ORIGINAL

Effect of energy sources on the apparent total tract digestibility and excretion of nutrients by bovine cattle

Efecto de fuentes energéticas sobre la digestibilidad aparente total y excreción de nutrientes por bovinos

Laura Romero S,¹* M.Sc, Paulo HM Rodrigues,¹ Ph.D, Carolina T Marino,¹ Ph.D, Lerner A Pinedo,¹ Ph.D, Maurício F Martins,¹ M.Sc, Eduardo CO Cassiano,¹ M.Sc, Flavio Perna Jr,¹ M.Sc.

¹Universidade de São Paulo. Departamento de Nutrição e Produção Animal. Faculdade de Medicina Veterinária e Zootecnia. Campus de Pirassununga. Rua Duque de Caxias Norte, 225, Cep:13635-900. Pirassununga, SP. Brazil.

*Correspondence: laurazootec@hotmail.com

Received: June 2013; Accepted: December 2013.

ABSTRACT

Objective. To evaluate the effect of three energy sources on the intake, total apparent digestibility and excretion of nutrients in cattle diet. Materials and methods. Six ruminally cannulated cows (730 ± 70 kg) were distributed into three treatments in a replicated 3x3 Latin square experimental design, where: (I) Control: Low ether extract diet (3.50% EE); (II) Soybean: High ether extract diet (5.30% EE) with inclusion of 15% soybean and (III) Citrus pulp: Low ether extract diet (3.00% EE) and high pectin involvement with inclusion of 15% citrus pulp. To determine the digestibility of DM and its fractions, chromic oxide was used as a marker. Nutrient excretion was calculated from the digestibility coefficient of each fraction. Results. The soybean treatment reduced (p<0.05) dry matter, crude protein, nitrogen-free extract and organic matter intake and increased ether extract intake. There was no effect (p>0.05) of the energy source on the digestibility coefficients of DM, CP, NDF, EE, NFE or OM. The TDN value was higher for the soybean treatment. The excretion of DM, NFE and OM was lower (p<0.05) for the soybean treatment. All energy sources influenced the excretion of crude protein. Conclusions. The energy sources used did not affect the digestibility of the diets and are indicated as high potential sources to be used in cattle.

Key words: Citrus pulp, digestibility, food consumption, nutrients, ruminants (Source: USDA).

RESUMEN

Objetivo. Evaluar el efecto de tres fuentes energéticas sobre el consumo, la digestibilidad aparente total y la excreción de nutrientes de la dieta en bovinos. Materiales y métodos. Seis vacas (730±70 kg) canuladas en rumen fueron distribuidas en tres tratamientos, en un diseño experimental cuadrado latino 3x3 replicado, a saber: (I) Control: Dieta de bajo extracto etéreo (3.50% de EE); (II) Soya: Dieta de alto extracto etéreo (5.30% de EE) con inclusión de 15% de grano de soya y (III) Pulpa Cítrica: Dieta de bajo extracto etéreo (3.00% de EE) y alta participación de pectina con inclusión de 15% de pulpa cítrica. Para determinar la digestibilidad de la MS y sus fracciones, fue utilizado el marcador de óxido de cromo. La excreción de nutrientes, fue calculada a partir de los coeficientes de digestibilidad de cada fracción. Resultados. El tratamiento con soya redujo (p<0.05) el consumo de materia seca, proteína bruta, extracto no nitrogenado y materia orgánica, de igual manera, incrementó el consumo de extracto etéreo. No no se observó efecto (p˃0.05) de fuente energética para los coeficientes de digestibilidad de la MS, PB, FDN, EE, ENN y MO. El valor de NDT fue mayor para el tratamiento con soya. La excreción de MS, ENN y MO fue menor (p<0.05) para el tratamiento con soya. Todas las fuentes energéticas influyeron en la excreción de proteína bruta. Conclusiones. Las fuentes energéticas utilizadas, no afectaron la digestibilidad de las dietas, y estan indicadas como fuentes de elevado potencial en la alimentación de bovinos.

Palabras clave: Consumo de alimento, digestibilidad, nutrientes, pulpa cítrica, rumiantes (Fuente: USDA).

INTRODUCTION

Nutrient consumption and digestibility and their use in the different compartments of the digestive tract are estimated to be the closest approximation to the real nutritional value in food. The knowledge of the characteristics of food and its balance in the formulation of portions is a fundamental tool to meet animal needs, in order for them to express their genetic potential for production. Currently, there is variety of food that may be used in ruminant nutrition. Meanwhile, their nutritional value and quality are determined by the complex interaction between nutrients and the microorganisms in the digestive tract, digestive process, absorption, transport, and metabolite use, aside from the animal’s own physiological condition (1). The search for alternative ingredients for ruminant nutrition leads to permanent investigation on the dynamics of fermentation and digestion of these ingredients, in processes related to production animal nutrition (2).

The digestibility coefficient of a diet is important to indicate the real available nutrients in food for the animal, aside from describing their nutritional value (3), since this shows how much food the microorganisms in the rumen actually use and expresses the capacity of the animal to use each nutrient in a higher or lower scale.

Regarding energy sources, such as citrus pulp and soybean pulp, they are characterized by their ability to alter the fermentative profile, which results in changes in the rumen environment, altering in a certain way the digestibility of some nutrients by rumen pH modulation, as a result of the short chain fatty acid proportion that is formed and the high fermentation speed.

Pectin fermentation in citrus pulp provides a higher pH in comparison to other diets with corn, fat or oils (4). Even though pectin is rapidly fermented in the rumen, it produces acetate as a final product, as occurs in cellulose fermentation. This way, replacing the sources of starch with citrus pulp may promote beneficial effects, mainly related to the ruminal environment, because of the buffer effect of pectin, resulting in better conditions for the digestibility of fiber in forage, when having diets rich in concentrates (5). On the other hand, fats and oils have been added to ruminant diets with the purpose of increasing the energetic concentration of the diet. However, one of the main setbacks with the use of fats in ruminant diets, specially, when they are unsaturated, is the negative effect on the consumption of dry matter and the reduction of fiber digestibility (5).

As previously mentioned, the nutritional evaluation of the animals feed is necessary to characterize their potential and use in ruminant diet formulation. This way, the purpose of this study was to evaluate the effect of three energetic sources on consumption, total apparent digestibility, and nutrient excretion in bovines.

MATERIALS AND METHODS

Animals and infrastructure. The experiment was undertaken at the Department of Animal Nutrition and Production, of the Faculty of Veterinary Medicine and Animal Husbandry of the Universidad de São Paulo, Brazil, at the facilities of the Experimental Barn and the Laboratory of Animal Nutrition and Bromatology.

Six non-pregnant and non-lactating cows were used, with an average live weight of 730±70 kg and cannulated at the rumen with 10 cm diameter and 7.5 cm wide cannulas. The animals were kept in a roofed facility with individual compartments with cement feeders and automatic fountains.

Treatments and experimental design. The animals were assigned to one of the three isocaloric (1.55 Mcal of ELl/kg of DM) and isoproteic experimental diets (12.10% of CP), formulated with the program Spartan Dairy Ration Evaluator/Balancer, version 3.0.3., varying according to the energetic source used, as follows: 1) Control: Low ether extract (3.50% EE); 2) Soy: High ether extract (5.30% EE) with an inclusion of 15% soybean, and 3) Citrus Pulp: Low ether extract diet (3.00% EE) and high pectin participation with inclusion of 15% citrus pulp.

The experimental design used was a replicated 3x3 Latin square. The experimental unit was the animal within each period. The experiment included 18 experimental units: 3 animals, 3 periods and 2 squares.

Nutritional management and experimental period. The food was offered twice a day, at 08:00 and 16:00 hours, incomplete portions. In all the diets, the source of forage used was corn silo. The proportions of the different ingredients in the experimental diets and their bramatological composition are described in table 1.

Each experimental period lasted 15 days, considering the first 10 days as adaptation periods for the diets, and the last 5 days for data collection of the evaluated parameters.

The animals were weighted on the first and last day of all the periods of this experiment. The amounts of forage and concentrate offered to the animals were weighted daily, as well as the remainders of each experimental portion in order to estimate consumption per animal.

Evaluation parameters. Dry matter consumption (DMC) was evaluated daily, between days 10 and 15 of each experimental period. DMC was calculated as the amount of food provided in one days and withdrawn from its corresponding leftover, and weighted the next morning, upon offering the diets, multiplying this by the percentage of dry matter (DM) in food.

Samples of the food used in the diets were analyzed to determine the percentage of dry matter - DM (Method 2001.12), mineral matter - MM (Method 935.12), gross protein - GP (Method 968.06), ether extract - EE (Method 920.39), calcium - Ca (Method 935.13), Phosphorous - P (Method 964.06), according to methodologies described by AOAC (6); gross energy - GE, determined by adiabatic calorimeter PARR Instruments® and fiber in neutral detergent - FND, acid detergent fiber - ADF and lignin - LIG, according to Van Soest (3).

Total apparent digestibility of DM in the diet and its fractions (GP, EE, GE, ENN, FND, ADF y OM) were determined with a chromium oxide marker (Cr₂O₃), according to the technique mentioned by Bateman (7). For this, 2g of the marker Cr₂O₃ per kg of DM consumed were administered through the ruminal cannula. For such, between day 5 to day 15 of the supply of the diets of each experimental period, 2 g of the marker Cr₂O₃ per kg of DM of consumed food were administered two times a day via the rumen cannula through wrappers made from absorbent paper. The digestibility assay was established in two phases, the first five days for adaptation to the marker and the last five for stool collection.

For the analysis of the composition of fecal samples, an aliquot of 200 g per animal was directly removed from the rectum twice a day, which was preserved in the plastic wrap previously identified for each animal and experimental period. During that same period, approximately 200 g of each food offered in the total ration and stored in the plastic wraps previously identified were collected twice a day. All samples were kept at -20°C until analysis. Food and feces samples were homogenized and pre-dried in a forced ventilation stove at 65°C for 72 hours. They were subsequently crushed in a mill using a 1.0 mm sieve and coupled into closed bottles for the determination of the Cr₂O₃ concentration, according to the methodology described by Conceição et al. (8), and other lab tests.

The concentration of total digestible nutrients (TDN) of diets was calculated through the equation proposed by NRC (9):

TDN(%) = DCP+DNDF+DNFC+(2.25 x DEE)-7

Where:
DCP = digestible crude protein;
DNDF = digestible neutral detergent fiber;
DNFC = digestible not fibrous carbohydrates;
DEE = digestible ether extract.

The excretion of DM and the nutrients of the diet were calculated from the data of the DM digestibility coefficient and its fractions, multiplying the nutrient intake value by their respective digestibility coefficients and dividing it by 100.

Statistical analysis. The results were analyzed by the software Statistical Analysis System, Version 9.2 (10), before checking the normality of waste by the Shapiro-Wilk test. The data were subjected to analysis of variance by the SAS MIXED procedure, where the model included the effect of the treatment as a fixed factor and the effects of animal within the square, square and period as random factors. The effects of the treatment were evaluated by the Tukey test (p<0.05).

The mathematical model used was:

y_ijk= m+a_i+t_j +b_k+e_ijk

Where:
y_ijk is the observation in line I and column k of treatment j;
m is the general average;
a_i is the effect of column I in the square;
t_j is the effect of treatment j;
b_k is the effect of line k.
e_ijk is the random experimental error.

Ethical considerations. This experiment was conducted according to the guidelines established by the ethics committee on the use of animals of the Faculty of Veterinary Medicine and Animal Husbandry of the University of São Paulo (Brazil), under Protocol No. 2262/2011, in accordance with the ethical principles for animal experimentation, animal care and use.

RESULTS

Table 2 shows the mean values of the consumption of dry matter and nutrients for the effects of the energy source.

There was no effect of the energy source over the gross energy consumption (GEC) or neutral detergent fiber (NDFC), probably because the animals received isocaloric diets with similar values of NDF (Table 1), which provided a constant intake of these nutrients throughout the day, indicating that the ruminal conditions also remained constants for treatments.

A decrease in the consumption of dry matter (DMC), crude protein (CPC) and nitrogen- free extract (NFEC) was observed (p<0.05) for the soybean treatment as compared to the control and citrus pulp treatments, which in turn were not different from each other. The soybean treatment also reduced (p<0.05) the consumption of organic matter (OMC) when compared with the control treatment and there were no significant differences between these two treatments with regard to the citrus pulp treatment. The depressant effect of lipids on dry matter intake was due to satiety, the decrease in dry matter intake resulted in the decrease of the consumption of crude protein, nitrogen-free extract and organic matter.

The acid detergent fiber consumption (ADFC) was lower (p<0.05) for animals receiving the control treatment than in those that consumed soybean grains or citrus pulp, there being no statistical difference between these last two treatments. This is due to the fact that in the bromatological composition (Table 1), the value for ADF in the control treatment was lower when compared to the ADF content in soybean or citrus pulp treatments. In addition, the increase in the consumption of ADF for soybean or citrus pulp diets was due to the higher content of fibers in these diets, as these sources have a higher ADF percentage when compared with corn.

The effect of the energy source (p<0.05) was observed for the consumption of ether extract (EEC), being this higher for the soybean treatment in relation to the other treatments that, at the same time, were not different among them. This was to be expected since the treatment containing soybean grains was characterized for being a high ether extract diet (5.30% of EE), which means that a portion of non-fibrous carbohydrates was replaced by ether extract.

The results of the DM digestibility coefficients and its fractions, as well as total digestible nutrients, are described in Table 3.

The digestibility coefficients for DM, CP, GE, NDF, EE, NFE and OM were not affected by any of the treatments. There was a significant effect for the digestibility coefficient of ADF as well as for TDN.

The energy sources used in this experiment influenced the excretion values for DM and nutrients as shown in table 4. Moreover, no data were found in the literature about the effect of energy sources on the excretion of nutrients from cattle diet.

Significant differences (p˃0.05) were not observed between treatments for the excretion of gross energy (GEEx), and neutral detergent fiber (NDFEx). The excretion of dry matter (DMEx), nitrogen-free extract (NFEEx) and organic matter (OMEx) were lower (p<0.05) for the soybean treatment in comparison to the control treatment, without differences of these two with the citrus pulp treatment. This is related to the consumption (Table 2) obtained for these nutrients, being also lower when animals consumed the soybean treatment.

The excretion of acid detergent fiber (ADFEx) and ether extract (EEEx) was higher (p<0.05) for the soybean treatment in relation to the citrus pulp treatment, with these two treatments not being different from the control treatment.

The energy source effect was observed (p<0.05) for the excretion of crude protein (CPEx), being all treatments different among each other, while the citrus pulp treatment promoted an increased protein excretion, while the soybean treatment resulted in a lower excretion of this nutrient. The same effect (p<0.05) was observed for the excretion of nitrogen (NEx), being higher for the citrus pulp treatment as compared to the soybean treatment. Based on these findings it can be asserted that the increased excretion of protein crude, and consequently of nitrogen, for the citrus pulp treatment is due to a lower retention of the nitrogenous compounds by the animals that received this treatment.

DISCUSSION

The depressant effect of lipids on DMC and the nutrients mentioned above is associated with the inhibition of the microbial activity and consequently, with the rate of digestion. The use of lipids in the diet of bovine cattle may affect fiber digestibility, mainly when these are unsaturated fatty acids (11). This inhibitory effect on fiber degradation has been attributed to a coat of fibrous particles with fat, which generates a physical impediment that lipids exert on microorganisms through a hydrophobic layer, preventing the metabolism and perfect adherence of bacteria to the fiber, thus affecting the proximity of fibrolytic enzymes to the fibrous material (12). On the other hand, the reduction in DMC with the inclusion of lipids is associated with a reduction of ruminal motility and rumination time, which results in a slower transit of digestion and a satiety effect by physical filling based on lower fiber degradation (13). In the case of soybeans, the natural fibrous coverage of the seed shell that surrounds the whole oily grains, can potentially alter the ruminal passage rate or the release of oil within the rumen (14). The NRC (9) indicates a reduction in DMC in animals receiving soybeans, according to the reduction in the fiber digestibility and at the same time the increase in time of permanence of food in the reticulum-rumen.

The decrease of the CMS is also given by the interference of unsaturated lipids on the activity Gram - negative bacteria, mainly responsible for fiber fermentation (15). The excess of unsaturated fatty acids can cause alteration in ruminal fermentation due to the suppression of the activity of cellulolytic and methanogenic bacteria. This is due to a physicochemical effect generated by the interaction between free fatty acids and bacteria, through a toxic effect of unsaturated fatty acids on microorganisms, where an alteration in the cytoplasmic membrane occurs affecting its permeability (12). On the other hand, the high energy density of the diet might have led to an increase in the blood concentration of native metabolites from the diet (triglycerides and accordingly free fatty acids), which stimulated chemical receptors that activated the satiety center resulting in a decrease in food intake (16).

Similar results to the CMS and the nutrients found in this experiment were reported by Oliveira et al (17), when assessing the effects of different lipid sources on the consumption and digestibility of buffalo steers in confinement. The authors observed that the consumption of EE by animals fed with diets containing whole soybean grains or soybean oil was higher than those that received the treatment with no additional lipids. This greater intake of lipids resulted in lower consumption of DM, CP and CNF in animals receiving diets with whole soybean grains and soybean oil. This result can be explained by the satiety effect that was produced with the contribution of lipids in ruminant diet, explained by the theory of regulation of energy consumption described by Van Soest (3).

On the other hand, Bassi et al (12), working with 30 zebu heifers, evaluated the use of diets formulated with corn silage and four concentrates, one with no lipid supplementation and three including different oilseeds (soybean, cotton shell and flax seed) in concentrated isoproteic diets (13.3% of CP in DM). The authors observed that the inclusion of soybeans reduced the daily intake of DM when compared to the diet without lipids (8.18 and 8.70 kg, respectively). The same effect was observed for the consumption of OM (6.93 and 7.17 kg); however, for the consumption of CP and NDF, no differences were observed between diets. The consumption of EE increased (0.51 to 0.31 kg/day) with the inclusion of soybean in relation to the treatment without lipids, respectively. This reduction in the CMS, according to the same authors, can be attributed to the higher energy density of diets containing oilseed grains.

In the digestibility analysis it was not possible to demonstrate effect of the energy source on the digestibility coefficients of DM, CP, GE, NDF, EE, NFE and OM. Leite (18), when working with Holstein lactating cows with a live weight of 652 kg, indicates that there is a reduction in fiber digestibility when lipid sources such as soybean oil are added at a rate of 2% in the DM of the total diet. However, the extent of the reduction is related not only to the amount but also with the type of fatty acid present in the supplement, as rich lipids in unsaturated fatty acids tend to cause a greater reduction in digestibility. In contrast, Harvatine and Allen (19) did not observed the effects of the inclusion of up to 8.3% of saturated and unsaturated fatty acids on the digestibility of DM, OM, NDF and starch in multiparous Holstein cattle; hence suggesting that large quantities (8.3%) of fatty acids may be added to diets as this does not produce any effect on digestibility.

The citrus pulp treatment showed a greater (p<0.05) digestibility of the ADF fraction when compared with the control treatment. This is explained because the fibrous fraction of citrus pulp has a high ruminal digestibility, since, despite the ADF percentage around 24%, it exhibits a low percentage of lignin (1%), which means that almost all the fiber is digested in the rumen (20). Furthermore, the improvement in ADF digestibility in this study reflects the composition of the citrus pulp, which has been considered an intermediate food between forage and concentrate (21) by improving rumen fermentation, and the higher effectiveness of fiber as compared to corn or soybeans depending on pectin (5). In addition, citrus pulp is rapidly and extensively degraded in the rumen, being its degradation higher when compared to soybeans, as the citrus pulp has a high percentage of soluble carbohydrates and pectin; which is a high rumen degradability component in the cell wall (22).

There was a significant effect (p<0.05) of the energy source on the concentration of TDN, as the soybean treatment showed higher values as compared to other treatments. This was due to the greater use of TDN by animals, since the digestibility of the same was higher for animals receiving the soybean treatment in relation to all other treatments.

For the energy source effect obtained on the excretion of GE and NDF, the results were consistent with what was observed for the consumption and digestibility of these nutrients, as no significant differences for these variables were found, which confirmed once more the fact that the diets were isocaloric and had similar NDF values, indicating a fermentation profile and the constant and similar utilization of these nutrients and, therefore, no marked effect on the excretion of the same.

The increased excretion of ADF and EE for animals fed with soybeans is related to the composition of these nutrients in diets (Table 1), being higher for the soybean treatment in comparison with the other treatments. Similarly, such increase was also due to the higher consumption of these nutrients (Table 2) and the absence of the effect of the treatment on digestibility (Table 3) of these variables, which led to a lower retention and utilization of these nutrients and consequently, the increase in the excretion of the same.

On the other hand, while the citrus pulp has a lower CP percentage when compared with corn and soybeans, this protein can be even less digestible, which led to an increase in the excretion of CP and therefore nitrogen in this experiment. Porcionato et al (23), when working with mixed bulls (½ Holstein x ½ Zebu), found lower CP digestibility coefficients as the level of citrus pulp in the diet increased. This effect is due to the high percentage of protein retained in the fibrous portion of its composition, which reflects a lower retention of nitrogenous compounds in the rumen and consequently, an increase in the excretion of the same.

In contrast, Rodrigues et al (24), when replacing corn with citrus pulp in ovine diets, found no difference in the amount of nitrogen both in feces and urine; which did not alter the nitrogen metabolism. Henrique et al (21) showed a better utilization of nitrogen in sheep when receiving citrus pulp, justified by the increase in the intake of DM with the addition of this energy source.

According to the results obtained, it is concluded that the inclusion of 15% of soybean grains in the diet of cattle reduced the consumption of DM, CP, NFE and OM, while none of the sources altered the consumption of NDF, ADF, and EE. This indicates that the inclusion of citrus pulp is a satisfactory alternative to improve the intake of DM and its fractions.

A rich source of pectin, such as citrus pulp, or in unsaturated fatty acids, such soybean grains, with an inclusion of 15% in DM, was not detrimental for the digestibility of the diets, being these listed as high potential sources for use in cattle diets.

The inclusion of 5.30% of EE from unsaturated fatty acids in the diet of cattle can be carried out, since this does not cause negative effects in the apparent total digestibility of dry matter and its fractions.

The inclusion of citrus pulp proved to be efficient for reducing the excretion of certain nutrients; however, it resulted in a lower retention of nitrogenous compounds, thus increasing their excretion.

Acknowledgements

To the institutions that funded the research project, CNPq, CAPES and FAPESP, as well as to the scholarships awarded to the postgraduate learners.

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