El dilema de la ganadería extensiva y el mito de los muladares: Implicaciones en la contaminación por fármacos y su impacto en la salud de las aves carroñeras

The prohibition on abandoning the carcasses of extensively grazed animals in the wild in light of the Bovine Spongiform Encephalopathy (BSE) crisis has led to a scarcity of this type of carrion. As a result, avian scavengers are now being forced to congregate at muladares (tips where dead animals are thrown) and modern feeding stations supplied with carcasses originating from stabled animals under intensive exploitation that are thought not to represent a risk BSE transmission. In this article we present a compilation of existing knowledge regarding the impact in Spain of the ingestion of veterinary-prescribed drugs by avian scavengers feeding at muladares supplied with the carcasses of stabled cattle. The results indicate that the presence and concentration in vultures of the pharmaceutical products given to stabled animals, above all fluoroquinolone antibiotics, non-steriodal anti-inflammatories (NSAIDs) and anti-parasitic agents, have increased dramatically since the BSE crisis, with serious consequences for the health of individual vultures and thus the conservation and dynamics of vulture populations. We found that the presence in the blood of the residues of antibiotics is clearly associated with (a) the infection by opportunist pathogens of the nestlings of the three vulture species studied and (b) damage to internal organs in cinereous vultures Aegypius monachus. We also found residues of fluoroquinolones in the eggs of griffon vultures Gyps fulvus and red kites Milvus milvus that can be associated in embryos with damage to joint cartilages, bones and tendons. The change from abandoning carcasses in the wild to providing carrion at muladares has had implications for avian scavenger populations that vary according to the type of food supplied, the site chosen to deposit carcasses and their social and environmental impact. An evaluation of the costs and benefits of these two different ways of dealing with carrion indicates that the subjective prioritization of muladares as an ex situ strategy for the conservation of avian scavengers should be rethought given the negative consequences that this strategy has, firstly, on the health of these birds and, secondly, on their abundance, distribution and reproduction and hence on the conservation and dynamics of their populations. An awareness of the many problems linking muladares and the conservation of avian scavengers should lead to a prioritization of the practice of leaving carcasses originating from extensive animal husbandry in the wild as an effective conservation strategy that is in accordance with the life history, ecology and evolution of these birds of prey.