Recent Advances in Boar Sperm Cryopreservation: State of the Art and Current Perspectives

Abstract

ContentsWhile sperm cryopreservation is the best technology to store boar semen for long-term periods, only 1% of all artificial inseminations (AI) conducted worldwide are made using frozen-thawed boar sperm. With the emergence of long-term extenders for liquid storage, the use of cryopreserved sperm in routine AI is less required. However, banks of boar semen contain cryopreserved sperm and planning inseminations in AI centres may benefit from the use of frozen-thawed semen. Therefore, there is an interest in the use of this technology to preserve boar sperm. In this regard, although the first attempts to cryopreserve boar semen date back to the seventies and this technology is still considered as optimal, some relevant improvements have been made in the last decade. After giving a general picture about boar sperm cryodamage, the present review seeks to shed light on these recent cryopreservation advances. These contributions regard to protein markers for predicting ejaculate freezability, sperm selection prior to start cryopreservation procedures, additives to freezing and thawing extenders, relevance of the AI-technique and insemination-toovulation interval. In conclusion, most of these progresses have allowed counteracting better boar sperm cryodamage and are thus considered as forward steps for this storage method. It is also worth noting that, despite being lower than fresh/ extended semen, reproductive performance outcomes following AI with frozen-thawed boar sperm are currently acceptable.

Will AI in pigs become more efficient?

“…The improvements made in cryopreservation methods for the past 15 years, including in composition of freezing and thawing extenders, and the knowledge that not all boars are "good sperm freezers" have shown that AI-doses cryopreserved today show good sperm quality and functionality at thawing [30]. Certainly, post-thaw sperm recovery rates over 70% in motility and viability are now usual, resulting in fertility outcomes near to those achieved with liquid-stored semen.…”

“…New extenders for extending lifespan of FT-sperm and for cryopreserving sexed sperm are imperative [30,47].…”

Markers for Sperm Freezability and Relevance of Transcriptome Studies in Semen Cryopreservation: A Review

“…Moreover, selection of animals with good semen freezability for cryopreservation and AI is a crucial step to improve the fertility levels of frozen-thawed semen [9,10]. Furthermore, in some animal species, despite satisfactory results of fertility in liquid-stored semen, frozen-thawed semen does not give acceptable fertility results in AI practice in the commercial industry [2,3,9].…”

“…Cryopreservation of semen allows the preservation of good genetic resources and the protection of endangered species [1][2][3][4][5]. While a great deal of eforts has been done over the last several years to improve the semen cryopreservation technology, efective cryosurvival of spermatozoa from various animal species, including the boar and stallion, still remains elusive and a cryobiological enigma [1].…”

“…Cryo-induced oxidative stress is associated with excess production of reactive oxygen species (ROS), resulting in biochemical and physical damage to the sperm membrane structures and subsequently leading to reduced fertilizing ability of spermatozoa [4][5][6]. In the artiicial insemination (AI) industry, there is a need to optimize the selection strategy for individuals with good freezability, so as to incorporate this information in the breeding program to improve the fertility of post-thaw semen [2,3,7]. Moreover, selection of animals with good semen freezability for cryopreservation and AI is a crucial step to improve the fertility levels of frozen-thawed semen [9,10].…”