Abstract
A study was conducted in 18 lactating dairy cows (mean milk yield 10 kg/day) for 6 months by feeding paddy straw based complete rations containing different levels of NDF, in two phases, viz. early and mid lactation, to assess the microbial protein synthesis using purine derivatives (PD) excreted in urine. Isonitrogenous and isocaloric complete rations; T1, T2 and T3 with 25, 30 and 35 per cent NDF, respectively were formulated as per ICAR (1998). Paddy straw was the sole source of roughage NDF and the rest of NDF met by non-forage sources, in 3 diets. PD excreted through urine were comparable between the dietary treatments, in phases 1 and 2. The microbial protein (MBP) synthesis in T1, T2 and T3 were 997.01, 825.91, 842.06 g, respectively, in phase 1 and 1127.93, 1106.74 and 1157.24 g, respectively, in phase 2. The TDN intake calculated from the values of digestibility coefficients of nutrients in T1, T2 and T3 were 5.18, 5.86, 6.10 kg in phase 1 and 8.63, 8.81, 9.00 kg, in phase 2, respectively. The efficiency of MBP production/kg of TDN was 192.47, 140.94, and 138.04 g in phase 1 and 130.70, 125.62 and 128.58 g in phase 2, respectively in T1, T2 and T3. Results suggest that complete diets with 25 per cent are the most ideal NDF level in early lactation while all three NDF levels, viz. 25, 30 and 35% are ideal in mid lactation.