Effect of cutting interval of Taiwan grass (Pennisetum purpureum) and partial substitution with duckweed (Lemna sp. and Spirodela sp.) on intake, digestibility and ruminal fermentation of Pelibuey lambs

The effects of Taiwan grass (TW) cutting interval and partial substitution with duckweed on dry matter intake (DMI), in vivo DM digestibility (DMD), and digestibility of organic matter (OMD), crude protein (CPD), neutral (NDFD) and acid detergent fiber (ADFD), as well as on nitrogen balance, ruminal pH, production of volatile fatty acids (VFA) and ammonia nitrogen (NH3–N), was evaluated. For each experimental period (P) of 30 (P1), 45 (P2), and 60 (P3) days of TW grass cutting interval, twelve Pelibuey lambs were randomly assigned to three groups of four lambs each in a completely random design. Average weights of lambs were 25.1±1.5, 27.6±1.9 and 28.6±1.8 kg. Lambs were housed in individual metabolic cages, and assigned to three treatments (n=4): (T1) 100% TW, (T2) 80% TW+20% DW, and (T3) 70% TW+30% DW. Each experimental period lasted 16 days: 8 days for adaptation to the diet and 8 days for total feces collection and rumen liquor sampling; urine was collected the last two days. Data were analyzed with MIXED procedure and means compared with the Tukey test. Inclusion of DW decreased DMI (P<0.01), whereas DMD, OMD, CPD, and NDFD increased (P<0.05) as the age of the TW increased; besides, ADFD showed differences (P<0.05) among treatments only in P3. Nitrogen retention improved by DW (P<0.05) in the three periods, and pH was affected by periods (P>0.05) only in P3 (P<0.05). In the three periods, 20 and 30% DW increased NH3–N concentration and the acetate: propionate ratio (P<0.05), but the VFA proportion did not change.