know
to concentrates, feeding high protein what substrates the rumen microbes are
forages and concentrates close to feeding sensitive to so they can be avoided whenPART I: BACKGROUND IN BASIC NUTRITION OF DAIRY CATTLE 11
Dry matter intake and calving difficulties, and more infections Palatability is also a concern,
its effect on the cow such as mastitis. Low-producing and especially in conventional feeding
The main objective in feeding manage late-lactation animals will sometimes systems. Certain feedstuffs and additives
ment is to increase the dry matter intake consume more feed than is necessary to may depress intakes of concentrates
of the cows. With this increase should meet energy needs; thus body condition when fed conventionally compared to a
come higher levels of milk production. should be monitored closely with these total mixed ration (TMR). For example,
In order for this to happen, close atten animals. Dry cows may consume double animal protein blends may have to be
tion to energy, ration digestibility, rumen their needs if allowed to eat free choice. limited in the grain mix used on a
fill, palatability, temperature, body When ration digestibility is too low, conventional ration compared to higher
weight of the animal, feeding conditions, animals usually cannot eat enough to levels that can be fed in a TMR. Some
environment, ventilation, frequency of meet their nutrient needs. If the energy species and varieties of forage are less
feeding, and water intake and quality are density in the diet is less than .66 Mcal palatable than others and may have to be
necessary. Establishing optimal standards NEL, then it may be impossible for high- restricted.
in each category should result in optimal producing cows to meet their energy Both feeding conditions and
dry matter intake. requirements. environmental climate can limit intake.
Most lactating cows will eat to Some rations that are relatively high When the climate exceeds 65oF and 65
satisfy energy needs if presented with a in digestibility may be consumed at percent humidity, dry matter intake and
sound and balanced ration. Yet cows lower levels since energy needs may be often milk production and fat test may
producing over 85 pounds of milk often met with less intake. High-quality rations decrease. A substantial decrease in total
cannot eat enough to meet their energy for high-producing dairy cattle should ration dry matter may occur at over 80oF
needs. They may utilize body energy contain around .74 Mcal NEL. Rations and 80 percent humidity. Thus there is a
reserves, mostly fat, to make up at least containing too much concentrate and not seasonal effect on dry matter intake with
part of any energy deficiency. One pound enough forage and effective fiber may higher consumption usually occurring
of body fat may be utilized to effectively actually depress intakes, milk produc during cool weather and depressed
produce 7 to 9 pounds of milk, depend tion, and fat test and may adversely intakes occurring during hot, humid
ing on the fat test. affect health. Ration digestibility may weather. Forage quality and the energy
High-producing cows should be in also be depressed by an improper content of the concentrates as well as the
good body condition before they go dry. balance of nutrients. Low-quality forage density levels of protein, minerals, and
Table 11 gives the recommended range is a more frequent cause of lowered effective fiber generally need to be
for body condition scores for the different intakes and performance than the lack of increased during the summer months.
stages of lactation. Each score change energy in the concentrate portion of the Poorly ventilated feeding or housing
represents 120 to 150 pounds of body ration. Improper forage and grain areas can increase heat and humidity and
weight gain or loss. Obesity should be preparation may depress digestibility, allow strong odors, such as ammonia, to
avoided because cows will be more performance, and sometimes total ration become concentrated, which can cause a
susceptible to going off feed, ketosis, dry matter intake. decline in consumption because animals
When feeding rations with low spend less time in those areas.
digestibility, rumen fill is quickly Dry matter intake can be depressed
achieved. These rations are digested when heating, putrefaction, and mold
Table 11. Target scores for stages of lactation slowly and, to a lesser extent, pass out of occur in ensiled feeds or TMR’s. This can
using the 5-point body condition scale.
the rumen at a slower rate. When rumen be minimized by not removing ensiled
STAGE OF TARGET BODY fill occurs, a signal is sent to the brain feeds from the silo much in advance of
LACTATION CONDITION SCORE
stem to stop intake as part of the overall feeding. Ensiled feeds that have under
Cows at calving 3+ to 4
process of intake regulation. gone abnormal fermentation may
Early lactation 3- to 3 The use of sodium bicarbonate or depress intakes. The presence of certain
Mid-lactation 3 sesquicarbonate at .80 percent in the total toxins, such as mycotoxins, alkaloids,
Late lactation 3 to 3+ ration dry matter can increase digestibil and tannin, can cause problems. In order
Dry 3+ to 4 ity by raising the rumen pH. This can to minimize their effects on low perfor
result in higher dry matter intakes. An mance, feed more often throughout the
Source: Body-condition Scoring as a Tool for
Dairy Herd Management. Penn State Extension
increase in milk production and/or fat day, especially during the summer, to
Circular 363. test may be noted when these additives keep feed fresh and from heating. Avoid
are fed. using problem feeds for milk cows,You can also read
