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As maintenance of the immune system is energetically costly and resource-limited, trade-offs among immune function, body condition, and reproductive allocation are expected. In this study, we experimentally test the possible trade-off between immune response, self maintenance, and reproductive output in breeding grey partridges Perdix perdix. Before laying, half the females were immune challenged with a novel antigen vaccine (Newcastle disease virus, NDV). The challenged females showed a higher erythrosedimentation rate, a serum parameter related to worsened health conditions, but their cell-mediated immune reaction (PHA test) did not differ from that of controls. The NDV-treated females laid smaller eggs (mass, length, and breadth), while the concentrations of antibacterial substances (lysozyme and avidin, two enzymes that confer innate antibacterial immunity) were unrelated to the hen's immune challenge. Our study suggests that an immune challenge can have physiological consequences in terms of self-maintenance and reproductive allocation to the egg.

Early maternal effects in the form of substances accumulated in the egg, such as carotenoids and hormones, can be physiologically relevant for a good development of offspring. It has been found in different species that testosterone (T) can be beneficial to offspring by increasing growth rate, but detrimental by reducing immunocompetence and increasing oxidative stress. Carotenoids on the other hand are suggested to be beneficial because they can counteract the oxidative stress and the immune-depressive effect of T. In this study we analyzed the effect of prenatal T exposure in the grey partridge. We injected eggs with three doses of T (high, intermediate, and physiological). After hatching, chicks exposed to a prenatal high dose of T were fed with two diets (rich or poor) differing in beta-carotene content. We found a significant effect of T on both chick growth and cell-mediated immunity, with high T doses resulting in detrimental effects while low doses were beneficial. Detrimental effects of the high dose of T on immunity were mitigated by beta-carotene consumed in the diet. The differences between groups were observed in the early period of life (age 10 days for mass, and age 10 and 21 days for immunity), and disappeared in the following period, and up to 1 and 2 years later. Overall, our observations show that T in the egg is not detrimental but beneficial, and that negative effects are found only at supraphysiological concentrations. The negative effects of T on immunity could be balanced if chicks could consume a diet rich in beta-carotene.

Carotenoids are important dietary constituents in birds. Their functions are numerous and complex, and breeding females are potentially faced with an optimal allocation of these resources between themselves and offspring. We conducted a dietary experiment (low and high supply of beta-carotene) to examine the effect of beta-carotene on health and immune response of 64 reproducing pairs of Grey Partridge (Perdix perdix L.) and on the quality of their eggs, as revealed by the measurement of biochemical components in yolk and albumen, the egg hatching rate and chick survival. We found a beneficial effect of beta-carotene on the erythrosedimentation rate and immune response of females (PHA reaction), while the diet did not significantly affect these variables in males. In both sexes, the plasma level of carotenoids was not related to the quantity of beta-carotene supplied. A higher quantity of beta-carotene in the diet did not induce a variation of egg nutrients (proteins and lipids), nor an increase of yolk beta-carotene concentration. We detected a higher concentration of lysozyme, an enzyme with antibacterial activity, in the albumen of eggs laid by females with a high supply of beta-carotene. These eggs showed higher hatching rates. The present study indicates that although carotenoid supplementation does not influence blood and yolk carotenoid levels, it results in better immune conditions of females, eventually translated into increased antibacterial activity of the eggs. The broad range of beneficial effects of carotenoids is discussed.