Out-of-season breeding of Romney sheep using artificially induced long days
G. deNicolo A , S. T. Morris A B , P. R. Kenyon A , P. C. H. Morel A and T. J. Parkinson AA College of Sciences, Massey University, Private Bag 11222, Palmerston North, New Zealand.
B Corresponding author. Email: S.T.Morris@massey.ac.nz
Australian Journal of Experimental Agriculture 48(7) 961-965 https://doi.org/10.1071/EA07406
Submitted: 10 December 2007 Accepted: 8 April 2008 Published: 20 June 2008
Abstract
This experiment investigated the effects of subjecting Romney ewes to artificially induced long days (24 L : 0 D) in spring for 30 days, then abruptly applying 8 hours of darkness (16 L : 8 D) to induce the onset of reproductive activity. The treatment groups were: light + progesterone; light + progesterone + eCG; and progesterone + eCG (ambient photoperiod; control). Blood samples were collected over a 24-h period for analysis of serum melatonin concentrations. Ewes’ ovaries were examined laparoscopically 9 days after progesterone removal. Duration of secretion and maximal concentrations of melatonin were lower in ewes treated with light + progesterone (±eCG) compared with the control ewes. Fewer light + progesterone treated ewes displayed oestrus (66%) and were subsequently identified as being pregnant (28%) compared with ewes treated with light + progesterone + eCG (98% and 53%) and control ewes (97% and 65%, respectively). Conception rates were lower in light + progesterone treated ewes (43%) compared with light + progesterone + eCG (55%) and control ewes (67%). Results obtained indicate that artificially induced long days did not improve the results of out-of-season breeding program beyond that achieved with the use of eCG.
Acknowledgements
The authors wish to thank Massey University, Meat and Wool New Zealand, AgMARDT, the C. Alma Baker Trust and Riverside Farm Research Fund for financial support.
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