Table 4.
Overview of the effect of play opportunities on outcomes relating to disease, behaviour, and production measures in pigs inoculated with porcine reproductive and respiratory syndrome virus (PRRSV) as provided by separate multilevel multivariable regression models. The model output presented includes the p-value of treatment and interaction effects where applicable, along with pairwise comparisons and their threshold of significance, model fit (Akaike information criterion; AIC) and the intraclass correlation coefficient for random effects (ICC).
| Outcome measures | Treatment | Interaction effect with treatment | p-value for threshold of significance for pairwise comparisons (number of comp.) | Type of pairwise comparisons | AIC | ICC | |
|---|---|---|---|---|---|---|---|
| p-value | p-value (overall, and for pairwise comparisons) | ||||||
| Proxy of aggression | Total skin lesion score | 0.727 | Day overall: ≤0.001 | 0.003 (18) | Between treatments within day & comparisons across consecutive days; bas vs. last^ | 767.652 | Pig: 0.042 |
| D35, D40 (-2DPI), D63 ± 2 (21DPI): all ≤ 0.001 | |||||||
| Systemic immune response | VL (AUC) | 0.362* | – | – | – | 1,639.932 | – |
| WBC | 0.001 | ADG pre-inoculation overall: 0.002 | 0.017 (3) | Between treatments within weight category | 932.432 | Sow: 0.140, pig: 0.446 | |
| Slow-growing pigs pre-inoculation: 0.001 | |||||||
| Lymphocytes | 0.068 | – | – | – | 824.013 | Pig: 0.354 | |
| Monocytes | 0.201 | DPI overall: 0.006 | 0.002 (21) | Between treatments within DPI & comparisons across consecutive DPIs; bas vs. last | 115.658 | Pig: 0.157 | |
| 8DPI: 0.005+, 21DPI: ≤0.001 | |||||||
| Neutrophils | 0.005 | ADG pre-inoculation overall: 0.007 | 0.017 (3) | Between treatments within weight category | 811.634 | Pig: 0.360 | |
| Slow-growing pigs pre-inoculation: 0.002 | |||||||
| Clinical signs | RT | 0.223 | – | – | – | 121.867 | Sow: 0.136, pig: 0.182 |
| Mild, moderate, severe RD (score ≥ 1) | 0.075 | Birth weight overall: 0.086 | 0.017 (3) | Between treatments within weight category | 238.972 | Sow: 0.147, pig: 0.538 | |
| Light pigs at birth: 0.061 | |||||||
| Moderate, severe RD (score ≥ 1.5) | ≤0.001 | – | – | – | 248.032 | Pen: 1.19e−34, sow: 0.118, pig: 0.512 | |
| Duration (days) of mild, moderate, severe RD (score ≥ 1) | 0.098 | – | – | – | 153.153 | NA | |
| Duration (days) of moderate, severe RD (score ≥ 1.5) | ≤0.001 | – | – | – | 155.385 | NA | |
| Active behaviour | During play sessions | ≤0.001 | DPI overall: ≤0.001 | 0.003 (18) | Between treatments within DPI & comparisons across consecutive DPIs; bas vs. last | 827.354 | NA |
| 2, 3, 7, 11, 16, and 20DPI: all ≤ 0.001 | |||||||
| AM | 0.683 | DPI overall: 0.042 | 0.003 (18) | Between treatments within DPI & comparisons across consecutive DPIs; bas vs. last | 495.965 | NA | |
| 11DPI: 0.003, 16DPI: ≤0.001 | |||||||
| PM | ≤0.001 | – | – | – | 497.294 | NA | |
| Feeding behaviour (bouts) | During play sessions | 0.870 | – | – | – | 544.937 | NA |
| AM & PM | 0.092 | – | – | – | 566.251 | NA | |
| Performance | ADG pre-weaning | 0.270 | – | – | – | −348.553 | Sow: 0.139 |
| ADG post-inoculation | 0.940 | DPI period overall: 0.063 | 0.004 (12) | Between treatments within DPI period & comparisons across consecutive DPI periods; bas vs. last | −166.739 | Pig: 0.365 | |
| DPI period 3: 0.003, DPI period 4: 0.027+ | |||||||
| T3 | ≤0.001 | DPI overall: ≤0.001 | 0.002 (22) | Between treatments within DPI & comparisons across consecutive DPIs; bas vs. last | 59.820 | Pig: 0.166 | |
| −1DPI: ≤0.001 | |||||||
| Feed intake | 0.139 | – | – | – | 14.193 | Pen: 0.301 | |
| Post-mortem examination | Lung lesions | 0.821 | – | – | – | 246.370 | NA |
Significant treatment and interaction effects are in bold (p ≤ 0.05). Locomotor, social, and object play, and exploratory behaviours were observed only in the PLY treatment, so comparison between the treatments was not possible (Model fit of those final models is in Supplementary material Section 3d). +Not significant in pairwise comparisons after Bonferroni correction but close to the threshold of significance. ^Definition of the abbreviation ‘bas vs. last’: comparison of baseline versus last time point. Where ‘–’ appears in a cell, no interaction effect was present. *Viral load: this model included all pigs (n = 28); for the predicted means and p-value from the model without the outlier from the CON treatment, see Supplementary material Section 3a. ADG, average daily gain; AUC, area under the curve; D, day; DPI, days post-inoculation; NA, ICC not applicable for this type of regression; RD, respiratory distress; RT, rectal temperature; T3, triiodothyronine; VL, viral load; WBC, white blood cells.