The viscosity of poultry feeds : utilization for predicting the water consumption and excretion in 5 week-old meat-turkey poult

Abstract

A method for measurement of viscosity of aqueous extracts from raw materials and poultry feeds is described. Two viscosity determinations are carried out : for the first one, a treatment in boiling 80% ethanol is applied prior to aqueous extraction in order to deactivate endogenous enzyme activities. For the second one, no previous ethanol treatment is applied, which enables the expression of endogenous enzyme activities. These determinations are called "potential viscosity" and "real viscosity", respectively. Data are expressed as the Logarithm of relative viscosity, divided by the concentration of the original material in extract. This expression is called "applied viscosity". The repeatability of applied viscosities is about 5%. The potential applied viscosity (PAV) is additive. PAV measured on 26 types of raw material vary widely (1 : 100, minimum : maximum). The lowest PAV values are observed for sorghum, tapioca roots, peas and maize, and the highest for barley and rye. For cereals, PAV can be properly estimated using an extraction at pH 1.5 without prior ethanolic treatment.

Outlet temperature of pelleting (2.5 mm diameter) affects the values of real applied viscosity (RAV), high RAV values being observed only if PAV is high and if temperature is above 90°C. Particle size of extracted flours greatly changes the RAV values, coarse grinding resulting in low RAV values. It is demonstrated that the particle size effect is not due to an enzyme activity.

Excretion and consumption of water relative to feed intake are measured in 5 week-old meat-turkey poults using 27 diets. Regression lines are calculated with the bird data (means per diet) as the dependant variables, and the diet parameters as the independant variables. The most efficient equations are based on RAV and potassium, or on PAV, outlet temperature of pelleting and potassium. The highest R² values reach 0.758. According to the expressions of equations, the effects of dependant variables are not additive.