Exogenous adrenocorticotrophic hormone does not elicit a salt appetite in growing pigs

In rodents, rabbits, and sheep, exogenous adrenocorticotrophic hormone (ACTH) leads to a marked increase in sodium appetite. It has been suggested that if pigs show a similar response to stress, an appetite for salt could increase their attraction to blood and contribute to the development of tail biting. The aim of this study was to examine the effects of ACTH on salt appetite in growing pigs. Individually housed Yorkshire pigs (45 kg) were divided into three groups of four. Group 1 had free access to water, 0.5 M NaCl, and 0.5 M KCl solutions; Group 2 to water, 0.5, and 0.25 M NaCl solutions; Group 3 to water, 0.25, and 0.125 M NaCl solutions. Intramuscular injection of long-acting synthetic ACTH (50 IU twice daily for 5 days) did not elicit increases in intakes of any of the available salt solutions compared to pretreatment intakes. However, there was a 1.6-fold increase in both water and feed intake during ACTH treatment. ACTH treatment also stimulated significant increases in salivary cortisol concentrations. Although increases in salivary cortisol concentrations and in water and feed intake indicate that there were physiological responses to the treatment, exogenous ACTH given for 5 days did not elicit a sodium appetite in growing pigs. These findings do not support the notion that a stress-induced salt appetite serves as an underlying mechanism for tail biting.