Sperm cryopreservation is an important adjunct to assisted reproduction techniques (ART) for improving the reproductive efficiency of dairy cattle and buffaloes. Improved understanding of mechanisms and challenges of bovine semen cryopreservation is vital for artificial insemination on a commercial basis. Although cryopreservation of bovine spermatozoa is widely practiced and advanced beyond that of other species, there are still major gaps in the knowledge and technology. Upon cryopreservation, disruption of spermatozoal plasma membrane configuration due to alterations in metabolic pathways, enzymes and antioxidants activity add to lower efficiency with loss of sperm longevity and fertilising ability. Therefore, the effective amalgamation of cryo‐variables like ambient temperature, cooling and thawing rates, nucleation temperature, type and concentration of the cryoprotectant, seminal plasma composition, free radicals and antioxidant status are required to optimise cryopreservation. Novel strategies like supplementation of cholesterol‐loaded cyclodextrins (CLC), nanovesicles, osteopontin, antioxidants, etc., in an extender and recent techniques like nano‐purification and modified packaging have to be optimised to ameliorate the cryodamage. This article is intended to describe the basic facts about the sperm cryopreservation process in bovine and the associated biochemical, biophysical, ultra‐structural, molecular and functional alterations.

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Semen cryopreservation plays a vital role in the success of artificial insemination (AI), which is the mostly applied technology for the production and genetic improvement of bovine (Lone et al., 2019;Vishwanath & Shannon, 2000). Although the quality of cryopreserved semen has enhanced during the past several decades, around 50% of the spermatozoa are damaged during the freeze-thaw process, leading to reduced freezability and capacity to fertilise (Layek et al., 2016), which is responsible for the limited genetic impact of proven sires in AI industry (Celeghini et al., 2008;Woelders et al., 1997).AI doses containing less number of spermatozoa are increasing widely to exploit the potential of genetically prestigious sires and make the potential use of sex-sorted semen (Lone et al., 2017;Mohanty et al., 2018;Negoita et al., 1979). One of the critical elements for an outstanding breeding programme is deciding the sperm dosage to achieve reasonable pregnancies without compromising the bull fertility. Numerous factors are responsible for compromised fertility level of the spermatozoa, including inherent fertility

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