Supply Organ Development in Young Broilers in Response to Changing Dietary Fat and Amino Acids in the Starter Period

Early growth in broilers depends on the rapid development of supply organs that enable nutrient use and support the growth of demand tissues such as muscle and bone. This study evaluated whether increasing dietary fat (and thereby AME) and amino acid concentration in starter diets enhances supply organ development and growth performance in Cobb male broilers. A 2 × 2 factorial design compared two fat levels, corresponding to two AME levels (F− 2750 vs. F+ 3050 kcal/kg), and two standardized ileal digestible lysine levels (AA− 1.0% vs. AA+ 1.2%) in an ideal ratio, to other essential AAs during days 0–11. Higher amino acid concentration consistently improved body weight gain, feed efficiency, and nutrient utilization throughout the trial, whereas the benefits of higher AME were mainly observed during the first 11 days. Diets high in both fat and amino acids reduced early feed intake, suggesting satiety effects. The effects on supply organ development were limited; only the pancreas and small intestine exhibited treatment-related differences in relative weight or allometric growth. In conclusion, increased amino acid concentration in starter diets improved overall broiler performance and nutrient efficiency, whereas dietary fat provided only short-term benefits. These improvements were not consistently associated with morphological changes in supply organs.