How do stocking density and straw provision affect fouling in conventionally housed slaughter pigs?

The aim of the study was to investigate when fouling appears in conventionally housed slaughter pigs and whether stocking density and straw provision are risk factors to fouling. During four batches of a total of 112 pens with slaughter pigs, pens were randomly assigned to one level of each of two treatments: (1) stocking density of 1.21 (low, n = 56) v. 0.73 m2/pig (high, n = 56), (2) 150 g of straw provided per pig per day on the solid floor (n = 56) v. no straw provided (n = 56). Fouling was recorded each day, and a pen had an event of fouling if at least half of the solid floor was wet with excreta and/or urine. Only the first event of fouling for each pen was included, and thus results represent whether a pen had a fouling event or not and when it happened. Data was analysed by using a Cox regression assuming proportional hazard and with right censoring of pens that never developed fouling. First event of fouling was mostly seen during the first week after insertion and in the last 3 weeks prior to slaughter (10 week study period). Pens with high stocking density had a 90% higher hazard of fouling compared to pens with low stocking density (P = 0.016), meaning that pens with a high stocking density had a higher risk of fouling and of developing it earlier. Pens with straw provided had a 49% higher hazard of fouling compared to pens with no straw provided (P = 0.14). No interaction was seen between stocking density and straw provision (P = 0.80). In conclusion, stocking density was a significant risk factor of fouling, whereas straw provision only indicated this numerically within the used experimental setup and chosen sample size. The results suggest that lowering the stocking density to a level of around 1.21 m2/pig could reduce the risk of fouling in slaughter pigs. The relationship between fouling and straw provision needs further investigation.