Hill, Elizabeth, Hailey Hegland, Dana Wolak, Andrea Maxwell, and Amanda Witkowski
In many animal species, maternal care is critical for survival of offspring. The mother’s behavior is responsive to environmental events. For example, separation from the pups causes maternal responses to increase upon reunion (reviewed in Millstein & Holmes, 2007). Maternal behavior is very intensive right after birth, but then it quickly declines over succeeding days (Champagne et al., 2007; Shoji & Kato, 2006). The present study examined the effect of a brief separation from their litter of pups on maternal behavior, with tests conducted on two occasions, when the pups were 3 and 7 days of age.
Subjects were six mouse mothers with litters (CD-1 strain). Mice were tested in their home cages. Mice were videotaped for 15 minutes, then the litter was removed to another room for 10 minutes. Afterward, two pups were placed in the corner of the cage opposite the nest, to test maternal retrieval behavior. After these two pups were retrieved, the rest of the litter was returned to the nest site, and behavior was videotaped for 15 minutes. Behaviors were coded from videotapes using the Noldus Observer software system. Maternal behavior measures included nursing, pup-licking, nest-building, hovering over the pups, and pup retrieval. Behavior away from pups included locomotion, sniffing/rearing, and other (such as self-grooming). A maternal total duration was calculated by summing all interactions with pups. Locomotion, sniffing/rearing, and other were combined into a non-maternal total.
The most common maternal responses were nest-building and hovering. Little nursing was seen in the 15-minute observation periods. Contrary to prediction, maternal behavior on day 3 was not higher than on Day 7. Pup retrieval latencies were similar on day 3 and 7 for retrieving the first pup, and slightly shorter on day 7 than day 3 for the second pup, but the difference was not significant. As predicted, maternal behavior appeared to increase after a brief separation from the pups (mean maternal total= 144.8 sec before, 316.1 sec after), but the difference was not statistically significant. Non-maternal behavior decreased slightly after separation (also n.s). There was a high variance among mice on most of the measures. Nevertheless, maternal responses were generally consistent for individual mothers over the two observation days.
Increased maternal responding after separation from pups is consistent with previous studies (see Millstein & Holmes, 2007). Maternal behavior generally declines as pups age, but the degree of decline over days 3 to 7 is not steep (Champagne et al., 2007; Shoji & Kato, 2006). A much larger sample of mice is necessary to show a small effect. Future research will determine the impact of maternal separation on the pups when they are adults.