Nutritive value and manure quality in supplemented maize stover and grass hay diets for ruminants.
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Date
2007
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Abstract
Production of ruminants is highly dependent on utilization of roughages. In tropical regions,
particularly Sub-Saharan Africa, the roughages are predominantly of poor quality due to high
fibre and low protein content. For these reasons supplementation with protein sources and
other feeds with high degradability is essential. Maize is an important cereal in the world, and
in Africa it produces the highest amount of crop residue. The stovers left after harvesting maize
grain are potentially an important feed resource. The overall goal of this study was to identify
nutritive attributes of diets comprised of maize stovers or grass hay and their mixtures with
different protein supplements for ruminant production, and to determine the influence of the
diets on manure quality.
There were three different roughages and three different protein supplements used in the study.
The roughages were grass hay and maize stovers harvested when the grain was at milk stage or
when the grain was dry (approximately 80% DM content).The roughages were characterized
by high fibre and low protein content. The protein supplements included lucerne, Sericea
lespedeza and sunflower oil cake. Although lucerne has been widely used as a model protein
source for ruminant production there are agronomic and climatic limitations which constrain its
widespread use, particularly in smallholder systems. Hence there is a need for alternative
protein sources such as those included in the present evaluation.
There were three sets of investigations carried out: The first set involved laboratory chemical
composition and in vitro rumen fermentation of feeds using automated gas production
technique (IVGPT). Over forty feed rations were evaluated. Multivariate cluster analysis was
performed to create clusters of diets exhibiting homogeneous nutritive characteristics from
IVGPT measurements. The diets were grouped into three different clusters. Ten diets were
selected, with each cluster represented, and tested in a second set of investigations. These
investigations involved conducting feeding trials using Damara rams. Data collected included
intake, digestibility, weight gain and manure (faeces) production. The third set of
in
investigations involved manure quality analyses. This was done by determining the mineral
composition and nutrient release, particularly nitrogen mineralization. The relationships among
chemical composition, IVGPT, in vivo and manure quality measurements were determined.
Models to predict in vivo performance from chemical composition and IVGPT measurements
were derived.
Maturity stage influenced the nutritive characteristics of the forages whereby both maize
stovers and lespedeza depreciated in quality with age, but the effect was small in the stovers
with regard to degradability. The stovers harvested at grain milk, stage showed superior
nutritive quality over stovers harvested at dry stage by having higher soluble carbohydrate,
lower fibre content and shorter lag time (time taken for microbes to colonize and begin
fermenting the substrate) under in vitro fermentation.
The positive effects of supplementation with lespedeza included enhancing fermentation of
fibre fraction of and decreasing lag time. However, increasing the ratio of lespedeza caused a
decrease in degradability, and this was attributed to the presence of tannins in lespedeza.
In vitro gas production technique (IVGPT) is currently one of the most widely used methods in
ruminant feed evaluation. It measures the gas production arising from fermentation of feeds,
and the degradability can be measured by weighing the residues left at the end of incubation.
Gas production profile from IVGPT can be fitted in models to derive parameters of
fermentation kinetics. Although IVGPT can give several nutritive measurements to help in
understanding the fate of substrates in the rumen, this study obtained inconsistent and
confounding results in some parameters. These included gas volume, microbial yield and
degradability:gas production ratio or the partitioning factor-PF (mg of DM Degraded/ml of gas
produced). On the other hand, it was found that time taken to produce half of the maximum gas
(T (1/2)) was consistent across rations. The degradation efficiency factor (DEF), calculated as the
ratio of degraded material : gas produced X T(1/2), was also consistent across rations. These
parameters therefore showed potential of being useful to include as indices for evaluating
ruminant diets.
The study demonstrated that the measurements derived from gas production technique can be
used in multivariate cluster analysis to logically separate feeds into distinct homogeneous
groups of nutritive characteristics, and this was helpful in identifying diets for the in vivo trial.
The directly measurable variables from in vitro gas production technique which significantly
contributed to distinctiveness of the clusters included degradability, microbial yield, T(1/2), PF
and DEF. Other significant distinguishing variables for the clusters were derived from kinetic
of gas production. They included lag time, gas from the Fibre or soluble fraction of the feed
and the rate of gas production from the fibre fraction.
Diets induced different performances by sheep, with the best (60:40 grass:sunflower cake)
having an intake of 43 g DM/kg liveweight and weight gain of 172 g/d. The poorest
performance was obtained in 60:40 milk stage maize stover:lespedeza diet where the intake
was 25 g DM/kg liveweight and marginal weight loss of 11 g/d was recorded.
Evidence in the literature indicates that lespedeza has a great potential due to adaptation to
poor climate and low inputs requirements. Though not determined in this study, the major
limitation to lespedeza nutritive value is high tannin content. Reports in the literature indicate
that presence of tannins can be of nutritional and health benefits, and negative effect of tannins
can be moderated through use of chemical additives. Also, there are reports indicating that
lespedeza can be invasive, hence its cultivation may require effective control. Further work is
recommended to investigate means of optimizing lespedeza utilization in ruminant production
systems, particularly where it can have climatic and economic advantages.
Ideally, evaluation of diets should be done by conducting in vivo trials. However, in vivo trials
are widely considered to be impractical due to many reasons including high costs, animal
welfare and inflexibility. In vitro methods are therefore widely used as alternative to mimic and
predict what would happen in vivo. This study showed that in vivo performance of sheep was
predictable with high precision (R(2) = 0.75-0.85 for intake, 0.70-0.89 for Digestibility and 0.77-
0.82 for weight gain) by use of models combining chemical composition and IVGPT
measurements. The important chemical composition measurements included fibre (NDF or
ADF) and protein contents, while important IVGPT measurements included degradability (true
or apparent), T(1/2) and DEF. There were confounding factors affecting the validity of gas
volume, microbial yield and PF measurements as predictors of nutritive value. Consequently,
these measurements lacked consistency and generally had poor relationships with in vivo
measurements.
Drying fresh manure caused 25 to 89 % loss of ammonium (NH4
+), emphasising the need to
avoid drying manure in order to maximise the quality. Mineralization results showed that
manure from diets with crude protein content above 170 g/kg can be similar to limestone
ammonium nitrate (LAN) fertilizer in supplying N. Notwithstanding, the manures would have
additional advantage of improving soil humus and supply more nutrients as decomposition
continues.
In the overall, the results demonstrated that maize stover or grass hay supplemented with
sunflower cake or lucerne can support high ruminant (sheep) production while at the same time
yield good quality manure. For practical purposes, diets containing 20-40% of DM contributed
by these supplements showed high potential in this dual purpose role. The choice between
these two supplements would therefore depend on socio-economic considerations. As for
lespedeza, high tannin content is stipulated to be responsible for depression of microbial
activity, hence nutritive value. However, given that lespedeza may have agronomic and
climatic advantages, plus the fact that the impact of tannin can be ameliorated, it is viewed that
lespedeza has potential to boost productivity in specific situations. Further evaluation of
lespedeza should therefore focus on detailed chemical composition analyses at its different
stages of maturity, in vivo trials using different ruminants and measures to moderate tannin
effects.
Description
Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.
Keywords
Ruminants--Feeding and feeds., Ruminants--Feed utilization efficiency--Mathematical models., Sheep--Feeding and feeds., Sheep--Feed utilization efficiency., Forage plants., Feeds--Composition., Theses--Animal and poultry science.