Influence of lambing date on subsequent ovarian cyclicity and ovulation rate in ewes

Abstract

Link to this article: http://journals.cambridge.org/abstract_S1357729800016325How to cite this article: L. M. Mitchell, M. E. King, R. P. Aitken and J. M. Wallace (1997). Inuence of lambing date on subsequent ovarian cyclicity and ovulation rate in ewes. AbstractThe effect of lambing date on the subsequent onset and duration of ovarian cyclicity in Mule (Bluefaced Leicester X Scottish Blackface) ewes was investigated. Nineteen ewes which had lambed in January (16 January 1993 (s.e (14 May 1993 (s.e. 2 days)) and been weaned on 23 August were maintained at pasture as two isolated groups. A raddled vasectomized ram was continually present with each group from 14 July 1993 to 26 May 1994 and marked (oestrous) ewes were recorded twice weekly. Ovarian activity was assessed by measuring peripheral progesterone concentrations in blood samples collected twice weekly and by laparoscopic viewing of the ovaries of all ewes during October, January and March. The onset and duration of ovarian activity were significantly affected by the previous lambing date. For January and May lambing ewes, mean dates of onset were 5 September 1993 (s.e. 2 days) v. 25 September 1993 (s.e. 4 days) (P < 0-001) and of cessation were 5 April 1994 (s.e. 5 days) v. 10 April 1994 (s.e. 3 days). Mean durations of ovarian activity were 212 (s.e. 6) and 195 (s.e. 5) days (P < 0-05) during which 12-4 (s.e. 0-29) and 11-5 (s.e. 0-38) ovarian cycles respectively were recorded. Ovulation rate was not affected by previous lambing date but was significantly lower in March compared with October (January lambing ewes 1-7 (s.e. 0-1) v. 2-3 (s.e. 0-1) (P < 0-001); May lambing ewes 1-6 (s.e. 0-1) v. 2-1 (s.e. 0-1) (P < 0-01)). Results demonstrate that (i) Mule ewes have a potential breeding season of up to 8 months duration; (ii) the onset and duration of ovarian activity can be influenced by previous lambing date; and (Hi) a seasonal decline in ovulation rate may, in practical terms, result in a lower lambing percentage for animals bred towards the end of their natural breeding period. . 3 days)) and been weaned in February-March and 22 comparable ewes which had lambed in May

Resumption of oestrous and ovarian cyclicity during the post-partum period in autumn-lambing ewes is not influenced by age or dietary protein content

“…Cessation of ovarian cyclicity in multiparous ewes occurred at a similar time to that reported for naturally cyclic Mule ewes at the same latitude (Mitchell et al, 1997) suggesting that pregnancy and parturition had not interfered with the interpretation of photoperiodic signals relating to the current breeding season, and that the end of the breeding season is largely independent of its beginning. For primiparous ewes, however, cessation of ovarian cyclicity occurred about 1 month earlier, a possible reflexion of their young age and/or low live weight.…”

“…The breeding season of Mule ewes at 57°N extends from September to April (Mitchell et al, 1997). Ewes in the present study lambed during late October, towards the beginning of their natural breeding season and at a time when the majority of ewes in Britain are normally being mated.…”

Effect of Nutrition, Lactation and Gonadotropin Stimulation on Ram-Induced LH Surge and Subsequent Fertility in Early Post-Partum Ewes during Seasonal Anestrous

“…An early lambing date is associated with an early onset of the subsequent breeding season. In a study to determine the effect of lambing date on the subsequent breeding season, Mitchell et al (1997) reported that the onset and duration of ovarian activity but not its cessation were significantly affected by the previous lambing date,. According to this author, the mean dates of onset of ovarian activity for January and May lambing ewes were 5 September and 25 September while those of cessation were 5 April and 10 April, with the number of the ovarian cycles been 12.4 (s.e.…”

Μικροκλιματικές Συνθήκες Και Φυσιολογία Αναπαραγωγής Προβάτων

“…Η έναρξη και η διάρκεια της εποχής αναπαραγωγής επηρεάζεται από προηγούμενη ημερομηνία τοκετού. Μια πρώιμη ημερομηνία τοκετού σχετίζεται με πρώιμη έναρξη της μεταγενέστερης εποχής αναπαραγωγής (Haresign, 1992και Mitchell et al, 1997, αλλά όχι με την παύση της (Mitchell et al, 1997).…”