Welgevonden has now embarked on a contraception programme for their lionesses, which involves the implantation of a slow-release contraception pellet under the lionesses' skin. The implant will render a lioness sterile for one year to eighteen months, and is reversible. The pellet, containing a substance called deslorelin, can be used on both male and female animals. Both deslorelin and human contraceptives work on the sex hormones, but they act on different aspects of the hormonal cycle.
This is completely different to how contraception in elephants is currently achieved. In humans, women take synthetic versions of the hormones oestrogen and progesterone, which are usually produced in the ovaries. The pituitary gland in the brain detects the oestrogen and progesterone levels in the blood. Depending on the level of these hormones, the brain regulates the amount of other sex hormones, known as gonadotrophins, which are produced in the brain and help produce fertile eggs.If gonadotrophin hormone levels are lowered, no eggs are produced and pregnancy cannot occur. Lion contraception enters the hormonal loop at a different point. The implants used contain a chemical that works directly on the brain, fooling it into lowering its production of gonadotrophins, and therefore stopping egg production but bypassing the input from oestrogen and progesterone. Gonadotrophins are found in both males and females.
They act on the ovaries in females and the testes in males, and so lowering gonadotrophin levels prevents both egg and sperm production. However, it also affects the levels of male hormones like testosterone, and so if given to male lions they would lose their manes. Parker comments that on Welgevonden, "The intention is not to stop breeding altogether, but rather to control the population growth rate."
At the moment, all the lionesses got contraceptive implants in September last year, partly to allow the plains game that will be introduced to get settled in. Then selected lionesses will be allowed to breed, depending on whether she has previously had cubs and the chances of her breeding with related animals. As the prides in the reserve rearrange themselves, this will also be taken into account. Kilian comments that the challenge will be managing the breeding rate so that it does not have such a big impact on the general prey population.
The drug used is not expensive, but it has to be placed under the skin of the lions and cannot be given to the animal with a dart. This means that the lions have to be knocked for the implant to be inserted, which involves expensive veterinary and capture costs.
The deslorelin implant contraceptive has been successfully used on male and female wild dogs, tigers, cheetahs, jackals and leopards. Including those on Welgevonden, Bertschinger has treated at least 70 lionesses, with some lionesses having had more than one treatment.
By Melissa Wray
In Welgevonden Private Nature Reserve