Yeast protein as a fishmeal substitute: impacts on reproductive performance, immune responses, and gut microbiota in two sow hybrids

Yeast protein supplementation showed no significant effects on most reproductive parameters of different sow hybrids, but reduced backfat loss by 30.5% during lactation (<i>P</i> < 0.05) and demonstrated a numerical reduction in mummification rate of fetuses (<i>P</i> = 0.06). Immunological assessments revealed that LLY sows exhibited 26.8% lower serum IgM concentration than LY sows (<i>P</i> < 0.05), while yeast protein supplementation significantly reduced serum IL-1β levels by 45.6% (<i>P</i> < 0.05) on day 18 of lactation. 16S rRNA gene sequencing analysis revealed comparable fecal microbial diversity across treatments (<i>P</i> > 0.05), though differences were observed in certain bacterial genera between LY and LLY sows during late gestation and lactation. Yeast protein supplementation enriched beneficial bacteria including <i>Ruminococcaceae_UCG-002</i>, <i>Rikenellaceae_RC9_gut_group</i>, and <i>Christensenellaceae_R_7_group</i>, while suppressing potentially detrimental bacteria such as <i>Family_XIII_AD3011_group</i> (<i>P</i> < 0.05). These findings demonstrate the practical feasibility of retaining LLY sows for commercial breeding. Yeast protein supplementation, as a substitute for fishmeal during late gestation and lactation, significantly reduced lactational backfat loss, moderately attenuated inflammatory response, and enhanced gut microbiome homeostasis through selective microbial enrichment in sows.