Effect of treatment with progesterone and oestradiol when starting treatment with an intravaginal progesterone releasing insert on ovarian follicular development and hormonal concentrations in Holstein cows

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Abstract

Ovarian follicular development and concentrations of gonadotrophin and steroid hormones were studied in non-lactating Holstein cows following administration of progesterone (P4) or oestradiol benzoate (ODB) at the start of treatment with an intravaginal progesterone releasing insert (IVP4) in a 2 by 2 factorial experiment. Cows were treated at random stages of the oestrous cycle with an IVP4 device (Day 0) and either no other treatment (n=8), 200 mg of P4 IM (n=9), 2.0 mg of ODB IM (n=8) or both P4 and ODB (n=9). Seven days later devices were removed and PGF was administered. Twenty-four hours later 1.0 mg of ODB was administered IM. Oestrus was detected in 97.1% and ovulation in 64.7% (effect of treatment, P=0.41) of cows within 96 h of removing inserts. In the cows that ovulated, day of emergence of the ovulatory follicle was delayed (P<0.01) and more precise (P<0.05) in cows treated with ODB compared to the cows treated with P4. Interval from wave emergence to ovulation and the diameter of the ovulatory follicle was less (P<0.05) in cows treated with ODB compared to cows treated with P4. Combined treatment with P4 and ODB at the time of starting treatment with an IVP4 device did not significantly change the pattern of ovarian follicular development compared to treatment with ODB alone. Concentrations of LH and FSH in plasma were less in cows treated with ODB between Days 0 and 4 (P<0.05) while treatment with P4 increased concentrations of FSH in plasma between Days 0 and 4 (P<0.05). When anovulatory cows were compared to ovulatory cows, diameters of follicles (P<0.001) and growth rate of follicles (P<0.01) were less in anovulatory cows between Days 7 and 9, while concentrations of FSH in plasma were greater (P<0.01), concentrations of LH similar (P>0.90) and concentrations of oestradiol were less (P=0.01) in the anovulatory cows between Days 4 and 10.

Our findings support a hypothesis that ovarian follicular development following administration of P4 or ODB at the start of treatment with an IVP4 device differs. Anovulatory oestrus may have been associated with reduced maturity and/or later emergence of ovarian follicles.

Introduction

Fertility and synchrony of oestrus can be affected in cattle by the stage of development of preovulatory ovarian follicles when pro-oestrus is induced. Cows with preovulatory follicles that are still in a growing phase of development at the onset of pro-oestrus take longer to enter oestrus than cows that have follicles that have plateaued in their growth (Austin et al., 1999). Fertility is reduced at a synchronised oestrus when dominant follicles persist on the ovary for extended periods of time (Savio et al., 1993, Stock and Fortune, 1993, Mihm et al., 1994; Cooperative Regional Research Project, NE-161, 1996; Austin et al., 1999). This is thought to be related to detrimental effects on the oocyte with a subsequent increase in embryonic loss rates (Ahmad et al., 1995).

Methods to induce precise synchrony of oestrus with normal fertility have concentrated on producing a homogenous population of follicles with a short duration of dominance (<10 days) at the onset of pro-oestrus (Roche et al., 1999). Both treatment with oestradiol (E2) and progesterone (P4) have been used for this purpose. Treatment with E2 has resulted in the consistent emergence of a new follicular wave 3–5 days (mean of 4.3 days) after treatment (Bo et al., 1995) regardless of the stage of development of the dominant follicle at the time of treatment. Treatment with P4 has resulted in emergence of a new follicular wave 2–5 days after treatment (Cavalieri et al., 1997, Cavalieri et al., 1998, McDowell et al., 1998, Cavalieri et al., 2001). In one study treatment with P4 was less successful in inducing new wave emergence in cows in which follicles were in a growing phase of development compared to cows in which follicles had reached a plateau phase of growth (Cavalieri et al., 1998). Studies that have examined the effects of P4 and E2 on follicular development in cattle have been undertaken in different types of cattle with ovarian follicles at different stages of follicular development. There are no studies that have examined the effects of both P4 and E2 on ovarian follicular development when administered to Holstein cows at random stages of the oestrous cycle.

Although administration of E2 and P4 has improved the synchrony of emergence of a new follicular wave compared to untreated control cows, intervals to new wave emergence and oestrus are still variable (Roche et al., 1999). One method that has been used to reduce the variation in intervals to oestrus following treatment is to synchronise a preovulatory rise in concentration of E2 during pro-oestrus (Roche et al., 1999, Lane et al., 2001). The principle of controlling follicle emergence and synchronising pro-oestrus has been developed into an oestrous synchronisation treatment that involves treatment with an intravaginal progesterone releasing insert (IVP4) for 7 days, PGF at device removal and administration of oestradiol benzoate (ODB) at the time of device insertion and 24–48 h after device removal. An oestrous detection rate of 95.7% and a pregnancy rate of 57.8% were recorded using such a system in dairy cows in New Zealand (Day et al., 2000). That study found that pregnancy rates of cows that were in oestrus 24–48 h after removal of inserts tended to be lower than cows that were detected in oestrus later in the synchrony period. This reduction in pregnancy rate was speculated to be due to an inability of the ODB administered at the start of the treatment with an IVP4 to cause atresia of dominant ovarian follicles and emergence of a new follicular wave during the treatment period. Doubt was therefore raised in this study as to whether or not exogenous treatment with ODB was providing optimal control of follicular wave emergence during the synchrony treatment.

The objectives of this study were to determine if the pattern of ovarian follicular development and changes in concentrations of P4, E2, LH and FSH in plasma differed following the administration of P4 and/or E2 at the time of commencing a treatment to synchronise oestrus in dairy cows that also involved induction of oestrus with an injection of ODB.

Section snippets

Oestrous synchronisation protocol

Qestrus was synchronised in 34 non-lactating, non-pregnant Holstein cows using four different treatment protocols in a 2 by 2 factorial arrangement. Each cow was treated with an intravaginal hormone release device (CIDR cattle device, Genetics Australia, Bacchus Marsh, Vic.) for 7 days, 0.5 mg of cloprostenol IM (CIDR-PG, Genetics Australia, Bacchus Marsh, Vic.) at the time of removal of inserts and 1.0 mg of ODB IM (Cidirol, Genetics Australia, Bacchus Marsh, Vic.) 24 h after removal of inserts.

Ultrasonography

Every cow with the exception of one cow treated with both P4 and ODB was detected in oestrus within 96 h of removing inserts (97.1%; (33/34)). Ovulation was detected in this cow 2.5 days after removing inserts. The proportion of cows within each group that ovulated within 96 h of removing inserts was 50% (4/8), 77.8% (7/9), 50% (4/8) and 77.8% (7/9) for the control, P4, ODB, and P4+ODB groups, respectively (P=0.41).

A corpus luteum was observed in 94.1% (32/34) of the cows using ultrasonography

Discussion

The results of this study provide evidence that the pattern of ovarian follicular development and concentrations of gonadotrophins differ following treatment with P4 or ODB at the time of starting treatment with an IVP4 device. While treatment with P4 or ODB improved the synchrony of follicular wave emergence, the synchrony of wave emergence was greater following administration of ODB compared to P4. An unexpected finding in this study was the occurrence of anovulatory oestrus in 35% of the

Conclusion

Injecting ODB at the time of starting treatment with an IVP4 device resulted in greater suppression of mean concentrations of LH, a more synchronous emergence of a new follicular wave, a shorter interval from emergence to ovulation and reduced diameter of the ovulatory follicle compared with cows treated with P4 at the start of treatment. There was no evidence that combining treatment of ODB with P4 had any significant effect on follicular dynamics compared to treatment with ODB alone when

Acknowledgements

We thank T. Squires and T. Moyes for technical assistance, J. Borman and F. Davidson for performing assays and A. Rabiee for providing the progesterone injection. We thank D. Robertson for supervision of and description of the FSH assay. Financial support was provided under the Strategic Partnerships with Industry Research and Training Scheme, of the Australian Research Council and the Department of Education, Training and Youth Affairs. We thank the industry partners Genetics Australia and

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