Progesterone supplementation in cattle hastens conceptus development and secretion of pregnancy-associated glycoproteins

Post-ovulatory supplementation of progesterone (P4) to cows has been associated with enhanced conceptus elongation. The aim of the present study was to investigate the impact of P4 supplementation on peri-implantation conceptus signaling including the secretion of interferon tau (IFNT), the maternal response to IFNT (mRNA abundance of interferon-stimulated genes [ISG; ISG15 and MX2]), and circulating pregnancy-associated glycoproteins (PAG). Two cohorts (A and B) of primiparous Angus beef cows were synchronized to estrus, artificially inseminated (d0), and assigned randomly to receive intravaginal P4 device (CIDR, 1.38 mg) from d3 to d12 or remain as untreated controls. Blood and cervical cytobrush were collected from d3 to d24 and a uterine cytobrush was collected on d24 from Cohort A to assess circulating concentrations of P4, PAG, mRNA abundance of ISG, and concentrations of IFNT, respectively. Blood and cytobrush (cervical and uterine) were collected from Cohort B on d18 to assess circulating concentrations of P4, mRNA abundance of ISG, and concentrations of IFNT, respectively. The mRNA abundance of ISG was assessed in luteal biopsies on d18 and d22. There was no effect of P4 supplementation on concentrations of IFNT in the uterus on d18. There was no effect of supplemental P4 on mRNA abundance or timing of ISG in endometrial, cervical, or luteal tissue. The earlier detection of PAG in circulation and lower uterine fluid concentrations of IFNT on d24 in P4-supplemented cows suggests advanced trophoblast differentiation and enhanced conceptus development beyond previously reported advances in conceptus elongation alone.