The study evaluated the influence of age (30, 60, 90 and 120 days) on dry matter (DM), crude protein (CP), neutral detergent fiber (NDF), free condensed tannins (FCT), fiber-bound condensed tannins (FBCT), protein-bound condensed tannin content (PBCT), in vitro degradation rate of DM (DMkd), CP (CPkd) and NDF (NDFkd) of Morus alba (MA) and Hibiscus rosa-sinensis (HRS). For MA leaves, there was a quadratic (p < 0.01) relationship between CP content and age: the CP content of 60, 90 and 120 days-old leaves was similar, but it was lower than that of 30 days-old leaves. For HRS leaves, CP content decreased linearly (p < 0.01) as age increased, and NDF content increased linearly (p < 0.01). For both MA and HRS, there were cubit (p < 0.01) effects of age on FCT, FBCT and PBCT content, in which the highest values were found in 120-d-old leaves and the lowest in 30 and 90 d-old leaves. Furthermore, old leaves had a linear decrease in DMkd, CPkd, and NDFkd. DMkd, CPkd, and NDFkd negatively correlated (p < 0.001) with FCT, FBCT, and PBCT content. For both MA and HRS, 90 days-old leaves had higher nutritional value than 120 days-old leaves.
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