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ABSTRACTThe present study was carried out to examine the effects of a trace mineral premix (MP) reduction or withdrawal from finisher diet (29–42 d) on performance, meat lipid oxidation, and immune system of chicks fed wheat- or barley-based diet. The diets were formulated based on wheat and barley for seven treatments and five replicates of each treatment. At 29 and 36 d, 4 birds from each replicate were injected with sheep red blood cells. The cell-mediated immunity was determined via phytohemagglutinin and dinitrochlorobenzene at 34 and 42 d of age. At 35 and 42 d of age, the oxidative stability was evaluated by thiobarbituric acid reactive substances on the thigh samples that were stored for 180 days at −20˚C. The reduction or withdrawal of MP from diets did not affect the performance or the immune system. Results of TBARS showed that lipid peroxidation of the treatment without MP was significantly higher than of the other treatments when slaughtered at 42 days of age. Finally, the results of this study demonstrated that it is not possible to remove the MP in finisher broilers’ diets without negative effects on meat quality during the time of freezing.

Three hundred and twenty day-old chicks were assigned to four experimental treatments of positive control (standard diets with recommended levels of calcium and phosphorus), negative control (diets containing calcium and phosphorus at the 50% of recommended levels), Negative control plus in ovo injection of 1α-OHD3 (50 ng/egg 1α-OHD3 on day 18 of incubation), and negative control plus feeding of 1α-OHD3 (5 µg/kg of diet). Four replications assigned for each treatment with 20 birds per each. Diets consisted of a starter phase from 0 to 14 days and a grower phase from 15 to 28 days. At 28 days, feed intake (FI), body weight gain (BWG) and feed conversion ratio (FCR) were determined. Two birds per pen were killed to evaluate the carcass and tibia traits. No differences in FI, FCR, carcass traits, tibia weight and length, ash, Ca, P and Seedor index were observed at 28 days of age. Supplementation of dietary 1α-OHD3 significantly increased BWG in compare to negative control. Between treatments, negative control had lowest breaking strength. The current study indicated that supplementation of dietary 5 µg/kg of 1α-OHD3 may improve performance and tibia strength of broilers fed low-calcium and low-phosphorus diets.

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 predomi-nandy 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 predominandy chosen.

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 significandy more of the food other than die 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 concurrendy; (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 a high-protein food, and lice 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.