Exposure of Thawed Frozen Bull Sperm to a Synthetic Peptide Before Artificial Insemination Increases Fertility

Abstract

ABSTRACT: We evaluated the effect on fertility of in vitro exposure of thawed frozen bull sperm to synthetic FertPlus• peptide prior to artificial insemination (Al). The peptide represented a 60‐amino acid sequence within rat prosaposin. Commercial cryopreserved semen was from three Holstein bulls. Onset of estrus in groups of Holstein nulliparous heifers was synchronized via injection of prostaglandin F2‐α, and heifers were scheduled for Al 8–24 hours after estrus was detected. Semen was thawed, diluted to 2.4 × 105 sperm/ml with buffer, and split to provide control and exposed aliquots (0 or 30 μ.M peptide) that were incubated at 37°C 10 minutes and then were held at 32°C. The two aliquots of semen then were used on an alternate basis 2–65 minutes later to inseminate females. Each Al (one per female) involved the deposit of ∽250,000 sperm into each uterine horn. This procedure for Al was used to reduce the pregnancy rate with control semen to below the maximum value for a given bull and to facilitate detection of any beneficial effect of the peptide. For each bull, ∽32 heifers were inseminated with control semen, and ∽32 heifers were inseminated with peptide‐exposed semen. Pregnancy was evaluated ultrasonically ∽60 days after Al. After excluding one group of heifers with unusually low fertility, averaged across all animals, a 29% increase in pregnancy rate resulted from exposure of sperm to peptide (P < 0.04; one‐tailed chi‐square test; means were 48 vs. 62%). Pregnancy rates for the three bulls for control and peptide‐exposed semen, respectively, were 42 and 62%, 44 and 64%, and 56 and 61%: means in the first two pairs of values tended to differ (P ⋍ 0.10). These observations should be confirmed with sperm from other bulls used in a more conventional manner. However, with insemination of a limiting number of cryopreserved sperm, brief exposure of the thawed bull sperm to FertPlus® peptide appeared to improve fertility dramatically.