«Department of Animal Production1, Department of Poultry Production2, Faculty of Agriculture, Ain Shams University, Cairo, Egypt KARIMA A. SHAHIN1 and ...»
Arch. Tierz., Dummerstorf 48 (2005) 6, 612-626
Department of Animal Production1, Department of Poultry Production2, Faculty of Agriculture, Ain Shams
University, Cairo, Egypt
KARIMA A. SHAHIN1 and FATHY ABD ELAZEEM2
Effects of breed, sex and diet and their interactions on carcass
composition and tissue weight distribution of broiler chickens
The effects of breed (Hubbard and Anak), sex and diet (two levels of protein (high or low) with two levels of
crude fiber (low or high) at each level of protein) on carcass composition and distribution of tissues over the carcass were studied.
Carcass composition and ratios of muscle: bone, muscle: fat and meat: bone in the carcass did not differ significantly between breed groups. Male carcasses had more muscle, more bone, more fat-free carcass, higher ratios of muscle: bone, muscle: fat but less fat, less meat and lower meat: bone ratio than female carcasses.
Carcasses of chicks fed high protein (with either low or high fiber) diet had more muscle than carcasses of chicks fed low protein (with either low or high fiber) diet. Carcasses of chicks fed high fiber (with either low or high protein) diet had more bone but less meat than carcasses of chicks fed low fiber (with either low or high protein)
diet. Increasing both protein and fiber in the diet resulted in lowering carcass fat, consequently raising muscle:
fat ratio. Breed and sex did not influence the distribution of muscle and meat throughout the carcass parts. Breed differences in fat weight distribution were not significant. Anak had significantly higher proportions of bone in wing and neck than Hubbard did. The proportion of total carcass muscle in breast, drumstick, wing were not significantly affected by diet. Carcasses of chicks fed high fiber (with either low or high protein) diet had higher proportion of total meat in thigh and neck than carcasses from chicks fed low fiber (with either low or high protein) diet. Diet had no significant effect on bone weight distribution. Increasing crude fiber in diets resulted in lowering proportion of total fat in breast, thigh but increasing proportion of total fat in drumstick and wing.
Breed x sex, breed x diet and sex x diet interactions did not significantly influence most of carcass traits indicating that the factors under consideration act independently of each other's. Significant sex x diet interactions was found for carcass fat and boneless carcass relative to live body weight: the sexual dimorphism in low protein diet is more pronounced than in high protein diets.
Key Words: chicken, breed, sex, diet, carcass composition, tissues distribution, genotype x nutrition interactions Zusammenfassung Titel der Arbeit: Der Einfluss der Rasse, des Geschlechtes und der Fütterung auf die Schlachtkörperzusammensetzung bei Broilern An147 Broilern der in Ägypten gehaltenen Rassen Hubbard und Anak wurde der Einfluss der Rassse, des Geschlechtes sowie von vier Fütterungsvarianten auf unterschiedliche Schlachtkörpermerkmale untersucht. Die Fütterungsvarianten unterschieden sich hinsichtlich des Eiweiß- und Rohfaseranteils in der Ration (hochniedrig). Bei den Schlachtkörpermerkmalen ergaben sich keine signifkanten Unterschiede zwischen den Rassen.
Höhere Fleischanteile erreichten die männlichen Tiere sowie die mit der eiweißreichen Ration gefütterten Tiere.
Unabhängig vom Eiweißanteil führte ein höherer Rohfaseranteil zu erhöhtem Knochen- und geringerem Fettanteil, vor allem im Brustfleisch und damit zu verändertem Fleisch:Fettverhältnis im Schlachtkörper. Ein signifkanter Einfluss hinsichtlich Geschlecht und Fütterung konnte für den Fett- und Knochenanteil in Beziehung zum Lebendgewicht nachgewiesen werden. Der Geschlechtsdimorphismus war bei niedrigerem Eiweißniveau ausgeprägter als bei höherer Eiweißversorgung.
Schlüsselwörter: Broiler, Rasse, Geschlecht, Fütterung, Schlachtkörperzusammensetzung, Gewebeanteile, Genotyp : Fütterungsinteraktion Arch. Tierz. 48 (2005) 6 Introduction A superior carcass is characterized by a desirable composition: maximum proportion of muscle, minimum proportion of bone and optimum proportion of fat dictated by specific trade preference. Also, superior carcass must contain high proportion of most valuable muscles (i.e. breast and thigh muscles). Carcass composition in broilers can be manipulated through genetic and nutritional routes. Increasing protein: energy ratio resulted in increasing carcass leanness and decreasing body fatness with the opposite effect was elicited by a low protein: energy ratio (JONES and WISEMAN, 1985;
LEENSTRA, 1986; BARTOV and PLAVNIK, 1998). Also, carcass leanness can be achieved by feeding animals and birds low energy, low-cost high fibrous diets and by restricted feeding (GODFREY et al., 1991; LEESON et al., 1992; LEESON et al., 1996; KHANTAPRAB et al., 1997).
Separate effects of breed, sex and nutrition on carcass composition of chickens were reported by BROADBENT et al. (1981); ORR et al. (1984); MARKS (1990);
BARTOV (1998); SMITH and PESTI (1998) and WISEMAN and LEWIS (1998).
Variation in lean, bone and fat distribution due to breed have been investigated by ABDALLAH et al. (1990), SHAHIN et al. (1990) and SHAHIN et al. (1996). The combined effects of breed, sex, and diet and their interactions on carcass characteristics have received little attention and partitioning of bird response due to these effects have not been widely reported. To test the hypothesis that the similarity of breeds and sexes in their response to diets, this study was designed to consider simultaneously the effects of breed-type, sex and diet and their respective interactions on compositional relationships and tissue weight distribution of broiler chickens.
Materials and methods The study contained dissection data from 147 broiler chickens, 74 males and 73 females; from 72 (36male, 36 female) Hubbard and 75 (38, 37) Anak broilers. These birds were from the Poultry Nutrition Research Station, Department of Poultry Production, Ain Shams University. Chicks of each breed were divided equally into four groups, and randomly assigned to one of four diets (37 birds/treatment) in four replicates. The diets were formulated to contain two levels of protein (high or low) with two levels of crude fiber (low or high) at each level of protein. The ingredients and chemical composition of the four diets are given in Table 1.
Diet I ‘commercial, high protein- low fiber’, comprised of approximately 21% protein and a metabolizable energy of 3000 Kcal/kg during starter phase (1 to 4 weeks) and contained approximately 18% protein and a metabolizable energy of 3120 Kcal/kg during finisher phase (5 to 8 weeks). The percent of fiber in both phases was 4%. Diet II 'high protein- high fiber', was similar to diet I in protein but different in metabolizable energy (2750 Kcal/kg in starter phase and 2862 in finisher phase) and in fiber (8%). Diet III 'low protein- low fiber', was similar to diet I in metabolizable energy and fiber but lower in protein (19 % protein during starter phase and 16 % protein during finisher phase). Diet IV 'low protein- high fiber', contained similar levels of protein to diet III and higher fiber (8%) but the metabolizable energy was similar to that in diet II. All the diets were provided ad. libitum and conventional brooding and rearing practices were followed.
SHAHIN; ELAZEEM: Effects of breed, sex and diet of broiler chickens
At the time of slaughter (8 weeks of age) the birds were individually weighed and killed by severing the carotid artery and jugular veins. The head was removed at the atlanto-occipital articulation. After dressing the carcass was stored in closed bags at °C. Prior to dissection, carcasses were thawed for approximately 20 hr. at 5 °C while being in their bags. The breast was removed from the carcass. It composed of the sternum and its associated muscles. The hind leg was removed from the carcass at the acetabulum so that the pelvic muscles and bones were left attached to the leg. The proximal part 'thigh' of the hindleg was separated from the distal part 'drumstick' at the tibio-femoral joint. The thigh included proximal hindleg muscles and bones. The glutes 'oyster' muscles were removed and included with the thigh muscles. The foreleg ‘wing’ was separated from the carcass. The neck was removed from the Arch. Tierz. 48 (2005) 6 carcass as close to the clavicle as possible. Thus the right side was divided into the following commercial cuts: drumstick, thigh, breast, wing, neck, rib plus abdominal wall. The breast and thigh were considered as highly desired cuts. The skin, subcutaneous fat, muscle, bone and intermuscular fat in each cut were dissected and weighed. For each cut, the total weight of muscle, bone and fat was referred to as the ‘entire’ cut and the total weight of muscle and fat was referred to as ‘boneless’ cut.
The sum of muscle, intermuscular fat and subcutaneous fat forms the edible meat. The sum of these parts over all cuts gives total side muscle, total side edible meat, total side bone and total side fat. The sum of the dissected muscle, fat and bone was used as dissected side weight.
To assess breed-type, sex and diet influences on carcass composition, the data were analyzed by the General Linear Models procedures of SAS (SAS Institute, 1995) according to the following model Y ijkl = µ + Bi + Sj+ Dk + (BS)ij + (BD)ik + (SD) jk+ Eijkl Where, Y ijkl = weight (g) or percentage of the component Y of the ijkl bird;
µ = grand mean;
Bi = fixed effect of the breed group (i= 1,2);
Sj = fixed effect of the sex (j= 1,2);
Dk = fixed effect of the diet (k=1… 4);
(BS) ij = the interactions between breed and sex;
(BD)ik = the interactions between breed and diet;
(SD) jk = the interactions between sex and diet;
Eijkl = the random error assumed N.I.D. (0, s 2 e).
DUNCAN’S multiple range test was used to test for significant differences between pairs of means.
Results Table 2 presents the means, standard deviations, and coefficient of variability and ranges for live weight and muscle, fat and bone traits. Live body weight averaged 2350 g and ranged from 1400 to 3500 g. Total carcass muscle ranged from 468 to 1492 g with a mean of 951 g, total carcass fat ranged from 182 to 586 g with a mean of 364 g and total carcass bone ranged from 146 to 424 g with a mean of 266 g.
Among the major carcass tissues, fat was the most variable tissue (CV= 12.7%) followed by bone (CV= 9.1%) and then muscle (CV= 4.8%).
SHAHIN; ELAZEEM: Effects of breed, sex and diet of broiler chickens Table 2 Means, standard deviations (SD), coefficient of variability (CV%) and minimum and maximum values for live body weight and carcass traits in broiler chickens. (Durchschnitt, Standardabweichung (SD) Variationskoeffizient (CV%) sowie Minimum- und Maximumwerte für Lebendgewicht- und Schlachtkörpermerkmale von Broilern)
Live body weight Differences in live body between breeds were found to be significant. The live body weight of the Hubbard was significantly heavier than that of the Anak (Table 3).
Sexual dimorphism for live body weight favored males, where they weighed 14% heavier than females (Table 3).
Chicks fed diet 1 (high protein- low fiber) had significantly heavier live body weight than those fed other diets (Table 3). On the other hand chicks fed diet II (high proteinhigh fiber) did not differ significantly from those fed diet 4 (low protein – high fiber) in their live body weight.
Arch. Tierz. 48 (2005) 6
Expressed as a percentage of live body weight, males and females did not differ significantly from each other in carcass muscle, carcass bone and fat-free carcass, but they differed significantly in carcass fat and carcass meat which were higher in females than in males. Expressed as a percentage of carcass weight, male carcasses had more muscle, more bone and more fat-free carcass but less fat, less boneless carcass than female carcasses (Table 3). Males had higher muscle: bone ratios and higher muscle: fat ratios but they had lower meat: bone ratios than females.
Expressed as a percentage of live body weight, broilers fed high level of protein (with either low or high fiber) and those fed low level of protein (with either low or high fiber) did not differ significantly from each other in carcass muscle, fat-free carcass and boneless carcass. Carcasses of chicks fed high level of protein- high level of fiber had significantly lower carcass fat than those of chicks fed other diets which were not significantly different from each other (Table 3). Carcasses of chicks fed high level of protein with high level of fiber (diet 2) were significantly higher in carcass bone than those of chicks fed high protein with low level of fiber.
SHAHIN; ELAZEEM: Effects of breed, sex and diet of broiler chickens Expressed as a percentage of carcass weight, carcasses of chicks fed high protein (with either low or high fiber) diet had more muscle than carcasses of chicks fed low protein (with either low or high fiber) diet (Table 3 ). Carcasses of chicks fed high fiber (with either low or high protein) diet had more bone but less boneless than carcasses of chicks fed low fiber (with either low or high protein) diet. Diets with a constant level of protein but with increasing levels of fiber decreased fat-free carcass. The relative decrease in fat-free carcass was greater with high protein level than with low protein level (-12.2% vs. – 4.4).
Significant (P 0.05) sex x diet interactions were revealed by analysis of variance for carcass fat and boneless carcass (meat) relative to live body weight (Table 3).
Interaction analysis of major carcass tissues relative to carcass weight (Table 3) indicated that the effect of breed was essentially the same regardless of sex and that differences between sex tended to be similar for different breeds. Also, the effect of diet on carcass composition was independent of the breed of bird.
Distribution of carcass parts 'entire cuts' The yield of the various cuts expressed as a percentage of carcass weight. There were no significant differences between Hubbard and Anak in proportion of total carcass weight occurring in all cuts other than wing which constituted a significantly higher proportion of the Anak carcasses than the Hubbard carcasses. Sex did not significantly affect carcass weight distribution.