enhanced embryo development especially when added at later stages of embryonic development. Serum addition at morula and early blastocyst stage produced blastocyst, including fully expanded and hatched blastocyst.
Serum contains beneficial substances for embryonic development such as growth factors and chelators of heavy metals. The omission of serum in the co-culture system resulted only in blastocyst formation and no hatched and hatching blastocyst.
Zona hardening has been reported to occur when serum or cumulus cells were excluded (Mochizuki et al. 1991). Habsah (2006) observed the mono-culture system resulted in slightly higher blastocyst rate compared to the co-culture system, and suggesting that omission of serum in co-culture system lowered the blastocyst formation. Serum in culture medium has been reported to promote hatching by providing a pool of plasminogen which in cattle embryos was converted to plasmin that proteolytically degraded the zona pellucida and facilitates hatching (Kaaekuahiwi and Menino, 1990).
Many investigators have reported the improvement in embryonic development with serum-supplemented media (Pinyopummintr and Bavister, 1991; Takagi et al.,
1991; Yoshioka et al., 1997; Khurana and Niemann, 2000). The result obtained in the present study was in agreement with Lonergan et al. (1999), where they found that BSA and FCS significantly improved embryonic development when added to SOF which resulted in superior embryo quality. Additional FCS resulted in significant accelerated embryonic development such as more blastocyst development (on Day 6) and higher overall percentage of blastocyst with higher total cell numbers and hatching rates. Van Langendonckt et al. (1997) reported that the addition of FCS to mSOF at 42 hours post-insemination accelerated the development of bovine embryos between the 9- to 16-cell and morula stages and that the first blastocyst was observed 0.9 day earlier in mSOF supplemented with FCS. Yoshioka et al. (1997) reported that the development of morula to blastocyst was 1 day earlier in SOF plus FCS than in SOF plus BSA, even when the FCS supplementation was at 120 hours post-insemination. They suggested that FCS initiates earlier blastulation with fewer cells in the morula than when using BSA. Wang et al. (1997) reported that the development to the blastocyst stage and hatching rate were better in FCS-supplemented media than in media supplemented with BSA. The proportion of embryos that ceased development at the morula stage was greater in BSA-supplemented media.
Jung and Willard (2009) found that supplementation with FBS did not statistically improve the rate of blastocyst formation, although embryos were derived from culture medium with FBS supplementation exhibited a numerical increase in apparent developmental competence with 36.6% and without serum with 24.3%
blastocyst formation. Pinyopummintr and Bavister (1991) found that serum supplementation exhibited a biphasic effect, with inhibition at the first cleavage and stimulation of morula compaction and blastocyst formation. However, blastocyst
development in TCM-199 supplemented with 10% BCS (29.7%) or with BCS + oviduct cell-conditioned medium (21.6%) was significantly greater than in non-supplemented HECM (hamster embryo culture medium), (9.7%) or TCM-199 (13.8%). Fukui and Ono (1989) reported that even the effectiveness of serum supplementation in the culture medium varies by different components of culture conditions used in vitro.
It has been reported that some batches of serum decreased the blastocyst rate and cell number and increase apoptotic cells on a particular culture system (Van Langendonckt et al., 1997). Caro and Trounson (1984) did not find any improvement of the embryonic development with the serum-supplemented medium versus non-supplemented medium in the mouse. This was in an agreement with Abe and Hoshi (2003) who evaluated the quality of bovine embryos developed from IVM and IVF oocytes cultured in either serum-free or serum-containing media. Their result showed that bovine embryos cultured in serum-supplemented medium contain numerous cytoplasmic lipid droplets and immature mitochondria compared to those cultured in serum-free medium. The accumulation of cytoplasmic lipids in embryos developed in serum-containing medium may be a result of incorporation of lipoproteins from the serum and may result in impaired function of mitochondria. The survival and hatching rates of embryos produced in serum-free media after post-thaw culture were superior to those of embryos produced in the serum-containing medium, suggesting that the abnormal accumulation of cytoplasmic lipids in embryos may have a negative effect on the sensitivity of embryos to chilling and freezing.
Serum is a pathological fluid formed by blood clotting, which may induce chemical alterations with possible harmful effects for embryo culture. Serum and
serum albumin are two commonly used protein sources in media for the in vitro culture of mammalian embryos. Albumin not only serves as a low-affinity, high-capacity reservoir for certain beneficial components (e.g. steroids, vitamins, fatty acids and cholesterol), but also scavenges ions and small molecules (Maurer, 1992).
Serum contains a variety of known and unknown substances which may stimulate or inhibit embryo development in vitro (Maurer, 1992; Bavister, 1995). Studies have shown that serum supplementation during the early cleavage stages of culture can inhibit the first cleavage but enhances the formation of morulae and blastocyst when serum is added during the later stage of embryo development (Pinyopummintr and Bavister, 1991; Lim et al., 1994).
5.1.4 Effect of COC Quality on Fertilisation and Cleavage Rate after ICSI