An important factor for animal welfare is temperature, because if it is too hot, heat stress can occur. Heat stress can lead to poorer growth performance, have a negative impact on feed intake and even lead to the death of the animals. The addition of insoluble dietary fiber to the feed could increase the capacity of the gastrointestinal tract, especially the stomach in younger animals at the time of gastrointestinal development, increase the surface area of the intestine and ensure good production results. The main objective of the MSc thesis was to investigate the effects of dietary programming, i.e. the addition of insoluble fiber, on the production, intake and gastrointestinal development of broiler chickens reared in different feeding periods and rearing conditions, i.e. thermoneutral or in a warm environment, depending on the programme. The nutritional study included 360-day-old broilers divided into three experimental groups according to the nutritional strategy, supplemented with 20 % insoluble fibre (nPV-20) compared to a control group without supplementation (nPV-0) in the second phase of the study. In the third phase of the study (from day 27), the broilers were exposed to different housing conditions and a 3-phase feeding schedule, with half of the birds in the nPV-20 group receiving a diet without supplementation (nPV-20-0) or continuing to receive supplemented diet (nPV-20-20) until the end of experiment, compared to the control group. We measured the differences in the animal weight of the animals until day 33 of the study, the broilers without fibre supplementation were heavier. In the third phase, on the day of slaughter, day 41, no weight differences were observed between the groups. In the last phase of the study, under heat stress conditions, the broilers consumed more feed, but also utilised it less efficiently. The broilers exposed to heat stress had a lighter full gastrointestinal tract, and the group without nPV supplement had the lightest empty tract compared to the groups fed with nPV supplement. The length of the cecum was longer in the nPV-fed groups, under both rearing conditions. In conclusion, feeding nPV during gastrointestinal tract development has a positive effect on gastrointestinal capacity, resulting in animals consuming more feed and maintaining good production performance even under heat stress.
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