The effects of early social environments on the behavioral development of pigs and raccoons

Vanessa Tavares Kanaan, Purdue University

Abstract

In this dissertation I tested the hypothesis that early social environments could affect behavioral development in two species, domestic swine ( Sus scrofa domesticus) and wild raccoons (Procyon lotor). Allowing two or more litters of pigs in production systems to co-mingle during the lactation period, as it occurs in nature, improves responses to social and non-social challenges after weaning. In chapter 2, I examined the effect of co-mingling litters on piglet growth, ear injuries, suckling behavior and responses to behavioral tests before weaning. Thirty sows and their respective litters were housed in standard farrowing crates until day 13 after birth. On day 13, the partition between two neighboring pens was removed for 20 litters allowing piglets to interact (forming 10 co-mingled litters). The remaining 10 litters served as controls. Weight gain, ear injuries, suckling behavior data were collected before and after co-mingling. The results suggest that co-mingling litters during lactation affects the development of piglets’ social behavior before weaning, as indicated by responses to the social challenge. In chapter 3, I investigated how increasing the frequency of co-mingling affected piglets’ growth, ear injuries and social behavior before and after weaning. Fifty-six sows and their litters were assigned to one of three treatments: control (CM0), co-mingling once (CM1) and co-mingling twice (CM2). Piglets in the CM0 treatment were raised in standard farrowing crates from birth until weaning (n=16 litters), CM1 piglets were allowed to comingle with one unfamiliar litter from day 10 until weaning (n =16 litters) and CM2 piglets were allowed to co-mingle with one unfamiliar litter from day 10 until day 14, and with another unfamiliar litter from day 14 until weaning on day 18 (n=16 litters). There were no treatment differences in weight gained and ear injury scores throughout the experiment. Following mixing at weaning, piglet behavior was recorded for a 48-hour period. The CM2 piglets spent a higher proportion of observations performing belly nosing than CM0 piglets (P= 0.05), CM0 spent a higher percentage of the observations engaged in aggressive interactions (P<0.05). During a social challenge, CM2 piglets spent more time in proximity to one another, had shorter latencies to first aggressive interaction, and spent a lower percentage of time engaged in fights and more time in bullying than CM0 piglets (P<0.05). Although co-mingling treatments did not differ from one another, increasing the frequency of co-mingling from once to twice increased the difference from control significantly for some variables. Increasing the frequency of co-mingling altered the development of social behavior in piglets. In a final experiment, reported in Chapter 4, a similar concept was investigated for the first time in raccoons under wildlife rehabilitation conditions. The purpose of this experiment was to determine how early social environments providing different levels of social complexity affected the pre- and post-weaning behavior and growth of raccoons. At 7 weeks of age, 24 orphaned raccoons were assigned to one of three social environments: littermate pairs (LM, n=4, 8 raccoons), non-littermate pairs (NL, n=4, 8 raccoons) or housed singly with a stuffed animal (S, n=8, 8 raccoons). S cubs spent a smaller proportion of the observation time interacting with the stuffed animal than LM and NL cubs spent interacting with their cagemates during the first two weeks of the pre-weaning period (all comparisons P<0.05). However, during the second week, S cubs spent more time resting in physical contact with the stuffed animal than LM (P< 0.05) and NL (P=0.07) with their cagemates. NL spent more time engaging in activities alone than LM (P <0.05). At 12 weeks of age weaning was completed and one cub from each treatment were mixed in outdoor pens (8 pens of 3 animals). Behavioral responses of individual animals to the novel pens were collected prior to mixing. When introduced to the novel pens, S cubs vocalized more and investigated the wall of the pens less than individuals from the LM and NL treatments (all comparisons P< 0.05). Group responses to an unfamiliar human were recorded. S cubs spent less time exposed to the unfamiliar human than LM (P<0.05) and NL (P=0.08), and spent less time investigating the human than LM (P<0.05) and NL (P<0.05). Increasing social complexity before weaning altered raccoons’ responses to social and non-social challenges after weaning. The hypothesis that early social environments would affect behavioral development in domestic swine and wild raccoons was supported by the results of all the experiments described in this dissertation. Further studies on other welfare indicators are needed in order to assess the overall welfare of these species in captivity and make decisions about adopting the social environments investigated in this dissertation. (Abstract shortened by UMI.)

Degree

Ph.D.

Advisors

Pajor, Purdue University.

Subject Area

Organismal biology|Animal sciences

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