Twenty-four primiparous pregnant pigs were randomly assigned to three handling treatments: Minimal, Positive and Negative. The pigs were moved individually to indoor concrete-floored partial stalls with neck-tethers, 2 days before handling commenced. Positive (stroking and patting on approach to an experimenter) and Negative (brief electric shock of < Is when failing to withdraw from the outstretched hand of an experimenter) handling was imposed for 3min day-1 and the amount of physical contact between handler and pig was recorded. The Minimal treatment group was subjected to routine husbandry practices only. After 3 weeks of the handling treatments and tether-housing, all pigs were catheterized under full surgical anaesthesia. The pigs were allowed 4 days of recovery before collecting the following data: daytime plasma Cortisol concentration profiles, behavioural responses to a human in an arena test, Cortisol responses to human proximity, Cortisol responses to an A CTH-challenge and immunological responses to an injected mitogen.
In the Positive treatment, the amount of physical contact between pig and handler increased during the course of the experiment, while the amount of physical contact did not change in the Negative treatment. There were no effects of treatment on behavioural responses in the arena test. The average daytime concentration of free plasma Cortisol was lower in the Positive treatment than in the Negative or Minimal treatments. The Positive treatment also showed lower total and free plasma Cortisol concentrations pre- and posthuman proximity when compared with the Negative treatment. No differences were found between treatments in total and free plasma Cortisol concentrations following an ACTH challenge. The immunological response was greater in the Positive treatment compared with the Negative treatment and tended to be greater when compared with the Minimal treatment.
It was concluded that the nature of the human-animal relationship affected the physiological stress responses of pregnant pigs to tether-housing. Indications are that a positive human-animal relationship would obviate some of the negative effects of being kept in tether-stalls by lowering the basal cortisol concentration and by increasing immunological responsiveness.