Impact of Housing Condition on Welfare and Behavior of Immunocastrated Fattening Pigs (Sus scrofa domestica)

Simple Summary This study aimed to analyze if the well-known positive effects of immunocastration on the behavior and welfare of pigs are robust to varying environments. One hundred forty-four male pigs were studied with regard to their sex category (EM: entire males, IC: immunocastrates, BA: barrows) and housing environment (ENR: enriched, STD: standard, MIX: repeated social mixing). The second (=effective) vaccination was administered to the immunocastrates 5 or 6 weeks before slaughter according to the standard protocol. Regardless of housing conditions, beneficial effects of immunocastration on a reduction in undesired agonistic and sexual behavior, including penis biting and penile injuries, were observed. Enriched housing showed a beneficial effect on play, whereas the social mixing environment reduced the number of social nosing events. The novel result is that the beneficial effects of immunocastration on behavioral and welfare aspects apply independent from the housing environments assessed in this study. Abstract The aim of this study was to investigate whether the well-known positive effects of immunocastration on the behavior and welfare of pigs persist under varying environments. One hundred forty-four male pigs were studied with regard to their sex category (EM: entire males, IC: immunocastrates, BA: barrows) and housing environment (ENR: enriched, STD: standard, MIX: repeated social mixing). The vaccination of immunocastrates included two injections at the age of 12 and 22 weeks. Regardless of the housing conditions, frequencies of sexual and fighting behavior expressed by immunocastrates shifted from boar-like to barrow-like behavior after the second immunocastration vaccination (Mixed model analysis, p < 0.05). Penis biting decreased in IC after the second vaccination (Wilcoxon signed-rank tests, p = 0.036) and penile injuries were lower in IC animals compared to EM (Mixed model analysis, p < 0.001). Housing-dependent effects on behavior could also be observed in the animals at a relatively young age. Enriched housing showed a beneficial effect on play behavior (Chi-square test, p < 0.001) and the social mixing environment reduced the number of social nosing events (Mixed model analysis, p < 0.05). The positive effects of immunocastration thus are robust to all housing conditions assessed in this study.

: Ethogram of scored behaviors. A new behavior was scored after 3 seconds of pausing a previous behavior. (Jensen, 1980 andDonaldson et al., 2002) Reciprocal pressing

Total Aggressive Behavior
The pigs stand parallel or inverse parallel and push hard with the shoulders against each other, throwing their heads against the neck, head or flanks of the other pig. Reciprocal pressing-cum-bite As above, but with bites directed towards the head, ears and flanks of the other pig.
Head knock A rapid thrust upwards or sideways with the head or snout against any part of the body of the other pig. The performing pig's mouth is shut. Head knock-cum-bite As above, but with bites. The performing pig's mouth is open. Biting (attempt) The pig's mouth is being opened and snapped shut against an opponent.

Penis biting
Biting towards the extruded penis of another pig.

Levering
The pig puts its snout under the body of another pig (in all observed cases from behind) and raises its snout to topple the other pig. Chasing Following a fleeing animal at high speed. Total defensive behavior (modified after Jensen, 1980 andCamerlink et al., 2015) Retreat The pig moves away from another pig at its usual walking speed directly after a social interaction.

Fleeing
The pig moves away from another pig rapidly with its head held high directly after a social interaction. This is often accompanied by a shrill scream.
Mounting escape (attempt) Occurs in response to mounting. The pig tries to or moves away from the mounting pig rapidly. The activity is often accompanied by a shrill scream. Social nosing behavior (modified after Jensen, 1980 andCamerlink et al., 2015) Nosing The nose of the pig approaches any body part except the genital region of another pig up to at least 5 cm distance. No agonistic behaviors follow for at least 3 seconds. Total sexual behavior (modified after Booth and Baldwin, 1980) Mounting attempt The pig lifts the front part of its torso to put it on top of the torso of another pig (usually from behind), but is not successful.

Mounting
The pig lifts the front part of its torso and puts it on top of the torso of another pig (usually from behind).

Mounting with pelvic thrusts
While maintaining the mounting position, the pig moves its pelvis for-and backward. Mounting with extruded penis While maintaining the mounting position, the pig extrudes its penis. Mounting with pelvic thrusts and extruded penis While maintaining the mounting position, the pig moves its pelvis for-and backward and extrudes its penis. Anal-genital-nosing (modified after Jensen, 1980) The nose of the pig approaches the genital region of another pig up to at least 5 cm.
Play behavior (Donaldson et al., 2002) Scamper A sequence of at least two forward hops in rapid succession, usually accompanied by ear flapping.

Other play
Pivot (a jump on the spot in which the pig rapidly turns its body at least 90° in the horizontal plane), head toss (exaggerated lateral displacements of the head and neck, involving at least one full movement to each side), flop (the pig rapidly falls down from an upright position into sternal or lateral recumbency on its own initiative without contact with another pig). Abnormal behavior (modified after Jensen et al., 2010) Chewing pen mate The pig chews at a body part of a (mostly lying) pen mate, except ears and tail.

Chewing tail
The pig chews with the tail of another pig in its mouth.

Chewing ear
The pig chews with the ear of another pig in its mouth. Body-Nosing (modified after Fraser, 1978) The rhythmic up-and-down movement of one pig rubbing the body, especially the belly, of another with its snout.