during feed restriction

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Growth performance, liver and kidney functions, blood hormonal pro ﬁ le, and economic ef ﬁ ciency of broilers fed different levels of threonine supplementation

during feed restriction

Mahmoud M. Abo Ghanima,*Mohamed E. Abd El-Hack ,^y^,1Aljohara M. Al-Otaibi,^zSamia Nasr,^x Najlaa H. Almohmadi,^#Ayman E. Taha,^kMariusz Jaremko,^{and Nagwa I. El-Kasrawy*

*Department of Animal Husbandry and Animal Wealth Development, Faculty of Veterinary Medicine, Damanhour University, Damanhour 22511, Egypt;^yPoultry Department, Faculty of Agriculture, Zagazig University, Zagazig 44511, Egypt;^zDepartment of Biology, College of Science, Princess Nourah bint Abdulrahman University, Riyadh

13225, Saudi Arabia;^xChemistry Department, Faculty of Science, King Khalid University, Abha 61413, Saudi Arabia;^#Clinical Nutrition Department, College of Applied Medical Sciences, Umm Al-Qura University, Makkah 24381, Saudi Arabia;^kDepartment of Animal Husbandry and Animal Wealth Development, Faculty of Veterinary Medicine, Alexandria University, Edﬁna 22758, Egypt; and^{Smart-Health Initiative (SHI) and Red Sea Research

Center (RSRC), Division of Biological and Environmental Sciences and Engineering (BESE), King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia

ABSTRACT The objective of the existing investigation was to determine the effect of dietary inclusion of threonine amino acid at different levels during feed restriction on growth indices, liver and kidney function parameters, and some hormonal proﬁles along with economic indicators in broiler chickens. A total of 1,600 from 2 different breeds (800 Ross 308 and 800 Indian River) at 21-day-old age were incorporated. Chicks were randomly assigned into 2 main groups, control and feed-restricted (8 h/d), during the fourth week of age. Each main group was subdivided into 4 groups.

The ﬁrst group was fed a basal diet without adding extra threonine (100%), the second, third, and fourth groups were fed a basal diet with extra threonine levels of 110, 120, and 130%, respectively. Each subgroup consisted of 10 replicates of 10 birds. We noticed that

the dietary inclusion of threonine at extra levels in the basal diets signiﬁcantly enhanced ﬁnal body weight, body weight gain, and better feed conversion ratio.

This was mainly due to the enhanced levels of growth hormone (GH), insulin-like growth factor (IGF1), tri- iodothyronine (T3), and thyroxine (T4). Moreover, the lowest feed cost per kilogram body weight gain and improved return parameters were reported in control and feed-restricted birds fed higher levels of threonine than other groups. Also, a signiﬁcant increase in alanine aminotransferase (ALT), aspartate aminotransferase (AST), and urea levels was observed in feed- restricted birds supplemented with 120 and 130% levels of threonine. Hence, we recommend supplementing threonine at levels of 120 and 130% in the diet of broilers to promote growth and proﬁtability.

Key words:threonine supplementation, feed restriction, broilers, growth

2023 Poultry Science 102:102796 https://doi.org/10.1016/j.psj.2023.102796

INTRODUCTION

Over the past few years, the demand for poultry products has steadily grown globally (FAO, 2013). As a result, various efforts are being made to look for new ways to enhance poultry productivity (Adedokun et al., 2014;

Alagawany et al., 2014;Abbasi et al., 2018;Abou-Kassem et al., 2022). According toKidd and Kerr (1996), threonine is poultry’s third limiting amino acid. Threonine exhibits a vigorous role in cellular development. It improves intestinal mucosa and digestive enzyme activity (Dozier et al., 2001), immune system functions, barrier integrity, and antioxidant capacity (Chen et al., 2016;Bi et al., 2018). Nearly a third of the proteins used in mucin are estimated to be found in peptides rich in threonine (Corzo et al., 2007; Rehman et al., 2017; Soomro et al., 2017;Saeed et al., 2020;Chandra et al., 2021a,b). Threo- nine deﬁciency in meat-type poultry causes decreased growth performance, feed consumption, and carcass

Ó2023 The Authors. Published by Elsevier Inc. on behalf of Poultry Science Association Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/

4.0/).

Received April 16, 2023.

Accepted May 17, 2023.

1Corresponding author:[email protected]

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weight (Zhang et al., 2014). Financial losses can arise from slight dietary shortages of digestive threonine because of elevated feed efﬁciency and decreased breast meat production (Khan et al., 2008).

Feed restriction programs have become more popular due to rising feed costs and their ability to decrease abdominal fat deposition and enhance feed efﬁciency.

Broiler production is characterized by a fast growth rate linked with impaired reproductive competence, ascites, lameness, and mortality. Hence feed restriction has been applied (Ebeid et al., 2022;Ogbuagu et al., 2023).

The effectiveness of several feed restriction strategies, such as controlling the amount of time that animals can access food each day (Bordin et al., 2021;Tumova et al., 2022), removing food for up to 8 h at a time or skipping a day of feeding, permitting animals to eat only once every hour, and feeding only once every other day (Boos- tani et al., 2010; Saffar and Khajali, 2010) have been assessed, but the findings have been varied (Khetani et al., 2009; Ghazanfari et al., 2010). The present study hypothesized that supplementing threonine to broiler diet may have a positive impact on its growth and profit- ability. Hence, the existing treatise aimed to inspect the effect of threonine dietary inclusion with various levels in 2 breeds of broiler chickens, either feed-restricted birds or not, on growth performance, liver and kidney function parameters, hormonal profile, and economic efficiency.

MATERIALS AND METHODS

The care of the birds used in this experiment and the experimental methods followed the guidelines set forth by the Animal Care and Ethics Committee of the Fac- ulty of Veterinary Medicine at Damanhur University in Egypt (DMU/VetMed-2021-/0013).

Experimental Birds, Design, and Management

A total of 1,061-day-old chicks from 2 different breeds (800 Ross 308 and 800 Indian River) were obtained from commercial chickens hatcheries, at 21-days old, birds for each breed. Birds were separated randomly into 2 main groups. The ﬁrst group was fed ad libitum as a control (n= 400), while the second group was subjected to feed restriction as fed 8 h/d during the fourth week of age (n= 400). Within each of the last divided groups, birds were subdivided into 4 groups, theﬁrst group fed on the basal ration (Table 1) without any supplementation 100%

(threonine level was 0.9%), the second group 110% fed basal diet threonine level, the third group fed 120% of basal diet threonine level. The fourth group fed 130% of basal diet threonine level (n =100). Each subgroup was divided into 10 replicates, each of 10 birds.

Productive Performance

In this experiment, the growth indices, including weight gain (WG), body weight (BW), and feed

conversion ratio (FCR), were measured. Birds were independently weighed over a weekly interval period from the start of the third week of age until the seventh week of age. In the early morning and before the start- ing, feed and birds were weighed weekly. The weekly WG of birds was considered by subtracting the bird’s BW at a deﬁnite week from the BW of the same chicken the following week. For assessing the FCR, we were allo- cating the quantity of feed uptake (g) throughout the week by the WG (g) during a similar week.

Liver and Kidney Functions

The ALT kit of Bio-diagnostic determined alanine aminotransferase(ALT) and aspartate aminotransferase (AST) conferring to the technique previously reported by Reitman and Frankel (1957). Urea and creatinine were determined conferring to the procedures ofFawcett and Scott (1960)and Bartle (1972), respectively.

Hormonal Proﬁle

Following the method described byKelly and Alworth (2013), blood samples were picked up from the brachial wing vein (6 birds/group) and placed into sterilized tubes with anticoagulant at the termination of the experiment.

Table 1.Basal diet composition and chemical analysis.

Ingredients Starter diet % Grower diet %

Soybean meal (44%) 32.6 29.5

Yellow corn 53.65 58.15

Vegetable oil¹ 2.0 2.0

Corn gluten (60%) 8.0 6.5

DCP² 1.7 1.5

Limestone³ 1.3 1.6

Lysine⁴ 0.05 0.05

DL-methionine⁵ 0.15 0.15

Premix (vitamin)⁶ 0.15 0.15

Mineral premix⁷ 0.1 0.1

Salt 0.3 0.3

Chemical analysis

Crude protein 22.85 21.12

ME kcal/kg diet 3039.8 3058.7

Crudeﬁber 2.79 2.65

Moisture 12.14 12.98

Ash 6.79 6.55

Total phosphorus 0.73 0.68

Calcium 1.10 1.09

Methionine 0.67 0.56

Lysine 1.23 1.19

Ether extract 4.68 5.25

1Vegetable oil (mixture of sunﬂower oil and cottonseed oil).

2DCP = dicalcium phosphate (18% P and 25% Ca).

3Limestone (34% calcium).

4Lysine = lysine hydrochloride (98.5% lysine).

5DL-methionine (produced by Evonic Co. and contain 99.5%

methionine).

6The premix used was Heromix produced by Heropharm and composed of (per 1.5 kg) vitamin A 12,000,000 IU, vitamin D3 2,500,000 IU, vitamin E 10,000 mg, vitamin K3 2,000 mg, thiamin 1,000 mg, riboﬂavin 5,000 mg, pyridoxine 1,500 mg, cyanocobalamin 10 mg, niacin 30,000 mg, biotin 50 mg, folic acid 1,000 mg, pantothenic acid.

7Mineral premix: formulated and composed of (each 1 kg) 70,000 mg Mn, 60,000 mg Zn (using zinc oxide (ZnO) and replaced by zinc polysac- charide complex or nano zinc particles), 8,000 mg Cu, 1,000 mg I, 250 mg Se, and 150 mg Co.

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Then, the collocated samples were preserved at room temperature for separating the plasma, centrifuged at 3,000 rpm/15 min, and then transferred into a sterilized Eppendorf tube (1.5 mL). Samples were preserved at 20°C until the exploration of hormonal assays.

The values of plasma hormones such as insulin-like growth factor-1(IGF-1) and growth hormone (GH) were assessed by radioimmunoassay utilizing the commercial kit (Diagnostic Products Corporation, Angeles, CA). The determinations of GH and IGF-1 followed the methods of Huybrechts et al. (1985) and Berghman et al. (1988), respectively. For assessing the plasma thyroid hormones such triiodothyro- nine (T3) and thyroxine (T4), we followed the RIA procedure stated by Akiba et al. (1982), utilizing the Gamma-Coat 125I RIA Kits.

Economic Evaluation

Expenses.The expenses and proﬁts conferred by the dominant prices in the Egyptian market during the research. Feed cost (EGP/kg feed) was considered by multiplying the whole FI/chicken by the cost of 1 kg feed (11.30 EGP/kg feed). The cost of the threonine sup- plement (0 for the 100% group, 0.004 EGP/kg for 110%

and 0.008 EGP/kg for the 120% group, and 0.012 EGP/kg for 130% group) was comprised in the feed costs of the experimental groups.

The average cost offeed

kg body weight EGP kg gain

¼

feed cost EGP kg feed

FI per bird kgð Þ WG per bird kgð Þ

where FI is the feed intake and WG is the weight gain.

Other costs, comprising the price of day-old chickens, disinfectant, veterinary supervision labor, housing, drugs, depreciation, and vaccines, were reflected infixed expenses as the animals had identical management and equal (15.25 EGP)/bird. The sum offixed and variable costs calculates the total costs.

Proﬁts. The return was the income from selling birds, where the total return equals the bird live BW multiplied by the price of 1 kg of meat (31.98 EGP/kg live BW). The difference between the total return and total costs was calculated to obtain the net return. Net return per kg gain = net return/kg body BW. The economic efﬁciency was assessed according to Hassan and Awad (2017)as the following equation:

Economic efficiency

¼net return per kg gain=feed cost per kg gain

Statistical Analysis

The body weight records were normally distributed and subjected to analysis covariance for initial body

weight data using the general linear model (GLM) of the SPSS software (ver. 20 for Windows, SPSS, Inc., Chicago, IL). The following statistical model was:

Y_ijkl¼mþW_iþB_jþF_kþT_lþðFTÞ_klþe_ijkl

where Yijklis the value of dependent variables; Wiis the effect due to covariance of initial body weight; Bjis the effect of the breed; F_kis the effect of feed restrictions; T_l is the effect of threonine treatment; (FT)_klis the interaction between feed restriction and threonine treatment;

eijklis the error related to individual observation. While other records were normally scattered and subjected to statistical analysis using the GLM of the SPSS software (ver. 20 for Windows, SPSS, Inc., Chicago, IL). The test of Duncan’s multiple ranges was utilized to determine the signiﬁcance among the means and the signiﬁcance wasP≤0.05.

RESULTS Productive Performance

The effect of chicken breeds fed-restricted diets and various levels of threonine and their interactions on growth indices are listed inTable 2. It was clear that Ross and IR broiler breeds did not vary significantly infinal BW, WG, FI, and FCR. Moreover, broilers fed control diets did not differ significantly from those fed the restricted diets in thefinal BW and FI. In addition, birds with control diets had a greater WG and FCR (P< 0.05) than those fed- restricted diets. Concerning the effect of threonine supplementation, broilers fed diets enriched with 130% threonine level had greater significant BW, WG and the greatest FCR compared to other treated groups. Regarding feed restriction*threonine interaction, both groups of broilers (control and feed restriction) received diets containing a threonine level of 130% had higher significant values for BW, WG, and best FCR with the lowest feed intake compared with other experimental groups.

Kidney and Liver Functions

Some kidney and liver functions of 2 broiler breeds fed- restricted diets and different threonine levels and their interactions are listed in Table 3. The results discovered that Ross and IR broilers did not vary (P>0.05) in urea and ALT levels. In contrast, IR broilers exhibit higher creatinine (P<0.05) than Ross broilers. On the other hand, Ross broilers had greater (P <0.05) AST levels than IR broilers. Concerning the feed restriction effect, broilers fed-restricted diets showed a signiﬁcant elevation in urea, creatinine, ALT, and AST levels compared to control birds fed full diets without restriction. The results regarding threonine supplementation revealed that broilers supplemented with threonine levels at 120 and 130% of basal diets contents increased (P<0.05) urea and ALT levels, while threonine levels at 110% signiﬁcantly increased creatinine levels compared to other groups.

Moreover, threonine supplementation in broiler diets at 130% elevated (P < 0.05) AST level

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compared to other treated groups. Regarding the feed restriction * threonine interaction results, the results showed that broilers fed-restricted diets and supplemented with threonine levels at 110, 120, and 130%

had increased levels of urea and AST. While broilers fed-restricted diets supplemented with 110% threonine level displayed an increase (P < 0.05) in creatinine levels compared to other experimental groups, restricted diets with 120 and 130% threonine levels also produced a signiﬁcant increase in ALT levels related to other treated diets.

Hormonal Proﬁle

The inﬂuences of breed feed restriction, threonine and feed restriction*threonine interactions on some

hormonal parameters are presented in Table 4. Breed factor did not affect T3, T4, IGF1, and GH. T3 level of feed-restricted broilers didn’t differ with the broilers fed ad libitum. However, feed-restricted birds disclosed a signiﬁcant reduction in T4, IGF1, and GH related to control broilers. Threonine at level 120 and 130% of the basal diet increased T3 level compared to other levels.

Moreover, threonine at 130% increased T4, IGF1, and GH levels more than broilers supplemented with other threonine levels. Regarding the feed restriction*threonine interaction effect, the T3 level increased signiﬁ- cantly (P < 0.05) at 120 and 130% threonine levels in feed-restricted groups. But T4, IGF, and GH increased signiﬁcantly (P < 0.05) in control birds supplemented with 130% threonine level compared to other supplemented groups.

Table 2.The effect of broiler breeds fed-restricted diets and different levels of threonine and their interactions on growth performance criteria.

Items/breed Final weight Feed intake (g) Total weight gain Feed conversion ratio

Ross 2194.25§13.79 2606.43§9.74 1449.88§13.42 1.80§0.02

IR 2131.71§18.07 2636.12§9.22 1404.22§18.28 1.88§0.03

Feed restriction

Control 2153.26§15.35 2627.76§8.50 1477.58§11.46^a 1.78§0.02^b

Feed restriction (%) 2172.70§17.56 2614.79§10.60 1376.52§18.21^b 1.89§0.03^a

Threonine

100 2016.05§21.02^d 2652.59§13.53 1432.13§16.18^b 1.85§0.03^b

110 2128.13§14.67^c 2615.04§13.05 1356.94§24.15^c 1.93§0.04^a

120 2207.85§17.13^b 2632.55§11.50 1395.68§26.64^bc 1.89§0.04^ab

130 2299.90§13.13^a 2584.92§14.25 1523.46§13.88^a 1.70§0.03^c

Feed restriction*threonine (%)

Control 100 2025.40§21.16^d 2683.90§24.52^a 1429.21§9.75^c 1.88§0.04^b

110 2097.85§29.83^c 2644.10§19.30^ab 1449.70§16.91^bc 1.82§0.03^bc 120 2193.15§25.08^b 2620.15§22.47^bc 1513.05§9.75^ab 1.73§0.03^cd

130 2296.65§16.21^a 2562.88§19.73^d 1518.35§17.94^ab 1.69§0.02^d

Feed restriction 100 2006.70§36.85^d 2621.27§21.75^bc 1435.05§23.52^c 1.83§0.06^bc 110 2158.40§19.84^bc 2585.99§33.41^cd 1264.18§18.00^d 2.04§0.04^a

120 2222.55§23.52^b 2644.95§30.98^ab 1278.31§20.79^d 2.07§0.02^a

130 2303.15§18.43â 2606.96§19.99^bcd 1528.56§21.48â 1.71§0.01^d The mean values in the same column within each division with different superscripts (a−d) differ significantly (P<0.05).

Table 3.The effect of broiler breeds fed-restricted diets and different levels of threonine and their interactions on kidney and liver functions.

Items/breed Urea Creatinine ALT AST

Ross 5.08§0.04 0.48§0.01^b 21.35§0.33 98.08§1.08^a

IR 5.10§0.05 0.84§0.19^a 21.63§0.28 94.88§1.18^b

Feed restriction

Control 4.89§0.07^b 0.47§0.01^b 20.48§0.27^b 91.43§1.04^b

Feed restriction 5.29§0.02â 0.85§0.19â 22.50§0.25â 101.53§0.57â

Threonine (%)

100 5.00§0.06^b 0.48§0.01^b 19.65§0.36^c 91.80§1.58^d

110 5.02§0.09^b 1.16§0.37^a 21.30§0.34^b 95.15§1.55^c

120 5.14§0.04^a 0.49§0.01^b 22.15§0.31^a 98.00§1.43^b

130 5.19§0.05â 0.51§0.01^b 22.85§0.36â 100.95§1.32â

Control 100 4.83§0.09^ef 0.46§0.02^b 18.50§0.34^f 86.00§1.16^d

110 4.73§0.10^f 0.45§0.01^b 20.30§0.39^e 89.40§1.51^cd

120 4.98§0.04^de 0.48§0.01^b 21.30§0.36^cde 93.00§1.73^c

130 5.01§0.03^cd 0.49§0.01^b 21.80§0.41^cd 97.30§2.03^b

Feed restriction 100 5.16§0.04^bc 0.49§0.01^b 20.80§0.38^de 97.60§1.32^b

110 5.31§0.05âb 1.86§0.68â 22.30§0.38^bc 100.90§0.75âb

120 5.31§0.03âb 0.51§0.01^b 23.00§0.33âb 103.00§0.33â

130 5.37§0.04â 0.53§0.01^b 23.90§0.37â 104.60§0.56â

The mean values in same column within each division with different superscripts (a−f) differ signiﬁcantly (P<0.05). ALT: alanine aminotransferase.

AST: aspartate aminotransferase.

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Economic Evaluation

The impacts of breed, feed restriction, threonine, and feed restriction * threonine interaction on some economic parameters are listed inTable 5. It was clear that Ross and IR broilers did not vary (P > 0.05) in feed cost/bird. Meanwhile, Ross broilers had the lowest (P<

0.05) feed cost per kg gain and the highest (P <0.05) total return/bird, net return/bird, net return/kg gain, and economic efﬁcacy compared to IR broilers. Concern- ing the feed restriction effect, the feed-restricted birds exhibit greater (P <0.05) feed charge/kg gain and net return per/gain relative to control broiler groups. Regard- ing the threonine effect, diets containing 130% threonine resulted in inferior feed cost/kg gain (P<0.05) and significantly increased total return/bird, net return/bird, net return /kg gain, and economic efﬁcacy compared to broilers fed other threonine levels.

DISCUSSION

Generally, the breed differences between broiler strains in growth performance parameters are due to differences in the genetic makeup of different breeds (El- Tahawy et al., 2017;Nangsuay et al., 2017;Taha et al., 2019). The feed restriction program manipulates the broiler growth curve to improve production efﬁciency.

Feed restriction aims to decrease metabolic and growth rates to about scope. It relieves some metabolic syn- dromes such as lameness, ascites, sudden death syndrome, and mortality, reduces feed cost and improves feed conversion (Sahraei, 2012).

In the existing study, feed restriction diminished the total weight gain and recorded the worst FCR. The improvement of broiler BW, WG, and FCR in feed- restricted and control broilers may be due to threonine’s role in developing intestinal mucosa, intestinal villi, and

digestive enzymes function (Dozier et al., 2001;Qaisrani et al., 2018). In an experiment,Najaﬁ et al. (2017) fed broilers various levels of threonine (0.89, 0.93, and 0.97%) from 1 to 14 d of age alongside a control diet hav- ing 0.65% of threonine to examine the effects on growth performance, the authors reported that as compared to broilers on a control diet, broilers received diets containing 0.97% of threonine presented 5.1% greater FI, 1.4%

better FCR, and 6.4% higher body WG. Moreover,Bas- sareh et al. (2023) informed that adding threonine (115% more than the basic requirements) positively affected BW and WG and improved the FCR in the broiler. Greater intestinal function (villus surface and crypt depth) was also detected in the birds fed with threonine (105% dietary, P< 0.05) (Bassareh et al., 2023;

Hussein et al., 2023).

The serum biochemical proﬁle details animals’ immune systems and general health. The values of these biochemical parameters depend on factors like breed, species, sex, age, season, location, diet, and physiological conditions (Kokore, 2021). The increased levels of AST in birds and animals indicate degenerative liver changes and diseases (Beaufrere and Vergneau-Grosset, 2021).

Our outcomes agree with those acquired by Min et al.

(2017), who supplemented broilers with various levels of threonine (85%, 100%, 125%, and 150% of recommended basal diet), and found that the excess dietary threonine levels signiﬁcantly affected AST and ALT activities and these might be owing to the metabolism of extra amino acids. The increase in urea levels in higher levels of threonine-supplemented broilers, as reported byWang et al.

(2006), noticed that the consumption of true ileal digestible promotes augmented from 5.0 to 6.6 g/d, and the serum urea nitrogen levels also rose. Moreover, serum urea levels would raise once one or some amino acids are scarce or in a spare (Gong et al., 2005). The alterations in blood biochemical parameters owing to feed Table 4.The effect of broiler breeds fed-restricted diets and different levels of threonine and their interactions on some hormonal parameters.

Items/breed T3 T4 IGF1 GH

Ross 1.04§0.01 0.89§0.01 27.60§0.49 40.93§0.71

IR 1.09§0.02 0.89§0.02 28.68§0.73 39.33§0.82

Feed restriction

Control 1.04§0.01 0.93§0.02â 29.18§0.66â 42.23§0.71â

Feed restriction 1.08§0.02 0.85§0.01^b 27.10§0.56^b 38.03§0.68^b

Threonine (%)

100 1.01§0.01^b 0.79§0.01^d 24.10§0.35^d 34.50§0.58^d

110 1.03§0.02^b 0.83§0.01^c 26.05§0.28^c 38.80§0.67^c

120 1.11§0.02^a 0.95§0.02^b 29.15§0.42^b 41.95§0.66^b

130 1.11§0.01â 0.99§0.02â 33.25§0.63â 45.25§0.64â

Control 100 1.00§0.01^b 0.79§0.01^f 25.10§0.46^d 36.50§0.58^d

110 1.02§0.01^b 0.85§0.02^e 26.60§0.40^cd 40.80§0.77^c

120 1.08§0.02^ab 1.02§0.01^b 30.30§0.47^b 44.00§0.42^b

130 1.08§0.02âb 1.06§0.01â 34.70§0.92â 47.60§0.60â

Feed restriction 100 1.01§0.04^b 0.79§0.01^f 23.10§0.31^e 32.50§0.45^e

110 1.04§0.04^b 0.82§0.01^f 25.50§0.34^d 36.80§0.64^d

120 1.14§0.04^a 0.88§0.01^d 28.00§0.49^c 39.90§0.84^c

130 1.14§0.01^a 0.93§0.01^c 31.80§0.61^b 42.90§0.43^b

The mean values in same column within each division with different superscripts (a−f) differ signiﬁcantly (P<0.05). T3: triidothyronine. T4: thyroxine. IGF1: insulin-like growth factor. GH: growth hormone.

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restriction were also informed byKarabayir and Mendes (2008)that increasing the period of feed restriction insti- gated a severe stage of stress on chickens, thus may lead to impairment in liver and kidney functions.

Feed restriction-induced stress may cause a signiﬁcant alteration in plasma thyroid hormone levels. The most likely cause of the change in thyroid hormone levels in feed-restricted chickens is the change in the percentage of T4 deiodination by altering T3 degradation and hepatic D1 and D3 deiodinases (Farag and Alagawany, 2018).

During feed restriction, mono-deiodinase activity declines, which contributes to variations in the T3 level.

Accordingly, it was hypothesized that metabolic fre- quency would decrease and hormonal activity related to growth would decline. In the current investigation, feed- restricted broilers had reduced T4 during the feed restriction phase. This may result from the birds con- serving energy with a low basal metabolism (Zhan et al., 2007; Ogbuagu et al., 2023). Nevertheless, there was no statistically substantial difference between the 2 feed- restricted and ad libitum birds regarding the level of T3.

According to the results, the T3 level, the active form of thyroid hormone in the restricted chicks, is normalized and maintains its value during compensatory growth as that of ad libitum broilers. A noteworthy observation is that early feed restriction statistically decreased (P <

0.05) levels of IGF-1 and GH compared to ad libitum birds.

Similarly, Giachetto et al. (2003) found that broiler chickens also had lower IGF-1 plasma levels during the feed restriction period. The results of GH levels are har- monious with Ghazanfari et al. (2010), who informed that growth hormone levels lowered in feed-restricted birds at the age of 22 to 32 d. Increasing dietary threonine was associated with greater levels of the T3 and T4 hormones in the chickens. This association was most likely caused by the occurrence of the receptors of threonine in the thyroid gland that are crucial for synthesiz- ing the T3 hormone (Wu, 2013;Azzam and El-Gogary, 2015). The T4 is crucial for energy and protein metabolism (Decuypere et al., 2005;Jahanpour et al., 2020) and increases IGF-I hormone concentrations (Hemmati et al., 2019). A sufﬁcient amount of T4 is required for improved GH activity, protein synthesis, and muscle mass conservation (Jahanpour et al., 2020). Our results agree with Al-Hayani’s (2017) results, which showed that increasing threonine in the diet by 600 or 900 mg/kg raised GH concentration. Our ﬁndings strongly suggest that adding threonine at 120 and 130%

in broilers’ diets exposed to feed restriction programs enhances concentrations of GH and IGF-1.

Regarding feed restriction*threonine interaction, broilers fed 130% threonine level either in control and feed restriction groups exhibit lower (P<0.05) feed cost per kg gain (P<0.05) and significantly enhanced total return/bird, net return/bird, net return per kg gain, and economic efficacy compared to broilers of the other treated groups. A lowered feed cost per kilogram gain in feed-restricted groups supplemented with higher doses Table5.Theeffectofbroilerbreedsfed-restricteddietsanddifferentlevelsofthreonineandtheirinteractionsonsomehormonalparameters. Items/breedTotalfeedcost/ bird(EGP)Feedcostper kggain(EGP)Totalcost (EGP)/birdTotalreturn/ bird(EGP)Netreturn/ bird(EGP)Netreturnper kggain(EGP)Economic efficiency Ross29.36§0.1920.34§0.19b44.61§0.0870.17§0.38a25.56§0.38a17.63§0.01a0.86§0.01a IR29.59§0.1921.44§0.19a44.84§0.0868.17§0.57b23.35§0.57b16.62§0.02b0.77§0.01b Feedrestriction Control29.56§0.1920.11§0.19b44.81§0.0868.86§0.5724.05§0.5716.28§0.19b0.81§0.01 Feedrestriction29.40§0.1921.67§0.19a44.65§0.0969.48§0.5724.83§0.5718.04§0.57a0.83§0.01 Threonine(%) 10029.57§0.5720.96§0.01b 44.82§0.1564.47§0.76d 19.65§0.76d 13.72§0.38c 0.65§0.02d 11029.37§0.5721.97§0.02a44.62§0.1568.05§0.38c23.44§0.57c17.27§0.76b0.79§0.02c 12029.62§0.5721.52§0.01ab 44.87§0.1270.61§0.57b 25.74§0.57b 18.44§0.38a 0.86§0.02b 13029.35§0.5719.10§0.01c44.60§0.1473.55§0.19a28.89§0.57a18.96§0.19a0.99§0.02a Feedrestriction*threonine(%) Control10029.93§0.1721.26§0.36b45.18§0.1964.77§0.71d19.59§0.76d13.70§0.44d0.64§0.03d 11029.78§0.1720.59§0.36bc45.03§0.1967.09§0.71c22.17§0.75c15.29§0.44c0.74§0.03c 12029.51§0.1719.56§0.36cd44.76§0.1770.14§0.71b25.38§0.76b16.77§0.44b0.86§0.03b 13029.13§0.1718.99§0.36d44.38§0.2073.44§0.71a29.07§0.57a19.14§0.44a1.01§0.03a Feedrestriction10029.21§0.1720.66§0.36bc 44.46§0.1964.17§00.71d 19.71§0.75d 13.74§0.44d 0.67§0.03cd 11029.06§0.1723.34§0.36a44.31§0.1969.03§0.71bc24.72§0.76b19.55§0.44a0.84§0.03b 12029.74§0.1723.48§0.36a 44.99§0.1771.08§0.71b 26.09§0.76b 20.41§0.44a 0.87§0.03b 13029.58§0.1719.20§0.36d44.83§0.1973.65§0.71a28.82§0.75a18.86§0.44a0.98§0.03a Themeanvaluesinsamecolumnwithineachdivisionwithdifferentsuperscripts(a−d)differsignificantly(P<0.05).

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of threonine was obtained from higher body WG. Our findings agreed withCorzo et al. (2004), who concluded that amino acid supplements above recommended levels could increaseflock homogeneity, which has a significant economic effect. Also,Yaqoob et al. (2018) found that higher levels of threonine do not affect total feed cost.

CONCLUSIONS

The dietary inclusion of threonine amino acid in feed- restricted broiler chickens enhanced growth performance parameters. This effect was linked to altered GH, IGF, T3, and T4 levels. Also, it was found higher levels of threonine in control or feed-restricted birds have a favor- able effect on return parameters. In addition, the supplementation of threonine signiﬁcantly increased urea and AST levels in feed-restricted birds. Ross breed exhibited a lower feed cost/kg gain and a higher proﬁtability than IR breed.

ACKNOWLEDGMENTS

The authors extend their appreciation to the Ministry of Education in KSA for funding this research work through the project number KKU-IFP2-P-1.

Author Contributions: All authors contributed equally to this work. All authors read and approved the ﬁnal version of this manuscript.

DISCLOSURES

All authors have no conﬂicts of interest to disclose.

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