In this study, 176 day-old male broiler chickens (Ross strain) were allocated to four treatments in pens (120x100x90 cm) with four replicates (11 birds /pen) in a completely randomized design to evaluate the effect of sunflower seed meal (SFSM) on histological alterations of the small intestine in broiler chickens. Treatments were 0, 7, 14 and 21 percent of SFSM for 1-28 days and calculated to contain 20.86% CP and 2900 kcal of ME per kg of diet. At the end of the experiment (28 days of age) one bird from each treatment was killed by cervical dislocation, and segments were removed from the duodenum, jejunum, and ileum as follows: 1) intestine from the gizzard to pancreatic and bile ducts was referred to as the duodenum, 10 cm of first section of which was taken for microscopy; 2) 10 cm of first section, between the point of entry of the bile ducts and Meckel’s diverticulum (jejunum), and 3) 10 cm of first section from Meckel’s diverticulum to the ileocecal junction (ileum). The samples were flushed with physiological saline and fixed in 10% formalin. Cross sections for each intestinal sample were prepared after staining with hematoxylin and eosin using standard paraffin embedding procedures. Villus height was measured from the tip of the villus to the villus-crypt junction; crypt depth was defined as the depth of the invagination between adjacent villi. The villus width measured at the bottom of villi. The slides were evaluated using Olympus (BX51, Japan) microscope coupled with camera and the computer image analysis software for the morphometrical research was used. The results showed that by increasing levels of SFSM in the diets, villus height and crypt depth of duodenum and jejunum were significantly (p<0.05) decreased and increased, respectively. But SFSM did not affect the villus of the ileum. Also, incorporation of SFSM had a significant effect on villus width (p<0.05). We concluded that the high fiber content of SFSM had a negative effect on histological parameters of the small intestine of broilers.

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