title: Response of anoestrous ewes pre-treated with a single dose of oestradiol-17 beta, or progesterone and oestradiol-17 beta, to the introduction of rams and ewes in oestrus.
abstract: OBJECTIVE
  To determine if the frequency distribution of time to oestrus observed after the introduction of rams, and additional ewes in oestrus, is affected by the administration of oestradiol- 17beta. To determine if the fertility following mating at the first induced oestrus in progesterone-primed ewes may be increased with administration of oestradiol-17beta.
  
  
  METHODS
  In Experiment 1, ewes received 40 mug oestradiol- 17beta 3 (E3; n=61) or 5 (E5; n=56) days before the introduction of rams; 61 ewes were controls (C1). In Experiment 2, a controlled internal drug-releasing (CIDR) device was inserted in 95 ewes on Day -5 (Day 0 = introduction of rams). In addition, 47 ewes received oestradiol-17beta on Day 0 (CE), and the remaining 48 were controls (C2). In both experiments, additional ewes, brought into oestrus between Days 0 and 2 by hormonal treatments, were introduced with the rams. Onset of oestrus was estimated by visual observation of ewes marked by rams. Pregnancy status of ewes in Experiment 2 was determined using ultrasound, 30 days after oestrus.
  
  
  RESULTS
  The total number of ewes detected in oestrus in Experiment 1 was similar between the three groups. The frequency distribution of ewes in oestrus in the E5 group differed from that of ewes in both C1 (p=0.05) and E3 (p<0.001). A similar number of ewes were detected in oestrus between Days 16-20, but the proportion of ewes in oestrus between Days 21-26 was greater for ewes in C1 than E5 or E3. Mean interval to the onset of oestrus was shorter in C1 than E3 which was shorter than E5 ewes (p<0.001). In Experiment 2, the total number of ewes in oestrus were similar between groups. Ewes in oestrus between Days 1-4 (65% and 64% for C2 and CE, respectively) and conception rates over the same period (81% and 80% for C2 and CE, respectively) were also similar between groups.
  
  
  CONCLUSIONS
  Administration of oestradiol-17beta to anoestrous ewes altered the pattern of onset of oestrus, but it did not affect submission or conception rates, regardless of whether or not a short period of progesterone priming with a new CIDR device was included prior to the introduction of rams.
authors.affiliation: Departamento de Fisiologia, Facultad de Veterinaria, Lasplaces 1550, Montevideo 11600, Uruguay. piub@internet.com.uy
authors.forename: R
authors.initials: R
authors.lastname: Ungerfeld
mesh_terms: D000780:Anestrus / Q000187:drug effects* / Q000502:physiology; D000818:Animals; D003692:Delayed-Action Preparations; D004359:Drug Therapy, Combination; D004958:Estradiol / Q000494:pharmacology*; D004971:Estrus / Q000502:physiology; D004973:Estrus Synchronization / Q000379:methods*; D005260:Female; D008297:Male; D011247:Pregnancy; D018873:Pregnancy Rate; D011374:Progesterone / Q000494:pharmacology*; D012756:Sheep / Q000502:physiology*; D013997:Time Factors
chemical_list: D003692:Delayed-Action Preparations; D011374:Progesterone; D004958:Estradiol