Náttúrufræðingurinn

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Náttúrufræðingurinn - 1980, Qupperneq 34

Náttúrufræðingurinn - 1980, Qupperneq 34
Pálsson, Iialldór. 1962. Augmentation of fertility of Iceland ewes with pregnant- mare serum in successive years. J. Re- prod. Fert. 3, 55—63. Yeates, N. T. M. 1949. The breedingseason of the sheep with particular reference to its modification by artificial means using light. J. agric. Sci., Camb. 39, 1—43. SUMMARY Puberty and breeding activity of Icelandic sheep by Dr. Ólafur R. Dýrmundsson The Agricultural Society of Iceland Bœndahöllin, P. 0. Box 7080, Reykjavík The paper reports on studies which have been in progress since 1972 concerning various aspects of sexual development and breeding activity in both females and males of the Iceland breed of sheep. Most Icelandic lambs are born in May and they are found to be early maturing. Thus ewe lambs normally attain puberty in their first year of life, on average at 7 months of age, as indicated by the onset of oestrous activity. Exceptional cases of late summer or autumn born ewe lambs attaining puberty and conceiving at 4 months of age have been reported. Most ram lambs appear to have attained physiological puberty by 4 months of age, judged by their anatomical develop- ment. In either sex marked individual vari- ation is evident both in puberal age and body weight, largely due to differences in growth rate. Ewe lambs generally show oestrus slightly later in the season than mature ewes and they have a shorter breeding season (1 — 4 months) than ewes (4—6 months). Further- more, the duration of oestrus is shorter and the cyclic activity is less regular in the young females. With seasonal breeding of Icelandic ewes ranging from November to May the mid-breeding season occurs some 4 — 7 weeks after the shortest day, i. e. consider- ably later than what is generally found in breeds with seasonal breeding patterns. It is suggested that the distribution of sexual activity over the season may be an inherent characteristic evolved by natural selection in the breed and its North European ancestors in the past. Although Icelandic ewes have a pro- nounced breeding season, limited sporadic out-of-season oestrous activity (May — November) may take place resulting in con- ception. However, such cases appear to be relatively rare, particularly during mid summer, and are of little practical import- ance. A comparatively high ratio of out-of- season lambings has been recorded in coloured (nonwhite) ewes. Icelandic rams appear to display normal mating behaviour when introduced to ewes in oestrus outside the normal breeding season. They do not seem to have a distinct seasonal breeding pattern corresponding to that experienced by the ewes. 288
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