The concept of stress is defined as a biological reaction of the organism where several mechanisms play its role of defence to front a situation that is seen as dangerous and that alters the internal balance of the body and tightly related with animal welfare.

When this natural response is played so often and is maintained for a long time, a tension overcharge is produced with changes at hormonal level that finally produces alterations in vital functions, fluid composition and organic functioning, generating important decreases in production, and what complicates even more things is that from the beginning the immune response is notably altered. As we know that welfare is linked to production and to help animals to be efficient, we should actuate or fight and modify those situations that make decrease or affects negatively on it.

Stress is a natural response and necessary for surviving, is similar in all animal species, but when happening in a large period there is an unspecific answer to environmental adverse conditions that affect the welfare trying to maintain the balance of theses changes and generating the tension status.

So stress can:

• Make psychosomatic diseases to appear.

• Increase susceptibility in front of microbiological infections.

• Leds the welfare conditions of the animal to unacceptable levels.

• Reduces efficiency in production with growing delays.

• Modification of motility of intestinal tract.

• Reproductive disorders (sterility by affectation of the hipophiso- gonad axis, ovarian cysts and decrease of spermatogenesis)

• Decrease of production (meat, milk, eggs)

• Ketosis

• Miopatic disorders (Pig stress síndrome)

• Cardiovascular disorders (degeneration and necrosis of myocardium).

Some examples of the factors producing stress can be:

Environmental:

Temperature: excessive hot or cold, flavours, radiations, noises, bad ventilation, lack of shade and so on.

Psychic and behavioural:

Presence of strange animals, presence of strange people, abuse, harassment, social pression (hierarchy), loss of territory, competence, regrouping in new batches, isolations.

Other factors:

Post weaning, confinement, immobility, transports, hunger, thirst, sudden feed and water changes, changes in the facilities, physical effort and so on.

Advices to control stress:

Because there are a lot of variables that affect the causing agents of stress what is most convenient is trying to act reducing the tiggering effects. The used infrastructure must be attended to control temperature, ventilation systems, effective moisture according to temperature, considering that high humidity helps the pathogen germs growing and reduces life time of materials. Bacterial concentration in slops is multiplied per 10 when moistures goes from 40 % to 80 %.

Feed: Net energy must be regaled but also aminoacids in all stages of the production to achieve the optimum feed consumption to reach the productive potentials.

To create an adequate aerial environment must make the practice of sanitary depopulation: all in, all out. Environmental disinfection by nebulisation when animals are inside, water and feed disinfection, feed manufacturing last technology use (granulation quality), feeders quality avoiding feed losses specially important in liquid feed.

Sanitary environment: the environment stress reduces efficacy of immune system response in front of infections. All the previous advices help to improve the sanitary aspect but someone more can be included as strict cleaning of corridors, avoid contact with pets, vector controls, specific programs of disinfestations (flies) and so on.

The same happens when mixing animals of different ages, with less space of the needed, the social structure is altered.

The actions that each farmer run is decisive to reduce stress effects and achieve positive effects on the production. Although we use pharmacological products, additives and vaccines to improve performance parameters, the control of stress will also help to achieve this objective.