Effect of fat coating on rumen degradation and
intestinal digestibility of soybean meal
F. Rossi
*, L. Fiorentini, F. Masoero, G. Piva
Istituto di Scienze degli Alimenti e della Nutrizione, UniversitaÁ Cattolica del Sacro Cuore, FacoltaÁ di Agraria,Via Emilia Parmense 84, 29100 Piacenza, Italy
Received 2 December 1998; received in revised form 23 April 1999; accepted 19 May 1999
Abstract
Three rumen and duodenum fistulated dairy cows were used to determine the effects of fat and methionine addition to soybean meal on rumen degradation of crude protein, the amino acid pattern and the intestinal digestibility of undegraded residues. The addition of 10% and 25% fat resulted in lower DM degradation after 8 and 24 h of incubation. Protein degradation was reduced by 10% fat addition at 8 and 24 h, while 25% fat addition considerably lowered crude protein disappearance after only 8 h of incubation. A 10% fat addition increases the content of essential amino acids in the undegraded residue vs. the control, while 25% fat addition only increases the concentration of lysine, histidine and arginine. Standard soybean meal has higher intestinal dry-matter digestibility than fat-coated soybean, probably due to interference between the lipid matrix and the enteric enzyme attack which, most likely, does not affect the proteolytic enzymes, given the small
differences in intestinal nitrogen disappearance found among the different soybean types.#1999
Elsevier Science B.V. All rights reserved.
Keywords: Protective treatment; Ruminal degradability; Amino acids; By-pass protein
1. Introduction
The recent European limitations concerning the use of animal meals in the formulation of ruminant feeds (94/381/EC; 95/60/EC) have made it more difficult to meet the by-pass protein requirements in high-yielding cows. This has increased the interest in plant-protein sources of low rumen degradability and good supply of essential amino acids like
81 (1999) 309±318
*Corresponding author. Tel.: ++39-523-599-286; fax:++39-523-599-259
E-mail address: rossi@pc.unicatt.it (F. Rossi)
lysine and methionine. Corn gluten, is the only vegetable feed with high protein content of low rumen degradability, but with low content of lysine (Masoero et al., 1994) and high cost. Coconut meal has also a low degradability but its protein content is only slightly higher than 20% (NRC, 1988). Soybean meal is the main source of plant proteins, but its
rumen degradability is >60% (I.N.R.A., 1988; NRC, 1988). Higher values (75%) are
found for sunflower meal. Both these meals are characterized by lower methionine and lysine supply when compared to fish meal (Erasmus et al., 1994; Masoero et al., 1994); in particular, soybean meal lacks methionine and sunflower has a low content of lysine. A reduction in the rumen degradation of oil-free soybean can be obtained by treatment with heat (Faldet et al., 1991; Schroeder et al., 1995), formaldehyde (Subuh et al., 1994 et al., 1996), lignosulfonate (Waltz and Stern, 1989; Standford et al., 1995), xylose (Nakamura et al., 1992) or protein coatings (Mahadevan, 1990; Atwal et al., 1995; Matsumoto et al., 1995). The efficacy of some treatments is poor (e.g. xylose); others reduce lysine availability (e.g. heat) or generate problems of toxicity (e.g. formaldehyde). Furthermore the high cost of the protective treatment is the major disadvantage that occurs when protein coatings are used. Recently, Kowalski et al. (1997) suggested that Ca-salts of highly unsaturated oil (from rapeseed) could be used for coating soybean meal and reducing protein rumen degradation. However, they did not evaluate the effect of this treatment on the amino acid pattern of undegraded residue.
This study was carried out to evaluate the effectiveness of using saturated fat-coating and methionine addition as a means of protecting soybean meal protein against degradation in the rumen and increasing the amount of essential amino acids available for the animal.
2. Materials and methods
Soybean was protected against rumen degradation by adding two different levels (10% and 25%) of long-chain triglycerides (palmitic and stearic acids) salified with Ca++and mixed with tristearate and tripalmitate. Methionine was also added in amounts of 2 and 6 g/kg for profiles 10 and 25, respectively, the efficiency of methionine addition technology was ca. 30%. A patent for this technique was requested (application number FI96A29). Two samples, taken from the same lot of feed, underwent treatment and the untreated residue was used as control. The products obtained were marked as Profile 10 and Profile 25, depending on the amount of added fat. Normal and fatted soybean meal were analyzed for their content in fibrous fractions (Goering and Van Soest, 1970) ether extract (Commission of the European Communities, 1998), ash (AOAC, 1980), the analytical composition of these feeds is shown in Table 1.
Dry-matter and nitrogen solubilities were assessed by incubating 0.5 g of feed in a borate-phosphate buffer (Krishnamoorty et al., 1983) at 398C for 8 and 24 h; the insoluble amount was collected on an ash-free filter paper (S&S No. 589, Germany), washed with bidistilled water and analyzed for nitrogen content using the Kjeldhal method.
Rumen degradability was determined in situ in three Friesian cows (576 kg live-weight), with rumen fistulae, and fed with grass hay (24.9% of DM), corn silage (32.2% of DM) and concentrate (42.9% of DM); the protein level of the ration was 14.6% while
energy concentration was 0.86 forage unit lactation (FUL) (Jarrige, 1998) /kg DM. This diet, administered in the morning (8:00 a.m.) and in the evening (5:00 p.m.), was started
15 days before the beginning of the experiment. Using nylon bags (12.5 cm7.5 cm;
pore size 46 mm) (Michalet-Doreau et al., 1987), filled with5 g of feed, three kinetic studies were performed for each animal with two replicates for feed and incubation time (8 and 24 h), thus 18 replicates for feed and incubation time were obtained. To assure enough residue after rumen incubation, particularly for the 24-h incubation time, the amount weighted in each nylon-bags was higher than that suggested by Michalet-Doreau et al. (1987). Once extracted, the bags were machine-washed for 15 min with cold water, dried in an oven at 658C for 48 h and analyzed for their nitrogen content; the amino acid content was determined by means of ion exchange chromatography using Amino Analyzer 3A30 (Carlo Erba, Milan, Italy) on the original feeds and the undegraded residues of all the bags incubated for 24 h. The effect of fat-coating on amino acids rumen degradation was assessed considering the following ratio:
AAn=SEAA before rumen incubation
AAn=SEAA post rumen incubation
where: AAnis the content (g/100 g CP) of a single essential amino acid, andEAA the
total essential amino acids (g/100 g of CP).
Using the data of rumen degradability for crude proteins and the amino acid composition of the undegraded residue, the amount of by-pass essential amino acids after 24 h of rumen incubation was calculated as follows:
100 g of feed CP g=100 g CP rumen byÿpass AAncontent of undegraded residue %
where AAnis referred to each single essential amino acids.
In order to evaluate the effect of fat-coating on intestinal digestibility, nitrogen disappearance from the intestinal mobile bags was evaluated using the method proposed by Peyraud et al. (1988).
3. Results
Addition of fat reduces nitrogen solubility in proportion to the lipid content. Particularly marked was the drop observed with Profile 25 (Table 2). The addition of a
Table 1
Chemical analysis (% on DM basis) of the tested soybean meal
Feedstuffs Dry
Soybean meal 89.90 52.34 1.33 12.25 6.02 1.88 6.40
Profile 10 91.74 42.85 1.49 11.99 7.15 12.87 6.68
Profile 25 93.70 32.71 1.90 12.60 7.08 20.13 6.81
aAfter hydrolysis with HCl 3 N.
lipid matrix on the surface reduces the rumen degradability of soybean meal (Table 3) already after 8 h of incubation, both in terms of dry matter and proteins. The highest lipid coating yielded the lowest rumen protein degradation. By extending the time of residence in the rumen up to 24 h the increase in the amount of by-pass protein tends to decrease compared to the control soybean, keeping significantly high only for the Profile 10 product, while differences between treatments were null.
Apart from protein degradability, also the amino acid composition of undegraded residues is changed by fat addition after 24 h (Table 4). In particular, the concentration of lysine and threonine increases while reductions are observed for valine, methionine and isoleucine. Profile 10 induces greater availability of all essential amino acids vs. the control soybean and of lysine, threonine, valine, leucine and total essential amino acids vs. Profile 25. When compared to standard soybean meal, the 25% fat-coated soybean allows for higher intestinal supply of lysine, methionine, histidine and arginine (Table 5).
Table 2
Nitrogen solubility in a borate±phosphate buffer of normal and two types of fat-coated soybean meal
Feedstuffs N solubility (% on total N)
8 h of incubation 24 h of incubation
Soybean meal 4.41 16.83
Profile 10 3.26 13.38
Profile 25 1.26 3.18
Table 3
Dry matter (DM) and crude protein (CP) in situ rumen degradation of normal and fat coated soybean meal (profiles 10 and 25)a
8-h Rumen degradation (%) 24-h Rumen degradation (%)
D.M. C.P. D.M. C.P.
Soybean meal 34.83Bb 23.57C 70.20B 61.14b
Profile 10 30.53ABa 17.53B 57.87A 44.72a
Profile 25 26.25Aa 9.08A 56.74A 50.82AB
SE 1.409 1.013 2.421 4.772
aMeans in the same column with different letters are significantly different: A,B,C Ð.(P<0.01); a,b Ð (P<0.05).
Table 4
Essential amino acids-to-total amino acids ratio in normal and fat-coated soybean meal (profiles 10 and 25) before and after rumen incubation
Lysa His Arg Thra Vala Meta Ilea Leu Phe SEAA
Soybean meal 0.93a 1.09 0.78 1.04A 1.13Bb 1.00B 1.07B 1.05 1.04 45.61 Profile 10 1.00b 1.00 0.79 1.06A 1.13ABb 0.90B 1.05A 1.05 1.04 46.69 Profile 25 1.00b 1.11 0.80 1.09B 1.08Aa 0.71A 1.06AB 1.06 1.04 46.65
SE 0.020 0.036 0.010 0.006 0.012 0.034 0.005 0.006 0.010 0.844
aA,B Ð (P<0.01); a,b Ð (P<0.05).
Table 5
Estimation of essential amino acids by-pass (g/100 g of feed CP) of normal and fat-coated soybean meal (profiles 10 and 25): calculations are based on 24 h of incubation
Essential amino acid (EAA)a EAA (g /100 g CP)a
Lys His Arg Thr Val Met Ile Leu Phe
Soybean meal 2.22Aa 1.07Aa 2.32Aa 1.83Aa 2.22Aa 0.56A 2.11A 3.33Aa 2.19A 17.85Aa Profile 10 3.69Bc 1.61Bb 3.74Bb 2.89Bb 3.49Bb 0.89B 3.28B 5.17Bb 3.41B 28.18Bb Profile 25 2.91ABb 1.36ABb 3.05ABb 2.34ABa 2.74ABa 0.71AB 2.66AB 4.12ABa 2.76AB 22.64ABa
SE 0.278 0.124 0.291 0.215 0.271 0.080 0.253 0.401 0.262 2.14788
aA,B Ð (P<0.01); a,b,c Ð (P<0.10).
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Intestinal digestibilities as assessed by the mini-bags technique, were different among the feeds, with soybean meal showing higher values of DM disappearance than fat-coated soybean types. Minor and insignificant differences were observed for nitrogen digestibility (Table 6).
4. Discussion
The lower nitrogen solubility found in fat-coated soybean vs. the control suggests an effective physical protection induced by the lipid matrix, which in the Profile 25 was found to persist even after 24 h of incubation. The analysis of the degradability data in situ is more complex.
The reduction in nitrogen disappearance from the bags following lipid coating of soybean meal is in fact variable: after 8 h incubation, rumen protein degradability may be reduced to 40% of the original value, whereas after 24 h, the amount of degradable nitrogen is only 25% lower for Profile 10 compared to the control soybean. The range of reduction observed for rumen degradation after 24 h of incubation is greater than the one
stated by Waltz and Stern (1989) for soybean treated with ethanol (ÿ4.8%) or NaOH
(ÿ16.1%), similar to the one obtained with heat treatments (Faldet et al., 1991; Subuh et al., 1996), but lower than the one obtained with the addition of formaldehyde (Waltz and Stern, 1989; Cho et al., 1990; Subuh et al., 1994, 1996), which reduces rumen
degradability down to40% of the original value, or with a zein coating which causes a
reduction of rumen degradability by almost 90% (Mahadevan, 1990).Our results are comparable to the ones of Kowalski et al. (1997), although in this work the high levels of fat addition (from 50% to 87.5%) resulted in a reduction of nitrogen intake for kilograms of ingested dry matter.
Several works have demonstrated that mono- and poly-unsaturated fatty acids (particularly those present in rapeseed) have a lower rumen stability than saturated ones, like stearate and palmitate utilized for the production of profiles 10 and 25 (Sukhija and Palmquist, 1990; Tamminga and Doreau, 1991; Gulati et al., 1997). These results are not affected by salification with Ca++.
This suggests that a comparable result obtained by the use of saturated fatty acids can be achieved by the input of high levels of unsaturated fatty acids addition.
Increasing fat addition from 10% to 25% reduces protein rumen degradability at 8 h, but not at 24 h; similar results at 24 h might be explained by the higher methionine
Table 6
Intestinal dry matter (DM) and nitrogen disappearance (%) from mini nylon-bags of normal and fat coated (profiles 10 and 25) soybean meal
Feedstuffs DM disappearance (%)a Nitrogen disappearance (%)
Soybean meal 86.14B 97.90
Profile 10 77.86A 96.17
Profile 25 77.31A 97.03
SE 1.923 1.767
aA, B Ð (P<0.01).
inclusion within the lipid matrix of Profile 25 compared to Profile 10 and to the amino acid rumen degradation (Table 1). No differences were observed for DM rumen degradation at 24 h, which indicates a higher fat loss for Profile 25 and the methionine rumen degradation associated with it.
Rumen incubation does not always change the soybean amino acid profile homogeneously (Erasmus et al., 1994; Tagari et al., 1995; Ivan et al., 1996; O'Mara et al., 1997); probably the way of expressing the amino acid content (on crude proteins, on total essential amino acids) affects this variability. It is possible to define some changes induced by rumen proteolysis on the amino acid pattern of the undegraded residue: the concentration of lysine and arginine tends to decrease (Susmel et al., 1989; Rossi et al., 1994; Maiga et al., 1996; O'Mara et al., 1997) together with that of histidine (Susmel et al., 1989; Rossi et al., 1994; Maiga et al., 1996) while threonine increases (Susmel et al., 1989; Rossi et al., 1994; Maiga et al., 1996; O'Mara et al., 1997). There is a trend toward increased isoleucine, leucine, phenylalanine and valine (Susmel et al., 1989; Rossi et al., 1994; Maiga et al., 1996; O'Mara et al., 1997).
Compared to these results, fat addition leads to some modifications in the amino acids composition of the undegraded residues (Table 4). In particular, the concentration of lysine and threonine increases while a reduction is observed in the concentration of valine, methionine and isoleucine. The higher percentage of lysine in the undegraded residue is particularly important since this amino acid, apart from being the one mostly limiting milk yield (Schwab et al., 1992), is mainly derived from animal protein sources (Masoero et al., 1994) whose use is now subject to limitations. Comparing soybean meal to Profile 10, we observed that each fed kilogram of Profile 10 supplies 6.17 g of lysine and 1.3 g of additional methionine. These amounts represent, respectively, 25% and 10% of the levels of rumen-protected amino acids normally used. By protecting soybean with blood meal, Matsumoto et al. (1995) were able to obtain even more marked improvements in the amino acid pattern; it should be noted, however, that in their experiment degradability of nitrogen at 24 h in the proteinaceous feed was 100% Ð definitely, a high value.
The reduced methionine concentration in soybean type Profile 25 shows less protection for the amino acid added to the lipid matrix which is more degraded than the similar monopeptide which is present in the native protein. Schwingel and Bates (1996) have determined the amino acid composition of the final products of the degradation, induced byPrevotella ruminicola, of the protein sub-unitsa anda0of b-conglycinine, the most degradable ones in soybean meal. The concentration (g/100 g of amino acids) of lysine, arginine and valine becomes markedly reduced while leucine, phenylalanine and, above all, threonine show increased concentrations; also, the methionine content decreases, as reported by Susmel et al. (1989), but not by Rossi et al. (1994) and O'Mara et al. (1997). The protective action performed by fat-coated soybean against lysine and arginine may be due to less exposure of the proteolytic enzymes of protein sub-unitsaanda0.
The lower DM digestibility in fat-coated soybean types is probably due to interference between the lipid matrix and the enteric enzyme attack, which most likely does not affect the proteolytic enzymes, given the small differences in nitrogen intestinal disappearance among the different soybean types. Kowalski et al. (1997) reported a lower disappearance of nitrogen and dry matter from intestinal nylon bags when the level of added fat
increased. The data obtained are similar to those obtained by Frydrich (1992), Masoero et al. (1994), Van Straalen and Tamminga (1990) for soybean meal.
In assessing the efficacy of the different methods, one should consider that the price of fat is 25±30% lower than that of blood; this fact, together with the concern about the use of formaldehyde and the reduced bioavailability of lysine induced by heating, makes the addition of fat to soybean particularly attractive in order to reduce its rumen degradability.
5. Conclusions
The addition of saturated long chain Ca-soaps of fatty acids or tri-glyceride to soybean meal is an effective tool in limiting its rumen degradation and improving its amino acid pattern; levels of 25% fat addition do not seem to yield better results than the addition of a 10% lipid matrix.
Acknowledgements
This research was supported by MURST 40%. Project ``Energy and Protein Value of Ruminant Diets''. A special acknowledgement to S.I.L.O. (Firenze, Italy) for the supply of fat-coated soybean. The authors wish to thank Dr. Barbara Sozzi, Mr. Sergio Bagnalasta and Mr. Vittorio Rossi for their skilful technical assistance.
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