Immunization against androstenedione and out of season breeding.

Abstract

Proc. Aust. Soc. Anim. Prod. Vol. 16 IMMUNIZATION AGAINST ANDROSTENEDIONE AND OUT-OF-SEASON BREEDING IN SHEEP T.J. ROBINSON and R.J. SCARAMUZZI SUMMARY Five experiments were conducted in anoestrous Border Leicester x ewes. Ovulation and oestrus were induced using progestagen sponges and Half the ewes in each experiment were immunized with Fecundin? were The ewes mated and oestrus, ovulation conception rate and lambing performance w rate, recorded. There was no effect of immunization ofor Pregnant Mare Serum Gonadotophin (PMSG) on the percent of ewes mated. Immunization delayed mating b 6 h and there was a dose related advancement of mating with increasing PMSG. Both increasing dose of PMSG and immunization increased litter si improved lambing performance while the former also increased the percenta ewes lambing.These increases are attributed to the action of immuniza PMSG on ovulation rate.These data highlight the importance of mul ovulations in ensuring optimum fertility and prolifacacy, (Keywords: Fecundin, sheep, PMSG, anoestrus) INTRODUCTION The commercial development of antibodies to androstenedione ( Glaxo Australia Pty Ltd) the enhancement of ovulation rate in the for (Scaramuzzi and Hoskinson 1984) raises the question of the potential such products used with the current techniques for out-of-season breeding anoestrous ewes (Robinson 1976). This paper reports the results of an invest gation of the use of Fecundin@ progestagen/PMSG in treated anoestrous ewes. MATERIALS AND METHODS Ewes were 2-4 yr old Border Leicester x Merino, about l/3 of which were lactating during Experiments 1, 2 and 3. Rams were Poll Dorsets and South Suffolks. Numbers of ewes joined are indicated in Table 2. Half the ewes were selected at random and immunized with 2 ml of Fecundin@. Four weeks was allowed to elapse between primary and booster immunization, with a further interval of 15 days (Expts 1 and 3), 23 days (Expts 4) or 49 days (Expts 2 and 5) to mating. The experiments were conducted on a property in the central west of NSW. Sponges impregnated with 30 mg of Cronolone@ were inserted intravaginally to batches of ewes for 12 days. At removal PMSG (dose range 250-1000 IU) was injected intramuscularly into groups of ewes selected at random. Three sources of PMSG were used in Experiment 3 namely Gravimed (Beresford Laboratories, Cheltenham, Vic.), Pregnecol (Heriot Agencies, Boronia, Vic.) and PMSG prepared by Dr. A. Gidley-Baird (Dept. Veterinary Physiology, University of Sydney] while the remaining experiments used only one or two of these. An intensive mating procedure was used, this involved removing sponges from batches of 25-35 ewes every 12 h over several days and joining to 8-l 0 harnessed rams. Ewes in oestrus were recorded 3-4 times daily and mated ewes were drafted off every 12 h. Pregnancy was diagnosed from plasma progesterone levels (Early Pregnancy Diagnosis: EPD), and endoscopy, 19-20 days post mating. Progesterone concentrations were determined by radioimmunoassay (Pearce and Robinson 1985). Ewes diagnosed pregnant were distributed between several small paddocks. A continuous watch was kept for ewes lambing. Ewes and lambs were moved to a larger paddock Department of Animal Husbandry, University of Sydney, Sydney 2006, N.S.W. and CSIRO, Division of Animal Production, P.O. Box 239, Blacktown 2148, N.S.W. 323 Proc. Aust. Soc. Anim. Prod. Vol. 16 48-72 h after lambing. Data were analysed by the Chi variance as appropriate. RESULTS Oestrus was recorded in 1244 ewes following 1309 treatments. There was no significant effect of immunization or dose of PMSG on the percentage of ewes mated but there were significant effects on the time of mating. The onset of oestrus was delayed by a mean of 6 h in immunized ewes which received a booster immunization 3 weeks or less before mating (Fig. I). There was a consistent linear effect of dose of PMSG advancing the time of mating. 2 test or by an analysis of The distribution of onset of oestrus for immunized and non-immunized Fig. I. ewes expressed as 2hours from the removal of progestagen sponges. Data are from Experiment I. (Chi = 20.1; P < 0.01). Endoscopy was performed on II34 ewes. The immunized ewes shed more ova than non-immunized (Table 2). There was a significant linear effect of dose of PMSG and an interaction between immunization and dose of PMSG (P < 0.001) on ovulation rate. Immunized ewes were more responsive to high doses of PMSG than were non-immunized (Fig.2) and there was a significant interaction between dose and source of PMSG (Fig. 3). Of the 1062 ewes with complete data, 660 (62%) were diagnosed pregnant by EPD and 616 (58%) by endoscopy but a total of only 569 ewes lambed (54%), there were effects of dose of PMSG (Table I) and of the time between booster immunization and mating (Table 2). Table 1 Effect of PMSG on lambing performance (pooled data from Experiments l-5) Group sizes vary because all doses of PMSG were not used in all experiments, see Table 2 324 Proc. Aust. Soc. Anim. Prod. Vol. 16 Associated with these effects was Ewes which lambed had a mean ovulations. did not had a 'mean of I.8 (P < 0.001). percentage of ewes lambing with an increase increase above three (Table 3). Table 2 a relationship with the number of of 2.2 ovulations whereas those that There was a linear increase in the from one to three ovulations with no Lambing in Fecundin@ treated anoestrous ewes bred out-of-season DISCUSSION The technologies of synchronized out-of-season breeding and immunization 325