Rosa PS2,3 Faria Filho DE4 Dahlke F5 Vieira BS3 M acari M3 Furlan RL3,6
1 The aut hors t hank PRODETA (Projet o de Desenvolvimento de Tecnologia Agrícola) for financial support.
2 Em brapa Suínos e Aves and Universidade do Contestado, UnC. Concórdia, SC, Brazil. 3 Universidade Est adual Paulist a
Facu l d ad e d e Ci ên ci as A g r ár i as e Vet erinárias. Depart ament o de M orf ologia e Fisiologia Animal. Jaboticabal, SP, Brazil. 4 Universidade Federal de M inas Gerais
Núcleo de Ciências Agrárias. Departamento de Zootecnia. M ontes Claros, M G, Brazil. 5 Universidade Federal do Paraná
Depart ament o de Zoot ecnia. Curit iba, PR, Brazil.
Renato Luis Furlan
Dep art am en t o d e M o rf o lo g ia e Fisio lo g ia Animal.
Via de acesso Prof . Paulo D. Cast elane, s/n. 14.884-900. Jaboticabal, SP, Brazil.
E-mail: rlf urlan@f cav.unesp.br
Allom et ric grow t h, broiler chickens, carcass composition, energy intake, genetic strains.
Effect of Energy Intake on Performance and
Carcass Composition of Broiler Chickens from
Two Different Genetic Groups
1Mail Address
Keywords Author(s)
Arrived: M arch / 2007 Approved: June / 2007
ABSTRACT
In order to evaluate the effect of energy intake and broiler genotype on performance, carcass yield, and fat deposition, 600 one-day-old male chicks from tw o different genetic groups (AgRoss 308 – commercial line and PCLC – Em brapa non-im proved line) w ere f ed diet s w it h different metabolizable energy level (2950, 3200 and 3450 kcal/kg). A co m p let ely ran d o m ized exp erim en t al d esig n in a 2 X3 f act o rial arrangem ent w it h f our replicat ions of 25 birds per t reat m ent w as applied. In order to ensure different energy intake among treatments w it hin each st rain, f eed int ake w as daily adjust ed by pair-f eeding schemes. AgRoss 308 broilers had better performance and carcass yield, and presented low er abdominal fat deposition rate. In both genetic groups, the highest dietary energy level increased w eight gain, heart relative w eight, and fat deposition. How ever, it reduced the difference betw een AgRoss 308 and PCLC for feed conversion ratio and carcass prot ein deposit ion. These f indings allow concluding t hat genet ic improvement had a significant effect on broiler energy metabolism, and that the highest performance differences betw een genetic groups are found w hen low -energy intake is imposed.
INTRODUCTION
Energy intake is considered a fundamental factor in broiler production, not only because it af f ect s grow t h rat e and carcass charact erist ics
(Boekholt et al., 1994; Leeson et al., 1996), but also because it is
indirectly involved in metabolic diseases, such as ascites (Leeson et al., 1995). Theref ore, f inding t he opt imal point bet w een economic and physiological optimal dietary energy level for broilers has been the goal of many researchers.
Leeson et al. (1996) show ed that broiler feed intake increases linearly w ith decreasing dietary energy level. Albuquerque et al. (2003) also described reduction in feed intake due to higher dietary energy density. In addition, Leeson et al. (1996) found that broilers fed free-choice on diets w ith either 2700 or 3300 kcal metabolizable energy/kg presented the same grow th rate and constant energy consumption. These findings together suggest that broilers do control their feed intake in order to su p p l y en er g y r eq u i r em en t s, an d o n e o f i t s m o st i m p o r t an t consequences is the possibility of formulating feeds based on predicted intake according to dietary energy level.
level does not affect broiler feed intake in some cases remains unansw ered. In f act , t he nut rit ional f act ors involved in broiler feed intake control mechanisms are not com plet ely underst ood, and seem ingly ot her macronutrients than energy influence feed behavior. In mammals it is w ell established that protein is the first nutrient in the hierarchy of oxidation, follow ed by carbohydrat es and f at , w hich corresponds t o t heir ability to induce satiety (Stubbs et al., 1997). In avian species, this chain is not w ell described, and differences may influence feeding behavior.
On e p o ssib le n eg at ive co n seq u en ce o f b ro iler genetic improvement is the loss of sensitivity to regulate feed intake according to dietary energy level. In fact, Richards (2003) reported that broilers selected both for rapid w eight gain and muscular mass deposition do not properly regulate voluntary feed intake according t o energy level, as in an ad libit um program t hey sh o w ed co m p u lsive ap p et it e an d excessive f at accumulation. Taking this statement to an experimental vision it is clear that it is difficult to assess different energy consumption of broilers if their feed intake w as not restricted.
In the few last years, the close link betw een dietary energy to protein ratio and broiler carcass composition w as invest igat ed by several researches (Summers et al., 1992; Leeson et al., 1996; Sw ennen et al., 2004). In general, energy ret ent ion as f at increases as t he ratio rises. This statement could explain many of the
differences in carcass chemical composition found in lit erat ure; nevert heless, t he dif f erences in broiler r esp o n siven ess t o d iet ar y en er g y level t h r o u g h selection for increased grow th rate w ere little explored in literature. Thus, the objective of the present study w as t o evalu at e t h e ef f ect o f en erg y in t ak e o f genetically selected or non-selected broiler chickens on performance, carcass yield and fat deposition.
MATERIAL AND METHODS
Eggs from a broiler line selected for rapid grow th rat e (AgRoss 308) and f rom a genet ically st abilized populat ion (PCLC – an Embrapa experiment al meat line maintained by random mating since 1984) w ere incubat ed according t o com m ercial pract ices in a Petersime machine w ith capacity of 5,000 eggs. The initial chick w eight w as 47.5±0.01 and 45.8±0.01 g for PCLC and AgRoss 308, respectively.
A total of 600 chicks w ere randomly placed in floor p en s, an d su b m i t t ed t o d i et s w i t h d i f f er en t metabolizable energy levels (2950, 3200, and 3450 kcal/kg). A completely randomized experimental design in a 2X3 f act orial arrangement (genet ic group and diet ary m et abolizable energy level), t ot alizing six treatments w ith four replicates of 25 birds each, w as applied. Diets (Table 1) w ere formulated according to the NRC (1994) recommendations. In order to ensure different energy consumption among treatments w ithin
Table 1 - Composition of starter (from 1 to 21 days of age) and grow ing diets (from 22 to 42 days of age).
Ingredient s (% ) Starter diets Grow er diets
Corn 57.43 51.54 45.61 67.10 61.21 55.30
Soybean meal (45% ) 36.49 37.60 38.70 29.20 30.30 31.40
Soybean oil 2.27 7.07 11.89 0.46 5.27 10.08
Dicalcium phosphat e 1.81 1.82 1.84 1.30 1.32 1.33
Lim est one 1.10 1.09 1.07 1.22 1.21 1.19
Sodium chloride 0.41 0.41 0.41 0.29 0.29 0.29
Choline chloride 60% 0.10 0.10 0.10 0.10 0.10 0.10
DL-M et hionine 98% 0.16 0.16 0.17 0.07 0.07 0.08
L-Lysine HCl 98% 0.02 - - 0.02 -
-L-Threonine 98% - - - 0.03 0.02 0.02
Coxist ac 12%® 0.05 0.05 0.05 0.05 0.05 0.05
Zinc bacit racine 15% 0.04 0.04 0.04 0.04 0.04 0.04
Ant ioxidant (Banox) 0.02 0.02 0.02 0.02 0.02 0.02
Suplement1 (1 kg/t on) 0.10 0.10 0.10 0.10 0.10 0.10
Tot al 100.0 100.0 100.0 100.0 100.0 100.0
Energy and Nutrients Calculat ed Composit ion
M et abolizable energy (kcal/kg) 2,950 3,200 3,450 2,950 3,200 3,450
Crude prot ein (% ) 21.50 21.50 21.50 19.00 19.00 19.00
Calcium (% ) 1.00 1.00 1.00 0.90 0.90 0.90
Available phosphorus (% ) 0.45 0.45 0.45 0.35 0.35 0.35
Sodium (% ) 0.20 0.20 0.20 0.15 0.15 0.15
Energy/Prot ein rat io (kcal/g CP) 137.2 148.8 160.5 155.3 168.4 181.6
1 - Vit amin/M ineral supplement – Levels per kg diet : vit amin A, 7,000 IU; vit amin D 3
, 3,000 IU; vit amin E, 25 mg; vit amin K, 1 mg; t hiamin, 1.8 mg; ribof lavin, 9.6 mg; pyridoxine, 3.5 mg; vit amin B
12
each genetic group, feed intake w as daily adjusted by pair-feeding schemes. Thus, the amount of feed provided f or all replicat ions w it hin each genet ic group w as equivalent to the mean feed intake of the treatment w ith low er consumption obtained in the day before. Water w as supplied ad libitum throughout the experiment.
The trial w as carried out in climatic chambers, w here the chicks w ere reared during 42 days. Light regime w as cont inuous, w it h 24-hour art if icial light , and temperature w as kept at thermoneutrality: 29.5 ± 1.2ºC from 1 to 7 days of age; 26.7 ± 0.6ºC from 8 to 14 days of age; 26.0 ± 1.2ºC from 15 to 21 days of age; and 25.2 ± 1.3ºC from 22 to 42 days of age.
Broilers and f eeds w ere w eight ed at day 42 t o calculat e perf orm ance charact erist ics. In order t o assess carcass charact erist ics, t w o broilers in each replicate (mean group w eight ±100g) w ere w ater- and feed-deprived for 5 hours, and w ere subsequently bled. Br o i l er s w er e t h en scal d ed , d ef eat h er ed , an d eviscerated. Carcasses (w ithout head, neck, feet and l u n g s) w er e cu t i n t o p i eces t o o b t ai n b r east , thighs+drumsticks, and w ings w eights (w ith skin and bones). After that, one carcass w as frozen at –20 °C for further chemical evaluation. Liver and heart w ere w eig h t ed , as w ell as ab d o m in al f at , w h ich w as considered as all of adipose tissues surrounding the cloaca and adhering to the gizzard. Carcass, breast, thighs+drumsticks, w ings, heart, liver, and abdominal fat yield values w ere calculated relative to broiler live w eight at slaughter.
In order to obtain total dry matter, carcasses w ere
ground, hom ogenized, pre-dried (60oC/72 h), and
completely dried (100oC/24 h). Seubsequently, crude
prot ein (micro Kjeldahl) and et her ext ract (Soxhlet ) analyses w ere perf ormed f ollow ing t he procedures described by AOAC (1990).
Data w ere first tested for normality (Shapiro-Wilk t est ), and homogeneit y of variances (Levene’s t est ). As these assumptions w ere not violated, data w ere submitted to analyses of variance by the General Linear
M odel procedure of SAS®®®®®. When statistical difference
w as detected (p<0.05), means w ere compared by the t est of Tukey (5% ). Dat a are expressed as mean ± st andard error of t he m ean (SEM ). Abdom inal f at d ep o sit io n rat e w as evalu at ed b y t h e allo m et ric
coef f icient β (bet a) value in t he allom et ric grow t h
equation: log y (abdominal fat) = α + β [log x (body
w eight)], as proposed by Huxley & Teissier (1936). In order to assess allometric nature, the hypothesis w as t est ed β= 1 vs β> 1 by St udent ’ s t t est . Thus, β= 1 indicat es sim ilar rat es of f at deposit ion and body
grow t h, and β> 1 show s higher f at deposit ion as
compared to body grow th. All statistics w ere performed
using the Statistical Analysis System – SAS® (Littell et
al., 2002).
RESULTS AND DISCUSSION
Performance
Analysis of variance w as not applied for feed intake, since it w as kept constant among treatments w ithin the same strain. M ean feed intake for PCLC and AgRoss 308 broilers w as 3,235± 32.6 and 4,312± 41.6 g, respect ively, w hich represent a dif f erence of 25% betw een genetic groups.
No signif icant int eract ion w as observed bet w een genetic group and dietary metabolizable energy level f or w eight gain (Table 2); t heref ore, only t he main treatment effects w ill be discussed. AgRoss 308 group w eight gain w as 46% higher than PCLC. Analyzing perf ormance dif f erences bet w een t ypical 1957 and 1991 broilers, Havenst ein et al. (1994a) report ed a w eight gain improvement of more than 300% during this period. The authors also found the diet based on 1991 recommendat ions improved non-select ed line w eight gain in 26% at 43 days. As PCLC line represents a more modern broiler than 1957 one, these significant dif f erences w ere expect ed. A comparison bet w een diets reveals progressive rise in w eight gain according t o elevat ion in energy consum pt ion. Leeson et al. (1996) also observed im provem ent in w eight gain according to rise in energy consumption; how ever, as broilers are capable of controling feed intake according t o energy requirement s, t he same result s w ere not described w hen diets w ith different energy levels w ere applied in an ad libitum feed program.
The difference betw een AgRoss 308 and PCLC for f eed co n ver sio n r at io d ecr eased as t h e en er g y consumption increased, changing from 12% to 8% for t he low est and t he highest diet ary energy levels, respectively. This finding is important, and show s that PCLC broilers have bet t er capacit y t o increase t heir w eight gain in response an increase in energy intake, since the feed intake w as maintained the same inside each genetic group.
Carcass, parts, viscera, and abdominal fat yields
Th ere w as n o sig n if ican t in t eract io n b et w een genetic group and dietary metabolizable energy level for carcass, parts, viscera, and abdominal fat yields of broilers at 42 days of age (Table 3). As to genetic group, AgRoss 308 broilers show ed higher carcass, breast, and t h i g h s+ d r u m st i ck s yi el d s t h an PCLC b r o i l er s. Commercial broilers show ed almost 5% better carcass yield, w hich difference is very similar to that described by Havenstein et al. (1994b) betw een 1957 and 1991 broilers at 43 days of age. This w as also observed for breast yield. In addit ion, Havenst ein et al. (1994b) observed that the difference betw een genetic groups in breast yield increased w ith time, an indication that selected broilers do deposit more muscular mass in the breast than the non-selected ones.
AgRoss 308 broilers had low er heart, liver, and w ings yield s t h an PCLC. Sim ilar resu lt s w ere f o u n d b y
Havenst ein et al. (1994b) f or heart and w ings. The
low er heart and liver relat ive w eight of t he AgRoss 308 group m ay indicat e t hat genet ically select ed broilers are more sensitive to metabolic diseases. In fact, higher mortality levels associated w ith metabolic d iseases h ave b een o b served in m o d ern b ro ilers (Gonzales & M acari, 2000).
Commercial broilers deposited less abdominal fat than PCLC broilers. Considering the precocity of the improved line, an opposite behavior w as expected. In
fact, Havenstein et al. (1994b) found that genetically improved broilers deposited abdominal fat at a higher rat e t han t he non-select ed unt il 85 days of age. Nevertheless, after this time, total carcass fat w as the same betw een genetic groups. Such discrepant results may have occurred due genetic differences betw een PCLC line and the 1957 line used by the authors.
Dietary energy level did not affect carcass, breast, an d w in g s yield s (Tab le 3 ), even t h o u g h en erg y consumption w as directly related to w eight gain (Table 2). Leeson et al. (1996), Oliveira Neto et al. (1999), Albuquerque et al. (2003), and Sakomura et al. (2004) also found that dietary metabolizable energy level did not af f ect carcass yield in broilers at slaught e age. How ever, Araújo (1998) found that broilers fed 3600 k cal / k g i n cr eased car cass an d b r east yi el d s as compared to those fed 3200 kcal/kg. Broilers fed the 2950-kcal/kg diet increased thighs+drumsticks yield, and reduced relative heart w eight. Broilers fed 3200 kcal/kg presented the low est liver percentage.
The low est energy diet (2950 kcal/kg) decreased abdominal fat as compared to the other diets. Leeson et al. (1996) found that an increase in dietary energy level w as f ollow ed by higher abdom inal f at deposit ion. How ever, Oliveira Neto et al. (1999) and Albuquerque et al. (2003) did not find significant effect of dietary energy level on abdominal fat deposition in broilers. In fact, abdominal f at depot areas are considered as main location of excessive energy deposition (Summers et al., 1992). Therefore, w e could conclude that the tw o highest energy consumption levels in this trial w ere not very different in terms of total energy available to the broilers. How ever, this kind of measurement could be a poor p aram et er w h en st u d yin g carcass f at d ep o sit io n (Summers et al., 1992), and a more precise interpretation of energy metabolism w ould be assessed by measuring total fat deposition in the carcass. Excessive abdominal fat deposition delays processing procedures, and may cause problems during carcass evisceration.
Table 2 - Weight gain (g) and feed conversion (g/g) of broilers at 42 days of age.
Variables M et abolizable Genetic group M ean
energy (kcal/ kg) PCLC AgRoss 308
2,950 1599± 14 2387± 21 1993± 150c
W eight gain 3,200 1714± 22 2499± 19 2106±149b
3,450 1781± 19 2550± 18 2165± 146a
M ean 1698±23B 2478± 22A
2,950 2.02±0.01aA 1.81±0.01aB 1.92± 0.04
Feed conversion rat io1 3,200 1.89±0.01bA 1.73±0.01bB 1.81± 0.03
3,450 1.82±0.01cA 1.69±0.02bB 1.75± 0.03
M ean 1.91± 0.03 1.74± 0.02
Carcass chemical composition
A signif icant int eract ion w as observed bet w een genetic group and dietary metabolizable energy level for crude protein and ether extract carcass percentages (Table 4). A comparison of dietary energy levels w ithin each genetic group indicates differences in their protein and energy metabolism. In AgRoss 308 strain, ether ext ract carcass deposit ion w as direct ly relat ed t o en er g y co n su m p t i o n , i . e. , t h e h i g h est en er g y consumption promotes the fattest carcass. Opposite behavior w as observed f or crude prot ein carcass deposit ion. W hen f eed int ake w as m aint ained t he sam e w it hin each genet ic group, diet ary energy: protein ratio linearly dropped as energy consumption decreased. Thus, the low er the dietary energy: protein ratio, the leaner the carcass. This find is consistent w ith Summers et al. (1992) and Boekholt et al. (1994), w ho also f ound a reduct ion in f at deposit ion due t o a decrease in dietary energy: protein ratio.
W hen t he ef f ect of genet ic group w it hin each dietary energy level w as analyzed, it w as observed that AgRoss 308 genetic superiority for carcass composition w as lost as energy consumption increased. Thus, total prot ein deposit ion w as low er and equal f or bot h genetic groups at the highest energy: protein ratio. Similarly, AgRoss 308 deposit ed less f at t han PCLC w hen fed w ith the low est dietary energy level. These f indings may corroborat e t he t endency of reducing
diet ary energy level f or m odern broilers; how ever, although low -energy diets promote low fat and high protein deposition in carcasses – w hich is desirable –, it is important to emphasize that a decrease in energy consumption leads to low er productive performance.
Allometric coefficient “βββββ” for abdominal fat
The interaction betw een genetic group and dietary m et abolizable energy level w as not signif icant f or
abdominal fat (Table 3). Thus, allometric coefficient β
estimates for abdominal fat show n on Table 5 consider
only the mean effects. All estimates show ed β > 1,
indicat ing higher abdom inal f at deposit ion rat e as com pared t o grow t h rat e, independent of genet ic
group or dietary energy level. How ever, β coefficient
w as low er in AgRoss 308 broilers than in PCLC ones, sh o w in g t h at t h e co m m ercial lin e d ep o sit s less abdominal f at t han non-improved line. In addit ion,
allometric coefficient β for abdominal fat increased as
diet ary m et abolizable energy level rose, indicat ing higher rate of abdominal fat deposition.
CONCLUSIONS
1. Commercial broilers do respond differently than n o n - sel ect ed o n es t o d i et ar y en er g y consumption level, and the highest differences
Table 3 - Carcass, breast, thighs+drumsticks, w ings, heart, liver, and abdominal fat yields of broilers at 42 days of age.
Yield Genetic group M etabolizable energy (kcal/ kg)
(% of body w eight) PCLC AgRoss 308 2,950 3,200 3,450
Carcass 62.4±1.5B 67.1±1.2A 65.3± 2.1 64.6± 3.0 64.2± 3.3
Br east 17.3±0.8B 22.8±0.9A 20.3± 2.6 20.3± 3.4 19.5± 3.0
Thighs+ drum st icks 22.2±0.6B 22.9±0.7A 23.0± 0.9a 22.2± 0.6b 22.4± 0.4b
Wings 8.7± 0.2A 7.9±0.2B 8.4± 0.6 8.2± 0.5 8.2± 0.5
Heart 0.56±0.03A 0.45±0.03B 0.48±0.05b 0.50±0.06ab 0.53±0.07a
Liver 1.9± 0.1A 1.7±0.1B 1.8± 0.1a 1.7±0.14b 1.8±0.15a
Abdominal f at 2.6± 0.5A 2.1±0.5B 1.9±0.4b 2.6± 0.6a 2.6± 0.3a
Dif f erent capit al let t ers indicat e signif icant dif f erence am ong m eans in t he sam e row (Tukey’ s t est ; p< 0.05). Dif f erent sm all let t ers indicat e signif icant dif f erence among means in t he same column (Tukey’s t est ; p<0.05).
Table 4 - Crude protein and ether extract in the carcass of broilers at 42 days of age.
Variables M et abolizable Genetic group M ean
energy (kcal/ kg) PCLC AgRoss 308
2,950 50.7±0.9abB 59.4±0.4aA 55.0±4.7
Crude protein1 3,200 51.4±1.3aB 54.0±0.5bA 52.7±1.7
3,450 49.4±0.5bA 50.9±0.3cA 50.1±0.9
M ean 50.5±1.2 54.8±3.7
2,950 41.2±0.9abA 31.7±0.3cB 36.4±5.2
Et her ext ract1 3,200 39.7±1.2bA 38.5±0.5bA 39.0±1.0
3,450 42.5±0.8aA 41.7±0.3aA 42.1±0.7
M ean 41.2±1.5 37.3±4.4
betw een genetic groups are found w hen low -energy consumption is imposed.
2. Gen et ic im p ro vem en t allo w ed co m m ercial broilers to reduce allometric grow th of abdominal f at d esp i t e en er g y co n su m p t i o n l evel . Nevert heless, t ot al carcass f at deposit ion w as reduced only in a low -energy consum pt ion schedule.
REFERENCES
Albuquerque R, Faria DE, Junqueira OM , Salvador D, Faria Filho DE, Rizzo M F. Effects of energy levels in finisher diets and slaughter age of on performance and carcass yield in broiler chickens. Brazilian Journal of Poultry Science 2003; 5(2):99-104.
AOAC - Association of Official Analytical Chemists. Official M ethods of Analysis of the Association of Official Analytical Chemists. 15t h ed. Washington (DC); 1990. p.1094.
Araújo LF. Avaliação do desempenho e rendimento de carcaça de frangos de corte submetidos a dietas com altos níveis de energia, metionina+cistina e lisina na fase final de criação [dissertação]. Jaboticabal (SP): UNESP; 1998.
Boekholt HA, Van Der Grinter PH, Schreurs VVAM , Los M JN, Lefering CP. Effect of dietary energy restriction on retention of protein, fat and energy in broiler chickens. British Poultry Science 1994; 35(4): 603-614.
Gonzales E, M acari M . Enfermidades metabólicas em frangos de corte. In: Berchieri Júnior A, M acari M , editor. Doenças das aves. Jaboticabal: FUNEP-UNESP; 2000. p. 449-464.
Havenstein GB, Ferket PR, Scheideler SE, Larson BT. Grow th, livability, and feed conversion of 1957 vs 1991 broilers w hen fed “ Typical” 1957 and 1991 broiler diets. Poultry Science 1994a; 73(12):1785-1794.
Havenst ein GB, Ferket PR, Scheideler SE, Rives DV. Carcass composition and yield of 1991 vs 1957 broilers w hen fed “ Typical” 1957 and 1991 broiler diets. Poultry Science 1994b; 73(12):1795-1804.
Huxley JS, Teissier G. Terminology of relative grow th. Nature 1936; 137:780-781.
Leeson S, Caston L, Summers JD. Broiler response to diet energy. Poultry Science 1996; 75(4):529-535.
Leeson S, Diaz G, Summers JD. Ascites. In: Leeson S, Diaz G, Summers JD. Poultry metabolic disorders and mycotoxins. Guelph: University Books; 1995. p. 43-44.
Littell RC, Stroup WW, Freund RJ. SAS for Linear M odels. 4t h ed. Cary (NC): SAS Institute; 2002.
NRC - National Research Council. Nutrient Requirements of Poultry. Washington: National Academy Press; 1994.
Oliveira Neto AR, Oliveira RFM , Donzele JL, Albino LFT, Valerio SR, Carmo HM . Níveis de energia metabolizável para frangos de corte no período de 22 a 42 dias de idade mantidos em condições de estresse de calor. Revista Brasileira de Zootecnia 1999; 28:1054-1062.
Richards M P. Genetic regulation of feed intake and energy balance in poultry. Poultry Science 2003; 82(6):907-916.
Sakomura NK, Longo FA, Rabello CBV, Watanabe K, Pelicia K, Freitas ER. Efeito do nível de energia metabolizável da dieta no desempenho e metabolismo energético de frangos de corte. Revista Brasileira de Zootecnia 2004; 33(6):1758-1767.
Stubbs RJ, Prentice AM , James WPT. Carbohydrates and energy balance. Annals of the New York Academy Sciences 1997; 819 (1):44-69.
Summers JD, Spratt D, Atkinson JL. Broiler w eight gain and carcass composition w hen fed diets varying in amino acid balance, dietary energy, and protein level. Poultry Science 1992; 71(2):263-273.
Sw ennen Q, Janssens GPJ, Decuypere E, Buyse J. Ef f ect s of subst it ut ion bet w een f at and prot ein on f eed int ake and it s regulat ory mechanisms in broiler chickens: energy and prot ein metabolism and diet-induced thermogenesis. Poultry Science 2004; 83(12):1997-2004.
Table 5 - Allometric coefficient β for abdominal fat of broilers at 42 days of age.
Genetic group M etabolizable energy (kcal/ kg) a* b* * P R2
PCLC - -8.7129 1.68772a <0.0001 0.955
AgRoss 308 - -6.6157 1.35320b <0.0001 0.952
- 2,950 -5.6702 1.22977b 0.0059 0.893
- 3,200 -6.9992 1.42713ab <0.0001 0.910
- 3,450 -7.3691 1.47751a <0.0001 0.920
