Thus, suckling bout duration in captive animals does not necessarily reflect evolutionary adaptation to an arid environment. Although suckling bout duration and frequency is not a good indicator of milk transfer (Cameron, 1998; Cameron et al., 1999), it can be useful to assess the amount of maternal care in current offspring (Mendl & Paul, 1989; Cassinello, 2001; Therrien et al., 2007; Pluháček et al., 2010a) and specifically the needs of the offspring (e.g. suckling frequency in Therrien et al., 2007). Our results suggested that suckling bout duration increased with intraspecific aggression rate among adult females of the
species (i.e. longest duration recorded in mountain zebras, followed by plains zebras and Grévy’s Erlotinib zebras). A similar effect of relationships among adults, including aggression among female adults on maternal style, was recorded in interspecific comparisons of several macaque species (Kaufman & Rosenblum,
1969; Thierry, 1985; Maestripieri, 1994a,b). This has been given as a possible explanation for high-suckling frequency in studies on white-tailed deer Odocoileus virginianus and fallow deer (Lavigueur & Barrette, 1992; Therrien et al., 2007). In primates suckling duration is correlated with stress reduction (Gomendio, 1990; Clutton-Brock, 1991; Redondo, Gomendio & Medina, 1992), and in cattle with socialization with the dam (Das Selleckchem Adriamycin learn more et al., 2000). Therefore, suckling bout duration and the time spent suckling can reflect the social needs of the foal, whereas termination and rejection seems to be affected by ecological adaptation. Because our results came from captive animals living in limited space,
the high aggression rate among mares could strengthen the social demands of the foal to the mother, in mountain zebras in particular. The artificial setting may also have affected the results likely by two factors: smaller space than in the wild and high-quality diet of predictable delivery. Our results dealing with suckling bout duration and frequency are a little different from those of Becker & Ginsberg (1990). In both studies the lowest suckling frequency and time spent suckling was observed in Grévy’s zebras. However, contrasting with the results of Becker & Ginsberg (1990) we recorded longer suckling bout duration in plains than in Grévy’s zebras. In our earlier study on captive plains zebras, we found that suckling bout duration was highly affected by the animal terminating the bout and by the pregnancy status of the nursing mare (Pluháček et al., 2010a); in this study we excluded pregnant mares and did separate analyses depending on the animal terminating the bout. These factors could have affected the results of Becker & Ginsberg (1990). Nevertheless, we cannot omit the effect of captivity as an explanation for the difference in suckling bout duration between our and their studies.