Effect of intra-uterine oestradiol-17β administration on inter-oestrous interval in the pig

The effect of intra-uterine administration of oestradiol-17β (E2) on the life-span of the corpora lutea (CL) of non-pregnant gilts and gilts pregnant up to Day 10 was investigated. Injection of 380 ng E2 every 6 h from Day 11 (08:00 h) to Day 15 (02:00 h) into both uterine horns resulted in a cycle length of 21.7 ± 1.0 days (mean ±SD) in non-pregnant gilts (n = 7) and 22.4 ± 1.7 days in gilts pregnant up to Day 10 (n = 5). Implantation of three E2-releasing micropellets into each uterine horn of non-pregnant gilts on Day 10 of the cycle resulted in an inter-oestrous interval of 21.0 ± 2.3 days (n = 5). These results indicate that administration of a small physiological or supraphysiological dose of E2 into the uterus lumen (the presumed site of action in the maternal recognition of pregnancy), does not result in a substantial CL maintenance in non-pregnant gilts.