SODIUM BALANCE IN FEEDER STEERS

by

MICHAEL W. SMITH, B.S.

A THESIS

IN

ANIMAL NUTRITION

Submitted to the Graduate Faculty of Texas Tech University in

Partial Fulfillment of the Requirements for

the Degree of

MASTER OF SCIENCE

Approved

Accepted

August, 1974

1V:S -WD

"EOS rs

Cop* 2

ACKNOWLEDGMENTS

I am deeply indebted to Dr. Robert C. Albin for

his direction of this thesis and to the other members of

my committee. Dr. Leland Tribble and Dr. Frank Hudson,

for their able advice and guidance. I am also indebted to

Dr. Charles Gaskins and Phil Thompson for so competently

conducting the statistical analysis.

11

TABLE OF CONTENTS

ACKNOWLEDGMENTS ii

LIST OF TABLES iv

LIST OF FIGURES V

I. INTRODUCTION 1

II. LITERATURE REVIEW 3

III. EXPERIMENTAL PROCEDURE 17

IV. RESULTS AND DISCUSSION 21

V. SUMMARY 40

LITERATURE CITED 42

111

LIST OF TABLES

Table Page

1. Basal Ration Composition 18

2. Chemical Composition of Rations Containing Various Levels of Sodium . . . 20

3. Digestion Coefficients for Ration Components as Affected by Level of Na in the Ration 22

4. Analysis of Variance Between Sodium Levels 23

5. Linear Regression Due to

Sodium Levels 24

6. Mean Daily Sodium Retention 32

7. Nitrogen Digestion Coefficients and Retention 33

IV

LIST OF FIGURES

Figure Page

1. Dry Matter Digestibility as Affected by Level of Sodium in the Ration 25

2. Gross Energy Digestibility as Affected by Level of Sodium in the Ration 26

3. Organic Matter Digestibility as Affected by Level of Sodium in the Ration 27

4. True Digestibility of Nitrogen as Affected by Level of Sodium in the Ration 29

5. Sodium Retained Per Day (g) as Affected by Level of Sodium in the Ration 30

6. Sodium in Urine Cg) as Affected by Level of Sodium in the Ration 31

V

CHAPTER I

INTRODUCTION

Cattle feeding on the High Plains of Texas, as well

as in many other areas of the central and western United

States, has expanded rapidly in recent years. Many factors

have contributed to this rapid expansion and development.

At the present time, cattle feeding costs on the High Plains

are higher than they have ever been before. Some of the

factors which have contributed to this elevation in feeding

costs are: the ban on diethylstilbestrol, which prolongs

the feeding time of cattle; the recent grain transactions

with Russia and other foreign countries, which increased

domestic grain prices; and the present energy crisis, which

increased the cost of production. Because of high costs

of feed ingredients and environmental laws, now would seem

to be the appropriate time to re-evaluate each ingredient

associated with the nutrition of feedlot cattle before

incorporating it into feedlot rations.

The feed ingredient evaluated in this research

project was sodium chloride. The need to comply with state

and federal pollution laws requires the reduction of

components of solid-waste materials removed from feedlots

that might affect soil or plants when applied as a fertil­

izer. One major problem related to the use of feedlot

manure on soils for crop production is sodium salts. The

quantity of sodium present in the manure depends primarily

upon the amount of salt in the ration. Sodium (Na) is

considered to be a macro-mineral and is essential for the

proper functioning of many major systems in the body. The

exact requirement for sodium has not been established,

since most research has been focused mainly on the value

of salt and factors affecting consumption. The N.R.C.

(1970) recommends salt levels of 0.25% added to feedlot

rations. A common practice in feeding ruminants has been

to add 0.50% salt to rations.

The primary purpose of this study was to determine

the amount of sodium contained in feces and urine in

relation to the amount of sodium in the ration. Also

studied was the effect of different sodium levels upon

nutrient and energy digestibility.

CHAPTER II

LITERATURE REVIEW

Specific requirements for sodium and chlorine

(salt) for beef cattle are being questioned at the present

time. Most research in this area has dealt with the value

of salt and factors affecting consumption. Salt is commonly

fed free-choice rather than being mixed with other ration

ingredients. Therefore, the intake of salt may exceed

animal requirements and will vary from animal to animal.

Babcock (1905) stated that most research with dietary

salt has been done with farm animals and optimum amounts

have been determined covering all types of climate, produc­

tion, and work. Differences in weather, feeding habits,

types of feed, and forms of feeding have caused these

optimum amounts to vary greatly. Green roughages and grain

generally contain less than 0.1% sodium. Dry roughages

usually contain between 0.1 and 0.5% sodium. Researchers

have become interested in the functions of sodium in the

animal body and the minimum requirement of sodium. Since

large quantities of feedlot manure are being applied to

the land as a fertilizer, emphasis should be placed on the

minimum requirement of sodium. Bennett (1970) stated that

a high quantity of sodium could be detrimental to plant

growth.

Sodium is present in animals largely as the sodium

ion (Na+). Sodium is generally said to be confined to the

extracellular fluids (plasma, cerebrospinal, and inter­

stitial fluids). Sodium is also known to be bound to a

number of organic molecules, such as chondroitin sulfate,

brain lipids, sodium complexes of ATP, DNA, phosphopeptides

of casein, hemoglobin and muscle myosin. Church (1972)

and Forbes (1962) found that such binding of organic

molecules did not appear to be specific for sodium,

however. Forbes also found that an appreciable amount of

body storage of sodium was found in bone or cartilage.

Dukes (1970) noted that about 45 percent of the body store

of sodium was found in extracellular fluid and about 45

percent in bone, and the remainder as intracellular sodium.

Most body sodium was in an exchangeable, ionic form. One-

half of the sodium in bone did not exchange with sodium ions

in the various body fluids. None of the bone sodium was

osmotically active, although part of it may have become

available to the osmotic effects of extracellular fluid

dilution.

The major functions of sodium are for the maintenance

of a desirable osmotic pressure, acid-base balance, trans­

mission of nerve impulses, and regulation of body fluid

volume. The absorption, excretion, deficiency, and toxicity

of sodium were also of major importance.

Aines and Smith (1957) stated that several workers

found sodium to be the limiting factor in the requirement

for sodium chloride. Studies of Na, K, and Cl ions in

the nutrition of chickens by Burns et al . (1953) revealed

that sodium was the critical ion in sodium chloride.

Studies by Meyer et al. (1950) with growing pigs, showed

a sodium chloride to be no more severe than a sodium

deficiency.

Osmotic Pressure

The chief cation of extracellular fluids is the

sodium ion. Potassium and magnesium are the principal

intracellular cations. Of the osmotically effective

bases of extracellular fluids, sodium makes up more than

90 percent of the total- Thus, changes in osmotic pressure

are largely dependent on sodium concentration. Under

stress conditions, a loss of sodium may be compensated for

by an increase in potassium, but the organism is limited

in its capacity to substitute bases (Dukes, 1970). Kay

and Hobson (1963) stated that when sheep were depleted of

sodium, potassium took its place in parotid saliva and

a similar change took place in the composition of the rumen

fluid so that the sheep withdrew sodium from its gut into

the body fluid. McCance (1938) reviewed the literature

on the effect of salt deficiency on the electrolyte

composition of body secretions. He found that in mixed

saliva, gastric secretion and sweat, there was a fall in

sodium concentration when there was a rise in potassium

concentration. Major losses of sodium led to a significant

lowering of osmotic pressure and therefore, a loss of water

or dehydration. Dukes (1970) and Van Weerden (1961) showed

that sodium and chloride made important contributions to

the osmotic pressure in the abomasum and upper part of

the small intestine. At the lower end of the small

intestine sodium was the most important cation. Weeth

and Lesperance (1965) stated that an animal's ability to

maintain osmotic equilibrium depended partly on its ability

to reabsorb filtrate water and excrete a high osmolal

urine. The bovine kidney responded to water deprivation

by reducing urine volume and to a limited extent, by

increasing urine osmolarity. In an experiment by Weeth,

an average of 99.8% of the fittered sodium was reabsorbed

during fasting.

Regulation of Body Fluid Volume

The body content of sodium determines to a great

extent the volume of extracellular fluid. Gamble (1951)

stated that extracellular water consisted of water of the

blood plasma and of the interstitial fluid. The inter­

stitial fluid was that which was found between plasma and

tissue. Dukes (1970) stated that if an animal was deprived

of sodium chloride for a few days, its extracellular fluid

volume would drop a few percent. Also, extracellular

fluid would rise if a large amount of salt was ingested

daily for a few days. Hix et al. (1953) found that the

feeding of silage brought about a loss of extracellular

sodium and.consequently a reduction in extracellular water

through sodium diuresis. Sodium exists in a freely

diffusable state in the plasma water as shown by the fact

that its distribution between plasma, pleural, peritoneal,

and subcutaneous fluids (all extracellular) is constant.

The exchange between these fluids is rapid. Changes in the

quantitation of body sodium therefore will bring about a

change in extracellular volume in its endeavor to maintain

its iso-osmolarity. Crawford and Guadine (1952) stated

that there was a rapid expansion of extracellular water in

the early sodium retention stage due to rapid transfer of

intracellular water to the extracellular compartment.

This was followed by an abrupt check in its expansion as

demonstrated by a sodium balance; The renal mechanism

was induced to an increased excretion of sodium in an effort

to establish a normal balance in body fluids. Kay (1960)

showed that, each day, sheep could secrete an amount of

sodium in saliva approximately equal to that in the extra­

cellular space. The prompt absorption of this sodium was

therefore necessary in order not to deplete the sodium in

the extracellular fluid. A time lag between secretion and

8

absorption appeared to give rise to changes in volume and

composition of the urine (Stacy and Brook, 1964).

Dobson ejt al_. (1963) stated that an increase in

ruminal sodium at the expense of extracellular sodium

presupposes that the sodium in the rumen was outside the

extracellular space. Medway et aJ. (1958) stated that rapid

absorption of salt results in a marked increase in the

osmotic pressure of the blood. This in turn caused a

movement of water from the interstitial space into the

plama, initially increasing its volume. At the same time,

salt diffused out into the interstitial space. This caused

a secondary outflow from blood by osmotic pressure. The

increased salt content of the extracellular fluid resulted

in an osmotic pressure greater than that within the cells.

This caused a flow of water out of the cells into extra­

cellular fluid by osmosis. The final result was a uniform

increase in the electrolyte concentration and osmotic

pressure throughout the body fluid. Nichols et al_. (1956)

stated that most sodium lost from the body was from extra­

cellular phase and bone mineral. Sodium content of body

cells was not easily lowered by sodium depletion.

Excretion

Dukes (1970) stated that a relatively constant

sodium content of the extracellular fluid is attained by

regulation of both intake and excretion of sodium so as to

maintain a "salt balance." Relatively little is known of

the mechanism of salt hunger or appetite, but many sodium

deficient animals have a strong behavioral drive to ingest

salt and show a remarkable ability to control ingestion

of sodium chloride or sodium solutions so that they replace

a deficiency of body sodium. When more than minimal

amounts of salt are ingested with the ration, as is usually

the case, salt hunger will not be evident and excess salt

will be excreted. Presumably, sodium appetite is controlled

by a neuromuscular system similar to that for thirst.

Excretion of sodium by the kidney involves first,

filtration by the glomerulus of plasma sodium and then re-

absorption from the tubule of most of the filtered sodium.

Glomerular filtration (GF) is the physical process of

ultrafiltration through the glomerular membranes of a

portion of the plasma water and contained solutes as the

blood passes through the glomeruli. Urine remains approxi­

mately iso-osmotic to plasma throughout the proximal tubule

and that 80 to 99% of the filtered water is reabsorbed

by the glomeruli consequent to active reabsorption of solute

in the proximaltubule, the bulk of which is sodium

chloride. Selkurt (1954) noted that tubular reabsorption

of sodium was regulated by both intrarenal and extra-renal

mechanisms. Intrarenal mechanisms were those conditions in

which the kidney was subjected to abrupt changes (increases)

in sodium load and promptly responded with an increased

10

urinary excretion of the cation. With reduced load,

reabsorption proceeded more effectively and excretion

diminished. In extrarenal mechanisms, it has been found

that the kinetics of the transfer process may be enhanced

or depressed. Thus, sodium reabsorption may be modified

by dietary intake of salt, state of hydration, acid-base

balance, O2 tension of blood, posture and exercise.

Dukes (1970) stated that changes in sodium excretion

can be affected in two ways. First, if plasma sodium or

glomerular filtration rate suddenly increased, the amount

of sodium filtered per unit time into the tubule would

also increase. Conversely, if plasma sodium or glomerular

filtration rate decreased, less sodium would be excreted.

Second, a rise of plasma sodium would cause decreased

secretion of aldosterone by the adrenal cortex. The primary

action of aldosterone is to increase sodium reabsorption

from the renal tubule. Beilhartz and Kay (1963) noted that

aldosterone secretion in sodium depleted sheep could also

be stimulated independently of an absolute fall in sodium

concentration of the plasma. Denton (1958) argued that

since water depletion affected both extra and intracellular

compartments, sodium depletion would cause a relative

change in sodium concentration and it was this change that

constituted a major stimulus to aldosterone secretion

under these conditions.

11

Selkurt (1954) stated that the factor which most

strikingly influenced the urinary excretion of sodium was

variation in load delivered to the tubular reabsorptive

system. Such variation could be the result of varying

independently or together the two factors which determine

overall loading. These two factors were glomerular

filtration rate and plasma sodium concentration.

Renkema (1962) noted that the kidney was well

known to be the principal organ regulating sodium retention

and excretion in order to maintain a constant sodium level

in the blood and tissues (sodium homeostasis) . Cardon ejt al

(1951) stated that if sufficient water was not available

for the kidney to eliminate the salt, an animal would

draw water from its tissues. On a restricted water intake,

the amount of water the animal can draw from the tissues

to eliminate salt was not sufficient to balance the amount

of salt going into the bloodstream. As a high concentration

of salt builds up in the blood and tissues under these

conditions, fatalities may occur. The elimination of salt

must be equal to the rate of absorption. Cardon et_ al.

(1951) stated that blood salt was eliminated via the urine.

According to Schmidt et a_l. (1948) the ruminant kidney

could eliminate salt in the urine at a higher concentration

than 2.3%. With adequate water intake, salt was rapidly

and quantitatively absorbed into the bloodstream. This

rapid absorption caused an immediate increase in the sodium

12

concentration of the blood, followed by an increased

excretion in the urine.

Absorption

Cardon ejt al . (1951) noted that sodium chloride

was readily absorbed through the rumen wall. With adequate

water intake, sodium chloride was rapidly and almost

quantitatively absorbed into the bloodstream. The blood

concentration remained high until the sodium chloride had

all been absorbed. The excretion rate remained high until

after absorption was complete and the blood level had

dropped to normal. For each pound of sodium chloride

absorbed, the animal must have produced about five gallons

of urine for its elimination. Gamble et aJL. (1929) stated

that if circumstances required excretion of a large amount

of substances with relatively little water, a level of

osmotic pressure may have been reached which would prevent

further withdrawal of water from the tubular fluid, with

the result that urine of the maximum possible concentration

was produced. Hyden (1952) on the basis of experiments

in which he studied the behavior of solutions containing

K, Na, Cl, P in a pouch of rumen in goats, found that the

rumen was selectively permeable to inorganic ions. In the

experiment, Hyden placed increasing concentrations of sodium

and potassium acetate in the rumen. He proved that by the

concentrations of these two ions in the blood coming from

13

the rumen in relation to the carotid blood, no absorption

occurred until the rumen concentration exceeded that of the

carotid blood. Beilhartz and Kay (1963) noted that sodium

is balanced electrically by absorption of acetate, and that

factors governing acetate may govern sodium. Sodium, and

potassium cations account for most of the cations in the

rumen. In the experiment by Hyden (1952) the net gain in

sodium was a clear indication that sodium was passing from

blood to the rumen. This showed that passage could occur

in either direction depending upon the concentration

gradient. Dobson et al. (1956) stated that the large

surface area, together with arrangement of epithelium

basal cells and the wide intracellular spaces accounted

for the rapid passage of some solutes in either direction

and for the active absorption of sodium ions. Sperber and

Hyden (1952) reported that sodium was absorbed from the

rumen against a concentration gradient, whereas Parthasarthy

and Phillipson (1953) did not demonstrate this occurence.

Dobson et aJ . (1966) noted that rumen sodium was determined

by rate of inflow of sodium in saliva and food, the rate

of absorption through the rumen wall and its rate of

passage down the gut. In this case, high salt levels may

have given a faster outflow since potassium was not readily

absorbed. Osmosis tends to keep the osmotic pressure near

the plasma level. Also, the coarseness of the diet may

increase saliva flow. Perry et al. (1966) noted that sodium

14

was absorbed from the rumen, but the quantity absorbed was

less than that entering the rumen through saliva.

It has been suggested that the sodium in the rumen

forms a store which can be drawn upon in times when dietary

sodium is low. (Denton, 1957; Kay and Hobson, 1963)

In some instances, this rumen function may be important.

During dietary changes, sodium accumulated within the r\imen

on one diet, becomes available on another diet when sodium

intake is low. Dobson et al. (1966) showed that sheep on

fresh grass were not losing or gaining sodium until a

change in diet was made. It was again suggested that

dietary change affected the sodium requirement, which was

related to the amount of sodium in the rumen.

Smith (1962) reported that 40% of the sodium intake

was absorbed at the lower end of the small intestine from

ingesta. Absorption of sodium from the small intestine

accounted for a greater percentage of the total sodium

from the gut to blood than the absorption in the large

intestine. The absorption of sodium from the lower gut

(small intestine) was 87% of the total sodium absorbed.

The other 13% was absorbed through the caecum and large

intestine. Horrocks (1964) stated that the intestines had

a remarkable capacity for retaining sodium, the kidneys

were superior, and when sodium was deficient, less was lost

via urine than the feces. When sodium was added to the

diet, there was a hundredfold increase in urine compared

15

to tenfold in the feces. Results showed that with increasing

amounts of dietary sodium, the intestines would retain

large amounts, and that large amounts would be excreted in

the urine. It would be expected that more intake than

8-lOg sodium per day would result in greater losses by

the kidneys. Van Weerden (1961) and Brouwer (1961) con­

firmed that intestinal reabsorption in the cow was of great

importance in sodium metabolism. Steers that were on trial

for 10 months showed no symptoms of sodium deficiency when

on low sodium diets.

In the case of sodium deficiency, absorption of the

element could take place from the lower part of the small

intestine against a concentration gradient. Fields (1954)

and Van Weerden (1961) showed that in the abomasum, the

concentration of dissolved sodium was lower than the blood.

In the duodenum, the concentration of sodium increased and

in the small intestine the concentration was almost equal

to that of the blood. This was due to the sodium containing

digestive juices such as bile, pancreatic, and intestinal

juice. In the distal end of the small intestine, sodium

concentration declined and in the caecum it was much lower

than in the blood. This indicated that in the lower part

of the small intestine, sodium was absorbed against a

concentration gradient. Renkema (1962) noted that with

regard to sodium absorption in the gut, the intestinal

wall would have equal concentrations of sodium in the

16

intestinal juices and in the blood plasma. In cows. Van

Weerden (1961) showed that sodium absorption occurred

against a concentration gradient in the small and large

intestine. This indicated that very little sodium was

lost in the feces. Also, this indicated that cows can

subsist on small quantities of sodium in the feed. This

is an important point since pasture and other cattle feeds

are low in sodium. Kay and Hobson (1963) noted that green

roughages contain 0.1% sodium and dry roughages contain

0.10 to 0.5%. Renkema (1962) showed that specific sodium

absorption in the intestine worked more efficiently when

sodium intake was lower than normal. In his studies, sodium

was absorbed from the intestinal content against a 75-

times greater concentration gradient. It is clear that,

besides the kidney, the gut plays an important part in the

regulation of sodium metabolism in the cow on sodium poor

diets.

CHAPTER III

EXPERIMENTAL PROCEDURE

Digestion and metabolism studies were conducted

using twelve feeding treatments, composed of various levels

of salt (NaCl) fed in a ration composed of dry-rolled

sorghum grain, cottonseed meal, alfalfa hay and cottonseed

hulls. The treatments were: (1) .11% Na, (2) .19% Na,

(3) .20% Na, (4) .29% Na, (5) .32% Na, (6) .33% Na,

(7) .34% Na, (8) .38% Na, (9) .42% Na, (10) .50% Na,

(11) .54% Na, (12) .65% Na. All rations were exactly the

same except for the levels of salt. The rations were

supplemented with urea, limestone, defluorinated rock

phosphate, vitamin A, and ammonimum sulfate (Table 1).

The study consisted of three digestion and metabolism

trials, which consisted of twenty-four mixed steers

averaging 500 pounds each. In each trial, two animals

were assigned to each of the twelve treatments after being

randomly selected. After allowing approximately 14 days

for the animals to adapt to the rations, two steers from

each treatment group were placed in individual stalls and

fed 5.4 kg for five days. Following this adjustment period,

the steers were confined in metabolism stalls for a three

day adjustment period and a seven day total collection

period.

17

18

TABLE 1

BASAL RATION COMPOSITION (AIR-DRY BASIS)

Ingredient %

82 ,

3,

5,

7,

0 .

0 ,

0 .

0,

0 ,

0 .

.7

.4

. 0

.0

.0

.5

.6

,2

.3

,1

Sorghum, dry-rolled

Cottonseed meal

Alfalfa hay, chopped

Cottonseed hulls

Salt^

Urea

Limestone

Rock phosphate, defluorinated

Vitamin K^^^^^^ ^y/g

Ammonium sulfate

Total 100.0

^Salt levels in rations 1-4 were 0.0, 0.25, 0.50, and 1.0% respectively, and was added to each ration by replacing an equal portion of grain.

While in the metabolism stalls, the steers were

offered 2.7 kg of feed twice daily and watered as many as

four times daily. During the week of collection, wet feces

were collected from each animal, mixed thoroughly, weighed

and a 5% aliquot taken. The samples were composited daily

and refrigerated in plastic bags until the end of each trial

At this time, the fecal samples from each animal was

19

mixed and a sample was taken for chemical analysis. Total

daily urine was collected, diluted to a constant volume,

and a 100ml sample was composited for chemical analysis.

Feed samples were taken at each feeding and composited at

the end of each trial for analysis (Table 2). The second

and third trials were duplications of the first, but

steers were assigned to the next level of salt in each

succeeding trial. Feed and fecal matter were analyzed for

gross energy, crude protein, dry matter, organic matter,

ash and sodium. Urine samples were analyzed for sodium

and nitrogen. Water samples were also analyzed for sodium.

Proximate analysis of feed and feces and the determination

of urinary nitrogen were conducted by A.O.A.C. methods

(1970). Gross energy determinations were made by using

an adiabatic bomb calorimeter. Sodium concentrations were

determined using a flame photometric method (A.O.A.C, 1970)

20

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CHAPTER IV

RESULTS AND DISCUSSION

Ration component digestibility data are presented

in Table 3. The data were analyzed using least-scjuares

analysis of variance procedures (Table 4). The various

levels of sodium tended to have an influence (P<.10) on

the digestion coefficients for dry matter, gross energy,

organic matter, crude protein, and true crude protein.

The various sodium levels also had a significant effect

(P <.01) on the digestion coefficients for sodium retained

per day and grams sodium in the urine. There was also a

significant effect (P <.10) on percent sodium retained and

percent sodium in feces (P <.05). The data were analyzed

for linear effects due to varying sodium levels (Table 5).

There tended to be a linear increase (P <.10) in the

digestibility of dry matter, gross energy, and organic

matter as levels of sodium increased (Figure 1-3).

In experiments by Nelson et al_. (1955), the

digestibility of various nutrients was slightly lower in

the high salt rations than in basal rations. The differences

were not significantly different. In another experiment

by Nelson et_ a]^. (1955), the addition of 42 grams of salt

to a lamb ration decreased digestibility of organic matter

from 69.2 to 66.8%, which was significant (P <.01).

21

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28

In the present study, there was a significant

linear increase (P <.10) in the true digestibility of crude

protein, in grams sodium retained per day (P <.01) and

in grams sodium in urine (P <.01) as levels of sodium

increased (Figures 4-6). There was no significant linear

increase in nitrogen retained per day. In both experiments

by Nelson, average nitrogen retention was decreased when

the ration contained high levels (5%) of salt because of

a larger loss in urine. Elam (1961) noted that 2% salt

decreased ether extract digestibility, but increased crude

fiber and crude protein digestibility. Water consumption

and urine excretion were increased by each level of salt

above 2 percent. In the present study, there was a signifi­

cant linear increase (P <.01) in grams sodium in urine as

levels of sodium increased (Figure 6) but there was no

significant decrease of grams sodium in the feces.

Riggs et aJ . (1953) had shown high salt intakes to have a

stimulatory effect upon digestibility of ration components

whereas Archer et al. (1952) and Cardon (1953) reported

opposite effects. Meyer et al. (1955) stated that there

was no indication that higher levels of salt in cattle

and sheep rations had any influence on the digestion of

protein and TDN, or on nitrogen retention. All data

relative to nitrogen and sodium in the present study

(Tables 6 and 7) are presented showing actual values with

the varying levels of sodium.

29

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31

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34

Babcock (1905) stated that when cattle were allowed

free access to salt, consumption varied from 1 to 8 ounces

daily, with the average being approximately 3 ounces. It

has been observed that cattle having free access to salt

had a better appetite and were less affected by changes in

the ration than were those receiving no supplemental salt.

In one experiment by Babcock, cattle were deprived of salt

for three weeks. All of the cows became exceedingly

hungry for salt and would lick the stables as well as the

hands and clothing of the attendants. In every instance,

the cows exhibited an abnormal appetite for salt, but in

no case did the health or live weight of the animals appear

to be affected. In the present study, the steers were

also observed chewing the wood in their bunks and licking

the attendants. However, this observation was not restricted

to any particular treatment level. As in Babcock's study,

the steers exhibited an abnormal appetite for salt, but

neither the health nor live weight of the animals appeared

to be affected.

Babcock, in 1905, noted that cows could go a year

before any ill effects would be noticed. Any deficiency

symptoms were most likely to occur soon after calving

or among high producing individuals. Horrocks (1964)

found that steers receiving Ig. of sodium per head daily

were not greatly inferior to those on an intake of 2g. of

sodium which has been found to be sufficient in enabling

35

cattle to attain adult weight. In the present study, the

lowest sodium level fed was 5.25g (Table 6). The lowest

amount of sodium retained was 1.33g (Table 6). The live

weight of the steers did not appear to be affected by

these sodium levels. Horrocks calculated that 0.5g per

day of sodium was the minimum amount that could be excreted

via urine and feces when steers were fed maintenance rations

of hay. The minimum amount of sodium excreted in the

present study was 5.54g (Table 6) when the steers were

fed the basal ration with .11% sodium (Table 1).

Walker (1957) reported that a supplement of 1 ounce

of salt (ecjuivalent to 11.2g Na) speeded up the growth rate

of cattle grazing on Rhodesian Veld. In the experiment,

no account was taken of losses of minerals through the skin

and the differences between the amounts ingested and

excreted. However, all of the animals on the low salt

diet excreted more salt in their feces and urine than they

consumed and must therefore have been in a true negative

balance for sodium. The same trend was noticed in the

present study until the 0.32% level of sodium was reached.

In Walker's experiment, there appeared to be no differences

in patterns of intake and excretion between breeds of

cattle. In contrast to previous experiments by Horrocks

(1964), animals on the high sodium diet gained weight

faster than those on low sodium diets. Thus, on an adequate

plane of nutrition, low sodium was partially limiting to

36

gro ;/th. The extent of the limitation was very small. Four

of eight steers on trial maintained a positive sodium

balance on a low sodium diet. Upon restriction of water,

more sodium was retained in the dry matter in the distal

end of the small intestine.

Wilson (1966) observed that sheep fed on saltbush

regulated their water intake according to the salt ingested

in the feed (1.9-2.0g NaCl/lOOml water). However, when

this concentration of salt was included in the drinking

water (Pierce, 1957; Weeth, Haverland, and Cassard, 1960)

there were marked influences (reductions) on feed intake

and body condition. This suggests that the means of

ingestion of the salt may affect food intake and the health

of the animal. Results of this experiment showed that

higher concentrations of salt in the feed or water led to

a progressive decline in feed intake. Meyer and Weir

(1954) found little reduction in food intake when 13.1%

salt was added to the feed of sheep. Sodium deficient

sheep were able to restore their sodium balance by

selecting solutions (Denton and Saline, 1961) or grasses

that contained more sodium. High levels (5%) of sodium

bicarbonate (Kromann and Meyer, 1966) and salt (Kromann

and Ray, 1967) fed to lambs caused a greater depression

in growth and energy retention than could be attributed to

a depression in food intake. Jackson et al_. (1971) noted

that sodium and potassium fed in excess of estimated

37

requirements had independent, detrimental effects on weight

and gain. When dietary levels exceeded 1.9% of the ration,

energy and weight gain decreased. Increased sodium levels

in the ration had a detrimental effect on body energy,

body weight gain, carcass weight and net energy retention.

In the present study, digestibility of gross energy tended

to increase as levels of sodium increased (Figure 2).

Kellison et al. (197 2) found no significant

differences in daily gain, feed intake, or carcass traits

when salt was added in feedlot cattle rations at 0, 0.5,

1.0% and free choice levels. There was a tendency for

increased average daily gains and feed consumption at the

0.0% level. Klett et, al. (1971) fed salt in steer finishing

rations at 1.0, 0.5, 0.25, 0.125, 0.0625, 0.00% and reported

no significant differences in average daily gain, feed

intake or carcass traits. However, there was a tendency

for reduced gains when salt was added at the 1.0% level.

Morris and Gartner (1970) conducted a feeding trail to

investigate the effects of three levels of sodium supple­

mentation (.1, 3.25, 6.50, and 13.Og sodium/head/day as

bicarbonate). Steers receiving 3.1g or more sodium per

day had significantly greater rates of body weight gain

and heavier carcass weights than steers fed the basal

ration containing O.lg of sodium per day. Feed intake was

also significantly greater for steers receiving the sodium

supplemented rations. Harbers and Warren (1971) noted

38

that cattle showed little response to high concentrate

rations with salt added to the diet. Cattle consuming

rations without salt performed as well as those supplemented

with 0.5% salt.

A decrease in percent body fat (Kromann and Ray,

1967) suggested that excess sodium ions in the rumen

caused a decrease in acetic acid production and elevated

butyric and propionic acid formation, which reduced fat

deposition in feedlot steers. Hubbert et al. (1958)

noted that iri vitro cellulose digestion was reduced by the

addition of excessive amounts of sodium.

Kellison et aJ. (1972) reported data on the rela­

tionship of sodium concentration in solid waste materials

to dietary sodium. Sodium concentration of the solid

waste was 0.14, 0.19, 0.36, and 0.58% for intakes of

16.0, 29.0, 48.5, and 68.Og of sodium per head daily.

These data showed linear decrease of sodium in the solid-

waste with lowered levels of salt in the ration. Sodium

in the solid-waste increased approximately 234% from

treatment 2 (0.0% salt) to treatment 4 (1.0% salt). The

linear decrease of sodium in the solid-waste with lowered

levels of salts (Kellison et al., 1972) is in accord with

the present study (Table 6). Careful consideration should

be given to this data since feedlot solid-waste is becoming

extremely important as a source of fertilizer. Bennett

(1970) reported sodium concentrations of samples of feedlot

39

manure that ranged from 0.15% to 1.50%, with 0.80% being

the average. He stated that at a rate of application of

10-15 tons of manure per acre every 3 to 4 years, these

sodium levels should not have adverse effects on the

physical condition of the soil or on plant growth. Data

from the present trial suggest that sodium concentration

in feedlot solid-waste could be regulated by restricting

levels of sodium in the ration. There were no adverse

effects on animal performance when salt was deleted from

the ration (Klett, et al., 1972). The data of Kellison

et al. (197 2), suggest that feed ingredients supplied

sufficient sodium and chlorine to meet the daily recjuire-

ments of feedlot cattle. One recommendation, however,

(Kellison et al., 1972) was to feed cattle a ration con­

taining 0.5% salt for the first 60 days in the feedlot.

This level of salt should give the cattle ample sodium

for a 140 day feeding pericDd.

CHAPTER V

SUMMARY

Digestion and metabolism studies were conducted

with steers to determine the amount of sodium in feces in

relation to the amount of sodium in the ration. Also

studied was the effect of different sodium levels on

nutrient and gross energy digestibility. The rations

consisted of: (1) .11% Na, (2) .19% Na, (3) .20% Na,

(4) .29% Na, (5) .32% Na, (6) .33% Na, (7) .34% Na,

(8) .38% Na, (9) .42% Na, (10) .50% Na, (11) .54% Na,

(12) .65% Na. These rations were fed twice daily at

2.7kg. The various levels of sodium tended to have an

influence (P <.10) on the digestion coefficients for dry

matter, gross energy, and organic matter. The various

levels of sodium had a significant effect (P <.10) on

sodium retained. There was also a significant effect

(P <.05) on the digestion coefficients for crude protein

and true crude protein. Various levels of sodium had a

significant effect (P<.01) on sodium retained per day,

% sodium in feces and grams sodium in urine. There was

no significant effect on grams sodium in the feces or %

nitrogen retained. There tended to be a linear increase

(P <.10) in the digestibility of dry matter, gross energy,

and organic matter as levels of sodium increased. There

40

41

was a significant linear effect (P <.05) for an increase

in true digestibility of crude protein. There was also

a significant linear increase (P <.01) in grams sodium

retained per day and in grams sodium in urine as sodium

levels increased. There was no significant linear decrease

in grams sodium in the feces as dietary levels of sodium

increased. These data indicated that sodium level in the

ration was the primary factor in determining the sodiuTi

concentration in feces and urine. These data indicated

that as the level of sodium in the ration increased, the

level of sodium in the feces decreased, whereas the level

of sodium in the urine increased.

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i