This interpretive review includes discussion of the available scientific literature with interpretations by the authors. The broad field of semiochemicals can be confusing to scientists and consumers. This review attempts to summarize the known scientific studies for pig and dog semiochemicals while at the same time attempting to refine our use of terminology. The specific objectives of this interpretive review are to summarize and interpret much of the key scientific literature (but not the lay literature) on semiochemicals in pigs and dogs to include (1) definitions of semiochemicals and related molecules including pheromones, (2) to briefly summarize olfactory organs, and (3) and to examine the scientific literature for semiochemical mechanisms and applications in dogs and pigs (two domesticated species with known olfactory acuity). Dogs and pigs have olfactory features that are similar in that they both lack certain olfactory organs (Grueneberg ganglion and Septal Organ) and they have a small vomeronasal organ (VNO) without some major receptors that are found in other species. The primary olfactory organs for both pigs and dogs are the main olfactory epithelium and perhaps the trigeminal nerve. Several examples of pheromones activating the brain via the MOE or Trigeminal nerve rather than the VNO challenge the concept that the VNO is the site of pheromone sensing. We believe it is not appropriate to label something a pheromone when evidence is not available to show that it is a pheromone. We offer definitions for the terms semiochemicals, pheromones, interomones and others and then determine if the evidence is sufficient to call certain semiochemicals a pheromone. Here we review mixed, largely negative, scientific reports of the efficacy of some products labeled as “pheromones” that are more appropriately called semiochemicals. Interomones can have a more powerful effect on dog behavior and physiology than semiochemicals marketed as pheromones. Because marketing of semiochemicals is far ahead of the science, bringing some logic and uniformity to the field will benefit animals and hopefully cause less consumer confusion. Semiochemicals have the potential to offer powerful solutions to behavioral problems using more naturally occurring molecules.

The post-weaning environment in commercial pig nursery buildings is typically devoid of both the sow and her semiochemicals. Among other factors, the loss of maternal odors may contribute to post-weaning stress. In this work, we report four studies (studies 1-4) using 192 weaned pigs to evaluate the effects of a maternal pheromone (MP) containing Myristic Acid and Skatole on weaned pig behavior and performance. Study 1 examined behavior among weaned pigs with a focus on lying, aggression and feeding behaviors. All studies used body weight gain and the percentage of pigs that lost weight the first 7 days after weaning as key response variables. The MP stimulated early feeding behavior and reduced aggressive behaviors among weaned pigs (p < 0.01). In study one, pigs were over 4 kg heavier 16 weeks post-weaning when the MP was present for 48 h post-weaning compared to control pigs (p = 0.05). The three other studies used a 7-days bioassay to assess the best dose and form of delivery of the MP among weaned pigs. The single measure that responded uniformly was the percentage of pigs that lost body weight in the first 7 days after weaning. Among control pigs in four separate studies, 25% of the weaned pigs in each study lost body weight by 7 days after weaning, while in 3 of the 4 bioassay studies, 0% of MP-exposed pigs lost weight after weaning (one study had 6% of pigs losing body weight with the MP). This MP effect is both highly statistically significant and, if found on commercial farms, would have a large positive economic benefit. Simultaneously, having fewer pigs losing weight and exhibiting less aggressive behavior will improve the health and welfare of weaned pigs. Providing biologically-relevant olfactory enrichment can improve pig health and welfare.