Abstract
The objective of this study was to ascertain the cellular and functional parameters as well as ROS related changes in sperm from bulls with varied sperm freezability phenotypes. Using principal component analysis (PCA), the variables were reduced to two principal components, of which PC1 explained 48% of the variance, and PC2 explained 24% of the variance, and clustered animals into two distinct groups of good freezability (GF) and poor freezability (PF). In ROS associated pathophysiology, there were more dead superoxide anion positive (Dead SO+) sperm in GF bulls than those in PF (15.72 and 12.00%; P = 0.024), and that Dead SO+ and live hydrogen positive cells (live H2O2+) were positively correlated with freezability, respectively (R2 = 0.55, P < 0.0130) and (rs = 0.63, P = 0.0498). Related to sperm functional integrity, sperm from PF bulls had greater dead intact acrosome (DIAC) than those from GF bulls (26.29 and 16.10%; P = 0.028) whereas sperm from GF bulls tended to have greater live intact acrosome (LIAC) than those from PF bulls (64.47 and 50.05%; P = 0.084). Sperm with dead reacted acrosome (DRAC) in PF bulls were greater compared to those in GF (19.27 and 11.48%; P = 0.007). While DIAC (R2 = 0.56, P = 0.0124) and DRAC (R2 = 0.57, P < 0.0111) were negatively correlated with freezability phenotype, LIAC (R2 = 0.36, P = 0.0628) was positively correlated. Protamine deficiency (PRM) was similar between sperm from GF and PF bulls (7.20 and 0.64%; P = 0.206) and (rs = 0.70, P = 0.0251) was correlated with freezability. Sperm characteristics associated with cryotolerance are important for advancing both fundamental andrology and assisted reproductive technologies across mammals.
Highlights
Bull fertility, regarded as the ability of viable sperm to fertilize the egg and support early embryonic development, is essential for the propagation of species, and it is an important economic trait for animal breeding programs
Using principal component analysis (PCA), we reduced the variables to two principal components, principal component 1 (PC1) explaining 48% of the variances and principal component 2 (PC2) explaining 24% of the variances, and clustered animals into two distinct groups of good freezability (GF) and poor freezability (PF), with an outlier for the GF (Figure 1)
Based on the patterns of these variables, PC1 was primarily correlated with Ferric-Reducing Antioxidant Power Assay (FRAP) (r = 0.91; P = 0.0002), live H2O2− (r = 0.97; P < 0.0001), dead H2O2− (r = 0.96; P < 0.0001), dead H2O2+ (r = 0.63; P = 0.052), live superoxide anion (SO)+ (r = 0.98; P < 0.0001), dead SO– (r = 0.95; P < 0.0001), dead intact acrosome (DIAC) (r = 0.68; P = 0.031), and dead reacted acrosome (DRAC) (r = 0.70; P = 0.025), live intact acrosome (LIAC) (r = −0.84; P = 0.003), live reacted acrosome (LRAC) (r = 0.63; P = 0.049), and MitoSOX– (r = 0.96; P < 0.0001)
Summary
Bull fertility, regarded as the ability of viable sperm to fertilize the egg and support early embryonic development, is essential for the propagation of species, and it is an important economic trait for animal breeding programs. The use of fresh or frozen sperm through artificial insemination (AI) combined with genomic selection has accelerated the genetic improvement of livestock [1, 2]. Cryopreservability of Bull Sperm as the successive stabilization of temperature with the process of dehydration, freezing, thawing, is a useful and profitable procedure for long-term storage of sperm in domestic animals and humans [3]. Cryopreservability or freezability of sperm is crucial for the success of AI, which has become the preferred method of breeding in the cattle industry, especially in dairy cattle agriculture. The bovine livestock industry has been evolved by more advanced protocols and cryoprotectants that has resulted in the improvements of the fertility of frozen-thawed sperm [4,5,6]
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