Long-term effects of straw blocks in pens with finishing pigs and the interaction with boar type

• Straw blocks reduced pen mate manipulation in pigs from boars with high growth rates.
• This behavior was not reduced in pigs from boars with better carcass traits.
• Straw blocks increased competition behavior in the beginning of the fattening period.
• Straw blocks did not affect growth, carcass traits and organ lesions.

This study verified the effect of straw blocks on the behavior and growth of finishing pigs and possible interactions with the genetic background (boar type). A total of 359 finishing pigs, which were offspring from different boar types, were housed in gender-mixed pens with slatted floors. Half of these pigs descended from sires selected for better carcass traits and lower growth rates (type C) and the other half from sires selected for better growth and poorer carcass traits (type G). The offspring of these two boar types were spread equally over control (only a chain) and treatment groups (chain and straw blocks in a dispenser). Direct individual behavioral observations were carried out once a week and the presence of lesions on the body was verified every two weeks. Individual weights were recorded at different weighing moments. Lesions on organs and carcass traits were obtained after slaughter.A lower frequency of pen mate manipulation was observed in pens with access to straw blocks in type G pigs. For type C pigs however, no significant difference was present in pen mate manipulation between groups with or without straw. It has been shown that pigs selected for high lean tissue growth rate show higher frequencies of tail biting behavior and in this study, providing straw blocks does not seem to be sufficient to decrease this behavior. These pigs also showed more pen manipulation, which might reflect an increased foraging motivation or motivation to explore. Mounting and fighting were recorded more frequently at the start of the finishing phase and in this period significantly more in pens with straw blocks, which might be related to both competition for straw and introduction in a new environment. Growth was not significantly affected by the presence of straw blocks. Type G pigs however reached higher slaughter weights compared to type C pigs, but no interaction with the presence of straw was seen.It can be concluded that in general, straw blocks decreased the manipulation of pen mates in finishing pigs, but this effect was only seen in pigs selected for better growth. Pigs predisposed to a higher lean meat percentage showed in general higher frequencies of this behavior and in these pigs, straw blocks did not reduce pen mate manipulation compared to more barren environments. In general, the presence of the straw blocks seemed to be associated with more competition related behavior in the beginning of the fattening period. The presence of straw did not affect growth or carcass traits.