| Abstract: | The effects of sorghum grain proanthocyanidins (PAs) on the digestive enzyme activity of broiler chickens were investigated in vitro and in vivo using seven sorghum varieties grown in Zimbabwe. All seven sorghum varieties, classified as either high‐PA (DC‐75, Mutode, Red Swazi and Chirimaugute) or low‐PA (SV2, Brown Tsweta and Chibonda), were used to assess the PA–protein binding capacity and inhibition of trypsin and amylase in vitro. Three of the varieties (Chirimaugute, Chibonda and Brown Tsweta) were subsequently used in broiler diets to test the effects of PAs on the growth performance and digestive enzyme activity of 48 broiler chicks at 42 days of age. Protein precipitation and trypsin and amylase inhibition increased (P < 0.05) with an increase in level of PAs from the low‐PA varieties (by 1–10%) to the high‐PA varieties (by 40–70%). The activity of trypsin in the duodenal lumen of chicks fed the control diet was almost double that of chicks fed Chirimaugute. Amylase activity in the high‐PA group was lowered significantly (P < 0.01) relative to the control and low‐PA groups. The difference between in vitro and in vivo residual enzyme activities was 10–20% for amylase and 5–10% for trypsin. Chicks fed the high‐PA diet showed lower performance than chicks fed the control and low‐PA diets. Mean body weight gains were 59.9, 34.4, 57.3 and 61.4 (SE 4.02) g day−1, final weights were 1936.4, 1363.3, 1773.2 and 1857.0 (SE 78.5) g and feed efficiencies were 1.85, 2.26, 1.65 and 2.13 (SE 0.014) for the control, Chirimaugute, Brown Tsweta and Chibonda groups respectively. The results indicate that PA–enzyme interaction, in addition to dietary protein–PA binding, contributes to the poor performance of chickens fed high‐PA sorghum diets. © 2000 Society of Chemical Industry |
