Abstract

Shortened daylight hours have been shown to advance the onset of puberty in ewe lambs. In this experiment the pineal hormone melatonin was administered to mimic short days with the aim of advancing the onset of first oestrus in September-born ewe lambs. Treatments were; no melatonin in 10 ml saline drenched daily (control), 2 mg melatonin in 10 ml saline drenched daily and 435 mg of melatonin implanted subcutaneously, each on 2 start dates - February 17 and March 17. Fertile rams were introduced on March 10 and April 7 respectively. All ewes were killed on July 28 and foetal crown-rump lengths measured to estimate the date of conception. The mean dates of first tup in the early treatments were not statistically different (May 25, May 9 and May 13) but there was a difference between the control and implant in the estimated dates of conception (June 1 and May 17, P<0.05). In the late treatment the mean dates of first tup were June 2, May 16 and May 10 respectively (P<0.01). However this difference did not lead to a treatment difference in the estimated date of conception because the percentages conceiving to the first tup were 38, 80 and 21 respectively.

JE, Wolff, and PM Dobbie

Proceedings of the New Zealand Society of Animal Production, Volume 44, , 15-18, 1984