PS3-7. Effects of Lysozyme Supplementation on Feed Efficiency and Rumen Function in Post-weaning Beef Cattle.

Abstract Dietary strategies that influence the rumen microbiome have the potential to improve rumen fermentation and nutrient utilization in beef cattle. Lysozyme, a bacteriolytic enzyme, may provide a novel approach to modifying rumen microbial communities and rumen function. The objective of this study was to evaluate the effects of dietary lysozyme supplementation on performance, rumen microbial populations, and rumen function in post-wean beef cattle. Forty Angus steers (268.74 ± 22.11 kg, and approximately five months of age) were used in a 70-day feeding trial, blocked by initial BW and randomly assigned to control or treatment groups (n = 20 per treatment). The treatment diet was supplemented with a protein pellet containing lysozyme, and the control diet was supplemented with the same protein supplement, substituting rice meal for lysozyme. Diets were offered ad libitum as a total mixed ration using a GrowSafe system to measure individual feed intake. Body weights were recorded at the beginning, midpoint, and end of the trial to calculate ADG, DMI, F:G, and RFI. Rumen fluid samples were collected at the end of the trial to evaluate rumen pH and microbial community composition. Data were analyzed using linear models with treatment as a fixed effect, and microbial abundance and diversity were analyzed using DESeq2 and phyloseq. Beta diversity was assessed using PERMANOVA. Average daily gain did not differ between control and treatment groups, respectively (1.35± 0.05 vs. 1.42± 0.05 kg/d; P = 0.37). Lysozyme supplementation reduced DMI (13.27± 0.42 vs. 11.85± 0.40 kg/d; P = 0.02) and improved feed efficiency, as indicated by lower F:G (9.92± 0.38 vs. 8.56± 0.37; P = 0.015). Residual feed intake was also decreased in supplemented cattle (0.602± 0.32 vs. −0.602± 0.33; P = 0.01), indicating improved efficiency independent of growth and body size. Rumen pH was not affected by treatment (7.17± 0.10 vs. 7.13± 0.10; P = 0.58). Lysozyme supplementation altered rumen microbial community structure, as indicated by differences in numerous bacterial taxa and diversity between treatments (P < 0.05), suggesting shifts in microbial ecology associated with improved feed utilization. Lysozyme supplementation improved feed efficiency through reduced feed intake without affecting growth performance or rumen pH, while also altering rumen microbial community structure. These results suggest that lysozyme may enhance nutrient utilization through microbial-mediated mechanisms without disrupting rumen conditions, supporting its potential as a novel feed additive in beef production systems.