In whole animal cloning ( eg. Dolly ) the nucleus is taken from a somatic cell. So isn't shortening of telomeres a problem ?
Yes, it is. Dolly died of cancer in early years. Length of the telomeres depends on the donor tissue: "In Dolly's study, the animal produced from fetal tissue appeared to have telomere lengths non-distinguishable from normal controls, while the other two, including Dolly, which originated from adult cells, were found to have shorter telomeres." (Xu & Yang, 2003) This statement doesn't mean that embryonic cells are the only cells able to maintain telomere length.
This also doesn't mean, that offspring of animals cloned from nuclei with shorter telomeres, inherits this shortedness: Miyashita et al, 2011
The Xu & Yang, 2003 review is pretty old, you can find newer articles on the topic.
After cloning, the recipient cell is converted into embryonic stem cell. When it is a stem cell, it can produce enzyme telomerase itself which a naturally occurring enzyme that maintains telomeres and prevents them from shortening during cell division in cells. So i think there are no problem on shortening of telomeres.