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Feed Intake Effects Upon Gain, Carcass Yield, and Ration Digestibility in Broilers Force Fed Five Feed Intakes
Feed Intake Effects Upon Gain, Carcass Yield, and Ration Digestibility in Broilers Force Fed Five Feed Intakes R. G. TEETER and M. O. SMITH Animal Science Department, Oklahoma State University, Stillwater, Oklahoma 74078 (Received for publication March 12, 1984)
1985 Poultry Science 64:2155-2160 INTRODUCTION Broiler g r o w t h rate and e x t e n t of g r o w t h are influenced by n u m e r o u s dietary factors such as p r o t e i n q u a l i t y (Askelson and Balloun, 1 9 6 5 ; Waldroup et al, 1 9 7 6 ) and overall n u t r i e n t a d e q u a c y of t h e diet. Equal in i m p o r t a n c e t o these considerations is t h e ability o r desire of t h e chick t o c o n s u m e feed. A m i n o acid imbalances have been o v e r c o m e w h e n chicks (Austic, 1 9 8 1 ) or rats (Leung et al., 1 9 6 8 ) are force fed larger quantities of feed, indicating t h a t t h e negative consequences of these imbalances are d u e t o reduced feed i n t a k e . Elevating feed c o n s u m p t i o n of rats (West et al., 1 9 8 2 ) and swine (Pekas, 1 9 8 3 ) fed balanced rations above ad libitum c o n s u m p t i o n has increased growth rate b y 63 and 4 0 % , respectively. Feed c o n s u m p t i o n b y broiler chicks is correlated (r2 = .87) with g r o w t h rate (Teeter, u n p u b l i s h e d d a t a ) and as such m a y provide p o t e n t i a l for m a n i p u l a t i o n t o increase g r o w t h rate. F e e d intake could conceivably be influenced directly by satiety or indirectly by increasing tissue g r o w t h rates, which increases
energy r e q u i r e m e n t s and t h e r e b y satiety. Several drugs have been d e m o n s t r a t e d t o play a role in satiety by increasing food c o n s u m p t i o n : muscimol (Morley et al., 1 9 8 1 ) , glutamic acid (Collins et al., 1 9 8 3 ) , opiates with affinity for k a p p a and mu o p i a t e receptors (Sanger a n d McCarthy, 1 9 8 1 ; Yim et al., 1980) in rats, cholecystokinin antisera in sheep (Della-Fera et al, 1 9 8 1 ) , and elfazepam in cattle, sheep, pigs, cats, and rats (Baile and McLaughlin, 1 9 8 5 ) . C o m p o u n d s t h a t regulate satiety m a y b e of value t o p o u l t r y if t h e greater quantities of c o n s u m e d n u t r i e n t s are used t o synthesize p r o t e i n a c e o u s carcass tissues. Before the potential value of satiety drugs can be fully evaluated, t h e role of feed intake on broiler g r o w t h rate needs t o b e clearly defined ind e p e n d e n t of drug-responses to tissue g r o w t h requirements. Lepkovsky a n d F u r u t a ( 1 9 7 1 ) force fed a d u l t Leghorn cockerels from t h e n o r m a l 4.3 t o 8.8% of b o d y weight a n d stimulated b o d y weight gains ( P < . 0 5 ) , although t h e gain appeared t o be principally fat. Nir et al. ( 1 9 7 4 ) ,
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ABSTRACT Broiler chicks were force fed 75, 100, 125, 140 and 160% of the consumption observed by ad libitum-fed controls to examine feed intake effects upon productivity. Live body weight gain increased with feed intake up to the 140% consumption but was depressed above this point. Feed efficiency and fat, ash, ration (corrected for uric excretion mass), protein (corrected for uric acid excretion nitrogen), and starch digestibility estimates declined by 30, 56, 25, 16, 16, and 2%, respectively, as feed consumption increased from 75 to 160% of ad libitum consumption. Neutral detergent fiber digestibility was not affected by amount of feed consumption. Initial digesta passage rate, estimated by first appearance of ferric oxide in feces, averaged 215 min and was not correlated (P>.4) with feed intake. Gastrointestinal tract mass plus contents increased with feed intake and accounted for up to 67% of the increased live body weight gain. Birds apparently adjusted to feed intake level by varying gastrointestinal tract size (mass) and not passage rate. Dressing percentage declined from a high of 73% for birds fed at the lowest feed intake to a low of 63% at the highest feed intake. Carcass gain was 50% greater for the 160 vs 75% group, but most of this (41%) was reached at the ad libitum consumption level. Carcass gain-to-feed ratios were .42, .41, .32, .27, and .21 for the five intakes, respectively. Drumstick, breast, and thigh gains were not (P>.01) influenced by increased feed consumption above the ad libitum-ied controls but were depressed (P>.05) at the 75% feed intake. Abdominal fat increased with feed intake to a level equal to 230% of that of birds fed at 75% level. Physiological processes other than those associated with feed intake regulation, including ability to digest feedstuffs and absorb nutrients, limit carcass growth rate of broilers reared in thermoneutral environments. (Key words.- feed intake, digestibility, growth, force feeding)
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MATERIALS AND METHODS Arbor Acre X Vantress broiler chicks were fed a corn-soybean meal starter diet during the first 3 weeks posthatching. On the 1st day of the 4th week following an overnight fast, 77 chicks were weighed and allotted to seven experimental groups at random. All birds were individually housed in 30 x 80-cm wire cages within a thermostatically controlled room maintained at 24 C with a 12 hr light-dark schedule. Water was provided ad libitum throughout the assay period. Feed consumption by birds consuming feed ad libitum (Groups 1 and 2) was monitored daily and coupled with body weight to compute consumption per body weight per day. Force-fed birds (Groups 3 to 7) were weighed every other day and fed an amount of feed equal to one-third the daily consumption per body weight of the ad libitum group, at 1, 5, and 9 hr of the light cycle; feed intakes of Groups 3 to 7 approximated 75, 100, 125, 140, and 160% of the consumption of the ad libitum group. The force-feeding technique has been previously described (Teeter et ah, 1984). Groups 2 to 7 received their respective treatment for 11 days while Group 1 was fed until their body weight was similar to the highest gaining force-fed group. Composition of the nutritionally complete basal diet is presented in Table 1. A mixture of 57% H 2 0 and 43% basal flowed easily through
the force-feeding gun at constant dry matter delivery. Chromic oxide was included so that diet, protein, starch, fat, ash, and neutral detergent fiber digestibility could be estimated by chromium ratio with feed and fecal grab samples. Fecal samples were collected daily on Days 7 to 10 of the experimental period and composited for further analyses. Dry matter was determined by drying (55 C) to a constant weight. Feed and feces were analyzed for chromium (Stevenson, 1962), starch (Macrae and Armstrong, 1968), fat as ether extract, protein (N X 6.25), and ash (Association of Official Analytical Chemists, 1970), neutral detergent fiber (McQueen and Nicholson, 1979), and uric acid (Alumot and Breloria, 1979). Feces were adjusted for uric acid mass and nitrogen content so that ration and protein digestibility estimates could be obtained independent of uric acid contamination. Initial digesta passage rate was estimated by force feeding birds 20 g of the feed-water mixture containing 1% ferric oxide in the 5 hr feed and
TABLE 1. Composition of basal ration*
Ingredient Ground corn Soybean meal Corn oil Meat plus bone meal Corn gluten meal Yeast culture Polyethylene Dicalcium phosphate Calcium carbonate Vitamin mix 3 Salt DL-Methionine Trace mineral mix 4 Chromic oxide
Numerical 2 name 4-02-931 5-04-604 4-07-822 5-07-822 5-02-900
6-01-080 6-01-069 6-14-013
(%) 37.95 33.0 10.0 5.0 5.0 3.0 3.0 1.0 .9 .5 .3 .15 .1 .1
1 Ration contained by laboratory analysis 24.3% crude protein, 35.1% starch, 11.8% fat, 6.6% ash, 13.3% neutral detergent fiber and 0% uric acid. 2 Atlas of Nutritional Data on United States and Canadian Feeds. 3 Mix contained vitamin A, 3,527,360 IU; vitamin D 3 , 1,322,760 IU; vitamin E, 11,905 IU; vitamin B12, 3.5 mg; riboflavin, 2,205 mg; niacin, 6,614 mg; d-panthothenic acid, 7,055 mg; choline, 176,368 mg; menadione, 291 mg; folic acid, 441 mg; pyridoxine, 882 mg; thiamine, 882 mg; d-biotin, 44 mg/kg.
"Mix contained manganese, 12.0%, zinc, 8.0%; iron, 6.0%; copper, 10%, iodine, .1%; calcium, 18.0%.
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who force fed New Hampshire X White Leghorn chicks to increase feed intake from the ad libitum 9.7% to 14% of body weight per day, observed body weight gain to increase linearly with feed consumption and suggested that the limiting factor for chick growth is appetite. However, force feeding White Rock (meat type) chicks (Nir et ah, 1978) did not favorably affect growth rate. Meat-type broilers normally have a greater growth rate and feed consumption than slower growing Leghorns. Whether these birds have reached a maximum genetic capacity for tissue growth rate or if some other factor limits production is not known. The following study was conducted to determine the influence of feed intake level upon growth rate of a second meat-type broiler strain and to evaluate the impact of feed intake level upon initial digesta passage rate, carcass yield, and ration, protein, starch, ash, fat, and neutral detergent fiber apparent digestibility.
FEED INTAKE AND BROILERS
RESULTS AND DISCUSSION
Chicks force fed for 11 days, to simulate feed dry matter consumption of control birds (Group 2) fed 11 days, gained similarly (P>.10) and had identical feed efficiencies, suggesting that the force-feeding technique employed is a valid approach to controlling feed consumption at the ad libitum consumption level (Table 2). Live body weight gains of force-fed chicks increased linearly with increasing feed intake above ad libitum consumption, although feed efficiency declined markedly (30%). Group 1 controls required an additional 6 days to
achieve the body weight gains observed by the 140% force-fed group. The reduced feed efficiency may be due to either increased fat deposition, increased energy requirements, or decreased ration digestibility. These will be considered in order. Abdominal fat per unit body weight increased by 268% (Table 3) whereas feed intake increased from 75 to 160% of ad libitum consumption, indicating that at least a portion of the reduced feed efficiency is related to increased body fat content. Broiler maintenance energy requirements could be impacted by feeding level, as in rats (Rothwell et al, 1980), but the impact cannot be deduced from this study. Nutrient digestion and absorption are involved as ration (corrected for uric acid fecal mass), protein (corrected for uric acid fecal nitrogen), fat, ash, and starch digestibility estimates were inversely related with feed intake. Fat, ash, protein, and starch digestibility coupled to account for 96% of the decline in ration digestibility between the 75 and 160% feed intakes. Pancreas wet and dry weight (Table 4) increased markedly with increased feeding level. Why fat and protein, but not starch digestibility, decline markedly is not known. Time available for digestion and nutrient absorption (Table 2), assuming that initial digesta passage rate is correlated with average passage rate, did not vary with feed intake. Digestibility of ration, fat, and protein was poorly correlated (P> .4) with initial digesta passage rate. Carcass gains (Table 3) were elevated (P<.05) as feed consumption increased from 75 to 100% of the consumption observed by the 11-day controls. Both control and those forcefed 100% feed had similar carcass gain (P>.01), again indicating that the force-feeding technique employed was valid at this level. At 140% consumption, carcass gains increased only 4% in sharp contrast to the 32% higher live body weight gains observed. In this study increasing feed intake above ad libitum consumption did not impact (P>.1) quantity of carcass weight gain. This is reflected in breast, leg, and thigh yields. Gastrointestinal tract wet full weight, obtained by summing gastrointestinal tract components (Table 4), however, did increase (P<.05) as feed intake increased and accounted for 67% of the increased body weight gain observed at 140% feed intake. Drugs that specifically impact feed consumption without altering the ability of the broiler to digest feed more efficiently and
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recording the time of first ferric oxide appearance in feces postdose. Feces were monitored once per 3-min interval by each of two trained observers. On Day 11 of the experimental period, after an overnight fast, birds were processed as follows. Birds were hung on a rail, stunned, bled for 15 min. following severing of jugular and carotid veins, passed through a scalding vat, plucked by machine, and hand eviscreated. Carcasses and gastrointestinal tracts were weighed and stored in separate polyethylene bags at —15 C for later analysis. Carcass yield of primary parts was estimated by separating breast, thigh, and drumstick. Quantification of abdominal fat was by hand separation. The gastrointestinal tract was segmented into crop, proventriculus, gizzard, small intestine, and large intestine plus cecum full wet weight, empty wet weight, and dry empty weight. At the outset (Day 1 of the experimental period), 15 original birds in addition to the 77 were chosen at random and processed as described so that individual tissue gains of test birds completing the experiment could be estimated by the equation: Test bird tissue gain (g) = Test bird final tissue weight — Test bird initial body weight X [Initial tissue weight -r Initial body weight (g)]. All data were subjected to analysis of variance using the General Linear Model of the Statistical Analysis System (Barr et al, 1976). Duncan's multiple range test was used to determine differences (P<.05) between means when a significant F statistic effect was indicated by the analysis of variance (Steel and Torrie, 1960). Control birds (Group 1) allowed to consume feed ad libitum until their live body weight was similar to the fastest gaining force-fed group were compared only to that group.
2157
249
271
72.8 b 88.8 b 98.8b 89.3 b 37.8 a 19.4
l,387 c 764 b .56*
Means within a row with unlike superscripts differ (P<.05).
Birds force fed for 11 days.
—
.53*
71.1* 89.5 98.4 88.8* 37.9* 17.9
965
1,820*
C-ll3
219
77. l a 95.la 99.3a 94.7 a 40.3 a 16.5
941d 529 c .56 a
75%
221
72.3 b 90.4 a b 98.8 b 89.8 b 36.9 a b 18.1
1,352C 752 b .56 a
100%
20
6 8 9 7 3 1
87
l,75
125
Forc
Control birds allowed to consume feed ad libitum for 11 days.
Corrected for uric acid excretion nitrogen.
•Significantly differs from 140% force-feed intake.
5
"Corrected for uric acid excretion mass.
3
2 Control birds allowed to consume feed ad libitum until body weight gain was similar to fastest gaining force-fe 140% feed intake.
1
Digesta passage rate, min
Digestibility Ration, %4 Protein, % s Starch, % Fat, % Ash, % NDF, %
Dry matter consumption, % Weight gain, g Gain/feed
C-172
TABLE 2. Dry matter consumption, body weight gain, feed efficiency, ration, protein, starch, fat, ash, and n and digesta passage rate of force-fed chicks
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FEED INTAKE AND BROILERS
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TABLE 3. Carcass gain with abdominal fat, liver breast, thigh, and drumstick weights Force-fed intakes 1 C-17 Carcass gain, g Abdominal fat, g Drumstick, g Thigh, g Breast, g
2
C-ll
3
572 a 10.9 d e 11.6 a 33.9 a l49a
785* 16.0* 25.2 53.2* 195*
75%
100%
125%
140%
160%
394 b 8.2 e .5b 18.9 b b 116
556 a 18.0 c d 10.0 a 33.6 a 144 a b
571a 20.6bc 12.5 a 32.8 a 149 a
578 a 27.4 a b 10.4 a 36.3 a 144 a b
486ab 30.2 a 5.3ab 31.8 a 140ab
Means within a row with unlike superscripts differ (P<.05). 1 2
Control birds allowed to consume feed ad libitum until body weight gain was similar to fastest gaining force-fed group (17 days). Values are compared only to the 140% feed intake. 'Control birds allowed to consume feed ad libitum for 11 days. •Significantly differs from 140% feed intake.
TABLE 4. Segmented gastrointestinal tract full, wet, and dry weights (g) Force-fed intakes' C-17
2
C-ll
3
Full croup, g Wet empty, g Dry empty, g
10* 8.9* 1.9*
Full proventriculus, g Empty, g Dry, g
12.8* 10.5* 2.7*
13c 8.3 C 1.7C 11.7 C 9.7 C 3.3ab
Full gizzard, g Empty, g Dry, g
37* 33 12.8*
47ab 42a 15.8bc
Full small intestine, g 122* Empty, g 64* Dry, g 16* Full ceca, g Empty, g Dry, g Pancreas, g Dry pancreas, g — 1
21.2 13.5 2.9 4.0 1.0*
127bc 69bc Igab 22.1ab 12.8 b 2.9
4.3b 1.2 bc
75%
100%
125%
140%
160%
9c
35bc
128 a 15.8 a 3.4 a b
109 a 14.6 a 3.8 a
24.5 a 13.5 a 4.0 a 54a 3 7 abc 18.1ab
21.0 a 14.7 a 3.9 a
8.3 C 1.7C
10.5bc 2.2bc
78ab 14ab 3.8 a
9.6C 8.9C 2.1b 37b 32 c 10.9 C 94d 48d 12 e 16.5 b 10.5 b 2.1
10.6 C 9.5 C 2.6ab
20.1ab 12.4 a b 3.2 a b
46ab 41ab 22.0 a
53a 40abc 18.1ab
3.8 b 1.0C
lllcd 67bc 18ab 16.5 b 11.3 b 2.4 4.3b 1.3 b c
125 b c 7iabc 19ab 17.3 b 11.4 b 2.4 4.8ab 1.4 ab
155ab 78ab 22 a 17.3 b 11.4 b 2.6 5.1ab 1.5 a
61a 44a 21.9 a 177 a 82 a 20ab 26.0 a 16.3 a 2.7 6.0 a 1.8a
Means within a row with unlike superscripts differ (P<.05).
Birds force fed for 11 days.
2
Control birds allowed to consume feed ad libitum until body weight gain was similar to fastest gaining force-fed group (17 days). Values are compared only to the 140% feed intake. 3
Control birds allowed to consume feed ad libitum for 11 days.
'Significantly differs from 140% force-fed intake.
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Birds force fed for 11 days.
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possibly synthesize carcass p r o t e i n a c e o u s tissue would be e x p e c t e d t o be of minimal value. T h e data r e p o r t e d herein suggest t h a t a physiological process o t h e r t h a n feed intake regulation limits carcass g r o w t h rate of A r b o r Acre X Vantress broilers housed in g o o d e n v i r o n m e n t .
REFERENCES
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Alumot, E., and R. Breloria, 1979. Colorimetric determination of uric acid in poultry excreta and in mixed feeds. J. Assoc. Offic. Anal. Chem. 62:1350-1352. Askelson, C. E., and S. L. Balloun, 1965. Influence of dietary protein level and amino acid composition on chick performance. Poultry Sci. 44:193—197. Association of Official Analytical Chemists, 1970. Official methods of analysis. 11th ed. Assoc. Offic. Anal. Chem., Washington, DC. Atlas of Nutritional Data on United States and Canadian Feeds. Austic, R. E., 1981. On the nature of amino acid interactions. Pages 5—13 in Proc. Cornell Nutr. Conf. Baile, C. A., and C. L. McLaughlin, 1985. Compounds for Regulating Intake Agricultural Chemicals of the Future, (in press). Barr, A. J., J. H. Goodnight, J. P. Sail, and J. T. Helwig, 1976. A User's Guide to SAS. Stati. Analy. Syst. Insti., Inc., Cary, NC. Collins, S., D. Walker, P. Forsyth, and L. Belbeck, 1983. The effects of proglumide on cholecystokinin, bombesin, and glucagon-induced satiety in the rat. Life Sci. 32:2223-2229. Della-Fera, M. C , C. A. Baile, and S. R. Peikin, 1981. Feeding elicited by injection of the cholecystokinin antagonist dibutyrl cyclic GMP into the cerebral ventricles of sheep. Physiol. Behav. 26:799-801. Lepkovsky, S., and F. Futura, 1971. The role of homeostasis in adipose tissue upon the regulation of food intake of white leghorn cockerels. Poultry Sci. 50:573-577. Leung, P.M.B., Q. R. Rogers, and A. E. Harper, 1968. Effect of amino acid imbalance in rats fed ad libitum, interval fed or force fed. J. Nutr. 95: 474-482. Macrae, J. C , and D. G. Armstrong, 1968. Enzyme method for determination of alpha-linked glucose polymers in biological methods. J. Sci. Food
Agric. 19:578. McQueen, R. E., and J.W.G. Nicholson, 1979. Modification of the neutral-detergent fiber procedure for cereals and vegetables by using Amylase. J Assoc. Offic. Anal. Chem. 62:676-680. Morley, J. E., A. S. Levine, and J. Knelp, 1981 Mucimol induced feeding: A model to study the hypothalamic regulation of appetite. Life Sci 29:1213-1218. Nir, I., N. Shapira, Z. Nitsan, and Y. Dror, 1974 Force feeding effects on growth, carcass and blood composition in the young chick. Br. J Nutr. 32:229-239. Nir, I., Z. Nitsan, Y. Dror, and N. Shapira, 1978 Influence of overfeeding on growth, obesity and intestinal tract in young chicks of light and heavy breeds. Br. J. Nutr. 39:27-35. Pekas, J. C, 1983. Superalimentation: Effect on rate and efficiency of growth in swine. J. Anim. Sci. 57:202. (Abstr.) Rothwell, N. J, and M. J. Stock, 1980. Hyperphagia, thermogenesis and leanness. Recent Advances in Obesity Research III. Proc. 3rd Intl. Congr. Obesity, ed. P. Bjornthorp, M. Clarella and A. N. Howard, ed. Sanger, D. J., and P. S. McCarthy, 1981. Increasing food and water intake produced in rats by opiate receptor agonists. Psychopharmacology 7 4 : 2 1 7 220. Steel, R.G.D., and J. H. Torrie, 1960. Principles and Procedures of Statistics. McGraw-Hill Book Co., New York, NY. Stevenson, A. E., 1962. Measurements of feed intake by grazing cattle and sheep. VIII. Some observations on the accuracy of the chromic oxide technique for the estimation of feces output of dairy cattle. N. Z. J. of Agric. Res. 5:339-345. Teeter, R. G., M. O. Smith, E. E. Murray, and H. Hall, 1984. Force feeding methodology and equipment for poultry. Poultry Sci. 63:573-575. Waldroup, P. W., R. J. Mitchell, J. R. Payne, and K. R. Hayden, 1976. Performance of chicks fed diets formulated to minimize excess levels of essential amino acids. Poultry Sci. 55:243—253. West, D. B., J. Dray, and S. C. Woods, 1982. Infant gastronomy and chronic formula infusion as a technique to overfeed and accelerate weight gain of neonatal rats. J. Nutr. 1 1 2 - 1 3 3 9 - 1 3 4 3 . Yim, G.K.W., M. T. Lowy, M. P. Holsapple, and M. D. Nichols, 1980. Peripheral mediation of opiate effects on feeding in rats. Soc. Neurosci. 6:528: (Abstr.)
1985 Poultry Science 64:2155-2160 INTRODUCTION Broiler g r o w t h rate and e x t e n t of g r o w t h are influenced by n u m e r o u s dietary factors such as p r o t e i n q u a l i t y (Askelson and Balloun, 1 9 6 5 ; Waldroup et al, 1 9 7 6 ) and overall n u t r i e n t a d e q u a c y of t h e diet. Equal in i m p o r t a n c e t o these considerations is t h e ability o r desire of t h e chick t o c o n s u m e feed. A m i n o acid imbalances have been o v e r c o m e w h e n chicks (Austic, 1 9 8 1 ) or rats (Leung et al., 1 9 6 8 ) are force fed larger quantities of feed, indicating t h a t t h e negative consequences of these imbalances are d u e t o reduced feed i n t a k e . Elevating feed c o n s u m p t i o n of rats (West et al., 1 9 8 2 ) and swine (Pekas, 1 9 8 3 ) fed balanced rations above ad libitum c o n s u m p t i o n has increased growth rate b y 63 and 4 0 % , respectively. Feed c o n s u m p t i o n b y broiler chicks is correlated (r2 = .87) with g r o w t h rate (Teeter, u n p u b l i s h e d d a t a ) and as such m a y provide p o t e n t i a l for m a n i p u l a t i o n t o increase g r o w t h rate. F e e d intake could conceivably be influenced directly by satiety or indirectly by increasing tissue g r o w t h rates, which increases
energy r e q u i r e m e n t s and t h e r e b y satiety. Several drugs have been d e m o n s t r a t e d t o play a role in satiety by increasing food c o n s u m p t i o n : muscimol (Morley et al., 1 9 8 1 ) , glutamic acid (Collins et al., 1 9 8 3 ) , opiates with affinity for k a p p a and mu o p i a t e receptors (Sanger a n d McCarthy, 1 9 8 1 ; Yim et al., 1980) in rats, cholecystokinin antisera in sheep (Della-Fera et al, 1 9 8 1 ) , and elfazepam in cattle, sheep, pigs, cats, and rats (Baile and McLaughlin, 1 9 8 5 ) . C o m p o u n d s t h a t regulate satiety m a y b e of value t o p o u l t r y if t h e greater quantities of c o n s u m e d n u t r i e n t s are used t o synthesize p r o t e i n a c e o u s carcass tissues. Before the potential value of satiety drugs can be fully evaluated, t h e role of feed intake on broiler g r o w t h rate needs t o b e clearly defined ind e p e n d e n t of drug-responses to tissue g r o w t h requirements. Lepkovsky a n d F u r u t a ( 1 9 7 1 ) force fed a d u l t Leghorn cockerels from t h e n o r m a l 4.3 t o 8.8% of b o d y weight a n d stimulated b o d y weight gains ( P < . 0 5 ) , although t h e gain appeared t o be principally fat. Nir et al. ( 1 9 7 4 ) ,
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ABSTRACT Broiler chicks were force fed 75, 100, 125, 140 and 160% of the consumption observed by ad libitum-fed controls to examine feed intake effects upon productivity. Live body weight gain increased with feed intake up to the 140% consumption but was depressed above this point. Feed efficiency and fat, ash, ration (corrected for uric excretion mass), protein (corrected for uric acid excretion nitrogen), and starch digestibility estimates declined by 30, 56, 25, 16, 16, and 2%, respectively, as feed consumption increased from 75 to 160% of ad libitum consumption. Neutral detergent fiber digestibility was not affected by amount of feed consumption. Initial digesta passage rate, estimated by first appearance of ferric oxide in feces, averaged 215 min and was not correlated (P>.4) with feed intake. Gastrointestinal tract mass plus contents increased with feed intake and accounted for up to 67% of the increased live body weight gain. Birds apparently adjusted to feed intake level by varying gastrointestinal tract size (mass) and not passage rate. Dressing percentage declined from a high of 73% for birds fed at the lowest feed intake to a low of 63% at the highest feed intake. Carcass gain was 50% greater for the 160 vs 75% group, but most of this (41%) was reached at the ad libitum consumption level. Carcass gain-to-feed ratios were .42, .41, .32, .27, and .21 for the five intakes, respectively. Drumstick, breast, and thigh gains were not (P>.01) influenced by increased feed consumption above the ad libitum-ied controls but were depressed (P>.05) at the 75% feed intake. Abdominal fat increased with feed intake to a level equal to 230% of that of birds fed at 75% level. Physiological processes other than those associated with feed intake regulation, including ability to digest feedstuffs and absorb nutrients, limit carcass growth rate of broilers reared in thermoneutral environments. (Key words.- feed intake, digestibility, growth, force feeding)
2156
TEETER AND SMITH
MATERIALS AND METHODS Arbor Acre X Vantress broiler chicks were fed a corn-soybean meal starter diet during the first 3 weeks posthatching. On the 1st day of the 4th week following an overnight fast, 77 chicks were weighed and allotted to seven experimental groups at random. All birds were individually housed in 30 x 80-cm wire cages within a thermostatically controlled room maintained at 24 C with a 12 hr light-dark schedule. Water was provided ad libitum throughout the assay period. Feed consumption by birds consuming feed ad libitum (Groups 1 and 2) was monitored daily and coupled with body weight to compute consumption per body weight per day. Force-fed birds (Groups 3 to 7) were weighed every other day and fed an amount of feed equal to one-third the daily consumption per body weight of the ad libitum group, at 1, 5, and 9 hr of the light cycle; feed intakes of Groups 3 to 7 approximated 75, 100, 125, 140, and 160% of the consumption of the ad libitum group. The force-feeding technique has been previously described (Teeter et ah, 1984). Groups 2 to 7 received their respective treatment for 11 days while Group 1 was fed until their body weight was similar to the highest gaining force-fed group. Composition of the nutritionally complete basal diet is presented in Table 1. A mixture of 57% H 2 0 and 43% basal flowed easily through
the force-feeding gun at constant dry matter delivery. Chromic oxide was included so that diet, protein, starch, fat, ash, and neutral detergent fiber digestibility could be estimated by chromium ratio with feed and fecal grab samples. Fecal samples were collected daily on Days 7 to 10 of the experimental period and composited for further analyses. Dry matter was determined by drying (55 C) to a constant weight. Feed and feces were analyzed for chromium (Stevenson, 1962), starch (Macrae and Armstrong, 1968), fat as ether extract, protein (N X 6.25), and ash (Association of Official Analytical Chemists, 1970), neutral detergent fiber (McQueen and Nicholson, 1979), and uric acid (Alumot and Breloria, 1979). Feces were adjusted for uric acid mass and nitrogen content so that ration and protein digestibility estimates could be obtained independent of uric acid contamination. Initial digesta passage rate was estimated by force feeding birds 20 g of the feed-water mixture containing 1% ferric oxide in the 5 hr feed and
TABLE 1. Composition of basal ration*
Ingredient Ground corn Soybean meal Corn oil Meat plus bone meal Corn gluten meal Yeast culture Polyethylene Dicalcium phosphate Calcium carbonate Vitamin mix 3 Salt DL-Methionine Trace mineral mix 4 Chromic oxide
Numerical 2 name 4-02-931 5-04-604 4-07-822 5-07-822 5-02-900
6-01-080 6-01-069 6-14-013
(%) 37.95 33.0 10.0 5.0 5.0 3.0 3.0 1.0 .9 .5 .3 .15 .1 .1
1 Ration contained by laboratory analysis 24.3% crude protein, 35.1% starch, 11.8% fat, 6.6% ash, 13.3% neutral detergent fiber and 0% uric acid. 2 Atlas of Nutritional Data on United States and Canadian Feeds. 3 Mix contained vitamin A, 3,527,360 IU; vitamin D 3 , 1,322,760 IU; vitamin E, 11,905 IU; vitamin B12, 3.5 mg; riboflavin, 2,205 mg; niacin, 6,614 mg; d-panthothenic acid, 7,055 mg; choline, 176,368 mg; menadione, 291 mg; folic acid, 441 mg; pyridoxine, 882 mg; thiamine, 882 mg; d-biotin, 44 mg/kg.
"Mix contained manganese, 12.0%, zinc, 8.0%; iron, 6.0%; copper, 10%, iodine, .1%; calcium, 18.0%.
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who force fed New Hampshire X White Leghorn chicks to increase feed intake from the ad libitum 9.7% to 14% of body weight per day, observed body weight gain to increase linearly with feed consumption and suggested that the limiting factor for chick growth is appetite. However, force feeding White Rock (meat type) chicks (Nir et ah, 1978) did not favorably affect growth rate. Meat-type broilers normally have a greater growth rate and feed consumption than slower growing Leghorns. Whether these birds have reached a maximum genetic capacity for tissue growth rate or if some other factor limits production is not known. The following study was conducted to determine the influence of feed intake level upon growth rate of a second meat-type broiler strain and to evaluate the impact of feed intake level upon initial digesta passage rate, carcass yield, and ration, protein, starch, ash, fat, and neutral detergent fiber apparent digestibility.
FEED INTAKE AND BROILERS
RESULTS AND DISCUSSION
Chicks force fed for 11 days, to simulate feed dry matter consumption of control birds (Group 2) fed 11 days, gained similarly (P>.10) and had identical feed efficiencies, suggesting that the force-feeding technique employed is a valid approach to controlling feed consumption at the ad libitum consumption level (Table 2). Live body weight gains of force-fed chicks increased linearly with increasing feed intake above ad libitum consumption, although feed efficiency declined markedly (30%). Group 1 controls required an additional 6 days to
achieve the body weight gains observed by the 140% force-fed group. The reduced feed efficiency may be due to either increased fat deposition, increased energy requirements, or decreased ration digestibility. These will be considered in order. Abdominal fat per unit body weight increased by 268% (Table 3) whereas feed intake increased from 75 to 160% of ad libitum consumption, indicating that at least a portion of the reduced feed efficiency is related to increased body fat content. Broiler maintenance energy requirements could be impacted by feeding level, as in rats (Rothwell et al, 1980), but the impact cannot be deduced from this study. Nutrient digestion and absorption are involved as ration (corrected for uric acid fecal mass), protein (corrected for uric acid fecal nitrogen), fat, ash, and starch digestibility estimates were inversely related with feed intake. Fat, ash, protein, and starch digestibility coupled to account for 96% of the decline in ration digestibility between the 75 and 160% feed intakes. Pancreas wet and dry weight (Table 4) increased markedly with increased feeding level. Why fat and protein, but not starch digestibility, decline markedly is not known. Time available for digestion and nutrient absorption (Table 2), assuming that initial digesta passage rate is correlated with average passage rate, did not vary with feed intake. Digestibility of ration, fat, and protein was poorly correlated (P> .4) with initial digesta passage rate. Carcass gains (Table 3) were elevated (P<.05) as feed consumption increased from 75 to 100% of the consumption observed by the 11-day controls. Both control and those forcefed 100% feed had similar carcass gain (P>.01), again indicating that the force-feeding technique employed was valid at this level. At 140% consumption, carcass gains increased only 4% in sharp contrast to the 32% higher live body weight gains observed. In this study increasing feed intake above ad libitum consumption did not impact (P>.1) quantity of carcass weight gain. This is reflected in breast, leg, and thigh yields. Gastrointestinal tract wet full weight, obtained by summing gastrointestinal tract components (Table 4), however, did increase (P<.05) as feed intake increased and accounted for 67% of the increased body weight gain observed at 140% feed intake. Drugs that specifically impact feed consumption without altering the ability of the broiler to digest feed more efficiently and
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recording the time of first ferric oxide appearance in feces postdose. Feces were monitored once per 3-min interval by each of two trained observers. On Day 11 of the experimental period, after an overnight fast, birds were processed as follows. Birds were hung on a rail, stunned, bled for 15 min. following severing of jugular and carotid veins, passed through a scalding vat, plucked by machine, and hand eviscreated. Carcasses and gastrointestinal tracts were weighed and stored in separate polyethylene bags at —15 C for later analysis. Carcass yield of primary parts was estimated by separating breast, thigh, and drumstick. Quantification of abdominal fat was by hand separation. The gastrointestinal tract was segmented into crop, proventriculus, gizzard, small intestine, and large intestine plus cecum full wet weight, empty wet weight, and dry empty weight. At the outset (Day 1 of the experimental period), 15 original birds in addition to the 77 were chosen at random and processed as described so that individual tissue gains of test birds completing the experiment could be estimated by the equation: Test bird tissue gain (g) = Test bird final tissue weight — Test bird initial body weight X [Initial tissue weight -r Initial body weight (g)]. All data were subjected to analysis of variance using the General Linear Model of the Statistical Analysis System (Barr et al, 1976). Duncan's multiple range test was used to determine differences (P<.05) between means when a significant F statistic effect was indicated by the analysis of variance (Steel and Torrie, 1960). Control birds (Group 1) allowed to consume feed ad libitum until their live body weight was similar to the fastest gaining force-fed group were compared only to that group.
2157
249
271
72.8 b 88.8 b 98.8b 89.3 b 37.8 a 19.4
l,387 c 764 b .56*
Means within a row with unlike superscripts differ (P<.05).
Birds force fed for 11 days.
—
.53*
71.1* 89.5 98.4 88.8* 37.9* 17.9
965
1,820*
C-ll3
219
77. l a 95.la 99.3a 94.7 a 40.3 a 16.5
941d 529 c .56 a
75%
221
72.3 b 90.4 a b 98.8 b 89.8 b 36.9 a b 18.1
1,352C 752 b .56 a
100%
20
6 8 9 7 3 1
87
l,75
125
Forc
Control birds allowed to consume feed ad libitum for 11 days.
Corrected for uric acid excretion nitrogen.
•Significantly differs from 140% force-feed intake.
5
"Corrected for uric acid excretion mass.
3
2 Control birds allowed to consume feed ad libitum until body weight gain was similar to fastest gaining force-fe 140% feed intake.
1
Digesta passage rate, min
Digestibility Ration, %4 Protein, % s Starch, % Fat, % Ash, % NDF, %
Dry matter consumption, % Weight gain, g Gain/feed
C-172
TABLE 2. Dry matter consumption, body weight gain, feed efficiency, ration, protein, starch, fat, ash, and n and digesta passage rate of force-fed chicks
om http://ps.oxfordjournals.org/ at Western Michigan University on May 7, 2015
FEED INTAKE AND BROILERS
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TABLE 3. Carcass gain with abdominal fat, liver breast, thigh, and drumstick weights Force-fed intakes 1 C-17 Carcass gain, g Abdominal fat, g Drumstick, g Thigh, g Breast, g
2
C-ll
3
572 a 10.9 d e 11.6 a 33.9 a l49a
785* 16.0* 25.2 53.2* 195*
75%
100%
125%
140%
160%
394 b 8.2 e .5b 18.9 b b 116
556 a 18.0 c d 10.0 a 33.6 a 144 a b
571a 20.6bc 12.5 a 32.8 a 149 a
578 a 27.4 a b 10.4 a 36.3 a 144 a b
486ab 30.2 a 5.3ab 31.8 a 140ab
Means within a row with unlike superscripts differ (P<.05). 1 2
Control birds allowed to consume feed ad libitum until body weight gain was similar to fastest gaining force-fed group (17 days). Values are compared only to the 140% feed intake. 'Control birds allowed to consume feed ad libitum for 11 days. •Significantly differs from 140% feed intake.
TABLE 4. Segmented gastrointestinal tract full, wet, and dry weights (g) Force-fed intakes' C-17
2
C-ll
3
Full croup, g Wet empty, g Dry empty, g
10* 8.9* 1.9*
Full proventriculus, g Empty, g Dry, g
12.8* 10.5* 2.7*
13c 8.3 C 1.7C 11.7 C 9.7 C 3.3ab
Full gizzard, g Empty, g Dry, g
37* 33 12.8*
47ab 42a 15.8bc
Full small intestine, g 122* Empty, g 64* Dry, g 16* Full ceca, g Empty, g Dry, g Pancreas, g Dry pancreas, g — 1
21.2 13.5 2.9 4.0 1.0*
127bc 69bc Igab 22.1ab 12.8 b 2.9
4.3b 1.2 bc
75%
100%
125%
140%
160%
9c
35bc
128 a 15.8 a 3.4 a b
109 a 14.6 a 3.8 a
24.5 a 13.5 a 4.0 a 54a 3 7 abc 18.1ab
21.0 a 14.7 a 3.9 a
8.3 C 1.7C
10.5bc 2.2bc
78ab 14ab 3.8 a
9.6C 8.9C 2.1b 37b 32 c 10.9 C 94d 48d 12 e 16.5 b 10.5 b 2.1
10.6 C 9.5 C 2.6ab
20.1ab 12.4 a b 3.2 a b
46ab 41ab 22.0 a
53a 40abc 18.1ab
3.8 b 1.0C
lllcd 67bc 18ab 16.5 b 11.3 b 2.4 4.3b 1.3 b c
125 b c 7iabc 19ab 17.3 b 11.4 b 2.4 4.8ab 1.4 ab
155ab 78ab 22 a 17.3 b 11.4 b 2.6 5.1ab 1.5 a
61a 44a 21.9 a 177 a 82 a 20ab 26.0 a 16.3 a 2.7 6.0 a 1.8a
Means within a row with unlike superscripts differ (P<.05).
Birds force fed for 11 days.
2
Control birds allowed to consume feed ad libitum until body weight gain was similar to fastest gaining force-fed group (17 days). Values are compared only to the 140% feed intake. 3
Control birds allowed to consume feed ad libitum for 11 days.
'Significantly differs from 140% force-fed intake.
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Birds force fed for 11 days.
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TEETER AND SMITH
possibly synthesize carcass p r o t e i n a c e o u s tissue would be e x p e c t e d t o be of minimal value. T h e data r e p o r t e d herein suggest t h a t a physiological process o t h e r t h a n feed intake regulation limits carcass g r o w t h rate of A r b o r Acre X Vantress broilers housed in g o o d e n v i r o n m e n t .
REFERENCES
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