Suppression of estrus in cats with melatonin implants

The objective of this study was to assess the efficacy of a subcutaneous melatonin implant to suppress estrus in queens (felis catus). The hypothesis was that this implant would temporarily and reversibly suppress estrus in queens without producing any clinically detectable side effects. Fourteen adult queens were maintained in cages under artificial illumination (14 h light:10 h dark) for 45 d and then randomly assigned to one of two treatments. At interestrus, queens received a single subcutaneous melatonin implant (18 mg; Melovine [CEVA Sante Animal, Libourne, France]; MEL: n = 9), or a single subcutaneous placebo implant without melatonin (0 mg; PLA; n = 5). At the next estrus, all queens received a second MEL (n = 9) or PLA (n = 5) implant. Blood samples were taken when queens displayed estrous signs and during interestrus to measure estradiol (E2) and progesterone (P4), respectively, by radioimmunoassay. There were no significant differences in duration of the interestrus interval in PLA cats, regardless of whether the implants were placed during interestrus or estrus (6.0 ± 9.7 d vs. 6.0 ± 9.7 d, respectively; least square means [LSM] ± SEM). However, when MEL implants were placed during interestrus, the duration of interestrus was approximately twice as long as that occurring when MEL implants were placed during estrus (113.3 ± 6.1 d vs. 61.1 ± 6.8 d, respectively; P < 0.01). Serum E2 and P4 concentrations were similar in queens with PLA and MEL implants and in queens that received implants in estrus and interestrus. In conclusion, a subcutaneous MEL implant effectively and reversibly suppressed estrus in queens for approximately 2 to 4 mo with no clinically detectable side effects.