Maternal behaviors of lactating dams towards their pups were blindly scored by well-trained observers daily as initially described by Myers et al.  and adapted and regularly used in our laboratory , , ,  and . Observations occurred three times in the light PTC-209 (1030, 1300, and 1700 h) and twice during the dark cycle (0700 and 2000 h), during 75-min observation periods for the first 6 postnatal days (PND 1–PND 6). During an observation period, each litter was observed at approximately three minute intervals (for a total of 25 observations per period and 125 per day) for the following behaviors adapted from Myers et al. : (1) maternal licking and grooming (LG) of pups, (2) nursing, (3) retrieving a pup to the nest, (4) being in contact with pups but not nursing, and (5) being away from the pups. Nursing was recorded when pups were attached to the mother's nipples and was scored as one of five postures: (1) passively (or supinely) nursing pups while laying on her side or back, (2) a blanket nursing posture, where the mother was over the litter but did not arch her back or extend her legs, and arch-back nursing (ABN), which was further divided into three categories; (3) ABN1, defined by the dam hovering over the litter, (4) ABN2, when the mother's back was arched and her back or front legs were half-way extended (also termed kyphosis) , and (5) ABN3, when the mother's back was arched and all her legs were completely extended so that the kyphosis was more pronounced (Fig. 1). These nursing postures demand different amounts of energy from the mother; passive and blanket nursing requires low energy expenditure, while ABN2 and ABN3 are more physically taxing. High arch-back nursing postures allow for more movement of the pups between nipples, which can be critical considering that a dam has only 12 nipples but can have up to 20 pups. It is important to note that while some of these behaviors are mutually exclusive (e.g. LG and away), some are not (e.g. LG and ABN), and such conditions were put into consideration throughout maternal observations and analysis.