The effect of intra-uterine devices on the reproductive physiology and behaviour of pony mares

Spherical (35 mm diameter) glass intra-uterine devices (IUDs) are commonly understood to modify sexual behaviour in performance mares. The effect of IUDs on the endocrinology (luteinising hormone, oestradiol, progesterone, testosterone), ovarian and uterine function, sexual and social behaviours associated with the ovarian cycle were evaluated during the natural breeding season in nine, nuliparous pony mares (4.6 ± 0.5 years old, 230 ± 12 kg bodyweight). Age and weight-matched groups were allocated to sham-treatment (n = 5) or IUD-implantation (n = 4) groups. Fifty complete ovarian cycles were evaluated, with 26 ovarian cycles monitored for the nine mares prior to treatment and a further 12 cycles were evaluated for mares in each of the groups post-treatment. Detailed characterisation of cyclic reproductive changes in the pony may be of value for controlled breeding programmes. The presence of an IUD was well-tolerated, but failed to modify any recorded aspect of reproductive physiology or behaviour.