A meta-analysis on in situ ruminal degradability of grains and meals for energy concentrate feeds

1Animal Science and Pastures, University of São Paulo College of Agriculture “Luiz de Queiroz” (ESALQ), Piracicaba, SP, Brazil, 2Department of Animal Science and Biological Sciences, Federal University of Santa Maria (UFSM) Campus Palmeira das Missões. Palmeira das Missões, RS, Brazil, 3Federal Institute Farroupilha, Campus São Vicente do Sul, São Vicente do Sul, RS, Brazil, 4Animal Science, Uniersity of the State of Santa Catarina (UDESC), Lages, SC, Brazil, 5Department of Animal and Food Production, University of the State of Santa Catarina (UDESC), Lages, SC, Brazil


INTRODUCTION
Energy is one of the main factors that directly affect the animal production systems.In ruminants, carbohydrates and protein are important nutrients used as substrates for microbial synthesis.Therefore, the formulation of diets for ruminants aims to enhance the production of microbial protein, the nutrient amount absorbed in the small intestine, and consequently, animal performance (Seo et al., 2010).However, ruminal metabolism is influenced by several factors such supply of carbohydrates and nitrogen for different pools of bacterial microbiota.Therefore, one factor that can interfere with the rumen fermentation of feeds is their physical form.Grains and other diet ingredients are processed to alter their physical structure and/or chemical composition (Nasri et al., 2008).Processing of energy ingredients aims to increase the availability of starch in the rumen, especially by weakening the bonds between protein and starch granules (Stevnebø et al., 2006).Processing of grain modifies the structural characteristics of starch and its interaction with other endosperm components by altering the digestibility (Svihus et al., 2005).Degradability of diet ingredients increases when the starch becomes more accessible to microorganisms (Tester et al., 2006).As a result, the meals last longer, with increased voluntary consumption and production of microbial protein, resulting in increased animal response (Pazdiora et al., 2011;Moharrery et al., 2014).
Various studies have been conducted in Brazil, focusing on in situ ruminal degradability.We used combined data from previous studies to perform a meta-analysis that would allow us to develop further correct estimates and increase the statistical power in a relatively inexpensive way (Hooijmans et al., 2014).Our objective was to assess whether ruminal degradability in situ is different for energy concentrated feeds with different physical forms.
In all studies, the potential degradability was estimated as described by Ørskov and McDonald (1979): , where p is the potential degradability; A is the watersoluble fraction; B is the insoluble fraction, but potentially degradable; and C is the degradation rate for 'b'.
The effective degradability of dry matter (EDDM) and crude protein (EDCP) was estimated as follows: where k is the particle passage rate in the rumen.In general, the recommended particle passage rates by the Agricultural and Food Research Council (AFRC, 1993) are 2% per h for animals with energy consumption lower than the maintenance; 5% per h for calves and cows producing less than 15 kg of milk per d, and beef cattle and sheep with energy consumption less than twice the maintenance; and 8% per h for dairy cows producing over 15 kg of milk per d or with energy consumption more than twice the maintenance.
Feeds were classified based on protein concentration as suggested by the Ministério da Agricultura, Pecuária e Abastecimento (MAPA, 2013).Analysis of variance was performed on SAS ® (SAS Institute, 2002) using the mixed model and considering each study as a random variable.Differences were considered significant at P < 0.05 and trend at P < 0.10.

RESULTS AND DISCUSSION
Based on the rates of DM (Table 1), the feeds were stored under appropriate conditions in all the studies.The rate of DM is important, since it protects feed nutrients from digestion and from being metabolized by microorganisms during storage (Santos et al., 2012).
The lack of differences could be attributed to the processing methods, such as fine grinding, coarse grinding, extrusion, and flocculation, used to facilitate microbial action (Vargas Jr. et al., 2008).These methods usually do not change the chemical composition of the feeds, except for oil extraction, peeling, and extrusion that reduce the ether extract and fibre contents in the meal (Cação et al., 2012).Therefore, processing changes the structural links between starch and protein and also the availability of the lipid fraction (Bertipaglia et al., 2008).
Studies indicated that processing could affect starch degradability (Ørskov, 1986;Simas et al., 2008), but our study found that processing on energy concentrated ingredients did not affect the DM and PB degradability.However, other factors also could affect the degradability of the feeds as cultivar (Rossi et al., 2016), feed origin like coproduct or others (Busanello et al., 2016a;Lee et al., 2016), soluble carbohydrate content (Poorkasegaran and Yansari, 2014), neutral detergent fibre (NDF) and acid detergent fibre (ADF) (Busanello et al, 2016b;Lee et al., 2016).
The readily water-soluble fraction of DM showed a higher degradability trend (P = 0.0888) in the grain than in the meal (Table 1).Processing reduces the water-soluble fractions and interferes with degradability parameters, making the meal more accessible to microbial action, and consequently, modifying the microbial protein production (Shabi et al., 1999;Dhiman et al., 2002;Dehghan-Banadaky et al., 2007;Sveinbjörnsson et al., 2007, Moharrery et al., 2014).However, further research is needed in order to uncover the differences in ruminal degradation between the grain and meal.
Without any significant differences in the ruminal potential and effective degradability of DM and CP between the grain and meal of energy concentrated ingredients, diet formulation depends on animal species and physiological state as well as the availability and cost of the ingredients.Bolzan et al. (2007) evaluated corn grain meal fed to the sheep and concluded that grinding is not necessary, because the liquid nutritional requirements can be met by the addition of concentrated feed in the diet.In primiparous young cows (22-24 months old) that produce approximately 30 kg of milk d -1 , the diet needs to optimize the voluntary intake, since the pass rate is between 5% and 8% per h and reduces feed utilization (Linden et al., 2014).Feeds with relatively high degradation rates (fraction c) are those that increase the voluntary intake (Pereira et al., 2003).
Most Brazilian studies on degradability have focused on the evaluation of DM and CP, since the available techniques have a relatively low cost and effort level.However, future studies need to investigate the relationship between starch (cell content) and cellulose, hemicellulose, and pectin (cell wall carbohydrates) by using gravimetric analysis (Hall, 2003).

CONCLUSION
Feed processing does not change the ruminal degradability of DM and CP of energy concentrated feeds with distinct physical forms.Further studies are needed to evaluate the in situ ruminal degradability of starch in Brazil.Ørskov and McDonald (1979); † Values determined at different passage rates as suggested by the agricultural and food research council (1993)

Table 1 : Adjusted mean of dry matter (DM), water-soluble fraction (a) of DM, potentially degradable fraction (b) of DM, degradation rate (c) of DM, and effective degradability at 2%, 5%, and 8% DM per h in grain and meal
Ørskov and McDonald (1979)ribed byØrskov and McDonald (1979); † Values determined at different passage rates as suggested by the agricultural and food research council(1993)

Table 2 : Adjusted mean of crude protein (CP), water-soluble fraction (a) of CP, potentially degradable fraction (b) of CP, degradation rate (c) of CP, and effective degradability at 2%, 5%, and 8% of CP per h in grain and meal
*Values determined as described by