Investigation of in vitro measurable sperm attributes and their influence on electroejaculated bull semen with a fixed‐time artificial insemination protocol in AustralianBos indicuscattle

Abstract

Increasing use of fixed-time artificial insemination (FTAI) in beef cattle production has presented an opportunity for the use of fresh or chilled semen as an alternative to standard cryopreserved semen. The objective of this study was to examine in vitro sperm function and pregnancy rate of electroejaculated semen, chilled and stored for 48 hr, compared to conventionally cryopreserved semen with an optimized FTAI protocol in Brahman cattle. Semen from three Brahman bulls was collected, and aliquots were extended in either chilled (at 5°C) or frozen (LN ) in a Tris-egg yolk extender base with 2.4% or 7.0% glycerol, respectively. Semen samples were assessed 48 hr after collection or post-thaw and warming, for sperm motility, in vitro sperm function and fertilizing ability, and used in a FTAI programme. The overall pregnancy rates was significantly different (p < .01) after FTAI with frozen (n = 173; 53.2%) and chilled semen (n = 174; 31.6%). In contrast, the in vitro sperm assessment showed that the chilled semen had significantly faster motility (p < .05), a higher proportion of progressively motile spermatozoa (p < .05), with significantly higher proportions of acrosome intact, viable spermatozoa (p < .01). This study showed that reasonable pregnancy rates in Brahman cattle can be achieved using FTAI with chilled semen collected using electroejaculation and stored for up to 48 hr. However, improvements in semen extenders are required in consideration of semen collection method to improve the longevity of sperm fertilizing ability to significantly increase FTAI output using chilled storage of bull semen.

Bull Semen Obtained on Beef Farms by Electroejaculation: Sperm Quality in the First Two Hours of Storing with Different Extenders and Holding Temperatures

“…Short-term storage may influence the final quality and reproductive efficiency of semen when used refrigerated or cryopreserved. In fact, studies of bull semen obtained at AI centres have pointed out these issues [24][25][26][27][28], thereby revealing that short-term cooling of bull semen doses after collection (instead of freeze-thawing) using an egg-yolk based extender [29,30] increased the conception rate. Consequently, further investigation into semen collection methods and handling to improve sperm longevity and fertilization ability was recommended [29][30][31].…”

“…In fact, studies of bull semen obtained at AI centres have pointed out these issues [24][25][26][27][28], thereby revealing that short-term cooling of bull semen doses after collection (instead of freeze-thawing) using an egg-yolk based extender [29,30] increased the conception rate. Consequently, further investigation into semen collection methods and handling to improve sperm longevity and fertilization ability was recommended [29][30][31]. On the other side, the demand for egg yolk replacement in extenders has increased in recent years due to the extremely wide variability of their composition based on their initial sources and the constant risk of contamination by bacteria or mycoplasma, which could be a source of endotoxins that could damage the fertilizing capacity of spermatozoa [32].…”