Effets du calcium, du magnésium et des sels biliaires sur l'énergie métabolisable apparente et la digestibilité des lipides, de l'amidon et des protéines chez le poulet en croissance

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Abstract
Two experiments were made in 3 wk-old chickens of a commercial breed to study the effects of either Ca or Mg alone or in association with bile salts on apparent metabolizable energy values (AME) and apparent digestibility (AD) of starch, proteins and lipids of 2 diets. These diets were mainly composed of ground maize and soybean meal and contained 150 g/kg of either animal fat (R1) or maize oil (R2). They were supplemented with either 50 g/kg of CaCO3, 20 g/kg of MgCO3, 2.5 g/kg of bile salts or with a mixture of either CaCO3 and bile salts or MgCO3 and bile salts. The AME values (with or without correction for N-balance) of the non-supplemented fractions were not affected by the addition of Ca, although fat AD was significantly lower in both diets (P < 0.05). The addition of bile salts, with or without Ca, significantly increased the AME values of diet R1 only. The energy values of diet R1 were significantly higher (P < 0.01) when Mg and/or bile salts were added. Neither Ca nor Mg with or without bile salts, affected the AME values of diet R2. The effect of Ca on fat AD, especially that of saturated fatty acids, was due to the formation of insoluble Ca soaps. Addition of bile salts reduced this reaction by increasing the solubilization of fatty acids in the intestinal pool and by accelerating the absorption of Ca. The improvement in protein AD compensated the deleterious effect of Ca on the AME values. The effect of Mg was partly explained by the improved digestibility of saturated fatty acids (palmitic and stearic). MgCO3 may exert an antiseptic action on the gut microflora by reducing its harmful effect on bile salt metabolism. The presence of Mg may bring about an increase in bile secretion. Thus, the availability of bile salts might be increased and consequently the AD of saturated fatty acids would be improved. The effects of these supplements on starch AD was negligible, irrespective of the type of dietary lipids but protein AD was always higher when the diet was rich in unsaturated lipids.