Abstract :
Short term preference for five tree fodders by cattle was assessed by their chemical composition, as well as in situ and in vitro gas production, in two studies. In study 1, five heifers (341 ± 36 kg liveweight) were offered Brosimun alicastrun (BA), Piscidia piscipula (PP), Leucaena leucocephala (LL), Lysiloma latisiliquum (TL) and Guazuma ulmifolia (GU) in a 6 h ‘cafeteria’ study over 5 consecutive days. In study 2, the same 5 heifers and tree fodders were used, but each heifer was offered a single tree fodder and fresh Taiwan grass (Pennisetum purpureum) ad libitum for 6 h. After 6 h, refusals were weighed and, for the rest of the day, only Taiwan grass was offered ad libitum. Forages offered in both studies were analyzed for dry matter (DM), crude protein, ash, neutral detergent fibre, acid detergent fibre, lignin, total polyphenols and condensed tannins, as well as for in situ DM degradation (0, 3, 6, 12, 24, 48, 72 and 96 h) and in vitro gas production (3, 6, 9, 12, 15, 18, 21, 24, 30, 36, 48, 60, 72, 96 and 120 h). In situ degradability was fitted to the equation p = a + b(1−e−ct), while the equation gas = GV(1 + (B/t)C−1) was used for in vitro gas production. Residues from in vitro gas production were used to estimate in vitro DM and organic matter digestibility. Relationship between tree fodder intake, chemical composition, and in situ and in vitro digestibility was assessed using Pearson correlation analysis. In study 1, tree fodder intake (g DM/kg LW0.75) was: PP 5.41, TL 5.62, LL 15.62, GU 17.31 and BA 55.36 (S.E.D. 1.63). Intake was correlated with lignin (Pearson coefficient, −0.898, P=0.039), IVDMD (r = 0.916, P=0.029) IVOMD (r = 0.902, P=0.036), parameter ‘b’ and ‘c’ from in situ degradability (r = 0.926, P=0.034 and r = 0.926, P=0.024, respectively) and with the 12, 24, 48, 72 and 96 h measurements, as well as parameter GV from in vitro gas production (r = 0.873, P=0.053) and 12, 15, 18, 21, 24, 30, 36 and 48 h cumulative gas readings. In study 2, tree fodder intake (g DM/kg LW0.75) was: PP 17.74, TL4.08, LL 22.18, GU 13.47 and BA 38.56 (S.E.D. 0.52). Grass intake (g DM/kg LW0.75) during the same time was: 79.41, 89.64, 87.69, 86.30 and 77.43 (S.E.D. 0.83) when PP, TL, LL, GU and BA, respectively, was offered. Total DM intake (in 6 h) increased (P<0.05) when LL and BA were offered. Tree fodder intake was related to IVDMD (r = 0.950, P=0.013), IVOMD (r = 0.942, P=0.017), parameter ‘c’ from in situ degradability (r = 0.908, P=0.033) and 12 and 24 h measurements, as well as parameter GV from in vitro gas production (r = 0.910, P=0.032) and 3, 6, 9, 12, 15, 18, 21, and 24 h cumulative gas readings. As feed preference is a short term response, lignin might be an indicator of intake preference.
