This study was designed to examine the effect of the age of rabbit oocytes on the developmental potential of cloned embryos. The metaphase II oocytes used for nuclear transfer (NT) were collected at 10, 12, 14, and 16 h post-hCG injection (hpi). The total number of oocytes collected per donor (21.4-23.7) at 12 to 16 hpi was similar, but significantly higher than that collected at 10 hpi (16.2). Additionally, a significant improvement in blastocyst development was achieved with embryos generated by electrically mediated cell fusion (56.0%), compared to those from nuclear injection (13.1 %) (Experiment 1). Markedly higher blastocyst development (45.8-54.5%) was also achieved with oocytes collected at 10-12 hpi than from those collected 14-16 hpi (8.3-14.3%) (Experiment 2). In Experiment 3, the blastocyst rates of NT embryos derived from oocytes harvested 12 hpi (39.2-42.8 %) were significantly higher than from those collected at 16 hpi (6.8-8.4 %) (p < 0.05), regardless of the donor cell age. Kinase activity assays showed variable changes of activity in rabbit oocytes over the period of 10-16 hpi; however, there was no correlation with preimplantational development (blastocyst rate vs. MPF, R = 0.326; blastocyst rate vs. MAPK, R = -0.131). Embryo transfer of NT embryos utilizing 12 hpi oocytes resulted in one full-term but stillborn, and one live cloned rabbit; thus, an efficiency of 1.7 % (n = 117) (Experiment 4). These results demonstrated that NT utilizing relatively young rabbit oocytes, harvested at 10-12 h after hCG injection, was beneficial for the development of NT embryos.

ABSTRACT. As one of the eight members in the 1-acylglycerol-3-phosphate-O-acyltransferase (AGPATs) family, AGPAT6 is a crucial enzyme for the biosynthesis of glycerolipids and triacylglycerol in eukaryotes, as well as catalyzing the conversion from lysophosphatidic acid to phosphatidic acid. AGPAT6 can be considered as a candidate gene for regulating milk composition. DNA sequencing and PCR-RFLP methods were applied to detect genetic variation in the AGPAT6 gene in 549 Chinese dairy goats. Four polymorphisms (NC_007328.3:g.152G>C, 8124G>A, 9263C>G, 16436G>A) were detected in 5'UTR, intron 2, exon 4, and 3'UTR, respectively. For the KpnΙ locus, the frequencies of the AGPAT6-G allele were 0.955 and 0.936 for SN (Xinong Sannen) and GZ (Guanzhong) dairy goat breeds, respectively. In the PCR-RFLP analysis for KpnΙ, EcoRII, NcoΙ, and BglΙ, the frequencies of the G allele of AGPAT6 were 0.955 and 0.936, 0.694 and 0.819, 0.206 and 0.254, 0.729 and 0.623 for SN and GZ dairy goat breeds, respectively. The 9263C>G mutation revealed a synonymous genetic code of Thr (threonine). Associations between the four mutations and milk traits were analyzed in two dairy goat breeds. At the 9263C>G locus, genotype GG and CG individuals showed significantly better milk performance than genotype CC individuals (P < 0.05). Therefore, the G allele is suggested to be a molecular marker for milk production in dairy goats.