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Intestine fullness influences feeding behaviour and crop filling in the domestic turkey
Physiology & Behavior, Vol. 58, No. 5, pp. 1027-1034, 1995 Copyright © 1995 Elsevier Science Inc. Printed in the USA. All rights reserved 0031-9384/95 $9.50 + .00
Pergamon 0031-9384(95)00151-4
Intestine Fullness Influences Feeding Behaviour and Crop Filling in the Domestic Turkey SUE J A C K S O N 1 A N D G A R Y E. D U K E
Department of Veterinary PathoBiology, University of Minnesota, 1988 Fitch Ave, St. Paul, MN 55108 USA Received 2 September 1994 JACKSON, S. AND G. E. DUKE. Intestine fullness influences feeding behavior and crop filling in the domestic turkey. PHYSIOI_, BEHAV 58(5) 1027-1034, 1995.--Image-intensification radiology showed that artificial introduction of food slurry into the intestines of 6-12 wk-old turkey hens significantly increased the proportion of boli entering the crop during an evening meal, hence decreasing the proportion of boli travelling directly to the gizzard. Since bolus movement is directed by esophageal motility, esophageal motility may be partially mediated by stretch or chemoreceptors iu the distal duodenum. Increased crop filling during afternoon meals lends support to the widely held belief that the crop increases gut storage capacity and helps "tide birds over" the nightly fast. Artificial filling of the distal duodenum paradoxically increased food intake in birds observed by radiology while eating a single meal (morning and evening), and in birds observed by eye over a 3 h period in the morning. This phenomenon is similar to that previously reported for rabbits and domestic chicken. Conversely, duodenal filling reduced food intake over a full day (11 h), more than compensating for the introduced food. Rapid filling of the small intestine (within 25 min. of the start of the meal) suggests a modification of the function of the domestic turkey duodenum to serve as a "mixing chamber," possibly enhancing digestive efficiency. The ways in which this modification affects digestion and absorption in the duodenum warrant investigation. Meleagris gallopavo Duodenal cannulation
Turkey Crop Duodenum Small intestine Crop filling Image-intensification radiology
THE effect of intestine fullness on food intake has been well studied in mammals (3,17',), but this aspect of peripheral control of voluntary feeding has received less attention from avian physiologists (3,13,18,23,24). Neural and hormonal feedback from the duodenum and ileum probably induce satiety in domestic poultry (3,4,10). Duodenal osmoreceptors are instrumental in decreasing voluntary food intake in domestic fowl when both nutritive and non-nutritive hyperosmotic solutions are infused into this organ (24). Glucose infusions into the duodenum have been reported to either reduce food intake in the fowl (23), or to have no effect on feeding behavior (13). Published studies of the role of the intestine in avian food intake control have concentrated on the domestic chicken: in view of the prevalence of interspecific differences in gastrointestinal feedback responses (3), we wished to investigate the effect of artificial duodenal and ileal filling on feeding behavior in turkeys. The importance of the avian crop as a food storage organ that helps "tide birds over" the nightly fast should be reflected in daily rhythms of crop tilling, with proportionally more food entering this organ in the afternoon and evening. Enhanced crop filling associated with increased food intake in the afternoon has
Feeding behaviour
been reported in domestic fowl (15) and other galliforms such as willow ptarmigan (11) and red grouse (19), and has been inferred from feeding rhythms in Japanese quail and domestic chickens (20). Chaplin et al. (2) reported differential filling of the turkey crop in the afternoon, but unequal preprandial fasting periods may have influenced these patterns (20), and further clarification of this pattern in turkeys is warranted. We used image-intensification radiology (IIR) to monitor gut motility and filling in habituated turkey hens feeding ad lib, testing the hypothesis that food slurry injected into the duodenum elicits satiety, and that duodenal and ileal fullness stimulate crop filling. We also investigate the daily pattern of food intake and crop filling; and present data and observations on on the rate of filling of the duodenum and ileum. METHODS
Bird Maintenance White Nicholas turkey hens (Meleagris gallopavo) 6-12 wk old were used throughout the study. All birds were obtained from a commercial hatchery, and kept for a minimum of one week
1 Requests for reprints should be addressed to Sue Jackson at her present address: Zoology Department, University of Cape Town, Private Bag Rondebosch, 7700, South Africa; E-Mail: [email protected]
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before the start of the experiments, to allow habituation to handling and to our presence. The hens were housed individually in rows of six wire mesh cages each measuring 60 X 60 x 40 cm, with mesh size 25 X 25 mm. Food and water were available ad lib in pans suspended outside the cages and accessible through windows in the mesh. Paper beneath the cages was changed and food ("T-10" turkey starter mash, prepared by the Animal Science Department at the University of Minnesota, comprising 25.9% protein, 2.4% fat, 48.7% carbohydrate 4.5% fiber, 6% ash and 12.5% water) and water were replenished daily. Ambient temperature was 22-24°C, and the light/dark cycle was 16 L/8D, with lights coming on at 07 h30.
Surgical Procedure General details of the surgical procedure used are given in Chaplin et al. (2). For both types of observations described below, birds were surgically prepared with implanted cannulas made of polyethylene tubing (inside diameter 5.28 mm, o.d. 6.86 mm, 20-30 mm long) and flared at the tip (proximal end) by heating to form a convex saddle-shaped flange conforming to the curve of the mucosal surface. The cannula was inserted through a longitudinal slit 8-15 mm long made in the distal limb of the duodenum, and the ends of the slit sewn closed around the base of the flange so that the saddle inside the duodenum prevented collapse or obstruction of the lumen. The flange also ensured that the cannula did not slip out. Loops of suture around the cannula secured it to the gut, the abdominal wall and to the skin at the entry wound. The cannula protruded through the abdominal cavity and skin on the ventral midline, the distal end capped with a plastic plug. During closure the cannula was gently pulled, "snugging" the duodenum against the muscular walls of the abdominal cavity and facilitating the formation of a ring of scar tissue which fused the duodenum and abdominal walls and stabilized the duodenum, prevented tearing of the gut around the cannula. During surgery, birds were anesthetised by intravenous injection of sodium pentobarbitol (65 mg/ml, Fort Dodge Laboratories Inc., Fort Dodge, IA, USA) with a dosage of 0.625 m l / k g body mass, via the brachial vein. Birds were fasted and denied access to water for at least 12 h before surgery to ensure emptying of the gut, minimizing the risk of peritonitis attendant on leakage of gut contents during insertion of the cannula. The procedure took approximately 45 min, and birds were invariably able to stand and were eager to eat within 3 h of surgery. During the l - 2 - w k postsurgery recovery period necessary to allow healing of the gut, the birds were handled and allowed to feed in front of the fluroscopy unit 2-5 times a day to ensure habituation to experimental conditions.
Satistical Analyses, Data Presentation and Experimental Procedure Two experimental approaches were taken--feeding observations of birds eating unaltered mash under their normal housing conditions, and radiographic observations of birds eating mash laced with BaSO 4 while being surveyed using an image-intensification radiograph (see below for details). Several comparisons were made and sample sizes differed among comparisons. Details of the exact experimental design are given below. The rapid growth rate of the experimental birds (80-150 g / d a y ) made it extremely difficult to standardize the body masses and sample sizes of individual birds used in each of the comparisons described below. First, small time differences between experiments resulted in large body mass differences. Second, it is impossible to predict exactly how long a cannula will remain open and functional in a growing bird, hence a certain
JACKSON AND DUKE
degree of opportunism was necessary in our selection of which subset of individuals to use for which comparisons. We controlled for variation in body mass by restricting all statistical comparisons for each parameter (listed below) to paired control and experimental feeding trials (see below for category definitions) performed within 3 days of each other on the same individual bird. A goodness-of-fit test revealed that the differences between experimental and control trials are not normally distributed. A nonparametric test (the Wilcoxon rank sum test for paired observations, 28) was therefore used to ascertain intra-individual differences between the paired experimental and control feeding trials. Each bird always acted as its own control, minimizing both the effects of body size and of inter-individual variation in feeding behavior on the parameters that we measured. Reports of variation in feeding patterns among Japanese Quail (20) highlight the need for such consideration of "eating idiosyncracies". " N " always refers to the number of individuals, not feeding trials--we avoided pseudoreplication, and used a single value for each individual bird to ensure that overall means were equally weighted across all birds used. Mean bird body mass varies within and between sets of comparisons because of the opportunistic selection of each subset of trials (see above), but for each individual bird the differences in body mass between experiment and control days never exceeded 250 g. The sequence of the experimental and control trials was randomized. Feeding in turkeys and other galliforms is affected by social factors (9,14,18), therefore we took care to randomize the treatment schedules of neighbouring birds. We present data in two ways. Firstly, we show overall means for each set of comparisons. These means were not used in the statistical analyses, and are included for descriptive purposes and to express inter-individual variation. Second, we show the numbers of instances for individual birds where the particular parameter measured during the experimental trial exceeded the same parameter measured during the paired control trial and vice versa (Tables 1 and 2). For instance, in Table 1, among birds that fed for 3 h, 7 birds ate more during the experimental trial than they did during the control trial, and the reverse was true for one bird. This result is depicted in the line " E / C " by the numbers " 7 / 1 . " The same approach was used to express data used for the comparison between morning and evening trials (Table 3). These data were used in the statistical tests, as shown by the asterisks denoting significant differences in the Tables. For both experimental series, birds were fasted for 10 h to ensure complete clearance of the intestine and to permit comparison with a previous study (2). Following the fast, the fullness of the distal duodenum was artificially manipulated by introduction of a slurry of water and finely powdered T-10 ration (2:3, v:v). The intestine was filled through a cannula in the distal loop of the duodenum (see below). This process took 2-3 min, during which time birds were restrained on their right sides with their legs taped together and their bodies wrapped with flexible plastic mesh. The slurry was injected into the duodenum using a 100 ml hypodermic syringe attached to a flexible rubber tube that fitted around the distal end of the cannula. The quantity of injected slurry varied between 15 and 30 ml, and was adjusted to weigh a constant 1% of the changing body weights of the rapidly growing birds. Control trials consisted of handled the birds exactly as though they were undergoing injection of slurry into the duodenum, without actual injection occurring. For both feeding and radiological observations, the total time for which a bird was handled was kept constant between experimental and control trials. The presence of BaSO 4 in the mash reduced the amount of food consumed (Tables 1 and 2), thus conclusions about the
INTESTINAL FULLNESS AFFECTS SATIETY IN THE TURKEY
TABLE 1. FEEDING OBSERVATIONS: THE EFFECT OF ARTIFICIAL DUODENUM FILLING ("EXPERIMENT") ON FEEDING BEHAVIOR Duration of Bird body Mass of food Foodeaten Treatment feeding mass (g) eaten (g) (% body mass)
N
18 Experiment
16.9 rain (5.7)
Control
16.9 rain
(7.0)
2814 (1008) 2592 (1095)
48.9 (12.2) 44.4 (10.9) 10/7~3
1.89 (0.69) 1.93 (0.74) 7/11
1602 (324) 1520 (305)
70.3 (11.0) 60.1 (14.3) 7/1"
4.48 (0.68) 3.97 (0.37) 6/2*
207.9 (39.1) 237.1 (34.6) 2/6*
8.36 (0.83) 10.43 (1.25) 0/8t
E/C
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T A B L E 3. RADIOGRAPHIC OBSERVATIONS: THE EFFECT OF TIME OF DAY ON FEEDING BEHAVIOR AND CROP FILLING Time of trial
N
Duration Mass Foodeaten of feeding Bird body food (% body (rain) mass (g) eaten(g) mass)
Experiment 7 AM PM
3 hr
Control
3 hr
E/C 8 Experiment
11 hr
Control
11 hr
2488 (406) 2303 (423)
E/C
"Control": no duodena[ filling. See methods section for protocol. N = sample size, figures in parentheses = 1 SD " E / C " : (no. of individual birds which ate more in the experimental feeding trial)/ (no. of individuals which ate more in the control feeding trial) Significant differences between experiment and control trials: * P < 0.025; i" P < 0.005 (1-tailed Wilcoxon rank sum test for paired samples). :~ One bird in this series of trials ate an identical mass of food during the experimental and control trials.
effects of experimental treatment or time of day on feeding behavior were not made on the basis of comparisons between these two food types.
TABLE 2. RADIOGRAPHIC OBSERVATIONS: THE EFFECT OF ARTIFICIAL DUODENUM FILLING ON FEEDING BEHAVIOR AND CROP FILLING Duration Treat- of feeding Bird body
N
ment
Mass Foodeaten food (% body eaten(g) mass)
(rain)
mas~ (g)
13.5 (3.9) 13.0 (7.3)
3315 (1178) 3221 (848)
32.4 (15.6) 26.8 (15.0) 6/2*
16.6 (7.9) 14.7 (3.6)
2224 (542) 2125 (672)
29.1 (9.0) 31.4 (16.3) 5/2':~
No.
% bol.
boli
to crop1
1.04 (0.53) 0.84 (0.45) 6/2"
26.5 (12.3) 20.3 (10.7) 5/3
52,5 (28.7) 34.2 (18.8) 6/2
1.38 (0.49) 1.52 (0.59) 3/5
26.9 (12.0) 25.2 (8.1) 3/4:~
58.0 (14.8) 50.2 (11.5) 7/1"
Morning
8
E C E/C
Afternoon
8
E C E/C
" E " experimental treatment and " C " control. " E / C " : (no. of trials on individual birds where a given parameter was greater following experimental treatmen0/(no, of trials on individuals where the same parameter was greater following control treatment). "Morning": 07:30-09:30, "Afternoon": 17:30-19:00. Birds fed food containing BaSO4, and protocols are described in methods section, and abbreviations as for Table 1. Significant differences between experimental and control trials:
* P < 0.05. 1 The remaining boli travelled directly to the gizzard, but for the sake of brevity w e have e:~:cinded these percentages. :~ One bird in this series of trials ate an identical mass of food or formed the same number c,f boli during the experimental and control trials.
% bol. to crop
13.2 (4.3) 11.8 (1.7)
3308 (1070) 3299 (966)
29.9 (11.1) 37.6 (15.9) 1/6"
0.96 (0.38) 1.15 (0.38) 2/5
26.4 (6.6) 20.9 (6.8) 4/3
57.3 (25.3) 57.7 (20.7) 4/3
10.5 (6.2) 12.6 (4.4)
2817 (407) 2331 (718)
28.9 (23.7) 36.9 (22.5) 2/5
0.99 (0.73) 1.64 (0.81) 2/5*
23.1 (22.4) 28.6 (12.4) 2/5
35.7 (26.3) 54.2 (24.4) 0/7t
AM/PM 8 Experiment
No. boli
Control
7 AM PM AM/PM
" A M " : 07:30 - 09:30, " P M " : 17:30 - 19:00. Protocols described in methods section, and abbreviations as for the previous tables. Note: means differ from corresponding values in Table 2 because a different subset of feeding trials was used for this comparison. " A M / P M " : (no. of birds which ate more in the morning)/(no, of birds which ate more in the afternoon) Significant difference between morning and afternoon trials: * P < 0.05; i" P < 0.01.
(i) Feeding Observations We wished to determine the effects of artificial duodenal filling (hereafter referred to as "experimental treatment") on birds feeding on pure mash (without BaSO 4) under their normal housing conditions. For this series of experiments, n = 18. Feeding observations were carried out between 08:00 and 10:00, in the rooms where the birds were housed. After an overnight fast of 10 h, slurry was introduced into each birds' gut as described above, and food was offered to the bird in a preweighed pan. The bird was observed for the duration of a single "feeding bout": when hungry, domestic turkeys feed for 10-20 min, with continuous pecking and swallowing interspersed with occasional drinking ( 0 - 3 episodes per feeding bout). Cessation of feeding is abrupt, and is marked by the bird either sitting down, or starting to preen or peck at its cage. A feeding bout was considered to have ended the when the bird did not take a mouthful for more than 2 min. Once turkeys cease feeding for this length of time, they rarely resume feeding. During the feeding bout, single boli were counted and the frequency of their passage down the oesophagus noted. Passage of boli was clearly discernible on the unfeathered section on the right side of the neck. The total time spent feeding was noted, as was the mass of food eaten to the nearest gram. For every bird, a control trial was carried out during which the bird was handled (see above), but no slurry injected. The apparent stimulation of feeding in the morning experimental trials (see below) prompted us to conduct two further experiments to determine total food intake over circumscribed, predetermined periods longer than the duration of a single feeding bout. Moreover, we wished to determine the effects of duodenal filling on food intake in the absence of an observer. The intestines of cannulated birds were filled with food slurry, and food pans were weighed at the beginning and end of 3- or 11-h feeding periods. The pans were half-filled to prevent spillage. Control trials were carried out in an identical fashion, but without the introduction of food slurry. Other details of the experiment are the same as those descibed above. In each case, n = 8. To investigate the possible effects of cannulation on feeding behavior, a separate set of control trials were also carded out
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using eight uncannulated birds which were handled to simulate duodenal filling in a manner identical to the birds which had undergone surgery. Differences in food intake over 11 h between this group and the l l - h control group above were tested for with the Kruskal-Wallis single factor ANOVA, a nonparametric test. Because cannulation is not an easily reversed process, this was the only statistical test in our study which was performed on two groups of entirely different individuals rather than using paired comparisons for the same individuals.
(ii) Radiographic Observations (a) The Influence of Artificial Duodenal Filling. We first measured feeding bout duration, mass of food eaten, and the number and destination (crop/proventriculus) of boli in birds subjected to experimental and control treatments (n = 8). These observations were made in two sets, one between 07:30 and 09:30 and the other between 17:30 and 19:00. Each bird was fasted for 10 h immediately prior to the experiment. For the afternoon trials, we ensured that birds had eaten to satiety after the lights came on and before the commencement of the 10 h fast. Food slurry then introduced into the duodenum as described above. The slurry was mixed with powdered barium sulphate (powdered mash:BaSO4:water::6:3:4, v:v:v) to render it radioopaque. The bird was then placed in a cardboard box set in front of a Philips Super M-100 Radiographic-Fluroscopy unit and offered food that had been mixed with powdered BaSO4 (mash:BaSO4::2:l, v:v). Water and food pans were attached in the same manner as the pans attached to the birds' cages. For ten days before the start of the experiments, birds were frequently handled, placed in the cardboard boxes, and fed in the same manner as during the experiments, until they were eating without hesitation or apparent nervousness when placed in front of the unit. A full set of both experimental and control trials were carried out both in the morning and in the afternoon, and comparisons between experimental and control treatments were not made across time periods (morning vs. afternoon). Second, we wished to estimate gastric evacuation rates, observe the movement of radio-opaque food slurry introduced into the duodenum, and to visually estimate the extent of fullness of the intestine following our experimental manipulation. Six birds were treated in exactly the same way as the experimental procedure described above, but radiographic observation was restricted to the abdominal cavity (ie; the proventriculus or glandular stomach, the gizzard or muscular stomach, and the intestines), and the food offered to the birds for ad lib consumption was not marked with BaSO 4. This facilitated distinction between ingested food from that artificially introduced via the cannula. Initially, the frequency of gastric contractions was noted by measuring the time taken for completion of fifteen full gastric contraction cycles as described by Duke et al. (6). This was possible because in every case, a variable amount of food refluxed back up into the gizzard from the duodenum immediately after injection through the cannula. Following this, the evacuation of radio-opaque food slurry from the gizzard was timed, and the occurrence of duodenal refluxes were noted. The time to first appearance of BaSO 4 in the ileum was noted. A series of control observations were carried out on the same birds, feeding ad lib. on radio-opaque food but without the introduction of food slurry into the duodenum. (b) The Influence of Time of Day. We assessed the effects of diel feeding patterns on food intake and crop filling. Experimental and control treatments were as described for the first series of radiographic observations (see above), except that comparisons were made within each treatment group (experimental or control) but between trials carried out at different times of day (morning,
JACKSON AND DUKE
07:30--09:30 VS. evening, 1 7 : 3 0 - 19:00). For this comparison, n=7. RESULTS
Feeding Observations Over the course of the single meal eaten immediately following introduction of food slurry into the duodenum, the mean duration of feeding activity and mass of food eaten were statistically indistinguishable between experimental and control feeding trials (Table 1). Slightly more individual birds showed higher absolute food intakes (g) following experimental treatment than after control treatment, but when food consumed was expressed as a percentage of body mass, this trend was reversed. The mean numbers of boli swallowed were similar between groups (36.5 _+ 15.1 and 37.9 __ 19.2 respectively). However, over a 3-h period more the mean mass of food eaten was significantly higher during the experimental trials, both in absolute terms and as a percentage of body mass. Moreover, the majority of birds ate more food (both in g and as a percentage of body mass) during the 3 h following experimental treatments. Artificial duodenal filling apparently stimulates feeding in the short term, but this trend was reversed for food consumption over the 11 h folllowing treatment. All comparisons within this group show that less food was eaten by birds after duodenal filling. The decrease in consumption was greater than the quantity of food introduced into the gut: less than 10 g (mash before addition of water) of food was injected, but mash intake decreased by a mean of 29 g in experimental trials. No significant differences in food intake (% body mass consumed over 11 h) occurred between cannulated and uncannulated control birds (10.43 _+ 1.25 and 9.78 _+ 0.45, n = 8), suggesting that surgery and the subsequent presence of a cannula did not affect feeding behavior. Moreover, birds that had undergone surgery regained normal growth rate within a week, showing a mean daily weight gain of 5.14 _+ 0.08% body mass per day during the experimental period, a value statistically indistinguishable from the weight gains of intact birds of the same age.
Radiographic Observations Unless otherwise stated, all food masses consumed include BaSO 4. (i) The Influence of Artificial Duodenal Filling. Among morning feeding trails, injection of slurry into the duodenum resulted in the same trend as did the feeding observations, causing an increase in the overall mean amount of food eaten (g and as a percentage of body mass, Table 2. See also Fig. 1 for an image showing duodenal fullness at the start of an experimental feeding trial). The majority of individual birds ate more during the experimental trials. Among trials carried out in the afternoon, individuals consumed significantly more food (g) following experimental treatments, but overall means show no difference because the two birds out of eight which did not fit this pattern ate disproportionately more after the control treatment, and one bird ate exactly the same amount in both trials. Normalization of intake to bird body mass reversed this pattern and rendered the difference between experimental and control treatments insignificant. In both the morning and afternoon feeding trials, a greater proportion of boli entered the birds' crops following duodenal filling, but this difference was only significant in the afternoon. Boli could clearly be seen entering the crop (Fig. 1.). Five minutes after the start of feeding, the proventriculi and gizzards of control birds were filling, but there was little or no
I N T E S T I N A L F U L L N E S S A F F E C T S S A T I E T Y IN T H E T U R K E Y
FIG. 1. Radiographic images (photographs of the radiograph video monitor) illustrating the methods ~ased for radiographic observations. In this and all subsequent figures, photographs are left lateral views, taken as the bird stood in a normal feeding position, with the its head toward the left of the photograph. Throughout the figure captions, "control" refers to birds which were cannulated Taut which had had no food introduced into the duodenum on the day of the feeding trial in question, and "experimental" refers to birds whiq:h had had 15 ml of food-BaSO 4 slurry introduced into the distal duodenum at the start of the feeding experiment. In all images of the abdomen, the cannula can be seen in the lower right quadrant, as some BaSO 4 res:idue remained in the cannula even on days when no slurry was introduced. The cannula is labeled in Fig. l(b), and not labeled thereafter. Times (rain) refer to times elapsed since the start of the feeding experiments, which coincided with the introduction of slurry and the commencement of feeding (the birds were hungry and began feeding as soon as food was placed in front of them). (a) The crop of a control bird at 5 min, showing a bolus entering the crop, and boli collected in the bottom of the crop. The outline of the crop wall can be seen faintly. N: neck; B: b,alus; BM: breast muscle. (b) The small intestine of an experimental b:Lrd immediately after introduction of 15 ml of food slurry into the duodelaum. The duodenum and jejunum are full, and a small amount of food has reftuxed into the gizzard. PD" proximal duodenum; DD: distal duodenum; G: gizzard; J: jejunum; C: cannula.
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FIG. 2. The abdomens of (a) a control and (b) an experimental bird at 5 min. The gizzard of the control bird is filling, but the duodenum is still empty. Note the bolus entering the gizzard to the top left. In both (a) and (b), the gizzard is in the phase of the gastric contraction cycle when the thick gizzard muscles contract, giving the organ a characteristic "dog bone" shape (Refs. 7, 8). The entire small intestine of the experimental bird is full, including the ileum. Comparison of (b) with Fig. 1 (b) shows the progression of digesta in the same individual. Abbreviations the same as for Fig. 1, with the addition of SI: small intestine (the duodenum, jejunum and ileum were not distinguishable from one another).
food in the d u o d e n u m (Fig. 2). After 15 m i n food had b e g u n to pass into this organ (Fig. 3). A m o n g experimental birds, the proventriculi and gizzards (hereafter referred to collectively as " s t o m a c h " ) , d u o d e n u m s and j e j u n u m s of experimental birds were filled with food after 5 min, and after 15 m i n the entire stomach and small intestine w e r e filled with food. At the cessation of feeding, 25 m i n after the start of a feeding trial, the small intestines of the control birds were completely radio-opaque, implying fullness. Control birds that did not experience duodenal filling, ate the same amount of normal m a s h (without B a S O 4) as did experimental birds that had had 15 ml of radio-opaque slurry introduced into their d u o d e n u m s (Table 4). One control bird exhibited
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JACKSON AND DUKE
duodenal refluxes during the feeding trials, and refluxes occurred in two experimental birds. Oi) The Influence of Time of Day. Among experimental trials, overall means show that birds ate significantly more in the afternoon than they did in the morning, but this difference was removed by normalization of food intake to body mass (Table 3). Control trials also revealed higher overall mean food intake in the evening when mass of food eaten was expressed as a percentage of body mass, but absolute food intake was unaffected by time of day. For both experimental and control series, most individual birds ate more in the evening than in the morning, but this difference was only significant among the control birds. A significantly greater proportion of boli entered the crop in the afternoon control treatment series. DISCUSSION
Crop emptying in the turkey is at least partially under the control of the stomach, which regulates delivery of food to itself
TABLE 4. RADIOGRAPHICOBSERVATIONS:THE EFFECT OF ARTIFICIAL DUODENUM FILLING ON GUT MOTILITY AND INTESTINE FILLING RATE Dur. of feeding trial (rain) Experiment 12.0 (2.8) Control 14.4 (4.45)
IncidBird ence of body reflux 1 mass (g)
Mass food eaten (g)
2
2444 (143)
56.5 (18.3)
1
2328 (94)
64.0 (16.3)
Time to Time to duod. ileal fill 2 fill 3
Store. Time to fullness stom. at start fill 4 (%)
0.67 (1.34)
8.73 (3.81)
8.76 (2.64)
44.0 (38.0)
Abbreviations and protocols as for Tables 1 and 2, with the exception that birds were fed their normal mash without BaSO 4 powder. N = 6 throughout. 1 The presence or absence of refluxes in each bird was noted, but refluxes were not counted. 2 The time (min) at which duodenum began to fill with ingested (non-radio-opaque) food. 3 Time (min) to filling of the ileum refers to the onset of filling of this organ, i.e.,: the time w h e n radio-opaque material was first observed in the ileum. 4 The time (rain) at which the stomach was no longer radio-opaque, i.e.,: the time at which it became filled with ingested (non-radio-opaque) food rather than with radio-opaque food refluxed from the duodenum. Note: T i m e s to filling of various intestinal sections could not be determined in control birds, which had no radio-opaque substance in their guts.
(2). The pausing or "backing up" of boli in the pre and post-crop esophagus described by these authors did not occur in the present study, perhaps because the degree of indirect stomach filling that resulted from duodenal injections of food slurry was not sufficient to initiate this pattern. The results of our feeding observations showing that artificial duodenal filling did not affect the amount of food and number of boli swallowed over one meal, are supported by a previous study (2) where manipulation of crop, stomach, and ileal fullness by introduction of food slurry per os did not affect food intake in similarly free-feeding birds. The drop in summed food intake (g eaten ad lib. plus injected slurry) below the level of control birds that we report after 11 h is consistent with studies on rats (12), and on domestic chickens (23). In contrast, the increased food intake that we observed after 3 h reflects that which we observed during our radiological trials, and possible explanations are discussed below.
Daily Rhythm in Crop Filling The length of the preprandial fast affects crop filling (20,23), but we report an afternoon increase in crop filling when the length of the preprandial fast is held constant at 10 hr. Our results suggest that the crop does act as storage organ to ensure a prolonged supply of food to the stomach and lower gut during the night. Fullness of the crop was highly variable and not associated with the ends of voluntary feeding bouts (see also Ref. 2). This observation does not support a primary regulatory role of the crop in food intake and satiety. Cropectomy has little effect on feeding patterns in birds fed energy-rich diets, but may limit intake in birds fed energy-dilute diets (17,20).
Gut Filling Times FIG. 3. The abdomens of (a) a control and (b) an experimental bird at 15 min. Note the beginning of duodenal filling in the control bird [compare with Fig. 2(a)]. Note also the segmenting contractions in the jejunum and ileum of the experimental bird (b). Abbreviations as for previous figures, with the addition of J/I: jejunum/ileum (these two sections were not distinguishable from each another).
An important finding of our study is that the ileum appears full at the end of a single meal of radio-opaque food. This may be partly a consequence of food consistency, because finely ground food may pass through the stomach relatively quickly. Such rapid food passage is unlikely in wild birds feeding on coarser foods,
INTESTINAL FULLNESS, AFFECTS SATIETY IN THE TURKEY
but may force us to reevaluate the functions of the duodenum in domestic poultry. Among domesticated birds, both the duodenum and the ileum are routinely exposed to large quantities of chemically undigested food soon after the commencement of feeding, and this may well affect both the function of gut chemo- and mechanoreceptors, and the role of these sections of the gut in peripheral feedback to cerebral satiety centers.
Duodenal Injections Paradoxically Stimulate Feeding Injection of food slurry frequently stimulated at least one duodenal reflux, resulting in partial filling of the gizzard before the start of the feeding trial. We therefore do not presume to isolate the effects of duodenal filling alone on feeding behavior, and must rather seek exphmations of how artificial filling of the gut as a whole affects feeding behavior. The short-term increases in food consumption following duodenal filling with food slurry contradict our hypothesis that duodenal fullness elicits the cessation of feeding. Increased food intake in response both to duodenal infusions of glucose (23) and to intraperitoneal injections of glucose (25,26) occurs in domestic chickens. The same phenomenon in rabbits has been attributed to a rise in circulating insulin levels in response to elevated blood glucose, leading to increased tissue absorption of glucose, followed by hyperglycemia, and hunger (16). Pharmacological doses of insulin may directly increase food intake in mammals (27), but the physiological relevance of this is questionable. The short-term increases and longer-term (albeit incomplete) compensation we report are consistent with those reported for rabbits by Rezek et al. (16). We are hesitant to adopt the above explanation for the patterns that we report, because the role of circulating blood glucose
1033
in the regulation of avian feeding behavior is still obscure (3), and manipulation of blood glucose levels in chickens has no effect on food intake over a 4 h period (25). Published data on chicken blood glucose levels during and immediately after meals are contradictory, with some studies reporting detectable increases within half an hour (1), and others detecting no short-term patterns consistent enough to be involved with satiety (21). Blood glucose levels in 24-hr fasted turkey poults increase measurably 1 h after feeding (5). Behavioral and tactile cues such as oral stimulation certainly influence avian feeding behavior (9), and in bypassing normal ingestion channels we may have triggered an inappropriate feeding response. Although discomfort resulting from artifially induced distension of the gut reduces rather than enhances food intake in the rat (12), handling and discomfort may cause release of central opioid peptides, leading to increased feeding in the domestic chicken (22). Full explanation of the response awaits further study such as monitoring of the blood levels of circulating nutrients and of insulin and other hormones after voluntary feeding of turkeys (25). Infusions of different substances into the turkey duodenum in a manner comparable to previous studies on chickens (23, 24) would also help elucidate the paradoxical stimulation of feeding that we report here. ACKNOWLEDGEMENTS We thank Drs. S.B. Chaplin, D.M. Denbow and T.F. Poppema for helpful discussions and comments on the manuscript, and Miss C. Chung for assistance in the laboratory. Darren Straub of Willmar Poultry generously supplied us with turkeys. The study was funded by the Minnesota Agricultural Experiment Station, Project 61-44, and by a postdoctoral bursary awarded to the senior author by the South African Foundation for Research and Development.
REFERENCES
1. Aramaki, J.; Weiss, H. S. Patterns of carbohydrate and protein digestion in the chicken as derived from sampling the hepatic portal system. Arch. Int. Physiol. Biochem. 70:1-15; 1962. 2. Chaplin, S. B.; Raven, J.', Duke, G. E. The influence of the stomach on crop function and feeding behavior in domestic turkeys. Physiol. Behav. 52:261-266;1992 3. Denbow, D. M. Food intake control in birds. Neurosci. Biobehav. Rev. 9:223-232; 1985. 4. Denbow, D. M. Peripheral and central control of food intake. Poult. Sci. 68:938-947;1989. 5. Donaldson, W. E.; Christensen, V. L. Dietary carbohydrate level and glucose metabolism in turkey poults. Comp. Biochem. Physiol. 98A:347-350; 1991. 6. Duke, G. E.; Dziuk, H. E.; Evanson, O. A. Gastric pressure and smooth muscle electrical potential changes in turkeys. Am. J. Physiol. 222:167-173; 1972. 7. Duke, G. E.; Evanson, O. A. Inhibition of gastric motility by duodenal contents in turkeys. Poult. Sci. 51:1625-1636; 1972. 8. Dziuk, H. E.; Duke, G. F;. Cineradiographic studies of gastric motility in turkeys. Am. J. Physiol. 222:159-166; 1972. 9. Gentle, M. J. Sensory involvement in the control of food intake in poultry. Proc. Nutr. Soc. 44:313-321; 1985. 10. Hill, K. J.; Strachan, P. J. Recent advances in digestive physiology of the fowl. Syrup. Zool. Soc. Lond. 35:1-12; 1975. 11. Irving, L.; West, G. C.; Peyton, L. J. Winter feeding program of Alaska willow ptarmigan shown by crop contents. Condor 69:69-77; 1967. 12. Koopmans, H. S. The role of the ileum in the control of food intake and intestinal adaptation. Can. J. Physiol. Pharmacol. 68:650-655; 1990. 13. Lacy, M. P.; van Krey, H. P.; Skewes, P. A.; Denbow, D. M.
14. 15. 16.
17. 18. 19. 20. 21. 22. 23. 24.
Intraduodenal glucose infusions do not affect food intake in the fowl. Poult. Sci. 65:565-569; 1986. Millam, J. R.; Ernst, R. A.; Voris, J. C.; Pfost, R. E. A data acquisition system for monitoring growing turkeys. Appl. Agric. Res. 3:75-80; 1988. Mongin, P. Composition and gizzard contents in the laying hen. Br. Poult. Sci. 17:499-507; 1976. Rezck, M.; Havlicek, V.; Hughes, K. R. Paradoxical stimulation of food intake by larger loads of glucose, fructose and mannose: Evidence for a positive feedback effect. Physiol. Bchav. 21:243-249; 1978. Richardson, A. J. The role of the crop in the feeding behaviour of the domestic chicken. Anim. Behav. 18:633-639; 1970. Savory, C. J. Meal occurrence in Japanese quail in relation to particle size and nutrient density. Anim. Behav. 28:160-171; 1980. Savory, C. J. Selection of heather age and chemical composition by Red Grouse in relation to physiological state, season and time of day. Orals. Scand. 14:135-143; 1983. Savory, C. J. An investigation into the role of the crop in control of feeding in Japanese quail and domestic fowls. Physiol. Behav. 35:917-928; 1985. Savory, C. J. How closely do circulating levels of blood glucose reflect feeding state in fowls? Comp. Biochem. Physiol. 88A:101106; 1987. Savory, C. J.; Gentle, M. J.; Yeomans, M. R. Opioid modulation of feeding and drinking in fowls. Br. Poult. Sci. 30:379-392; 1989. Shaobi, T.H.; Forbes, J. M. Feeding responses to infusions of glucose solutions into the duodenum of cockerels and the influences of prefasting or vagotomy. Br. Poult. Sci. 28:407-413; 1987. Shurlock, T. G. H.; Forbes, J. M. Factors affecting food intake in the domestic chicken:the effect of infusions of nutritive and nonnutritive
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substances into the crop and duodenum. Br. Poult. Sci. 22:323-331; 1981. 25. Smith, C. J. V.; Bright-Taylor, B. Does a glucostatic mechanism for food intake control exist in chickens? Poult. Sci. 53:1720-1724; 1974. 26. Smith, C. J. V.; Haffield, J.; Fowler, S.; Bright-Taylor, B. Changes in food consumption and blood glucose levels in the domestic
JACKSON AND DUKE
chicken Gallus domesticus in response to the administration of 2-oxy-D-glucose. Comp. Biochem. Physiol. 51A:811-814; 1975. 27. VanderWeele, D. A. Hyperinsulinism and feeding: Not all sequences lead to the same behavioral outcome or conclusions. Appetite 6:4752; 1985. 28. Zar, J. H. Biostatistical analysis, 2nd Ed. Prentice Hall; 1984.
Pergamon 0031-9384(95)00151-4
Intestine Fullness Influences Feeding Behaviour and Crop Filling in the Domestic Turkey SUE J A C K S O N 1 A N D G A R Y E. D U K E
Department of Veterinary PathoBiology, University of Minnesota, 1988 Fitch Ave, St. Paul, MN 55108 USA Received 2 September 1994 JACKSON, S. AND G. E. DUKE. Intestine fullness influences feeding behavior and crop filling in the domestic turkey. PHYSIOI_, BEHAV 58(5) 1027-1034, 1995.--Image-intensification radiology showed that artificial introduction of food slurry into the intestines of 6-12 wk-old turkey hens significantly increased the proportion of boli entering the crop during an evening meal, hence decreasing the proportion of boli travelling directly to the gizzard. Since bolus movement is directed by esophageal motility, esophageal motility may be partially mediated by stretch or chemoreceptors iu the distal duodenum. Increased crop filling during afternoon meals lends support to the widely held belief that the crop increases gut storage capacity and helps "tide birds over" the nightly fast. Artificial filling of the distal duodenum paradoxically increased food intake in birds observed by radiology while eating a single meal (morning and evening), and in birds observed by eye over a 3 h period in the morning. This phenomenon is similar to that previously reported for rabbits and domestic chicken. Conversely, duodenal filling reduced food intake over a full day (11 h), more than compensating for the introduced food. Rapid filling of the small intestine (within 25 min. of the start of the meal) suggests a modification of the function of the domestic turkey duodenum to serve as a "mixing chamber," possibly enhancing digestive efficiency. The ways in which this modification affects digestion and absorption in the duodenum warrant investigation. Meleagris gallopavo Duodenal cannulation
Turkey Crop Duodenum Small intestine Crop filling Image-intensification radiology
THE effect of intestine fullness on food intake has been well studied in mammals (3,17',), but this aspect of peripheral control of voluntary feeding has received less attention from avian physiologists (3,13,18,23,24). Neural and hormonal feedback from the duodenum and ileum probably induce satiety in domestic poultry (3,4,10). Duodenal osmoreceptors are instrumental in decreasing voluntary food intake in domestic fowl when both nutritive and non-nutritive hyperosmotic solutions are infused into this organ (24). Glucose infusions into the duodenum have been reported to either reduce food intake in the fowl (23), or to have no effect on feeding behavior (13). Published studies of the role of the intestine in avian food intake control have concentrated on the domestic chicken: in view of the prevalence of interspecific differences in gastrointestinal feedback responses (3), we wished to investigate the effect of artificial duodenal and ileal filling on feeding behavior in turkeys. The importance of the avian crop as a food storage organ that helps "tide birds over" the nightly fast should be reflected in daily rhythms of crop tilling, with proportionally more food entering this organ in the afternoon and evening. Enhanced crop filling associated with increased food intake in the afternoon has
Feeding behaviour
been reported in domestic fowl (15) and other galliforms such as willow ptarmigan (11) and red grouse (19), and has been inferred from feeding rhythms in Japanese quail and domestic chickens (20). Chaplin et al. (2) reported differential filling of the turkey crop in the afternoon, but unequal preprandial fasting periods may have influenced these patterns (20), and further clarification of this pattern in turkeys is warranted. We used image-intensification radiology (IIR) to monitor gut motility and filling in habituated turkey hens feeding ad lib, testing the hypothesis that food slurry injected into the duodenum elicits satiety, and that duodenal and ileal fullness stimulate crop filling. We also investigate the daily pattern of food intake and crop filling; and present data and observations on on the rate of filling of the duodenum and ileum. METHODS
Bird Maintenance White Nicholas turkey hens (Meleagris gallopavo) 6-12 wk old were used throughout the study. All birds were obtained from a commercial hatchery, and kept for a minimum of one week
1 Requests for reprints should be addressed to Sue Jackson at her present address: Zoology Department, University of Cape Town, Private Bag Rondebosch, 7700, South Africa; E-Mail: [email protected]
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before the start of the experiments, to allow habituation to handling and to our presence. The hens were housed individually in rows of six wire mesh cages each measuring 60 X 60 x 40 cm, with mesh size 25 X 25 mm. Food and water were available ad lib in pans suspended outside the cages and accessible through windows in the mesh. Paper beneath the cages was changed and food ("T-10" turkey starter mash, prepared by the Animal Science Department at the University of Minnesota, comprising 25.9% protein, 2.4% fat, 48.7% carbohydrate 4.5% fiber, 6% ash and 12.5% water) and water were replenished daily. Ambient temperature was 22-24°C, and the light/dark cycle was 16 L/8D, with lights coming on at 07 h30.
Surgical Procedure General details of the surgical procedure used are given in Chaplin et al. (2). For both types of observations described below, birds were surgically prepared with implanted cannulas made of polyethylene tubing (inside diameter 5.28 mm, o.d. 6.86 mm, 20-30 mm long) and flared at the tip (proximal end) by heating to form a convex saddle-shaped flange conforming to the curve of the mucosal surface. The cannula was inserted through a longitudinal slit 8-15 mm long made in the distal limb of the duodenum, and the ends of the slit sewn closed around the base of the flange so that the saddle inside the duodenum prevented collapse or obstruction of the lumen. The flange also ensured that the cannula did not slip out. Loops of suture around the cannula secured it to the gut, the abdominal wall and to the skin at the entry wound. The cannula protruded through the abdominal cavity and skin on the ventral midline, the distal end capped with a plastic plug. During closure the cannula was gently pulled, "snugging" the duodenum against the muscular walls of the abdominal cavity and facilitating the formation of a ring of scar tissue which fused the duodenum and abdominal walls and stabilized the duodenum, prevented tearing of the gut around the cannula. During surgery, birds were anesthetised by intravenous injection of sodium pentobarbitol (65 mg/ml, Fort Dodge Laboratories Inc., Fort Dodge, IA, USA) with a dosage of 0.625 m l / k g body mass, via the brachial vein. Birds were fasted and denied access to water for at least 12 h before surgery to ensure emptying of the gut, minimizing the risk of peritonitis attendant on leakage of gut contents during insertion of the cannula. The procedure took approximately 45 min, and birds were invariably able to stand and were eager to eat within 3 h of surgery. During the l - 2 - w k postsurgery recovery period necessary to allow healing of the gut, the birds were handled and allowed to feed in front of the fluroscopy unit 2-5 times a day to ensure habituation to experimental conditions.
Satistical Analyses, Data Presentation and Experimental Procedure Two experimental approaches were taken--feeding observations of birds eating unaltered mash under their normal housing conditions, and radiographic observations of birds eating mash laced with BaSO 4 while being surveyed using an image-intensification radiograph (see below for details). Several comparisons were made and sample sizes differed among comparisons. Details of the exact experimental design are given below. The rapid growth rate of the experimental birds (80-150 g / d a y ) made it extremely difficult to standardize the body masses and sample sizes of individual birds used in each of the comparisons described below. First, small time differences between experiments resulted in large body mass differences. Second, it is impossible to predict exactly how long a cannula will remain open and functional in a growing bird, hence a certain
JACKSON AND DUKE
degree of opportunism was necessary in our selection of which subset of individuals to use for which comparisons. We controlled for variation in body mass by restricting all statistical comparisons for each parameter (listed below) to paired control and experimental feeding trials (see below for category definitions) performed within 3 days of each other on the same individual bird. A goodness-of-fit test revealed that the differences between experimental and control trials are not normally distributed. A nonparametric test (the Wilcoxon rank sum test for paired observations, 28) was therefore used to ascertain intra-individual differences between the paired experimental and control feeding trials. Each bird always acted as its own control, minimizing both the effects of body size and of inter-individual variation in feeding behavior on the parameters that we measured. Reports of variation in feeding patterns among Japanese Quail (20) highlight the need for such consideration of "eating idiosyncracies". " N " always refers to the number of individuals, not feeding trials--we avoided pseudoreplication, and used a single value for each individual bird to ensure that overall means were equally weighted across all birds used. Mean bird body mass varies within and between sets of comparisons because of the opportunistic selection of each subset of trials (see above), but for each individual bird the differences in body mass between experiment and control days never exceeded 250 g. The sequence of the experimental and control trials was randomized. Feeding in turkeys and other galliforms is affected by social factors (9,14,18), therefore we took care to randomize the treatment schedules of neighbouring birds. We present data in two ways. Firstly, we show overall means for each set of comparisons. These means were not used in the statistical analyses, and are included for descriptive purposes and to express inter-individual variation. Second, we show the numbers of instances for individual birds where the particular parameter measured during the experimental trial exceeded the same parameter measured during the paired control trial and vice versa (Tables 1 and 2). For instance, in Table 1, among birds that fed for 3 h, 7 birds ate more during the experimental trial than they did during the control trial, and the reverse was true for one bird. This result is depicted in the line " E / C " by the numbers " 7 / 1 . " The same approach was used to express data used for the comparison between morning and evening trials (Table 3). These data were used in the statistical tests, as shown by the asterisks denoting significant differences in the Tables. For both experimental series, birds were fasted for 10 h to ensure complete clearance of the intestine and to permit comparison with a previous study (2). Following the fast, the fullness of the distal duodenum was artificially manipulated by introduction of a slurry of water and finely powdered T-10 ration (2:3, v:v). The intestine was filled through a cannula in the distal loop of the duodenum (see below). This process took 2-3 min, during which time birds were restrained on their right sides with their legs taped together and their bodies wrapped with flexible plastic mesh. The slurry was injected into the duodenum using a 100 ml hypodermic syringe attached to a flexible rubber tube that fitted around the distal end of the cannula. The quantity of injected slurry varied between 15 and 30 ml, and was adjusted to weigh a constant 1% of the changing body weights of the rapidly growing birds. Control trials consisted of handled the birds exactly as though they were undergoing injection of slurry into the duodenum, without actual injection occurring. For both feeding and radiological observations, the total time for which a bird was handled was kept constant between experimental and control trials. The presence of BaSO 4 in the mash reduced the amount of food consumed (Tables 1 and 2), thus conclusions about the
INTESTINAL FULLNESS AFFECTS SATIETY IN THE TURKEY
TABLE 1. FEEDING OBSERVATIONS: THE EFFECT OF ARTIFICIAL DUODENUM FILLING ("EXPERIMENT") ON FEEDING BEHAVIOR Duration of Bird body Mass of food Foodeaten Treatment feeding mass (g) eaten (g) (% body mass)
N
18 Experiment
16.9 rain (5.7)
Control
16.9 rain
(7.0)
2814 (1008) 2592 (1095)
48.9 (12.2) 44.4 (10.9) 10/7~3
1.89 (0.69) 1.93 (0.74) 7/11
1602 (324) 1520 (305)
70.3 (11.0) 60.1 (14.3) 7/1"
4.48 (0.68) 3.97 (0.37) 6/2*
207.9 (39.1) 237.1 (34.6) 2/6*
8.36 (0.83) 10.43 (1.25) 0/8t
E/C
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T A B L E 3. RADIOGRAPHIC OBSERVATIONS: THE EFFECT OF TIME OF DAY ON FEEDING BEHAVIOR AND CROP FILLING Time of trial
N
Duration Mass Foodeaten of feeding Bird body food (% body (rain) mass (g) eaten(g) mass)
Experiment 7 AM PM
3 hr
Control
3 hr
E/C 8 Experiment
11 hr
Control
11 hr
2488 (406) 2303 (423)
E/C
"Control": no duodena[ filling. See methods section for protocol. N = sample size, figures in parentheses = 1 SD " E / C " : (no. of individual birds which ate more in the experimental feeding trial)/ (no. of individuals which ate more in the control feeding trial) Significant differences between experiment and control trials: * P < 0.025; i" P < 0.005 (1-tailed Wilcoxon rank sum test for paired samples). :~ One bird in this series of trials ate an identical mass of food during the experimental and control trials.
effects of experimental treatment or time of day on feeding behavior were not made on the basis of comparisons between these two food types.
TABLE 2. RADIOGRAPHIC OBSERVATIONS: THE EFFECT OF ARTIFICIAL DUODENUM FILLING ON FEEDING BEHAVIOR AND CROP FILLING Duration Treat- of feeding Bird body
N
ment
Mass Foodeaten food (% body eaten(g) mass)
(rain)
mas~ (g)
13.5 (3.9) 13.0 (7.3)
3315 (1178) 3221 (848)
32.4 (15.6) 26.8 (15.0) 6/2*
16.6 (7.9) 14.7 (3.6)
2224 (542) 2125 (672)
29.1 (9.0) 31.4 (16.3) 5/2':~
No.
% bol.
boli
to crop1
1.04 (0.53) 0.84 (0.45) 6/2"
26.5 (12.3) 20.3 (10.7) 5/3
52,5 (28.7) 34.2 (18.8) 6/2
1.38 (0.49) 1.52 (0.59) 3/5
26.9 (12.0) 25.2 (8.1) 3/4:~
58.0 (14.8) 50.2 (11.5) 7/1"
Morning
8
E C E/C
Afternoon
8
E C E/C
" E " experimental treatment and " C " control. " E / C " : (no. of trials on individual birds where a given parameter was greater following experimental treatmen0/(no, of trials on individuals where the same parameter was greater following control treatment). "Morning": 07:30-09:30, "Afternoon": 17:30-19:00. Birds fed food containing BaSO4, and protocols are described in methods section, and abbreviations as for Table 1. Significant differences between experimental and control trials:
* P < 0.05. 1 The remaining boli travelled directly to the gizzard, but for the sake of brevity w e have e:~:cinded these percentages. :~ One bird in this series of trials ate an identical mass of food or formed the same number c,f boli during the experimental and control trials.
% bol. to crop
13.2 (4.3) 11.8 (1.7)
3308 (1070) 3299 (966)
29.9 (11.1) 37.6 (15.9) 1/6"
0.96 (0.38) 1.15 (0.38) 2/5
26.4 (6.6) 20.9 (6.8) 4/3
57.3 (25.3) 57.7 (20.7) 4/3
10.5 (6.2) 12.6 (4.4)
2817 (407) 2331 (718)
28.9 (23.7) 36.9 (22.5) 2/5
0.99 (0.73) 1.64 (0.81) 2/5*
23.1 (22.4) 28.6 (12.4) 2/5
35.7 (26.3) 54.2 (24.4) 0/7t
AM/PM 8 Experiment
No. boli
Control
7 AM PM AM/PM
" A M " : 07:30 - 09:30, " P M " : 17:30 - 19:00. Protocols described in methods section, and abbreviations as for the previous tables. Note: means differ from corresponding values in Table 2 because a different subset of feeding trials was used for this comparison. " A M / P M " : (no. of birds which ate more in the morning)/(no, of birds which ate more in the afternoon) Significant difference between morning and afternoon trials: * P < 0.05; i" P < 0.01.
(i) Feeding Observations We wished to determine the effects of artificial duodenal filling (hereafter referred to as "experimental treatment") on birds feeding on pure mash (without BaSO 4) under their normal housing conditions. For this series of experiments, n = 18. Feeding observations were carried out between 08:00 and 10:00, in the rooms where the birds were housed. After an overnight fast of 10 h, slurry was introduced into each birds' gut as described above, and food was offered to the bird in a preweighed pan. The bird was observed for the duration of a single "feeding bout": when hungry, domestic turkeys feed for 10-20 min, with continuous pecking and swallowing interspersed with occasional drinking ( 0 - 3 episodes per feeding bout). Cessation of feeding is abrupt, and is marked by the bird either sitting down, or starting to preen or peck at its cage. A feeding bout was considered to have ended the when the bird did not take a mouthful for more than 2 min. Once turkeys cease feeding for this length of time, they rarely resume feeding. During the feeding bout, single boli were counted and the frequency of their passage down the oesophagus noted. Passage of boli was clearly discernible on the unfeathered section on the right side of the neck. The total time spent feeding was noted, as was the mass of food eaten to the nearest gram. For every bird, a control trial was carried out during which the bird was handled (see above), but no slurry injected. The apparent stimulation of feeding in the morning experimental trials (see below) prompted us to conduct two further experiments to determine total food intake over circumscribed, predetermined periods longer than the duration of a single feeding bout. Moreover, we wished to determine the effects of duodenal filling on food intake in the absence of an observer. The intestines of cannulated birds were filled with food slurry, and food pans were weighed at the beginning and end of 3- or 11-h feeding periods. The pans were half-filled to prevent spillage. Control trials were carried out in an identical fashion, but without the introduction of food slurry. Other details of the experiment are the same as those descibed above. In each case, n = 8. To investigate the possible effects of cannulation on feeding behavior, a separate set of control trials were also carded out
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using eight uncannulated birds which were handled to simulate duodenal filling in a manner identical to the birds which had undergone surgery. Differences in food intake over 11 h between this group and the l l - h control group above were tested for with the Kruskal-Wallis single factor ANOVA, a nonparametric test. Because cannulation is not an easily reversed process, this was the only statistical test in our study which was performed on two groups of entirely different individuals rather than using paired comparisons for the same individuals.
(ii) Radiographic Observations (a) The Influence of Artificial Duodenal Filling. We first measured feeding bout duration, mass of food eaten, and the number and destination (crop/proventriculus) of boli in birds subjected to experimental and control treatments (n = 8). These observations were made in two sets, one between 07:30 and 09:30 and the other between 17:30 and 19:00. Each bird was fasted for 10 h immediately prior to the experiment. For the afternoon trials, we ensured that birds had eaten to satiety after the lights came on and before the commencement of the 10 h fast. Food slurry then introduced into the duodenum as described above. The slurry was mixed with powdered barium sulphate (powdered mash:BaSO4:water::6:3:4, v:v:v) to render it radioopaque. The bird was then placed in a cardboard box set in front of a Philips Super M-100 Radiographic-Fluroscopy unit and offered food that had been mixed with powdered BaSO4 (mash:BaSO4::2:l, v:v). Water and food pans were attached in the same manner as the pans attached to the birds' cages. For ten days before the start of the experiments, birds were frequently handled, placed in the cardboard boxes, and fed in the same manner as during the experiments, until they were eating without hesitation or apparent nervousness when placed in front of the unit. A full set of both experimental and control trials were carried out both in the morning and in the afternoon, and comparisons between experimental and control treatments were not made across time periods (morning vs. afternoon). Second, we wished to estimate gastric evacuation rates, observe the movement of radio-opaque food slurry introduced into the duodenum, and to visually estimate the extent of fullness of the intestine following our experimental manipulation. Six birds were treated in exactly the same way as the experimental procedure described above, but radiographic observation was restricted to the abdominal cavity (ie; the proventriculus or glandular stomach, the gizzard or muscular stomach, and the intestines), and the food offered to the birds for ad lib consumption was not marked with BaSO 4. This facilitated distinction between ingested food from that artificially introduced via the cannula. Initially, the frequency of gastric contractions was noted by measuring the time taken for completion of fifteen full gastric contraction cycles as described by Duke et al. (6). This was possible because in every case, a variable amount of food refluxed back up into the gizzard from the duodenum immediately after injection through the cannula. Following this, the evacuation of radio-opaque food slurry from the gizzard was timed, and the occurrence of duodenal refluxes were noted. The time to first appearance of BaSO 4 in the ileum was noted. A series of control observations were carried out on the same birds, feeding ad lib. on radio-opaque food but without the introduction of food slurry into the duodenum. (b) The Influence of Time of Day. We assessed the effects of diel feeding patterns on food intake and crop filling. Experimental and control treatments were as described for the first series of radiographic observations (see above), except that comparisons were made within each treatment group (experimental or control) but between trials carried out at different times of day (morning,
JACKSON AND DUKE
07:30--09:30 VS. evening, 1 7 : 3 0 - 19:00). For this comparison, n=7. RESULTS
Feeding Observations Over the course of the single meal eaten immediately following introduction of food slurry into the duodenum, the mean duration of feeding activity and mass of food eaten were statistically indistinguishable between experimental and control feeding trials (Table 1). Slightly more individual birds showed higher absolute food intakes (g) following experimental treatment than after control treatment, but when food consumed was expressed as a percentage of body mass, this trend was reversed. The mean numbers of boli swallowed were similar between groups (36.5 _+ 15.1 and 37.9 __ 19.2 respectively). However, over a 3-h period more the mean mass of food eaten was significantly higher during the experimental trials, both in absolute terms and as a percentage of body mass. Moreover, the majority of birds ate more food (both in g and as a percentage of body mass) during the 3 h following experimental treatments. Artificial duodenal filling apparently stimulates feeding in the short term, but this trend was reversed for food consumption over the 11 h folllowing treatment. All comparisons within this group show that less food was eaten by birds after duodenal filling. The decrease in consumption was greater than the quantity of food introduced into the gut: less than 10 g (mash before addition of water) of food was injected, but mash intake decreased by a mean of 29 g in experimental trials. No significant differences in food intake (% body mass consumed over 11 h) occurred between cannulated and uncannulated control birds (10.43 _+ 1.25 and 9.78 _+ 0.45, n = 8), suggesting that surgery and the subsequent presence of a cannula did not affect feeding behavior. Moreover, birds that had undergone surgery regained normal growth rate within a week, showing a mean daily weight gain of 5.14 _+ 0.08% body mass per day during the experimental period, a value statistically indistinguishable from the weight gains of intact birds of the same age.
Radiographic Observations Unless otherwise stated, all food masses consumed include BaSO 4. (i) The Influence of Artificial Duodenal Filling. Among morning feeding trails, injection of slurry into the duodenum resulted in the same trend as did the feeding observations, causing an increase in the overall mean amount of food eaten (g and as a percentage of body mass, Table 2. See also Fig. 1 for an image showing duodenal fullness at the start of an experimental feeding trial). The majority of individual birds ate more during the experimental trials. Among trials carried out in the afternoon, individuals consumed significantly more food (g) following experimental treatments, but overall means show no difference because the two birds out of eight which did not fit this pattern ate disproportionately more after the control treatment, and one bird ate exactly the same amount in both trials. Normalization of intake to bird body mass reversed this pattern and rendered the difference between experimental and control treatments insignificant. In both the morning and afternoon feeding trials, a greater proportion of boli entered the birds' crops following duodenal filling, but this difference was only significant in the afternoon. Boli could clearly be seen entering the crop (Fig. 1.). Five minutes after the start of feeding, the proventriculi and gizzards of control birds were filling, but there was little or no
I N T E S T I N A L F U L L N E S S A F F E C T S S A T I E T Y IN T H E T U R K E Y
FIG. 1. Radiographic images (photographs of the radiograph video monitor) illustrating the methods ~ased for radiographic observations. In this and all subsequent figures, photographs are left lateral views, taken as the bird stood in a normal feeding position, with the its head toward the left of the photograph. Throughout the figure captions, "control" refers to birds which were cannulated Taut which had had no food introduced into the duodenum on the day of the feeding trial in question, and "experimental" refers to birds whiq:h had had 15 ml of food-BaSO 4 slurry introduced into the distal duodenum at the start of the feeding experiment. In all images of the abdomen, the cannula can be seen in the lower right quadrant, as some BaSO 4 res:idue remained in the cannula even on days when no slurry was introduced. The cannula is labeled in Fig. l(b), and not labeled thereafter. Times (rain) refer to times elapsed since the start of the feeding experiments, which coincided with the introduction of slurry and the commencement of feeding (the birds were hungry and began feeding as soon as food was placed in front of them). (a) The crop of a control bird at 5 min, showing a bolus entering the crop, and boli collected in the bottom of the crop. The outline of the crop wall can be seen faintly. N: neck; B: b,alus; BM: breast muscle. (b) The small intestine of an experimental b:Lrd immediately after introduction of 15 ml of food slurry into the duodelaum. The duodenum and jejunum are full, and a small amount of food has reftuxed into the gizzard. PD" proximal duodenum; DD: distal duodenum; G: gizzard; J: jejunum; C: cannula.
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FIG. 2. The abdomens of (a) a control and (b) an experimental bird at 5 min. The gizzard of the control bird is filling, but the duodenum is still empty. Note the bolus entering the gizzard to the top left. In both (a) and (b), the gizzard is in the phase of the gastric contraction cycle when the thick gizzard muscles contract, giving the organ a characteristic "dog bone" shape (Refs. 7, 8). The entire small intestine of the experimental bird is full, including the ileum. Comparison of (b) with Fig. 1 (b) shows the progression of digesta in the same individual. Abbreviations the same as for Fig. 1, with the addition of SI: small intestine (the duodenum, jejunum and ileum were not distinguishable from one another).
food in the d u o d e n u m (Fig. 2). After 15 m i n food had b e g u n to pass into this organ (Fig. 3). A m o n g experimental birds, the proventriculi and gizzards (hereafter referred to collectively as " s t o m a c h " ) , d u o d e n u m s and j e j u n u m s of experimental birds were filled with food after 5 min, and after 15 m i n the entire stomach and small intestine w e r e filled with food. At the cessation of feeding, 25 m i n after the start of a feeding trial, the small intestines of the control birds were completely radio-opaque, implying fullness. Control birds that did not experience duodenal filling, ate the same amount of normal m a s h (without B a S O 4) as did experimental birds that had had 15 ml of radio-opaque slurry introduced into their d u o d e n u m s (Table 4). One control bird exhibited
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JACKSON AND DUKE
duodenal refluxes during the feeding trials, and refluxes occurred in two experimental birds. Oi) The Influence of Time of Day. Among experimental trials, overall means show that birds ate significantly more in the afternoon than they did in the morning, but this difference was removed by normalization of food intake to body mass (Table 3). Control trials also revealed higher overall mean food intake in the evening when mass of food eaten was expressed as a percentage of body mass, but absolute food intake was unaffected by time of day. For both experimental and control series, most individual birds ate more in the evening than in the morning, but this difference was only significant among the control birds. A significantly greater proportion of boli entered the crop in the afternoon control treatment series. DISCUSSION
Crop emptying in the turkey is at least partially under the control of the stomach, which regulates delivery of food to itself
TABLE 4. RADIOGRAPHICOBSERVATIONS:THE EFFECT OF ARTIFICIAL DUODENUM FILLING ON GUT MOTILITY AND INTESTINE FILLING RATE Dur. of feeding trial (rain) Experiment 12.0 (2.8) Control 14.4 (4.45)
IncidBird ence of body reflux 1 mass (g)
Mass food eaten (g)
2
2444 (143)
56.5 (18.3)
1
2328 (94)
64.0 (16.3)
Time to Time to duod. ileal fill 2 fill 3
Store. Time to fullness stom. at start fill 4 (%)
0.67 (1.34)
8.73 (3.81)
8.76 (2.64)
44.0 (38.0)
Abbreviations and protocols as for Tables 1 and 2, with the exception that birds were fed their normal mash without BaSO 4 powder. N = 6 throughout. 1 The presence or absence of refluxes in each bird was noted, but refluxes were not counted. 2 The time (min) at which duodenum began to fill with ingested (non-radio-opaque) food. 3 Time (min) to filling of the ileum refers to the onset of filling of this organ, i.e.,: the time w h e n radio-opaque material was first observed in the ileum. 4 The time (rain) at which the stomach was no longer radio-opaque, i.e.,: the time at which it became filled with ingested (non-radio-opaque) food rather than with radio-opaque food refluxed from the duodenum. Note: T i m e s to filling of various intestinal sections could not be determined in control birds, which had no radio-opaque substance in their guts.
(2). The pausing or "backing up" of boli in the pre and post-crop esophagus described by these authors did not occur in the present study, perhaps because the degree of indirect stomach filling that resulted from duodenal injections of food slurry was not sufficient to initiate this pattern. The results of our feeding observations showing that artificial duodenal filling did not affect the amount of food and number of boli swallowed over one meal, are supported by a previous study (2) where manipulation of crop, stomach, and ileal fullness by introduction of food slurry per os did not affect food intake in similarly free-feeding birds. The drop in summed food intake (g eaten ad lib. plus injected slurry) below the level of control birds that we report after 11 h is consistent with studies on rats (12), and on domestic chickens (23). In contrast, the increased food intake that we observed after 3 h reflects that which we observed during our radiological trials, and possible explanations are discussed below.
Daily Rhythm in Crop Filling The length of the preprandial fast affects crop filling (20,23), but we report an afternoon increase in crop filling when the length of the preprandial fast is held constant at 10 hr. Our results suggest that the crop does act as storage organ to ensure a prolonged supply of food to the stomach and lower gut during the night. Fullness of the crop was highly variable and not associated with the ends of voluntary feeding bouts (see also Ref. 2). This observation does not support a primary regulatory role of the crop in food intake and satiety. Cropectomy has little effect on feeding patterns in birds fed energy-rich diets, but may limit intake in birds fed energy-dilute diets (17,20).
Gut Filling Times FIG. 3. The abdomens of (a) a control and (b) an experimental bird at 15 min. Note the beginning of duodenal filling in the control bird [compare with Fig. 2(a)]. Note also the segmenting contractions in the jejunum and ileum of the experimental bird (b). Abbreviations as for previous figures, with the addition of J/I: jejunum/ileum (these two sections were not distinguishable from each another).
An important finding of our study is that the ileum appears full at the end of a single meal of radio-opaque food. This may be partly a consequence of food consistency, because finely ground food may pass through the stomach relatively quickly. Such rapid food passage is unlikely in wild birds feeding on coarser foods,
INTESTINAL FULLNESS, AFFECTS SATIETY IN THE TURKEY
but may force us to reevaluate the functions of the duodenum in domestic poultry. Among domesticated birds, both the duodenum and the ileum are routinely exposed to large quantities of chemically undigested food soon after the commencement of feeding, and this may well affect both the function of gut chemo- and mechanoreceptors, and the role of these sections of the gut in peripheral feedback to cerebral satiety centers.
Duodenal Injections Paradoxically Stimulate Feeding Injection of food slurry frequently stimulated at least one duodenal reflux, resulting in partial filling of the gizzard before the start of the feeding trial. We therefore do not presume to isolate the effects of duodenal filling alone on feeding behavior, and must rather seek exphmations of how artificial filling of the gut as a whole affects feeding behavior. The short-term increases in food consumption following duodenal filling with food slurry contradict our hypothesis that duodenal fullness elicits the cessation of feeding. Increased food intake in response both to duodenal infusions of glucose (23) and to intraperitoneal injections of glucose (25,26) occurs in domestic chickens. The same phenomenon in rabbits has been attributed to a rise in circulating insulin levels in response to elevated blood glucose, leading to increased tissue absorption of glucose, followed by hyperglycemia, and hunger (16). Pharmacological doses of insulin may directly increase food intake in mammals (27), but the physiological relevance of this is questionable. The short-term increases and longer-term (albeit incomplete) compensation we report are consistent with those reported for rabbits by Rezek et al. (16). We are hesitant to adopt the above explanation for the patterns that we report, because the role of circulating blood glucose
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in the regulation of avian feeding behavior is still obscure (3), and manipulation of blood glucose levels in chickens has no effect on food intake over a 4 h period (25). Published data on chicken blood glucose levels during and immediately after meals are contradictory, with some studies reporting detectable increases within half an hour (1), and others detecting no short-term patterns consistent enough to be involved with satiety (21). Blood glucose levels in 24-hr fasted turkey poults increase measurably 1 h after feeding (5). Behavioral and tactile cues such as oral stimulation certainly influence avian feeding behavior (9), and in bypassing normal ingestion channels we may have triggered an inappropriate feeding response. Although discomfort resulting from artifially induced distension of the gut reduces rather than enhances food intake in the rat (12), handling and discomfort may cause release of central opioid peptides, leading to increased feeding in the domestic chicken (22). Full explanation of the response awaits further study such as monitoring of the blood levels of circulating nutrients and of insulin and other hormones after voluntary feeding of turkeys (25). Infusions of different substances into the turkey duodenum in a manner comparable to previous studies on chickens (23, 24) would also help elucidate the paradoxical stimulation of feeding that we report here. ACKNOWLEDGEMENTS We thank Drs. S.B. Chaplin, D.M. Denbow and T.F. Poppema for helpful discussions and comments on the manuscript, and Miss C. Chung for assistance in the laboratory. Darren Straub of Willmar Poultry generously supplied us with turkeys. The study was funded by the Minnesota Agricultural Experiment Station, Project 61-44, and by a postdoctoral bursary awarded to the senior author by the South African Foundation for Research and Development.
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1. Aramaki, J.; Weiss, H. S. Patterns of carbohydrate and protein digestion in the chicken as derived from sampling the hepatic portal system. Arch. Int. Physiol. Biochem. 70:1-15; 1962. 2. Chaplin, S. B.; Raven, J.', Duke, G. E. The influence of the stomach on crop function and feeding behavior in domestic turkeys. Physiol. Behav. 52:261-266;1992 3. Denbow, D. M. Food intake control in birds. Neurosci. Biobehav. Rev. 9:223-232; 1985. 4. Denbow, D. M. Peripheral and central control of food intake. Poult. Sci. 68:938-947;1989. 5. Donaldson, W. E.; Christensen, V. L. Dietary carbohydrate level and glucose metabolism in turkey poults. Comp. Biochem. Physiol. 98A:347-350; 1991. 6. Duke, G. E.; Dziuk, H. E.; Evanson, O. A. Gastric pressure and smooth muscle electrical potential changes in turkeys. Am. J. Physiol. 222:167-173; 1972. 7. Duke, G. E.; Evanson, O. A. Inhibition of gastric motility by duodenal contents in turkeys. Poult. Sci. 51:1625-1636; 1972. 8. Dziuk, H. E.; Duke, G. F;. Cineradiographic studies of gastric motility in turkeys. Am. J. Physiol. 222:159-166; 1972. 9. Gentle, M. J. Sensory involvement in the control of food intake in poultry. Proc. Nutr. Soc. 44:313-321; 1985. 10. Hill, K. J.; Strachan, P. J. Recent advances in digestive physiology of the fowl. Syrup. Zool. Soc. Lond. 35:1-12; 1975. 11. Irving, L.; West, G. C.; Peyton, L. J. Winter feeding program of Alaska willow ptarmigan shown by crop contents. Condor 69:69-77; 1967. 12. Koopmans, H. S. The role of the ileum in the control of food intake and intestinal adaptation. Can. J. Physiol. Pharmacol. 68:650-655; 1990. 13. Lacy, M. P.; van Krey, H. P.; Skewes, P. A.; Denbow, D. M.
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Intraduodenal glucose infusions do not affect food intake in the fowl. Poult. Sci. 65:565-569; 1986. Millam, J. R.; Ernst, R. A.; Voris, J. C.; Pfost, R. E. A data acquisition system for monitoring growing turkeys. Appl. Agric. Res. 3:75-80; 1988. Mongin, P. Composition and gizzard contents in the laying hen. Br. Poult. Sci. 17:499-507; 1976. Rezck, M.; Havlicek, V.; Hughes, K. R. Paradoxical stimulation of food intake by larger loads of glucose, fructose and mannose: Evidence for a positive feedback effect. Physiol. Bchav. 21:243-249; 1978. Richardson, A. J. The role of the crop in the feeding behaviour of the domestic chicken. Anim. Behav. 18:633-639; 1970. Savory, C. J. Meal occurrence in Japanese quail in relation to particle size and nutrient density. Anim. Behav. 28:160-171; 1980. Savory, C. J. Selection of heather age and chemical composition by Red Grouse in relation to physiological state, season and time of day. Orals. Scand. 14:135-143; 1983. Savory, C. J. An investigation into the role of the crop in control of feeding in Japanese quail and domestic fowls. Physiol. Behav. 35:917-928; 1985. Savory, C. J. How closely do circulating levels of blood glucose reflect feeding state in fowls? Comp. Biochem. Physiol. 88A:101106; 1987. Savory, C. J.; Gentle, M. J.; Yeomans, M. R. Opioid modulation of feeding and drinking in fowls. Br. Poult. Sci. 30:379-392; 1989. Shaobi, T.H.; Forbes, J. M. Feeding responses to infusions of glucose solutions into the duodenum of cockerels and the influences of prefasting or vagotomy. Br. Poult. Sci. 28:407-413; 1987. Shurlock, T. G. H.; Forbes, J. M. Factors affecting food intake in the domestic chicken:the effect of infusions of nutritive and nonnutritive
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substances into the crop and duodenum. Br. Poult. Sci. 22:323-331; 1981. 25. Smith, C. J. V.; Bright-Taylor, B. Does a glucostatic mechanism for food intake control exist in chickens? Poult. Sci. 53:1720-1724; 1974. 26. Smith, C. J. V.; Haffield, J.; Fowler, S.; Bright-Taylor, B. Changes in food consumption and blood glucose levels in the domestic
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chicken Gallus domesticus in response to the administration of 2-oxy-D-glucose. Comp. Biochem. Physiol. 51A:811-814; 1975. 27. VanderWeele, D. A. Hyperinsulinism and feeding: Not all sequences lead to the same behavioral outcome or conclusions. Appetite 6:4752; 1985. 28. Zar, J. H. Biostatistical analysis, 2nd Ed. Prentice Hall; 1984.