Double cloprostenol administration during mid luteal phase of oestrus cycle does not modify the interoestrus interval in gilts

The present study was undertaken to test the effect of two vulva injections of double (D)-cloprostenol on day 7, 9 and 10 of oestrous cycle on the duration of the interestrous interval in gilts. Following a pre-treatment oestrous cycle, 87 gilts were assigned to receive vulva injections of 75 μg D-cloprostenol at 08:00 and 14:00 h on day 7 (D7; n=30), day 9 (D9; n=29) and day 10 (D10; n=28) of their second observed oestrous cycle. Across the treatments, the duration of the oestrous cycle period with D-cloprostenol treatment (19.1±0.1 d) was not different from that of the previous oestrous cycle (20.1±0.4 days). Plasma progesterone concentrations were evaluated 6 h before and 24 and 72 h after D-cloprostenol treatment in the D9 group. Compared to pre-treatment levels (9.6±0.4 ng/mL), plasma progesterone concentrations were reduced (P<0.05) at 24 h (6.3±1.0 ng/mL) and 72 h after treatment but complete luteolysis did not occur. These data indicate that in gilts double vulva administration of D-cloprostenol is not able to induce a complete luteolisys and hence the duration of the oestrous cycle is not modified.