Effect of urea treatment and diet composition on, and prediction of nutritive value of rice straw of different cultivars

Straws of seven rice cultivars from a plant breeding experiment were analyzed for their chemical composition and nylon bag organic matter (NBOMD) and cell wall degradability (NDFD) with and without 3 or 4% level of urea treatment. A significant (P < 0.01) variation of 70 and 100 g/kg in NBOMD and NDFD respectively was found among the different cultivarʹs untreated straws. Urea treatment improved NBOMD and NDFD by 80 and 100 g/kg, respectively, without differences between 3 or 4% levels of urea. The improvement in dry matter degradability (DMD) due to urea treatment was found higher in rice straw having lower DMD in untreated straw and was found to be negatively correlated (r = −0.87∗) with the digestibility of untreated straw. In another in vivo digestion trial on crossbred heifers, the organic matter digestibility (OMD), NDFD and digestible organic matter intake (DOMI) were found significantly (P < 0.01) higher in straw of Kasturi cultivar over that of Sita. In nylon bag studies, the soluble fraction a and degradation rate constant c were found higher for Kasturi straw over that of Sita. The DMI was dependent on fraction a (r = 0.98∗) and c (r = 0.97∗ at P < 0.05). In another study, nine straw samples of different cultivars were incubated for 48 h in the rumen of two fistulated animals fed on 4 different diets consisting of; I: Wheat Bhusa (WB) + Sorghum (S) + 1 kg Concentrate (C); II: S + 1.5 kg C; III: S + 200 g Sodium Bicarbonate (Bic) and IV: S + 450 g bic. The DMD, NDFD and ADFD of straws were significantly (P < 0.01) higher on diet II and IV than that on diets I and III. However, hemicellulose degradability was reduced on diets III and IV. Different straws of rice cultivars also differed significantly (P < 0.01) among themselves in their nutrient degradability. Bicarbonate-supplemented diets III and IV had significantly (P < 0.01) higher rumen pH over diets I and II. The zero h DM disappearance (solubility) of straws determined at 0, 1, 2 and 3 h post feeding differed significantly (P < 0.01). The initial pH of the straw was found to have positive effect on the degradability of NDF (r = 0.74∗ at P < 0.05), DM (r = 0.71∗ at P < 0.05), nylon bag solubility (r = 0.88∗∗ at P < 0.01) and acid insoluble ash (AIA) in NDF of digested (r = 0.81∗∗ at P < 0.01) and undigested straw (r = 0.71∗ at P < 0.05). However, rumen pH was negatively correlated (r = −0.75∗∗ at P < 0.05) with rumen nylon bag DM solubility and hemicellulose degradability (r = −0.81∗∗ at P < 0.01). Loss of DM due to 1 h hot water refluxing at pH 7.6 was found negatively correlated (r = −0.81∗∗ at P < 0.01) with NDF content of the straw.