Effect of freeze-dried pasture herbage on ileal digestibility of amino acids and fatty acids in chickens

The ileal digestibility of amino acids and fatty acids in young chickens fed control diet or experimental diets supplemented with freeze-dried pasture herbage at 20 or 40 g/kg was studied. Control diet contained wheat, maize, and soybean meal. Predominant species in the pasture herbage harvested in May were Lolium perenne, Festuca pratensis, and Trifolium pratense. Freeze-dried pasture herbage contained less protein (169 g/kg) and fat (24 g/kg) and more neutral detergent and acid detergent fibre (340 and 210 g/kg) and tannins (12.38 g/kg) than control diet. Concentrations of amino acids, except phenylalanine and threonine, were lower in pasture herbage than in control feed. In both the control feed and freeze-dried pasture herbage, unsaturated fatty acids occurred in higher proportions than saturated fatty acids. In freeze-dried pasture herbage linolenic acid was the main fatty acid. In chickens fed freeze-dried pasture herbage the ileal digestibility of amino acids and fatty acids decreased in a dose-dependent manner. Freeze-dried pasture herbage at 4% in diet had negative effect (P < 0.05) on the digestibility of amino acids and fatty acids in comparison with control diet. But there was no significant effect of 2% freeze-dried pasture herbage in diet on amino acids digestibility. This suggests that pasture herbage contains anti-nutritional factors that inhibit proteolysis and lipolysis. The effect of pasture herbage on digestibility was variable. In chickens fed diets containing 4% freeze-dried pasture herbage, apparent ileal digestibility of amino acids varied from 0.39 (cysteine) to 0.91 (methionine). Variability in the ileal digestibility of fatty acids was less pronounced (from 0.65 to 0.89).