| dc.description.abstract | Energy and protein are the major limiting nutrients in dairy production on the
small scale mixed farms in Kenya. Commercial feed supplements are expensive and
therefore multipurpose fodder trees (1-1PT) and forage crops are advocated. as the
alternative supplements, because they are inexpensive, able to provide green forage
even in dry season and have high protein content. These trees have tannins whose
levels, seasonal and altitude distribution have not been established. Previous studies
have indicated that tannins may have either beneficial effects like bloat control and
increased protein bypass, or deleterious effects like the reduction feed intake and
digestibility of protein in animals fed on tanniferous feed. The objectives of this study
were to determine the tannin levels in the MPT, as influenced by altitude and season,
and the effect of these tannins on ruminal degradation and intestinal digestion of the
diet.
Samples of four multipurpose fodder trees and four forage crops viz. leucaena,
sesbania, gliricidia, calliandra, velvet bean, green leaf and silver leaf desmodium and
cassava, were collected at Mombasa (low altitude, below 300 m ASL.) in the wet
season and at Embu (high altitude, 1500 m ASL.) in both wet and dry season. Tannin
and protein content were determined using gravimetric and wet oxidation nitrogen
determination methods respectively. The effect of tannin on protein degradability was
determined by comparing the polyethylene glycol (pEG) treated with untreated forage
samples using the mobile nylon bag technique. The treated and untreated samples were
incubated separately in the rumen of four Holstein cows with both rumen and
duodenal cannula for 0, 6, 12, 24, 48 and 96 hours. Afterwards two sample of each
species from time 12 and 24 hours were inserted into the intestine through duodenal
cannula, and recovered from the feces. The dry matter (DM) and protein of samples
recovered from the rumen and feces were determined and these values were fitted in a
non linear regression equation P = a + b( 1-e-ct).
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The results indicated that the MPT had ytterbium-precipitatable tannins
ranging from 16.08 (±2.39)% of the DM in Gliricidia sepium to 30.31 (±2.42)% in
Desmodium. intortum. The tannin content varied significantly (P<0.05) with species.
The altitude did not have significant effect on tannin content, but tannins within
species behaved differently with season. The protein content differed significantly
(P<0.05) with species. Proteins were significantly (P<0.05) higher in wet than in the
dry season. The altitude had no effect on protein content. The tannin : protein ratio
also varied significantly (P<0.05) with species. Species also had a significant
interaction with season.
Tannins significantly (P<0.05) reduced the rumen effective degradability of
both DM and crude protein in all species, resulting in large quantities of undegraded
dietary nitrogen(N). Tannin also significantly (P<0.05) decreased the total tract
digestion of the DM (DMD) and depressed the digestible crude protein (DCP) of
leucaena, calliandra, cassava and D.intortum, but had no effect on gliricidia, sesbania
and velvet bean DCP. A large proportion of the rumen undegraded dietary protein that
reached the intestines was degraded in most species except calliandra. Tannin
significantly (P<0.05) altered the degradability constants a, b, and c for both DM and
CP by reducing fraction a and the rate of degradation c and increasing the b fraction.
From the study it was concluded that the MPT and forage crop species, despite
their high protein content, are not good protein supplements. Their tannins reduce
both the CP digestibility and the DM degradability in the rumen. Lastly, potentially
viable treatments that reduce the effect of tannin on digestibility are suggested. | en |
