Chemical Composition, Nutrient Digestibility, and True Metabolizable Energy of Differentially Processed Chicken-Based Pet Food Ingredients Using the Precision-Fed Cecectomized Rooster Assay

In addition to the nutrient composition of raw ingredients, processing conditions may greatly affect the quality and digestibility of protein-based ingredients used in pet food products. Testing the quality of protein sources undergoing different processing conditions provides important information to pet food producers. Therefore, the objective of this study was to determine the chemical composition, nutrient digestibility, and nitrogen-corrected true metabolizable energy (TMEn) of chicken-based ingredients that had undergone different processing conditions using the precision-fed cecectomized rooster assay. Chicken meal was compared to raw (no processing; frozen), steamed (cooked to 200^oF and held for 10 min at 200^oF, cooled, and frozen), and retorted (retorted at 250^oF for 30 min, cooled, and frozen) chicken ingredients. Chicken meal had higher ash [16.3% of dry matter (DM)] and crude protein (CP; 67.4% of DM), but lower acid-hydrolyzed fat (AHF; 15.7% of DM) and gross energy (GE; 5.09 kcal/g of DM) than raw chicken (5.8% ash; 41.7% CP; 52.4% AHF; 6.98 kcal/g), steamed chicken (6.7% ash; 53.0% CP; 44.8% AHF; 6.59 kcal/g), and retorted chicken (7.6% ash; 55.6% CP; 41.8% AHF; 6.68 kcal/g). Chicken meal had lower digestibility of DM (60.0%) and organic matter (OM; 65.9%), but higher AHF digestibility (90.3%) than the raw (DM: 75.9%; OM: 80.5%; AHF: 88.3%), steamed (DM: 76.5%; OM: 80.6%; AHF: 86.5%), and retorted (DM: 73.5%; OM: 77.8%; AHF: 83.5%) ingredients. For all essential and non-essential amino acids, steamed chicken had the highest digestibilities. For all essential amino acids and all but one non-essential amino acid (proline), raw and retorted chicken digestibilities were similar to one another and greater than that of chicken meal. For proline, steamed and retorted chicken had a similar digestibility and was greater than that of raw chicken and chicken meal, which were similar to one another. TMEn was lower for chicken meal (3.43 kcal/g) than raw (5.37 kcal/g), steamed (4.88 kcal/g), and retorted (4.99 kcal/g) ingredients. This study demonstrates how greatly processing method may affect the chemical composition, nutrient digestibility, and energy content of protein-based ingredients intended for use in dog and cat foods. Based on our results, the use of slightly cooked ingredients can be expected to deliver a higher quality protein to pets than that provided by rendered meals.