The effect of type of environmental enrichment on development and indicators of stress in nursery age growing pigs

Forty-eight Yorkshire sired cross-bred pigs were sorted by size and weight at weaning and placed into the nursery facility at the Knoxville Experiment Station, Louisville, Tennessee. They were separated into three treatment groups each containing 16 individuals. Treatment A which was considered the "rooting group" received two heavy plastic Boomer Balls per pen, each measuring 25.4 cm in diameter.

Treatment B, the "oral group" was provided with three lengths of chain suspended from a notched 2" by 4" (nominal) lumber which was suspended across the center of the pen. Each length of chain was 55 cm in length and there was approximately 20 cm distance between each chain. This type of enrichment provided the animals with an opportunity for a redirected oral behavior.

Treatment C was the control group and received no enrichment. All animals were provided a standard ration of 19% protein. Each pen had unlimited access to water from nipple waterers.

Three variables were quantified: weight gain, physiological indicators of stress as measured by cortisol binding globulin (CBG) and behavioral indicators of stress as measured by oral manipulative behaviors and passive sitting. These variables were quantified on day 24 of the study, and on day 42 of the study. At the same time, each animal was bled using vena cava puncture and plasma was later analyzed for the presence of Cortisol Binding Globulin (CBG). Throughout the six week trial period the animals were videotaped for six hours daily and tapes were analyzed for the occurrence of behavioral indicators of stress.

Weight gain was unaffected by treatment when using beginning weight as a covariate. There was a highly significant difference (p < .0001) in the frequency of behavioral indicators of stress between the enrichment groups (A & B) and the control group (C). There was no difference between treatment groups in the amount of cortisol binding globulin (CBG) present in the plasma, but there was a significant difference (p < .05) between the amount of CBG present across treatment groups between different time samples.

Although the results of this study cannot confirm the effect of environmental enrichment on weight gain or cortisol binding globulin, there is support for the hypothesis that environmental enrichment can affect the development of growing pigs, and that the type of enrichment may be important as well. Further, the use of behavioral indicators of stress is supported as an affordable and efficient method of assessing animal welfare.