The effect of ACTH on pigs? attraction to salt or blood-flavored tail-models

Abstract

Exogenous adrenocorticotrophic hormone (ACTH) leads to a marked increase in salt appetite in mice, rats, rabbits and sheep. In a previous study, pigs treated with ACTH did not increase their ingestion of salt solutions [Physiol. Behav. 78 (2003a) 277], but providing salt in solution may not be an appropriate vehicle for studying salt appetite in pigs. Therefore, in this study, the effect of ACTH on chewing behavior directed at rope tail-models flavored with whole pig’s blood, tap water or a salt solution having the same salt content as blood was examined. Sixteen individually housed pigs (33 kg) were divided into two groups: an ACTH-treatment group, receiving intramuscular injections of long-acting ACTH (50 IU twice daily for 5 days) and a control group, receiving no injections. Chewing behavior directed at water-soaked, salt-flavored or blood-flavored tail-models was observed during two 30-min periods per day for 15 days. Overall, chewing of tail-models tended to decrease in ACTH-treated pigs during the injection period with a significant reduction in chewing directed at blood-flavored models ( P <0.05). A decrease in standing ( P <0.05) and sitting ( P <0.05) was also observed in ACTH-treated pigs during the injection period. Water ( P <0.05) and feed intakes ( P <0.001) significantly increased during the period of ACTH treatment. The incidence of chewing directed at blood-flavored models was greater than that directed at models soaked in water or salt for all pigs, regardless of treatment or period ( P <0.05). Growing pigs do not appear to develop a salt appetite or attraction to blood when given exogenous ACTH. It does not appear that salt content is what is attracting pigs to blood.