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Introduction
The yak, known in China as the 'almighty livestock', is well adapted to low temperatures, low oxygen levels, and the low pressure environment found at high altitudes (e.g. at 3500 m above sea level). These animals are able to make full use of alpine grasslands, which other livestock find difficult to utilize. However, this environment provides primitive grazing with vegetation that grows slowly, resulting in low animal production yields, in addition the deteriorating environment makes yak populations vulnerable to environmental pressures. How to accelerate the genetic breeding of yaks, thereby not making them vulnerable to extinction, and to increase the value of their production is an important problem with a worldwide focus.
Much progress has been made towards applying assisted breeding to aid yak conservation, such as hybridization between cattle and yak species. In particular, interspecies somatic cell nuclear transfer (iSCNT) is a novel method that has been shown to protect species that are not subject to genetic variation and are in danger of extinction. The sand cat (Gómez et al., 2008), gaur (Vogel 2001), mouflon (Loi et al., 2001) and grey wolf (Oh et al., 2008) have all been cloned successfully using iSCNT, although the efficiency is still extremely low. The efficiency of iSCNT depends on a variety of factors, such as the status of donor cells, the quality of recipient oocytes and the environment of the in vitro operation. However, the low success rate found with this technique has been widely attributed to incomplete reprogramming of epigenetic modifications or to epigenetic errors (Couldrey & Lee, 2010).
It has been reported that histone acetylase levels in cloned SCNT embryos of intraspecies bovine, mouse, pig, sheep and rabbit that had been treated with histone deacetylases inhibitors (HDACi), such as TSA and VPA, were improved significantly compared with untreated animals and were similar to their in vitro fertilization (IVF) or in vivo counterparts (Lager et al., 2008). Furthermore these embryos showed improved development to the blastocyst stage (Beebe et al., 2009; Shao et al., 2009; Costa-Borges et al., 2010; Zhao et al., 2010), plus there was an increase in the number of live offspring after transfer to foster mothers (Maalouf et...