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Fat Deposition in Broilers: Effect of Dietary Energy to Protein Balance, and Early Life Caloric Restriction on Productive Performance and Abdominal Fat Pad Size
Fat Deposition in Broilers: Effect of Dietary Energy to Protein Balance, and Early Life Caloric Restriction on Productive Performance and Abdominal Fat Pad Size L.
GRIFFITHS, 1 S. LEESON AND J. D .
SUMMERS
Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario Canada (Received for publication August 20, 1976)
POULTRY SCIENCE 56: 638-646,
INTRODUCTION
I
N recent years there has been an increased public a w a r e n e s s of t h e possible health p r o b l e m s associated with an excessive consumption of fat. In broiler c h i c k e n s , while s u b c u t a n e o u s fat is associated with finish and eating qualities, that fat located in the a b dominal and visceral areas is considered a w a s t e p r o d u c t to both processor and consumer. T h e size of adipose d e p o t areas d e p e n d s o n t h e n u m b e r and size of their constituent cells and is thus influenced by factors affecting either cell division a n d / o r cell enlargement. In most m a m m a l s , including m a n , stages in t h e p r o c e s s of fat depot development are related to age. T h u s , in early life, increased cell n u m b e r s rather t h a n cell size is the p r e d o m i n a n t factor affecting the size of adipose d e p o t a r e a s , while this trend reverses with a d v a n c e m e n t in age to the stage w h e n increased cell size is the sole c a u s e of increased adipose depot size in the sexually m a t u r e animal (Hirsch and H a n , 1969; Hirsch
1. Present address: Agricultural Division, Maritime Co-operative Services, Nova Scotia, Canada.
1977
a n d Knittle, 1970; J o h n s o n et al., 1971; G r e e n w o o d and H i r s c h , 1974). H u m a n nutrition studies h a v e also shown that a p e r m a n e n t reduction in the size of fat depot areas can result only from a decrease in adipose cell n u m b e r s (Hirsch and Knittle, 1970), while work with rats has shown that this can be achieved through caloric restriction early in life (Knittle and H i r s c h , 1968; Oscai et al., 1972). Since c o m p a r a b l e studies with broiler chickens have not been reported, two experim e n t s were u n d e r t a k e n t o study t h e effect of early nutrition and caloric restriction on fat deposition in t h e broiler c h i c k e n , a n d in particular the formation of the abdominal fat pads.
MATERIALS AND METHODS Experiment 1. This experiment w a s designed to study the effect of dietary protein and energy level on abdominal fat-pad d e p o sition during t h e 4 - 8 w e e k finishing period. D a y old male broiler chicks were reared to 4 w e e k s of age in raised wire floor P e t e r s i m e b a t t e r y b r o o d e r s , being offered a commercial broiler starter diet ad libitum throughout this
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ABSTRACT The effect of dietary energy to protein balance, and early life caloric restriction on abdominal fat pad development in the male broiler chicken was studied. Dietary energy concentration had no significant (P s 0.05) effect on abdominal fat pad size, although decreasing the calorie.protein ratio of the diet resulted in a significant (P £ 0.05) reduction in the proportion of this tissue in the body. Reducing the calorie: protein ratio from a level considered optimum, by the addition of feather meal to the diet was equally as effective in reducing fat pad size as was the addition of a higher quality protein as exemplified by soybean meal plus DL-methione. Restricting the caloric intake of broilers in the 0-3 week growing period by the use of an ad libitum fed low energy diet (2233 kcal. M.E./kg.) had no significant (P s 0.05) effect on fat pad development. It is suggested that the degree of calorie restriction was not of sufficient magnitude to influence adipocyte hyperplasia. These results are discussed in relation to findings with other avian and mammalian species.
FAT DEPOSITION IN BROILERS
aC:Pratioof 159.5, considered to be optimum for growth and feed efficiency (Bartov et al., 1974), was employed for each energy level (diets 2 and6, Table 1). Calorie:protein ratio's of 187.6 and 138.7 (diets 1 and 5, 3 and 6 respectively, Table 1) were also utilized, and were considered to be high and low respectively in terms of optimum growth and feed efficiency. Diets were formulated such that methionine, the first limiting amino acid, represented an equal proportion of dietary crude protein. In the case of diets 4 and 8 however, (Table
TABLE 1.—Percentage composition Diet no. Ground yellow corn Cornstarch Alpha floe Stabilized animal tallow Soybean meal (49% protein) Feather meal Limestone Dicalcium phosphate (20% P) Iodized salt (0.15% KI) Vitamin mix 1 Mineral mix 2 DL-methionine L-lysineHCl Calculated analysis Metabolizable energy (kcal./kg.) Crude protein (%) Calorie:protein (C:P) ratio Methionine (g. /16 g.N) Lysine (g./16 g.N) Available phosphorus (%) Calcium (%)
of diets (experiment 1)
1 47.00 8.41 10.67
2 47.00 4.42 8.96
47.00 0.43 7.24
47.00 1.71 8.38
47.00 12.76 3.93
47.00 8.48 2.09
47.00 4.20 0.24
47.00 5.57 1.47
6.50
6.50
6.50
6.50
6.50
6.50
6.50
6.50
23.67 — 1.25
29.37 — 1.25
35.08 — 1.25
29.37 3.29 1.25
26.06 — 1.25
32.18 — 1.25
38.31 — 1.25
32.18 3.53 1.25
1.50
1.50
1.50
1.50
1.50
1.50
1.50
1.50
0.25 0.50 0.25 0.098 0.020
0.25 0.50 0.25 0.116
0.25 0.50 0.25 0.135
0.25 0.50 0.25 0.116
0.25 0.50 0.25 0.127 _
0.25 0.50 0.25 0.148 _
0.25 0.50 0.25 0.148 _
0.25 0.50 0.25 0.127 _
_
_
_
2970 15.83
1970 18.62
2970 21.42
2970 21.42
3190 17.00
3190 20.00
3190 23.0
3190 23.00
187.6
159.5
138.7
138.7
187.6
159.5
138.7
138.7
2.26 5.50
2.23 5.55
2.22 5.67
2.03 5.08
2.25 5.50
2.23 5.62
2.22 5.73
2.03 5.15
0.44 0.84
0.45 0.85
0.46 0.87
0.47 0.86
0.44 0.85
0.46 0.86
0.47 0.87
0.48 0.87
'Supplies per kg. of diet: vit. A, 8,000 I.U.; vit. D 3 , 1600 I.U.: vit. E, 11 mg.; riboflavin, 9 mg.; pantothenic acid, 11 mg.; vit. B , 2 , 13 (j,g.; niacin, 26 mg.; choline, 900 mg.; vit. K, 1.5 mg.; folic acid, 1.5 mg.; biotin, 1.5 mg. 2 Supplies per kg. of diet: manganese, 55 mg.; selenium, 0.1 mg.; zinc, 50 mg.; copper, 5 mg.; iron, 30 mg.
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period. At this age all birds were weighed, wingbanded and weight sorted such that 8 chicks of mean body weight were allotted to each raised wire floor pen housed in a windowless, temperature controlled room. A f actorially arranged randomized block design involving two levels of dietary energy (2970 and 3190 kcal. M.E./kg.) and four calorie:protein (C:P) ratios (188,160,139,139) were used, with protein sources varying for the C:P ratios of 139. The composition and calculated analysis of these diets are shown in Table 1. Diets were formulated such that
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L. GRIFFITHS, S. LEESON AND J. D. SUMMERS
Experiment 2. The effect of low energy starter diets on fat pad development was
studied in this experiment. Treatments consisted of feeding either a low energy or control starter diet from 0-4 weeks followed by a conventional finisher diet to 8 weeks of age. Male broiler chicks were used, with housing and management procedures being as described in Experiment 1. The composition and calculated analysis of these diets are shown in Table 2. Treatments 1, 2 and 3 involved feeding the low energy starter diet (2233 kcal. M.E./kg., Table 2) for the first 1,2 and 3 weeks of age respectively, followed by the control starter diet (Table 2) for the remainder of the 4 week starting period. With treatment 4, the control starter diet was fed from 0-4 weeks. All birds received the same finisher diet (Table 2) to 8 weeks of age. Eight replicates of 10 birds each were used during the starter period (0-4 weeks) while 5 replicates of 10 birds each were used during the finishing period (4-8 weeks). All diets were fed in crumbled form, and together with water were available ad libitum. Feed intake and body weight gains were recorded weekly during the 0-4 week starting period and as
TABLE 2.—Percentage composition of diets (experiment 2) Diet Ground yellow corn Oat meal Soybean meal (49% protein) Stabilized animal tallow Limestone Dicalcium phosphate (20% P) Iodized salt (0.015% KI) Vitamin mix' Mineral mix 2 DL-methionine Alpha floe Calculated analysis Metabolizable energy (kcal./kg.) Crude protein (%) Lysine (%) Methionine (%) Available phosphorus (%) Calcium (%) 12
See footnotes, Table 1.
Low energy starter
— 55.90 27.25
— 1.35 1.50 0.25 0.50 0.25
— 13.00 2233 20.10 1.10 0.30 0.43 0.94
Control starter 52.40
— 39.25 4.50 1.35 1.50 0.25 0.50 0.25 0.075
— 3087 24.0 1.36 0.46 0.43 0.91
Finisher diet 60.00
— 30.75 5.50 1.25 1.50 0.25 0.50 0.25 0.075
— 3200 20.5 1.10 0.41 0.42 0.86
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1) protein quality was not maintained. Thus, although diets 4 and 8 provided crude protein in excess of requirement (Bartov et at., 1974), this extra protein, as feather meal, was of poor amino acid balance, and allowed the comparison of effects of excess protein of good amino acid balance (diets 3 and 6, Table 1) on the parameters measured. Four replicates of 8 birds were used for each treatment, with the steam pelleted diets and water being available ad libitum. Birds were reared under constant white light. Feed intake and body weight gains were recorded to 8 weeks of age. At this time birds were exsanguinated, New York dressed and cooled in running water at 4° C. overnight. Carcasses were then eviscerated and abdominal fat pads disected and weighed. Adipose tissue considered to represent the abdominal fat pad is given in a previous report (Griffiths et al., 1977). Samples of complete abdominal fat pad were freeze-dried to ascertain moisture content.
641
FAT DEPOSITION IN BROILERS
single ishing minal in the
measurements for the 4-8 weeks finperiod. Carcass preparation and abdofat pad dissection were as described previous experiment.
RESULTS Experiment 1. Means of body weight gain, feed intake, caloric intake, feed:body weight gain ratio, and both abdominal fat pad weight and moisture content, are shown in Table 3. Both dietary energy level and C:P ratio failed to influence body weight gain. Feed intake and feed:body weight gain of birds fed the low energy diet was significantly (P =£ 0.05) greater than birds fed the higher energy diet. This increased feed intake and feed:body weight gain ratio was also noted for birds fed the diet providing the greatest C:P ratio, and was significantly (P < 0.05) greater than for birds fed the lower C:P ratios when the diets contained balanced levels of
TABLE 3.—Effect of energy level and calorie'.protein ratio on mean 4-8 week body weight gain, caloric intake, feed:body weight gain, abdominal fat pad size and abdominal fat pad moisture content
(gm.)
Feed intake (gm.)
Caloric intake (kcal., metabolizable energy
Metabolizable energy 2970 kcal. /kg. 3190kcal./kg.
1448a1 1454a
3503a 3268b
Calorieiprotein ratio 187.6 159.5 138.7 138.72
1451a 1463a 1440a 1450a
3503a 3352b 3296b 3389ab
4-8 week body weight gain Contrasts
Abdominal fat pad Feed: body weight gain
Weight (gm./lOO grams body weight)
Moisture
10,404a 10,425a
2.42a 2.25b
2.57a 2.55a
17.1 16.7
10,789a 10,324b 10,152b 10,466ab
2.41a 2.29b 2.29b 2.35ab
3.19a 2.61b 2.22c 2.22c
14.3 17.0 17.5 18.5
%
'Within each column and contrast values bearing the same letter are not significantly different (P2< 0.05). Describes diets #4 and #8 (Table 7), formulated to contain feather meal.
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Statistical Analysis. Analysis of variance was calculated on a pen average basis using the method outlined by Steel and Torrie (I960). Abdominal fat pad size and 8 week body weight were subjected to regression analysis on an individual bird basis within each treatment.
amino acids. Birds fed the lowest dietary C:P ratio and providing an imbalanced amino acid profile (through the addition of feathermeal, diets 4 and 8, Table 1) also exhibited an increased feed intake and feed:body weight gain ratio, although these values were not significantly (P =s 0.05) different from those recorded for any of the other dietary treatments (Table 3). Caloric intake followed the same trend as feed intake for the C:P ratio treatments, although it was not affected by dietary energy level (Table 3). Abdominal fat pad weight was not affected by dietary energy concentration, although decreasing dietary C:P ratios resulted in significant (P < 0.05) decreases in abdominal fat pad deposition. Lowering the C:P ratio by adding protein in the form of feathermeal was as effective in reducing abdominal fat pad deposition, as using the addition of a higher quality protein to the diet (diets 4 and 8 versus 3 and 7, respectively, Table 1). A comparison of the coefficients of variation for abdominal fat pad weight and 8 week body weight are shown in Table 4, indicating a greater variability in the former measurement. In an attempt to quantify the relationship between abdominal fat pad weight and body size, regression analysis utilizing linear, quadratic and cubic effects as sources of variation between these
642 TABLE 4.—Coefficient Metabolizable energy (kcal./kg.) Calorie:protein ratio Diet No. 1 Abdominal fat (gm. /100 gm. body weight) 8 week body weight Number of observations
L. GRIFFITHS, S. LEESON AND J. D. SUMMERS
of variation (%) for abdominal fat pad weight and eight week body weight
187.6
159.5
1
2
21.4 5.0 28
297C1 138.7
319C1 138.7
138.7
187.6
159.5
3
4
5
6
7
8
30.7 5.9
45.6 9.6
26.6 6.5
24.2 7.2
32.9 7.2
33.7 5.9
35.5 6.1
30
31
28
27
31
26
29
138.7
'See Table 1.
Experiment 2. Weekly means for weight gain, feed intake, caloric intake and feed:body weight gain ratios's to 4 weeks of age are presented in Table 6. Body weight gains of birds fed the very low energy starter diet from 0-1 or 0-2 weeks of age were not significantly (P < 0.05) different at any time from 0-4 weeks, to those of birds fed the control starter diet throughout this period (treatments 1 and 2 versus 4, Table 6). Only when the low energy starter diet was fed for the first 3 weeks of the starter period was body weight gain significantly (P s 0.05) depressed, (treatment 3 versus 4, Table 6)
with this reduction in weight gain at 3 weeks of age being corrected by the introduction of the control starter diet during the last week of the starting period. In attempting to compensate for the low energy starter diet, birds provided with the low energy starter diets in weeks 2 and 3, consumed significantly more feed than control fed birds (treatments 2 and 3, and treatment 3 during the second and third weeks respectively, Table 6), although these increases in feed intake still resulted in a reduced caloric intake (Table 6). Feedrbody weight gain followed the same pattern as feed intake only during the first two weeks of growth. During the third week of the starting period, birds still receiving the low-energy diet (treatment 3) showed a significantly (P < 0.05) increased feed:body weight gain ratio compared to the control fed birds (treatment 4) while the converse
TABLE 5.—Error degrees of freedom, correlation coefficients and mean square values of regression of abdominal fat (gm./lOO gm. of body weight) on eight week body weight by energy level and calorie:protein ratio Metabolizable energy (kcal./kg)
2970
3190
Calorie:protein ratio Error degrees of freedom Correlation coefficient
187.6
159.5
138.7
138.7
187.6
159.5
138.7
138.7
25 0.119
27 0.332
28 0.438
25 0.448
24 0.278
28 0.286
23 0.136
29 0.526
Source of variation Linear Quadratic Cubic Residual
0.179 0.291 0.071 1.486
2.097 1.171 1.139 0.542
5.21" 1.00 0.606 0.724
1.860 1.274 1.666 0.639
0.274 0.005 0.067 0.632
4.517" 0.749 0.191 0.109
Significant at P s 0.05.
Mean square values 2.03" 1.242 0.586 0.969 0.084 0.194 0.297 0.572
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two parameters was undertaken. A significant (P < 0.05) linear effect was shown only for the lowest dietary C:P ratio; mean square values for analysis of regression and correlation coefficients are presented in Table 5.
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F A T DEPOSITION IN BROILERS
TABLE 6.—Mean weight gain, feed intake, caloric intake and feed:body weight gain ratios for broiler cockerels fed a low energy starter ration for varying lengths of time 0-1 week
1 2 3 4
120.7a 123.2a 116.4a 115.9a
1 2 3 4
270.3a 275.9a 260.6a 356.8b
1 2 3 4
1.66a 1.58a 1.54a 1.51a
1-2 weeks 2-3 weeks Weight gain (gm.) 131.6a 226.4ab 123.9a 237.6c 123.0a 220.2a 126.4a 230.3bc Feed intake (gm.) 197.8a 377.9a 253.4b 380.6a 248.8b 484.8b 206.0a 395.1a Caloric intake (kcal.) 609.1a 1163.9a 567.7b 1172.2a 557.3b 1085.8b 634.4a 1216.9a Feed:gain ratio 1.50a 1.67ab 2.05b 1.60a 2.00b 2.21c 1.62a 1.72b
73.1a2 78.6a 75.6a 77.0a
3-4 weeks 272.9a 288.8a 276.1a 279.3a 458.9a 477.4a 465.0a 465.3a 1413a 1470a 1432a 1433a 1.68a 1.65a 1.69a 1.67a
1 Treatments 1—Fed low energy starter 1 week, regular starter 3 weeks \ 2.—Fed low energy starter 2 weeks, regular starter 2 weeks V see diets Table 2. 3—Fed low energy starter 3 weeks, regular starter 1 week j 4.—Fed regular starter 0-4 weeks. 2 Within each contrast and for each age classification, means bearing the same letter are not significantly different (P < 0.05).
TABLE 7.—Mean 8 week body weight, 4-8 week body weight gain, 4-8 week feed intake, 4-8 week feedigain ratio and abdominal fat pad weight (gm./lOO gm. body weight) for birds fed low energy starter diets for varying lengths of time Treatments' 8 week body weight (gm.) 4-8 week body weight gain (gm.) 4-8 week feed intake (gm.) 4-8 week feed:body weight gain ratio Abdominal fat pad size (grams/100 gm. body weight)
1 1980a2 1226a 2877a 2.35a
2
3
2070a 1310a 3058a 2.34a
2006a 1270a 2947a 2.32a
2023a 1258a 2882a 2.29a
1.87a
2.05a
1.86a
1.93a
•Treatments as shown in Table 6. Values within each parameter bearing the same letter are not significantly different (P : ; 0.05).
2
TABLE 8.—Coefficient
of variation (%) for abdominal fat pad weight and eight week body weight
Treatment'
1
2
3
4
Average of all treatments
Abdominal fat (grams/100 gms. body weight) 8 week body weight Observations
35.2 10.4 45
43.6 7.4 45
38.7 9.6 45
43.5 9.2 45
40.3 9.2 45
1
Treatments as shown in Table 6.
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Age of bird Treatments' 1 2 3 4
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L. GRIFFITHS, S. LEESON AND J. D. SUMMERS
DISCUSSION That neither dietary energy level nor C:P ratio significantly (P < 0.05) influenced 4-8 week body weight gain in experiment 1 (Table 3), indicates the ability of the broiler chicken to adapt to varying dietary regimes. Birds adapted to energy concentration by adjusting their feed intake such that caloric intake remained constant. These results support the premise that broiler chickens eat to satisfy their energy requirement. That abdominal fat pad size was not influenced by dietary energy concentration is not in agreement with findings on total carcass fat (Gooch et al., 1971; Kubena et al, 1972; Farrell, 1974). Since these latter workers generally increased the energy level of their diets by the incorporation of fat while C:P ratios were held constant, compared with the substitution of corn starch for cellulose (alpha floe) in these studies, it is tempting to speculate on the relationship of dietary fat and carcass fat deposition. However, Mersman et al. (1976) working with swine reported that the rate of lipogenesis
was not affected by the fat content of the diet, and previous work from our laboratory (Griffiths et al., 1977) indicated that both visceral and carcass fat in the male broiler chicken were not influenced by dietary fat inclusion. Alternatively if one accepts an 'extra caloric' effect of dietary fat (Jensen et al., 1970; Sell et al., 1976) these same workers may have underestimated the energy value of fat, thus inadvertantly increasing the C:P ratio of the diet, a phenomenon known to favour increased carcass fat deposition (Donaldson et al., 1956; Summers et al., 1965; Bartov et al., 1974). In this work, decreasing the C:P ratio of the diet resulted in a decreased quantity of abdominal fat (Table 3). Lowering the C :P ratio from a level considered optimum (159.5 to 138.7) by the addition of feather meal to the diet, was equally as effective in lowering abdominal fat pad size as was the addition of higher quality protein, in terms of amino acid balance, as provided by soybean meal plus DL-methionine (Diet 3 vs. 4 and 7 vs. 8 Tables 1 and 3). Hence if a leaner carcass is desired from birds already being fed a diet of optimum C:P ratio, the addition of a poor quality protein such as feather meal would be as effective as the addition of any higher quality protein. The increased feed intake noted for birds fed diets providing the highest C:P ratio (Table 3) suggests that birds were eating in an attempt to satisfy a protein requirement, while the concomitant increased caloric intake contributed to increased abdominal fat pad deposition. Similar findings were reported by Bartov et al. (1974) in terms of skin fat analysis. Since experiment 1 indicates that the amount of carcass fat as exemplified by abdominal fat pad size is affected by the level of dietary protein (Table 3), a C:P ratio which is optimum for feed efficiency and carcass finish at one level of dietary energy, may not be optimum at alternative levels. The quantity of abdominal fat recorded in these
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was true for those birds that had received the low energy diet only during the first one or two weeks of growth; (treatments 1 and 2, respectively; this latter effect was significant (P < 0.05) for treatment 2. Dietary treatment had no significant (P £ 0.05) effect on any of the parameters measured during the 4th week of the starting period (Table 6). The starting diet treatments had no significant (P £ 0.05) effect on either 8 week body weight, 4-8 week weight gain, feed intake or feed:body weight gain ratio, or abdominal fat pad size (Table 7). The variation in abdominal fat pad size and 8 week body weight as described by coefficient of variation, are presented in Table 8. Regression analysis failed to indicate any significant (P < 0.05) linear, quadratic or cubic effects between abdominal fat pad weight and 8 week body weight.
F A T DEPOSITION IN BROILERS
low energy starter diet, abdominal fat pad size at 8 weeks of age was not affected (Table 7). It is possible that the degree of caloric restriction was not of sufficient magnitude to retard adipocyte hyperplasia or that if such an effect did occur that it was nullified by adipocyte hypertrophy when a nutritionally adequate finishing diet (Table 2) was offered during the 4-8 week growing period. Alternatively caloric restriction in early life may not affect avian adipocyte development. That body weight gain to 8 weeks of life was not adversely affected by 0-3 week caloric restriction, supports the premise that the degree of restriction was not severe enough, since comparable studies with rats invariably indicate a permanent reduction in mature body weight (Knittle and Hirsch, 1968; Oscai et al., 1972). Pfaff and Austic (1974) and Austic and Pfaff (1975) attempted to reduce adipose depot areas in leghorn chicks during the growing phase by caloric restriction. Although both low energy and high protein diets resulted in reduced abdominal fat pad size from 0-20 weeks of age, this difference had disappeared by 48 weeks of age again suggesting that caloric restriction was not severe enough. It is possible that protein, as well as caloric restriction should be considered, since it is well known that in situations of caloric deficiency, protein will be extensively utilized as an energy source. That caloric restriction or post-hatch starvation can affect broiler carcass fat content was recently shown by Moran (1976), although results from the present study suggest that ad libitum feeding of low energy diets does not represent a suitable method for controlling abdominal fat pad size. If work conducted with the duck can be applied to the broiler chicken, then perhaps caloric restriction at times other than immediate post hatch should be considered, since Evans (1972) showed that inguinal, subcutaneous and peritoneal depots in the domestic duck are, respectively, early, intermediate and late
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experiments (Tables 3 and 7) was much greater than previously reported (Griffiths et al., 1976) and is more in agreement with values reported by Deaton et al. (1974) using commercial broiler diets. Variation in abdominal fat pad weights as measured by coefficient of variation was high (Tables 4 and 8), and in agreement with values reported by Deaton et al. (1974) and Griffiths et al. (1977). By restricting caloric intake of broilers during early life (0-3 weeks) it was hypothesized that a permanent reduction in fat cell numbers would occur, leading to a reduction in the size of the adipose depot areas, and in particular abdominal fat pad size. During the first week of life, birds fed a low energy diet (2233 kcal. M.E./kg., Table 2) did not increase their feed consumption (Table 6) and although caloric intake was reduced some 25%, body weight gain was similar to that of birds fed the control starter diet (3087 kcal. M.E./kg.). It is possible that these chicks may have had sufficient body energy stores in the yolk sac to meet requirements for gain during the first week. The ability of the broiler chicken to adjust feed intake to extremes in dietary energy level was evident during weeks 2, 3 and 4 of the starting period however, (Table 6). These data show that birds consuming a low energy diet during weeks 2 and 3 increased their feed intake by 25%, and that upon being returned to a conventional type starter diet, their feed intake was adjusted to that of the control birds (treatment 4) within one week (Table 6). Birds fed the low energy diet to 3 weeks of age (treatment 3) exhibited compensatory growth when switched to the control starter diet during the fourth week (Table 6). Thus although these birds were significantly (P s 0.05) smaller in body size at 3 weeks of age compared to control fed birds (treatment 3 vs. 4), this difference was not evident 7 days later, although these birds consumed no more feed than did birds fed the control diet (Table 6). Although a caloric restriction was imposed by the use of a very
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L. GRIFFITHS, S. LEESON AND J. D. SUMMERS
in their development. Further work is envisaged to ascertain the affects of 'alternate' degrees of caloric restriction and time of implementation, on abdominal fat pad development. It is possible that too fine a balance exists between abdominal fat pad size, an uneconomic trait, and total carcass fat which is economically desirable as regards finish grade, for these two characteristics to be both advantageously influenced by nutritional adabdominal fat pad size noted in this work (Table 4 and 8) and that previously reported (Griffiths et al., 1977) questions the genetical involvement of abdominal fat pad development. ACKNOWLEDGEMENT The authors would like to thank the Ontario Ministry
of
Agriculture
and
the
Ontario
Chicken Producers Marketing Board, for financial support of this work. REFERENCES Austic, R. E., and P. E. Pfaff, Jr., 1975. A new look at restricted feeding of pullets. Proc. 1975 Cornell Nutr. Conf. p. 34-37. Bartov, I., S. Bornstein and B. Lipstein, 1974. Effect of calorie to protein ratio on the degree of fatness in broilers fed on practical diets. Br. Poultry Sci. 15: 107-117. Deaton, J. W., L. F. Kubena, T. C. Chen and F. N. Reece, 1974. Factors influencing the quantity of abdominal fat in broilers. 2. Cage versus floor rearing. Poultry Sci. 53: 574-576. Donaldson, W. E., G. F. Combs and R. L. Romoser, 1956. Studies on energy levels in poultry rations. 1. The effect of calorie:protein ratio of the ration on growth, nutrient utilization and body composition of chicks. Poultry Sci. 35: 1100-1105. Evans, A. J., 1972. Fat accretion during postembryonic growth in the domestic duck, with additional data from the Mallard. Physiol. Zool. 45: 167-177. Farrell, D. J., 1974. Effects of dietary energy concentration on utilization of energy by broiler chickens and on body composition determined by carcass analysis and predicted using tritium. Br. Poultry Sci. 15: 25-41. Gooch, P., J. D. Summers and E. T. Moran, Jr., 1971. Effect of varying nutrient concentrations on broiler performance using computer formulated ra-
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aptation. The high degree of variability of
tions. Proc. Univ. Guelph Nutr. Conf. 1971. Greenwood, M. R. C , and J. Hrisch, 1974. Post-natal development of adipocyte cellularity in the normal rat. J. Lipid Res. 15: 474-483. Griffiths, L., S. Leeson and J. D. Summers, 1977. Influence of energy system and level of various fat sources on performance and carcass composition of broilers. Poultry Sci. 55: in press. Hirsch, J., and P. W. Han, 1969. Cellularity of rat adipose tissue; effect of growth, starvation and obestity. J. Lipid Res. 10: 77-82. Hirsch, J., and J. L. Knittle, 1970. Cellularity of obese and non-obese human adipose tissue. Fed. Proc. 29: 1516-1521. Jensen, L. S., G. W. Schumaier and J. D. Latshaw, 1970. "Extra caloric" effect of dietary fat for developing turkeys as influenced by calorie-protein ratio. Poultry Sci. 53: 974-978. Johnson, P. R., L. M. Zucker, J. A. F. Cruce and J. Hirsch, 1971. Cellularity of adipose depots in the genetically obese zucker rat. J. Lipid Res. 12: 706-714. Knittle, J. L., and J. Hirsch, 1968. Effect of early nutrition on the development of rat epididymal fat pads; cellularity and metabolism. J. Clin. Invest. 47: 2091-2098. Kubena, L. F., B. D. Lott, J. W. Deaton, F. N. Reece and J. D. May, 1972. Body composition of chicks as influenced by environmental temperature and selected dietary factors. Poultry Sci. 51: 517522. Mersman, H. J., C. D. Allen, D. G. Steffen, L. G. Brown and D. M. Danielson, 1976. Effect of age, weaning and diet on swine adipose tissue and liver lipogenesis J. Anim. Sci. 43: 140-150. Moran, E. T., J., 1967. Broiler carcass finish: alterations with nutrition, egg source and chick management. Proc. 1976 Maryland Nutr. Conf. p. 44-53. Oscai, L. B., C. N. Spirakis, C. A. Walff and R. J. Beck, 1972. Effect of excercise and of food restriction on adipose tissue cellularity. J. Lipid Res. 13: 588-592. Pfaff, F. E., Jr., and R. E. Austic, 1974. Influence of diet on adipose tissue accumulation in the pullet. Proc. 1974 Cornell Nutr. Conf. p. 82-86. Sell, J. L., F. Horani and R. L. Johnson, 1976. The "extra caloric" effect of fat in laying hen rations. Feedstuffs, 48: 28-29. Steel, R. G. D., and J. H. Torrie, 1960. Principles and Procedures of Statistics. McGraw-Hill Book Co., Inc., Toronto. Summers, J. D., S. J. Slinger and G. C. Ashton, 1965. The effect of dietary energy on carcass composition with a note on a method for estimating carcass composition. Poultry Sci. 44: 501-509.
GRIFFITHS, 1 S. LEESON AND J. D .
SUMMERS
Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario Canada (Received for publication August 20, 1976)
POULTRY SCIENCE 56: 638-646,
INTRODUCTION
I
N recent years there has been an increased public a w a r e n e s s of t h e possible health p r o b l e m s associated with an excessive consumption of fat. In broiler c h i c k e n s , while s u b c u t a n e o u s fat is associated with finish and eating qualities, that fat located in the a b dominal and visceral areas is considered a w a s t e p r o d u c t to both processor and consumer. T h e size of adipose d e p o t areas d e p e n d s o n t h e n u m b e r and size of their constituent cells and is thus influenced by factors affecting either cell division a n d / o r cell enlargement. In most m a m m a l s , including m a n , stages in t h e p r o c e s s of fat depot development are related to age. T h u s , in early life, increased cell n u m b e r s rather t h a n cell size is the p r e d o m i n a n t factor affecting the size of adipose d e p o t a r e a s , while this trend reverses with a d v a n c e m e n t in age to the stage w h e n increased cell size is the sole c a u s e of increased adipose depot size in the sexually m a t u r e animal (Hirsch and H a n , 1969; Hirsch
1. Present address: Agricultural Division, Maritime Co-operative Services, Nova Scotia, Canada.
1977
a n d Knittle, 1970; J o h n s o n et al., 1971; G r e e n w o o d and H i r s c h , 1974). H u m a n nutrition studies h a v e also shown that a p e r m a n e n t reduction in the size of fat depot areas can result only from a decrease in adipose cell n u m b e r s (Hirsch and Knittle, 1970), while work with rats has shown that this can be achieved through caloric restriction early in life (Knittle and H i r s c h , 1968; Oscai et al., 1972). Since c o m p a r a b l e studies with broiler chickens have not been reported, two experim e n t s were u n d e r t a k e n t o study t h e effect of early nutrition and caloric restriction on fat deposition in t h e broiler c h i c k e n , a n d in particular the formation of the abdominal fat pads.
MATERIALS AND METHODS Experiment 1. This experiment w a s designed to study the effect of dietary protein and energy level on abdominal fat-pad d e p o sition during t h e 4 - 8 w e e k finishing period. D a y old male broiler chicks were reared to 4 w e e k s of age in raised wire floor P e t e r s i m e b a t t e r y b r o o d e r s , being offered a commercial broiler starter diet ad libitum throughout this
638
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ABSTRACT The effect of dietary energy to protein balance, and early life caloric restriction on abdominal fat pad development in the male broiler chicken was studied. Dietary energy concentration had no significant (P s 0.05) effect on abdominal fat pad size, although decreasing the calorie.protein ratio of the diet resulted in a significant (P £ 0.05) reduction in the proportion of this tissue in the body. Reducing the calorie: protein ratio from a level considered optimum, by the addition of feather meal to the diet was equally as effective in reducing fat pad size as was the addition of a higher quality protein as exemplified by soybean meal plus DL-methione. Restricting the caloric intake of broilers in the 0-3 week growing period by the use of an ad libitum fed low energy diet (2233 kcal. M.E./kg.) had no significant (P s 0.05) effect on fat pad development. It is suggested that the degree of calorie restriction was not of sufficient magnitude to influence adipocyte hyperplasia. These results are discussed in relation to findings with other avian and mammalian species.
FAT DEPOSITION IN BROILERS
aC:Pratioof 159.5, considered to be optimum for growth and feed efficiency (Bartov et al., 1974), was employed for each energy level (diets 2 and6, Table 1). Calorie:protein ratio's of 187.6 and 138.7 (diets 1 and 5, 3 and 6 respectively, Table 1) were also utilized, and were considered to be high and low respectively in terms of optimum growth and feed efficiency. Diets were formulated such that methionine, the first limiting amino acid, represented an equal proportion of dietary crude protein. In the case of diets 4 and 8 however, (Table
TABLE 1.—Percentage composition Diet no. Ground yellow corn Cornstarch Alpha floe Stabilized animal tallow Soybean meal (49% protein) Feather meal Limestone Dicalcium phosphate (20% P) Iodized salt (0.15% KI) Vitamin mix 1 Mineral mix 2 DL-methionine L-lysineHCl Calculated analysis Metabolizable energy (kcal./kg.) Crude protein (%) Calorie:protein (C:P) ratio Methionine (g. /16 g.N) Lysine (g./16 g.N) Available phosphorus (%) Calcium (%)
of diets (experiment 1)
1 47.00 8.41 10.67
2 47.00 4.42 8.96
47.00 0.43 7.24
47.00 1.71 8.38
47.00 12.76 3.93
47.00 8.48 2.09
47.00 4.20 0.24
47.00 5.57 1.47
6.50
6.50
6.50
6.50
6.50
6.50
6.50
6.50
23.67 — 1.25
29.37 — 1.25
35.08 — 1.25
29.37 3.29 1.25
26.06 — 1.25
32.18 — 1.25
38.31 — 1.25
32.18 3.53 1.25
1.50
1.50
1.50
1.50
1.50
1.50
1.50
1.50
0.25 0.50 0.25 0.098 0.020
0.25 0.50 0.25 0.116
0.25 0.50 0.25 0.135
0.25 0.50 0.25 0.116
0.25 0.50 0.25 0.127 _
0.25 0.50 0.25 0.148 _
0.25 0.50 0.25 0.148 _
0.25 0.50 0.25 0.127 _
_
_
_
2970 15.83
1970 18.62
2970 21.42
2970 21.42
3190 17.00
3190 20.00
3190 23.0
3190 23.00
187.6
159.5
138.7
138.7
187.6
159.5
138.7
138.7
2.26 5.50
2.23 5.55
2.22 5.67
2.03 5.08
2.25 5.50
2.23 5.62
2.22 5.73
2.03 5.15
0.44 0.84
0.45 0.85
0.46 0.87
0.47 0.86
0.44 0.85
0.46 0.86
0.47 0.87
0.48 0.87
'Supplies per kg. of diet: vit. A, 8,000 I.U.; vit. D 3 , 1600 I.U.: vit. E, 11 mg.; riboflavin, 9 mg.; pantothenic acid, 11 mg.; vit. B , 2 , 13 (j,g.; niacin, 26 mg.; choline, 900 mg.; vit. K, 1.5 mg.; folic acid, 1.5 mg.; biotin, 1.5 mg. 2 Supplies per kg. of diet: manganese, 55 mg.; selenium, 0.1 mg.; zinc, 50 mg.; copper, 5 mg.; iron, 30 mg.
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period. At this age all birds were weighed, wingbanded and weight sorted such that 8 chicks of mean body weight were allotted to each raised wire floor pen housed in a windowless, temperature controlled room. A f actorially arranged randomized block design involving two levels of dietary energy (2970 and 3190 kcal. M.E./kg.) and four calorie:protein (C:P) ratios (188,160,139,139) were used, with protein sources varying for the C:P ratios of 139. The composition and calculated analysis of these diets are shown in Table 1. Diets were formulated such that
639
640
L. GRIFFITHS, S. LEESON AND J. D. SUMMERS
Experiment 2. The effect of low energy starter diets on fat pad development was
studied in this experiment. Treatments consisted of feeding either a low energy or control starter diet from 0-4 weeks followed by a conventional finisher diet to 8 weeks of age. Male broiler chicks were used, with housing and management procedures being as described in Experiment 1. The composition and calculated analysis of these diets are shown in Table 2. Treatments 1, 2 and 3 involved feeding the low energy starter diet (2233 kcal. M.E./kg., Table 2) for the first 1,2 and 3 weeks of age respectively, followed by the control starter diet (Table 2) for the remainder of the 4 week starting period. With treatment 4, the control starter diet was fed from 0-4 weeks. All birds received the same finisher diet (Table 2) to 8 weeks of age. Eight replicates of 10 birds each were used during the starter period (0-4 weeks) while 5 replicates of 10 birds each were used during the finishing period (4-8 weeks). All diets were fed in crumbled form, and together with water were available ad libitum. Feed intake and body weight gains were recorded weekly during the 0-4 week starting period and as
TABLE 2.—Percentage composition of diets (experiment 2) Diet Ground yellow corn Oat meal Soybean meal (49% protein) Stabilized animal tallow Limestone Dicalcium phosphate (20% P) Iodized salt (0.015% KI) Vitamin mix' Mineral mix 2 DL-methionine Alpha floe Calculated analysis Metabolizable energy (kcal./kg.) Crude protein (%) Lysine (%) Methionine (%) Available phosphorus (%) Calcium (%) 12
See footnotes, Table 1.
Low energy starter
— 55.90 27.25
— 1.35 1.50 0.25 0.50 0.25
— 13.00 2233 20.10 1.10 0.30 0.43 0.94
Control starter 52.40
— 39.25 4.50 1.35 1.50 0.25 0.50 0.25 0.075
— 3087 24.0 1.36 0.46 0.43 0.91
Finisher diet 60.00
— 30.75 5.50 1.25 1.50 0.25 0.50 0.25 0.075
— 3200 20.5 1.10 0.41 0.42 0.86
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1) protein quality was not maintained. Thus, although diets 4 and 8 provided crude protein in excess of requirement (Bartov et at., 1974), this extra protein, as feather meal, was of poor amino acid balance, and allowed the comparison of effects of excess protein of good amino acid balance (diets 3 and 6, Table 1) on the parameters measured. Four replicates of 8 birds were used for each treatment, with the steam pelleted diets and water being available ad libitum. Birds were reared under constant white light. Feed intake and body weight gains were recorded to 8 weeks of age. At this time birds were exsanguinated, New York dressed and cooled in running water at 4° C. overnight. Carcasses were then eviscerated and abdominal fat pads disected and weighed. Adipose tissue considered to represent the abdominal fat pad is given in a previous report (Griffiths et al., 1977). Samples of complete abdominal fat pad were freeze-dried to ascertain moisture content.
641
FAT DEPOSITION IN BROILERS
single ishing minal in the
measurements for the 4-8 weeks finperiod. Carcass preparation and abdofat pad dissection were as described previous experiment.
RESULTS Experiment 1. Means of body weight gain, feed intake, caloric intake, feed:body weight gain ratio, and both abdominal fat pad weight and moisture content, are shown in Table 3. Both dietary energy level and C:P ratio failed to influence body weight gain. Feed intake and feed:body weight gain of birds fed the low energy diet was significantly (P =£ 0.05) greater than birds fed the higher energy diet. This increased feed intake and feed:body weight gain ratio was also noted for birds fed the diet providing the greatest C:P ratio, and was significantly (P < 0.05) greater than for birds fed the lower C:P ratios when the diets contained balanced levels of
TABLE 3.—Effect of energy level and calorie'.protein ratio on mean 4-8 week body weight gain, caloric intake, feed:body weight gain, abdominal fat pad size and abdominal fat pad moisture content
(gm.)
Feed intake (gm.)
Caloric intake (kcal., metabolizable energy
Metabolizable energy 2970 kcal. /kg. 3190kcal./kg.
1448a1 1454a
3503a 3268b
Calorieiprotein ratio 187.6 159.5 138.7 138.72
1451a 1463a 1440a 1450a
3503a 3352b 3296b 3389ab
4-8 week body weight gain Contrasts
Abdominal fat pad Feed: body weight gain
Weight (gm./lOO grams body weight)
Moisture
10,404a 10,425a
2.42a 2.25b
2.57a 2.55a
17.1 16.7
10,789a 10,324b 10,152b 10,466ab
2.41a 2.29b 2.29b 2.35ab
3.19a 2.61b 2.22c 2.22c
14.3 17.0 17.5 18.5
%
'Within each column and contrast values bearing the same letter are not significantly different (P2< 0.05). Describes diets #4 and #8 (Table 7), formulated to contain feather meal.
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Statistical Analysis. Analysis of variance was calculated on a pen average basis using the method outlined by Steel and Torrie (I960). Abdominal fat pad size and 8 week body weight were subjected to regression analysis on an individual bird basis within each treatment.
amino acids. Birds fed the lowest dietary C:P ratio and providing an imbalanced amino acid profile (through the addition of feathermeal, diets 4 and 8, Table 1) also exhibited an increased feed intake and feed:body weight gain ratio, although these values were not significantly (P =s 0.05) different from those recorded for any of the other dietary treatments (Table 3). Caloric intake followed the same trend as feed intake for the C:P ratio treatments, although it was not affected by dietary energy level (Table 3). Abdominal fat pad weight was not affected by dietary energy concentration, although decreasing dietary C:P ratios resulted in significant (P < 0.05) decreases in abdominal fat pad deposition. Lowering the C:P ratio by adding protein in the form of feathermeal was as effective in reducing abdominal fat pad deposition, as using the addition of a higher quality protein to the diet (diets 4 and 8 versus 3 and 7, respectively, Table 1). A comparison of the coefficients of variation for abdominal fat pad weight and 8 week body weight are shown in Table 4, indicating a greater variability in the former measurement. In an attempt to quantify the relationship between abdominal fat pad weight and body size, regression analysis utilizing linear, quadratic and cubic effects as sources of variation between these
642 TABLE 4.—Coefficient Metabolizable energy (kcal./kg.) Calorie:protein ratio Diet No. 1 Abdominal fat (gm. /100 gm. body weight) 8 week body weight Number of observations
L. GRIFFITHS, S. LEESON AND J. D. SUMMERS
of variation (%) for abdominal fat pad weight and eight week body weight
187.6
159.5
1
2
21.4 5.0 28
297C1 138.7
319C1 138.7
138.7
187.6
159.5
3
4
5
6
7
8
30.7 5.9
45.6 9.6
26.6 6.5
24.2 7.2
32.9 7.2
33.7 5.9
35.5 6.1
30
31
28
27
31
26
29
138.7
'See Table 1.
Experiment 2. Weekly means for weight gain, feed intake, caloric intake and feed:body weight gain ratios's to 4 weeks of age are presented in Table 6. Body weight gains of birds fed the very low energy starter diet from 0-1 or 0-2 weeks of age were not significantly (P < 0.05) different at any time from 0-4 weeks, to those of birds fed the control starter diet throughout this period (treatments 1 and 2 versus 4, Table 6). Only when the low energy starter diet was fed for the first 3 weeks of the starter period was body weight gain significantly (P s 0.05) depressed, (treatment 3 versus 4, Table 6)
with this reduction in weight gain at 3 weeks of age being corrected by the introduction of the control starter diet during the last week of the starting period. In attempting to compensate for the low energy starter diet, birds provided with the low energy starter diets in weeks 2 and 3, consumed significantly more feed than control fed birds (treatments 2 and 3, and treatment 3 during the second and third weeks respectively, Table 6), although these increases in feed intake still resulted in a reduced caloric intake (Table 6). Feedrbody weight gain followed the same pattern as feed intake only during the first two weeks of growth. During the third week of the starting period, birds still receiving the low-energy diet (treatment 3) showed a significantly (P < 0.05) increased feed:body weight gain ratio compared to the control fed birds (treatment 4) while the converse
TABLE 5.—Error degrees of freedom, correlation coefficients and mean square values of regression of abdominal fat (gm./lOO gm. of body weight) on eight week body weight by energy level and calorie:protein ratio Metabolizable energy (kcal./kg)
2970
3190
Calorie:protein ratio Error degrees of freedom Correlation coefficient
187.6
159.5
138.7
138.7
187.6
159.5
138.7
138.7
25 0.119
27 0.332
28 0.438
25 0.448
24 0.278
28 0.286
23 0.136
29 0.526
Source of variation Linear Quadratic Cubic Residual
0.179 0.291 0.071 1.486
2.097 1.171 1.139 0.542
5.21" 1.00 0.606 0.724
1.860 1.274 1.666 0.639
0.274 0.005 0.067 0.632
4.517" 0.749 0.191 0.109
Significant at P s 0.05.
Mean square values 2.03" 1.242 0.586 0.969 0.084 0.194 0.297 0.572
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two parameters was undertaken. A significant (P < 0.05) linear effect was shown only for the lowest dietary C:P ratio; mean square values for analysis of regression and correlation coefficients are presented in Table 5.
643
F A T DEPOSITION IN BROILERS
TABLE 6.—Mean weight gain, feed intake, caloric intake and feed:body weight gain ratios for broiler cockerels fed a low energy starter ration for varying lengths of time 0-1 week
1 2 3 4
120.7a 123.2a 116.4a 115.9a
1 2 3 4
270.3a 275.9a 260.6a 356.8b
1 2 3 4
1.66a 1.58a 1.54a 1.51a
1-2 weeks 2-3 weeks Weight gain (gm.) 131.6a 226.4ab 123.9a 237.6c 123.0a 220.2a 126.4a 230.3bc Feed intake (gm.) 197.8a 377.9a 253.4b 380.6a 248.8b 484.8b 206.0a 395.1a Caloric intake (kcal.) 609.1a 1163.9a 567.7b 1172.2a 557.3b 1085.8b 634.4a 1216.9a Feed:gain ratio 1.50a 1.67ab 2.05b 1.60a 2.00b 2.21c 1.62a 1.72b
73.1a2 78.6a 75.6a 77.0a
3-4 weeks 272.9a 288.8a 276.1a 279.3a 458.9a 477.4a 465.0a 465.3a 1413a 1470a 1432a 1433a 1.68a 1.65a 1.69a 1.67a
1 Treatments 1—Fed low energy starter 1 week, regular starter 3 weeks \ 2.—Fed low energy starter 2 weeks, regular starter 2 weeks V see diets Table 2. 3—Fed low energy starter 3 weeks, regular starter 1 week j 4.—Fed regular starter 0-4 weeks. 2 Within each contrast and for each age classification, means bearing the same letter are not significantly different (P < 0.05).
TABLE 7.—Mean 8 week body weight, 4-8 week body weight gain, 4-8 week feed intake, 4-8 week feedigain ratio and abdominal fat pad weight (gm./lOO gm. body weight) for birds fed low energy starter diets for varying lengths of time Treatments' 8 week body weight (gm.) 4-8 week body weight gain (gm.) 4-8 week feed intake (gm.) 4-8 week feed:body weight gain ratio Abdominal fat pad size (grams/100 gm. body weight)
1 1980a2 1226a 2877a 2.35a
2
3
2070a 1310a 3058a 2.34a
2006a 1270a 2947a 2.32a
2023a 1258a 2882a 2.29a
1.87a
2.05a
1.86a
1.93a
•Treatments as shown in Table 6. Values within each parameter bearing the same letter are not significantly different (P : ; 0.05).
2
TABLE 8.—Coefficient
of variation (%) for abdominal fat pad weight and eight week body weight
Treatment'
1
2
3
4
Average of all treatments
Abdominal fat (grams/100 gms. body weight) 8 week body weight Observations
35.2 10.4 45
43.6 7.4 45
38.7 9.6 45
43.5 9.2 45
40.3 9.2 45
1
Treatments as shown in Table 6.
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Age of bird Treatments' 1 2 3 4
644
L. GRIFFITHS, S. LEESON AND J. D. SUMMERS
DISCUSSION That neither dietary energy level nor C:P ratio significantly (P < 0.05) influenced 4-8 week body weight gain in experiment 1 (Table 3), indicates the ability of the broiler chicken to adapt to varying dietary regimes. Birds adapted to energy concentration by adjusting their feed intake such that caloric intake remained constant. These results support the premise that broiler chickens eat to satisfy their energy requirement. That abdominal fat pad size was not influenced by dietary energy concentration is not in agreement with findings on total carcass fat (Gooch et al., 1971; Kubena et al, 1972; Farrell, 1974). Since these latter workers generally increased the energy level of their diets by the incorporation of fat while C:P ratios were held constant, compared with the substitution of corn starch for cellulose (alpha floe) in these studies, it is tempting to speculate on the relationship of dietary fat and carcass fat deposition. However, Mersman et al. (1976) working with swine reported that the rate of lipogenesis
was not affected by the fat content of the diet, and previous work from our laboratory (Griffiths et al., 1977) indicated that both visceral and carcass fat in the male broiler chicken were not influenced by dietary fat inclusion. Alternatively if one accepts an 'extra caloric' effect of dietary fat (Jensen et al., 1970; Sell et al., 1976) these same workers may have underestimated the energy value of fat, thus inadvertantly increasing the C:P ratio of the diet, a phenomenon known to favour increased carcass fat deposition (Donaldson et al., 1956; Summers et al., 1965; Bartov et al., 1974). In this work, decreasing the C:P ratio of the diet resulted in a decreased quantity of abdominal fat (Table 3). Lowering the C :P ratio from a level considered optimum (159.5 to 138.7) by the addition of feather meal to the diet, was equally as effective in lowering abdominal fat pad size as was the addition of higher quality protein, in terms of amino acid balance, as provided by soybean meal plus DL-methionine (Diet 3 vs. 4 and 7 vs. 8 Tables 1 and 3). Hence if a leaner carcass is desired from birds already being fed a diet of optimum C:P ratio, the addition of a poor quality protein such as feather meal would be as effective as the addition of any higher quality protein. The increased feed intake noted for birds fed diets providing the highest C:P ratio (Table 3) suggests that birds were eating in an attempt to satisfy a protein requirement, while the concomitant increased caloric intake contributed to increased abdominal fat pad deposition. Similar findings were reported by Bartov et al. (1974) in terms of skin fat analysis. Since experiment 1 indicates that the amount of carcass fat as exemplified by abdominal fat pad size is affected by the level of dietary protein (Table 3), a C:P ratio which is optimum for feed efficiency and carcass finish at one level of dietary energy, may not be optimum at alternative levels. The quantity of abdominal fat recorded in these
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was true for those birds that had received the low energy diet only during the first one or two weeks of growth; (treatments 1 and 2, respectively; this latter effect was significant (P < 0.05) for treatment 2. Dietary treatment had no significant (P £ 0.05) effect on any of the parameters measured during the 4th week of the starting period (Table 6). The starting diet treatments had no significant (P £ 0.05) effect on either 8 week body weight, 4-8 week weight gain, feed intake or feed:body weight gain ratio, or abdominal fat pad size (Table 7). The variation in abdominal fat pad size and 8 week body weight as described by coefficient of variation, are presented in Table 8. Regression analysis failed to indicate any significant (P < 0.05) linear, quadratic or cubic effects between abdominal fat pad weight and 8 week body weight.
F A T DEPOSITION IN BROILERS
low energy starter diet, abdominal fat pad size at 8 weeks of age was not affected (Table 7). It is possible that the degree of caloric restriction was not of sufficient magnitude to retard adipocyte hyperplasia or that if such an effect did occur that it was nullified by adipocyte hypertrophy when a nutritionally adequate finishing diet (Table 2) was offered during the 4-8 week growing period. Alternatively caloric restriction in early life may not affect avian adipocyte development. That body weight gain to 8 weeks of life was not adversely affected by 0-3 week caloric restriction, supports the premise that the degree of restriction was not severe enough, since comparable studies with rats invariably indicate a permanent reduction in mature body weight (Knittle and Hirsch, 1968; Oscai et al., 1972). Pfaff and Austic (1974) and Austic and Pfaff (1975) attempted to reduce adipose depot areas in leghorn chicks during the growing phase by caloric restriction. Although both low energy and high protein diets resulted in reduced abdominal fat pad size from 0-20 weeks of age, this difference had disappeared by 48 weeks of age again suggesting that caloric restriction was not severe enough. It is possible that protein, as well as caloric restriction should be considered, since it is well known that in situations of caloric deficiency, protein will be extensively utilized as an energy source. That caloric restriction or post-hatch starvation can affect broiler carcass fat content was recently shown by Moran (1976), although results from the present study suggest that ad libitum feeding of low energy diets does not represent a suitable method for controlling abdominal fat pad size. If work conducted with the duck can be applied to the broiler chicken, then perhaps caloric restriction at times other than immediate post hatch should be considered, since Evans (1972) showed that inguinal, subcutaneous and peritoneal depots in the domestic duck are, respectively, early, intermediate and late
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experiments (Tables 3 and 7) was much greater than previously reported (Griffiths et al., 1976) and is more in agreement with values reported by Deaton et al. (1974) using commercial broiler diets. Variation in abdominal fat pad weights as measured by coefficient of variation was high (Tables 4 and 8), and in agreement with values reported by Deaton et al. (1974) and Griffiths et al. (1977). By restricting caloric intake of broilers during early life (0-3 weeks) it was hypothesized that a permanent reduction in fat cell numbers would occur, leading to a reduction in the size of the adipose depot areas, and in particular abdominal fat pad size. During the first week of life, birds fed a low energy diet (2233 kcal. M.E./kg., Table 2) did not increase their feed consumption (Table 6) and although caloric intake was reduced some 25%, body weight gain was similar to that of birds fed the control starter diet (3087 kcal. M.E./kg.). It is possible that these chicks may have had sufficient body energy stores in the yolk sac to meet requirements for gain during the first week. The ability of the broiler chicken to adjust feed intake to extremes in dietary energy level was evident during weeks 2, 3 and 4 of the starting period however, (Table 6). These data show that birds consuming a low energy diet during weeks 2 and 3 increased their feed intake by 25%, and that upon being returned to a conventional type starter diet, their feed intake was adjusted to that of the control birds (treatment 4) within one week (Table 6). Birds fed the low energy diet to 3 weeks of age (treatment 3) exhibited compensatory growth when switched to the control starter diet during the fourth week (Table 6). Thus although these birds were significantly (P s 0.05) smaller in body size at 3 weeks of age compared to control fed birds (treatment 3 vs. 4), this difference was not evident 7 days later, although these birds consumed no more feed than did birds fed the control diet (Table 6). Although a caloric restriction was imposed by the use of a very
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in their development. Further work is envisaged to ascertain the affects of 'alternate' degrees of caloric restriction and time of implementation, on abdominal fat pad development. It is possible that too fine a balance exists between abdominal fat pad size, an uneconomic trait, and total carcass fat which is economically desirable as regards finish grade, for these two characteristics to be both advantageously influenced by nutritional adabdominal fat pad size noted in this work (Table 4 and 8) and that previously reported (Griffiths et al., 1977) questions the genetical involvement of abdominal fat pad development. ACKNOWLEDGEMENT The authors would like to thank the Ontario Ministry
of
Agriculture
and
the
Ontario
Chicken Producers Marketing Board, for financial support of this work. REFERENCES Austic, R. E., and P. E. Pfaff, Jr., 1975. A new look at restricted feeding of pullets. Proc. 1975 Cornell Nutr. Conf. p. 34-37. Bartov, I., S. Bornstein and B. Lipstein, 1974. Effect of calorie to protein ratio on the degree of fatness in broilers fed on practical diets. Br. Poultry Sci. 15: 107-117. Deaton, J. W., L. F. Kubena, T. C. Chen and F. N. Reece, 1974. Factors influencing the quantity of abdominal fat in broilers. 2. Cage versus floor rearing. Poultry Sci. 53: 574-576. Donaldson, W. E., G. F. Combs and R. L. Romoser, 1956. Studies on energy levels in poultry rations. 1. The effect of calorie:protein ratio of the ration on growth, nutrient utilization and body composition of chicks. Poultry Sci. 35: 1100-1105. Evans, A. J., 1972. Fat accretion during postembryonic growth in the domestic duck, with additional data from the Mallard. Physiol. Zool. 45: 167-177. Farrell, D. J., 1974. Effects of dietary energy concentration on utilization of energy by broiler chickens and on body composition determined by carcass analysis and predicted using tritium. Br. Poultry Sci. 15: 25-41. Gooch, P., J. D. Summers and E. T. Moran, Jr., 1971. Effect of varying nutrient concentrations on broiler performance using computer formulated ra-
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aptation. The high degree of variability of
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