Adeltrida Triana Patmawan Pengarang PUTRI PANDARANGGA Dosen Pembimbing 2 Prof. Ir Frans Umbu Datta,M.App.Sc.,Ph.D Dosen Pembimbing 1 Frans Umbu Datta Ketua Penguji Putri Pandarangga Penguji 1 drh. Meity M. Laut, M.V.St Penguji 2

The use of antibiotics and monensin as feed additives in the poultry industry aims to enhance growth and prevent diseases. However, their effects on the small intestine morphology of joper chickens still need to be thoroughly evaluated. This study aimed to evaluate the effects of amoxicillin antibiotic and monensin administration on the histological morphology of the digestive system, particularly the duodenum, jejunum, and ileum in 8-week-old joper chickens. The research was conducted from December 2022 to January 2023 using 100 8-week-old joper chickens divided into 5 treatment groups (20 chickens each): P0 (control), P1 (amoxicillin 0.1 g/day), P2 (monensin 0.11 g/day), P3 (monensin 0.22 g/day), and P4 (monensin 0.33 g/day). After 30 days of treatment, tissue samples from the duodenum, jejunum, and ileum were collected, fixed with 10% formalin, and processed using Haematoxylin-Eosin staining. The observed parameters included villus height and width using light microscopy at 400x magnification. Data were analyzed using One Way ANOVA and Duncan's test. The analysis results showed that antibiotic and monensin administration did not significantly affect the weight and length of small intestine organs (P>0.05). However, there were significant differences in villus morphological parameters: duodenal villus height showed significant differences (P=0.006) with P1 and P2 significantly different compared to P0, P3, and P4; ileal villus width showed significant differences (P=0.041) with P0 significantly different compared to other treatment groups; duodenal villus width in P3 showed significant differences. Meanwhile, jejunum morphology showed no significant changes in all observed parameters. The administration of amoxicillin antibiotic and monensin induced segment-specific morphological responses in the small intestine of joper chickens. The duodenum showed the highest sensitivity with significant changes in villus height, the ileum experienced changes in villus width, while the jejunum maintained stable morphology. These findings indicate that each small intestine segment has different responses to pharmacological interventions, which may impact digestive efficiency and nutrient absorption. Keywords : Antibiotics, Histology, Joper Chicken, Monensin, Morphology , Small Intestine, Villus