The purpose of the study was to compare the effect of feeding broiler chickens with mixtures containing raw or extruded soybean seeds on the performance indices, slaughter value and liver histology of the animals. The research began with an analysis of the chemical composition of selected high protein feeds. A nutritional experiment was then performed on 108 sexed Ross 308 chickens, which were allocated to 3 equal groups (I, II, III). The chickens were reared for 42 days with ad libitum feeding. The birds from the control group (I) received mixtures in which the only high protein component was soybean meal extracted. Extruded soybeans and raw soybeans were fed to chickens in experimental groups II and III, respectively, in quantities that replaced 30% of soybean meal extract protein in the Starter mixture and 50% of this protein in the Grower and Finisher mixtures. During the experiment, the body weight of the birds (BW) and their feed intake (FI) were recorded. At the end of rearing, 12 chicks of body weights representative of their group and sex were slaughtered in each group. The results of the slaughter analysis were used to calculate the percentage of muscles, skin with subcutaneous fat and abdominal fat in the carcass. The weights of selected internal organs were also determined, and then their proportion in the chilled carcass weight was determined. In addition, after slaughter, chicken livers were collected to assess the histological image. Raw soybean meal extrusion resulted in an increase in protein content and a decrease in crude fibre by about 10%. Quantities of individual amino acids in the analysed material were proportional to the protein content. The extrusion of full-fat soybean seeds reduced the content of trypsin inhibitors by more than a half (to 9 mg/g), but the least of these compounds (1.2 mg/g) was found in soybean meal extract. The tannin content of extruded soybeans was about one-third of that of extracted meal and less than one-fourth of that of raw soybean. It was shown that the chickens receiving extruded soybeans reached a weight similar to that of the control group, with similar FCRs for individual rearing periods, whereas the use of raw soybean significantly (P ≤ 0.01) decreased both parameters. In addition, group III had a significantly lower dressing percentage (P ≤ 0.05) and a higher proportion of abdominal fat (P ≤ 0.01) compared to the other groups. The introduction of extruded or raw soybeans into the mixtures increased (P ≤ 0.05) the proportion of total internal organs. The microscopic image revealed that all chickens had a similar, normal histological structure. The results of this study show a beneficial effect of raw soybean extrusion on the nutritional value of soybeans. Extruded soybeans can therefore be recommended as a partial substitute for protein (30% in Starter and 50% in Grower and Finisher) from soybean meal extract in chicken broiler mixtures. Raw soybeans should not be used in the above amounts, mainly because of the clearly worse rearing results.
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