Influence of Dietary Energy Restriction on Yield and Quality of Broiler Parts1

Influence of Dietary Energy Restriction on Yield and Quality of Broiler Parts1 A. S. ARAFA, 2 S. M. BOOTWALLA, and R. H. HARMS3 Poultry Science Department, University of Florida, Gainesvile, Florida 32611 (Received for publication September 4, 1984) ABSTRACT A total of 768 broilers were used in two studies to investigate the effect of dietary energy restriction on yield, fat and moisture contents, and organoleptic characteristics of broiler parts. Four dietary treatments were used with six replications of each sex. Energy intake was restricted during the last 12 days of the finishing period with full minimum daily requirements of all other nutrients maintained. Energy restriction reduced the live and ready-to-cook (RTC) weight of the whole carcass. Percentage distributions of the cut-up parts of RTC broiler carcasses were also changed due to restriction. Energy restriction changed fat composition of the RTC broiler parts. A 15% dietary restriction did not significantly affect flavor, tenderness, or juiciness of dark meat based on organoleptic tests. Higher levels of dietary restriction, however, resulted in a significant reduction (indicating an adverse effect) in juiciness scores of broiler meat. (Key words: energy, restriction, broiler parts, processing yield) 1985 Poultry Science 64:1914-1920 INTRODUCTION Broilers b e c o m e excessively fat with abdominal fat comprising 3 t o 5% of t h e t o t a l b o d y weight (Leeson and Summers, 1 9 8 0 ) . This excessive a b d o m i n a l and visceral fat is becoming an increasing concern t o t h e c o n s u m e r as well as t h e broiler processor. G o o d w i n ( 1 9 7 9 ) r e p o r t e d t h a t a p o u l t r y plant processing 5 0 , 0 0 0 broilers/day lost an average of 2 oz in fat pad per bird. A t a 50^/lb m a r k e t value, this plant would lose $ 8 1 2 , 5 0 0 / y e a r . Factors which influence fat deposition in broilers include breed or strain of bird, sex, age, diet, e n v i r o n m e n t a l factors such as season of t h e year, and t e m p e r a t u r e (Arafa et al, 1 9 8 3 ) . Manipulation of these factors usually results in a b o d y weight r e d u c t i o n greater t h a n t h a t due t o fat loss. D e a t o n et al. ( 1 9 8 1 ) r e p o r t e d t h a t as dietary energy level increased, t h e a m o u n t of a b d o m i n a l fat in broilers increased. Energy restriction during t h e finishing period was reported by Arafa et al. ( 1 9 8 3 ) as a practical m e a n s of reducing a b d o m i n a l fat pads. T h e p o u l t r y f o o d industry in recent years is experiencing an increased d e m a n d for cut-up

'Florida Agricultural Experiment Stations Journal Series No. 5019. 2 Present address: Food Science Department, Faculty of Agriculture, King Saud University, Riyadh, Saudi, Arabia. 3 To whom correspondence should be addressed.

broilers in t h e p o u l t r y food m a r k e t . According t o t h e m o s t recent survey m a d e b y National Broiler Council (NBC), a b o u t 4 9 % of t h e broiler processors' volume was m a r k e t e d as cut-up broilers or parts (NBC, 1 9 8 1 ) . A l t h o u g h t h e effect of sex, age, and strain of t h e birds on yields of broiler parts have been r e p o r t e d (Dodge a n d Stadelman, 1 9 5 9 ; Moran and Orr, 1 9 7 0 ; B o u w k a m p et al, 1 9 7 3 ; Walter et al., 1 9 6 3 ; and H u d s p e t h et al., 1 9 7 3 ) , little or n o i n f o r m a t i o n is available o n t h e effect of dietary m a n i p u l a t i o n on broiler p a r t yields. Arafa et al. ( 1 9 8 3 ) s h o w e d a positive correlation o n energy restriction as a means of reducing a b d o m i n a l fat pad in w h o l e broiler carcasses. Therefore, this s t u d y was c o n d u c t e d to d e t e r m i n e t h e effect of d i e t a r y energy restriction during t h e finishing period o n yield and quality of broiler p a r t s .

MATERIALS AND METHODS Seven-hundred sixty-eight C o b b color-sexed broilers were used in t w o trials. Chicks at 1 day of age were placed i n t o 2 4 pens (12 pens of males and 12 pens of females) w i t h 16 b i r d s / pen. T h e y were grown on commercial-type starter a n d finisher diets. During t h e last 12 days of t h e growing period (Days 4 0 to 51), four d i e t a r y t r e a t m e n t s were used (Table 1) to restrict energy i n t a k e b y restricting t h e a m o u n t of feed t h a t t h e birds were allowed t o c o n s u m e each day (Arafa et al, 1 9 8 3 ) .

1914

Diet

1 was a broiler

corn-soybean

meal

1915

ENERGY RESTRICTION AND YIELD

TABLE 1. Composition of the experimental diets used during the last 12 days of the growing period Dietary treatment Ingredient 1

1

2

4

3

- (%) Yellow corn Soybean meal, 49% protein Animal fat Dicalcium phosphate, 22.5% Ca, 18% P Limestone Microingredients Salt DL-Methionine Protein, % ME,2 kcal/kg

63.89 30.92 2.00 1.20 1.02 .50 .40 .07 20.36 3102

61.76 32.19 2.69 1.31 1.04 .50 .43 .09 20.19 3102

58.72 34.38 3.36 1.44 1.05 .50 .45 .10 21.99 3102

55.69 36.56 4.03 1.57 1.06 .50 .47 .12 22.79 5102

1

Ingredients supplied per kilogram of diet: vitamin A, 6600 IU; vitamin D3, 2200 ICU; menadione dimethylpyrimidinol bisulfite, 2.2 mg; riboflavin, 4.4 mg; pantothenic acid, 13.2 nig; niacin, 39.6 mg; choline chloride, 449.4 mg; vitamin B, 2 , 22 ug; ethoxyquin, .0125%; manganese, 60 mg; iron, 50 mg; copper, 6 mg; cobalt, .198 mg; zinc, 35 mg. 2 ME = Metabolizable energy.

finisher diet (Table 1). All nutrients were increased in the other three diets with the exception of energy so that each diet contained 5% more of all nutrients except energy than the proceeding diet. This resulted in Diet 4 having a 15% greater nutrient density than Diet 1. The amount of feed that the birds were allowed to consume on Diets 2 , 3 , and 4 was restricted to 95, 90, and 85% respectively, of the amount of feed that these birds had consumed prior to the start of the experiment. The birds on restricted diets were given their feed allocation at 0900 hr daily. Due to increased feed consumption as the birds aged, the restriction was actually greater than indicated earlier. The actual restriction was calculated from feed intake during the experimental period as compared to the control (Table 2). The experiment was conducted for a 12-day period. Birds were then processed by conventional methods and a 1 C overnight chill in slush ice was used. After chilling, carcasses were suspended from the evisceration line and allowed to drain 15 min prior to weighing (chilled, ready-to-cook weight). Individual chilled-carcass weight did not include giblet nor neck. The coccygeal region (tail) was removed and the anterior half of each carcass was separated from the posterior half at a point between the seventh thoracic and the first lumbar-sacral

vertebra before the cuts were made (Hudspeth et ah, 1973). The wings were removed by a cut through the shoulder joint at the proximal end of the humerus. The thigh-drumstick portion was obtained by cutting through the joint between the femur and the ilium bone of the pelvic girdle; included in this portion was the loin or "oyster" muscle, the leg portion off with the thigh. The drumstick was then separated from the thigh by a cut through the joint formed by the femur, fibula, and tibia. The breast and the back portions were obtained by

TABLE 2. Ready to cook (RTC) weight of broiler carcasses with dietary restriction during the last 12 days of the growing period Carcass weight Female

Dietary restriction

Male

(%) 0 15 19 23 Average weight

1213a 1180ab 1167b 1143c

990a 95oab 945 b 918c

1175

953

-(g)-

' 'cMeans within a column not followed by the same common superscript are significantly different (P«.05).

1916

ARAFA ET AL.

cutting on each side of the vertebral column beginning at the midpoint of the sternal ribs until the breast portion was completely severed from the back portion (Hudspeth etal, 1973). This cutting procedure resulted in two wings, two drumsticks, two thighs, one breast and one back. Parts from each carcass were weighed individually and their relative distribution was expressed as a percentage of the respective chilled ready-to-cook (RTC) carcass weight. Parts from each carcass were then vacuum packaged in Cry-O-Vac® bags, heatshrunk, and stored at —23 C until further analysis. The parts from eight carcasses from each replication of males or females were thawed in a walk-in cooler at 2 C/48 hr. Parts were then cooked in an oven at 177 C to an end point internal temperature of 85 C on a special rack designed to allow for the separation of the drip. Cooked parts were allowed to cool for 2 hr 2 C in a walk-in-type cooler before their cooked weights were recorded. Cooked yield was determined as follows: (part wt after cooking/ part wt before cooking) X 100. Samples for proximate analysis were obtained by combining all similar parts from four carcasses of the same sex. This resulted in six composited samples per dietary treatment of the same cut-up broiler part. Composited parts were ground through .95-cm plate. After thorough hand mixing, these composite samples were again ground using a .32-cm plate to help ensure sample uniformity. Proximate chemical analysis for fat and moisture were made (in triplicate) according to methods described by the Association of Official Analytical Chemists (AOAC, 1970). Similar parts from another four carcasses were kept in a cooler at 2 C for 24 hr before they were used for determination of organoleptic characteristics. Thirty-two taste panel sessions in the two trials were conducted using untrained taste panelists. At least 16 panelists were used in each evaluation session. Organoleptic evaluations were made using a 5-point descriptive hedonic scale (1 = very undesirable chicken flavor to 5 for very desirable chicken flavor), tenderness (1 = very tough to 5 = very tender), and juiciness (1 = very dry to 5 = very juicy). Samples for organoleptic evaluations were prepared according to methods described by Arafa and Chen (1976). Data were analyzed using analysis of variance procedures described by Steel and Torrie

(1980). Significant differences between treatment means were determined using Duncan's New Multiple Range Test (Steel and Torrie, 1980). As there was no significant trial x treatment interaction, data were pooled. RESULTS AND DISCUSSION

Dietary energy restriction during the final 12 days of the finishing period resulted in a reduction of the RTC weight of both male and female broiler carcasses (Table 2). These results confirm previous reports by Arafa et al. (1983) who reported that reducing energy intake by feed restriction during the last 10 days of the growing period resulted in a significant reduction in carcass weight as well as a reduction in the percent fat pad. In the present study with a 15% restriction of dietary energy, the differences in RTC carcass weight, as compared with the control, were not statistically significant (33 g and 31 g for male and female, respectively). However, when the dietary restriction was increased to 19%, the reduction in the RTC weight became statistically significant (P<.05) 46 g and 45 g for male and female, respectively, (Table 2). Increasing the dietary energy restriction to 23% resulted in a further significant reduction in the RTC weight for both sexes (70 g and 72 g for male and female, respectively). Restricting dietary intake during the last 12 days of the growing period changed the percent distribution of the parts (Table 3). The male breast proportion was significantly increased as a result of the dietary restriction at the 15% level (30.38 vs. 31.30). The proportions of the back part and wings were decreased. The drumstick portion showed a similar trend to that observed for the breast. Further restriction above the 15% level did not yield any significant effect on the percent distribution of the cut-up parts. Energy restriction for females resulted in similar changes on the percentage of breast and back parts that were observed with males; however, no significant differences were observed for the thighs, drumstick, or wing portions (Table 3). Regardless of the treatment involved, the female carcasses yielded a higher percentage distribution for the breast and wings portions and less percentage distribution for back, thigh, and drumstick parts. These data agree with and confirm the report by Swanson et al, (1964)

ENERGY RESTRICTION AND YIELD

1917

TABLE 3. Percentage1 distribution of breast, back, thighs, drumsticks, and wings from ready-to-cook broiler carcasses with dietary energy restriction during the last 12 days of the growing period

(RTC)

Cut-up broiler parts Dietary restriction

Breast

Back

Thighs

Drumsticks

Wings

Male 0 15 19 23 Average

30.38C 31.30 b 31.26 b 30.68 b c 30.91

20.31 a 19.45 b 19.38 b 19.50 b 19.66

18.82 a 18.55 a 18.63 a 18.39 a 18.60

16.67 a b 17.40 a 17.20 a 17.20 a 17.12

13.70 a b 13.30 b 13.52 b 14.22 a 13.69

Female 0 15 19 23 Average

31.11 b 32.73 a 32.18 a 31.87 a b 31.97

20.15 a 19.10 b 19.02 b 19.08 b 19.34

18.71 a 18.10 a 18.26 a 18.38 a 18.36

15.86 c 15.86 c 16.16 b c 16.29 b 16.04

14.28 a 14.21 a 14.37 a 14.37 a 14.31

a

' ' c Means within a column not followed by the same common superscript are significantly different (P<.05).

1

Each value represents a mean of at least 48 total observations.

Restriction above 15% did n o t result in any appreciable reduction of t h e fat c o n t e n t of t h e broiler parts. Energy restriction at t h e 1 5 % level h a d m o r e influence o n fat r e d u c t i o n in broiler parts o b t a i n e d from t h e female carcasses as c o m p a r e d with those o b t a i n e d from male carcasses (Table 4 ) . A reduction of fat c o n t e n t

and Moran and Orr ( 1 9 6 9 ) w h o observed t h e female broiler t o have a larger p r o p o r t i o n of breast b u t smaller percentage of drumstick t h a n t h e male. Dietary energy restriction during t h e final 12 days of t h e growing period significantly reduced fat in all broiler cut-up parts (Table 4 ) .

TABLE 4. Percent1 fat content of breast, back, thighs, drumsticks, and wings from ready-to-cook broiler carcasses with dietary energy restriction during the last 12 days of the growing period

(RTC)

Cut-up broiler parts Dietary restriction

Breast

Back

Thighs

Drumsticks

Wings

(/u)

Male 0 15 19 23 Average

10.98 a b 9.05 c 9.01 c 9.36C 9.60

18.64 a 16.69 b 15.56 b c 15.21 c 16.53

16.52 b 15.46 c 14.68 c 15.47 c 15.53

11.63 b 9.93 c 9.04 c d 8.92 d 9.88

14.88 a 13.24 b 13.08 b 13.14 b 13.58

Female 0 15 19 23 Average

11.44 a 9.18 c 10.60 b 10.75 a b 10.49

19.40 a 16.93 b 15.66 b c 15.35 c 16.84

17.59 a 16.59 b 16.58 b 16.28 b 16.76

13.64 a 11.30 b 10.79 b c 11.37 b 11.78

14.77 a 13.49° 13.99 a b 13.87 b 14.03

' ' ' Means within a column not followed by the same common superscript are significantly different (P<.05). 1

Each value represents a mean of at least 24 triplicate observations.

ARAFA ET AL.

1918

of 1.93% for the breast, 1.95% for the back, and 1.70% for the drumstick from the male carcasses were obtained when the dietary energy was restricted at the 15% level. The values obtained for the same parts at the same dietary restriction level from the female carcasses were 2.26, 2.47, and 2.34%, respectively. Regardless of the dietary treatment involved in this study, all cut-up broiler parts obtained from female carcasses had higher fat content as compared with similar parts obtained from the male carcasses (Table 4). As expected, and contrary to the observation made with the percent fat content, dietary energy restriction increased the percent moisture of cut-up broiler parts from both male and female carcasses (Table 5). Again, it was observed that increasing the dietary restriction level above 15% did not result in a significant increase in the moisture content of the different cut-up parts. Regardless of the dietary treatment involved, parts obtained from male carcasses had a higher percent moisture content when compared with those parts obtained from female carcasses. A significant improvement in percent cook yield of breast, back, thighs, drumstick, and wing parts from male carcasses, and breast, back, drumstick, and wings parts from female carcasses, was obtained when the diet available to the bird during the final 12 days of the finishing period was restricted (Table 6). The

same improvement trend in cook yield was observed for the thigh parts obtained from the female carcass; however, it was not statistically significant. Breast, thighs, drumsticks, and wing parts from male carcasses had a higher cook yield when compared with similar parts obtained from the female counterpart. An opposite trend was observed from the back part. A 15% dietary energy restriction resulted in an increase of 1.63, 1.13, .14, .95, and 1.68% from male breast, back thighs, drumstick, and wing portions, respectively. The corresponding values for the same parts from the female carcasses were 1.88, 1.81, .34, 1.0, and 1.62%. These data indicate that energy restriction exerted a more pronounced effect on the yield of the thigh and drumstick parts. Dietary restriction at the 15% level did not significantly affect flavor, tenderness, or juiciness scores from either dark or light broiler meat (Table 7). Increasing the dietary restriction level to 19% resulted in a similar trend except for juiciness, where a significantly lower score was observed indicating an adverse effect on juiciness of the light meat at that level of dietary restriction. Increasing the dietary restriction level to 23% resulted in a similar adverse effect on juiciness score in the dark meat (Table 7). When this dietary restriction program was used during the finishing period, fat pad weight

TABLE 5. Percent* moisture content of breast, back, thighs, drumsticks, and wings from ready-to-cook (RTC) broiler carcasses with dietary energy restriction during the last 12 days of the growing period Cut-up broiler parts Dietary restriction

Breast

Back

Thighs

Drumsticks

Wings

V'O)

Male 0 15 19 23 Average

66.80 68.57 a 68.73 a 68.67 a 68.19

63.46 a b 64.81 a 64.91 a 64.85 a 64.51

61.67 b 64.31 a 64.65 a 64.22 a 63.71

66.54 b 67.88 a 67.98 a 67.27 a 67.42

63.58 a b 64.43 a 64.00 a 64.05 a 64.02

Female 0 15 19 23 Average

65.30 c 68.55 a 68.17 a 67.97 a b 67.49

61.40 c 62.94 b 63.55 a b 63.42 a b 62.83

60.12 c 63.59 a b 63.85 a b 63.14 a b 62.68

65.08 c 67.04 a b 66.39 b 66.36 b 66.22

61.74 c 63.38b 63.97 a 63.59 a b 63.17

b

a,b,c Means within a column not followed by the same common superscript are significantly different (P<.05). 1 Each value represents a mean of at least 24 triplicate observations.

ENERGY RESTRICTION AND YIELD

1919

TABLE 6. Percent1 cooked yield2 of breast, back, thighs, drumsticks, and wings from ready-to-cook broiler carcasses with dietary energy restriction during the last 12 days of the growing period

(RTC)

Cut-up broiler parts Dietary restriction

Breast

Back

Thighs

Drumsticks

Wings

(%) Male 0 15 19 23 Average

79.4a 81.03D 82.74c 84.40 d 81.89

65.06a 66.19b 66.91° 67.66° 66.46

75.99b 76.13D 77.11c 78.82d 77.01

76.37° 77.32C 77.95c 78.40 d 77.51

72.22c 73.9d 74.12 d 74.00 d 73.56

Female 0 15 19 23 Average

78.62 a 80.50 b 81.37° 81.74 DC 80.56

64.72 a 66.53° 67.20° 70.31 c 67.91

73.9 a 74.24 a 74.57 a 75.08 a b 74.45

74.48 a 75.48 a 75.37 a 76.77° 75.53

69.10 a 70.72 b 70.92° 71.07° 70.45

' ' ' Means within a column not followed by the same common superscript are significantly different (P<.05). 1

Each value represents a mean of at least 24 triplicate observations.

2

Cooked yield = (part wt after cooking/part wt before cooking) X 100.

of t h e broiler was decreased (Arafa, et al., 1 9 8 3 ) . A l t h o u g h fat pad was reduced, this did n o t influence carcass yield. This p r o c e d u r e

TABLE 7. Flavor, tenderness, and juiciness scores of cooked light and dark meat from broilers with restriction during the last 12 days of the growing period Organoleptic scores Dietary restriction 1 Flavor

Tenderness

Juiciness

(%) Dark meat 0 15 19 23 Average

2.88 a b 2.78° 2.82° 2.71° 2.79

2.89° 2.76° 2.78° 2.90° 2.83

2.86 b 2.71 b 2.50 b c 2.42C 2.62

Light meat 0 15 19 23 Average

3.01 a 3.21 a 2.96 a ° 2.70° 2.97

3.07 a 3.07 a 3.03 a 3.09 a 3.07

2.71 b 2.70 b 2.46 c 2.16 d 2.62

' ' ' Means within a column not followed by the same common superscript are significantly different (P<.05). 1 Possible scores ranged from 1 to 5 with higher scores indicating higher desirability.

resulted in a significant decrease in t h e a m o u n t of feed required t o p r o d u c e a gram of cooked carcass. A l m o s t all previous research w o r k t h a t has a t t e m p t e d t o reduce t h e a m o u n t of abd o m i n a l fat pad in broilers resulted in an increase in t h e a m o u n t of feed required t o p r o d u c e a unit of edible m e a t . It is evident from t h e results r e p o r t e d here and earlier (Arafa et al., 1983) t h a t as t h e a b d o m i n a l fat pad was reduced, t h e a m o u n t of feed required t o p r o d u c e a u n i t of cooked ready-to-eat carcass was also reduced. F u r t h e r m o r e , it is c o n c l u d e d from this r e p o r t t h a t t h e d i e t a r y energy restriction at t h e 15 and 19% level could have a beneficial effect on t h e c o o k e d yield of t h e different broiler parts. Such restriction altered t h e percentage distribution of t h e parts of t h e R T C broiler carcasses and decreased t h e fat c o n t e n t of t h e broiler parts, while having n o significant effect on t h e organoleptic characteristics of b o t h light and dark m e a t . However, it is evident from this research t h a t dietary energy restriction at t h e 2 3 % level is n o t desirable, because it had an adverse effect o n t h e organoleptic score and did n o t s h o w a beneficial influence on m o s t of t h e criteria tested. Adding this information t o t h e finding r e p o r t e d earlier b y Arafa et al. ( 1 9 8 3 ) w h o f o u n d t h a t increasing feed restriction to 2 4 % resulted in a significant increase in feed-to-gain

1920

ARAFA ET AL.

ratio, it is therefore concluded t h a t restriction a t this level will n o t be desirable and is n o t reco m m e n d e d for practical application.

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Hudspeth, J. P., C. E. Lyon, B. G. Lyon, and A. J. Mercuri, 1973. Weights of broiler parts as related to carcass weights and type of cut. J. Food Sci. 38:145-150. Leeson, S., and J. D. Summers, 1980. Production and carcass characteristics of the broiler chickens. Poultry Sci. 59:786-798. Moran, E. T., Jr., and H. L. Orr, 1969. A characterization of the chicken broiler as a function of sex and age: live performance, processing, grade and cooking yield. Food Technol. 2 3 : 1 0 7 7 1084. Moran, E. T., Jr., and H. L. Orr, 1970. Influence of strain on the yield of commercial parts from the broiler chicken carcass. Poultry Sci. 49:725-729. National Broiler Council, 1981. Survey of Broiler Industry Merchandising Practices. Washington, DC. Smidt, M. J., S. D. Formica, and J. C. Fritz, 1964. Effect of fasting prior to slaughter on yield of broilers. Poultry Sci. 43:931-934. Steel, R.G.D., and J. H. Torrie, 1980. Principles and Procedures of Statistics. McGraw-Hill Book Co., New York, NY. Swanson, M. H., C. W. Carlson, and J. L. Fry, 1964. Factors affecting poultry meat yield. Minn. Agric. Exp. Sta. Bull. 476. Walter, R. E., K. N. May, and P. D. Rodgers, 1963. Relations of weights and sizes of broiler parts to carcass weight. Mark. Res. Rep. #604. Agric. Exp. Sta., Univ. Georgia, Athens, GA.