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amino acids and more.Information for the Feed Industry Volume 08/Number 01 March 2007

Special Issue

Volume 08/Number 01/March 2007

The Potential for Using Low CrudeProtein Diets for Broilers and Turkeys

Part 1: A Literature Review

byDr. Robert L. Payne

Degussa Feed Additives

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The Potential for Using Low CrudeProtein Diets for Broilers and Turkeys Part 1: A Literature Review

Poultry

Key information

Low Crude Protein diets allow nutritionists

to formulate diets that are less expensive

and more environmental friendly.

Low Crude Protein diets support broiler and

turkey performance equal to that achieved

with typical conventional diets.


Crude Protein levels in broiler diets can be

reduced by 3 4 percentage points provid-

ed supplemental amino acids are used to

maintain the levels found in conventional

diets.

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Volume 08/Number 01 March 2007 amino acids and more.

3 Degussa Feed Additives

use of low CP diets. Since the time of his

review, reports have been published that

suggest what some of these limiting fac-

tor(s) could be. Therefore, the purpose of

this paper is to address the possibility of

using low CP diets for broilers.

Digestibility and availability of supplemental

free amino acids

Most often when we discuss digestibility

and availability, we are making some ref-

erence to the quality of a raw material.

Many factors can influence the digestibil-

ity and availability of amino acids in raw

materials, including processing condi-

tions, presence of anti-nutritional factors

or fibers, or physical and chemical com-

position of the protein (Lewis and Bay-

ley, 1995; Parsons, 2002). Several au-

thors have reported difficulties associated

with predicting poultry performance

when diets are formulated on a total

amino acid basis when using raw materi-

als containing low levels of digestible

amino acids (Esteve-Garcia et al., 1993;

Fernandez et al., 1995; Pertill et al.,

2001a; Rostagno et al., 1995). Today,

these problems are overcome by first de-termining the digestible amino acid con-

tent of raw materials and then by formu-

lating diets using these digestible rather

than total amino acid levels. This allows

raw materials to be ranked according to

their usable amino acid content, which

improves the precision of diet formula-

tion and reduces N excretion. The con-

cept of digestible amino acids, as well as

the standardized ileal digestible amino

acid contents of several commonly used

raw materials has been recently dis-

cussed and summarized by Lemme et al.,(2004b).

Conversely, we seldomly think of supple-

mental amino acids being any less than

100 % digestible and available to the

animal. Lewis and Bayley (1995) re-

viewed the research data and concluded

that supplemental free AA were 100 %

digestible and available for poultry. How-

ever, most of the research used in their

review was based on total tract or excre-

ta amino acid digestibility. Therefore, a

Non essential amino acids play an important

role in broiler nutrition.

Understanding the interactions of amino

acids in low Crude Protein diets has in-

creased over recent years.

Introduction

More than ever before, supplemental

amino acids (AA) are being incorporated

into diets for swine and poultry to re-

place a portion of the essential amino

acids provided by protein-rich raw mate-

rials. As a result, the levels of Crude Pro-

tein (CP) in todays diets are generally

decreasing. Because of these advances,

nutritionists have the ability to more

precisely formulate diets to meet the ani-

mals amino acid needs, as well as giving

them more flexibility in raw material se-

lection. The result is more environmen-

tally friendly diets via reduction in N ex-

cretion and often decreased diet cost, es-

pecially when those protein-rich raw

materials become expensive.

However, despite relative acceptance of

using low CP diets for swine and turkeys,

the utilization of low CP diets for broilersis still limited. As a result, minimum con-

straints are often placed on the CP level

or maximum constraints on the level of

supplemental AA. One potential reason

for limiting any further reduction in CP

is the concern that commercially pro-

duced amino acids are less than 100 %

digestible and available to the animal.

However, probably the greatest point of

concern is that growth and carcass per-

formance seems to be impaired when

broilers are fed diets that are low in CP

despite being formulated to meet allknown nutrient requirements. Consider-

ing that Met, Lys, Thr, and Trp are com-

mercially available today and other

amino acids, such as Arg, Ile, or Gly,

could become available in the future,

the potential for using low CP diets for

broilers could improve even further.

Waldroup (2000) reviewed the effects of

using low CP diets with broilers, and he

suggested that there were some uniden-

tified factor(s) that were still limiting the

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Volume 08/Number 01 March 2007amino acids and more.

4

trial was conducted to determine the

ileal digestibility of free AA in broilers.

After determining the apparent ileal di-

gestibility of each free AA, the digestibili-

ties were standardized by correcting for

basal endogenous losses. Lemme et al.

(2005) reported that the digestibility fig-

ures for all free AA measured were very

close to 100 % regardless of the stan-

dardization method (protein-free or en-

zymatically hydrolyzed casein diet),

which suggests a complete absorption of

the dietary AA before the terminal

ileum.

Supplemental free AA are 100 % di-

gestible and available. However, this

does not mean that they will be 100 %

utilized by the animal in every situation.

Both supplemented and protein bound

amino acids can also have adverse effects

on growth, which are widely recognized

as dietary imbalances and antagonisms.

An imbalance is defined as a change to

the pattern of dietary amino acids that

results in decreased feed intake and

growth, while an antagonism is a nega-

tive interaction between structurally

similar amino acids (DMello, 2003). An

imbalance is most often caused in prac-tice by either a small addition of an es-

sential amino acid to a low CP diet or an

unbalanced mixture of amino acids

added to a diet. An example of this

would be when a broiler diet calls for

0.20 % DL-Met but the addition of DL-

Methionione is overlooked when the

feed is being mixed. Protein synthesis,

thus, will be limited by the low dietary

methionine content which means both

reduced feed intake due to specific feed

back mechanisms as well as desamina-

tion and oxidation of the amino acidswhich are in relative excess to methion-

ine. The latter process depending on

the degree of imbalance can also be

detrimental to the animals welfare. An

antagonism, on the other hand, such as

the Arg:Lys antagonism, can occur re-

gardless of another amino acid being

more limiting. For example, a typical

broiler diet being adequate in arginine

calls for 0.10 % L-LysineHCl to meet the

Lys needs, but by a mixing error more

L-LysineHCl than desired is supplement-

ed. Then, the surplus Lys load will not

only be degraded but might also activate

the arginase activity resulting in an in-

creased arginine degradation. This in

turn might lead to a marginal arginine

deficiency limiting performance. Both

imbalances and antagonisms decrease

the efficacy of utilization of amino acids;

however, both of these adverse effects

can be easily avoided by ensuring that

diets are formulated according to the ide-

al protein concept, which ensures that

dietary essential amino acids are main-

tained in the proper ratios to each other

(Baker, 1994; NRC, 1994; Emmert and

Baker, 1997; Mack et al., 1999; Lemme,

2003).

Supplemental free AA are able to be

used to their fullest potential by:

1. ensuring that the animals are fed at or

near ad libitum levels,

2. formulating and mixing the diets on a

digestible AA basis, and

3. formulating and mixing the diets in

accordance with the ideal protein con-

cept.

In doing so, there should be no AA im-

balance or antagonism.

The effects of feeding low CP, amino acid

supplemented diets

The effects of feeding low CP diets to

turkeys and broilers on body weight or

feed conversion (gain:feed) are reviewed

in Tables 1 and 2, respectively. The data

reported in Tables 1 and 2 for the low CP

treatments correspond to the low CP

treatment indicated in bold, and these

treatments were selected because theywere the most promising results out of

all low CP treatments reported by each

research group.

The effects of low CP diets in turkeys

For turkeys, there are 19 datasets sum-

marizing recent low CP research in Table

1. Of the 19 datasets, only 4 for body

weight and 3 for gain:feed (21 and 16 %,

respectively) suggest significantly differ-

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ent performance when turkeys were fed

low CP than those fed the conventional

diets. Most of these datasets suggest that

low CP diets have a negative effect on

body weight but, only 32 % of the data-

sets indicate any negative impact on feed

conversion. In most of the trials reported

in Table 1, CP could be lowered by ap-

proximately 4 percentage points com-

pared with the conventional diet before

a decrease in body weight was reported.

Kidd et al., (1997) reported the most neg-

ative impact on performance as body

weight was reduced by over 2.5 kg when

CP was reduced by 5 % or more from

0 to 18 weeks of grow-out. It should be

noted that Kidd et al., (1997) also report-

ed that performance was not significant-

ly affected (+/- 0.5 kg) over this same 18

week period when CP was reduced by

less than 5 %. Overall, the turkey data

reported in Table 1 suggests that low CP

diets can work well, and these data seem

to agree with those summarized by Fir-

man (1994). The reviews in Table 1, al-

beit brief, generally suggest that low CP

diets support growth performance of

turkeys similar to a typical conventional

diet.

Table1: Effects of low crude protein diets on performance of turkeys1

Age, Conventional Low CP, Low CP Relative ReferenceBreed CP, treatment(s) Performance

% % BW, kg Gain:Feed

7 to 28 d, 28.4 24.8 As-is, +Thr, +Val, or +Ile +0.03 +0.04 Waibel et al., 2000bB.U.T. 6 20.9 As-is, +Thr, Val, Ile, Arg, Lys & Trp, -Arg, -Lys & Trp, +0.02 +0.03 Exp. 1

-Ile,-Val,or -Thr

18.2 As-is or +Thr, Val, Ile, Arg, Lys, & Trp -0.01 +0.02

8 to 12 wks, 23.4 19.5 As-is, +Thr, +Val, or +Ile +0.01 -0.01 Waibel et al., 2000bB.U.T. 6 16.3 As-is, +Thr,Val,Ile, Arg,Lys & Trp, -Arg, -0.07 -0.01 Exp. 2

-Lys & Trp, -Ile,-Val,or -Thr

14.2 As-is or +Thr,Val,Ile, Arg,Lys,& Trp -0.25* -0.01

16 to 20 wks, 16.8 14.4 As-is, +Thr, +Val,or +Ile -0.18 0 Waibel et al., 2000bB.U.T. 6 12.0 As-is, +Thr,Val, Ile, Arg, Lys & Trp, -Arg, -0.25 -0.01 Exp. 3

-Lys & Trp, -Ile,-Val,or -Thr

10.4 As-is or +Thr,Val, Ile, Arg, Lys & Trp -0.36 -0.01

0 to 18 wks, 29.0/26.9/ 26.7/23.8/Nicholas 22.7/19.6/ 20.9/18.0/ +0, 0.1, or 0.2% Thr +0.03 +0.02 Kidd et al., 1997

16.8/14.2 15.4/13.1

24.4/22.6/(6 phases) 19.1/16.5/ +0, 0.1, or 0.2% Thr -0.41 +0.04

14.1/11.9

22.0/20.4/17.3/14.9/ As-is -2.61* -0.0212.7/10.8

3 to 20 wks, 26.5/24.0/ 23.9/21.6/ +EAA = Conventional AA levels or Lemme et al., 2004aB.U.T. 6 21.0/18.0/ 18.9/16.2/ + commercial avail. AA = PC -0.21 +0.01

16.0 14.4

21.2/19.3/(5 phases) 16.9/14.5/ + EAA = Conventional AA levels -0.68* +0.01*

12.9

6 to 20 wks, 23.1/20.7/ 21.2/19.0/ As-is or +Thr -0.06 0 Waibel et al., 2000a,B.U.T. 6 18.0/15.7/ 16.5/14.5 Exp. 1

(4 phases) 19.8/17.8/ As-is, +Thr, or +Ile,Val,Arg, & Trp +0.15 +0.01*15.5/13.6

6 to 21 wks, 25.3/22.2/ 23.7/20.7 As-is, +Thr, or +Trp, Lys, Met, Cys, Val, & Thr -0.16 0 Waibel et al., 2000aB.U.T. 6 20.0/17.8/ 18.7/16.6/ Exp. 2

16.0 14.9

22.1/19.3/ As-is, +Thr, or +Trp,Lys,Met, Cys,Val,& Thr -0.77* 0(5 phases) 17.3/15.4/

13.8

20.4/17.8/ As-is, +Thr, +Lys & Trp, +Lys & Trp & Ile, -0.10 +0.01*16.0/14.1/ Val,& Arg, or +All & Glu

12.7

1 Relative performance of low CP diets correlates to the low CP treatment in bold under the low CP diet section, and this performance level was the most promising result of all low CP treatments withineach dataset. All trials were conducted with males, and unless otherwise indicated,each trial was conducted over a single growth phase. Within each dataset,every attempt was made to include alltreatments pertinent to the discussion of low CP diets.

*Low CP treatment means are significantly different from the Conventional CP diet, P < 0.10.

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6Degussa Feed Additives

The effects of low CP diets in broilers

A total of 59 datasets are reported in

Table 2, which spans over 15 years worth

of research. The datasets are strongly

dedicated to the first 21 days of age with

39 of the 59 datasets dedicated to this

age group. Conversely, there are 15 and

5 datasets for 21 to 42 and 42+ days of

age, respectively. A majority of the

datasets (66 and 71 % for gain and

gain:feed, respectively) suggest that

growth performance is reduced when

broilers are fed low CP diets. However,

only 19 for average daily gain and 24 for

gain:feed (32 and 41 %, respectively) in-

dicate statistically significantly different

performance (both positive and nega-

tive) when broilers are fed low CP com-

pared with those fed conventional diets.

Of the significantly different datasets, 15

and 17 (79 and 71 %, respectively)

data-sets for daily gain and gain:feed, re-

spectively, report negative impact on

performance. Similar to the data for

turkeys, the previous statement is made

with caution, because this negative trend

of low CP diets on performance is often

in the magnitude of 2 g or less per daily

gain and approximately 0.03 or lesschange in gain:feed.

As shown in Table 2, there have been

several hypotheses and research dedicat-

ed to understanding low CP diets. These

efforts include: effects of potassium or di-

etary electrolyte balance (Fancher and

Jansen, 1989a,b; Waldroup, 2000); alter-

ations in the Trp:LNAA ratio or effects of

excessive Met (Si et al., 2004a,b); addi-

tion of a non-specific N source (Fancher

and Jensen, 1989a; Pinchasov et al.,

1990; Parr and Summers, 1991; Han etal., 1992; Kerr and Kidd, 1999a); effects

of the concentration of essential AA

(Fancher and Jansen, 1989a,b; Pin-

chasov et al., 1990; Cabel et al., 1991;

Parr and Summers, 1991; Han et al.,

1992; Kerr and Kidd, 1999a,b; Kidd and

Kerr, 2000; Bregendahl et al., 2002;

Dean, 2005); effects of the concentration

of nonessential AA (Fancher and Jansen,

1989b; Pinchasov et al., 1990; Parr and

Summers, 1991; Bregendahl et al., 2002;

Fritts et al., 2004; Dean, 2005); and ef-

fects of meeting all known nutrient re-

quirements, providing nutrients in an

ideal protein pattern or at the same or

similar level as conventional diet (Fanch-

er and Jansen, 1989a,b; Pinchasov et al.,

1990; Ferguson et al., 1998a,b; Aletor et

al., 2000; Payne, 2000; Brooks et al.,

2003; Fritts et al., 2004; Dean, 2005).

While much of the research cited above

has resulted in performance that is close

to but often lower than broilers fed a

conventional diet, some has been very

positive.

Aletor et al., (2000) reduced the dietary

CP content fed to 21 to 42-d old broilers

from 22.5 % to 21, 19, 17.2, or 15.3 %.

They reported that weight gain was simi-

lar but gain:feed and nitrogen excretion

were reduced among the broilers fed the

low CP or conventional diets. Brooks et

al., (2003) reported similar findings as CP

was reduced in 7 to 21-d old broilers

from 23 to 15 % without affecting

growth performance provided that the

low CP diets were formulated to contain

the same AA content as the conventional

diet. However, Brooks et al. (2003) also

reported that performance began to de-

crease when CP was below 15 %. Dean(2005) evaluated the effects of CP in 1 to

17-d old broilers by titrating CP from

22.2 to 16.2 % while providing the same

AA content as the conventional diet.

Dean indicated that CP could be reduced

by 3 % from 22.2 to 19.2 % before per-

formance was negatively affected. Next,

Dean (2005) supplemented a 16.2 %

low CP diet with all essential AA to

equal the levels in the conventional diet,

and again reported that performance

comparable to broilers fed a convention-

al diet could not be maintained by sup-plementing essential AA only.

The differences in broiler performance

between the low CP and conventional

treatments for each research trial are

illustrated in Figure 1. Surprisingly, the

differences in performance are not as

great in magnitude as perhaps has been

suggested over time. As stated above, the

magnitude of difference is roughly 2 g of

gain or 0.03 points of gain:feed per day.

Certainly this reduced performance can

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Table2: Effects of low crude protein diets on performance of broilers 1

Age (Sex) Conventional Low CP Conventional Low CP ReferenceDiet Diet(s)

CP, % CP, % ADG, g G:F ADG, g G:F1 to 17 d 22.2 20.7, 19.2, 17.7, & 16.2 29.97 0.817 28.04 0.759 Dean, 2005, Exp. 1(F)

1 to 17 d 22.2 16.2 + NEAA = Conventional 29.27 0.797 28.32 0.807 Dean, 2005, Exp. 2(F) + EAA = Conventional + EAA & NEAA

1 to 17 d 22.2 16.2 + Gly, + Glu, + Ala, + Asp, 28.70 0.766 + Gly + Gly Dean, 2005, Exp. 3(F) + Pro, or + All 28.50 0.801*

+ All + All27.79 0.806*

1 to 17 d 22.2 16.2 (1.23% Gly+Ser) + Gly = 1.35, 1.47, 26.50 0.808 25.91 0.791 Dean, 2005, Exp. 4(F) 1.59, 1.71, 1.83, 1.95, or 2.07% Gly+Ser + Glu

1 to 17 d 22.2 16.2 (1.60% Gly+Ser) + Gly = 1.72, 1.84, 28.98 0.800 29.60 0.797 Dean, 2005, Exp. 5(F) 1.96, 2.08, 2.20, or 2.32% Gly+Ser

1 to 14 d 22.8 20.9 (1.76% Gly+Ser) +EAA + EAA & Gly = 33.86 0.873 34.50 0.876 Schutte et al., 1997,(M + F) 1.85, 1.94, 2.03, or 2.12% Gly+Ser + Glu Exp. 2

1 to 21 d 22.3 18.6 (1.56% Gly+Ser) +EAA +EAA + Gly = 41.5 0.764 40.76 0.756 Schutte et al., 1997,(M + F) 1.65, 1.74, 1.83, 1.92, or 2.01% Gly+Ser + Glu Exp. 1

1 to 21 d 22.0 20.0 37.6 0.709 36.2* 0.694 Ferguson et al., 1998a(M)

1 to 21 d 26.4 21.9 37.7 0.758 36.5 0.714* Ferguson et al., 1998b(M)

1 to 21 d 23.0 22, 20, 18, & 16 1) No difference in performance between Si et al., 2004a(M) +Trp = 5 & 6 Trp: LNAA conventional and 22% CP, but BW gain

and FCR decrease as CP level decrease2) No effect of AA levels @ 100 or 110% NRC3) No effect of Trp:LNAA ratio

1 to 21 d 23.0 22, 20, 18, & 16 1) No difference in performance between Si et al., 2004b(M) +DL-Met or to meet Met and/or TSAA conventional and 22% CP, but BW gain

and FCR decrease as CP level decrease+DL-Met & L-Cys to meet Met and TSAA 2) No effect of AA levels @ 100 or 110% NRC

or of DL-Met or L-Cys

1 to 21 d 23.0 21, 19, 17, & 15 28.6 0.694 26.5* 0.640 Cabel and Waldroup,(M + F) 1991

5 to 21 d 22.0 18.0 1) No significant difference in BW gain or FCR Fritts et al., 2004(M) +Gly, +Leu, +Asp, +Glu, +Ala, +Pro, or +All between traditional and low CP + all treatments (abstract)

2) +Gly,+Asp, or +Leu treatments performedbest of single AA, but always lower thanconventional

7 to 21 d 24.0 17.0 +K intermediate +K = Conventional 33.3 0.691 29.6* 0.613* Fancher and Jensen,(M) 1989b, Exp. 3

7 to 21 d 23.0 20.0 @ 93.5 or 100% NRC 36.5 0.712 33.8 0.680* Pinchasov et al., 1990,(M) Exp. 1

17.0 @ 87.5, 93.5,or 100% NRC 31.8* 0.630*

7 to 21 d 23.0 17.0 37.0 0.703 35.1 0.690 Pinchasov et al., 1990,(M) 21,19,& 16 +Glu = Conventional CP Exp. 2

7 to 21 d 23.0 21.0 32.3 0.630 32.3 0.617 Parr and Summers,(M + F) +10% NRC Lys 1991, Exp. 1

7 to 21 d 23.0 20.3 25.3 0.559 27.8* 0.595* Parr and Summers,(M + F) +10% NRC Arg +Gly to equal 23.0 CP 1991, Exp. 2

+Gly & 10% NRC Arg

7 to 21 d 23.0 20.1 28.9 0.541 31.3* 0.585* Parr and Summers,(M + F) +10% NRC Thr +Gly & 10% NRC Thr 1991,Exp.3

19.7 31.0* 0.571*+10% NRC Trp +Gly & 10% NRC Trp

7 to 21 d 23.0 17.8 +10% NRC Ile 36.7 0.654 38.0* 0.617* Parr and Summers,(M + F) +10% NRC Phe + NEAA 1991, Exp. 4

7 to 21 d 23.0 17.4 +10% NRC Leu 33.0 0.654 34.6 0.617 Parr and Summers,(M + F) + NEAA 1991, Exp. 5

7 to 21 d 23.0 16.5 +10% NRC His 33.9 0.637 36.6 0.625 Parr and Summers,(M + F) + NEAA 1991, Exp. 6

7 to 21 d 23.2 18.6 +1% triammonium citrate 46.7 0.739 44.3* 0.679* Bregendahl et al.,(M) + 1% Gln + 1% Asn 2002, Exp. 1

7 to 21 d 24.0 18.5 52.2 0.762 46.9* 0.710* Bregendahl et al.,(M) +15, 30, or 45% more CAA 2002,Exp.2

7 to 21 d 23.4 17.6 +1, 2, or 3% NEAA (Glu-Asp) 43.9 0.753 42.6 0.723* Bregendahl et al.,(M) + 45% more CAA 2002, Exp. 3

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Table2: Effects of low crude protein diets on performance of broilers 1 (continued)

Age (Sex) Conventional Low CP Conventional Low CP ReferenceDiet Diet(s)

CP, % CP, % ADG, g G:F ADG, g G:F7 to 21 d 23.0 20, 19, 18, 17, 16, 15, 14, & 13 No difference in BW gain between Brooks et al., 2003(M + F) traditional and CP diets (20 trough 15%), (abstract)

but performance began to decrease at 14,and was significantly lower at 13%.

8 to 22 d 23.0 19.0 +Met,Lys,Arg,Val, & Thr +K 20.7 0.675 20.8 0.660 Han et al., 1992,(M) +AA & 3.36 or 4.62% Glu, +AA, Glu, & K Exp. 1

19.0 +EAA +K +EAA & 3.36 or 4.62% Glu 20.6 0.672+EAA,GLU & K

8 to 22 d 23.0 19.0 +4.62% Glu, +Glu & DLM, 20.5 0.671 21.1 0.687 Han et al., 1992,(M) +Glu, DLM & Lys, +Glu, DLM & Arg, Exp. 2

+Glu,DLM,Lys, & Arg,+ All & Thr+All,Thr, & Val

8 to 22 d 23.0 19.0 +4.62% Glu, +Glu & DLM, 19.7 0.682 19.9 0.680 Han et al., 1992,(M) +Glu, DLM & Lys, +Glu, DLM & Arg, Exp. 3

+Glu,DLM,Lys, & Arg,+ All & Thr,+All,Thr, & Val

8 to 22 d 23.0 19.0 +4.62% Glu, & 100,75,or 50% DLM, 19.3 0.675 19.4 0.696 Han et al., 1992,(M) Lys,& Arg +/-100 or 50% Val & Thr Exp.4

8 to 22 d 23.0 19.0 +EAA, +EAA & 1.16, 2.31, 3.47, 19.1 0.675 18.9 0.661 Han et al., 1992,(M) or 4.62% Glu Exp. 5

8 to 22 d 23.0 19.0 19.1 0.697 19.3 0.694 Han et al., 1992,(M) +EAA & 2.31% Glu Exp.6

8 to 22 d 23.0 19.0 45.4 0.776 44.9 0.771 Han et al., 1992,(M) +EAA Exp.7

9 to 21 d 20.9 17.1 41.18 0.790 37.49* 0.690* Payne, 2000(M) + soy isoflavones = Conventional

21 to 42 d 18.3 15.9 42.3 0.487 38.9* 0.463* Fancher and Jensen,(F) +7.5% EAA, +15% EAA 1989a, Exp. 1

21 to 42 d 19.0 16.6 +7.5% Met & Lys +7.5% Arg, Thr, 50.1 0.494 47.6* 0.469* Fancher and Jensen,(F) Ile, & Trp, +7.5% All 1989a, Exp. 2

16.6 +15% Met & Lys +15% Arg,Thr, 47.0* 0.474*Ile,& Trp,+15% All

21 to 42 d 19.4 16.4 44.0 0.458 43.9 0.437* Fancher and Jensen,(F) +7.5% EAA +7.5% EAA +pH-buffer 1989a, Exp. 3

16.4 +Glu = Conventional CP 44.7 0.466+7.5% EAA, +7.5%EAA +pH-buffer

21 to 42 d 22.0 19.0 61.0 0.487 60.6 0.478 Fancher and Jensen,(M) 1989b, Exp. 1

16.0 +Glu = 59.8 0.466Conventional CP +Arg, Thr,Ile, & Trp +K

21 to 42 d 22.0 19.0 +K 62.0 0.538 60.6 0.511 Fancher and Jensen,(M) 1989b, Exp. 2

16.0 +K 57.0* 0.488*+Arg,Thr, Ile,&Trp +Arg,Thr,I le, & Trp +K

21 to 42 d 22.5 21.0, 19.0, 17.2, or 15.3% Similar weight gain among all treatments, Aletor et al., 2000,(M) but gain:feed and nitrogen excretion reduced Exp. 1

21 to 42 d 22.5 21.0, 19.0, 17.2, or 15.3% No effect of adding NEAA on growth Aletor et al., 2000,(M) + NEAA = Conventional CP performance Exp. 2

21 to 43 d 17.6 13.5 73.73 0.560 68.09* 0.520* Payne, 2000(M) +soy isoflavones = Conventional

22 to 42 d 20.6 18.2 81.0 0.490 78.8 0.500 Ferguson et al.,(M) 1998a

22 to 43 d 21.5 16.5 90.6 0.479 86.4* 0.427* Ferguson et al.,(M) 1998b

28 to 42 d (M) 19.0 17,15,& 13 As-is +Glu +EAA 75.1 0.433 73.6 0.431 Kerr and Kidd,42 to 52 d (M) 18.0 16,14,& 12 As-is +Glu +EAA 1999a

28 to 45 d 19.4 18.2 +Thr 81.6 0.478 80.6 0.478 Kerr and Kidd,(M) 1999b, Exp. 1

16.7 +EAA 80.2 0.470*

42 to 52 d 17.2 15.9 +Thr 79.0 0.379 76.0 0.372 Kerr and Kidd,(M) 1999b, Exp. 2

14.7 +EAA 73.3* 0.366*

43 to 54 d 15.6 11.7 69.69 0.420 64.94* 0.440* Payne 2000(M) + soy isoflavones = Conventional

1

Relative performance of low CP diets correlates to the low CP treatment in bold under the low CP diet section, and this performance level was the most promising result of all low CP treatmentswithin each dataset.Within each dataset, every attempt was made to include all treatments pertinent to the discussion of low CP diets.. G:F = gain:feed; M = male; F = female.*Low CP treatment means are significantly different from the Conventional CP diet, P < 0.10.

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accept that their respective species gen-

erally have more animal to animal varia-

tion, so these minor changes are not as

troubling. Granted the data shown in

Figure 1 are the best results reported by

each group, and even then they are not

as consistent as we would wish, but they

are nonetheless impressive in their gen-

eral suggestion that broilers fed low CP

diets can grow similar to those fed a con-

ventional high CP diet.

The Role of Nonessential Amino Acids in Low

CP Diets for Broilers

In addition to the positive results report-

ed above, there also have been some po-

tential breakthroughs in our understand-

ing of low CP diets, especially concerning

the role that nonessential AA play. Fritts

et al., (2004) reported no differences in 5

to 21-d old broilers fed a low CP diet

with supplemental nonessential AA (Gly,

Leu, Asp, Glu, Ala, and Pro) compared

with those fed a conventional diet. Addi-

tionally, Fritts et al., (2004) tested a low

CP diet with single additions of each

nonessential AA, and regardless of AA

added performance was always lowerthan with a conventional diet. But, it is

interesting to note that of the single

amino acid diets, those supplemented

with Gly, Asp, or Leu outperformed the

Glu, Ala, or Pro diets. Dean (2005) also

investigated the effect of nonessential

amino acids, and he reported that broil-

ers fed the low CP supplemented with

nonessential AA (Gly, Leu, Asp, Glu, Ala,

and Pro) performed comparable with

those fed a conventional CP diet, which

agrees with the results of Fritts et al.,

(2004). Dean (2005) confirmed these re-sults in a follow-up trial, and then he at-

tempted to determine which nonessen-

tial amino acid stimulated growth in a

low CP diet similar to the conventional

diet. Dean reported that broilers fed a

diet with the single addition of Gly per-

formed as well as those fed the conven-

tional diet.

Corzo et al., (2004) and Dean (2005)

each conducted trials to determine the

Gly needs of broilers fed low CP diets

add up considering the number of broil-

ers produced commercially today, but

these results are very much in line with

the magnitude of difference for both

swine and turkeys. Perhaps some of the

reasons for claiming that low CP diets do

not work in broilers or that they do work

in swine and turkeys is simply the signi-

ficantly different growth phases for these

species. That is, perhaps swine and

turkey nutritionists can more willingly

accept minor changes in gain or

gain:feed because of the longer feeding

period to reach processing weights. Or

perhaps swine and turkey nutritionists

Figure 1: Average daily gain (top) and gain:feed (bottom) performance of

broilers fed Low CP diets (dots) compared with broilers fed con-

ventional CP diets (bars) across all experiments in Table 4.

50

45

40

35

30

25

20

15

50

45

40

35

30

25

20

15

Conventional

Low CP,%

Conventional CP, %

17.1

20.0

19.2

16.2

16.2

16.2

16.2

16.2

18.6

20.9

21.0

21.0

21.0

20.3

20.1

20.0

19.7

19.0

19.0

19.0

19.0

19.0

19.0

19.0

19.0

17.8

17.4

17.0

16.9

16.5

18.6

17.6

18.5

17.0

21.9

20.9

22.0

22.2

22.2

22.2

22.2

22.2

22.2

22.3

22.8

23.0

23.0

23.0

23.0

23.0

23.0

23.0

23.0

23.0

23.0

23.0

23.0

23.0

23.0

23.0

23.0

23.0

23.0

23.0

23.0

23.2

23.4

24.0

24.0

26.4

AD

G,g

Low CP

0.90

0.85

0.80

0.75

0.70

0.65

0.60

0.55

0.90

0.85

0.80

0.75

0.70

0.65

0.60

0.55

Conventional

Low CP,%

Conventional CP, %

17.1

20.0

19.2

16.2

16.2

16.2

16.2

16.2

18.6

20.9

21.0

21.0

21.0

20.3

20.1

20.0

19.7

19.0

19.0

19.0

19.0

19.0

19.0

19.0

19.0

17.8

17.4

17.0

16.9

16.5

18.6

17.6

18.5

17.0

21.9

20.9

22.0

22.2

22.2

22.2

22.2

22.2

22.2

22.3

22.8

23.0

23.0

23.0

23.0

23.0

23.0

23.0

23.0

23.0

23.0

23.0

23.0

23.0

23.0

23.0

23.0

23.0

23.0

23.0

23.0

23.2

23.4

24.0

24.0

26.4

ADG,g

Low CP

0.50 0.50

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from 7 to 20 and 1 to 17 d, respectively.

Each reported that growth performance

was improved as Gly level was increased.

Corzo et al., (2004) estimated that the

Gly level necessary to support growth

was 1.00 % Gly (1.78 % Gly+Ser).

Dean (2005), however, suggested that

the Gly level needed for broilers fed low

CP diets to grow similar to those fed a

conventional diet was 1.57 % Gly

(2.14 % Gly+Ser). It is unlikely that the

Gly requirement of broilers changes as

much as suggested by these authors over

the first 21 d of life, so perhaps some of

these differences could be due to the de-

gree by which CP was reduced (18.0 vs.

16.2 %). Another potential reason is that

the trial by Corzo et al. (2004) was de-

signed to determine the Gly require-

ment, whereas Dean (2005) trial was

designed to determine what level of Gly

(or Gly+Ser) would maintain growth

similar to that in a conventional diet.

Corzo et al. (2004) did not use a positive

control conventional diet in their trial.

These are not the first indications of a

larger role for Gly in broiler nutrition. As

early as 1944, Almquist and Grau sug-

gested that Gly could limit the growth ofbroilers, which was supported by Parr

and Summers (1991), especially when

CP is reduced. Heger and Pack (1996)

estimated that the Gly+Ser requirement

ranged from 1.50 to 1.80 % in 5 to 22-d

old broilers depending on CP level

(Gly+Ser needs increase as CP increases).

Schutte et al., (1997) estimated that the

Gly+Ser requirement for 1 to 21-d old

broilers ranged from 1.80 to 1.90 %.

Their results also supported those of Parr

and Summers (1991), as the supplemen-

tation of Gly into a low CP (19.0 %) dietallowed broilers to grow at levels equal

to a conventional CP diet (22.3 %).

These data combined with the findings of

Corzo et al. (2004) and Dean (2005) defi-

nitely indicate that the Gly+Ser require-

ment for broilers is higher than 1.25 %

as suggested by the NRC (1994). It is

known that Gly is essential for a number

of metabolic functions including synthe-

sis of proteins, purines, glutathione, and

creatine (Corzo et al., 2004). Perhaps the

most important role of Gly in broiler nu-

trition is that of synthesizing uric acid in

order to excrete excess nitrogen. Regard-

less of its exact role, it is clear that Gly is

more than just a non-specific nitrogen

source in low CP diets. Nutritionists are

encouraged to be mindful of the Gly or

Gly+Ser levels in their diets, regardless of

CP level, if they wish to achieve optimal

growth performance.

Conclusions

The overall results of this review suggest

that we have made great progress in un-

derstanding how to utilize low CP diets

in broiler production. It seems that the

CP levels in broilers diets can be reduced

by 3 to 4 % percentage points without

sacrificing performance provided that

free AA are supplemented in the diet to

equal the AA nutrient levels in a con-

ventional diet. Furthermore, the results

of Fritts et al. (2004), Corzo et al. (2004),

and Dean (2005) highlight the important

role that nonessential AA play in broiler

nutrition. Their results emphasize the

importance of Gly in broiler nutrition,

particularly when low CP diets are used.

Although more research needs to beconducted to fully understand the role of

Gly, it seems that Gly is at least a semi-

essential AA. The advancement of our

understanding of low CP diets will allow

nutritionists to formulate diets that are

less expensive and more environmental-

ly friendly without sacrificing growth

performance.

Outlook

In trials recently conducted in coopera-tion with Degussa Feed Additives the po-

tential of low protein diets in poultry

diets has been further evaluated. The

technical results as well as some eco-

nomic considerations will be presented

in part 2 of this article in a future

AminoNews.

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Fancher, B. I., and L. S. Jensen. 1989a. Di-

etary protein level and essential amino acid

content: Influence upon female broiler perfor-

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Fancher, B. I., and L. S. Jensen. 1989b. Male

broiler performance during the starting and

growing periods as affected by dietary protein,

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Proc. 47thAnnual Maryland Nutrition Con-

ference, College Park, MD. March 22-24.

pages 119-134.

Dr. Robert L. Payne

email:

rob.payne@

degussa.com

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Volumen 08/Number 01 March 2007 amino acids and more.

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