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Evaluation of sorghum–soybean (Sorghum bicolor (L.) Moench – Glycine max (L.) Merr.) silage as ruminant feed

(2011)
Author
Promoter
(UGent) and Andrés Castro Alegria
Organization
Abstract
The development of tropical ruminant production is a challenge for farmers from these regions due to several climatic factors directly or indirectly affecting ruminant productivity. One of the challenges concerns the lack of feed during a long period with shortness of rainfall. Thus, a stable feed quality is required throughout the year in which silage plays an important role. However, not all forages are adequate to ensile or as ruminant feeds; e.g., grasses, due to their low crude protein contents and legumes due to their bad fermentation quality when ensiled. Sorghum might be an option for conservation as it shows relatively high crop yields and ensilability, combined with acceptable energy values. However, sorghum silages are low in protein. Hence, combined silage of sorghum and legumes could be an interesting feeding option for ruminants during the Cuban dry season. In this PhD soybean was studied in combination with sorghum, based on previous knowledge of their combined culture. For this a systematic screening of sorghum varieties, proportions and the application or not of additives such as molasses and/or lactobacilli was required. Obviously, large scale silos are inappropriate for this purpose and small or laboratory-scale silos, in which conditions could be controlled better, should be used. Still, laboratory silos might be too laborious when a large number of variables and their interactions are to be evaluated. For this reason, other methods, allowing the evaluation of numerous treatments within a short time period, are required prior to selection for further upscaling. The Rostock Fermentation Test (RFT) was selected for this purpose. Hence, a first aim of this PhD was to assess crop productivity of sorghum in association with soybean. In addition, as second goal, to identify the optimal ratio of sorghum-soybean and the need to use additives like molasses and bacterial inoculants to obtain excellent silage quality. The Rostock Fermentation Test was used for this purpose and its effectiveness was validated using lab scale silages of 30 d. Further, the evaluation of sorghum-soybean (silage) as ruminant feed was approached both, in vitro as well as in vivo. The in vitro rumen fermentation technique allowed the assessment of the nutritional quality of a high number of treatments, whereas an in vivo digestibility trial, including gas collections, was required to assess the energy and N balance on an animal level. Moreover, these measurements allowed to evaluate emissions towards the environment. Chapter 1 is giving a general orientation, describing the Cuban context (agrometeorological conditions, productive indices and characterization of feed systems used during rainy and dry season), challenges in the tropics related to year-round forage availability and the need to store feed for the dry season. Special emphasis was given to literature on grass-legume silages as ruminant feed. Chapters 2 to 4 report the experimental work, evaluating sorghum-soybean silage as ruminant feed, especially for the Cuban dry season. The evaluation included selection of optimal ensiling conditions, monitoring of rumen fermentation characteristics and determination of metabolisable energy and protein value. In Chapter 2, optimal ensiling conditions were assessed based on 72 treatments applied to a RFT. A quadratic multifactorial model was run to assess the response of sorghum proportion (SGP) and water soluble carbohydrate (WSC) on silage characteristics (i.e., pH, NH3-N/N and lactic acid). The multifactorial models allowed to identify the most appropriate sorghum-soybean ratio, as well as to predict minimum SGP or WSC contents to reach target values of silage characteristics. Moreover, quantification of equivalent responses to WSC and SGP allowed to assess their exchange rates. RFT results (i.e., pH and lactic acid) were used to select treatments of acceptable quality for laboratory silages. In both procedures (i.e., RFT and lab scale silos), fermentation of good quality could be produced with both sorghum varieties alone, but combined silages showed improved quality compared to soybean silage (p<0.05), where 0.4 and 0.6 SGP were preferred. Addition of WSC and bacterial inoculant further improved silage quality (p<0.05). Outputs of the Rostock Fermentation Test were shown to be quantitatively (pH, lactic acid, acetic acid) to semi-quantitatively (alcohol, lactate to total fermentation acids and NH3-N) correlated with output data of lab scale silages. The multivariate surface response curves, developed for the first time, were from Rostock Fermentation Test results gives scope for an improved and integrated treatment of data from this test. Hence, this test fits within the current evolution towards more high throughput procedures within biological testing. In Chapter 3, both sorghum varieties intercropped with soybean showed a higher or similar forage yield as compared with other forages reported in literature. In addition, the selected combined treatments as well as pure sorghum (SG1 (CIAP 2E-95) and SG2 (CIAP 49V-95)) and soybean were assessed by in vitro rumen fermentation (gastight plastic syringes and gastight incubation flasks) both as fresh as well as ensiled forage. All plant material was harvested during the Cuban rainy season. The in vitro incubation (24 h) of ensiled material resulted in lower acetate and higher propionate proportions compared with fresh forages. However, ensiling without molasses and inoculant reduced in vitro short chain fatty acid production and hence, the apparent rumen degradability of organic matter as well as the fermentation rate. As expected, a higher proportion of sorghum (0.6 vs. 0.4) increased the molar propionate proportion (387 vs. 370 mmol/mol total SCFA) and the fractional fermentation rate (0.09 vs. 0.07 /h). SG1 silages produced higher molar propionate proportions (398 vs. 360) and lower acetate proportions (472 vs. 520 mmol/mol total SCFA). In Chapter 4, sorghum (SG1) and soybean were sown, harvested (at pasty grain state), chopped and ensiled (CIAP, Cuba) during the Cuban rainy season. Sorghum (0.60) and soybean (0.40) were ensiled with molasses (35 g/kg FM) and bacterial inoculant (Lactobacillus plantarum, 3×105 colony forming units/g FM). Silos were opened between 162-182 d post ensiling during the Cuban dry season and were fed to six sheep (including two fistulated). Six other sheep (also including two fistulated) were fed sorghum and soybean in the same proportion, but freshly harvested during the dry season. The experiment lasted 21 d (14 d adaptation and 7 d collection period). Silage of excellent quality was produced as reported in Chapters 2 and 3. Compared to fresh forage, feeding the silage diet reduced methane emissions (19.8 vs. 32.8 L/d), increased molar propionate proportions (265 vs. 204 mmol/mol total SCFA) and rumen microbial protein outflow (22.8 vs. 15.9 g N/kg ERDOM). Fresh forage stimulated dry matter intake, but fresh forage available during the Cuban dry season showed lower rumen and total degradability (e.g., less than 90% of DM, OM, GE, CP and cellulose faecal degradability of silage). Further, the higher content of ME (11.2 vs. 10.3 MJ/kg DM) and crude protein digestible at the small intestine (84.7 vs. 56.1 g/kg DM) of the silage would allow a higher milk production (>4.00 kg/d) or daily gain (>230 g/d) as compared with fresh forage available during the Cuban dry season. Finally, a general discussion (Chapter 5) aims at interrelating all data. In agreement with literature, forage yield was not affected by intercropping and resulted in a forage with 40% soybean, which could be used readily to ensile. The combined silage showed acceptable and balanced ME and digestible protein contents, although ratio rumen degradable protein to apparently rumen degradable OM is at the lower limit. The results of this thesis shows the potential of combined sorghum-soybean as an alternative ruminant feed under Cuban – or more general tropical conditions – particularly during the dry season. It opens perspectives for new studies in the field of combined sorghum-legume silages, particularly with legume species which are more adapted to specific tropical regions and/or with higher forage yield.
Keywords
soybean (Glycine max), in vivo digestibility, sorghum (Sorghum bicolor), in vitro degradability, Silage quality, multifactorial models

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Citation

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Chicago
Lima Orozco, Raciel. 2011. “Evaluation of Sorghum–soybean (Sorghum Bicolor (L.) Moench – Glycine Max (L.) Merr.) Silage as Ruminant Feed”. Ghent, Belgium: Ghent University. Faculty of Bioscience Engineering.
APA
Lima Orozco, R. (2011). Evaluation of sorghum–soybean (Sorghum bicolor (L.) Moench – Glycine max (L.) Merr.) silage as ruminant feed. Ghent University. Faculty of Bioscience Engineering, Ghent, Belgium.
Vancouver
1.
Lima Orozco R. Evaluation of sorghum–soybean (Sorghum bicolor (L.) Moench – Glycine max (L.) Merr.) silage as ruminant feed. [Ghent, Belgium]: Ghent University. Faculty of Bioscience Engineering; 2011.
MLA
Lima Orozco, Raciel. “Evaluation of Sorghum–soybean (Sorghum Bicolor (L.) Moench – Glycine Max (L.) Merr.) Silage as Ruminant Feed.” 2011 : n. pag. Print.
@phdthesis{1182441,
  abstract     = {The development of tropical ruminant production is a challenge for farmers from these regions due to several climatic factors directly or indirectly affecting ruminant productivity. One of the challenges concerns the lack of feed during a long period with shortness of rainfall. Thus, a stable feed quality is required throughout the year in which silage plays an important role. However, not all forages are adequate to ensile or as ruminant feeds; e.g., grasses, due to their low crude protein contents and legumes due to their bad fermentation quality when ensiled. Sorghum might be an option for conservation as it shows relatively high crop yields and ensilability, combined with acceptable energy values. However, sorghum silages are low in protein.
Hence, combined silage of sorghum and legumes could be an interesting feeding option for ruminants during the Cuban dry season. In this PhD soybean was studied in combination with sorghum, based on previous knowledge of their combined culture.
For this a systematic screening of sorghum varieties, proportions and the application or not of additives such as molasses and/or lactobacilli was required. Obviously, large scale silos are inappropriate for this purpose and small or laboratory-scale silos, in which conditions could be controlled better, should be used. Still, laboratory silos might be too laborious when a large number of variables and their interactions are to be evaluated. For this reason, other methods, allowing the evaluation of numerous treatments within a short time period, are required prior to selection for further upscaling. The Rostock Fermentation Test (RFT) was selected for this purpose. 
Hence, a first aim of this PhD was to assess crop productivity of sorghum in association with soybean. In addition, as second goal, to identify the optimal ratio of sorghum-soybean and the need to use additives like molasses and bacterial inoculants to obtain excellent silage quality. The Rostock Fermentation Test was used for this purpose and its effectiveness was validated using lab scale silages of 30 d. 
Further, the evaluation of sorghum-soybean (silage) as ruminant feed was approached both, in vitro as well as in vivo. The in vitro rumen fermentation technique allowed the assessment of the nutritional quality of a high number of treatments, whereas an in vivo digestibility trial, including gas collections, was required to assess the energy and N balance on an animal level. Moreover, these measurements allowed to evaluate emissions towards the environment. Chapter 1 is giving a general orientation, describing the Cuban context (agrometeorological conditions, productive indices and characterization of feed systems used during rainy and dry season), challenges in the tropics related to year-round forage availability and the need to store feed for the dry season. Special emphasis was given to literature on grass-legume silages as ruminant feed.
Chapters 2 to 4 report the experimental work, evaluating sorghum-soybean silage as ruminant feed, especially for the Cuban dry season. The evaluation included selection of optimal ensiling conditions, monitoring of rumen fermentation characteristics and determination of metabolisable energy and protein value.
In Chapter 2, optimal ensiling conditions were assessed based on 72 treatments applied to a RFT. A quadratic multifactorial model was run to assess the response of sorghum proportion (SGP) and water soluble carbohydrate (WSC) on silage characteristics (i.e., pH, NH3-N/N and lactic acid). The multifactorial models allowed to identify the most appropriate sorghum-soybean ratio, as well as to predict minimum SGP or WSC contents to reach target values of silage characteristics. Moreover, quantification of equivalent responses to WSC and SGP allowed to assess their exchange rates. RFT results (i.e., pH and lactic acid) were used to select treatments of acceptable quality for laboratory silages. In both procedures (i.e., RFT and lab scale silos), fermentation of good quality could be produced with both sorghum varieties alone, but combined silages showed improved quality compared to soybean silage (p{\textlangle}0.05), where 0.4 and 0.6 SGP were preferred. Addition of WSC and bacterial inoculant further improved silage quality (p{\textlangle}0.05). Outputs of the Rostock Fermentation Test were shown to be quantitatively (pH, lactic acid, acetic acid) to semi-quantitatively (alcohol, lactate to total fermentation acids and NH3-N) correlated with output data of lab scale silages. The multivariate surface response curves, developed for the first time, were from Rostock Fermentation Test results gives scope for an improved and integrated treatment of data from this test. Hence, this test fits within the current evolution towards more high throughput procedures within biological testing.
In Chapter 3, both sorghum varieties intercropped with soybean showed a higher or similar forage yield as compared with other forages reported in literature. In addition, the selected combined treatments as well as pure sorghum (SG1 (CIAP 2E-95) and SG2 (CIAP 49V-95)) and soybean were assessed by in vitro rumen fermentation (gastight plastic syringes and gastight incubation flasks) both as fresh as well as ensiled forage. All plant material was harvested during the Cuban rainy season. The in vitro incubation (24 h) of ensiled material resulted in lower acetate and higher propionate proportions compared with fresh forages. However, ensiling without molasses and inoculant reduced in vitro short chain fatty acid production and hence, the apparent rumen degradability of organic matter as well as the fermentation rate. As expected, a higher proportion of sorghum (0.6 vs. 0.4) increased the molar propionate proportion (387 vs. 370 mmol/mol total SCFA) and the fractional fermentation rate (0.09 vs. 0.07 /h). SG1 silages produced higher molar propionate proportions (398 vs. 360) and lower acetate proportions (472 vs. 520 mmol/mol total SCFA).
In Chapter 4, sorghum (SG1) and soybean were sown, harvested (at pasty grain state), chopped and ensiled (CIAP, Cuba) during the Cuban rainy season. Sorghum (0.60) and soybean (0.40) were ensiled with molasses (35 g/kg FM) and bacterial inoculant (Lactobacillus plantarum, 3{\texttimes}105 colony forming units/g FM). Silos were opened between 162-182 d post ensiling during the Cuban dry season and were fed to six sheep (including two fistulated). Six other sheep (also including two fistulated) were fed sorghum and soybean in the same proportion, but freshly harvested during the dry season. The experiment lasted 21 d (14 d adaptation and 7 d collection period). Silage of excellent quality was produced as reported in Chapters 2 and 3. Compared to fresh forage, feeding the silage diet reduced methane emissions (19.8 vs. 32.8 L/d), increased molar propionate proportions (265 vs. 204 mmol/mol total SCFA) and rumen microbial protein outflow (22.8 vs. 15.9 g N/kg ERDOM). Fresh forage stimulated dry matter intake, but fresh forage available during the Cuban dry season showed lower rumen and total degradability (e.g., less than 90\% of DM, OM, GE, CP and cellulose faecal degradability of silage). Further, the higher content of ME (11.2 vs. 10.3 MJ/kg DM) and crude protein digestible at the small intestine (84.7 vs. 56.1 g/kg DM) of the silage would allow a higher milk production ({\textrangle}4.00 kg/d) or daily gain ({\textrangle}230 g/d) as compared with fresh forage available during the Cuban dry season. 
Finally, a general discussion (Chapter 5) aims at interrelating all data. In agreement with literature, forage yield was not affected by intercropping and resulted in a forage with 40\% soybean, which could be used readily to ensile. The combined silage showed acceptable and balanced ME and digestible protein contents, although ratio rumen degradable protein to apparently rumen degradable OM is at the lower limit. The results of this thesis shows the potential of combined sorghum-soybean as an alternative ruminant feed under Cuban -- or more general tropical conditions -- particularly during the dry season. It opens perspectives for new studies in the field of combined sorghum-legume silages, particularly with legume species which are more adapted to specific tropical regions and/or with higher forage yield.},
  author       = {Lima Orozco, Raciel},
  isbn         = {9789059894259},
  keyword      = {soybean (Glycine max),in vivo digestibility,sorghum (Sorghum bicolor),in vitro degradability,Silage quality,multifactorial models},
  language     = {eng},
  pages        = {VIII, 161},
  publisher    = {Ghent University. Faculty of Bioscience Engineering},
  school       = {Ghent University},
  title        = {Evaluation of sorghum--soybean (Sorghum bicolor (L.) Moench -- Glycine max (L.) Merr.) silage as ruminant feed},
  year         = {2011},
}