While it is true that sheep and mice cloned through nuclear transfer have shown shortened telomeres compared to in vivo derived embryos this is by no means universal. Cows produced through NT actually have longer telomeres than in vivo derived embryos in some instances, it varies depending on the somatic tissue source.
See
Betts D, Bordignon V, Hill J, Winger Q, Westhusin M, Smith L, King W. Reprogramming of telomerase activity and rebuilding of telomere length in cloned cattle.
Proc Natl Acad Sci U S A. 2001 Jan 30;98(3):1077-82.
Miyashita N, Shiga K, Yonai M, Kaneyama K, Kobayashi S, Kojima T, Goto Y, Kishi M, Aso H, Suzuki T, Sakaguchi M, Nagai T.
Remarkable differences in telomere lengths among cloned cattle derived from different cell types.
Biol Reprod. 2002 Jun;66(6):1649-55.
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