Replacing chicken yolk with yolks from other sources in ram semen diluents and their effects on fertility <i>in vitro</i>

Abstract

Over the past 70 years, egg yolk (EY) has been continuously used as a cryoprotectant in semen diluents. Earlier studies have shown that the composition of different EYs showed that the basic components were present in similar levels. However, further breakdown and analysis revealed significant differences between EY sources. The objective of this study was to evaluate and compare the effect of substitution chicken EY in ram semen diluents with yolks from other species on in vitro fertilization, subsequent embryonic development and total blastocysts formation. Through the breeding season, ejaculates were collected weekly from five Sarda breed rams of proven fertility, divided equally and diluted in Tris–citrate–fructose–glycerol based diluents containing 20% (v/v) of either partridge, ostrich, turkey, duck, tortoise, or chicken EYs (as a control) at 37 °C. Extended semen was cooled to 4 °C and preserved as a 0.25 mL pellet in LN2. Adults Sarda ewe ovaries were collected from a local slaughterhouse and a total of 913 collected oocytes were divided randomly and matured oocytes were fertilized in vitro with frozen–thawed spermatozoa prepared as described above, and cultured until Day 8. The proportions of cleaved and expanded blastocysts/groups were evaluating after 46, and 144–192 h post-insemination (hpi), respectively. Among all sources of EYs, semen cryopreserved in presence of partridge EY significantly increased the proportion of fertilized matured oocytes compared with semen preserved in presence of tortoise or chicken EYs (105/131, 80.1%), (74/123, 60.2%), and (189/270, 70.0%), respectively. Interestingly, using partridge, ostrich, turkey, and duck EYs in ram semen diluents increased significantly (P &lt; 0.001) the number of blastocysts formation on Day 6 after IVF versus tortoise or chicken yolks. However, there was no significant difference in total blastocysts yield between all sources of EY. In conclusion, the different compositions of yolks did offer different levels of in vitro production embryos. Specifically, semen diluents in presence of partridge yolks improved cleavage rates, and the numbers of early embryonic development. Whereas using ostrich, turkey, and duck EYs offered comparable fertilization and embryonic development versus conventional semen diluents with 20% chicken EY