The original test procedure for measuring nipple attachment latency. (A) The experimental platform to test nipple attachment latency. The lactating dam was anesthetized and placed in a test cage. (B) The experimental procedure for measuring nipple attachment latency during development. Pups were separated from their mothers for 7 hours before the test. (C) The percentages of pups that were able to attach to a nipple within 180 sec. The percentage gradually increased after P4. (D) Latency between being placed in the cage and nipple attachment. Nipple attachment latency significantly decreased after P6 (*p < 0.05, Scheffe’s F test following Kruskal-Wallis test, mean ± SD).