Odors and pheromones: influences of olfaction on behavior, physiology, and performance to reduce stress in pigs
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Reducing stress in pig husbandry has become a priority for economical and ethical reasons. The stress axis is anatomically linked to the olfactory system. Pigs have a very developed sense of olfaction. Reducing weaning or handling stress using the sense of olfaction would be a non-invasive and welfare-friendly technique. Exposing pigs at weaning individually to amyl acetate (banana smell, novel odor) or maternal pheromone did not reduce stress within the 2 h of the onset of weaning. Odors and pheromones increased lying behavior but the effects on cortisol concentration and immunology were limited compared to a control odor like water. An induced maternal odor was obtained by feeding sows an onion-flavored diet during lactation. Pigs were weaned onto onion-flavored diet. Onion-exposed pigs fought less at weaning but performance was not affected compared to pigs that had never been exposed to onion. Finishing pigs were trained to an olfactory/gustatory reward (maple syrup) at the finishing barn. When exposed to a novel environment (simulated pre-stun area) with the same reward present, handling time and pig welfare were improved compared to control pigs that had never been trained and were not exposed to maple syrup. Innate preferences to odors were assessed in domestic pigs (tested in a Y-maze) as a model to feral pigs' preferences to odors. Piglets were attracted to boar urine, fox urine, ChileGard™ (habanero pepper extract) and maple syrup and were repulsed by sour milk. Similar results were obtained in feral pigs.