Life history theory predicts that when food intake and body reserves are insufficient to maintain all life processes, resource allocation trade-offs should occur. Lactation is costly and requires increased food intake. In spotted hyaenas, energy expenditure on lactation is high, particularly for mothers rearing twin litters, and foraging effort and food intake are influenced by social status. We investigated whether lactation in this species results in a reduction in resource allocation to immune processes sufficient to increase parasite infection. We expected higher parasite infection in lactating than non-lactating females, in mothers nursing twin than singleton litters, in females of lower than higher social status and in less than more experienced foragers. We quantified Ancylostoma egg load (AEL) and the presence of oocysts of Cystoisospora spp. as a proxy measure of immune function in 58 females. Lactating females were significantly more often infected with Ancylostoma, and their AEL was higher than in non-lactating females. Females nursing twins had significantly higher AELs than those nursing singletons. As social status increased, AELs significantly declined. This relationship was modulated by lactation status and litter size, being strongest in nonlactating females, moderate in females with twin litters and weakest in females with singleton litters. The decrease in AEL with increasing social status was greater for experienced than inexperienced females. Concurrent infection with Cystoisospora significantly increased with increasing AEL. Our results provide evidence for a resource allocation tradeoff in lactating spotted hyaenas.

Allostatis is the process of maintaining homeostatis through behavioural or physiological responses to challenges, and its cumulative energetic cost is termed allostatic load. The allostatic load hypothesis predicts that hunger and the mechanisms that establish and maintain social dominance should have a strong impact on allostatic load. In spotted hyaenas, dominance between twin siblings emerges during intense early competition for maternal milk and involves trained winner/loser effects. Conflict over access to teats declines with age as behavioural dominance conventions are established. In young litters, the allostatic load of subordinates measured in terms of faecal glucocorticoid metabolite concentrations (fGMCs) should be higher than that of dominants. When low milk provisioning threatens survival, hungry subordinates are more assertive, particularly when competing against a dominant sister. Dominants challenged by assertive subordinates should have allostatic loads and fGMCs above those of dominants with subordinates that adhere to dominance conventions. We show that in young litters, subordinates had significantly higher fGMCs than dominants, and dominant sisters had significantly higher fGMCs than dominant brothers. When hungry, both dominants and subordinates had significantly higher fGMCs than when fed. Our results provide evidence that hunger and sibling competition affect allostatic load in spotted hyaenas.