Growing deterministic and stochastic threats to many wild populations of large vertebrates have focused attention on the significance of captive breeding for conservation. Nanger dama mhorr and Gazella cuvieri, two Sahelo-Saharan species, have declined dramatically since the 1950s, apparently due to excessive hunting and habitat degradation. Today, the earlier is extinct in the wild and the latter survives only in small numbers in a few isolated parts of their range, and captive breeding programmes currently provide an important tool for rearing sustained populations. In natural and captive populations, the largest percentage of mortality is among juveniles. This is most relevant, from an evolutionary perspective, as it has a profound influence on population dynamics and demography, and is pivotal to the conservation and management of captive endangered populations. This study explored the juvenile mortality curve during the first 6 months of life of the species mentioned earlier in captivity. Then, we looked at the causes of this mortality by examining potential mother-dependent as well as offspring-dependent sources of juvenile mortality. The resulting curves show that the critical period of mortality is the first 14 days of life. We also found that parity and longevity of the mother affected juvenile mortality in Mohor gazelles. Calves born to primiparous as well as those born to short-lived mothers were more prone to die than those born to either multiparous or long-lived mothers. In Cuvier's gazelles, juvenile mortality was explained by the interaction between parity and mother's age and litter composition. Neither mother nor offspring inbreeding had any effect on juvenile mortality in either population. Precise knowledge of the biological factors affecting juvenile mortality is increasingly important for the conservation of large mammals, whether they are captive, managed, reintroduced or simply fragmented, as the neonates are the population's potential recruits.