No abstract

Two trials were undertaken to investigate the effects of treating seasonally anoestrous ewes with melatonin implants on date of first oestrus and other aspects of reproductive performance.Trial 1 involved a total of 368 Mule ewes and 79 Scottish Blackface ewes on five farms, approximately half of which were treated with a single subcutaneous implant of melatonin (Regulin®), containing 18 mg melatonin, between 23 July and 6 August 1986 and the remainder acted as untreated controls. Treatment had no significant effect on the date of first oestrus or conception rate in Mule ewes, although it increased the number of Scottish Blackface ewes mating (92% v. 73%) and the number of mated ewes conceiving (69% v. 54%) in a 5-week mating period, resulting in significantly more treated ewes lambing (63% v. 37%; P < 0·01). Litter size was higher in 4/5 flocks, although this only reached statistical significance in one Mule flock and the Scottish Blackface flock.A total of 2116 ewes from 17 commercial flocks were used in trial 2, approximately half of which were Suffolk/Suffolk-cross ewes and the remainder Mule/Mule-cross ewes. Implantation with melatonin occurred between 22 June and 24 July 1987. Flocks with over 100 ewes were divided into three equal-sized groups and treated with either 18 mg melatonin (one implant of Regulin, 36 mg melatonin (two implants of Regulin given at the same time) or acted as untreated controls. Flocks with less than 100 ewes contained only the 18 mg melatonin and untreated control groups. Treatment with melatonin significantly advanced the date of first oestrus in most flocks of both breeds (P < 0·05) but the magnitude of this effect was variable. Significant (P < 0·05 at least) increases in ‘potential’ (from scanning) mean litter size (+0·13 to +0·18) and actual mean litter size (+0·11 to +0·14) resulting from treatment with melatonin were apparent in ewes of both breeds when the data were pooled across all flocks, but only in 4/17 of the individual flocks.These results indicate that treatment with melatonin implants may be a simple and effective way of advancing the breeding season and enhancing litter size of early lambing flocks under commercial farming conditions in the United Kingdom, but treatment must be given >60 days before the start of the natural breeding season for benefits in date of first oestrus to be manifest.

No abstract

A total of 18 fallow does, including pubertal, non-pregnant and pregnant adult does (6 per class), each received a single subcutaneous implant containing 18 mg melatonin on 4 occasions at 29-30-day intervals from 10 November 1986 (approximately 120-day treatment period). A further 18 contemporary does served as herd-mate controls. Two adult fallow bucks were treated the same and were run with the does until 16 March. Thereafter, 1 of 4 control bucks was run with the does until 1 June. Of the 6 pregnant does receiving implants within the last 40 days of their gestation, 4 failed to lactate after parturition in December 1986. The remaining 2 does successfully reared their fawns, as did the 6 contemporary controls. Mean (+/- s.e.m.) dates of first oestrus in 1987 were 27.6 February (+/- 3.0 days) and 22.9 April (+/- 0.8 days) for all treated and all control does respectively (P less than 0.001). Pubertal does were generally later to exhibit first oestrus than were older does within their respective treatment groups. Return oestrus occurred only in 2 pubertal does (1 treated and 1 control) with remaining does conceiving to their first oestrus, as verified by plasma progesterone profiles. However, 5 (28%) of the treated does and 3 (17%) of the control does failed to maintain pregnancy and fawn in 1987. The mean (+/- s.e.m.) 1987 fawning date of the remaining does was 22.4 October (+/- 2.7 days) for the treated group (N = 13) and 13.1 December (+/- 0.8 days) for the control group (N = 15; P less than 0.001). Mean (+/- s.e.m.) gestation length of treated does (238.9 +/- 0.6 days) was significantly longer than that of control does (234.5 +/- 0.4 days; P less than 0.001). Of 13 fawns born to treated does, 4 (31%) died within 24 h of birth (mainly due to hypothermia) whereas all 15 fawns born to control does survived to weaning. Melatonin-treated bucks exhibited a marked advancement of neck muscle hypertrophy during the treatment period and displayed normal rutting activity (e.g. vocalization) in response to early oestrus in the treated does.

Melatonin pretreatment to improve the reproductive performance of first-cross Poll Dorset x Merino ewes joined in early summer was investigated in 2 experiments conducted in consecutive years. In experiment 1, melatonin pellets were administered subcutaneously to 1 of 3 groups of ewes; 14 days later they were joined with testosterone-primed wethers ('teasers'), followed after 15 days by entire rams (melatonin-teased group). The other groups were untreated and teased only. Experiment 2 consisted only of teased and melatonin-teased groups, with the ewes from experiment 1 being reallocated, as well as maiden ewes being joined for the first time. In this experiment melatonin pellets were inserted 38 days before the start of joining. Treatment with melatonin resulted in increased reproductive performances. The responses were characterised by an earlier (P<0.05) conception pattern in both experiments and higher (P<0.001) lambing percentages than controls in experiment 1. Up to 22% more lambs were born to melatonin-teased ewes than to teased ewes, and stimulatory effects were similar for ewes of different ages. In experiment 2, ewes that had received melatonin in both experiments tended (P>0.05) to have higher lambing percentages than teased ewes (up to 17% more lambs born), while ewes that had received melatonin in only experiment 1 tended (P>0.05) to have lower lambing percentages than ewes that were not treated with melatonin in either experiment (4-11%). The higher lambing performances of the melatonin-treated ewes were independent of ewe liveweights. Reproductive activity was also stimulated by the use of teasers alone in experiment 1. Conception patterns were advanced (P<0.01) and there was a trend for more (P>0.05) lambs to be born in the teased group than in the control group. The results show that both teasers and melatonin treatment will advance the conception patterns of first-cross Poll Dorset x Merino ewes joined in early summer, but the melatonin treatment also stimulated fecundity.