Proligestone* is alleged to suppress feline oestrus. However, no comparative data exist. The objective of the study was to estimate the impact of proligestone administration on the suppression of oestrus and on the prevention of recurrence of feline oestrous cycle and its probable unwanted effects.

The duration of behavioural alterations indicative of oestrus was recorded in 22 young cats during two consecutive oestrous periods. During the 1st oestrus (puberty), the animals received no treatment while on the 2nd day of overt oestrous sign manifestation of the 2nd oestrus, 18 cats were sc treated with proligestone (33 mg/kg) while the remaining 4 cats received normal saline (NS, 0.33 ml/kg), sc. Of the 18 proligestone-treated cats, 12 and 6, further received a 2nd and a 3rd proligestone administration, respectively, at 12-week intervals. The animals were observed for oestrous behaviour for a 12-week period following NS, 1st, 2nd and 3rd proligestone administration. Data were subjected to nonparametric tests and are presented as median (min-max).

The pre-treatment oestrous period in the 18 cats was significantly longer [7.5 days (3-42)] compared to the proligestone affected one [6.0 (4-7), P<0.05, Wilcoxon Signed Ranks Test]. A significantly earlier withdrawal of oestrous symptoms was recorded following proligestone than NS administration [4.0 (3-6) vs. 7.0 days (5-15), P<0.01, Mann-Whitney Test]. On the contrary, no significant differences (P>0.05) were detected a) between the pre-treatment oestrous period of proligestone- and NS-treated cats [7.5 days (3-42) and 6.5 days (5-14), respectively] and b) between the pre- and the post-treatment oestrous period of NS-treated cats [6.5 days (5-14) and 9.0 days (7-16)]. No recurrence of oestrus was observed in any proligestone-treated cat, while all NS-treated ones re-exhibited oestrous symptoms once (50%), twice (25%) and three times (25%). Proligestone side effects observed included pain reaction during or immediately after its administration (in 66.6% of the treated animals and in 58.3% of the injections) and temporary aggressive behaviour in 2/18 animals (11.1%) only after its administration during oestrus. In addition, 6/12 repeatedly proligestone-treated cats showed an impaired response to stressful conditions (surgery) at the end of the 12-week study period.

Data suggest that proligestone effectively suppresses and prevents feline oestrus while veterinary surveillance is required after its use.

*Delvosteron ®, Intervet International, Boxmeer, The Netherlands.