Epigenetics and the periconception environment in ruminants

Particularly in ruminant species, conclusive evidence has been accrued that environmental influences to which gametes or embryos are exposed to before, during and after conception (i.e. the periconception period) can in-duce epigenetic changes in the genome. Such epigenetic changes may adversely affect the future health, development, productivity and fertility of those offspring, in some cases even leading to the so-called “Large Offspring Syndrome”. Epigenetics are adjustments in gene expression which are established "on top" (i.e. “epi” in Greek) of the genes. Earlier data obtained in ruminants have demonstrated changes in DNA-methylation of imprinted genes in the placenta and in the organs of calves or lambs born after cloning or in vitro culture, but more recently dietary changes have also been implicated in changes in the phenotype of resulting offspring, causing insulin resistance and hypertension. In this review paper we will first explain how epigenetics can influ-ence gene expression and why gametes and embryos are especially vulnerable to epigenetic changes caused by environmental influences at periconception, next we will describe how placental function is affected by epigenet-ic changes in “Large Offspring Syndrome” and finally we will discuss how maternal nutrition can affect in an epigenetic way ruminant embryonic and fetal development.