Out-of-season breeding of Romney sheep using artificially induced long days

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.