Physiological aspects of the use of non-traditional feeds for non-ruminant species

Aspectos fisiológicos de la utilización de alimentos no tradicionales en especies monogástricas

Lourdes Savón Valdés,^I

^IInstituto de Ciencia Animal, Apartado Postal 24, San José de las Lajas, Mayabeque, Cuba.

ABSTRACT

This paper summarizes the studies carried out for 50 years at the Institute of Animal Science, on the use of non-traditional feeds in non-ruminant species and its effect on the physiology of the animal. The results were analyzed in two stages: the first took into account the digestive and metabolic effect of by-products of sugar cane on poultry and pigs; the second studied the influence of the inclusion of bio-transformed feeds, subjected to biotechnological methods, such as solid state fermentation, in the digestive and metabolic processes of non-ruminant species. The effect of using forages composed by grasses, grains and legume forages on the digestive physiology of birds, pigs and rabbits was studied. Other physiological researches were analyzed with protein, energy and mineral sources of national origin and their impact on feeding poultry, pigs and rabbits.

Key words: non-conventional feeds, digestive processes, metabolism, non-ruminant species.

RESUMEN

Se resumen los estudios realizados durante 50 años en el Instituto de Ciencia Animal, acerca de la utilización de alimentos no tradicionales en especies monogástricas y su efecto en la fisiología del animal. Los resultados se analizaron en dos etapas: la primera tuvo en cuenta el efecto digestivo y metabólico de los subproductos de la caña de azúcar en el ganado avícola y porcino; la segunda estudió la influencia de la inclusión de alimentos bio-transformados, sometidos a métodos biotecnológicos, como la fermentación en estado sólido, en los procesos digestivos y metabólicos de especies monogástricas Se estudió el efecto de la utilización de forrajes de gramíneas, granos y forrajes de leguminosas en la fisiología digestiva de aves, cerdos y conejos. Se analizan otras investigaciones fisiológicas con fuentes proteicas, energéticas y minerales de origen nacional y su repercusión en la alimentación de aves, cerdos y conejos.

Palabras clave: alimentos no convencionales, procesos digestivos, metabolismo, especies monogástricas.

INTRODUCTION

At the end of the 80´s and early 90´s, the prices of industrial by-products, like sugar cane molasses, increased, so their use was not feasible in the preparation of diets for pigs and poultry. Under these conditions, alternatives were searched, such as the use of sugar cane meal and other local resources, like meals of legume foliages, foliages and forages of tree and shrub species with good nutritional content, especially protein, but they showed two problems: high fiber levels and occasional representation of secondary metabolites that diminished its nutritional value and affected the digestive and metabolic processes of poultry, pigs and rabbits. All this affected the productive performance of birds, which, due to the nature of their digestive tract, are more sensitive to the effects of fibrous feeds.

In order to achieve an increase in the nutritional quality of these feeds, simple biotechnological processes such as solid state fermentation (SSF) were tested, and the epiphytic flora of the sugar cane was used, with the addition of urea and mineral pre-mixture (Elías et al. 1990), the SSF of temporary legume grains and foliages with strains of cellulolitic fungi (Valiño et al. 2004), and the germination of legume grains (Díaz et al. 2004).

This review deals with the studies on the physiological effect of the use of non-traditional feeds on non-ruminant species, which have been carried out for 50 years at the Institute of Animal Science, designed according to the policy of import substitution that prevailed in Cuba, with the objective of achieving a sustainable animal husbandry.

DIGESTIVE AND METABOLIC ASPECTS OF THE USE OF BY-PRODUCTS FROM THE SUGAR INDUSTRY IN POULTRY AND PIGS

In tropical countries, sugar cane is a food with great economic advantages, because it has no competition with any other crop cultivated by man, from the point of view of efficiency of solar energy collection per surface unit, in an annual cycle for its transformation into carbohydrates.

From the point of view of its industrial exploitation, sugar cane, as a raw material, provides different products such as sugar and sugar cane juice, from which the molasses are obtained: high-test molasses (which contains all its sugars), integral molasses (similar to the previous one, but without eliminating impurities), A and B intermediate molasses (with 75 and 70% of sugar, respectively) and final molasses or C molasses, which only have 58% of sugar, when it is not possible to extract more sucrose. Table 1 shows the composition of the high-test molasses and the final molasses that, from the point of view of their digestive and metabolic utilization, have been the most studied in non-ruminant species.

Initial researches were directed to study digestion and metabolism of carbohydrates in molasses diets for pigs. Several researches were conducted to compare these aspects in growing pigs who received a diet based on high-test molasses (Ly 1971) and on torula yeast respectively, as the only source of protein (Carrillo 1971 and Carrillo and Benavides 1971) in relation to a conventional diet of cereals.

As the most relevant result, it was confirmed that maize was progressively digested in the small intestine and it provided the available glucose to the animal in small amounts during a relatively long period. In contrast, a very different digestion pattern was found when pigs were fed diets based on high-test molasses. A large amount of carbohydrates were available for the animals in a short period of time. This situation was also confirmed indirectly in the peripheral blood by Ly and Velázquez (1970). However, a part of dietary carbohydrates, fructose but not sucrose, escaped from absorption in the small intestine, due to the increased speed of digesta passage.

In the intestinal phase (6 hours after the meal), there was a higher retention of DM for maize (46.1%) compared to the high-test molasses (29.9%). The prececal disappearance of carbohydrates with the diet of high-test molasses (1.99g/kg LW/h) was higher than with maize (0.51 g/kg LW/h). The digest was more humid in all sections of the GIT of pigs fed with high-test molasses, indicating a different digestive pattern regarding maize. Dilution of digesta should be considered by the presence of hypertonic solutions, which can cause certain functional disability in the small intestine, although this organ tends to equalize the osmotic pressure of digesta. Besides the water absorption effect, a higher peristaltic activity could occur. All this confirmed the presence of certain amount of carbohydrates in the caecum, according to Ly (1974).

Boucourt and Ly (1975) found a large microbial population, constituted by lactobacilli, streptococci, yeasts, Clostridia and E. colli, in the stomach and small intestine of pigs, which was associated with large amounts of organic acids, when animals consumed diets based on molasses, with respect to a diet with maize.

Ly and Boucourt (1975) researched the fermentation pattern of organic acids present in the gastrointestinal tract of pigs fed with two carbohydrate sources and found marked differences between them. The colon had the highest content of fermentation products for maize diet, while the high-test molasses produced an unexpected increase in the function of the stomach as virtual fermentation area. The amount of organic acids found in the first part of the tract (stomach and small intestine) exceeded the second (caecum and large intestine). Compared to the diet with maize, the pattern was different. The acetic acid was predominant in the diet of maize in all organs, while the diet with high-test molasses determined a higher proportion of butyric acid.

Ly (1974), after studying the caecal function, confirmed that the levels of short chain fatty acids (SCFA) were higher in a diet with high-test molasses (2mmol/g OM) than in one with maize (0.9mmol/g OM). Therefore, it was inferred fermentation was caused by materials that escaped to digestion in the small intestine (a fraction of dietary fructose and sucrose). The lowest available energy for the host could explain the difference in production and growth indicators (Diéguez and Menchaca 1973), verified among pigs consuming high-test molasses and maize.  

Final molasses is another widely used by-product for feeding pigs. Its use has been limited from the nutritional point of view, due to two simultaneous events: the worsening of performance traits and the occurrence of diarrheas in animals, when it was used at levels greater than 30%. In contrast, the high-test molasses did not determine any laxative effect on recently weaned animals or during growth and fattening stages. At the same time, there was an evident improvement in the performance traits of economic interest (Ly and Castro 1984), when compared with the final molasses.

Several hypotheses were stated to explain the phenomena of liquid feces or diarrhea. Some were attributed to the high content of ashes in the final molasses or to the large amounts of potassium (Velázquez and Preston 1970).  

Ly (1985a) studied the status of Na and K in the large intestine of pigs and demonstrated that the fecal emission, with high or low liquid concentration, could not be interpreted from the presence of Na and K in it. This confirms unsuccessful attempts to demonstrate that high levels of these electrolytes in the diet can provoke diarrhea in pigs or birds. To know exactly the factors involved in the regulatory processes of material exchange between the intestinal lumen and the internal medium, it would be necessary to explore other areas, such as nerve or hormone regulation.

A more coherent hypothesis, regarding the laxative properties of final molasses, was supported on its chemical composition, but it was centered on the fraction of organic matter, which is neither protein nor carbohydrate, and it is been called “non-identified organic substances”, according to Figueroa and Macías (1988). These authors suggested that this fraction could be constituted by compounds similar to pectin, which is not very digestible, so they should be highly hydrophilic compounds, and their permanence in the intestinal lumen demands a very large water flow. This would explain, together with the emission of watery feces, the excessive thirst of pigs that makes them drink a lot of water (Marrero and Ly 1977), besides presenting a determined intake pattern (Ly and Castro 1984). Summarizing, the intestine of pigs receiving final molasses loses its ability to retain digesta, decreases the ability of water absorption, with the following liquid fecal emission. According to Ly (1985b), this is accompanied by an excessively fast digestive flow, like the one verified in the pre-caecal areas.

Regarding the speed of production of SCFA, Ly (1986) confirmed that the determining factor on the fermentative activity in the large intestine was the permanence time of the digestive content in this region of the GIT. It was evident that the SCFA, produced in the large intestine of pigs fed with high-test molasses, had the highest contribution to the energy metabolism of animals. This contribution was lower with maize diet, and significantly smaller with final molasses.

As a conclusion, it was considered that the excessive intake of water with the diet of final molasses led to an accelerated flow of digesta in the ileum (Ly 1985a), and determined the inefficiency in water absorption in the large intestine, due to the absence of production of SCFA in the caecum and colon and, therefore, its poor absorption. 

Ly and Mollineda (1983) found changes in the morphology of the large intestine in diets with final molasses that could explain the lowest digestive use in pigs fed with this feed.

In order to improve the use of nutrients in diets with high amounts of final molasses, Brito et al. (1985) and Díaz and Rodríguez (1987) tested on growth-fattening pigs and pregnant sows, respectively, the addition of different levels of filter cake mud oil (by-product extracted from the process for obtaining cake from sugar cane), which is an energy source, but they did not obtained the expected benefits. Savón (1984) and Rodríguez et al. (1988) the use of meal of bermuda (Cynodon dactylon) hay. These authors obtained that the addition of 5 % of this fiber source decreased the flow speed, favored the water absorption at the level of large intestine and prevented the release of soft feces, which is a characteristic of this diets, without affecting the use of dry matter, nitrogen and energy.

Another important aspect to analyze is that, due to the ingestion of high levels of final molasses and the intrinsic characteristics of this by-product (high content of soluble sugars, low fiber content and excessive content of minerals), some changes in the acid-basic homeostasis could be produced, mainly because of the nature of the products resulting from the metabolic processes. The previous information was studied by Savón (1984) and Savón et al. (1987), who found that high levels of final molasses (up to 71 %) in the diets for growing pigs did not provoke changes in the acid-basic homeostasis until around 8 h after the ingestion, despite the high concentration of dietary magnesium, potassium and carbohydrates.  

Savón et al. (1989) discovered that the homeostatic capacity of pigs is able to regulate the serum profile of electrolytes like potassium and magnesium, despite the pigs ingested several times their requirements in diets with high levels of final molasses. After supplementing the diets of final molasses with phosphorous and zinc, the apparent absorption and retention of calcium, potassium and sodium was not affected. However, the absorption of phosphorous and magnesium increased and the water excretion decreased.

Taking into account these results, the cited authors demonstrated that, in fattening of pigs with final molasses at 30 % or more, it is only necessary to adjust the mineral supplementation to the requirements of zinc and phosphorous, without presenting changes in the indicators of health and blood biochemistry, like total proteins, albumin, hemoglobin, hematocrit, total leukocytes and differential counting. This represents a considerable saving of currency to the country.  

In poultry, studies were focused on the different factors that limit the use of final molasses in the formulation of diets for broilers, which influenced on their poor productive performance.

Álvarez and Ly (1975) conducted preliminary studies to analyze the effect of including different proportions of final molasses/maize, up to replace 54.7% of the DM of the diet by final molasses in the active degradation of the energy components of the ration by the micro-flora within in the pre (crop) and post gastric (caecum) areas of the gastrointestinal tract. Among the most interesting results, it was confirmed that final molasses induced a better flow of digesta in animals receiving this feed, so the crop lost its capacity as reserve organ. The pH values showed differences between crop and caeca, being these last the ones that showed the highest values. In both organs, diets with higher content of final molasses determined higher concentrations of SCFA and lactic acid. In the caeca, mainly, there was an increase of the fermentative activity due to the increase of the unexpected lactate, which could come from pre-caecal areas. This may be a result from the fast flow of digesta reaching these organs, and exceeds the amount that they can absorb or evacuate.

Similar to the observed in pigs, Álvarez (1976a) found that the inclusion of final molasses in diets for broilers caused an increase on the passage speed of digesta through the gastrointestinal tract of animals, with maximum values maximum for the diets with higher percentage of substitution of maize for final molasses. The increase was attributed to some intrinsic factors of the molasses composition (González and Ibañez 1973ab), which originated a higher water intake and generated a decrease of metabolizable energy, as the level of final molasses increased in the ration. In addition, another factor that could influence was the fermentation activity in the crops and caeca of poultry (Alvarez 1975), because high concentrations of lactic acid in the crops affects the intake of animals.

Ibañez and González (1981) analyzed the effect of the inclusion of different levels of final molasses, in the relation between different organs from the digestive tract and weight of the birds (relative weight) and confirmed the previous results. Functional modifications were observed, which were induced by final molasses in the digestive tract of birds. These changes could influence on digestibility and other digestive indicators.

Álvarez (1982) proposed that the lower digestibility of diets with final molasses, combined to a low feed efficiency of birds that consumed this by-product, were the factors that determined the decrease of the apparent retentions of DM, OM and N, as well as low values obtained for the ME of this type of diet (Álvarez  1977). Thus, the animal is able to metabolize 66% of the GE in the diet, where final molasses is the   main energy source, compared to 80% obtained with the maize diet. This seems to be determined by the high fecal humidity and high ash content of feces, as well as the laxative effect observed in animals consuming final molasses.

These results suggested the use of certain additives like formaldehyde and sodium sulfite (Brito and Álvarez 1982) to improve the utilization of dietary energy caused by a higher fermentation in the GIT of birds consuming the highest levels of final molasses. This could contribute to improving the poor conversion and gain values obtained in nutritional experiments, after providing final molasses to the poultry.

In order to reduce the laxative effect of final molasses diets, it was subjected to a thermal treatment and centrifugation, to try to reduce the high ash content (Álvarez 1980), but there was no favorable effect. Final molasses were treated also with sulfuric acid and zeolite at 3 % (Savón et al. 1983), also to reduce its laxative effect. The levels of sodium, potassium and magnesium in the ileum and caeca of birds consuming treated and untreated molasses showed no significant differences. The same occurred with the dry matter from excretions.

Previously, Savón and Álvarez (1982) studied the effect of mineral composition of different levels of a product called dehydrated final molasses (DFM) on the humidity of excretions, excretions of minerals, serum profile of macro-elements and its content in the ashes of the tibias. The product was obtained from drying final molasses with calcium oxide. There was a decrease of the serum profile of Ca, Mg and K with the increase of dehydrated final molasses, while Na and P values showed no significant differences.

There was an increase of Ca, Mg and K excretion in poultry consuming the highest levels of DFM (30, 40 and 50% of DM). The authors recommended not to use high levels of this product in the diet for birds, despite the decrease of humidity in the excretions, because the animals presented bone fragility and disorders due to the excess of consumed calcium. In addition, there are low values of ME in diets with high amount of DFM, associated to ash content, primarily calcium, which is high in the DFM.

The low content of protein on diets based on sugar cane molasses favored the search for alternative protein sources, as a supplement to these diets, in poultry and pigs. There were Saccharomyces (alcohol distillery by-product) and torula yeasts (developed in final molasses), allowing considerable savings of protein sources.

 The first researches on the use of torula yeast, as the only protein source, were conducted by Carillo and Benavides (1971). These authors studied the digestibility and rate of passage through the gastrointestinal tract of pigs consuming diets based on torula/high-test molasses. They found that, although the molasses, as it is known, induces the passage of a large volume of digesta through ileum, this did not affect apparent digestibility of DM and N, probably due to the osmotic effect.

This finding was confirmed when Carrillo (1973) analyzed the proteolysis of Saccharomyces and torula yeasts, for two tests were conducted with pigs provided with a reentrant cannula in the first part of the duodenum and a single cannula in the stomach. The results of both experiences showed evidence of poor digestion of yeasts, and suggested that the favorable effect expected for molasses, after diminishing the speed of stomach emptying due to its osmolarity, was counteracted because of its high buffering ability. The previous results did not allow the pepsin to achieve its optimal pH for yeast proteolysis in the stomach and that around 80% of the ingested nitrogen passed into the small intestine.

Studies on protein digestion in torula yeast, in diets based on high levels of final molasses as an energy component, were conducted by Boucourt (1982). For this, the effect of bonding the pancreas to pigs over 11 weeks old that received these diets was analyzed. It demonstrated that pigs are able to digest 60% of dietary protein, despite the lack of pancreatic juice. This percentage of digestibility represented 81% of the real potential of this indicator for this diet.

As for the amino acid and protein digestibility of torula yeast in pigs fed final molasses, Boucourt (1982) found lower digestibility than those reported for traditional diets. This author also determined the effect of digestibility of protein, amino acids and dry matter in the ileum and feces of pigs consuming torula yeast and molasses. DM, protein and amino acids, except methionine, showed higher digestibility in feces. This may suggest the need to supplement methionine when torula yeast was included as a protein source in diets of final molasses for pigs. However, this author found that the protein digestibility of torula yeast did not increase with the DL-methionine supplementation.

Álvarez (1976c) determined the nutritional value of Cuban torula yeast and stated that it was variable and depended on the substrate of the used strain, but not on the industrial processing. Thus, he found that the nutritional quality did not vary with the drying method (spray or drum). In this sense, the comparative study of lysine availability, suitable indicator for determining its quality, indicated no significant difference among the yeasts produced in different factories of the country (Tillán and Álvarez 1983).

Valdivié (1976) analyzed different levels of inclusion of torula yeast on indicators of productive performance of broilers with potential slow growth, and suggested levels of up to 20%, because higher values deteriorated gain and feed conversion, plus the humidity and sticky consistency presented by the excretions. Precisely, Álvarez (1976c) stipulated that an aspect to be taken into account for including torula in poultry rations was its high content of NPN (12% of Nt expressed as nucleic acids) and its low biological value. Regarding the former, the nitrogen of purine bases is not used by the animal, and uric acid is the final product of catabolism, so when its concentration in blood increases, the bird increases water intake and kidney activity, releases the excess of uric acid. The final result is higher humidity in the excretions when torula is included with more than 20% of DM of the diet and decrease of the performance of production indicators.

Álvarez and Valdivié (1980), to confirm the previous results, determined the effect of the inclusion of 0, 10, 20 and 30% of torula yeast in ME and apparent retention of DM and N in broilers. They found no significant differences of ME among treatments. However, apparent retentions of DM and N decreased from 20% of torula inclusion.

These results differ from those previously stated by Valdivié (1976). The low use of nitrogen from 20% of yeast inclusion could be caused by the already mentioned high content of nucleic acids. Another limiting factor could be not to use DL-methionine as supplement, which is a deficient amino acid in torula yeast, as in the case of diets formulated by Álvarez and Valdivié (1980), in contrast to the positive response to supplementation obtained by Valdivié (1976). However, this last was discarded in researches of Tillán et al. (1984), who found that enzyme activities of protease and trypsin were similar, with DL-methionine supplementation or not in broilers. Apparently methionine deficiency in these diets of torula yeast does not affect the production of proteolytic enzymes. Therefore, differences in N digestibility in diets with high levels of torula are mainly caused by inner characteristics of this protein source. It is important to point out that the nitrogen from the wall remains in a medium resistant to enzyme action (Carrillo 1971), and the nitrogen from nucleic acids is less digestible than the one from protein.

Studies conducted in poultry did not allow to determine the real use of nitrogen in this species. Therefore, Tillán et al. (1986) studied the apparent digestibility of N and DM in diets with the inclusion of 0, 10, 20 and 27% of torula yeast, for replacing soy bean. As a result, they found that the digestibility of these indicators decreased significantly after 10% of yeast in the diet, which could be related to the high water intake of the birds that received high levels of torula yeast. These authors also found a high relation (r=0.83) between water intake and urine excretion. This supports the studies of Lon-Wo and Valdivié (1981), who found a negative relationship between water intake and DM percentage in the excretions.

Considering the increase of prices of sugar cane molasses and its derivative products in the market, researchers evaluated the possibility of using fresh and ground sugar cane meal, without processing, for feeding pigs, in substitution of cereals. Nutritional studies were conducted by Lamazares et al. (1988) and demonstrated that the inclusion of up to 30% of dehydrated sugar cane meal in the diets for pre-fattening pigs for replacing cereals could be feasible, without changing the productive indicators or feed costs per increased kilogram. Sugar cane meal was obtained by steam dehydration method.  Before that, the clean sugar cane was grinded in a mill, without any straw or bud, dried for 6 to 8 h, and, finally, it was grinded.

Undoubtedly, the inclusion of fibrous feeds on diets for pigs, especially in the pre-fattening stage, raises questions as to their effect on the digestive physiology. Thus, researches on the pattern index of intake (Rodríguez et al. 1989) were performed in the fifth week after weaning, and digestive indexes (Rodríguez et al. 1991), from five to nine weeks after weaning, in pre-fattening pigs receiving 0, 20 and 40% of dehydrated sugar cane meal in diets. As a result, intake, speed and frequency of ingestion decreased significantly with the highest level of inclusion of dehydrated sugar cane meal. The level of ingestion and energy dilution were interrelated (r = 0.71, P < 0.001). The inclusion of 20% of dehydrated sugar cane meal did not influence on the intake pattern of pigs. The analysis of digestive indexes (digesta distribution, pH and fermentation of SCFA) in pigs of nine weeks after weaning, receiving 20 and 40% of sugar cane meal in place of cereals in the diet, indicated a faster pre-caecal evolution with the ingestion of sugar cane meal. It also suggested that the inclusion of 20 and 40% of sugar cane meal did not affect the level of fermentation in the tract, nor apparently caused changes in the pH of the digestive content. The previous information confirmed the results of Lamazares et al. (1988) with an inferior level (20%) of dehydrated sugar cane meal in the diets of pre-fattening pigs, and adequate productive performance was achieved.

DIGESTIVE AND METABOLIC ASPECTS OF THE USE OF NEW FEEDS DERIVED FROM SUGAR CANE AND ITS BY-PRODUCTS, SUBJECT TO BIOTECHNOLOGICAL PROCESSES

From the 90´s of last century, the economic crisis in Cuba worsened and became more difficult the acquisition of raw materials for feed production, mainly for non-ruminant species, which, due to their digestive physiology, need cereals such as maize and proteins like soy bean, in order to achieve appropriate growth rates. Therefore, the development of feed resources with domestic alternatives was very important. Elías et al. (1990), considering the abundant amount of nutritional elements within sugar cane and its by-products, developed a technology based on solid state self-fermentation of sugar cane, with the addition of urea and mineral salts. The process consisted on transforming the food energy source in a product enriched with available carbohydrates and nitrogen precipitating to tri-chloride acetic acid (TCA), through a physical and biological process where the microorganisms of sugarcane had an important function. The result was a new protein-energy food, called Saccharina.

As the most relevant aspects of its bromatological composition, these authors found that the product reached between 11 and 16% of CP, superior to the values of cereals such as maize or wheat, and 16 MJ/kg DM of gross energy. The levels of CF ranged between 24 and 25% of the product and most of the CF consisted on cellulose and hemicellulose. This fact  led to nutritional studies, where levels of inclusion were valued as a replacement of cereals in different species: 30% in the feed for post-weaning piglets (Lezcano et al. 1990), 60% of cereals from the supplement in diets based on  B molasses for pigs (Castro et al. 1990), 100% of the cereals for pregnant sows (Díaz et al.1991), 30% in starter diets for geese, and between 40 and 60% in finishing diets for replacing cereals (Valdivié et al. 1990a), and 10% of Saccharina as the limit of inclusion in feed for broilers from 28 to 54 d (Valdivié et al. 1990b).

The first physiological studies were conducted by Ly et al. (1991), in order to determine the nitrogen and energy balance in pigs fed with variables levels of Saccharina (0, 20, 40 and 60% of the diet under dry basis) include on cereal diets. These authors found that, with the increase of Saccharina in the diet, energy and N digestibility, as well as nitrogen retention and energy, expressed as intake percentage, significantly decreased (P <0.001). However, retention expressed as a digestion percentage had less importance for nitrogen (P <0.05) and none for energy. The decrease of nitrogen and energy digestibility is related to the increase of cell wall content. It is known that fiber decreases digestive utilization of energy, which is the immediate cause of these results. The fact that there was no effect of treatment on digested energy retention suggests that the main difference in the energy balance, between cereal and Saccharina diets, lies on its digestive use. This fact implied a change of starch (cereals) per sucrose and cell wall (Saccharina), which modifies the extent and location of fermentation of different types of carbohydrates, with an increase of their function in the large intestine and the native micro-flora in the digestion of different fiber fractions.

The analysis of the previous results suggests that the N digestibility and energy could be the main nutritional limiting aspect for including large amounts of Saccharina on cereal diets for pigs. This was confirmed by Díaz et al. (1992), who assessed the digestibility of energy after replacing feedstuff wheat by 20, 40 and 60% of Saccharina, but in a feeding system that included B molasses as an energy source for developing females. These authors observed the negative effect of Saccharina on energy digestibility, so they recommended the increase of the energy level of diets, when more than 20% of feedstuff wheat is replaced by Saccharina.

Subsequently, Ly and Castro (1995) studied the effect of replacing 20% of wheat meal diets (control) for different types of Saccharina, obtained under pilot plant conditions, b) from sugar cane stems, c) or industrially, from return bagasse pith and sugar cane juice, and d) or with unfermented sugarcane meal, in the balance of N and energy of growing pigs. Energy digestibility was superior in the control, while this indicator did not differ among Saccharina treatments. There was also no effect of treatment on nitrogen balance, retention expressed as intake percentage and digestion. The results of energy balance confirm the previously obtained by Ly et al. (1991). Regarding the status of N, like the results of the authors, there was a redistribution of the routes for removing nitrogen, probably due to differences among treatments regarding the level of dietary fiber. It was concluded that the inclusion of Saccharina on the diet has more influence on the digestive use of energy than in the dietary N for pigs, if the inclusion of this product reaches 20% of the food.

In order to determine protein quality and energy value on diets containing Saccharina for pigs, Ly (1999) performed two experiments. The first experiment was conducted with ileo-rectomized animals and the other with intact animals, which were fed with Saccharina (0, 10 and 20%). This author noted a significant reduction in ileal and total nutrient digestibility, and energy with the increase of Saccharina on the diet. The reduction of nitrogen digestibility in the digestive tract is possibly caused by the increased of bacterial protein synthesis in the caecum and colon. This implies a reduction of non-amino acid nitrogen absorption in the large intestine, which is not useful to the host.

A relevant aspect is that Saccharina caused reduction in the contribution of the large intestine to the total digestion of crude fiber. This means that the biotransformation process, carried out in the stems of sugar cane, had a positive influence on the use of cellulose during pre-caecal digestion, although it is known that fiber degradation does not normally occur in the small intestine of pigs. In addition, the reduction of ileal and total digestibility was accompanied by a tendency towards the increase of daily ileal flow digesta and feces, together with ileal and fecal flow of short chain fatty acids and ammonia, which is a phenomenon attributed to the level of crude fiber in the diet for pigs. It is important to mention the high microbial activity determined by Saccharina in the digestive tract of these animals. In this regard, Rodríguez et al. (2000) found that cellulolitic activity in the caecum of pigs depends on the fiber level and its physical and chemical composition, and it caused by the cellulolitic fungi, and not by bacteria. It means that high levels of fiber in diets that include Saccharina, affect the counts of caecal cellulolitic fungi and the specific activity of cellulase enzyme complex in pigs. Rodríguez et al. (2001) confirmed this statement in further ]]> studies.

The results confirmed the need for low levels of Saccharina in pig diets, in order to avoid a negative effect on nutrient digestibility, which is more remarkable, from an energy point of view, than that of nitrogen in the entire process of digestion of Saccharina in pig diets.

Marrero et al. (1995) and Marrero (1998) analyzed the implications of the use a food with high fiber content, as Saccharina, on poultry physiology. So, these authors determined apparent retentions of DM, N, energy and cell wall components of the plant in broilers consuming different levels (0, 5, 10 and 15%) of industrial Saccharina for replacing maize in diets. Apparent retention of dry matter (ARDM) and apparent retention of neutral detergent fiber (ARNDF) decreased in the diet with 15%, compared to the remaining treatments, while the highest value was obtained in 10% of inclusion of Saccharina. Similar to the results in pigs, the apparent retention of nitrogen (ARN) did not differ among treatments, but the ME decreased as the fiber increased in the diet. The results suggest the use of up to 10% of Saccharina in the ration, so the apparent retentions of nutrients are not affected.

Rodríguez et al. (1996) isolated cellulolitic fungi in the caecum of broilers consuming different levels of fiber provided by Saccharina. This discovery is very important because, until that moment, the main difference between ruminal and caecal flora, and the functioning of both organs, was the absence of fungi and protozoa in non-ruminant species.

The finding of these microbial species in the large intestine completes the possibilities of fiber digestion at this level, which could be important for performing specific nutritional approximations, and for achieving the accurate interpretation of phenomena taking place in the ecosystem.

Marrero et al. (1998) evaluated the possibility of using fecal contents of pigs to determine in vitro digestibility of total dietary fiber in poultry diets. There was an underestimation of the digestibility of CP, DM and energy, when compared to the values obtained in vivo. The apparent digestibilities of NDF were similar to those obtained by Marrero et al. (1995) in broilers. The error was very small among the methods, only 0.99 for NDF digestibility and 69% of the values were similar. The results showed that it was possible to use pig fecal inoculum for simulating digestion studies of dietary fiber in broilers. This is probably caused by the similarity between the fecal ecosystem of pigs and poultry caecum. In addition, this in vitro method was cheaper, when practical conditions do not allow the work with animals.

PROTEIN SUGAR CANE JUICE AND HOMEMADE PROTEIN MOLASSES 

Previous studies have stated that pig production in Cuba mainly depends on the application of feeding systems with a high proportion of national products, and, specially, with the use of low cost protein sources. 

In order to fulfill these needs, Elías et al. (1990) reported the feasibility of obtaining new protein sources from the fermentation of sugar cane and its juice, or from sugar cane molasses (B molasses), with the addition of 2 % of urea and mineral pre-mixture. The products were called protein sugar cane juice “Guarapró” (GP) and homemade protein molasses (MPC), respectively.

Savón et al. (1995a) conducted several studies to understand the implications of ingesting diets with a high inclusion of an unconventional food on nitrogen metabolism of growing pigs. Therefore, these authors replaced 0, 50 and 75% of the protein in feedstuffs for homemade protein molasses and increased fecal nitrogen compounds, leading to low digestive utilization of nitrogen. An interesting fact is that nitrogen retention, from a metabolic point of view, had no variations among treatments. After analyzing the urinary excretion, it increased with the inclusion of homemade protein molasses, which corresponded with the increase of dietary nitrogen intake. The increase of homemade protein molasses in the ration provoked a lower contribution of available protein. As a conclusion, the authors suggested that it is possible to increase the use efficiency of digested nitrogen in growing pigs consuming low levels of available protein, as the one provided by this product. 

However, the protein digested in the large intestine does not contribute to protein synthesis within the animal, so the analysis of digestibility in the ileum is suggested, because it provides better prediction of the value of final use of the protein than fecal data. Considering this fact, Savón and González (1995) evaluated the digestive process and efficiency use of DM and N in the ileum and feces in pigs fed homemade protein molasses as a substitute for soybean in a B molasses system plus feedstuff. As a result, the homemade protein molasses generated an increase of the flow of digesta in the ileum, which determines a lower digestive use of DM and N. Likewise, Savón and González (1996) also analyzed the digestion of other nutrients, such as OM and ashes, and found that the homemade protein molasses generated an increase of OM flow, and, to a less extent, of ashes, while the digestive utilization could diminish in the large intestine.

In other study, Savón et al. (1997) evaluated the use efficiency of MPC and molasses-urea-superphosphate mixture without fermentation, using blood and biological performance of protein metabolism in pigs. Results suggested that the use of molasses-urea-superphosphate mixture without fermentation was not advisable for pigs, and that there was no effect on the productive performance and on blood figures of protein metabolism, when it was replaced by half of the protein provided by soy bean, per homemade protein molasses in a system that included B molasses as energy source. An interesting fact is that these authors observed a remarkable increase (almost the double) of serum urea concentration after replacing half of soy bean by homemade protein molasses without differences among treatments.

The previous results led Savón et al. (1999a) to study the protein quality of homemade protein molasses. Therefore, these authors analyzed different indicators of N metabolism, such as apparent biological value of protein, retained N/digested N, urea concentration in serum and fractioning of urinary nitrogen, which contributes to a better interpretation of these results, when a product of microbial origin was included on the diet. This way, after evaluating 0, 25, 50 and 75 % of substitution of soy bean protein for MPC in a feeding system with raw sugar as energy source, digested nitrogen and nitrogen retention had no differences among treatments, while there was a square regression (r = 0.98 P<0.001) between retained N/digested N (biological value) and the levels of homemade protein molasses. The analysis of urine nitrogen fractions did not show differences among fractions (g/d) for creatinine-N, alpha amino-N, ammonia-N, while the ureic-N increased (P < 0.001) with the level of MPC. A similar response was obtained with the concentration of serum urea.

According to these results, the partial substitution of soy bean protein for that provided by homemade protein molasses generates a decrease of the (apparent) biological value and, therefore, of the quality of this nutrient in rations based on raw sugar.

PHYSIOLOGICAL ASPECTS OF THE USE OF GRAINS AND FORAGES OF SHRUBS, TREES AND TEMPORARY LEGUMES

At the end of the 90´s, Díaz and Padilla (1998) and Díaz (2000) started agronomical researches with temporary legumes, which were based on the scarcity of protein sources and on competence with human consumption, as well as on the increased content of protein and high yields of forages and grains. However, there is a high representation of antinutritional factors so the massive use of these plants is not possible. Some of the studied legumes were Vigna unguiculata (vigna), Lablab purpureus (dolicho), Stizolobium aterrimun (mucuna) and Canavalia ensiformis (canavalia).

In this sense, Díaz et al. (2001, 2002ab) compared the potential of producing forage meals, integral forages and grain meal in varieties of V. unguiculata of grouped maturation (INIFAT 93, Cubanita 666, and Trópico 782) and non-grouped maturation (Habana 82 and Viñales 144A), and determined their bromatological composition and content of antinutritional factors (trypsin inhibitors and tannins). These authors suggested the use of INIFAT 93, among the grouped varieties, and Habana 82, among the non-grouped ones, for running physiological and nutritional studies, with the objective of offering them as non-conventional animal feed under Cuban conditions.

Aguirre et al. (1999) evaluated the protein quality of five varieties of meals of vigna raw grains in growing rats, which received isoprotein and isoenergetic diets. These authors found no differences among them. In addition, the protein quality was similar to that of soy bean grain meal.

The previous results were later confirmed by Lon-Wo et al. (2001), when, in isoprotein diets for broilers, they substituted up to 30 % of protein, at expense of wheat and soy bean, for a meal of raw grains of V. unguiculata var. 93. In its formulation, these researches substituted up to 60 % of soy bean, with favorable economic benefits (Cino et al. 1999). Castro et al. (2002) proposed to substitute up to 20 % of soy bean meal (25 % of the protein of this legume) in growing pigs with up to 30 kg, which implied a decrease of  feeding costs per ton of increase, without having negative effects of antinutritional aspects of the untreated grain.

Aguirre et al. (2002a) evaluated the physiological response of growing rats to the intake of meal of V. unguiculata var. INIFAT-93 raw grains (20, 40, 60, 80 and 100%) in substitution for the meal of commercial soy bean cake, in the morphometry and histology of digestive and accessory organs of the gastrointestinal tract. As a conclusion, these authors stated that it was possible to substitute, physiologically, up to 60 % of commercial soy bean cake for meal of V. unguiculata var. INIFAT-93 raw grains, without affecting the organs related to protein metabolism. A similar response was obtained (Aguirre et al. 2002b) after analyzing the state of protein conversion in these animals through the indicators of blood biochemistry related to this nutrient (total protein, albumin, globulin,  alanine aminotransferase (ALT), and other indicators like serum cholesterol, hemoglobin, hematocrit, and total and differential leucocytes).   

It can be concluded that meal of V. unguiculata var. INIFAT-93 raw grains is a promising source for its use in diets for broilers and growing pigs up to 30 kg, as a substitute for soy bean cake with economic advantages.

Díaz et al. (2002c) also stated the need of performing physiological and nutritional studies with foliage meal, forage or integral forage meals of temporary legumes. An important aspect of these sources is their high fiber content. Therefore, in order to conduct these researches, Savón (2002) analyzed the characteristics of the fiber matrix of these highly fibrous sources. These characteristics included origin, chemical composition, physical properties (particle size, solubility, volume, surface properties like capacity of water adsorption, capacity of cationic exchange and buffer capacity), and others like fermentability and viscosity, and their impact on the digestive physiology of animals consuming them. The use of suitable analytic techniques for studying chemical composition is also important and, in fact, it is a challenge for physiologists to reach a better understanding of fiber function on non-ruminant species.

This author defined the concept of “dietary fiber”, from the nutritional point of view, as a heterogeneous fraction, where the components are resistant to enzyme activity of the digestive tract. There are five main components among them. There are structural polysaccharides, constituting the cell wall of plants (homo-polysaccharides like cellulose and hetero-polysaccharides like hemicellulose and pectin) and forming insoluble carbohydrates or non-starched polysaccharides, gums, which are reserve polysaccharides and lignin, with a phenolic nature and bonds the previous groups. There are also small amounts of other compounds like dextran, inulin, polyphenols and starch. Anyway, fiber is not a simple sum of isolated compounds, but a biological unit. According to the type of plant or feed, their presence will vary, as well as the proportion in which they are combined with their intrinsic properties, which, at the same time, will have a great influence on the digestive physiology of animals. 

Savón et al. (2000) characterized, through the chemical composition and physical properties, the fiber fraction of five varieties of V. unguiculata foliage meal for feeding non-ruminant species. Three of them have grouped maturation (INIFAT 93, Cubanita 666 and Trópico) and two have non-grouped maturation (Habana 82 and Viñales 144 A). As a result, INIFAT 93 showed the highest digestive potentiality due to the low content of cell wall (NDF) and lignin, the lowest solubility of its fiber fraction and low packing volume regarding the other varieties.

Another important aspect for including forage meals in diets of non-ruminant species is the determination of digestibility of its fiber fractions. Martínez et al. (2003) analyzed the possibility of including V. unguiculata var. Blanca on poultry diets. Therefore, these authors determined in vitro total apparent digestibility of nutrients during a specific time, by means of fecal inoculum of pigs. Foliage meal of V. unguiculata var. Blanca was recommended by Díaz (2000), after considering its bromatological composition and good agronomical yield. However, results showed that 32.54 g of this variety could be included on poultry diets, which represents 5.46 g of the protein. This suggests the increase of nutritional values through the use of physical, chemical or biotechnological methods.

Using the method of Verveaker et al. (1989), Dihigo (2004) performed an in vitro simulation of DM digestibility of foliage meal of V. unguiculata var. Habana 82 in the stomach of rabbits, and compared it to other fiber sources like sugar cane meal, and citric meal, as well as citroína, which is a result from the solid state fermentation of citric meal with Aspergillus niger. As a result, this author discovered that Habana 82 foliage meal had lower nutritional quality for its degradation in the stomach of rabbits than other foliage meals. Later, Dihigo et al. (2004) used caecal inoculum of rabbits and, according to the methodology proposed by Pascual et al. (2000), analyzed in vitro digestibility of DM and NDF of four forage plants (Neonotonia wightii, Pennisetum purpurteum, and Lippia dulcis), and compared it to V. unguiculata var. Habana 82.  These researchers also found that vigna showed lower degradability by caecal microorganisms of rabbits, and suggested further studies of biological performance to demonstrate the results.

Regarding the previous, Scull and Savón (2003) determined the content of total polyphenols and condensed tannins of four varieties of V. unguiculata (Habana 85, Cubanita 666, Trópico 762 and Viñales 144a). Habana 82 had the lowest content of total polyphenols (0.332 %) and condensed tannins (0.10 %), but all of the varieties showed potentialities for animal feeding due to the composition of phenolic compounds.

The physical and chemical characteristics of fiber fraction of other foliage meals of temporary legumes (C. ensiformis, L. purpureus and S.aterrimun), a shrub (Trichantera gigantea) and a tree (Morus alba) were determined by Savón et al. (2004), and Savón (2005) analyzed the intrinsic factors (antinutritional factors and dietary fiber) that, according to their chemical nature, source and origin, may have an effect on voluntary intake, flow speed, intestinal morphometry and fermentation, which influence on digestive use of nutrients. Other important factors are the extrinsic ones (fiber level and feeding system, digestion place, species, age, breed and physiological conditions). Table 2 shows some studies conducted with different fiber sources. 

Savón et al. (2007) also suggested the possibility of using temporary legumes (canavalia, mucuna and dolicho) in the phenological state  of integral foliage for poultry feeding, taking into account the nutritional quality of its fiber fraction, because mucuna integral foliage meal, unlike foliage meal of this temporary legume, contains no alkaloids.

In order to diminish antinutritional factors and improve the quality of fiber fraction, Díaz et al. (2004, 2007) proposed a simple biotechnological method: germination, in the case of legumes, in the phenological state of grains. Meanwhile, Valiño et al. (2004, 2014) indicated the SSF with inoculation of strains of T. viride (M5-2 and 137MCX.1), for legumes in the phonological states of foliages and integral foliages.

Regarding this aspect, physiological studies with germinated grains of C. ensiformis and V. unguiculata, offered to broilers, were conducted by Savón et al. (2013) and Martínez et al. (2013), respectively. These researchers concluded that the process of germination in both legumes provides the grain meals with superior nutritional quality to the raw one, so these are more digestible and useable for broilers.

It is necessary to continue the evaluation of these bio-transformed products in other poultry categories and other species like pigs and rabbits.

OTHER PHYSIOLOGICAL RESEARCHES ON MINERAL, ENERGY AND PROTEIN SOURCES OF NATIONAL ORIGIN

During 50 years of development in the Cuban Journal of Agricultural Science, there have also been publications on physiological researchers with other protein energy and mineral sources of national origin, in poultry and pigs.

Royal palm nut was another evaluated source. Ly (2000) and Ly et al. (2000) determined its nutritional value for growing pigs, and suggested that this feed has more values as energy component than as protein source, due to its high digestive usage of ether extract.

Regarding protein sources, Hardy and Elías (1974) developed a method for ensilaging bovine excretions with final molasses and urea. This product was evaluated as protein source in experiments with fattening pigs and female reproducers (Lezcano et al. 1977 and Díaz et al. 1979), together with its nutritional value.  From a biological point of view, it is possible to provide 25 % of manure silage to growing and fattening pigs, in substitution of protein sources. Before gestation, sows cannot receive high levels of manure silage because it produces a delay on growth and on reproductive traits. There have been anatomical and pathological disorders in the liver and kidneys of pigs receiving high levels of manure silage.

Another protein source, evaluated in growing pigs, was fleshing (García and Lezcano 1987), which is a mixture of fat and meat tissue, separated from bovine skins using the tanning process. These researchers substituted protein of diets for fleshing (0, 34, 66 and 100 %) and determined the digestive use of N and its efficiency. As a result, there was a decrease of N retention while the fleshing is unstable in essential amino acids. Therefore, it should be used with quality sources and supplemented with synthetic amino acids.

The aerial part of banana (Musa spp.) is a very abundant residue in tropical areas, where it is usually used as a protein source for feeding pigs and rabbits. Ly et al. (1998) found that ileal digestibility of nutrients decreased with the increase of foliar residues in the feeds. The inclusion of up to 20 % of these residues on molasses diets for pigs had no effect on ileal digestibility of nutrients, although the N usage of this type of biomass is not high.

Alberto et al. (2011) evaluated distillery vinasse as a partial substitute of the protein source for growing pigs. These authors found that it was possible to include 30 % of distillary vinasse on diets for growing pigs without affecting its physiological and metabolic composition.

Regarding mineral sources, Delgado et al. (1988) determined the state of macroelements (Ca, Mg and P) within the blood plasma and bones of broilers, and concluded that it was possible to completely substitute calcium carbonate for entire or ground sea shells (0.2 cm2) on the diets formulated for these birds.

Ly et al. (1996) also analyzed the effect of different deposits of natural zeolite in the country (Tasajeras, La Pita, Chorrillo, Piojillo and San Andrés) and found a beneficial effect of this mineral source on energy and N balance in growing pigs. Zeolite, regardless of the deposit, produced an increase of energy retention and, mainly, of N retention in feed, which could be explained by a low production of ammonia in the intestinal lumen and, mainly, by a low absorption.

In Cuba, salts of Cu and Fe have been obtained as a by-product of the mineral and metallurgic industry, and Savón et al. (1999) evaluated copper and iron sulfates for replacing imported sources in diets for pre-fattening pigs. These authors found that national sources had a high availability of nutrients.

Acosta et al. (2009)  determined the relative availability of phosphorous from Trinidad de Guedes phosphoric rock (a national source of this mineral) and stated that it was similar to a high quality dicalcium phosphate. As an availability criteria, these authors measured ashes from the tibia of broilers. 

FINAL CONSIDERATIONS 

According to the results, the suggestions are the following:

-  Perform an inventory on non-traditional sources existing in each region of the country, which could be included as feed on rations for non-ruminant species, in order to guarantee a sustainable production system.

-  Consider the availability of sources to be used as an important aspect.

-  Characterize its nutritional content, taking into account the advantages and disadvantages of this feed

-  Consider the role of intrinsic (inherent to feed), such as antinutritional factors and high content of cell wall, and extrinsic factors (inherent to the animal) like sex age and feeding system, which influence on the digestive and metabolic use of tropical fiber sources.

-  It is necessary to increase the nutritional value of non-conventional feeds through simple biotechnological processes like solid state fermentation (SSF) and germination, which produce biological changes leading to a more efficient use of feeds.

-  It is essential to perform researches that analyze not only the effect of use of biotransformed or not non-conventional feeds on digestive physiology of non-ruminant species, but also to evaluate metabolic aspects that influence on its use.

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Aguirre, L. A., Savon, L., Dihigo, L. E. & Santos, Y. 1999. ‘‘Protein quality of raw grain meal of five Vigna unguiculata varieties in growing rats’’. Cuban Journal of Agricultural Science, 33 (4): 395–399.

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Received: August 4, 2015
Accepted: October 7, 2015

Lourdes Savón Valdés, Instituto de Ciencia Animal, Apartado Postal 24, San José de las Lajas, Mayabeque, Cuba. Email: lsavon@ica.co.cu