Environmental temperature, space allowance, and regrouping: Additive effects of multiple concurrent stressors in growing pigs-

Objective: To determine the effects of multiple concurrent stressors on hematologic and behavioral measurements in growing pigs. Materials and methods: Two hundred and fifty-six growing pigs (Yorkshire x Hampshire or purebred Duroc barrows and gilts, initial body weight 34.7 ± 0.5 kg) were used in a randomized block design with a 2 x 2 x 2 factorial arrangement of treatments to determine effects on hematologic and behavioral measures of environmental temperature (constant-thermoneutral at 24°C or cycling-high from 28°C to 34°C), space allowance (0.56 or 0.25 m ² per pig), and regrouping (static, ie, not regrouped, or regrouped at start of Weeks 1 and 3 of the study). After a 7-day adjustment period at 24°C and 0.56 m ² of space per pig, treatments were imposed for the study period of 4 weeks. Results: At end of Week 4, the cycling-high temperature treatment group had lower lymphocyte concentrations, higher neutrophil concentrations, and, consequently, higher neutrophil:lymphocyte (N:L) ratios (P < .05). Neither space allowance nor regrouping influenced N:L ratio. No stressor affected hematocrit (HCT) or plasma cortisol concentration. However, cortisol and N:L ratio were higher and HCT was lower as number of stressors increased. Pigs on the cycling-high temperature treatment were less active than those on the constant-thermoneutral treatment. Standing activity was higher and lying activity was lower as number of stressors increased (P < .05). Implications: The three stressors tested in this study influenced hematological and behavioral measurements indicative of stress in growing pigs, and some of these effects were additive.