Introduction A considerable work has been made to increase
the livestock output: firstly, by increasing the number
The economical and social development that has of animals reared, secondly, by improving the animal
taken place in several countries in different times and efficiency.
for different factors, following the industrial de- When and where the countries became able to
velopment on the last century, determined an in- cover their needs for quantity, the next step was to
crease in animal proteins demand. As a consequence, obtain products of high quality to satisfy the consumthe
general interest moved from the multipurpose ers who ask for ‘safe and tasty’ products (Mercier,
objectives of animal husbandry (from drought power 1997). On the contrary, in those countries where the
to manure) to specific animal products. most important aim is still to increase the output at
low costs, only the sanitary guarantee is requested.
*Corresponding author. This paper will take into consideration some of the