title: Ovarian activity and fertility during the first breeding season of Friesland ewe lambs.
abstract: The onset and duration of ovarian activity was assessed in 19 March-born, pure bred Friesland ewe lambs. Blood samples were collected for progesterone assay from 6 August-27 March when the lambs were 5-12 months of age. From 23 January a harnessed vasectomised ram was introduced. Colour marks on the rumps were taken as presumptive evidence of oestrus. During 1-25 March the vasectomised ram was replaced by a harnessed entire ram in order to assess fertility. The mean onset of the first normal luteal cycle, when progesterone levels exceeded 2 ng/ml-1 for two consecutive plasma samples, was on 7 October. The mean age and weight at this time were 29.9 +/- 2.73 weeks and 36.71 +/- 1.39 kg respectively. One ewe lamb became pregnant and lambed on 27 July. The mean date for cessation of ovarian activity (n = 18) was 1 March and the mean number of normal cycles monitored was 8.8 +/- 0.38. Few short luteal cycles were recorded (7/18 lambs) when only transient increases in progesterone levels were detected. The average duration of the breeding season was 142.6 +/- 4.95 days. It is concluded that pure bred Friesland ewe lambs, born during March, will reach puberty around 30 weeks of age and continue regular cyclic activity for approximately 5 months. Entire rams should be joined during January or February to ensure successful matings for lambing and milk production in late summer/early autumn.
authors.affiliation: Royal Veterinary College, University of London, Herts, UK.
authors.forename: S J
authors.initials: SJ
authors.lastname: Ward
authors.forename: H L
authors.initials: HL
authors.lastname: Williams
mesh_terms: D000818:Animals; D001947:Breeding; D004971:Estrus / Q000502:physiology; D004972:Estrus Detection / Q000662:veterinary; D004973:Estrus Synchronization; D005260:Female; D005298:Fertility / Q000502:physiology*; D008297:Male; D010053:Ovary / Q000502:physiology*; D011247:Pregnancy; D011374:Progesterone / Q000097:blood; D012621:Seasons; D012756:Sheep / Q000502:physiology*
chemical_list: D011374:Progesterone