Authors: U.Y. Anelea, K.H. Südekum, J. Hummela, O.M. Arigbede, A.O. Onic, J.A. Olanite, C. Böttgera, V.O. Ojob, A.O. Jolaosho
Animal Feed Science and Technology 163 (2011) 161–169
Abstract
A study was carried out to evaluate the chemical composition, in vitro apparently and truly
degraded dry matter (DM), utilizable crude protein at the duodenum (uCP) (total CP at the
duodenum minus endogenous CP), methane production, and short chain fatty acid production
of haulms of six cowpea varieties. The study was arranged in a 2×2×2 factorial design,
with three replicates. Three improved (ITA2, ITA6 and ITA8) and three commercial (Oloyin,
Peu and Sokoto) cowpea varieties harvested during wet and dry seasons were used for the
study. After an initial gas test to evaluate 96 h gas production profiles of haulms with and
without polyethylene glycol (PEG), the time to half maximal gas production was calculated
and a second incubation conducted with fermentation stopped at substrate specific half
time (t1/2) and 24 h for each substrate. True DM degradability was measured from incubated
residues and combined with gas volume to estimate the partitioning factor. Crude
protein flow to the duodenum was estimated by combining gas volume with the measured
ammonia nitrogen in the incubated fluid. Addition of PEG did not have any effect
(P>0.05) on all the variables determined. Interaction between group (improved vs. commercial)
and season was observed for CP (P=0.002), lignin (P=0.003) and hemicellulose
(P=0.030) contents of the haulms. A group×season interaction was also observed for some
of the variables at both substrate specific t1/2 and 24 h. Commercial cowpea haulms had
greater (P=0.002) microbial mass and produced less (P<0.05) methane than the improved
cowpea haulms. The improved cowpea haulms were less (P<0.001) degraded in the rumen
and as a result ensured greater (P<0.001) amount of uCP. The results validated that cowpea
haulm is an important agro-based by-product that is adequate in protein and energy to
sustain ruminant animal production in Nigeria and other Sub-Saharan African countries
during the extended dry season.