Determining effective dietary and ruminal fermentation parameters on live weight gain in diets formulated with selected agro-industrial by-products and their validation in performance fattening lambs.

The objective of this study was to determine the effects of dietary agro-industrial by-products (AIBP) with different amounts of metabolizable energy (ME) and crude protein (CP) on fermentation (96 h) and gas production (GP) kinetics in vitro, as well as acceptability, animal performance, digestibility, and blood parameters in lambs. The gas production technique (GPT) and fermentation characteristics were used in an in vitro trial. This experiment used diets with ME contents of 6.28, 7.53, and 9.62 MJ/kg, as well as levels 120, 140, and 160 g/kg CP. Principal component analysis (PCA) was used to select the most important dietary ingredient ruminal fermentation parameters. The in vitro results showed that increasing ME and CP content increased and decreased GP (P < 0.05), respectively. An increase in CP content caused an increase in ruminal ammonia nitrogen (NH₃-N) concentration (P < 0.05) and an increase in ME caused a decrease in pH (P < 0.05). PCA, by reducing the dimensions of the variables, shows that neutral detergent fiber (NDF), synchronization index (SI), and lignin as dietary parameters and pH and NH₃ as fermentation quality parameters were the main variables in predicting LWG (P < 0.05). Next, to prove the ineffectiveness of dietary protein content on LWG, the highest ME content (ME = 9.62 MJ/kg) was selected for in vivo experiment. For the in vivo trial, eighteen male lambs of 6-7 months of age and 30.6 ± 2.27 kg body weight were randomly fed on three diets containing 120, 140, and 160 g/kg CP and ME 9.62 MJ/kg. There was no effect of the experimental diets on acceptability, performance characteristics, or apparent digestibility in an in vivo trial (P > 0.05). NH₃-N concentration was affected by the varying content of CP (P < 0.05). The results of this study indicate that Khorasan Kurdish lambs have a high potential for using AIBP in their diet. Additionally, lamb producers can prevent N wastage without worrying about the loss of animal performance by using 120 g/kg CP, which meets the animals' needs and has beneficial environmental consequences.