Melatonin implants to control estrus in Belgian breeding queens

Introduction and aim. Seasonal anestrus in the queen is associated with high levels of melatonin. The use of subcutaneous melatonin implants developed for ovine estrus stimulation (Melovine® 18mg; CEVA santé animale) has been tested in queens with variable results depending on environmental conditions. The aim of this clinical report is to evaluate the use of melatonin implants in field conditions in Belgian catteries.
Materials and methods. 13 melatonin implants (Melovine® 18mg) were injected subcutaneously in the neck of 12 pubescent and 1 prepubescent queens. All queens were in interestrus or in prepubescent anestrus. Absence of estrus was confirmed by vaginal smear stained with a modified Harris-Shorr (Kit Diag-Oestro®, RAL Diagnostics, France). Queens were considered not in estrus if less than 70% of the cells were keratinized. The owner was asked to report signs of estrus during the 10 first days following the injection and the duration of the subsequent interestrus. Observed matings after return to cyclicity and potential pregnancies were also recorded. Implants were considered efficacious if interestrus lasted more than 6 weeks.
Results. Pubescent queens: implants were efficacious in 11/12 queens with a mean duration of action (from implantation to estrus) of 106 +/- 40 days. 4/11 presented mild signs of estrus with meowing for 2 to 3 days within 10 days post implantation but none was mated during these periods. The queen that failed to respond had a vaginal smear of 70% of keratinized cells at the time of implantation with a history of a 3 week-long estrus ending the day before. It was however decided to try implantation on this unclear case. The next estrus started the very next day to last for another 3 weeks. The breeder then decided to mate her and she got pregnant. Following this pregnancy, this same queen was implanted 3 times during the breeding season on a confirmed absence of estrus and the mean duration of the provoked interestrus was 55 +/- 8 days. One fourth implantation was done 6 weeks post-partum, in October, while she was lactating and a prolonged anestrus until mid-February (130.9 days) was observed. There was no interference with milk production and the kittens were weaned 3 weeks after implantation. A different queen was also implanted in October, when natural secretion of melatonin increases, and anestrus was also prolonged until mid-February. These two cases with increased endogenous secretion of melatonin may have affected the overall efficacy of implants to postpone estrus we report here. However, 3 other queens resumed cyclicity after implantation in November and December. After cyclicity resumption, 6 queens were successfully mated while another one, where no successful cover was observed, failed to get pregnant. That queen was subsequently neutered. The prepubescent queen was 6 months old when implanted, estrus appeared 52 days after.
Conclusions. Melovine® was safely used on one lactating queen but its innocuousness should be confirmed by larger studies. Our results also suggest that melatonin should be considered to prolongate post-partum anestrus. Mean duration of action is comparable to that previously reported in French and Italian catteries. Some queens showed signs of estrus in November and December while they should have been in seasonal anestrus. Late in the year implantation of melatonin may provide a promising tool to obtain seasonal anestrus in queens that cycle all year round. In our field conditions, the one prepubescent implanted queen showed first estrus signs at the age of 7.5 months, which is normal for puberty. This is in agreement with results obtained under controlled conditions, where no significant delay in first estrus occurrence was observed. Our results support the observation that fertility does not appear to be compromised by melatonin implants, making it a viable option for cyclicity control in catteries.