Effect of natural extracts of Salix babylonica and Leucaena leucocephala on nutrient digestibility and growth performance of lambs

Thirty two Katahdin×Pelibuey crossbreed male lambs 3–4 months of age and 24 ± 0.3 kg body weight (BW) were used to study effects of administration of extracts rich in secondary compounds from Salix babylonica (SB) and Leucaena leucocephala (LL) on feed intake, nutrient digestibility and growth. After 2 weeks of adaptation consuming a total mixed ration (TMR; 219 and 141 g/kg of crude protein (CP) and neutral detergent fibre (NDFom), respectively), lambs were weighed and distributed by BW into 4 pens of 8 lambs/pen in a completely randomized design with: Control group TMR; SB group TMR (as Control plus S. babylonica extract at 30 ml/d); LL group TMR (as Control plus L. leucocephala extract at 30 ml/d); SBLL group TMR (as Control plus 30 ml/d of S. babylonica and L. leucocephala extracts in a (1:1, v:v) mixture) for a 63 days experiment. Weekly stock volumes (2 l each) of the individual extracts as well as their 1:1 mixture were prepared for daily administration. Extracts were orally administered before the 08:00 h feeding to each lamb. Feed intake was recorded daily and BW was recorded at d 22 (P1), d 43 (P2) and d 63 (P3) of the experiment. Each experimental period ended with a digestibility measurement. Average daily gain (ADG), metabolizable protein (MP) intake and metabolizable energy (ME) intake were calculated. Plant secondary metabolites of total phenolics, saponins and the aqueous fraction were 50% lower in SB versus LL extracts. An extract×experimental period interaction occurred for intake of all nutrients (SB > LL = Control > SBLL, P<0.05). Intake of DM, OM, CP and ADFom were lowest in P3 than other periods, whereas the highest nutrients intake were in P2 and P1 (P<0.05). Individual extracts improved (SB > LL, P=0.05) the digestible DM, OM, EE and CP more than their 1:1 mixture compared with control or SBLL. Digestible DM was improved (P=0.03) by 5 and 3% with SB and LL extracts respectively, compared to control, whereas digestible CP was improved (P=0.005) by 7 and 5%, respectively, compared to control. Digestible ADFom was drastically lower in P1 and increased steadily in periods P2 and P3 (P<0.001). Feed intake was not affected by extract addition although it was reduced from P1 and P2 to P3. Relative to control, addition of extracts increased (P=0.024) ADG while the other performance parameters (i.e., MP intake, ME intake) had a tendency (P=0.05) to improve with extract addition. ADG was improved by about 22 and 21% with SB and LL extracts respectively, while their mixture (i.e., SBLL) was 2% compared to control (i.e., SB = LL > Control = SBLL, P=0.024). MP and ME intakes were decreased (P<0.0001) from P1 and P2 to P3. Results show that daily administration of individual extracts of S. babylonica and L. leucocephala improved lamb performance by 22 and 21%, but that a mixture of both had a much lower benefit.