Crude protein requirements of free-range laying hens

Abstract

The goal of this study was to estimate the crude protein (CP) requirement for the maintenance, weight gain and egg production of free-range hens, and produce a predictive protein requirement equation. A linear regression equation of the nitrogen that was retained in the body relative to the production of eggs as a function of different nitrogen intake levels (ad libitum, 80%, 60% and 40% of the original ad libitum intake) provided the nitrogen requirement for maintenance. This relationship was determined at the x-axis intercept, and the efficiency of dietary nitrogen utilisation was expressed by the regression coefficient. The CP requirement for weight gain was estimated as a function of the nitrogen content in the carcass, and the dietary nitrogen utilisation efficiency was found after each week’s slaughter. The CP requirement for egg production was determined by comparing egg protein concentrations with the efficiency of egg protein deposition. The requirements and efficiency of maintenance protein utilisation were 4.7 g CP/kg0.75.day and 56%, respectively. Because there were no changes in the live bodyweights and nitrogen contents of bird carcasses, the CP requirement and efficiency value for weight gain were not estimated. The protein requirement and utilisation efficiency for egg production were 0.18 g CP/g egg mass (EM) produced and 62%, respectively. From the requirements that were estimated in the present study, the following equation can be used to predict the protein requirements of free-range hens during the laying phase: CP = 4.7 × W0.75 + 0.18 × EM (g/bird.day).