Dose-dependent effects of biochar inclusion on growth, hematological, manure and carcass characteristics of rabbits

A 10-week trial was conducted to evaluate effects of graded levels of rice husk biochar (RHB) on growth, digestibility, hematological and carcass characteristics of twenty-four (24) weaned crossbred rabbits averaging 840 g in weight. Animals were allotted to six dietary treatments in a 3 x 2 factorial arranged in Completely Randomized Design: Brachiaria mulato II (BM) + concentrate without RHB; BM + concentrate with 15 g/kg RHB; BM + concentrate with 30 g/kg RHB (BMB30); Brachiaria decumbens (BD) + concentrate without RHB; BD + concentrate with 15 g/ kg RHB and BD + concentrate with 30 g/kg RHB. All data were analyzed statistically with GLM procedure of Minitab® 18.1 and means were separated at 5% probability level using Tukey’s test. BM contained 35.25% fibre and 8.11% crude protein (CP) and BD contained 32.76% fiber and 6.90% CP. Concentrate contained 22.49% CP, and 11.75% fiber. As RHB was included, CP and fiber contents of concentrates declined. Dry matter (DM), CP and neutral detergent fiber (NDF) intake differed among treatments and ranged from 98.26-124.44 g/day, 8.75-10.92 g/day and 88.19 -98.39 g/day with BM based diets having highest DM and CP intakes. Average daily gain (ADG) ranged from 12.74-18.30 g/day and was highest for BD without RHB. Diets had no significant effect (p>0.05) on digestibility of DM and metabolizable energy (ME) but significantly affected (p<0.05) that of CP (61.03-68.34%), organic matter (OM) (51.87-54.31%) and NDF (48.07- 57.66%). For hematology, only platelet count (184-216.67 x 10*3 / uL) differed significantly (p<0.05) among treatments. RHB inclusion significantly affected (p<0.05) kidneys (11.00-13.33 g) and liver (38.67-52.98 g). N/P/K, C/N (18.37-28.24) and lignin/nitrogen (6.33-8.84) ratios as well as other mineral characteristics assessed for manure indicated RHB improved manure characteristics. Diets with or without RHB inclusion had no detrimental effect on rabbits hence up to 30 g/ kg of biochar produced from rice husk can be recommended as a feed additive for rabbits.