Ovarian follicular wave emergence after treatment with progestogen and estradiol in cattle

An experiment was designed to evaluate the effects of treatment with progestogen and estradiol-17β (E-17β), in combination, at different stages of development of the dominant follicle, on follicular development and subsequent wave emergence. Cross-bred beef cows (n = 12) and heifers (n = 25) were randomly allocated to one of four treatment groups on Day 0 (ovulation). Treatment groups were untreated control animals and those that were given progestogen ear implants on Day 2, 5 or 8 and injected intramuscularly with 5 mg E-17β in sesame oil on Day 3, 6 or 9, respectively. Ovarian ultrasonography was performed daily from Day 0 until progestogen implant removal, 4 days after the emergence of the post-treatment follicular wave. The mean (± SEM) time (days) to cessation of growth and onset of regression of the dominant follicle of the first wave were earlier (P < 0.05) in the Day 3 treatment group than in the control group (3.6 ± 0.2 vs. 5.6 ± 0.4 and 7.0 ± 0.3 vs. 11.0 ± 0.6, respectively). Characteristics of the dominant follicle of the first wave in the Day 6 and Day 9 treatment groups were not different from those of the control group. However, treatment on Day 9 resulted in earlier (P < 0.05) cessation of growth and onset of regression of the dominant and largest subordinate follicle of the second wave than in the control group (9.6±0.2 vs. 13.4±0.7 and 11.5±1.3 vs. 17.1±0.9, respectively). Follicle wave dynamics was affected by early emergence of the second follicular wave in heifers treated on Day 3 (Day 7.3 ± 0.3) and delayed emergence in those treated on Day 6 (Day 10.7 ± 0.2) compared with the control group (Day 8.6 ± 0.3; P < 0.05). Furthermore, treatment on Day 9 resulted in earlier (P < 0.05) emergence of the third wave (Day 13.1 ± 0.3) than the control group (Day 15.3 ± 0.6). The interval from treatment to wave emergence was not different among treatment groups (4.3 ± 0.2 days after E-17β) and supported the hypothesis that treatment with progestogen plus E-17β results in consistent emergence of a new follicular wave, regardless of the stage of development of the dominant follicle at the time of treatment. It was concluded that treatment with progestogen and E-17β in combination can be used effectively to control and synchronize follicle wave development.Fil: Bo, G.A. University of Saskatchewan; CanadáFil: Adams, G.P. University of Saskatchewan; CanadáFil: Caccia, M. Universidad Católica de Córdoba. Facultad de Ciencias Agropecuarias; ArgentinaFil: Martínez, M. Universidad Nacional de Río Cuarto. Facultad de Agronomía y Veterinaria; ArgentinaFil: Pierson, R.A. University of Saskatchewan; CanadáFil: Mapletoft, R.J. University of Saskatchewan; Canad

Follicular wave dynamics after estradiol-17β treatment of heifers with or without a progestogen implant

Two experiments were designed to evaluate the effects of estradiol-17β (E-17β) on follicular wave dynamics and gonadotropin in cattle. The first experiment was designed to evaluate the effect of 5 mg E-17β administered on Day 1 (ovulation=Day 0) in heifers with or without a progestogen (SMB) ear implant. The dominant follicle in heifers treated with E-17β+SMB ceased to grow 1 d after E-17β treatment and subsequently regressed resulting in early emergence of the next follicular wave. Conversely, E-17β treatment of non-implanted heifers resulted in transient or incomplete suppression of the dominant follicle, and delayed emergence of the next follicular wave (P<0.05). A post-treatment surge in plasma LH concentration was detected in 5 of 6 heifers treated with E-17β alone versus 1 of 6 treated with E-17β+SMB (P<0.05). In all but 1 heifer, the LH surge was accompanied by a concurrent FSH surge (18 to 36 h after E-17β). The second experiment was designed to determine an effective dosage regimen of E-17β for suppression of follicular growth in SMB-implanted heifers and to test the hypothesis that estradiol-induced follicle suppression will result in a synchronous emergence of the subsequent follicular wave. On Day 0,48 heifers were implanted with SMB and allocated to 1 of 7 treatment groups: control heifers, and those that received 10 mg or 5 mg E-17β i.m. on Day 1 or Day 3; or 2.5 mg E-17β b.i.d. on Days 1 to 3 or Days 3 to 5. The growth of the dominant follicle of the first follicular wave was suppressed in all the E-17β treated groups. Emergence of the second follicular wave was later (P<0.05) in control heifers than heifers treated with a single injection of E-17β on Day 1, but was not different from heifers treated on Day 3. Furthermore, the day of wave emergence was less variable (P<0.05) in heifers treated with 5 mg of E-17β than in control heifers. It was concluded that E-17β and progestogen treatment may be used to suppress follicular growth and cause the synchronous emergence of a new follicular wave in cattle.Fil: Bo, G.A. University of Saskatchewan; CanadáFil: Adams, G.P. University of Saskatchewan; CanadáFil: Pierson, R.A. University of Saskatchewan; CanadáFil: Tribulo, Humberto Elías. Universidad Católica de Córdoba. Facultad de Ciencias Agropecuarias; ArgentinaFil: Caccia, M. Universidad Católica de Córdoba. Facultad de Ciencias Agropecuarias; ArgentinaFil: Mapletoft, R.J. University of Saskatchewan; Canad