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Animal Science Journal (2003) 74, 457 469 457

Blackwell Science, LtdOxford, UKASJAnimal Science Journal1344-39412003 Blackwell Publishing Asia Pty LtdDecember 2003746457469Review ArticleAmino acid nutritionT. ISHIBASHI and C. YONEMOCHI

Correspondence: Teru Ishibashi, Japan Scientific Feed Asso-

ciation, 2-6-16 Sinkawa, Chuo-ku, Tokyo 104-0033, Japan.

(Email: [email protected])

Received 17 March 2003; accepted for publication 29 July

2003.

R E V I E W A R T I C L E

Amino acid nutrition in egg production industry

Teru ISHIBASHI and Chisato YONEMOCHIJapan Scientific Feeds Association, Chuo-ku, Tokyo, Japan

ABSTRACT

The egg production industry is facing various problems that need to be solved. For amino acid nutrition to achieve scientific

and economical feeding of laying hens, it is necessary to elucidate the content, digestibility, or availability of nutrients of

feedstuffs and feeds and the requirement of amino acids for laying hens. In addition, improvement to quality of eggs and

meat of spent hens, methods of management and development of new feedstuffs are essential. For sustainable animal

production, decrease in excreta and animal welfare should be studied. The real-time determination of content and digest-

ibility of amino acids in feedstuffs are essential for formation of feeds. Recent advances in the near infrared reflectance

analysis will be able to determine the content, digestibility and availability of nutrients in feedstuffs and feeds, if we have

a supplemental amount of conventional analysis to define the calibration population. The amino acid requirements are

affected by various factors. Therefore the method to quickly and exactly determine amino acid requirements in response

to various factors is necessary. By using plasma free amino acid concentration as a criterion, it is possible to determine

amino acid requirements in various conditions of laying hens within a short experimental period, repeatedly using the same

animals. Because the amino acid requirements differ among individual animals, it should be expressed as grams per hen

per day. Practically, it is impossible to formulate various feeds for individual hens. The various expressions have been devel-

oped and these expressions have advantages and disadvantages. The nitrogen excretion of laying hens is easily reduced

by reducing dietary nitrogen levels and restricting the feed intake. The availability of amino acid may be improved by feed-

ing management, and supplementing enzyme, but the quality of eggs and meat of spent hens and welfare of laying hens

are not affected by amino acid nutrition.

KEYWORDS: amino acid requirements, laying hens, nitrogen excretion, plasma amino acid concentration, qual-

ity of eggs.

INTRODUCTION

The total number of laying hens has increased 3.2%

per year since 1995 and the amount of eggs reached

51.11 million tons, which included 3.74 million tons

(6.4% of total) of eggs for hatchery, in 2000. Egg con-

sumption per head is increasing worldwide except for

the USA, Canada and Australia (USDA 2001; Fig. 1).In these countries, egg consumption decreased after

the 1970s because the cholesterol in egg yolk is

thought to cause heart and circulatory disease. The

Japanese consume the most eggs per head per day in

the World. Since 1995, an average 328 eggs per head

are consumed annually, which shares approximately

10% of the total protein intake of the Japanese

(Table 1). The amount of feed consumed by laying

hens is 6 million tons annually. More than 80% of

feedstuffs for laying hens are imported from abroad,

which is one of the largest factors affecting negative

balance of the trade. Some of the feedstuffs are com-

peting with human foods. Therefore, it is most impor-

tant to study the effective use of feedstuffs not only for

the improvement of negative balance of trade inJapan, but also the decrease in competition between


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T. ISHIBASHI and C. YONEMOCHI


feeds and foods in the world. In order to rear livestock

efficiently and economically, the information on con-

tents, digestibility or availability of nutrients in feed-

stuffs and feeds, and the exact requirements fornutrients to livestock, is essential. In addition to the

improvement of effective use of feedstuffs, the egg

production industry is facing a number of difficult

problems, which require solving, such as decrease in

excretion of nitrogen and phosphorus for the sustain-

able animal industry, supply of safe and tasty eggs and

meats, development of new feedstuffs, technology of

feeding management and animal welfare.

DETERMINATION OF CONTENTSOF AMINO ACIDS IN FEEDSTUFFS

AND FEEDS

The average content of nutrients in feedstuffs is avail-

able from Standard Tables of Compositions of Feed-

stuffs in Japan (National Agricultural Research

Organization 2001). However, the nutritive values of

feedstuffs are not constant, and differ depending on

factors such as the area of origin, harvest period, man-

agement and process after harvest. In addition to

these factors, the nutrient content in feedstuffs varies

among different batches of the same feedstuffs. Using

conventional chemical methods, it is impossible to

determine the nutrient content of feedstuffs on a real-

time basis. Therefore, there is a need for a new real-

time analysis of the formation of feeds. Near infraredreflectance analysis (NIRA) is not a new method, but

recent NIRA may be the answer for providing rapid

and accurate analysis of not only the nutrient content,

but also the digestibility of energy and amino acids

(Van Kempen & Simmins 1997; Dudley-Cash 1998).

It is an advantage of NIRA that it can very rapidly and

accurately determine the nutrient content of feed-

stuffs that are within the calculation population.

However, NIRA has the disadvantage that it requires a

suboptimal amount of conventional in vivoand/or in

vitroanalysis in order to adequately define the calibra-

tion population.

DETERMINATION OF DIGESTIBILITY

AND AVAILABILITY OF NUTRIENTSIN FEEDSTUFFS AND FEEDS

All nutrients in feeds are not always used efficiently.

Some are excreted into feces without being digested

and absorbed, and other absorbed nutrients are

excreted into urine without being metabolized in the

body. Therefore, it is important to determine whether

the ingested nutrients are digested, absorbed, and

metabolized, when the nutrients are slightly in excessof requirements.

Digestibility of nutrients in feedstuffs

and feeds

For the economical and scientific formulation of

poultry diets, the data of contents and digestibility or

availability of nutrients in feedstuffs are essential.

Because poultry excrete feces and urine together

from the cloaca, it is necessary to separate feces from

urine by setting a cannula to determine the digestibil-

ity of feeds. By the development of the reversed rec-

tum artificial anus (Isshiki & Nakahiro 1988), it iseasy to maintain a large number of operated hens

which continue high egg production rate without

special daily care for a long period. The digestibility of

crude protein (CP, N 6.25), determined from the

difference between CP in diet and feces, are ap-

parent digestibility and not true digestibility of CP. In

order to determine the true digestibility of CP, the

Fig. 1 Eggs produced per layer after 1925 (USDA 2001).

250

200

150

1001925 1950 1975 2000

Year

Eggp

roduce(/layer)

Table 1 Annual production and consumption of eggs in 2000

(USDA 2001)

Country Production

(milion tons)

Consumption

(eggs/head)

Total 51.11

China

USA 258

Japan 328

France 264

Germany 223

Italy 219

Data unavailable for these sections.


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Amino acid nutrition


endogenous CP derived from decomposed tissues and

intestinal microflora has to be subtracted from that in

feces. To determine endogenous nitrogen, we can use

three kinds of collected feces: (i) after feeding a diet

without CP and amino acids, (ii) after feeding a diet

with graded levels of CP, and (iii) with the removal of

a diet. In the case of feeding the diet with graded lev-els of CP, the excretion of nitrogen at zero point of

dietary CP is estimated by extrapolation method. This

method is the least stressful to hens.

Availability of dietary amino acids

in feedstuffs and feeds

Some amino acids are excreted into urine when

excess amino acids are fed to chickens. The urinary

amino acids must be corrected to evaluate a true

availability of amino acids. Yamazaki and Kaku

(1988) developed the new method to overcome this,

which was modified to determine true metabolizable

energy (ME) in feedstuffs (Sibbald 1979). This

method does not need hens with an artificial anus.

The endogenous amino acids are obtained by deter-

mining amino acids in the excreta from chickens

fasted or fed a nitrogen-free diet for more than 48 h.

The values obtained using this method coincide with

those determined using roosters with an artificial

anus. Although the digestibility of feedstuffs fed as a

sole source tends to be lower than that obtained by

feeding a mixture of feedstuffs, the digestibility of

mixed feedstuffs is calculated by adding each value

of feedstuffs, which is not affected by sex and age of

poultry. The digestibility of crystalline amino acids isestimated to be 100% (Yamazaki & Kaku 1988).

Digestibility of nutrients of feedstuffs

and feeds at the end of the ileum

In pigs, there are some differences between the digest-

ibility determined using feces and digesta at the end of

the ileum (Furuya et al. 1979). In poultry, there were

differences between the digestibility of amino acids

determined using excreta and digesta at the end of the

ileum. The degree of differences varied among feed-

stuffs and individual amino acids (Ravindran & Boy-

den 1999). To determine the digestibility at the end ofileum, samples have to be collected from the hens fit-

ted with a cannula at the end of ileum or digesta at the

end of the ileum after being killed. The volume of

cecum, colon and rectum of poultry is small compared

to other herbivores, the role of intestinal microflora in

the digestion of nutrients at the lower part of digestive

lumen is small.

Factors affecting digestibility of nutrientsof feedstuffs and feeds

The digestibility of nutrients in feedstuffs is affected by

various factors, such as process of feedstuffs and coex-

isted components, tannic acid (Yamazaki & Kaku

1988) and enzymes contained in feedstuffs (Acamovic

2001).

The suggestion by Dintzis et al. (1998) has to be con-

sidered to determine the exact digestibility of CP. The

digestibility of CP differed between CP calculated from

total nitrogen determined by the Kjeldahl method and

recovered amino acids plus ammonium nitrogen

determined by amino acid analysis. These differences

might be smaller in the digesta in the ileum than in

feces because the amount of ammonium nitrogen in

the digesta in the ileum might be smaller than in feces.

Determination of digestibility

of feedstuffs in vitroThe determination of digestibility of nutrients in feed-

stuffs in vivois time consuming and laborious, and the

digestibility of only one sample is determined from

one trial. Therefore, the rapid and accurate analysis

method, by which the digestibility of many samples is

estimated simultaneously within a short period, is pre-

ferred. The in vitro method has been developed to

determine the digestibility of dry matter, digestive

energy and CP using the liquid from the small intes-

tine of a pigs attached intestinal cannula (Furuya et al.

1979). The obtained values coincide with those at the

end of ileum. This method using the intestinal fluid ofpigs is applicable to laying hens (Sakamoto et al. 1980).

However, to increase the accuracy of this method,

some standard samples, of which in vivodigestibility is

known, should be included in each in vitroexperiment

and their values should be used for corrections. For

the effective use of NIRA for real-time estimation of

the digestibility of feedstuffs in the feed-formulating

industry, numerous data on the digestibility of nutri-

ents of feedstuffs determined by this method may be

available, and is expected to be accumulated further.

AMINO ACID REQUIREMENTSOF LAYING HENS

Approximately 40 years ago, poultry diets were for-

mulated largely on CP. As observed by Osborne and

Mendel (1914), the nutritive values of CP differ

among their sources. For example, when three corn-

based diets with whole egg powder, fish meal or


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soybean meal as main sources of CP were supplied, the

maximum performance of broiler chicks was achieved

at 15.0, 16.5 and 20.4% of CP, respectively. By adding

limiting amino acids to the soybean meal diet, chicks

achieved the same performance as those fed the whole

egg powder diet (Koide et al. 1992). These results indi-

cate that the scientific protein nutrition of poultry isno longer based on the CP content of the diet. The

dietary levels and biological availability of essential

amino acids have to be considered, together with suf-

ficient dietary levels of nonessential amino acid nitro-

gen at the cellular and molecular levels, and with all

elements needed to synthesize all body and egg pro-

teins efficiently and economically.

Historically, Rose and Meyer (1936) confirmed that

animals could be reared on a diet with amino acid as

the only nitrogen source. First, approximately 60% of

egg production rate, which was commercially average

egg production at that time, was achieved by feeding a

diet containing crystalline amino acids as a sole nitro-

gen source (Fisher & Johnson 1956). The egg produc-

tion rate of recent commercial hens exceeds 90% at

the peak egg production stage as shown in Fig. 2. This

high egg production rate was maintained for more

than six months on the amino acid diet (Ishibashi &

Kametaka 1984).

Numerous studies have been conducted to deter-

mine exact amino acid requirements and the results

are evident in feeding standards. The requirements of

CP and amino acids in the feeding standards are sum-

marized in Table 2. The recommended feed intake

decreased from 110 to 100 g in version 9 by the

National Research Council (NRC 1994), and the

amino acid requirements expressed as percentages of

diet increased. The amino acid expressed as grams per

hen decreased with advancing versions. The egg pro-

duction rate increased after the 1920s and the number

of eggs per hen is increasing at the rate of 1.25 eggs

annually over the last five years (Table 2). In spite ofthe increment of egg production rate, the amino acid

requirement decreased with advancing versions.

These decreases in amino acid requirements might be

caused by determination of exact requirements of

amino acids.

In the feeding standards, only one pattern of amino

acid requirement is shown. However, the amino acid

requirements of laying hens are affected by various

factors such as genetic, environmental, physical, and

managing factors (Ishibashi 1990). The genetic, envir-

onmental and managing factors are not so large

among present stocks (Pobrow & Morris 1974). The

amino acid requirements are most drastically affected

by egg production rate. The egg production rate is not

constant throughout the laying period and increases to

more than 90% at 17 weeks of age (Fig. 2). After this,

egg production rate and the quality of eggs decreases,

and egg size increases with advancing age. Because

amino acid composition of egg white and egg yolk

does not change, the amino acid requirements

decrease with advancing age and the decrease of egg

production rate. At the peak of egg production rate for

2030 weeks of age, the CP requirement was esti-

mated to be 15.7%. The CP requirements decreased to

Fig. 2 (), Average bodyweight (g); (), feed intake

(g/week); and (), egg production rate (%) cited from

pamphlets of nine breeding companies (average values of

data of seven breeding companies).

Bodyweight(g)

2000

1500

1000

500

020 40 60 80

0

20

40

60

80

100

Age (weeks)

Eggproduction(%)

Table 2 Protein and amino acid requirements of laying hens

recommended by NRC (% of diet) in 6th to 9th revised edition

(NRC 1971, 1977, 1984, 1994)

1971 1977 1984 1994

Feed intake (g/d) 110 110 100

ME (kcal/kg diet) 2850 2850 2900 2900

CP 15.0 15.0 14.5 15.0

Arg 0.8 0.8 0.68 0.70

Gly + Ser 0.5 0.50

His 0.22 0.16 0.17

Ile 0.5 0.5 0.50 0.65

Leu 1.2 1.2 0.73 0.82Lys 0.5 0.60 0.64 0.69

Met + Cys 0.53 0.50 0.55 0.58

Phe + Tyr 0.80 0.80 0.83

Thr 0.4 0.4 0.45 0.47

Trp 0.11 0.11 0.14 0.16

Val 0.5 0.55 0.70

NRC, National Research Council; ME, metabolizable energy; CP,

crude protein; not available.


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14.1% for 6080 weeks of age and 12.4% after then

with a decreasing egg production rate (Okazaki et al.

1994). In these diets, amino acid levels ranged from

130, 115 and 100% of the NRC requirement, respec-

tively. These depressions are mainly caused by

decrease in egg production rate, because the body-

weight gain is less than 200 g and the amino acidrequirements for maintenance do not increase after

20 weeks of age. Therefore, the CP level of diet for lay-

ing hens should be arranged according to the egg pro-

duction rate and other factors. In order to formulate

layer diets, it is very important to determine the exact

requirements of CP and amino acids. In practice, how

to express these requirements is also important.

Determination of amino

acid requirements

Throughout the study of animal nutrition, researchers

have tried to develop improved methods for determin-

ing amino acid requirements including using body-

weight gain, production, nitrogen balance and feed

efficiency. These parameters are insensitive for adult

animals, laborious and expensive, and require a long

period and large number of animals to be studied.

There are two methods which are able to predict

amino acid requirements within a short period and are

more sensitive for adult animals. In these methods the

oxidation of indicator amino acid labeled with radio-

active or stable isotope and the response of plasma-

free amino acid concentrations to the changes in

dietary amino acid levels are used as parameters.

Indicator amino acid oxidation method

In the indicator amino acid oxidation method, amino

acids labeled with radioactive or stable isotopes are

used as an indicator of oxidation. In both cases, the

used indicator isotope is the same as or different from

that to be determined as the requirement. When the

same indicator amino acid as the test amino acid is

used, the method is based on the principle that when

intake of the test amino acid is limiting, protein syn-

thesis and oxidation of the test amino acid is low. As

the test amino acid intake exceeds the requirement

levels, the excess test amino acid is oxidized andexpired as CO2. The requirements of Lys, Leu, and

Val of broiler chicks were determined in this method

(Ishibashi et al. 1977a,b).

In the case where the indicator amino acid is differ-

ent from the test amino acid, the method is based on

the principle that when intake of the test amino acid is

limiting, protein synthesis is low, and all other amino

acids are excess and oxidized. As the test amino acid

intake increases, protein synthesis increases and oxi-

dation of other amino acids decreases. Above the test

amino acid requirement, additional intake of test

amino acid will not increase protein synthesis, and the

oxidation of other amino acids remains constant. By

using a radioactive or stable isotope in humans, theoxidation of one of the other amino acids (i.e. the indi-

cator) can be measured at a given intake of the test

amino acid. In both cases, the break points change

from constant to increasing oxidation of the same kind

of amino acid and from decreasing to constant indica-

tor amino acid oxidation are deemed the requirement

and are statistically assessed (Chamruspollert et al.

2002; Tabiri et al. 2002a,b).

The determined value by feeding test is an average

amino acid requirement for a long feeding period.

Within a short period, the amino acid requirement

changes with changing physical, environmental con-

ditions and egg production rate. The indicator amino

acid oxidation method is superior to the feeding test to

determine amino acid requirement, because the

requirement of amino acid is determined at a given

age and egg production stage, 1 or 2 days, compared to

a much longer period for feeding trials, 1 or 2 weeks.

However, radioisotope is expensive, dangerous and

limited to use only in the isotope institute.

Response of plasma concentration of free amino acids

as a criterion

The method using the response of plasma-free amino

acid concentration to the changes in dietary aminoacid levels as an indicator, is able to predict amino acid

requirements within a shorter period than the indica-

tor amino acid oxidation method. The principle of this

method is based on when a given amino acid intake is

less than the requirement, the plasma concentration of

a given amino acid remains low. When the given

amino acid intake exceeds the requirement level, it

increases linearly with increasing intake of the given

amino acid (Fig. 3). The point where the plasma con-

centration of free-given amino acid starts to increase

corresponds with the requirement determined using

the traditional methods in rats (Stockland et al. 1970),chicks (Zimmerman & Scott 1965; Ishibashi 2000),

laying hens (Chi & Speers 1976; Yamamoto & Ishiba-

shi 1996, 1997a,b), pigs (Mitchell et al. 1968) and

young men (Young et al. 1972).

The plasma concentration of free amino acid

responds quickly, within 2 days, to changes in dietary

amino acid levels and the response is kept for a long


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such as Lys in pigs. In pigs, Lys is most liable to be

limiting and the data of analysis of Lys in feedstuffs

and requirements of Lys are accumulated as shown

in feeding standard for pigs (MAFFRC 1998).

Although Arg is synthesized in pigs, Arg is essential

for poultry. In broilers, Lys requirement is affected by

dietary Arg levels and expressed as a function ofdietary Arg levels and vice versa as follows: (Ueno

1998)

Yl = 0.00565Xa + 0.388 R2= 0.996

Ya = 1.55Xl 0.21 R2= 0.994

where Yl and Ya are requirements of Lys and Arg

expressed as percentages of diet, and Xa and Xl are

percentages of dietary Arg and Lys, respectively. The

levels of dietary Lys and Arg do not affect the require-

ments of other amino acids. In laying hens, sulfur con-

taining amino acids (Met +Cys; SAA) is most liable to

be limiting and Lys is the second-most limiting aminoacid. Therefore, another expression of amino acid bal-

ance should be developed.

Factors affecting amino acidrequirements

The requirements of CP and amino acids are not con-

stant and are affected by many factors (Ishibashi

1990). Among these are management factors; envir-

onmental temperature, housing style (cage or floor

pens), feeding space per hens, feeders, whether or not

the hens are properly debeaked, degree of crowding of

hens in pens, supply of drinking water, disease level inthe flock and physical and genetic factors; size and

breed of hen, and dietary factors; energy content of

diets and relationship among amino acids, such as

antagonism and imbalance.

Provided these factors are controlled satisfactory, the

amino acid requirements of laying hens are mainly

affected by egg mass.

The amino-acid requirement of laying hens is a

sum of amino acids demanded for growth of body

tissues and feathers, maintenance, and production of

an egg. Assuming that 18% of bodyweight gain is

protein, and the efficiency of converting the proteinof practical diet into bodyweight and egg protein

is 55% (Scott et al. 1976). The hen needs

bodyweight 0.18 0.5 g protein per 1 g of body-

weight gain at the early stage of egg production. The

daily total of endogenous nitrogen excretion in the

adult chicken, including normal feather loss, could

be expressed as 201 mg per kg bodyweight to the

0.72 power (Harris 1966). The CP requirement for

maintenance is calculated as

201 bodyweight (kg0.72) 6.25 of protein/day.

A fresh egg contains 66% water, 12% protein, 10%

fat, 1% carbohydrate and 11% ash (Researches Coun-

cil Science & Technology Agency 2000). Provided thatefficiency of protein use is 55%, the protein needed for

1 g of egg is calculated to be 0.66 0.55 g. Sixty grams

of egg contains 7.2 g CP and the efficiency of use of

amino acid for egg protein synthesis is 55%, the CP

requirement of laying hens at 100% egg production

rate is estimated to be 16.3 g per day. When 110 g of

diet is consumed, the dietary CP level is calculated to

be 14.8%. For 90, 80, and 70% of egg production, the

required CP levels are 13.3, 11.8, and 10.4%, respec-

tively. These values added to the requirement for

maintenance correspond with those determined by

Okazaki et al. (1994).

DECREASE IN NITROGEN EXCRETIONOF LAYING HENS

The scale of livestock production has become inten-

sive, and the number of livestock per farm has

increased in the intensive farms. The amount of feces

and urine excreted by livestock amounts to

92.9 million tons annually, in which 0.7 million tons

nitrogen and 0.5 million tons phosphorus are included

(Takemasa & Takagi 2001). Although there is a large

demand for excreta as composts, the amount of

excreta in intensive farms is exceeding the demand ofexcreta as composts locally. In these circumstances,

there is a need to develop a method to decrease not

only nitrogen and phosphorus, but also the total

amount of waste. In the case of phosphorus, it is pos-

sible to reduce phosphorus excretion by supplying

phytase in pigs, broilers and laying hens as summar-

ized by Saito (2001). By reducing dietary nitrogen

level, nitrogen excretion is reduced in broilers (Ishiba-

shi et al. 1997), but the excess reduction of dietary

nitrogen level causes the increment of abdominal fat

of broilers.

In practical farms, a laying hen excretes 75 gexcreta in the low floor cage and 100 g excreta in

the high floor cage. As shown in Table 3, when the

diets with 14.020.0% CP diets in which each

essential amino acid was adjusted to be 110145%

of the NRC requirement (1997), were supplied at

the peak egg production stage, excretory nitrogen

(Y, g/hen/day) increased with increasing dietary CP


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levels (X, % of diet) as follows (Ishibashi et al.

1977a):

Y = 0.121X 0.43 (14 X 20, R2= 0.992).

The retained nitrogen in the body increased

slightly, which might have caused the low accumula-tion of abdominal fat as observed in broilers (Bartov

& Plavnik 1998) and attribute the renewal of feath-

ers. By adding four enzymes (phytase, protease,

xylase, and cellulose) and five crystalline amino

acids, Arg, Lys, Met, Trp, and Val to meet 110% of

requirements of Japanese Feeding Standard for Poul-

try (MAFFRC 1998) to the diets, it was possible to

reduce the dietary CP level from 18% of commer-

cial level to 14% without affecting performance of

laying hens and the excretory nitrogen was reduced

drastically by 41% in a practical farm (Ishibashi,

unpubl. data, 2003).Although there are some differences in the reduc-

tion rate of excretory nitrogen among the reports as

summarized by Saito (2001), it is clear that a large

amount of excretory nitrogen is reduced by decreasing

dietary CP levels in laying hens. In the case of broilers,

the nitrogen excretion was reduced by restricting feed

intake (Ishibashi et al. 1977a). By restricting feed

intake, the excreta of laying hens as observed in broil-

ers may be reduced.

QUALITY OF EGGS AND MEAT

OF SPENT HENSQuality of eggs

In Japan, more than 70% of people believe that the

brown-shelled eggs are more favorable, tasty and

nutritious compared to white-shelled eggs, and eggs

produced in a free range are nutritious and better for

good health compared to those produced in a cage

(Horiguchi et al. 1996; Horiguchi 1998). Presently

more than 500 kinds of what are called specified eggs

are on sale, but there are less than 10 kinds of eggs

with the selling point of being more nutritious and

tasty. However, it is not proven that these eggs are

more nutritious and tasty. This fact indicates that it isdifficult to control the contents of taste active compo-

nents of eggs. In a series of sensory test, there were

no differences in the taste of eggs among strains of

hens in Japan, feeding managements, cage and free-

range feeding, and feeds, except that eggs of young

hens were preferred to those of old hens and those of

Silky hens were not preferred to those of Single

Comb White Leghorn hens.

Although eggs of Silky hens were not preferred to

those of Single Comb White Leghorn hens, no differ-

ences were found in the content of taste active com-

ponents, Glu, inosinic acid and other taste activecomponents among eggs of Silky, Single Comb White

Leghorn and Rhode Island Red hens. When 5% of

Glu was added to the CP 15% diet, the contents of

Glu in neither plasma nor meat increased (Horiguchi

1998). When Met was added to the diets with 16.5%

CP diet consisting of corn and soybean meal, CP and

DM contents of egg white increased, but DM content

of egg yolk and functional components as a food were

not affected (Shafer & Rose 1998). Although the

components of fatty acids and biological active sub-

stances in egg yolk is affected, that in egg white is not

affected by dietary components, feeding management

(Kishii 2002) and breeds of hens (Pobrow & Morris

1974).

Quality of meat of spent hens

In the last 5 years, approximately 89 billion spent hens

weighing 158 kilotons were slaughtered annually, and

more than half of them were rendered to produce

Table 3 Effects of dietary CP on nitrogen excretion of laying hens at 220230 days of age

Diet Dietary CP

(%)

BW change

(g/hen/d)

Feed intake

(g/hen/d)

Nitrogen (mg/hen/d)

Intake Egg Excreta Feather Retention

Experimental 14.0 6.0 100.0 2242d 955 (42.6)1 1274d(100.0)2 9 4d

16.0 9.1 98.9 2532c

949 (37.5) 1471c

(115.5) 15 97c

18.0 6.5 101.7 2929b 943 (32.2) 1778b (139.6) 8 200b

20.0 10.1 101.5 3428a 936 (28.8) 1978a(155.3) 11 303a

Commercial 19.8 7.1 99.4 3149a 968 (30.7) 1905a(96.3) 16 270a

Pooled SE 0.3 2.0 39 18 26 2

Each value is mean for 15 hens with 1680 11 g for initial bodyweight (BW), adMeans in the same column with different superscripts

differ significantly (P


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chicken meal and the remainders were used for meat,

soup and sausage. Egg producers have to pay approx-

imately 020 yen per hen to dealers of spent hens.

These differences in price of spent hens depend on

whether there is a rendering faculty or not. These

expenses have to be lowered or changed to produce

profits. In the case of old dairy cows after the lastbreeding, they are fattened for production of meat. In

the case of spent hens, they are all out to alternate to

young pullets, in spite of that, some of them are keep-

ing a high egg production rate. Because there are no

available reports studying the fattening of spent hens,

a new method to improve the cost of spent hens is

required.

ANIMAL WELFARE ANDINDUCED MOLT

The concept of animal welfare is to keep animals in a

comfortable condition. The present poultry produc-

tion system in Japan does not practice good animal

welfare but bad welfare and high production, involv-

ing high population density per cage, keeping birds in

low light intensities, beak trimming, fasting for

induced molt, transport and slaughter. The concept of

animal welfare often conflicts with economic and

effective animal production. The main object of nutri-

tion is to optimize productive efficiency, but this is

usually achieved only when health is also optimized.

Therefore, health and consequent welfare are major

priorities in modern nutritional practices. The present

egg production system will be improved step-by-stepin future.

In the case of group-fed laying hens, they are de-

beaked at a young age and confined in a narrow cage,

in which excess energy consumption and struggles

with other hens are decreased.

With advancing age, the egg production rate (Fig. 2)

and egg quality decrease. By induced molt, the egg

production rate is recovered to 90% of the maximum

egg production rate before molt. Induced molting is

repeated two or more times. Induced molting is prac-

ticed in more than 50% of farms in the world and is

increased especially when the chick feeding cost isexpensive and egg price is high. The main objective of

induced molting is to improve the quality of eggs and

to extend the productive life of hens. The most popu-

lar method of induced molting involves reducing

bodyweight by fasting for more than a week. Then the

layers are supplied a low CP post-molting diet until

their egg production rate reaches 5%, and then the

post-molting diet is switched to a layer diet. Single

Comb White Leghorn hens loose approximately 30%

of bodyweight (440 g) and 130 g of feather, which are

recovered within 2 weeks after refeeding (Fukuma &

Ishibashi 1997). The CP requirements during this

period were estimated to be less than 14.3% (Fukuma

& Ishibashi 1997), 12.4% (Hoyle & Garlich 1987) and13.0% (Koelkebeck et al. 1991), respectively, in which

the total SAA were contained 0.56, 0.62 and 0.46%,

respectively.

Because feather contains approximately 2% of Cys

and 0.7% of Met, the requirement of total sulfur con-

taining amino acid (SAA) may be high. The obtained

total SAA requirements from the data of performance

and plasma free Met concentration were estimated to

be 0.540.57% of diet, which were recalculated to be

0.47 and 0.50% on a digestible amino acid basis using

the data by Yamazaki and Kaku (1988). These results

corresponded with those of Carderon and Jensen

(1990) and Schutte and Smink (1998).

PROBLEMS TO BE SOLVED

IN THE FUTURE

The world population has increased annually at rates

ranging between 1.3 and 2.0% since the 1960s. The

general improvement in food consumption habits

throughout the world may prompt the increased con-

sumption of animal products, such as milk, meats and

eggs. Therefore, the challenges of developing effective

production of animal protein will be essential.

Injection of amino acid into hatching eggs

Large chicks are hatched from large eggs. Large chicks

tend to grow faster at hatching time. Administration of

amino acid mixture to hatching eggs increases body-

weight of chicks at hatching time (Ohta et al. 1999,

2001). The injection of nutrients into hatching eggs is

not technically difficult and will be in practice in the

future.

Amino acid requirements of

replacing pullets

It has been a standard practice to feed growing egg-type pullets a series of diets generally termed starter,

grower, and developer diets. In these rations, CP and

other nutrients decrease. The NRC lists the following

dietary CP requirements for pullets: 18% for 0

6 weeks, 16% for 712 weeks and 15% for 12

18 weeks of age. There are different approaches to

feeding replacement pullets for a number of reasons.


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During the last decade, the poultry industry has been

using pullets that mature earlier. With these birds, it is

of even greater importance that pullets come into pro-

duction at the proper weight and frame size. The more

important factors to be studied for nutritional require-

ments of pullets are concerning the subsequent laying

performance of pullets. There are a few available stud-ies regarding the effects of CP levels in pullet diets on

development and subsequent layer performance. Mor-

tality and days to 5% egg production, feed intake, feed

conversion and egg weight during the first 16 weeks

were not affected by rearing dietary treatments (Hus-

sein et al. 1996). It is difficult to confirm the effect of

pullet diet on the subsequent performance, but the

accumulation of more data on the subsequent perfor-

mance is expected.

Improvements of amino acid use

Phytase has been used as a commercial feed additivefor 10 years. In general, the addition of microbial

phytase to the diet improved the digestibility of CP by

13% in addition to positive effect on phosphate

digestibility (Saito 2001). However, the exact mecha-

nisms responsible for improvements remain unclear at

present (Kies et al. 2001). The digestibility of CP in

commercial diets is less than 90%. Therefore, a new

method to improve the digestibility of dietary CP

should be developed by supplementing enzymes, pro-

cessing feedstuffs and so on.

Development of new feedstuffsThe research into new feedstuffs has continued.

Recently new attention has been paid to the re-use of

food waste. The amount of food waste is not major

quantitatively. Importantly, the most attention is

focused on genetically modified plant feedstuffs.

Advances in plant breeding and genetic engineering

are resulting in many genetically altered feedstuffs

that have increased nutritional values for poultry

diets. For example, high oil corn, nutrient dense corn,

high Lys soybean and trypsin-inhibitor and lectin-free

soybean have increased nutritional value for poultry

compared to conventional feedstuffs. Trypsin-inhibitorand lectin are two major anti-nutritional factors in

soybean. These feedstuffs contain higher levels of

digestible amino acids (Howie 1998).

It has been reported that the share of planted area of

genetically modified plants in 2003 exceed 68% for

soybean and 36% for corn in USA, 63% for rape in

Canada, and 45% for cotton in Australia (Interna-

tional Service for the Acquisition of Agri-biotech

Applications 2003). The safety of these genetic modi-

fied plants on broilers, layers, pigs, and dairy cows is

being studied in our laboratory.

Timing of supply of amino acids

The accumulation rate of protein in egg yolk is con-

stant and it takes 810 days to make egg yolk, but the

synthesis of egg white is not constant and complemen-

tary, and is highest during 3 h before ovulation

(Table 4, Ishibashi & Kumagai 1984; Kumagai & Ish-

ibashi 1984).

When the dietary supply of amino acids is not

enough to meet the temporal high needs of amino

acids, the deficient amino acids may be supplied by the

degradation of muscle protein (Hayashi et al. 1991).

The rate of break down was 4.8% per day before ovi-

position and was 8.4% per day after. At these times

the absolute rates of muscle protein break down is cal-

culated to be 1.2 and 2.1 g/h, respectively, which is

enough to meet the temporal requirement for egg

white protein synthesis.Corticosteroides are known to strongly accelerate

muscle protein breakdown (Beuving & Vonder 1977)

and a maximum blood concentration of corticosterone

had been observed 44 min before oviposition. These

results might support that muscle protein is a temporal

source of amino acids for egg white synthesis.

Egg shell formation is accelerated 1820 h after ovi-

position. The need for Ca increases at night (Horikawa

et al. 1989). By supplying Ca during the night, the egg

shell quality is improved. Like this, by supplying

amino acids when egg white is synthesized, the use of

dietary amino acid for egg white synthesis may be

improved.

CONCLUSION

After the outbreak of bovine spongiform encephalop-

athy encephalitis, the use of protein derived from cat-

tle is prohibited and the use of animal protein is

Table 4 Apparent accumulation rate of soluble protein in the

magnum during egg formulation cycle

Hours after oviposition Accumulation rate (g/h)

02 0.200

25 0.100

510 0.140

1021 0.127

2124 0.447


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avoided. By increasing the use of plant protein, the

volume and moisture of excreta increase and the

importance of amino acids as supplements is increas-

ing. Because the concentration of SAA in an egg is

higher than in the protein derived from corn and soy-

bean meal, SAA is most liable to be limiting and fol-

lowed by Lys, Thr, and Trp in the feed of laying hens.The addition of Met is commonly in practice. In Japan,

12 amino acids including analogs are permitted as sup-

plements to feeds. The consumption of animal protein

is increasing with an increasing human population

and the improvement of the income levels of the

nation. For effective use of feedstuffs, the use of amino

acid additives is increasing 5% in developed countries

and 10% in underdeveloped countries annually.

Annual production of Lys, Met including DL-Met and

hydroxyanalogs of Met, Thr, and Trp amount to 550,

450, 50, and 0.5 kilotons, respectively. Other amino

acids liable to be limiting will be permitted in near

future. With effective use of these amino acids, feed-

stuffs will be spared, the competition between foods

and feedstuffs will decrease and excretion of waste,

especially nitrogen, will also be decreased.

A wave of free trade would hasten an increased

understanding of animal welfare and hazard analysis

critical control point in the world. Under these circum-

stances, it is expected that the poultry industry will

develop by improving feed efficiency with accom-

panying genetic, physiological and management

improvements.

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