Download Optimal dietary amino acid ratio for broilers based on dietary amino

Optimal dietary amino acid ratio for broilers based on dietary amino acid dilution
J.C.P. Dorigam1, N.K. Sakomura1, E.P. Silva1, C. Wecke2, A. Suender2, and F. Liebert2
1
Dept. of Animal Science, University of Agrarian and Veterinary Sciences of UNESP,
Jaboticabal, SP 14884900, Brazil
2
Division of Animal Nutrition, Dept. of Animal Sciences, Georg-August-University of
Goettingen, D-37077 Goettingen, Germany
Corresponding author: [email protected]
Introduction
In the poultry feed formulation the quality of a dietary protein can be considered the
degree to which the composition of the absorbed essential amino acid (EAA) mixture
satisfy the EAA balance required by animal (WANG and FULLER, 1989).
Consequently the estimation of the EAAs required by animal can be used as an
assessment of quality of any dietary protein based on the EAA pattern of a reference
protein considered to be ”ideal”. Traditionally, the EAA requirements for an ideal EAA
pattern have been assessed by dose-response studies (BAKER and HAN, 1994; MACK
et al., 1999; BAKER et al., 2002). However, this method is expensive and timeconsuming because multiple assays are needed. Therefore, another practical method has
been employed initially to measure the composition of the EAA in the ideal protein
required for swine (WANG and FULLER, 1989). The amino acid dilution method relies
on a single experiment to determine optimum ratios of all EAA. Another advantage of
this method is that all EAA ratios are determined simultaneously using the same stock
of animals and the same control diet. Consequently this allows better uniformity and
consistency, facilitating the precision to determine the optimum EAA ratios. Based on
efficiency of the EAA utilization, an approach has been developed in Goettingen
University and can be used to improve the EAA dilution procedure. Considering an
equal protein deposition, the EAA requirement is only dependent on its efficiency of
utilization (SAMADI and LIEBERT, 2008). In this way, it is possible to compare the
efficiency of utilization of individual EAA directly to evaluate the optimal AA ratio
(SAMADI and LIEBERT, 2008). This procedure to derive a scale of optimal EAA
ratios within one experiment is still under evaluation.
Objectives
The objective of this study was to reevaluate the actual assumptions of ideal ratio
between the essential amino acids (EAA) : lysine (Lys), methionine+cystine (M+C),
threonine (Thr), tryptophan (Trp), arginine (Arg), valine (Val), isoleucine (Ile), leucine
(Leu), phenylalanine+tyrosine (P+T), glycine+serine (G+S), and histidine (His) for
growing broilers of Cobb 500 genotype during three periods (6-21, 22-37, and 38-53 d).
Materials and methods
The experiments were carried out at the facilities of the Laboratory of Poultry Science
of Faculty of Agricultural and Veterinarian Sciences. One nitrogen balance trial was
performed per period (I: 6 to 21, II: 22 to 37, and III: 38 to 53 days) using male broiler
of Cobb 500® genotype. The experiment consisted on twelve experimental diets and six
replicates for each treatment. Within the age periods, the birds were randomly allotted
and individually housed in metabolism cages. A balanced control diet (CD) was
formulated according to recommendations of the Brazilian Tables for Poultry and Swine
(ROSTAGNO et al., 2011) for the ideal protein in growing broiler for each period.
Experimental diets with different limiting AAs were created by dilution of the CD with
corn starch to achieve 70% of the EAA level in CD and refilled with crystalline EAAs,
except the EAA under study. In all experimental diets, the remaining nutrient and
energy contents were the same respectively. The nitrogen balance trials were divided
into adaptation period (5 days) and two consecutive periods of excreta collection (5
days each). During this period the experimental diets were supplied until the end of
excreta collection. At the beginning of the adaptation period, diets were supplied ad
libitum to predict the feed intake (according to metabolic body weight) for the collection
period. The feed was supplied until the beginning of third day of the adaptation period.
Based on the measured consumption of the last three days of adaptation the feed supply
was slightly adapted for the next two days. At the beginning of collecting period the
feed intake was measured again and the individual feed supply was kept constant up to
the end of the collecting period. The excreta were collected directly from trays (free of
feathers) and immediately stored in freezer at -20°C until further analysis. The excreta
were freeze-dried at -90°C for 72 hours. The dried samples were ground in a micromill.
The excreta were analyzed for dry matter (DM) and crude protein (CP). DM was
obtained by drying at 105°C for 16 h and CP (N x 6.25) by the Kjeldahl method. All
statistics were performed using a SAS statistical package (version 9.1). Data were
submitted to variance analysis and averages EAA ratios were compared by the F test at
5% of probability. Significant differences between deficient treatments and the CD
treatment responses were tested using the Dunnett’s test and values of P<0.05 were
deemed statistically significant. In the nitrogen balance study the dietary protein quality
(b) in each treatment was estimated according to following equation (SAMADI and
LIEBERT, 2008): b = (lnNRmaxT-ln(NRmaxT-NR))/NI. Where: NRmaxT is the theoretical
maximum for N retention (mg N/BWkg0.67/d), NI is the N intake (mg N/BWkg0.67/d) and
NR is the N retention (mgN/BWkg0.67/d). The NRmaxT value is considered ‘theoretical’
because this value is not the same of practical performance data, but estimates the
genetic potential (SAMADI and LIEBERT, 2008). The NRmaxT value for Cobb 500
genotype was estimated in a previous study (DORIGAM, 2012, unpublished data). The
NRmaxT values inserted in the equation were 3,966 mgN/BWkg0.67/d (6-21d); 3,401
mgN/BWkg0.67/d (22-37d) and 2,480 mgN/BWkg0.67/d (38-53d). The slope of the linear
function between dietary limiting amino acid (LAA) concentration (c) (g AA/100 g CP)
and the feed protein quality (b) was directly utilized as model parameter (bc-1)
indicating the efficiency of LAA utilization (SAMADI and LIEBERT, 2008) and it is
only valid when the EAA is in limiting position. Consequently, it is possible to compare
the model parameters (bc-1) of individual EAA directly. Using this procedure for
evaluating the optimal EAA ratio, comparisons are only allowed within equal age
periods because NRmaxT is varying with body weight and affect the established value of
(bc-1). The relationship between lysine efficiency (reference) and efficiency of AA
under study is utilized to derive ideal AA ratios (IAAR): IAAR= (bcLys-1)/(bcLAA-1).
Results and discussion
All experimental diets were well accepted by the broilers. No mortality was observed
during the trial but feather abnormalities were observed in broilers on the treatments
which valine and leucine deficiency. The results of the N balance studies in each age
period (relative effects on protein quality) are summarized in Table 1.
Table 1. Effect of diluting a single EAA from the diet on mean body weight (BW), dry
matter intake (DMI), nitrogen intake (NI), nitrogen deposition (ND), protein quality (b),
and efficiency of AA utilization (bc-1) of fast growing broilers (Cobb500)1
T2
Lys
T3
M+C
T4
Trp
BW2
DMI2
NI
ND
b
bc-1
534 434
72
57
4430 4238
2960 2466
366 267*
82
507
71
4545
2604
275*
112
443
61
4364
2510
268*
468
BW2
DMI2
NI
ND
b
bc-1
1603
131
3448
2417
451
-
1512
117
3557
2042
320*
104
1514
123
3625
2137
339*
146
1469
102
2943
1955
360*
620
BW2
DMI2
NI
ND
b
bc-1
3205 3042
153 109
2346 1824
1610 990
611 393*
125
3028
140
2203
1241
430*
176
2993
121
1936
1150
442*
721
Diets
T1
CD
T5
T6
T7
Thr Arg Val
Period I (6 to 21 d)
394 472 446
51
59
55
4004 4078 3850
2387 2424 2386
268* 269* 279*
125
75
107
Period II (22 to 37 d)
1437 1506 1490
114 110 104
3441 3291 3211
2092 2009 1940
344* 337* 326*
164
99
137
Period III (38 to 53 d)
3027 2989 2998
131 105 129
2213 1752 2065
1155 982 1173
389* 405* 425*
191 119 164
T8
Ile
T9
Leu
T10
P+T
T11
G+S
T12
His
483 427 444 515 449
62
53
56
65
58
4203 4002 3904 3993 4192
2505 2402 2414 2556 2532
277* 271* 280* 303* 208*
123
77
71
58
229
1526
120
3469
2091
341*
156
1392
75
2381
1559
323*
97
1593
121
3436
2049
332*
92
1580
118
3371
2005
327*
77
1566
117
3232
2100
368*
301
2807 2811 3014 2910 3032
114
86
108 112 132
1983 1429 1725 1893 2088
1084 847 992 1035 1234
402* 422* 416* 398* 451*
185 117 108
93
362
*Significantly different from control treatment (p<0.05) by Dunnett’s test. 1Mean ± standard error of
mean (SEM). 2Average of two collecting periods.
Nitrogen deposition and protein quality were higher in CD (p<0.05) than in
reduced EAA treatments during trial. Dilution of individual EAA significantly reduced
nitrogen deposition, but the extent of reduction depended on the EAA removed. For
each EAA, a 30% reduction was sufficient to set it in limiting position. The dilution of
valine promoted the greatest reduction of N deposition (p<0.05) in period I (6-21d),
followed by leucine in period II and III (22-37 and 38-53d). This would lead to the
lower body weight and feather abnormalities observed in valine and leucine treatments,
similarly as observed by GRUBER et al. (2000). The effects of dilution of individual
EAA on protein quality in the experimental diets are of fundamental importance for
evaluation of the applied procedure. The observed protein quality (b) in this study
declined following dilution of crystalline EAA under study (p<0.05). In each treatment
the efficiency of utilization of dietary EAA (bc-1) was calculated. The ideal ratio
between EAA was derived by dividing efficiency of utilization of lysine by the
efficiency of utilization of the other EAA. The ratio between the EAA in each period
using this procedure is presented in Figure 1.
AA ratios in whole growth period
160
**
Ratio to lysine (100%)
140
120
**
100
**
80
**
Period I
60
Period II
40
Period III
20
0
Lys
Met+Cys
Thr
Trp
Arg
Gly+Ser
Val
Ile
Leu
His
Phe+Tyr
Period I
100
73
66
17
108
140
77
67
107
36
115
Period II
100
71
64
17
105
135
76
67
107
35
114
Period III
100
71
65
17
105
135
76
68
107
35
115
Essential amino acid (EAA)
Figure 1. The ideal dietary EAA profiles relative to lysine in each age period for fast growing broilers
(Cobb500) determined by Goettingen approach with nitrogen balance study. * significant difference by
test F at 5% of probability.
In the whole growth period the ideal ratios by Goettingen approach were similar
(p=0.287) except by AA ratios of Met+Cys, Thr, Arg and Gly+Ser in period I (p<0.05).
In this way we can consider the ratios between period II and III as comparable by
Goettingen Approach. In broiler chickens, estimation of the ideal dietary EAA profile
by the dilution method was already applied (GRUBER et al., 2000; ROTH et al., 2001)
but only from 7 to 28 days post-hatching. ROTH et al. (2001) estimated the EAA profile
for broiler chicks by the dilution method and values obtained are very consistent to
those estimated in the present study by Goettingen approach. The data are also
consistent with the recommendations of Brazilian tables (ROSTAGNO et al., 2011) for
the period I and II period and Illinois ideal protein pattern (BAKER and HAN, 1994;
BAKER et al., 2002) in the period I (Table 2).
Table 2. Ideal protein patterns based on literature
Amino acids
Lysine
Met+Cys
Tryptophan
Threonine
Arginine
Valine
Isoleucine
Leucine
Phe+Tyr
Gly+Ser
Histidine
1
Baker and Han Baker et al. Roth et al.
Rostagno et al.
Mack et al.
(1994)
(2002)
(2001)
(2011)
(1999)
8 to 21d
8 to 21 d
8 to 28 d 1 to 21d 22 to 56 d 21 to 42 d
100
100
100
100
100
100
1
72-75
nd
70
72
73
75
16-17
17-19
14
17
18
19
67-70
56-62
66
68
68
63
105-108
nd
108
105
105
112
77-80
77-87
81
79
80
81
67
60-72
63
67
68
71
109
nd
108
107
108
nd
105
nd
121
115
115
nd
nd
nd
150
137
nd
nd2
32-35
nd
38
37
37
nd
Ranges are due to differences in the criterion optimized and in the model fitted data.
nd: not determinate
Small variations can be attributed to methodological factors like the adopted criterion of
response (e.g. growth rate or feed conversion) or mathematical model used like linearplateau model in comparison to exponential models. In general, these EAA ratios are
derived from estimated EAA requirements whereas in studies from SAMADI and
LIEBERT (2008) the EAA ratios are derived from the relationship of the estimated
efficiencies of utilization from each EAA in N balance assays. Clearly, research is still
needed in order to clarify the potential limitations and development of this procedure.
Conclusion
The Goettingen approach gave values in accordance to the literature. For period I (6 to
21 d) the optimum EAA ratio considered was Lys100, M+C 73, Thr 66, Trp 17, Arg
108, Val 77, Ile 67, Leu 107, P+T 115, G+S 140, and His 36. For both period II and III
(22 to 53 d) the optimum EAA ratio considered was Lys100, M+C 71, Thr 64.5, Trp 17,
Arg 105, Val 76, Ile 67.5, Leu 107, P+T 114.5, G+S 135, and His 35.
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