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Early onset of reproductive senescence in domestic sheep Ovis aries


  • Atle Mysterud,

  • Geir Steinheim,

  • Nigel G. Yoccoz,

  • Øystein Holand,

  • Nils Chr. Stenseth

A. Mysterud, N. C. Stenseth, Dept of Biol., Div. of Zool., Univ. of Oslo, P.O. Box 1050 Blindern, N-0316 Oslo, Norway ( – G. Steinheim, Ø. Holand, Dept of Animal Sci., Agric. Univ. of Norway, P.O. Box 5025, N-1432 Ås, Norway. – N. G. Yoccoz, Dept of Arctic Ecol., Norwegian Inst. for Nature Res. (NINA), Polar Environm. Centre, N-9296 Tromsø, Norway.


A central theme in life history theory is to determine how reproduction varies with age in iteroparous organisms. Evidence of ageing and senescence, defined as the progressive loss of function accompanied by decreased performance with age, remains poorly documented for large herbivores, in particular as it relates to reproduction. Analyses of body weight of 87 532 domestic sheep lambs demonstrates that onset of reproductive senescence in ewes occurs already at 5 and 6 years of age when measured, respectively, as lamb weight and litter size produced. This provides convincing evidence of early onset of reproductive senescence in this highly domesticated sheep breed. As this is earlier than indicated for other Ovis species as well as for the Soay sheep, an ancient and lightly domesticated sheep, we hypothesize that there may be a cost of selection for large litter size in mammalian herbivores.