Abstract
In goats, oocytes derived from small follicles (<3 mm in diameter) have low developmental competence after IVF (Crozet et al. 1995). However, their performance is compatible to oocytes derived from large follicles (>3 mm) when intracytoplasmic sperm injection is used (Jimenez-Macedo et al. 2006). No data are currently available on the ability of oocytes derived from small follicles to support development to term after somatic cell nuclear transfer (SCNT) in goats. Here we evaluated the effect of follicular size of cytoplast donor on cloning efficiency in goats. Seven rounds of oocyte maturation and nuclear transfer were carried out on separate days. During each replicate, oocytes were collected separately from large follicles (LF, n = 378) and small follicles (SF, n = 981) from the same group of ovaries. First, only large follicles (>3 mm) were dissected and rinsed, and then an ovary was moved to another dish to dissect the rest of the follicles. The groups of oocytes derived from LF and SF were treated separately throughout the process including maturation, SCNT, embryo culture and embryo transfers. Neonatal skin fibroblasts derived from transgenic goats were used as nuclear donors in this study. Nine embryo transfers were conducted for LF group and 12 for the SF group. Oocytes from SF had significantly lower rate of nuclear maturation compared to oocytes derived from LF (33.5% ± 3.7 v. 54.3% ± 5.4; P < 0.01). There was no difference in fusion rate between these 2 groups (66 v. 69%; 215/325 v. 138/199; SF v. LF). Additionally, we found no statistical difference in Day 30 pregnancy rate (42% v. 33%; SF v. LF group) or birth rate (2 healthy kids produced from each of the groups, 16.7% v. 22.2%; SF v. LF). The results demonstrate that oocytes from small follicles have similar competence to support development to term as oocytes derived from large follicles following SCNT in goats. This work was supported by the Utah Multidisciplinary Arrhythmia Consortium and Utah Agricultural Experiment Station project #1100.
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