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1. The effects on food intake and weight gain of offering broiler chickens (2 to 7 weeks of age) dry food, wet food, wet food containing whey, whey as drinking liquid and combinations of two of these were studied in 5 experiments. 2. Wet feed generally improved both weight gain and feed efficiencies significantly. Feeding whey also improved weight gain and feed conversion efficiency, but whey offered as a drinking fluid had an adverse effect on broiler performance. 3. When whey was offered both as drinking liquid and added to the food it had a deleterious effect. 4. When whey was offered from 4 or 6 weeks of age, it had a better effect than when offered from 2 weeks of age. 5. There was better performance when whey in the drinking water was diluted and/or offered on alternate days or half-days. 6. Broilers allowed to choose between wet and dry feed when water was freely available chose mostly dry feed; in the absence of drinking water they chose mostly wet food. Birds offered water and liquid whey avoided whey completely. 7. It is concluded that whey can be used in diets for broiler chickens by incorporating it in the food as long as drinking water is offered ad libitum. Whey may be offered as a drink if the food is mixed with 1.8 times its weight of water but it is better to dilute the whey with an equal volume of water whether it is added to food or given as drink. Good results can also be obtained when undiluted whey is offered alternately with water, either in half-day or full-day periods.

1. Two experiments were carried out to investigate the addition of 1 3 kg water per kg air-dry mash diets containing high proportions (600 to 700 g/kg) of ground cereal grains (wheat, barley or oats) on broiler performance and the structure and function of the gastro-intestinal tract. 2. Chicks at the age of 7 d were fed on the wheat-, barley- or oats-based diets in the dry or wet forms for 35 d. Food and water intakes were recorded daily while body weight was measured weekly. Two birds from each treatment were killed each week to measure gut size and the viscosity of gut contents. Tissue samples from various digestive segments were histo-morphologically examined to determine the thickness of tissue layers, size of tissue glands, villa heights, crypt depths and thickness of tunica muscularis. Crypt cell proliferation rate (CCPR) for each segment was also determined using a metaphase arrest technique. 3. The results from both experiments showed that wetting food significantly (P<0.05) increased food intake, total water intake and body weight gain of broiler chickens. The body weight gains of birds were proportional to their food intakes so that the efficiency of food utilisation was similar for all treatments. Dry matter retention of food tended to increase in birds given wet food from 7 to 21 d but not thereafter, compared to the dry-fed birds. Although water intake from the water bottle was significantly (P<0.05) reduced in birds given wet food, total water intakes from the water bottle plus that from food were significantly (P<0.05) higher in the wet-fed birds than in the dry-fed birds. The ratio of total water to dry food intake was, however, similar in both feeding regimens. 4. The fresh empty weight of the gut was increased by wet-feeding while its relative weight to body weight and the length of gut was not affected by dietary treatments. Significantly greater development of the tissue glands in the proventriculus and gizzard was observed in the birds given wet food; this was associated with the reduced thickness of the muscular layer of these segments. An increase in villus height was also observed in duodenum, small intestine, caeca and colon of birds given wet food, compared to those given dry food. CCPR was significantly (P<0.05) reduced by wet-feeding throughout the digestive tract. This was associated with a significant decrease in the mean viscosity of the gut contents and the concentration of volatile fatty acids (VFAs) in the caeca. 5. Wetting diets based on cereal grains caused a significant improvement in the performance of broiler chickens. The mechanism of the beneficial effects of wet feeding could be attributed to the decreased viscosity of gut contents; the greater development of the layer of villi in the digestive segments and the reduced CCPR in the crypts of the epithelium.

1. Four experiments were carried out to investigate the effects on growth, food conversion efficiency (FCE) and apparent diet digestibility, of wetting food before offering it to individually caged growing chickens. 2. Female broiler chicks (8/treatment) were given grower food ad libitum from 28-49 d of age either in the dry form or wetted with 2.0 kg water/kg air dry food, or wet food restricted to the same daily amount of dry matter as eaten by the dry-fed birds. Ad libitum feeding of the wet food significantly increased food intake and body weight gain, compared to dry feeding, while weight gains of birds with restricted feeding of wet food were intermediate. 3. Experiments 2 and 3 studied the effects of the time interval between mixing the food with water and offering it to the birds. When pre-soaking times of 0, 12 and 24 h were compared with dry food for male broilers (8/treatment) from 25 to 40 d all wet treatments increased body weight gains significantly, the best results coming from the zero soaking time, when DM digestibility was increased significantly from 677 to 714 g/kg. When restricted amounts of food were offered hourly for 8 h on each of 4 d, DM digestibility was significantly increased from 634 for dry food to 659 for that freshly mixed with water and 664 g/kg for that soaked for 1 h between mixing and offering. 4. In a factorial experiment with wet and dry food, either in the standard form or with added enzyme or 400 g/kg cornflour, there were significant positive effects on growth and FCE of broilers (7/treatment) attributable to enzyme and wetting, while cornflour significantly reduced growth. However, wet cornflour-diluted food gave better growth than dry standard food. Wetting significantly increased the apparent digestibility of dry matter and protein while dilution with cornflour significantly reduced protein digestibility. 5. These results confirm those previously presented in terms of improved growth and FCE with wet feeding and demonstrate a large improvement in the proportion of the food absorbed from the digestive tract, of similar magnitude to the improvement in FCE. They also show that it is not necessary to pre-soak food in order to attain the maximum effect.

1. Growing male chickens of broiler and layer strains were allowed to eat either a high-protein food (HP) or a low-protein food (LP) for 10 min after an overnight fast and then offered a choice between HP and LP. During the next hour they ate significantly more of the food other than the initial meal. Similar results were obtained when there was a gap of 45 min without food between the initial meal and the choice period. 2. When the initial meal was given by tube into the crop, followed by 45 min without food, there was no significant effect on subsequent diet selection. These results show that it is necessary for the birds to eat the food themselves for it to exert its effect on subsequent choice. 3. Birds with experience of eating two foods identical in nutrient composition but different in colour did not select either food in preference to the other following an initial meal of one alone. This is evidence against the possibility that neophagia accounts for the results of the first two experiments. When an initial meal of low protein food was followed by a choice of high and low protein foods, birds ate a greater proportion of the high protein when it was placed on the opposite side of the cage from that in which the initial meal was given. Thus they are not choosing a food simply by its position within the cage. 4. To see the extent to which broilers can extend their ability to compensate for protein content over several weeks, male broilers were given one of 4 treatments from 5 to 10 weeks of age: (A) HP and LP concurrently; (B) HP and LP on alternate days; (C) HP in the morning and LP in the afternoon, (D) LP in the morning and HP in the afternoon. There was no significant effect of treatment on food intake, body weight gain or carcase protein content but carcases were significantly less fat after treatment (B) than treatment (D). 5. It is concluded that growing broiler chicks can compensate well for periods of access to only a low-protein food, by subsequent intake of high-protein food, and vice versa, as long as they are able to gauge the sensory properties of the foods. Offering two complementary foods in alternating half-day periods is an effective method of choice-feeding, allowing birds to select a diet to meet the requirements for growth.

1. Individually caged growing chickens were offered a commercial grower food mixed with 1.5 to 2.25 times the weight of water and the effects, compared to giving the same food in air-dry form, on food intake, body weight gain and carcase composition were investigated. 2. Male broilers (24) were given either a grower food in the air-dry form with access to drinking water or the same food mixed with 2.0 parts of water (700 g water/kg of mixed food) with no drinking water from 28 to 49 d of age. From 49 to 63 d all birds were given dry food and drinking water and were then killed for carcase analysis. Food intake and weight gain were significantly increased during the wet-feeding period, as was carcase protein but not abdominal or carcase fat at the end of the experiment. 3. Five male broilers were given each of 5 dietary treatments containing 0 (control), 1.5, 1.75, 2.0 and 2.25 times added water (640, 673, 700 and 723 g water/kg) from 28 to 49 d. Food intakes, body weight gains and carcase weights were significantly increased for all water additions compared with dry food, but there were no significant differences between different water additions. 4. Female broiler chicks responded to wet feeding (700 g water/kg) in a similar manner to males and the dry matter approximate digestibility was increased from 0.65 for the dry food to 0.73 for the wet. 5. Cockerels of an egg-laying strain did not increase their intake of dietary dry matter when it was fed in the wet form (700 g water/kg), but there was a significant increase in body weight gain. 6. Male broilers were offered wet food (700 g water/kg) with or without access to drinking water. There was equal stimulation of food intake, growth and carcase weight with both wet-feeding treatments. 7. Providing food mixed with sufficient water to give a porridge-like consistency significantly increased weight gains in each of the five experiments and significantly improved food conversion efficiency in three of the five. It is not necessary to withhold drinking water in order to obtain this effect.

1. The effects of corticosterone (CORT) on diet selection of broiler chickens offered a choice of a high protein concentrate (381 g CP/kg, 17.5 MJ/kg ME) and whole wheat (113 g CP/kg, 15.9 MJ/kg ME) in relation to age were examined in two experiments. 2. Daily intramuscular injections of 2 and 4 mg/kg of CORT for a 5-d period in both 2- and 5-week-old chickens resulted in increases in total food, protein and energy intakes. This led to a decrease in protein accretion in older but not younger chicks, an increase in total lipid contents of the carcase at both ages, and produced changes in internal organs. 3. CORT significantly reduced body weight gain of young but not old chickens, suggesting that mature birds respond better than young ones to the physiological changes caused by treatment, by making subsequent appropriate food choices. 4. Administration of CORT in young chicks increased wheat intake at 2 and 4 h after injection, while in older birds a similar increase was maintained up to 24 h after injection. Intake of HP food was decreased by both doses of CORT in young chicks but there was no significant effect in older chickens. 5. Changes in energy: protein ratio in the chosen diet appeared at 4 h after treatment in old chickens and at 24 h in younger chicks. 6. The results suggest that birds are able to detect metabolic changes caused by CORT administration and attempt to redress them by modifying their food pattern. The time course of the response of birds to these changes is age related. However, the food selection pattern did not completely compensate for the physiological defects.

1. Food intake, protein intake and body weight gain were measured in male broiler and layer strains of chickens offered approximately isocaloric diets containing various concentrations of protein from 4 to 9 weeks of age. The carcases were analysed for protein, fat and ash. 2. In the first experiment 5 birds of each strain were given diets containing either 65, 115, 172, 225 or 280 g protein/kg fresh matter. The sixth group was given a choice between 65 and 280 g/kg. There was an approximately linear increase in protein deposition with dietary protein content up to 280 g/kg with broilers and 225 g/kg with layers. When a choice of diets was offered, birds of both strains grew at a rate not significantly different from that of birds on the diets with the lowest protein content which gave maximal growth given singly, by making an apparently appropriate choice from the two diets. 3. In the second experiment broilers were offered a choice of two diets in the following combinations: 65 and 115, 65 and 225, 115 and 225, 225 and 280 and 280, and 320 g/kg protein. They were able to differentiate successfully between two diets on the basis of their protein content and, where the two diets were on either side of the optimum, to change the proportions selected as they grew to match their changing requirement for dietary protein. When given two diets, both of which had protein contents lower than the single diets which gave maximal growth, birds ate predominantly from that closer to that optimal diet. When both diets had a higher protein content than the optimum birds ate mostly from that closer to optimum. 4. The results show that growing chickens can match their protein intake closely to their requirements when given a pair of diets that allows this; if both diets are on the same side of the optimum then the one closest to that required is predominantly chosen.

Male chickens of an egg-laying strain were used in an investigation of the effects of pinealectomy at 1 d after hatching. Pinealectomised birds killed at 28 d of age were significantly heavier than sham-operated chickens; intraperitoneal treatment of intact birds during the same period with 10 mg melatonin/kg d depressed weight gain, while 200 micrograms triiodothyronine (T3)/kg d given intramuscularly had no effect. Pinealectomized birds aged 11 weeks ate some food during the night, in contrast to intact birds, and ate significantly more food per 24 h; their short-term food intake responded to melatonin and T3 in a manner similar to that of intact birds. The electroencephalogram (EEG) of pinealectomised birds was affected to a slight degree of darkness, while in intact chickens there is a rapid and marked change in the EEG.

The hepatic portal veins of cockerels were catheterised to study the effects of 3-h infusions of nutrient solutions on voluntary food intake. An amino acid mixture, infused at rates up to 800 mg N/3 h, depressed intake of a standard diet in a significant linear manner (intakes with the highest dose and control: 1.6 g and 22.6 g/3 h respectively). Infusion of the highest dose into the jugular vein had a smaller and nonsignificant effect (17.2 and 25.3 g/3 h). The effects of combined infusion of amino acids and glucose into the portal vein on food intake were approximately additive.

1. The duodenum of cockerels was chronically catheterised, to study the effects of 3 h infusions of glucose solutions on voluntary food intake. 2. Compared to water, solutions containing 30, 60 and 90 g glucose/l infused at 1 ml/min induced significant, dose-related depressions in intake after the first 30 min of infusion. 3. Fasting the birds for 3 h before the start of infusion resulted in higher intakes during the period of infusion than in unfasted birds. 4. Vagotomy at the level of the proventriculus prevented the inhibitory effects of glucose infusion into the duodenum, except at the highest concentration (120 g/l).

1. Infusions of 10 g of diet mashed in 20 ml of water, increasing glucose loads and hypertonic solutions of glucose, sorbitol and KCl, were introduced into the crop of the adolescent cockerel (1.5 to 2.0 kg body weight and 12 to 20 weeks of age). All caused a significant reduction of food intake over the following 3-h period. 2. Duodenal infusions of hyperosmotic solutions of sorbitol and KCl at 3 osm significantly decreased food intake within an hour of infusion. Glucose infusion decreased intake only in birds starved for 3 h before the experiment. 3. The results are discussed in relation to the site of infusion and nutritive visceral mechanisms of food intake control. It is likely that there is a major osmotic control in the duodenum which may affect a secondary control system in the upper gastro-intestinal tract.

1. Male birds of a laying strain had permanent catheters introduced into the hepatic portal vein via the coccygeo-mesenteric vein. 2. Infusions of 5 ml of 40, 100 or 150 g glucose/l solution over 2 min caused a non-significant depression of food intake compared with a 9 g NaCl/l control solution. 3. Infusions of a range of isotonic glucose solution (0 to 60 g glucose/l, 30- mosm) at 1.4 ml/min over 3 h caused food intake depression within the 3-h period (P less than 0.01) proportional to the logarithm of the dose. 4. This effect was not observed when 60 g glucose/l was infused at the above rates into the jugular vein. 5. Starvation of the bird for 21 h accentuated the depressive effect of glucose load on food intake, especially when birds were not given food until after the 3-h infusion. 6. The infusion of solutions of sodium chloride (1.0 to 13.0 g/l, 33 to 433 mosmoles/kg) at 1.4 ml/min over 3 h stimulated food intake within the range of 3 to 7 g NaCl/l (100 to 233 mosm) but suppressed intake outside this range. This can be interpreted as a possible interaction with water intake control. 7. Infusion of 20 ml of glucose solution (0, 18 or 54 g/l) over 5 min into the crop and 0, 3.75 or 60 g glucose/l at 1.4 ml/min over 3 h into the hepatic portal vein, caused an additive, linear depression of food intake.

1. Four experiments were carried out to study the effect of offering a 91.5 g/l solution of glucose, compared to tap water, on fluid intake, food intake and growth of individually-caged immature chickens of both layer and broiler strains. 2. Male chicks of an egg-laying strain were offered glucose solution or tap water from 27 to 62 d after hatching. There was no effect of glucose on fluid intake but it depressed food intake (P less than 0.01) to give equal total energy intakes for each treatment. Body weight gain was reduced (P less than 0.001) and carcase fat content increased (P less than 0.001) by the glucose to yield no difference to total carcase energy. 3. When birds were placed in a respiration chamber for two 23-h periods there was no effect of treatment on outputs of energy as faeces + urine or as heat. 4. Male broilers were offered glucose solution or tap water with diets containing either 150 or 195 g protein/kg from 20 to 55 d after hatching. With the low-protein diet glucose depressed food intake (P less than 0.01) but total energy intake and carcase energy were not significantly affected. With the high-protein diet glucose did not depress food intake but increased total energy intake and total body fat. 5. Layer and broiler chicks were offered either a choice of the low- and high-protein diets or a single diet intermediate in protein content, with glucose solution or tap water. With broilers total food intake was depressed by glucose, mainly by a reduced intake of the low-protein diet. Intake of neither diet by the layer chicks was significantly affected by glucose. 6. It is concluded that provision of extra energy in glucose solution depresses food intake when the resultant energy:protein ratio becomes limiting. With a higher protein diet, or with birds having lower protein requirements, glucose solution does not depress food intake and increased fat deposition occurs.

Cyproheptadine stimulates food intake and growth in some species of mammal; its effects are reported here in chickens. Growing cockerels of an egg-laying strain were given 0.32 mg/d by mouth, which resulted in significant increases in weight gain and food intake, including feeding during the night. Increasing daily doses of up to 1.6 mg/kg body weight stimulated intake in a dose-related manner, while 1.92 mg/kg had the same effect as 0.96 mg/kg. Neither pinealectomy, which is known to stimulate food intake, nor treatment with melatonin, which depresses intake, interacted with the effects of cyproheptadine on food intake, showing that its effect is not mediated by the pineal gland.