EFFECT OF BIOCHAR TREATMENT ON THE IN VITRO DIGESTIBILITY OF TANNIN-RICH BROWSE SPECIES FED TO LACTATING GALLA GOATS IN THARAKA-NITHI COUNTY, KENYA
Adan Denge Konchora - Master of Science in Animal Science, Tharaka University, Kenya
Dr. Duncan Wanjohi (PhD) - Department of Dryland Agriculture and Natural Resources, Tharaka University, Kenya
Prof. Levi Musalia (PhD) - Department of Dryland Agriculture and Natural Resources, Tharaka University, Kenya
ABSTRACT
Goat production in the arid and semi-arid lands (ASALs) of Kenya depends heavily on indigenous browse species such as Balanites aegyptiaca, Berchemia discolor, Acacia tortilis and Zizyphus mucronata, which remain available during prolonged dry seasons but contain high concentrations of condensed tannins that depress rumen microbial activity, nutrient digestibility and, ultimately, milk production in lactating Galla goats. Biochar has been proposed as a feed additive capable of adsorbing anti-nutritional compounds and improving rumen fermentation, yet empirical evidence on its effectiveness in tannin-rich indigenous browse remains limited. This study sought to determine the effect of graded biochar inclusion (0%, 1%, 2% and 3% of dietary dry matter) on the in vitro digestibility and fermentation characteristics of the four browse species. Each species was evaluated separately using a Completely Randomized Design with sixteen experimental units, and digestibility was assessed using the in vitro gas production technique with rumen fluid collected from a fistulated donor goat, incubated at 39°C for 96 hours. Cumulative gas production was recorded at 3, 6, 12, 24, 48, 72 and 96 hours, and dry matter degradability (DMD) and organic matter degradability (OMD) were determined from residue analysis. Biochar level had no significant effect on early-phase gas production (3-6 hours, P > 0.05) but produced highly significant treatment effects from 12 hours onward (P < 0.001) across all four species. At 96 hours, 2% biochar consistently produced the highest cumulative gas volumes, exceeding the untreated control by 12.1% to 17.9% depending on species, and corresponded with the highest pooled dry matter degradability (68.2% versus 61.4% for the control) and organic matter degradability (65.6% versus 58.7%). The 3% inclusion level did not sustain this advantage, indicating a curvilinear rather than linear dose-response relationship. Acacia tortilis recorded the highest condensed tannin concentration (61.83 mg catechin equivalents (CE)/g DM) and Zizyphus mucronata the lowest (31.57 mg CE/g DM), a gradient that broadly tracked the magnitude of the biochar-associated fermentation response. The findings demonstrate that moderate biochar supplementation, at approximately 2% of dietary dry matter, offers a practical, low-cost strategy for mitigating tannin-related digestibility constraints in browse-based diets for Galla goats in Kenyan drylands, with implications for extension advice, feed formulation and further in vivo validation.