The present study determined i) the presence of proteins (oviduct-specific glycoprotein, OVGP1; heat shock protein-70A, HSPA1A; heat shock protein-A8, HSPA8; annexin A1, ANXA1; annexin A5, ANXA5; and myosin-9, MYH9) known to be involved in early reproduction in the oviduct fluid (OF) of anestrous goats; and ii) the functional effect of during IVF on polyspermy modulation and embryonic development. In vitro-matured oocytes were co-cultured with spermatozoa (1.0, 2.0, or 4.0 x 106 cells/mL) for 18 h in SOF medium supplemented with 5 mg/mL of heparin, 4 mg/mL gentamicin, and 10% estrus sheep serum (CTRL1, CTRL2, and CTRL4 groups) or the same medium plus 10% OF (OF1, OF2, and OF4 groups) obtained from anestrus goats. The analysis of OF by western blotting confirmed the presence of the six proteins tested for. The increase in sperm concentration had no effect (P > 0.05) on the penetration rate in any group; however, monospermy rate decreased as sperm concentration was increased in both OF and CTRL. Regardless of the concentration used, when data were pooled, OF supplementation improved (P < 0.05) monospermy and tended (P <1/4> 0.057) to enhance IVF efficiency. Additionally, IVF efficiency was higher (P < 0.05) in OF1 than in OF4 [60 +/- 13 vs 37 +/- 5%). The development capacity was not affected (P > 0.05) by the sperm concentration and OF treatment, and the average values were cleavage (72 +/- 2.6%), blastocyst (37 +/- 3.0%), blastocyst in relation to the cleaved (51 +/- 4.8%), hatched (62 +/- 1.2%), and number of cells per blastocyst (174 +/- 1.8%). In conclusion, the six proteins analyzed are present in the OF of anestrous goats, and the supplementation of this OF during IVF may modulate the polyspermy incidence and enhance IVF efficiency, especially when 1x10(6) sperm per mL is used.