Does primiparity affect the efficiency of converting energy to offspring production in the guinea-pig?

In small mammals the reproductive performance of first-time breeders is of great relevance to fitness. However, young primiparous mothers reproduce ge nerally less successfully than multiparous ones. One constraining factor ma y be inefficiency of novice breeders in converting energy to offspring prod uction. To test this hypothesis I investigated the energy cost of gestation and lactation in the guinea-pig (Cavia porcellus). I compared mothers' off spring production (growth of pups), body mass, and energy intake, as well a s the solid-food intake of their pups (during lactation) and energy expendi ture (resting oxygen consumption) between young primiparous, old primiparou s, second-litter multiparous, and third-litter multiparous females. Young p rimiparous females showed significantly lower offspring production than mul tiparous females. For older primiparous females the level was intermediate. Both young and older primiparous females showed a lower efficiency of conv erting energy to offspring production than their multiparous conspecifics. Parity affected lactation most strongly. Part of the inefficiency of primip arous guinea-pig mothers can be explained by the lower contribution to the energy budget made by their offspring from independent consumption of solid food.