The modified test procedure for measuring nipple attachment latency. (A) The modified experimental platform. Two walls (arrows) were added to prevent pups from moving away from the nipples. (B) The percentages of pups that were able to attach a nipple within 180 sec. The percentage exceeded 85% after P5. (C) Latency between being placed in the cage and nipple attachment. Nipple attachment latency significantly decreased between P5 and P9 (*p < 0.05, **p < 0.01, Scheffe’s F test following Kruskal-Wallis test, mean ± SD).