Optimizing hammer mill speed: Impact on growth performance, pellet quality, and gizzard gene expression in broilers

Abstract

Background and Aim: Feed constitutes 60%–70% of total poultry production costs, and optimizing feed processing is critical for improving efficiency. This study evaluated the effect of varying hammer mill speeds (HMSs) during corn grinding on growth performance, pellet quality, gizzard morphology, and expression of growth-related genes (growth hormone [GH], GH receptor [GHR], insulin-like growth factors 1 and 2 [IGF1, IGF2]) in broiler chickens. Materials and Methods: A total of 1, 500 one-day-old Ross 308 broiler chicks were randomly divided into three groups: HMS100 (control, 100% HMS), HMS75 (75% speed), and HMS50 (50% speed), each with five replicates of 100 birds. Birds were fed isocaloric, isonitrogenous pelleted diets for 28 days. Performance metrics, pellet durability and hardness, gizzard morphology, and intestinal length were assessed. Gene expression analysis in gizzard tissue was conducted using quantitative reverse transcription polymerase chain reaction for GH, GHR, IGF1, and IGF2. Results: Broilers in the HMS75 and HMS50 groups exhibited significantly lower feed intake (by 4.03% and 3.99%) and higher body weight (BW) (by 5.29% and 3.53%) compared to HMS100 (p < 0.05). HMS75 significantly improved feed conversion ratio by 6.81% and BW gain by 5.04% (p < 0.05). Pellet durability and hardness were enhanced in both HMS75 and HMS50 groups (p < 0.05). Gizzard width and muscle thickness were significantly increased at reduced mill speeds, especially in HMS50. Intestinal length was longest in HMS75 (1.96 m). Gene expression analysis revealed a 113% increase in GH expression in HMS75 and a 303% upregulation of IGF2 in HMS50 compared to HMS100 (p < 0.05). Conclusion: Reducing HMS to 75% optimized broiler growth performance, pellet quality, and intestinal development, while 50% speed promoted IGF2-mediated gizzard hypertrophy. Hammer mill modulation provides a practical strategy to balance feed efficiency and targeted tissue growth in broilers.