CONICET | Buscador de Institutos y Recursos Humanos

New intravaginal devices made of ethylene vinyl acetate copolymer (EVA) were investigated for bovine estrus synchronization. Polymeric planar matrices containing progesterone were fabricated by a hot-melt extrusion procedure. In a first stage, progesterone delivery from these matrices were evaluated in vitro in a hydroalcoholic medium. Commercial silicone intravaginal devices were also tested. Results showed that the hormone can be released in vitro from EVA devices at a similar rate than from silicone devices. Besides, release rate showed to be dependent on initial load of hormone. In a second stage, EVA devices were evaluated in animals together with commercial references. In the less active non-lactating Bradford cows, two different shape devices were tested. Results showed that the shape of support and wings tension affect notoriously the hormone delivery in the vaginal cavity. More rigid supports generates injury and inflammation which could modify progesterone absorption. Contrary, more flexible EVA device did not generate tissue damage and yielded hormone levels in plasma very close to that obtained with the commercial device (> 2 ng ml-1 during 7 days). In the more active lactating Holstein cows, EVA devices did not allow to reach required levels in plasma. This result could be due to the higher clearance rate of progesterone in the liver of the more active animals. Metabolism rate in lactating cows is higher leading to lower plasma progesterone levels. Future research must be carried out to give solution to these shortcomings. The re-design of the wings to a less aggressive geometry together with the optimization of release surface and initial drug load could be key factors to increase release rate to permit successful results in the more active lactating Holstein cows.