ORIGINAL ARTICLE

Intake and in vivo digestibility of Tetrachne dregei differed from autumn supplemented with a ruminal protein activator

Consumo y digestibilidad in vivo de Tetrachne dregei diferido de otoño suplementado con un activador proteico ruminal

G. N. D’Ascanio,^I A. Elías,^II C. Frasinelli,^III R. Rodríguez,^II F. Herrera,^II

ABSTRACT

In order to evaluate the animal response of a ruminal protein activator in animals which intake a Tetrachne dregei summer grass, differed from autumn and ripe, with the purpose of improving the forages intake and the in vivo dry matter digestibility, two doses of a ruminal protein activator (200 and 400 g. head.d^-1) and a control without the activator in 280 kg steers were studied in a metabolism shed. These animals received Tetrachne dregei controlled in a completely randomized design with three treatments, three repetitions and four sampling days for food intake and feces collection measurements. The average composition was of 5.7 and 40.6 % of crude protein, 73.1 and 32.5 % of neutral detergent fiber, for Tetrachne dregei and the ruminal protein activator, respectively. It was estimated 77.52 % of degradable protein in the activator. The control animals, only fed with Tetrachne dregei had lower total dry matter intake, forage dry matter intake and dry matter digestibility with respect to the treated groups(P <0.001), without significant differences. The total dry matter intake, dry matter digestibility and the digestible dry matter intake, was increased in 18.9, 9.3 and 33.6 % respectively, compared to that obtained in the treated animals, (P <0.001) and the forage dry matter intake in 14.5 % (P <0.002), but there were not significant differences between doses. The ruminal protein activator achieved high response to low doses, when increasing the intake of digestible organic matter and degradable protein significantly in 34 and 50 %, respectively (P <0.001).

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

RESUMEN

Para evaluar la respuesta de un activador proteico ruminal en animales que consumen una gramínea estival Tetrachne dregei, madura y diferida de otoño, con el propósito de mejorar el consumo de forrajes y la digestibilidad de la materia seca in vivo, se estudiaron en un galpón de metabolismo dos dosis de un activador proteico ruminal (200 y 400 g.cabeza.d^-1) y un control sin el activador en novillos de 280 kg. Estos animales recibieron de manera controlada Tetrachne dregei  en un diseño completamente aleatorizado con tres tratamientos, tres repeticiones y cuatro días de muestreo para las mediciones consumo de alimento y recolección de heces. La composición promedio fue de 5.7 y 40.6 % de proteína bruta, 73.1 y 32.5 % de fibra neutro detergente, para Tetrachne dregei  y el activador proteico ruminal, respectivamente. Se estimó en el activador 77.52 % de proteína degradable. Los animales control, alimentados solo con Tetrachne dregei  tuvieron menor consumo de materia seca total, consumo de materia seca de forraje y digestibilidad de materia seca con respecto a los grupos tratados (P <0.001), sin diferencias significativas. El consumo de materia seca total, la digestibilidad de la materia seca y el consumo de materia seca digestible, se incrementó en 18.9, 9.3 y 33.6 % respectivamente, en comparación con lo obtenido en los animales tratados, (P <0.001) y el consumo de materia seca de forraje en 14.5 % (P <0.002), pero no hubo diferencias significativas entre dosis. EL activador proteico ruminal logró alta respuesta a bajas dosis, al incrementar de manera significativa el consumo de materia orgánica digestible y de proteína degradable en 34 y 50 %, respectivamente (P <0.001).

INTRODUCTION

In the central semiarid region of Argentina, meat production systems include, among other management factors, the perennial summer grasses intake in the forage chain which increase the stocking rate capacity, resulting in production increase, lower costs and productive stability. This region has an average annual precipitations   regime between 200 to 600 mm, which include La Pampa and San Luis provinces and the Mendoza center- east, with estimated total area of 260.000 km² (Chiossone 2011).The potential production of this environment is, as average, 1200 kg DM/ha year, which mean supporting an stocking rate of 0.2 a/ha (Sala et al. 1988).

These types of the described grasslands have in common two important characteristics: their low protein concentration during most of the year and their high fiber content. Therefore, any purpose to improve forage production, their quality or use, would result in a significant economic benefit.

The poor contribution of nutrients necessary for the ruminal microorganisms growth results on the microbial biomass decrease, reduction of the digestibility and the animal total intake, particularly in fibrous forages (Elías1983, Leng1991).

It has been proved that ruminal microorganisms need nutrients for their development (Elias 1971, Wallace and Newbold 1994).Some researchers propose the rumen manipulation to develop a favorable ecosystem, with the increase of the total volatile fatty acids production (Ortiguez and Majdoub 2003), mainly propionic, the escape of ruminal fermentation of true protein, degradable protein in rumen (Elías 1983, El-Kadi et al. 2003) and long chain fatty acids (Voigt et al. 2004). Moreover, it is suggested the protozoan control and the increase of structural carbohydrates digestion by means of physical or chemical forages treatment and fermentable nitrogen addition (urea, ammonia) accompanied by micronutrients, such as sulfur, phosphorus, amino acids and peptides (Preston 1991).

Ruminal protein activators (RPA), in hard tacos of slow release, function as a formula that accelerates the ruminal digestion processes. These activators, whose formulation consist on a combination of protein meals, urea, molasses and minerals, were designed to provide nutrients synchronously to populations of ruminal cellulolytic microorganisms of bovine (D´Ascanio 2014). They are characterized by insalivate and the animals swallow them whole or in big pieces, demonstrable within the animal rumen. They are cylindrical, between 0.8 and 1 cm in diameter, with specific weight of 1.2kg L^-1 and compressive resistance between 8 and 12 kgf cm². They are resistant to humidity between 8 and 12 h. The hard tacos dissolve their nutrients in the rumen slowly and synchronously during the day. They are used in feeding livestock rearing in the field, which under extensive conditions intake low nutritious quality forages, with crude protein (CP) concentration lower to 6%. Using the RPA is expected to maximize the fibrous forage intake and daily liveweight gain.

The objective of this research was to evaluate the effect of a RPA supplementation on the intake and in vitro digestibility of Tetrachne dregei grass, differed from autumn and ripe.

MATERIALS AND METHODS

The study was conducted in the field of Agricultural Experimental Station of INTA "San Luis" (33° 40'13 "South, 65° 23'25" West, 500 m o.s.l), San Luis province. The Tetrachne dregei growth from the 2009-2010 period deferred from autumn was used. During the winter of 2010, 400 kilos rolls were made and stored indoors until the evaluation time. For the study of voluntary intake (VI) and dry matter in vivo digestibility (DMIVD), a total of 9 Abeerden Angus castrated steers, of 18 months old and 280 kg of live weight (LW) were used under stabulation conditions. Before starting the experiment, they were dewormed with ivermectin, were identified with ear tags and individually weighed on a mechanical scale to adjust the VI. A completely randomized design was used, with three treatments per three replications. The treatments were:

T0= Control (T. degrei, without supplementation)

T1= T. degrei + 200 g of RPA

T2= T. degrei + 400 g of RPA

The experiment lasted 34 d, 30 of them were used for the adaptation of animals to the diet and four, to measure voluntary intake and in vivo digestibility for a total collection of feces. To estimate intake, a minimal refusal of 25%was set. The RPA was discontinuously supplied, three times a week (Monday, Wednesday and Friday), at a rate of 467 g and 934 g per steer in each supply (it represented the total weekly dose divided into three parts), for T1 and T2, respectively. It was verified that the animals do not intake the whole supplement the day they were given. Daily, the forage was supplied and weighed, the same as rejected. Samples from both were taken for their further analysis. Daily, feces were collected, weighed and samples were taken to estimate their dry matter. The samples were dried in an oven with forced air circulation at 60 °C until constant weight. The forage dried samples were ground in hammer mill until a particle size of 1 mm and were stored for subsequent chemical composition analysis. The DM was determined by forced air circulation at 105 °C during 4 h. The ashes (calcination) and CP (Kjeldahl NX6, 25) were determined by standard methods (Latimer 2012). The NDF and ADF, according to Goering and van Soest (1970) method .In addition, the DM in vitro digestibility (MDIVD) by Tilley and Terry (1963) method were estimated. The INFOSTAT statistical software, version 2012 (Di Rienzo et al. 2012) was used for the results interpretation.

RESULTS AND DISCUSSION

Table 1 shows the chemical composition of the two foods used in the assay. The T. degrei composition was among the parameters indicated for ripe forages of low nutritional quality (National Research Council 2000). The activator composition was also found between the parameters in its formulation. For DMIVD, difference was found between the estimated in laboratory (40.5%) and that found in the field (46%) by the in vivo method (5.5%), when comparing the data of table 1 and 2. Goering and van Soest (1970) pointed out that the differences between in vitro and in vivo methods for digestibility estimates were in the order of 11%.

Koster et al. (1997) concluded that, when the amount of urea exceeds 75% of the total equivalent of digestible protein (DP), the response of all the criteria about the forage intake, OM and NDF digestion significantly decreases, therefore they suggest as maximum substitution point 50%. For the RPA, the higher amount of urea used with respect to the total equivalent of DP was 37%, which remained in the recommended limit. Koster et al. (1997), from the mentioned results, determined as minimum limit 25% equivalent as supplementary DP. This must come from the true protein to maximize forage intake and digestion that, for this product, was 62% above the minimum limit recommended.

The results of animal response are shown in table 3. The total dry matter intake (total DMI) and forage intake (forage DMI) was similar. Both indicators, in the supplemented treatments, showed differences with respect to control, and there was no difference between doses.

The DMIVD and digestible dry matter intake (DDMI) showed similar tendency. There were no significant differences between the two RPA doses. Both improved these indicators with respect to the control. As shown in table 4, the average increase was 9.3 and 33.6% for DMD and DDMI respectively, when subjecting the forage to supplementation with RPA to low dose of 200 g/animal/d.

The forage CP intake (forage CP) was lower in the control than in the supplemented treatments, which not differ to each other, with 14.5 % of increase. With regard to the total CP intake (total CP), this indicator showed differences between all treatments, and it was increased as the RPA dose increased.

The NDF and ADF intake, total and of the forage (total NDFI, forage NDFI, total ADFI, forage ADFI), as well as to that of cellulose and hemicellulose (forage CDMCEL) fallow the same tendency, typical of the increase of the total intake of forage DM with the RPA addition. Effect was not observed between the doses of it.

The digestible organic matter intake (DOMI) was significantly different between the control and treatments, in those which the increase value was of 33.7 % (table 4), but there were not differences between the activator doses. On the other hand, the degradable protein intake (DPI) was different between treatments. This is typical of the addition of the different RPA doses, being 50.3% the increase with regard to the most efficient dose of the RPA, which was of 200 g (table 4). 

Koster et al. (1996) determined that the most appropriate relation that should exist between the total DP and the DOM intake is approximately 11%. Therefore, from the total of the daily DOMI, as average should be 11% of DP, to ensure an optimal rumen fermentation process. When using this same relation DPI / DOMI, differences between each of treatments were found in this study, placing this one between the lower and higher doses of the RPA. When using an approximation based on the average efficiency of microbial yield on varied diets, the National Research Council (2000) suggested that DP requirements were, as average, 13% of the total DNT. The Agricultural Research Council & Commonwealth Agricultural Bureaux (1980) suggested mean values of 30 g microbial N / kg OM, apparently digestible in the rumen. When applying the microbial efficiency suggested by the AgriculturalResearch Council & Commonwealth Agricultural Bureaux (1980) and the National Research Council (2000), it seems to be that the supplementation used on low quality forages, must maintain a minimum in the relation  DIP: TND from 12 to 13% approximately. This is possible when the supplements have concentrations higher than 20 % of CP. These relations are similar to those found in this experiment, being the closest 11%, determined by Koster et al. (1996.)

Moore et al. (1999) determined that the supplementation decreases forage voluntary intake, when the total intake of the supplemental TND was higher of 0.7% of LW, when the relation between the forage TND: CP was lower at 7 (adequate N) or when the voluntary forage intake during supplementation was higher than 1.75 % of the animal live weight. Therefore, a relation between forage and concentrate 60:40could be inferred.

However, supplementation increases voluntary forage intake when the relation of forage TND: CP was higher than 7 (deficit N), and when voluntary forage intake was lower to that relation. Considering that the TND is equal to the OMD, then it can infer that these results are conclusive and decisive for this experiment, as fitted to the established values (OMD: CP). This indicates that the response to forage intake in feeding systems with low quality forages depends, first, the contribution in supplementary CP as the main limiting factor.

Moore et al. (1999) indicated that the most of supplemented straws with different types of concentrated mixtures are placed in an OMD: CP relation between 4 and 8, in which a change in the OMI is achieved between - 0.5 to + 0.5, in % of the animal LW, which depends on how the supplements were mixed with the supplied straw. In this experiment, the exchange relation was 0.12

Held et al. (1997), when works with casein and different energy sources, obtained a similar response to Olson et al. (1997), who reached increases of 72 % in the DOMI with respect to the control, and 27 % when comparing high and low levels in the DPI. These authors concluded that the positive effect of supplementation with DP on the DOMI was due to the increase in the digestion and forage intake. This agrees with Owens et al. (1991) observations, who’s showed that many of the benefits of supplementation with DP can be attributed to its effect on the forage intake and digestion.

Bodine and Purvis (2003), in an experiment with steers in icy native pastures, studied supplementation with corn and soybean meal, supplied alone and in different combinations. These authors found that the best relations in DWG are achieved between DOMI: CP (g) of 5.7 and DPI: TND (g) of 7.2 , always referred to the total of diet.

Although in this study the animals receive supplementary doses much higher, close to 1 % of live weight, in the experiment in which the best response was achieved, at doses of 200 g of RPA, these relations were placed at 6.8 and 10.5, respectively. In the same experiment, the soybean meal performance was evaluated, at a rate of 0.3 % of LW, as a protein source of the same pastures. In this case, relations which were similar to those used in higher doses were obtained (400 g of RPA), of 4.8 vs. 5.6 and 15.0 vs. 12.8 for OMD: CP and DPI: DOMI, respectively.

As table 4 shows, the increase achieved with respect to the lower dose, being 18.9 and 14.5 % to one and another, respectively. These results agree with those reported by several authors, which indicated that the addition of protein to low quality forages causes increase in animals intake (Koster et al. 1996). The forage DMI in percent of animal LW was increase between control and the lowest RPA dose, being 1.4 and 1.6 %, respectively. Moore et al. (1999), from the review of published work about supplementation effects, they showed that with these levels of forage intake the supplementation effects respond positively.

Sawyer et al. (2012) evaluated in fistulated cows in rumen different types of proteins (high and low ruminal degradability) at low supplementation levels, for Eragrostis curvula or Sorghum bicolor hay (4.1 % CP and 75 % NDF or 3.7 % CP and 74 % NDF on organic matter, respectively). These authors did not found positive response to lower doses of 160 g d^-1 CP, for using the N and NDF digestibility, whatever is the type of protein. However, with doses close to 390 g d^-1 of cottonseed meal, obtained positive response in ruminal NH₃ concentration, N urea and blood glucose and DM disappearance.

Held et al. (1997) and Olson et al. (1997), in studies with casein as a source of degradable high protein solubility and different energy sources, achieved similar responses, with increase of 72 % in the DOMI with respect to control, and 27 % compared with high and low levels in the DPI. These authors concluded that the positive effect of supplementation with DP on the DOMI is due to an increase in forage digestion and intake. This agrees with Owens et al. (1991) previous observations, which showed that many of the effects of supplementation with DP can be attributed to effects on forage intake and digestion. Minson (1990), in reviews of supplementation studies, verified that the true protein and non-protein nitrogen (NPN) were able to stimulate forage intake.

The forages of the regions in which this study was carried out at certain times of the year they ripe or icy, or experience both affectations, which markedly reduce the CP concentration lower to 6 %, they responded positively to the use of RPA. The results between 7 and 8 % of the intake in CP and their responses on the DMI and DMD coincide with the values of 8%, recommended as a practical limit to achieve adequate concentration of nitrogen in the rumen fluid necessary for the flora growth and for the degradation of the fibrous structure of grasses (Elias 1983).

These results show that to achieve higher forage intake and higher weight gain, with lower use of supplementary concentrates, not only would be necessary to consider the DPI: DOMI relation, but should be consider other factors, linked to the flow of free amino acids and peptides towards the animal intestine, in order to efficiently use the total energy of the diet.

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