Effect of nutrition and dose level of PMS on oestrous response and ovulation rate in progestagen-treated non-cyclic Suffolk × Galway ewe lambs

Abstract

SUMMARYMarch-born non-cyclic Suffolk × Galway ewe lambs were treated with progestagen pessaries while being either fed fresh-cut grass ad libitum, or restricted to 50% of appetite and at pessary removal half of the animals on each nutritional treatment received either 600 i.u. or 300 i.u. PMS. Averaged over both levels of PMS, 97·5% of the lambs showed oestrus when fed ad libitum but only 67·5% of those on restricted feeding responded. When feed intake was not restricted there were no differences due to PMS level but when feed intake was restricted the higher dose level of PMS resulted in a greater percentage showing oestrus and a significantly higher ovulation rate. The dose level of PMS had no effect on the time of oestrous onset but restricted feeding resulted in delayed onset and poor synchronization of oestrus. Duration of oestrus was greatest for lambs fed ad libitum given 600 i.u. PMS and least for those on restricted feeding given 300 i.u. PMS but the difference was not significant. A minority of lambs showed broken oestrous periods.