Associations of short photoperiod and the male effect with fecal microbiota, metabolomic profiles, serum metabolites, and reproductive performance in dairy goats during the nonbreeding season.

Seasonal anestrus in Saanen dairy goats limits the continuity of year-round milk production, and the physiological and molecular mechanisms of seasonal estrus of dairy goats remain to be investigated. Eighty healthy female dairy goats aged 2.5-3.5 years were randomly divided into 2 groups during the non-breeding season (March to April): a control group (C, natural or long photoperiod) and a treatment group (T, short photoperiod combined with buck induction), comprising 40 goats each, housed 10 per pen. The experimental group additionally housed 2 bucks per pen, separated from the does by partitions. The trial lasted 4 weeks, estrus monitoring was conducted daily, and fecal and blood samples were collected weekly. Reproductive hormone levels (FSH, LH, E2, P4) were measured on d 7, 14, 21, and 28. On d 0 and 14, and at estrus (treatment group), serum and fecal samples underwent metabolomic analyses, and feces underwent 16S rRNA sequencing analyses, respectively. Results indicated that short photoperiod combined with the male effect significantly influenced the dynamic changes in serum reproductive hormones, with marked increases in E2 and FSH levels. Fecal microbial 16S rRNA analysis revealed changed microbial community structure at the phylum and genus levels, with Bacillota and Bacteroidota as the dominant phyla. Metabolomic analysis suggested that this treatment significantly altered the serum and fecal metabolite profiles. KEGG pathway enrichment analysis indicated that differentially abundant metabolites were primarily associated with reproduction-related pathways, including steroid hormone synthesis. The correlation analysis revealed a relationship between bacterial genera, reproductive hormones, and metabolites. Follow-up of does that conceived after induced estrus showed no seasonal difference in kid birth weight, whereas milk fat and total solids were higher in non-breeding season milk. In conclusion, the short photoperiod combined with the male effect could increase the estrus and pregnancy rate of dairy goats in the non-breeding season, and is associated with changes in endocrine, gut microbial, and metabolic networks.