School of Biodiversity, One Health & Veterinary Medicine

Nutritional factors influencing egg production in birds

There has been extensive research on the factors influencing egg production in wild birds. Many studies have shown that there is a correlation between food supplies and egg production, which suggests that food supply may limit laying. Experimental investigation of such a relationship has usually involved studies in which the natural food of wild birds has been supplemented in some way, to see is this results in enhanced egg production. Most such studies have assumed that it is the energy content of food which is limiting, and little consideration has been given to the quality of food provided in supplementary feeding trials. However, it may be that protein quality could limit egg production in some species. This is because the amino acid balance of egg proteins is slightlydifferent to that of most vegetable proteins, and many animal proteins. We have been making studies on several species of wild birds, such as tits and gulls, to investigate whether there is evidence that protein quality may limit egg production, and find that both the absolute availability of protein, and the amino acid balance of the protein can influence egg production.

If, in some species and some situations, protein quality may limit egg production, birds might have evolved mechanisms to deal with this by using endogenous sources of protein to contribute to egg production. In this way a female could store amino acids which are limiting in the diet in her muscle proteins before the start of laying, and use these to contribute to egg protein production. Research into the role of muscle condition in egg production has been conducted using mainly a captive breeding colony of Zebra Finches. This a a desert species from Australia which is adapted for breeding whenever feeding conditions are suitable, and they breed readily in captivity. We are investigating the effect of different quality diets on the amount of muscle tissue that the birds develop, and how these change during the breeding cycle. We are investigating whether the size and quality of muscle reserves is related to the number and size of eggs that the female will lay. Samples of muscle tissue are taken from birds at different stages of the laying cycle for examination of muscle proteins and how these vary with the stage of the laying cycle. The quality of diet that a bird obtains several weeks before the start of laying has been shown to have a marked effect on the number and size of eggs she will lay, suggesting that female muscle condition well before the start of the laying season can be an important factor in her reproductive output.

Selman, R. & Houston, D.C. 1996. The effect of prebreeding diet on reproductive investment in birds. Proc. Roy. Soc. B. 263:1585-1588.