problem in managing the prickly spines on the Mimosa pigra (K. Borin 1999)
invasive weed. Or a valuable feed for goats
| Livestock Research for Rural Development 33 (8) 2021 | LRRD Search | LRRD Misssion | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
Goats are sensitive ad intelligent animals as it concerns their feeding behaviour, an important feature that merits recognition by researchers and farmers charged with making decisions about their feeding system and associated welfare. Feeding fresh cassava foliage instead of sun-dried cassava foliage: reduced gas production in the rumen, increased DM intake and lower proportion of methane on the gas. The same effects are produced when equal proportions of sweet and bitter cassava foliage replace sweet cassava alone.
It is hypothesized that the reduction in the substrate fermented in the rumen leads to an increase in the escape of optimally fermentable substrate to the lower gut where the products of their digestion lead to increases in amino acids and glucose precursors at sites of metabolism.
Keywords: bypass protein, fermentation, gas production, methane, propionate
Goats are browsing animals and prefer to select their diet from the available resources. This characteristic of goats is well understood by farmers who manage goats for their livelihood (Photo 1). This goat farmer in Cambodia appreciates the selective characteristics of goats and their capacity to select the leaves and fine stems from an apparently low nutritive value resource such as Mimosa pigra (Photo 2). The encounter with the farmer provided the stimulus for a series of experiments designed to take advantage of this selective characteristic of goats.
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| Photo 1.
This lady farmer in Cambodia understands that goats are
browsers and have no problem in managing the prickly spines on the Mimosa pigra (K. Borin 1999) |
Photo 2. Learning from the farmer: Mimosa pigra is invasive weed. Or a valuable feed for goats |
In the follow-up experiment in Cambodia, the foliage from three trees was offered in different ways to confined goats (Photo 2) by suspending the branch above the feed trough, by placing the branch freely in the feed trough, or by feeding only with leaves after stripping them from the branches. There were major differences in the response of the goats to the different methods of feeding. When the branches were suspended in the trough the goats are faster (Figure 1).they consumed more dry matter (Figure 2) and they retained more nitrogen (Figure 3). These findings confirm what the farmer had learned by experience that goats are selective and this trait is facilitated by offering their feed in the form of foliage so that they could select the components of highest nutritive value and that the branches should be suspended to facilitate the process of selection.
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| Figure 1.
Goats can eat faster when foliage is hanging rather than
offered the leaves that had been separated from the branches (Theng Kouch et al 2003) |
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Figure 2.
Goats consume more feed DM when foliage is suspended above the feed trough (Theng Kouch et al 2003) | Figure 3.
Goats retain more nitrogen (grow faster wen) when tree
foliages are suspended above the feed trough (Theng Kouch et al 2003) |
Similar experiments in the Livestock Research Center in Laos (Figure 4) and the National University of Laos (Figure 5) confirmed the experience in Cambodia. Responses of the goats to suspending Stylosanthes, a prostrated legume, were similar to those observed with the forage treeGliricidia sepium. The response of goats to forage for the fruit tree Artocarpus heterophyllous was even more drastic with the goats eating 10% more dry matter when the foliage was suspended compared with leaves fed alone in the feed trough (Figure 5).
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| Figure 4. DM intake (% of Live weight) by goats offered Stylosanthes or Gliricidia as foliage hanging or placed in the feed trough, or as leaves in the feed trough |
Figure 5. Goats eat 100% more dry matter when Jackfruit is offered as a “branch” rather than as separated leaves (Ammaly and Kaensombath 2006) |
Hanging foliages in “branches” (Photo 3) is labour-intensive. The suspended “rack” traditionally used for feeding “hay” to horses in Europe was adapted for feeding foliages to goats in Colombia (Photo 4).
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| Photo 3. Foliage (Morus alba) is suspended in the goat pen in a farm in Colombia (Preston 2005) | Photo 4. A more convenient way to offer foliages to goats (Preston 2007) |
Our interest in feeding cassava foliage to goats was stimulated by the observations that goats were effective free of intestinal parasites when there was 100% cassava foliage. (Figure 6). It was hypothesized that cassava stems served as a barrier to the migration of infective larvae to the leaves. However, the reduced EPG values when cassava was fed as a supplement to grass, indicate a direct effect of compounds present in casava as affecting the viability of gastro-intestinal nematodes.
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| Figure 6.
EPG in goats supplemented with cassava foliage alone, mixed with grass or grass alone (Seng Sokery and Preston 2003) |
Repeated harvest at two-month intervals (Photo 7) was shown to be a sustainable management strategy over a period of at least 2 years provided there was support to soil fertility with regular application of goat excreta or biodigester effluent (Preston and Rodriguez 2004).
The initial observations on feeding cassava foliage to goats that they: “reduced gastric nematode parasites” led to studies with cassava foliage as a potential source of “bypass” protein to supplement basal diets of sugar cane and Gamba grass (Andropogon gayanus cv. Kent). The cassava foliage and Gamba grass were from plots harvested after 8 weeks of re-growth, the sugar cane stalks were from mature plants (about 10 months regrowth). The effect of sun-drying the cassava foliage was to increase the DM intake (Figure 7), decrease the live weight gain (Figure 8) and increase the amount of feed DM required per unit live weight gain (Figure 9). The interpretation of these findings is that the presence of the hydrocyanic glucosides (the amounts of which are reduced by sun-drying) is beneficial to the growth and feed conversion of the goats and has no apparent detrimental effects on their health. Sugar cane appeared to be a better basal diet than Gamba grass in that it supported a similar rate of live weight gain but with better feed conversion.
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| Photo 5.
Cassava foliage is ready for harvest after 2-months of regrowth (Preston and Rodriguez 2004) |
Figure 7.
Effect of sun-drying cassava foliage on feed DM intake of
goats fed basal diets of sugar cane or Gamba grass (Kounnavongsa et al 2010) |
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| Figure 8. Effect of sun-drying cassava foliage on live weight gain of goats fed basal diets of sugar cane or Gamba grass (Kounnavongsa et al 2010) | Figure 9. Effect of sun-drying cassava foliage on feed conversion of goats fed basal diets of sugar cane or Gamba grass (Kounnavongsa et al 2010) |
The next step was to set an in vitro rumen incubation with of understanding why sun-drying the cassava foliage should have a negative on the growth performance of the goats and to make a more contrasting difference in the composition of the basal diet by comparing sugar (molasse) and starch (cassava root) as contrasting basal diets. The results from the in vitro incubation revealed major differences among the treatments. Methane production was lower when: cassava root pulp rather than molasses was the basal substrate, when the cassava foliage was supplied a fresh rather than sun-dried and when it was from a bitter rather than a sweet variety (Figure 10).
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| Figure 10.
Effect on methane production in vitro incubation
of contrasting substrates (starch vs sugar), and supplements
(sweet vs bitter cassava foliage) and treatment of the cassava foliage (fresh or sun-dried) (Vor Sina and Preston 2016) |
The next experiment explored the possibility of using cassava foliage as the basal diet of growing goats in a comparison with water spinach as contrasting sources of foliage with no known content of secondary phenolic compounds and therefore with protein of high solubility. A contrasting treatment across both foliages was a supplement of brewers’ grains as a source of prebiotic expected to interact positively with the cassava foliage as reported by Binh et al (2015). In both cases, the foliages were present to the goats by suspended them above the feed trough.
The greater degree of response to the addition of Brewers’ grains on the cassava diet exceeded expectations (Figures 11-14). The brewer's grains had a minimal effect on the diet based on the water spinach diet but improved by 100% the weight of the goats fed cassava achieving a growth rate of 160 g/d. The interaction between supplementation with Brewer's grains and the nature of the basal diet was evident in most of the measured responses except for digestibility for which was slightly improved by brewers’ grains on the cassava diet but was not changed on the water spinach diet (Figure 14).
It is hypothesized that the improvement in live weight gain and feed conversion brought about by Brewer's grains on the cassava diet was a reflection of a greater supply of glucogenic precursors at sites of metabolism. This proposal is supported by the results of a parallel study in which it was shown that there were major differences in the production of methane when cassava foliage was replaced by water spinach as the protein source and when Brewer's grains were added to the substrate (Figures 15-16). The reduction in rumen methane attributed to cassava foliage replacing water spinach and to supplementation with Brewers’ grains would be expected to result in an increase in the proportions of propionic acid in the rumen and therefore improvements in growth and feed conversion but not in digestibility. The interpretation of the findings that proximal analysis can give an estimate of the potential nutritive value of a feed will not predict the degree to which that potential will be reflected in improved productivity and better feed utilization. As we discussed in an earlier review, in vitro incubations that measure methane production from the proposed dietary intervention are the most reliable guide to potential benefits from dietary manipulations.
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| Figure 11.
Effect of brewers’ grains on DM intake goats fed diets of cassava foliage or water spinach (Sina et al 2017) |
Figure 12.
Effect of brewers’ grains on live weight gain of goats fed diets of cassava foliage or water spinach (Sina et al 2017) |
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| Figure 13.
Effect of brewers’ grains on DM digestibility in goats fed
diets of cassava foliage or water spinach (Sina et al 2017) |
Figure 14.
Effect of brewers’ grains on N retention in goats fed
diets of cassava foliage or water spinach (Sina et al 2017) |
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| Figure 15.
Effect of brewers’ grains on gas production in an
in vitro incubation of a diet of cassava root-urea supplemented with brewers’ grains ad water spinach (Sina et al 2021) |
Figure 16.
Effect of brewers’ grains on methane in the gas in an
in vitro rumen incubation of a diet of cassava root-urea supplemented with brewers’ grains ad water spinach (Sina et al 2021) |
It is well understood that this classification of cassava varieties relates principally to the relative concentrations of cyanogenic glucosides (Figure 17) that are re hydrolyzed to toxic hydrocyanic acid in the digestive tract of animals and people. Sweet varieties of cassava have been developed exclusively for cassava that will enter the human food chain. Bitter varieties are those that have been selected/developed for industrial production of starch because of their higher yields. The association between yield potential and content of HCN precursors may be due to the potential resistance that the cyanogenic glucosides provide against attack by insects.
The reality is that foliages from bitter varieties of cassava will cause toxicity if fed as the sole diet of ruminants and may decrease animal performance when fed at lower levels (Binh et al 2015; Phanthavon et al 2000). In this context are the demonstrated benefits to be gained from respecting animal “wisdom”!!. Thus, offering growing goats the “opportunity to select” their diet revealed interesting results: the goats with free access to foliages of both sweet and bitter varieties demonstrated their “wisdom” by preferring to consume equally quantities of the sweet and bitter varieties (Figure 19). Even more interesting was the finding that goats with free access to both sweet and bitter cassava foliage consumed more feed and had a superior growth rate than goats fed only the sweet variety (Figure 20). Moreover, the goats that had free access to both sweet and bitter varieties ate more feed DM (Figure 19) and retained more nitrogen and once grew faster than goats that only had access to the sweet variety (Figure 20).
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| Figure 17. HCN equivalent in petiole and leaf from the foliage of sweet and bitter varieties of cassava |
Figure 18. Condensed tannin in petiole and leaf from the foliage of sweet and bitter varieties of cassava |
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| Figure 19. Goats with free access to foliage of sweet and bitter cassava varieties eat equal quantities of each |
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| Figure 20. Goats with access to sweet and bitter varieties of cassava foliage consumed more feed DM than when they only had access to foliage of the sweet variety |
Figure 21. Goats retained more nitrogen yet had free access to foliage of both bitter and sweet cassava varieties |
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| Figure 22.
Relationship between methane: carbon dioxide ratio in mixed eructed gas and air and nitrogen retention |
Photo 6.
A Bach Thao goat with free access to both bitter and sweet
cassava foliage at the end of the experiment showing excellent body condition |
It is relevant to speculate on why the goats consider that a 50:50 combination of bitter and sweet cassava foliage was more suited to their nutritional requirements than a diet of 100% sweet cassava. We have shown that nitrogen retention (= growth rate) is increased when methane emissions are reduced). In vitro studies have shown that methane production is reduced and propionate proportions in rumen VFA are increased when the sole protein source in the diet is the leaf of bitter rather than sweet cassava. It would appear that some feedback mechanism related to the presence/action of the cyanogenic glucosides plays a role in determining the feeding behaviour of the goats.
We hypothesize that the effect of the cyanogenic precursors is to depress slightly the overall fermentation in the rumen (see Figure 14) with the result that more than usual amounts of fermentable substrate escape from the rumen with the anticipated increase in digestible nutrient post-rumen leading to an overall improvement in animal performance. Evidence for such changes is the linear increase in nitrogen retention as the rate of methane emissions decreased (Figure 22). It is relevant to note that there was no difference in the level of condensed tannins (Figure 18) between sweet ad bitter cassava foliages; in contrast, the levels of HCN precursors were twice as high in bitter as opposed to sweet cassava foliage (Figure 17). This is supported evidence that it is the level of HCN precursors that determines the animal response to the contrasting sources of cassava foliage. The apparent good health (“shiny ”coat) of the goats eating the 50:50 combination of sweet: bitter cassava foliage is an indirect indicator of animal “well-being” on this diet.
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Keopaseuht Toum, Ty Chhay, Bouahom Bounthong and Preston T R 2004 Effect of method of offering foliages of Gliricidia sepium and Stylosanthes guianensis CIAT 184 (Stylo) to goats on intake and digestibility. Livestock Research for Rural Development. Vol. 16, Art. No. 31. http://www.lrrd.org/lrrd16/5/toum16031.htm
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Sina V, Preston T R and Tham T H 2017 Brewers’ grains have a synergistic effect on the growth rate of goats fed fresh cassava foliage (Manihot esculenta Crantz) as basal diet. Livestock Research for Rural Development. Volume 29, Article #137. http://www.lrrd.org/lrrd29/7/sina29137.html
Sina V and Preston T R 2021 Methane production in vitro rumen incubation of ensiled cassava root and urea is reduced by supplementation with low levels of Brewers’ spent grains and by supplementation with cassava foliage rather than water spinach. Livestock Research for Rural Development. Volume 33, Article #45. http://www.lrrd.org/lrrd33/3/sina3345.html
Theng Kouch, T R Preston and J Ly 2003 Studies on utilization of trees and shrubs as the sole feedstuff by growing goats; foliage preferences and nutrient utilization. Livestock Research for Rural Development. Volume 15, Article #50. http://www.lrrd.org/lrrd15/7/kouc157.htm
Thuy Hang L T, Preston T R, Ba N X and Dung D V 2018 Digestibility, nitrogen balance and methane emissions in goats fed cassava foliage and restricted levels of brewers’ grains. Livestock Research for Rural Development. Volume 30, Article #68. http://www.lrrd.org/lrrd30/4/thuy30068.html
Thuy Hang L T, Preston T R, Ba N X and Dung D V 2019 Effect of biochar on growth and methane emissions of goats fed fresh cassava foliage. Livestock Research for Rural Development. Volume 31, Article #67. http://www.lrrd.org/lrrd31/5/thuyhang31067.html