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Aggressive and submissive behavior in young swine given exogenous acth
DOMESTIC
ANIMAL
AGGRESSIVE
ENDOCRINOLOGY
Vol. 1(4):319-321,
1984
AND SUBMISSIVE BEHAVIOR IN YOUNG SWINE GIVEN EXOGENOUS ACTH J.J. McGlone Department of Animal Science University of Wyoming, Laramie 82071 Received
July
5. 1984
ABSTRACT Ten replicates of two pigs each were used to determine the effects of 10 IU/kg i.m. adrenocorticotropin hormone (ACTH) or physiological saline on aggressive and submissive behaviors. Behavior was recorded for 90 minutes after pigs of each treatment were grouped. Both duration and latency to attack were similar for ACTH- and salinetreated pigs. Submissive behavior was greater for ACTH-treated pigs (P<.Ol). In this species, ACTH increased submissive behavior which resulted in domination of ACTHtreated pigs by control pigs. INTRODUCTION
Domestic swine (Sus scrofa) exhibit agonistic behavior whenever previously unfamiliar conspecifics are grouped. The intensity of aggressive and submissive behavior is high even in prepubertal animals (1,2). In adult male swine, intraspecific aggression is so intense that unfamiliar males must be isolated on commercial farms. Thus, swine represent an interesting new model for the study of aggressive mechanisms. Basic information may also be used in the VRture to better manage this harmful behavior. Much of the work to date using the domestic pig focused on reducing aggression as a way of increasing measures of productivity such as bodyweight gain. It has been shown that pigs show increased agonistic behavior, and presumably reduced productivity, when hungry (3) or crowded (3,4,5). Hormone modulation of agonistic behavior is well documented in rodents. Current theories, outlined in a review by Leshner (6), suggest that ACTH, acting through glucocorticoids, has a short-term aggression-increasing effect. The predominant view has been that adrenocortical hormones are secreted at the end of a fight by the defeated animals (7,s). This study was conducted to evaluate the effects of pre-fight ACTH administration on swine aggressive and submissive behavior. MATERIALS
AND
METHODS
This experiment utilized prepubertal Yorkshire X Hampshire and Yorkshire X Duroc breeds of growing swine. Young pigs were 5-8 weeks of age at the start of the experiment. Pigs were weaned at 4 weeks of age and they remained in littermate groups until used in the study. Males were castrated at 10 days of age. Pigs were fed a fortified 18% crude protein corn-soybean meal diet. Animals were housed in a heated, mechanically ventilated building with dim lights on 24 hours. Agonistic behaviors were recorded using behavioral measures described previously (3). Aggressive behavior was defined previously as attack which Copyright@
1984 by DOMENDO,
Inc.
319
0739-7240/94/$3.00
McGLONE involved physical contact and this included bites and pushes. Submissive behavior was defined as one pig receiving attack and not retaliating. The submissive pig has a typical stance which seems to protect the ears and head from biting. The duration (minutes) of aggressive behavior (attack) and submissive behavior were summarized from video tape records’ using an electronic event recorder*. Video taping was performed at 5 frames per second. Typically, the sequence of events in an agonistic interaction included investigation, both pigs attacking, then one pig turning away (submission) while the other pig continued to attack. Ten castrated males and 10 females, weighing (X&SE) 14.9 f .58 kg (salinetreated) and 14.7 + .84 kg (ACTH-treated), were randomly assigned to receive either 10 W/kg body weight ACTH (Sigma Chemical, Product A-6002) or an equivalent volume of saline. Treatments were administered intramuscularly. The dose of ACTH used (10 W/kg) was chosen because a previous report (9) from our laboratory found a 278% increase over baseline in plasma cortisol concentration one hour after administration of 10 W/kg ACTH. One hour after ACTH or saline administration, this pair of pigs was placed in the observation pen for a 90-min observation period. The duration of aggressive and submissive behavior and time (latency) to first attack were determined for each individual pig. Dependent variables were examined statistically by analysis of variance procedures. RESULTS
Duration of aggressive behavior for pigs in both treatments was statistically similar. Latency to attack was also not different between treatments (1468 + 684 and 956 + 531 set, mean and SE for ACTH and saline, respectively). Pigs treated with ACTH showed significantly longer duration of submissive behavior (Table 1). Thus, ACTH caused increased submissive behavior which led to ‘ACTH-treated pigs becoming subordinate to control pigs. Overall, saline-treated pigs were dominant 6/L 0 times, ACTH-treated pigs 2/ 10 times (only marginally dominant), and the match seemed undecided 2/10 times. There was no significant correlation (r= .05, 19 d.f.; P<.lO) between body weight and dominance or duration of attack. However, in the two cases where ACTH-treated pigs were marginally dominant over control pigs, the ACTHtreated pigs were heavier. Young females were more aggressive than castrated males (1.3 f .41 and .34 f .12 min, respectively; P<.O5). The interaction between gender and treatment was not significant which indicates that drug-treated animals of each treatment were equally aggressive. Females and males showed similar durations of submissive behavior (.l 1 + .07 and .08 f .05 min, respectively). TABLE 1. AGGRESSIW AND SUBMISSM BEHAVIORS SHOWN BY Two YOUNG PIGS DURING A 90-MINUTE TEST NlUUber Aggressive behavior, ruin Submissive behavior, min of Standard Standard Treatment Pigs F-value Mean Error Mean Error F-value ACTH 10 .I8 ,073 .73 .35 .118, N.S. 16.97, P-C.01 Saline 10 .Ol ,010 .90 .33
DISCUSSION
ACTH-treated pigs attacked a similar amount but showed more submissive behavior than saline-treated control pigs. Therefore, saline-treated pigs, on average, dominated ACTH-treated pigs.
ACTH AND SOCIAL BEHAVIOR OF SWINE
321
Chronic administration of ACTH decreased mouse aggression (11) and had no effect on hamster fighting (10). Adrenalectomy reduced aggression, but fighting increased with dexamethazone treatment (12). Acute ACTH administration had the opposite effect, increased aggression (11). In a review, Leshner (6) concluded that acute ACTH caused release of corticoids, which facilitated aggression; however, he felt chronic ACTH had an extra-adrenal, extra-testicular effect of decreasing aggression. Leshner went on to suggest (13) that chronic ACTH may not only reduce aggressiveness, but may also increase fearfulness or submissive behaviors. The swine data reported here considered only the effects of acute ACTH on aggressive and submissive behavior. Leshner’s hypothesis (6) that acute ACTH acts through corticoids to increase aggression was not supported. However, acute ACTH administration in swine did have a greater effect on submissive behavior. Also, this increased submissive behavior observed in ACTH-treated pigs led to subordination of treated pigs by saline-treated control pigs. Thus, pigs entering a fight in a state of high adrenocortical activity are likely to be dominated by animals with more normal adrenocortical activity. ACKNOWLEDGEMENTS
AND
FOOTNOTES
The author wishes to thank Dr. Bill Murdoch, Mrs. Kay Harris and Mr. Tom Heald for technical assistance and advice. The experiment reported here was supported by a grant from the Harry Frank Guggenheim Foundation. This paper is Wyoming Paper No. JAI 256. 1 Video recorder: Panasonic model NV-8050; camera: Panasonic model WV-3 160. Panasonic, Inc., One Panasonic Way, Secaucus, NJ 07094. 2 Datamyte Model 800, Electrogeneral 55343.
Corp., 14960 Minnetonka
Industrial Road, Minnetonka.
MN
REFERENCES 1. Ewbank R. Social hierarchy in suckling and fattening pigs: A review. Livestock Prod Sci 3:363-372, 1976 2. Hansen LL, Hagelso AM. A general survey of environmental influence on the social hierarchy function in pigs. Acta Agr Stand 30:388-392, 1980. 3. Kelley KW, McGlone JJ, Gaskins CT. Porcine aggression during crowding and fasting. J Anim Sci 50:336-341, 1980. 4. Bryant MJ, Ewbank R. Some effects of stocking rate and group size upon agonistic behavior in groups of growing pigs. Brit Vet J 128:64-78, 1972. 5. Randolph JH, Cromwell GL, Stably TS, Kratzer DD. Effects of group size and space allowance on performance and behavior of swine. J Anim Sci 53:922-927, 1981. 6. Leshner Al. A model of hormones and agonistic behavior. Physiol Behav 15:225235, 1975. 7. Archer J. Effects of aggressive behavior on the adrenal cortex in male laboratory mice. J Mammol 51:327-333, 1970. 8. Bronson FH, Eleftherious BE. Chronic physiological effects of fighting in mice. Gen Compar Endocrinol 4 :9- 14, 1964. 9. McGlone JJ. Olfactory cues and pig agonistic behavior: Evidence for a submissive pheromone. Physiol Behav (accepted), 1985. 10. Brain PF. Some endocrine effects on fighting behavior in isolated male albino mice. J Endocrinol 51:R18, 1971. 11. Brain PF, Evans CM. Some recent studies on the effects of corticotrophin on agonistic behavior in the house mouse and the golden hamster. J Endocrinol 57:R39, 1973. 12. Leshner Al, Walker WA, Johnson AE, Kelling JS, Kreisler SJ, Vare BB. Pituitary adrenocortical activity and intermale aggressiveness in isolated mice. Physiol Behav 11:705-711, 1973. In: Brain PR, 13. Leshner AI. The role of hormones in the control of submissiveness. Benton D (Eds.) Multidisciplinary Approaches to Aggression Research, Elsevier, North Holland, NY, pp 309-322, 1981.
ANIMAL
AGGRESSIVE
ENDOCRINOLOGY
Vol. 1(4):319-321,
1984
AND SUBMISSIVE BEHAVIOR IN YOUNG SWINE GIVEN EXOGENOUS ACTH J.J. McGlone Department of Animal Science University of Wyoming, Laramie 82071 Received
July
5. 1984
ABSTRACT Ten replicates of two pigs each were used to determine the effects of 10 IU/kg i.m. adrenocorticotropin hormone (ACTH) or physiological saline on aggressive and submissive behaviors. Behavior was recorded for 90 minutes after pigs of each treatment were grouped. Both duration and latency to attack were similar for ACTH- and salinetreated pigs. Submissive behavior was greater for ACTH-treated pigs (P<.Ol). In this species, ACTH increased submissive behavior which resulted in domination of ACTHtreated pigs by control pigs. INTRODUCTION
Domestic swine (Sus scrofa) exhibit agonistic behavior whenever previously unfamiliar conspecifics are grouped. The intensity of aggressive and submissive behavior is high even in prepubertal animals (1,2). In adult male swine, intraspecific aggression is so intense that unfamiliar males must be isolated on commercial farms. Thus, swine represent an interesting new model for the study of aggressive mechanisms. Basic information may also be used in the VRture to better manage this harmful behavior. Much of the work to date using the domestic pig focused on reducing aggression as a way of increasing measures of productivity such as bodyweight gain. It has been shown that pigs show increased agonistic behavior, and presumably reduced productivity, when hungry (3) or crowded (3,4,5). Hormone modulation of agonistic behavior is well documented in rodents. Current theories, outlined in a review by Leshner (6), suggest that ACTH, acting through glucocorticoids, has a short-term aggression-increasing effect. The predominant view has been that adrenocortical hormones are secreted at the end of a fight by the defeated animals (7,s). This study was conducted to evaluate the effects of pre-fight ACTH administration on swine aggressive and submissive behavior. MATERIALS
AND
METHODS
This experiment utilized prepubertal Yorkshire X Hampshire and Yorkshire X Duroc breeds of growing swine. Young pigs were 5-8 weeks of age at the start of the experiment. Pigs were weaned at 4 weeks of age and they remained in littermate groups until used in the study. Males were castrated at 10 days of age. Pigs were fed a fortified 18% crude protein corn-soybean meal diet. Animals were housed in a heated, mechanically ventilated building with dim lights on 24 hours. Agonistic behaviors were recorded using behavioral measures described previously (3). Aggressive behavior was defined previously as attack which Copyright@
1984 by DOMENDO,
Inc.
319
0739-7240/94/$3.00
McGLONE involved physical contact and this included bites and pushes. Submissive behavior was defined as one pig receiving attack and not retaliating. The submissive pig has a typical stance which seems to protect the ears and head from biting. The duration (minutes) of aggressive behavior (attack) and submissive behavior were summarized from video tape records’ using an electronic event recorder*. Video taping was performed at 5 frames per second. Typically, the sequence of events in an agonistic interaction included investigation, both pigs attacking, then one pig turning away (submission) while the other pig continued to attack. Ten castrated males and 10 females, weighing (X&SE) 14.9 f .58 kg (salinetreated) and 14.7 + .84 kg (ACTH-treated), were randomly assigned to receive either 10 W/kg body weight ACTH (Sigma Chemical, Product A-6002) or an equivalent volume of saline. Treatments were administered intramuscularly. The dose of ACTH used (10 W/kg) was chosen because a previous report (9) from our laboratory found a 278% increase over baseline in plasma cortisol concentration one hour after administration of 10 W/kg ACTH. One hour after ACTH or saline administration, this pair of pigs was placed in the observation pen for a 90-min observation period. The duration of aggressive and submissive behavior and time (latency) to first attack were determined for each individual pig. Dependent variables were examined statistically by analysis of variance procedures. RESULTS
Duration of aggressive behavior for pigs in both treatments was statistically similar. Latency to attack was also not different between treatments (1468 + 684 and 956 + 531 set, mean and SE for ACTH and saline, respectively). Pigs treated with ACTH showed significantly longer duration of submissive behavior (Table 1). Thus, ACTH caused increased submissive behavior which led to ‘ACTH-treated pigs becoming subordinate to control pigs. Overall, saline-treated pigs were dominant 6/L 0 times, ACTH-treated pigs 2/ 10 times (only marginally dominant), and the match seemed undecided 2/10 times. There was no significant correlation (r= .05, 19 d.f.; P<.lO) between body weight and dominance or duration of attack. However, in the two cases where ACTH-treated pigs were marginally dominant over control pigs, the ACTHtreated pigs were heavier. Young females were more aggressive than castrated males (1.3 f .41 and .34 f .12 min, respectively; P<.O5). The interaction between gender and treatment was not significant which indicates that drug-treated animals of each treatment were equally aggressive. Females and males showed similar durations of submissive behavior (.l 1 + .07 and .08 f .05 min, respectively). TABLE 1. AGGRESSIW AND SUBMISSM BEHAVIORS SHOWN BY Two YOUNG PIGS DURING A 90-MINUTE TEST NlUUber Aggressive behavior, ruin Submissive behavior, min of Standard Standard Treatment Pigs F-value Mean Error Mean Error F-value ACTH 10 .I8 ,073 .73 .35 .118, N.S. 16.97, P-C.01 Saline 10 .Ol ,010 .90 .33
DISCUSSION
ACTH-treated pigs attacked a similar amount but showed more submissive behavior than saline-treated control pigs. Therefore, saline-treated pigs, on average, dominated ACTH-treated pigs.
ACTH AND SOCIAL BEHAVIOR OF SWINE
321
Chronic administration of ACTH decreased mouse aggression (11) and had no effect on hamster fighting (10). Adrenalectomy reduced aggression, but fighting increased with dexamethazone treatment (12). Acute ACTH administration had the opposite effect, increased aggression (11). In a review, Leshner (6) concluded that acute ACTH caused release of corticoids, which facilitated aggression; however, he felt chronic ACTH had an extra-adrenal, extra-testicular effect of decreasing aggression. Leshner went on to suggest (13) that chronic ACTH may not only reduce aggressiveness, but may also increase fearfulness or submissive behaviors. The swine data reported here considered only the effects of acute ACTH on aggressive and submissive behavior. Leshner’s hypothesis (6) that acute ACTH acts through corticoids to increase aggression was not supported. However, acute ACTH administration in swine did have a greater effect on submissive behavior. Also, this increased submissive behavior observed in ACTH-treated pigs led to subordination of treated pigs by saline-treated control pigs. Thus, pigs entering a fight in a state of high adrenocortical activity are likely to be dominated by animals with more normal adrenocortical activity. ACKNOWLEDGEMENTS
AND
FOOTNOTES
The author wishes to thank Dr. Bill Murdoch, Mrs. Kay Harris and Mr. Tom Heald for technical assistance and advice. The experiment reported here was supported by a grant from the Harry Frank Guggenheim Foundation. This paper is Wyoming Paper No. JAI 256. 1 Video recorder: Panasonic model NV-8050; camera: Panasonic model WV-3 160. Panasonic, Inc., One Panasonic Way, Secaucus, NJ 07094. 2 Datamyte Model 800, Electrogeneral 55343.
Corp., 14960 Minnetonka
Industrial Road, Minnetonka.
MN
REFERENCES 1. Ewbank R. Social hierarchy in suckling and fattening pigs: A review. Livestock Prod Sci 3:363-372, 1976 2. Hansen LL, Hagelso AM. A general survey of environmental influence on the social hierarchy function in pigs. Acta Agr Stand 30:388-392, 1980. 3. Kelley KW, McGlone JJ, Gaskins CT. Porcine aggression during crowding and fasting. J Anim Sci 50:336-341, 1980. 4. Bryant MJ, Ewbank R. Some effects of stocking rate and group size upon agonistic behavior in groups of growing pigs. Brit Vet J 128:64-78, 1972. 5. Randolph JH, Cromwell GL, Stably TS, Kratzer DD. Effects of group size and space allowance on performance and behavior of swine. J Anim Sci 53:922-927, 1981. 6. Leshner Al. A model of hormones and agonistic behavior. Physiol Behav 15:225235, 1975. 7. Archer J. Effects of aggressive behavior on the adrenal cortex in male laboratory mice. J Mammol 51:327-333, 1970. 8. Bronson FH, Eleftherious BE. Chronic physiological effects of fighting in mice. Gen Compar Endocrinol 4 :9- 14, 1964. 9. McGlone JJ. Olfactory cues and pig agonistic behavior: Evidence for a submissive pheromone. Physiol Behav (accepted), 1985. 10. Brain PF. Some endocrine effects on fighting behavior in isolated male albino mice. J Endocrinol 51:R18, 1971. 11. Brain PF, Evans CM. Some recent studies on the effects of corticotrophin on agonistic behavior in the house mouse and the golden hamster. J Endocrinol 57:R39, 1973. 12. Leshner Al, Walker WA, Johnson AE, Kelling JS, Kreisler SJ, Vare BB. Pituitary adrenocortical activity and intermale aggressiveness in isolated mice. Physiol Behav 11:705-711, 1973. In: Brain PR, 13. Leshner AI. The role of hormones in the control of submissiveness. Benton D (Eds.) Multidisciplinary Approaches to Aggression Research, Elsevier, North Holland, NY, pp 309-322, 1981.