A sow’s welfare may be in jeopardy if her piglets’ needle teeth are left intact during the lactation period. The current study was designed to determine the effects of clipping needle teeth or grinding needle teeth compared to leaving needle teeth intact, on the welfare of sows housed in farrowing crates. The sows’ teats were inspected for injuries at set intervals. Sow postural and lactational behaviours were also monitored. Findings indicated that intact teeth caused a greater number of udder injuries on days 11 and 18. Teeth that were ground also caused some injury, but not to the same extent as intact teeth. Sows housed with litters with intact teeth spent more time dog-sitting than sows in the other two treatments. On day 4, sows housed with litters with intact teeth allowed piglet suckling sooner after a 60 minute bout of separation than sows in the other two treatments, but terminated post-suckling udder massage sooner than sows in the other two treatments. Sows housed with litters with clipped or ground teeth spent more time lying on their chest (without their udder exposed) than sows in the clipped teeth treatment. Leaving needle teeth intact caused injury and disturbance to the sow, as did the grinding of needle teeth, but to a lesser extent. While in farrowing crates, leaving the piglets’ needle teeth intact was not recommended.