Lysozyme is a 1,4-β-N-acetylmuramidase, usually found in sow’s milk, and previous research has shown it might have strong antimicrobial properties. For commercial purposes, a trial was conducted in the U.S. to compare the effects of lysozyme as a replacement of antibiotics on piglet growth performance and immune response during an indirect immune challenge. Two replicates of 600 pigs each were weaned from the sow at day 26 and assigned to dietary treatments. Pigs were housed either in a nursery room that had been fully disinfected or a nursery room left unclean. Within a room, pigs were assigned to either control diets (2-phase nursery program), control diets + antibiotics (chlortetracycline/tiamulin), or control diets + lysozyme (100 mg/kg diet).

Results indicated that pigs receiving diets with antibiotics or lysozyme grew at a faster rate for the duration of the trial (28-days post-weaning) compared to control pigs (318, 320 versus 288 grams per day, respectively; P < 0.05), regardless of nursery environment (P > 0.05). The indirect immune challenge (from the unclean room environment) did not alter growth performance from days 0 to 14 of treatment but decreased growth from days 14 to 28 of the study (415 versus 445 grams per day; P < 0.05). Feed intake was not altered by the nursery environment or dietary treatments, but feed efficiency was worsened by the indirect immune challenge (P < 0.05) and improved by both antibiotics and lysozyme treatment (P < 0.01).

In addition, the immune challenge did not alter nutrient accretion, but antibiotics and lysozyme decreased accretion of whole-body lipid (P < 0.01) and tended to increase accretion of protein (P < 0.09). Blood levels of tumor necrosis factor-α (TNF-α; P < 0.01), haptoglobin (P < 0.09), and C-reactive protein (CRP; P < 0.01) were higher due to the indirect immune challenge compared to pigs reared in the clean nursery (P < 0.05). In addition, pigs consuming antibiotics or lysozyme had lower TNF-α, haptoglobin and CRP compared to control pigs, regardless of nursery environment (P < 0.04).

Thus, it appears lysozyme is a suitable alternative to antibiotics in piglet diets.