Cuban Journal of Agricultural Science, 50(2): 215-224, 2016, ISSN: 2079-3480

 

ORIGINAL ARTICLE

 

Effect of the supplementation with a ruminal protein activator on weight gain of steers fed rice straw

 

Efecto de la suplementación con un activador proteico ruminal en la ganancia de peso de novillos alimentados con paja de arroz

 

 

G. N. D’Ascanio,^I A. Elías,^II Angela J. Flores,^III R. Rodríguez,^II F. Herrera,^II

^INUTREZA SRL, Ruta 11, km 751. (3572) Malabrigo, Santa Fe, Argentina.
^IIInstituto de Ciencia Animal, Apartado Postal 24, San José de las Lajas, Mayabeque, Cuba.
^IIIINTA EEA Mercedes. Corrientes, Argentina.

 

 

---

ABSTRACT

In order to evaluate the animal response to supplementation with a ruminal protein activator to steers consuming rice straw rolls, an amount of 27 animals of 160 kg were used, distributed into three treatments (rice straw, rice straw + 200g of ruminal protein activator and rice straw + 400 g of ruminal protein activator.animal.d^-1). A random blocks design was applied, with three animals per treatment and three repetitions. Mean composition was 4.9 and 45.2 % of crude protein and 61.5 and 20.3 % of neutral detergent fiber for rice straw rolls and the ruminal protein activator, respectively. The control animals, fed only rice straw rolls, lost weight (-0.09 kg.animal.d^-1). Treated groups gained 0.242 and 0.325 kg.animal.d^-1 (P <0.001) for low and high doses, respectively, although without differences among them.  The intake of rice straw rolls increased in 16 % in the treatments supplemented with the activator (P < 0.01), but not  between doses. Final efficiency of the use of the activator was 1 g of ruminal protein activator per 1 g of daily weight gain. It is recommended the doses of 1.16 g of ruminal protein activator per kilogram of liveweight.

Key words: protein supplementation, low quality forages, protein activator.

---

RESUMEN

Para evaluar la respuesta animal a la suplementación con un activador proteico ruminal a novillos que consumen rollos de paja de arroz, se utilizaron 27 animales de 160 kg, distribuidos en tres tratamientos (paja de arroz, paja de arroz + 200 g de activador proteico ruminal y paja de arroz + 400 g de activador proteico ruminal.animal.d-1). Se aplicó un diseño de bloques al azar, con tres animales por tratamiento y tres repeticiones. La composición promedio fue de 4.9 y 45.2 % de proteína bruta y 61.5 y 20.3 % de fibra neutro detergente para rollos de paja de arroz y el activador proteico ruminal, respectivamente. Los animales control, alimentados solo con rollos de paja de arroz,perdieron peso (-0.09 kg.animal.d-1). Los grupos tratados ganaron 0.242 y 0.325 kg.animal.d-1 (P <0.001) para la baja y alta dosis del suplemento respectivamente, aunque sin diferencias entre estas. El consumo de rollos de paja de arroz se incrementó en 16 % en los tratamientos suplementados con el activador (P < 0.01), pero no entre dosis. La eficiencia final de uso del activador fue de 1 g de activador proteico ruminal por 1 g de ganancia diaria de peso vivo. Se recomienda la dosis de 1.16 g de activador proteico ruminal por kilogramo de peso vivo.

Palabras clave: suplementación proteica, forrajes baja calidad, activador proteico.

---

 

 

INTRODUCTION

The main basis of livestock in Argentine Republic is constituted by large areas of grassland. Currently, the animal husbandry activity in the country is displaced towards extra Pampas ecosystems that rely most of their productive livelihood on pastoral systems, mainly composed of seasonal growth grasses. These grassland ecosystems occupy more than 70% of the country (Chiossone 2011), with over 1,000,000 km² and 25,000,000 cattle heads, which represent 48% of total livestock from Argentina (Rossanigo et al. 2012).

The exploitation of C₄ photosynthetic pathway pastures, with marked seasonality on their yields and low nutritional value, due to their high fiber contents and low protein levels during most of the year, are features shared by animal husbandry ecosystems. Therefore, conserved forages have high fiber content and low proportion of nitrogen, with less than 8% of crude protein (CP).

These low quality feeds determine a ruminal environment that limits the development of cellulolytic bacteria, resulting in low rates of digestion of food passage fiber, have a negative influence on intake and restrict weight gain, especially in growing cattle (Elías 1983, Balbuena et al. 2000, Barbera and Sampedro 2010).

Intake may be increased by protein supplementation, in order to reduce the deficiency of CP available for ruminal microorganisms, with the consequent positive effect on the rate and extent of fiber fermentation. This is because, under conditions of forage availability, CP deficiency is the primary factor restricting weight gain of the animal (Del Curto et al. 2000).

The supply of non-protein nitrogen (urea, protected urea or cellulolytic enzymes) to ruminants reared extensively in the field, in order to increase efficiency of ruminal degradation of low quality forages, is limited because there are no practical ways to provide it in the needed doses.

Ruminal protein activators (RPA) of slow release, in form of hard cylindrical tacos with specific weight from 1.2 to 1.4 kg.L^-1 and resistance to compression between 8 and 12 kgf/cm², work as an accelerating formula of ruminal processes. They were designed to provide nutrients to populations of cellulolytic microorganisms and accelerate the ruminal processes of bovines (D'Ascanio et al. 2015). Formulation of this supplement includes a combination of protein meals, urea, molasses and minerals. These RPA are salivated and swallowed entirely or in pieces by the animals, which can be confirmed within the animal rumen, where they slowly and synchronically dissolve its nutrients (D'Ascanio 2014).   

The objective of this study was to evaluate the effect of RPA, as tacos, in the voluntary intake and weight gain of steers fed low-quality forage.

 

MATERIAL AND METHODS

The experiment was conducted at the Estación Experimental Agropecuaria of INTA "Mercedes" (27 ° 40'34 "South, 59 ° 48'25" West; 98 m o.s.l.), near the city of Mercedes (Corrientes, Argentine), during October and November, 2012. The experimental work consisted on evaluating, for 60 days, two levels of RPA, as hard tacos, as a supplement for Hereford and Braford calves and their crosses, weaned in autumn and reared in the field with winter supplementation, until their stabulation in pens with rice straw rolls ad libitum. Before starting the experiment, the animals were dewormed with ivermectin, were vaccinated against keratoconjunctivitis, ear tagged and weighed individually at 0, 30 and 60 d in a mechanical scale.

Three treatments were established:

T1) rice straw ad libitum (control)

T2) rice straw ad libitum + 200 g of RPA. head^-1/.d^-1

T3) rice straw ad libitum + 400 g of RPA. head^-1/.d^-1

The RPA were produced by the author of this study at the NUTREZA SRL (Ruta Nacional Na 11.Ciudad de Malabrigo, Santa Fe, Argentine), which is the enterprise that produces supplements and feeds for animals according to invention patent (D'Ascanio 2014).     

The voluntary intake of rice straw, as the difference in weighing the offer and rejection, was estimated. The supplement was delivered daily, during the morning, in feeding troughs, together and at open sky per each treatment, without recording rejection of RPA. On three occasions, feed samples were taken to determine chemical composition of used feeds. DM was determined by drying in an air forced oven, at 105 °C for 4 h. Ashes (A) were determined by calcination, CP by the Kjeldahl method and minerals by spectrophotometry, according to Latimer (2012). NDF and ADF were determined by the fractioning proposed by Goering and van Soest (1970).

An amount of 27 castrated male calves, with different sizes, were used in a random block design, which defined the range of initial weight of the animals as block. Three animals were allocated and three repetitions were included per treatment. The studied variables were analyzed by ANOVA, using the statistical package InfoStat (Di Rienzo et al. 2012). After detecting the differences (P<0.05), means of the treatments were compared by the multiple range test of Duncan (1955).

 

RESULTS AND DISCUSSION

Table 1 shows the chemical composition of the two feeds used in the experiment. The chemical composition of rice straw was in the range of the parameters indicated by the NRC (1996). The composition of the activator was also among the parameters foreseen for its formulation.

Table 2 presents the estimated mean composition of the activator, which is similar to some recommendations of different authors for this type of protein supplement. Before, Koster et al. (1997) determined that, when the amount of urea exceeds 75% of the total equivalent of degradable protein (DP), the response of all the criteria on forage intake, digestion of OM and NDF have a quadratic and substantial decrease. Therefore, the maximum point recommended for substitution is 50 %. For this RPA, the maximum amount of used urea from the total equivalent of DP was 37 %, maintained among the recommended limits. Kôster et al. (1997),  from the results cited before, determined a minimum limit of 25 %, equivalent to supplementary DP, which should come from true protein to maximize intake and digestion of forage. For this RPA, it was 62 %, over the minimum recommended limit.

In vivo estimations, conducted by Balbuena et al. (2002), determined degradation levels of CP, close to 60 % of cotton and soy bean pellets, and next to 85 % for sunflower pellets. These values are very close to those used for calculating the RPA in this experiment.

Table 3 shows the results of animal response. Regarding the analysis of initial liveweight (ILW), there were no differences among treatments. According to final liveweight (FLW), there was a decrease in the control group, unlike those consuming RPA. These last registered an increase of LW during the evaluated period, without differences among doses. The average FLW of both treatments was 182 kg, enough to exploit, in quantity and quality, the high forage production, taking place at the end of winter, which enables a compensatory growth with high LW gains.

Regarding weight difference (MLW), registered by the control group, it lost 5 kg of LW as average, similar values to those reported for mature forages during the winter period in grasslands from Chaco Húmedo Argentino (Peruchena and D’Ascanio 1992a). The supplemented groups increased between 14 and 19 kg of LW, with an average difference, regarding the control, of 21.5 kg. With similar forage bases, which are poor in CP (+ 4 %), for mature or frozen grasslands, but at the field, with implicit harvest cost in post weaning animals, the registered losses were superior, between 10 and 20 kg of weight, for a similar winter period (Peruchena and D’Ascanio 1992b).

Daily weight gains (DWG) differed between the control and supply of activators (200 and 400 g.animal^-1.d^-1). However, there were no differences among the used doses. Therefore, the doses of 200 g.animal^-1.d^-1 should be considered as the most convenient, from an economic point of view, which could also be expressed as 1.37 g of daily weight gain per kilogram of LW for those doses.

Balbuena et al. (2011) found in calves grazing Dichantium caricosum a higher weight gain, after supplementing with cotton and soy bean pellets (682 and 626 g.animal.d^-1), regarding the use of sunflower pellets (531 g.animal^-1.d^-1), respectively.  It is possible that differences obtained between this experiment and that conducted by Balbuena et al. (2011), are because of the use of calves grazing with the possibility of selecting a different material, with better nutritional quality and the possibility of selecting a different feed. In addition, the intake of protein supplement was provided in a higher amount: 3 g of byproduct per kilogram of LW as average.

Intake of total (total DMI) and forage dry matter (forage DMI) showed a tendency similar to previous results, being both superior for the treatments supplemented with different doses of RPA regarding the control. Mean increase was 16% for forage DMI and 21% for total DMI. It is possible that the lack of differences in forage DMI.kg^-1.PV^-1, obtained among the calves fed only rice straw and those receiving the lowest dose of the supplement, was caused by low CP intake (0.160 and 0.270 kg, respectively) of both groups, related to the low concentration of CP, of both diets (4.86 and 61 %) respectively.

It is known that, according to Elías (1983), intake of fibrous forages of CP content below 7% decreases and, due to high crude fiber content, digestibility of organic matter is limited by the low availability of amino acid or ammonia nitrogen for ruminal cellulolytic bacteria. In contrast, when animals fed those forages receive energy-protein-mineral supplementation, which reaches a protein concentration of the diet superior to 7% diet, the animals increase the DMI and DWG (Preston 1995, Galina et al. 1997, Delgado et al. 2002). Therefore, sufficient amounts of protein and energy should be provided for increasing forage digestion and NPN utilization (Elías 1983), as happened with the highest forage intake in absolute and relative values in animals that consumed higher amounts RPA (8.33% CP), compared to those that consumed only rice straw.

These results coincide with those stated by several authors, who indicated that the addition of protein to low quality forages provokes an increase of voluntary intake of animals (Köster et al. 1996). Heldt et al. (1997), conducting studies with casein and different energy sources, obtained a similar response to Olson et al. (1997). These authors reported 72% optimal increases of digestible organic matter intake (DOMI) regarding the control, and 27% when comparing high and low CP intake. In addition, these authors concluded that the positive effect of supplementation with CP in DOMI was caused by the increased of digestion and forage intake. This agrees with the information provided by Minson (1990), who in reviewing supplementation studies found that true protein and non-protein nitrogen were able to stimulate forage intake.

Forage DMI, in percent of animal LW (forage DMI/LW), was similar between control and the lowest dose of the supplement, but different with respect to that using the highest dose.

Regarding total dry matter intake, in percent of animal liveweight (totalDMI/LW), the same tendency of the previous case was found. There were differences between control and treatments with supplements, but there were no differences among doses.

Total intake of crude protein (ICP), and related to liveweight (ICP/LW), was different among treatments and increased as the RPA dose increased. Bailey et al. (2012) found positive results in cattle receiving increased doses of intra-ruminal casein on a natural pasture hay (5.8% CP), which increased the ruminal concentration of NH₃, acetate and propionate. They also increased pH, with higher flow of microbial N, when it passed from 120 to 240 g.d^-1 casein as DP. Unlike the doses used in this study, which were between 134 (173 g activator ICP x 77.52 % activator DP) and 268 g (346 g activator CP x 77.52 % activator DP) of DP per head and per day, the studies of Bailey et al. (2012) had no differential animal response in contrast with the positive results of ruminal fermentation.   

Sawyer et al. (2012) evaluated different types of protein (high and low ruminal degradability) at low levels of supplementation in diets based on hay, and found no responses to doses lower than 160 g.day^-1 of CP in the use of N and NDF digestibility, apart from the type of protein. However, with doses close to 390 g CP day^-1 of cotton seed meal, concentrations of ruminal ammonia, ureic N and blood glucose increased, as well as DM degradability

After analyzing the efficiency of utilization of the activator regarding weight gain reached by the animals (activator DMI/LW/DWG/LW), and considering the doses of 200 g of RPA as the most efficient with DWG and total intake of forage (there were no significant differences with 400 g of RPA), an efficiency of utilization of the supplement of 1:1 was obtained. This represents 1g of RPA per 1 g of gained liveweight. Revising different studies from different authors (Balbuena et al. 2002, Barbera et al. 2011, Rochinotti et al.  2011, Sampedro et al. 2004), it was concluded that average response to different protein supplements, especially those of sunflower, soy bean and cotton pellets, ranges between 2.2 and 2.5 g of supplement per 1g of gained LW. This means that from 1 to 1.5 g more of the supplement may be used to reach the response obtained in this study. 

The conducted analysis has an important economic effect because cited authors recommend a contribution close to 400g of supplementary protein. However, variations on the composition of oleaginous by-products provoke instability of the required amounts of this by-products (D’Ascanio and Peruchena 1992). Therefore, this may double or triple the costs of supplementation with low quality forages at the moment of its implementation. In addition, other costs should be considered, like those related to management and infrastructure (storage, distribution, supply and some others).    

Table 4 shows the efficiency of food conversion. There were no significant differences between both doses of the activator for any of the determined indicators, neither for forage matter intake nor for total or crude protein on daily weight gain. The most convenient dose was supplementation with 200 g of RPA for animals of 160 kg of mean LW, fed rice straw rolls. Thus, crude protein intake of activator/kg of gained weight was different between both doses. The best efficiency of utilization was obtained with 200 g of RPA.

From the production technology, and according to performance and physiochemical characteristics of the RPA, animals consume it entire or, mainly, in particles of big size. Due to its high content of CP and DP and its associative composition among different sources of protein meals, urea, molasses and minerals, it may be inferred that high response to supplementation with this activator is determined by slow and synchronic release of its nutrients to ruminal ecosystem. In order to debate this fact, there is a suggestion to consider first nutritional processes: nutrition of ruminal microbial population as an element, and nutrition of the host as another element, although they are together in their practical application. This way, it was demonstrated that ruminal microorganisms need important nutrients that allow their development (Elías 1971, Wallace and Newbold 1993).

Some researchers propose the manipulation of rumen to develop a favorable ecosystem that facilitates the increase of total volatile fatty acids, mainly propionic acid (Ortiguez-Marty and Majdowb 2003), through the supply of degradable protein in the rumen (Elías 1983, El-Kadi et al. 2003), starch (Voigt et al. 2003) and long chain fatty acids (Voigt et al. 2003). It was also suggested the control of protozoa and the increase of structural carbohydrate digestion through physical and chemical treatment of forages and addition of fermentable nitrogen (urea, ammonia) accompanied by micronutrients like sulfur, phosphorus, amino acids and peptides  (Elías 1971).

The main problem of this technique lies on making possible that rumen to reach its optimal useful condition in a cellulosic environment, from low quality forages. This demonstrates that, with the union of cited technological elements, it is possible to optimize the use of forage, focusing on the useful condition of the ruminal ecosystem in the portion of higher fermentative condition that may be reached in degradation of grass cellulose for benefiting animals and humans.

The use of RPA improved the productive response of calves fed rice straw due to the increase of intake of forage, total dry matter and crude protein, as well as improving conversion of these productive indicators.

 

REFERENCES

Bailey, E. A., Titgemeyer, E. C., Olson, K. C., Brake, D. W., Jones, M. L. & Anderson, D. E. 2012. “Effects of supplemental energy and protein on forage digestion and urea kinetics in growing beef cattle”. Journal of Animal Science, 90 (10): 3492–3504, ISSN: 1525-3163, DOI: 10.2527/jas.2011-4458.

Balbuena, O., Kucseva, C. D., Arakaki, C. L., Stahringer, R. C. & Velazco, G. A. 2000. “Fuentes de proteína en la suplementación invernal de la recría de bovinos en pasturas subtropicales”. Revista Argentina de Producción Animal, 20 (Supl 1): 62–63, ISSN: 0326-0550, 2314-324X.

Balbuena, O., Rochinotti, D., Arakaki, C. L., Kucseva, C. D., Somma,  de F. G. R., Slanac, A. L. & Koza, G. A. 2002. “Efecto de la suplementación proteica sobre la digestibilidad y flujo nitrogenado en novillos consumiendo pasto estrella”. Revista Argentina de Producción Animal, 22 (1): 13, ISSN: 0326-0550, 2314-324X.

Barbera, P. & Sampedro, D. H. 2010. “Suplementación con diferentes fuentes proteicas de novillitos a corral, consumiendo heno de paja de arroz”. Revista Argentina de Producción Animal, 30 (1): 488–489, ISSN: 0326-0550, 2314-324X.

Chiossone, G. O. 2011. “Pastizales naturales de Argentina”. In: IX Congreso Internacional de Pastizales, Santa Fe, Argentina: INTA y La Asociación Argentina de Pastizales (AAMPN), Available: <http://www.pregonagropecuario.com/cat.php?txt=2027>, [Consulted: April 4, 2016].

D´Ascanio, G. 2014. Formulación aceleradora de la celulólisis ruminal. no. INPI P-265/03, Inst. Instituto Nacional de la Propiedad Industrial. Administración Nacional de Patentes, República Argentina.

del Curto, T., Hess, B. W., Huston, J. E. & Olson, K. C. 2000. “Optimum supplementation strategies for beef cattle consuming low-quality roughages in the western United States”. Journal of Animal Science, 77: 1–16, ISSN: 0021-8812, 1525-3163.

Delgado, A., Crespo, G., Elías, A. & Yanes, A. 2002. “Fattening of grazing yearlings with molasses/urea supplementation”. Cuban Journal of Agricultural Science, 36 (1): 43–47, ISSN: 2079-3480.

Di Rienzo, J. A., Casanoves, F., Balzarini, M. G., González, L., Tablada, M. & Robledo, C. W. 2012. InfoStat. version 2012, [Windows], Universidad Nacional de Córdoba, Argentina: Grupo InfoStat, Available: <http://www.infostat.com.ar/> .

Elias, A. 1971. The rumen bacteria of animals feed on a high–molasses-urea-diets. Ph.D. Thesis, University of Aberdeen, Escocia.

Elías, A. 1983. “Digestión de pastos y forrajes tropicales”. In: Ugarte J., Herrera R., Ruiz R., García R., Vázquez C. & Senra A. (eds.), Los pastos en Cuba, vol. 2, La Habana, Cuba: Instituto de Ciencia Animal, pp. 187–246, Available: <http://www.sidalc.net/cgi-bin/wxis.exe/?IsisScript=catalco.xis&method=post&formato=2&cantidad=1&expresion=mfn=030111>, [Consulted: March 2, 2016].

El-Kadi, S. W., Sunny, N. E., Oba, M., Owens, S. L. & Bequette, B. J. 2003. “Glucose metabolism by the gastrointestinal tract of sheep as affected by protein supply”. In: Souffrant W. B. & Metges C. C., Progress in Research on Energy and Protein Metabolism, Netherlands: Wageningen Academic Pub, pp. 401–405, ISBN: 978-90-76998-24-4.

Galina, M. A., Pineda, J., Rosado, J., Aguilar, A., Puga, C., Rubio, C. & Murillo, J. C. 1997. “Fattening of steers zebu+ F1 cross feed high fermentable carbohydrate diet of a continuous non-protein nitrogen and by-pass protein supplement”. Advance Agricultural Research, 6 (3): 22–32, ISSN: 2053-1265.

Goering, H. K. & van Soest, P. J. 1970. Forage fiber analyses (apparatus, reagents, procedures, and some applications). (ser. Agriculture Handbook, no. ser. 379), Washington, DC., USA: U.S. Agricultural Research Service, 24 p.

Heldt, J. S., Cochran, R. C., Mathis, C. P., Woods, B. C., Stokka, G. L., Olson, K. C., Titgemeyer, E. C. & Nagaraja, T. G. 1997. “Evaluation of the effects of carbohydrate source and level of degradable intake protein on the intake and digestion of tallgrass-prairie hay by beef steers”. In: Cattlemen’s Day, Manhattan, KS: Kansas State University. Agricultural Experiment Station and Cooperative Extension Service, pp. 60–62, Available: <http://krex.k-state.edu/dspace/handle/2097/4816>, [Consulted: February 16, 2016].

Köster, H. H., Cochran, R. C., Titgemeyer, E. C., Vanzant, E. S., Abdelgadir, I. & St-Jean, G. 1996. “Effect of increasing degradable intake protein on intake and digestion of low-quality, tallgrass-prairie forage by beef cows”. Journal of Animal Science, 74 (10): 2473–2481, ISSN: 0021-8812, DOI: /1996.74102473x.

Köster, H. H., Cochran, R. C., Titgemeyer, E. C., Vanzant, E. S., Nagaraja, T. G., Kreikemeier, K. K. & St Jean, G. 1997. “Effect of increasing proportion of supplemental nitrogen from urea on intake and utilization of low-quality, tallgrass-prairie forage by beef steers”. Journal of Animal Science, 75 (5): 1393–1399, ISSN: 0021-8812, DOI: /1997.7551393x.

Latimer, G. W. 2012. Official Methods of Analysis of AOAC International. 19th ed., Gaithersburg, Md.: AOAC International, ISBN: 978-0-935584-83-7, Available: <http://www.amazon.com/Official-Methods-Analysis-OFFICIAL-ANALYSIS/dp/0935584838/ref=pd_sim_sbs_14_1?ie=UTF8&dpID=31iikC-xl2L&dpSrc=sims&preST=_AC_UL160_SR160%2C160_&refRID=101AB94246X0EM9N7XMW>, [Consulted: April 1, 2016].

López, V. S., Flores, A. J., Sampedro, D., Celcer, R. R. & Gómez, M. 2010. “Evaluación de fuentes proteicas en suplementación invernal de vaquillas de reposición”. Revista Argentina de Producción Animal, 30 (Supl. 1): 489–490, ISSN: 2314-324x, 0326-0550.

Minson, D. J. 1990. Forage in ruminant nutrition. Academic Press, 520 p., ISBN: 978-0-12-498310-6.

National Research Council (NRC) 1996. Nutrient Requirements of Beef Cattle. 7th ed., Washington, D.C.: National Academies Press, ISBN: 978-0-309-06934-2, Available: <http://www.nap.edu/catalog/9791>, [Consulted: May 19, 2016].

Olson, K. C., Cochran, R. C., Jones, T. J., Vanzant, E. S. & Titgemeyer, E. C. 1997. “Effects of various supplemental starch and protein levels on ruminal fermentation and liquid passage of beef steers fed tallgrass-prairie hay”. In: Cattlemen’s Day, Manhattan, KS: Kansas State University. Agricultural Experiment Station and Cooperative Extension Service, pp. 53–55, Available: <http://krex.k-state.edu/dspace/handle/2097/4813>, [Consulted: February 16, 2016].

Ortiguez, M., J. & Majdoub, L. 2003. “Ruminal acetate propionante pattern and nitrogenous fluxes across splanchnic and hind limb tissues in growing lambs”. In: Souffrant W. B. & Metges C. C., Progress in Research on Energy and Protein Metabolism, Wageningen Academic Pub, pp. 213–217, ISBN: 978-90-76998-24-4.

Peruchena, C. O. & D’Ascanio, G. 1992. “Suplementación energético-proteica de bovinos para carne en el centro-norte santafesino”. Revista Argentina de Producción Animal, 12 (supl. 1): 41–52, ISSN: 0326-0550, 2314-324X.

Preston, T. R. 1995. Tropical animal feeding. A manual for research works. Rome: Food and Agriculture Organization of the United Nations (FAO), ISBN: 92-5-103758-2, Available: <http://www.fao.org/docrep/003/v9327e/v9327e00.HTM>, [Consulted: April 4, 2016].

Rossanigo, M. V. C., Arano, P. A. A. & Vázquez, G. R. 2012. “Stock 2012 del ganado bovino”. Información Técnica, (187): 3–16, ISSN: 0327-425X.

Sawyer, J. E., Mulliniks, J. T., Waterman, R. C. & Petersen, M. K. 2012. “Influence of protein type and level on nitrogen and forage use in cows consuming low-quality forage”. Journal of Animal Science, 90 (7): 2324–2330, ISSN: 0021-8812, 1525-3163, DOI: 10.2527/jas.2011-4782.

Voigt, J., Gaafar, K., Hagemeister, H., Kanitz, W. & Precht, D. 2003. “Fat vs. starch as energy sources in diets for high yielding lactating dairy cows”. In: Soufrant W. B. & Metges C. C. (eds.), Progress in research on energy and protein metabolism. International Symposium, Rostock-Warnemünde, Germany: Wageningen Academic Publishers, pp. 445–448, ISBN: 90-76998-24-8.

Wallace, R. J. & Newbold, C. J. 1994. “Rumer fermentation and its manipulation: the development of yeast cutures as feed additives”. In: Lyons T. P. & Jacques K. A., Biotechnology in the Feed Industry: Proceedings of Alltech’s 10th Annuel Symposium, Loughborough, England: Nottingham University Press, p. 173, ISBN: 978-1-897676-51-6.

 

 

Received: 15/5/2015
Accepted: 30/6/2016

 

 

G. N. D’Ascanio, NUTREZA SRL, Ruta 11, km 751. (3572) Malabrigo, Santa Fe, Argentina. Email: www.nutreza.com.ar