Aim of this study was to compare different combinations of penetrating intracellular CPAs, i.e., glycerol (G), ethylene glycol (EG), propylene glycol (PG), dimethyl formamide (DM), and methyl acetamide (MA) and extracellular [egg yolk (EY), egg yolk plasma (EYP), low-density lipoproteins (LDL), and coconut water (CW)] in Tris-citric acid-fructose buffer (T) for Labrador dog semen cryopreservation. The study was conducted in two parts, first trial was conducted to assess optimum glycerol concentration (5-7%) in TEY and equilibration time (ET, 2-4 hrs) for Labrador dog semen cryopreservation. Secondly, compatibility of 15% TEY, 15% TEYP, 13% TLDL, and 25% TCW with G, DMF, MA, D + M, EG, and PG was evaluated for in vitro sperm function tests. Decline in sperm attributes, i.e., motility, viability, plasma membrane integrity (PMI), and acrosome integrity (AI)) was significantly (p < 0.05) less in 7% TEY-G and 4 h compared to other concentrations and ET at post-thaw. There was significantly (p < 0.05) less decline in sperm attributes in TEY-G, TEYP-G, TLDL-G, TLDL-D, TLDL-EG, and TCW-D extenders compared to other combinations at post-thaw. However, these parameters were significantly (p < 0.05) high in TEY-G and TEYP-G compared to TEYP-D, TLDL-G, TLDL-D, TLDL-EG, and TCW-D extenders at post-thaw. However, decline in motility, viability, PMI, and AI was identical in these seven extenders. This study concluded that glycerol at a concentration of 7% in TEY and 4 h ET were optimum for successful cryopreservation and besides TEY-G, other combinations of protectants may be an alternative for canine semen cryopreservation.
Keywords: Cryopreservation; Labrador dog; extenders; extracellular; intracellular; sperm attributes.