Testa and cotyledons were separated from white and coloured flowered varieties of field beans (Vicia faba) and incorporated into complete diets for rats.

Diets containing 10% testa from the coloured variety caused a 15% reduction in live weight gain compared with the diets containing testa from the white flowered variety. This was accompanied by a reduction in the true digestibility of nitrogen and the apparent digestibility of carbohydrates and lipids. The protein efficiency ratio and the net protein utilisation were also reduced but the biological value of protein was not significantly affected.

The efficiency of utilisation of ingested feed dry matter was significantly reduced for the diets containing coloured flower testa but when live weight gain was expressed as a fraction of ingested digestible dry matter there were no significant differences.

Live weight gain and digestibility of organic matter components were highly negatively correlated with the total phenolic content of the diet.

It was concluded that the reduction in live weight gain of animals fed diets containing testa of a coloured variety compared with that of a white flowered variety was caused mainly by the reduction in digestibility of organic matter brought about by the complexing of dietary and digestive enzyme proteins by the high content of phenolic compounds present in the testa of the coloured variety.

A 10% reduction in live weight gain was recorded for animals consuming diets containing cotyledons of coloured varieties compared with those consuming white flowered cotyledons. This reduction was not accompanied by any change in the digestibility of organic matter components and the true digestibility of nitrogen and protein efficiency ratio were not significantly different. There was, however, a significant reduction in the biological value which was a result of increased urinary nitrogen output. It was concluded that the cotyledons of the coloured flowered variety contained an anti-nutritive factor which was not a tannin-like compound and which had an effect on the protein metabolism of the animal.