RESUMEN
Embryo transfer is a surgical technique that is widely used in reproductive biotechnology. Despite the ethical obligation to relieve animals' post-operative pain, analgesia is not routinely provided after embryo transfer surgery because it has been suggested that analgesics may be detrimental to embryo survival. Studies suggest, however, that the potential for adverse effects varies depending on the type of analgesic used and the timing of its administration. The authors carried out a study to determine whether pre-operatively administered tramadol, a synthetic analogue of codeine, influenced birth rate, litter survival or the post-operative body weights of surrogate dams. Compared with controls that were not given any analgesic, surrogate dams given tramadol had similar birth rates and similar body weights at all time points. The tramadol-treated surrogate dams showed a statistically significant increase in the number of offspring that survived to weaning. The authors conclude that pre-operatively administered tramadol does not harm the success rate of embryo transfer surgery and even may improve litter survival.