Tree leaves of Ailanthus excelsa, Ziziphus nummularia and Prosopis cineraria were fed in complete feed block (CFB) to 36 weaner (91 d) lambs distributed equally (20.6 +/- 0.55 kg) in three groups (T-1, T-2 and T-3). The CFB of T-1 consisted of 40% A. excelsa leaves, which was replaced at 50% level with phytochemical rich Z. nummularia leaves in T-2 and P. cineraria leaves in T-3. There was decline (p < 0.05) in methane emission per kg digestible OM intake by 10.7 and 15.5% in T-2 and T-3 compared to T-1. Rumen fermentation pattern showed an increased trichloroacetic acid precipitable N with decreased ammonia N and ciliate protozoa population in T-3 compared to other two groups. Ruminal microbial protein synthesis as assessed from urinary purine derivatives excretion was higher (p = 0.012) in T-3 than T-1, while T-2 had an intermediate value. There was decreased (p < 0.05) digestibility of dry matter, organic matter (OM) and ADF in T-3, and that of crude protein (CP) and NDF in both T-2 and T-3. Lambs in T-1 and T-2 had higher (p < 0.05) intake of digestible OM, metabolizable energy (ME) and digestible CP than T-3. There was improved (p = 0.038) N utilization efficiency with a reduced (p = 0.041) excretion through urine, but increased (p = 0.004) excretion through feces in T-2 and T-3 compared to T-1. The live weight gain was lower in T-3 compared to T-1 with an intermediate performance in T-2, but feed conversion ratio with respect to digestible OM and ME intake was similar in all the three groups. It is inferred that inclusion of Z. nummularia and P. cineraria leaves in CFB reduced methane emission, improved ruminal attributes including microbial protein synthesis and N utilization, but lower digestibility and ME intake lead to lower gain. Thus, ration with phytochemicals-rich tree forages would support finished lamb production under greener environment.
