MMP9 and hydrops fetalis: On day 240 of pregnancy, the activity of the active isoform (act) of MMP-9 was 671.9 ± 191.1 (relative D.O units) in the HM-HF group (Figure 5B) and 1.12-fold lower in the USP group that delivered a healthy foal (HM-HF vs. USP-HF, p = 0.9819; Figure 5B).