Comparison of different protein evaluation systems for growing pigs: Digestible crude protein, and total, faecal digestible and ileal digestible amino acid intakes as performance response predictors Jarmo Valaja Valaja, J. 1994. Comparison of different protein evaluation systems for grow- ing pigs: Digestible crude protein, and total, faecal digestible and ileal digest- ible amino acid intakes as performance response predictors. Agricultural Science in Finland 3: 429-437. (Department of Animal Science, P.O. Box 28, FIN-00014 University of Helsinki, Finland.) The validity of apparent faecal digestible crude protein and total, apparent faecal or ileal digestible amino acid intakes (lysine, threonine and methionine) as animal performance predictors was evaluated on the basis of digestibility coefficients obtained from the literature and performance and carcass parameter data from five different experiments on growing pigs. Correlations and regression equations were calculated between daily digestible crude protein or amino acid intakes and the performance and carcass parameters of the pigs. No connection was found between digestible crude protein intake and the per- formance of the pigs. The correlations were highest between different lysine in- takes and daily gain (DG) (r = 0.808-0.867, p < 0,001). Ileal digestible lysine intake correlated with the performance of the pigs better than did intakes of total or faecal digestible lysine. The feed conversion ratio (FCR) (p < 0.05), and the thick- ness of back (BF) (p < 0.001) and side fat (SF) (p < 0.001) correlated highly with ileal digestible lysine intake. The correlations between these parameters and total or faecal digestible lysine intakes were lower but also significant (total lysine: BF p < 0.001, SF p < 0.01 and faecal digestible lysine: BF p < 0.01, SF p < 0.05). The regression equations agreed well with the coefficients of correlation. Ileal digest- ible lysine intake explained changes of performance and carcass parameters better than did intakes of total and faecal digestible lysine. The study confirms the advantage of using ileal digestibility coefficients of amino acids for detecting differences in the supply of amino acids from different feeds. Key words: swine, lysine, methionine, threonine, digestibility, daily gain, feed conversion ratio, back fat, side fat Introduction The practical formulation of swine diets in Fin- land is usually based on the total supply of es- sential amino acids (lysine, threonine and sul- phur containing amino acids) and digestible crude protein from dietary ingredients. However, wide variation is found in the digestibility of protein and amino acids between different feed ingredi- ents determined either at terminal ileum or in faeces (Jdrgensen et al. 1984, Sauer and Ozimek 1986, Knabe et al. 1989). For economic and envi- ronmental reasons, it is essential to take these dif- ferences into account in diet formulation. 429 Agricultural Science in Finland 3 (1994) https://www.c-info.fi/en/info/?token=wrfpx4tAhRQVuuGs.H-_ODOhz5VflMGYslhdKMw.5lBvqTSg2Vn4yhWcpNV8agqIMu3tOj7EJpsudL-s4VsA9zpXRsOj-foxIwTRhfdUkcNX0mUGt_4qIu64K5Mt9QqtO8kJL88KaofmIckn2boIcwxcxkDiDHf8-ub4vXXv7590IpEn6JbB4NmS0-RTro_9I-IH4_djGm53cXuh_UeqrGU5B78uovfZ6oiN4U9xOOSCfRkJWltYou44kVnBIRnbhS8q2uaxDEFqIHJTA7SwqQ__GyfcspiTe0VczLw3keS- It is generally agreed that only the nitrogen absorbed from the small intestine has nutritional value for pigs. Zebrowska (1973) showed that nitrogen infused into the terminal part of the ile- um was digested, but that it was almost com- pletely excreted in urine. Comparisons have been made between the ileal and faecal digestibilities of amino acids in different feeds (Jorgensen et al. 1984, 1985); the apparent faecal digestibility of amino acids usually gives higher values than does ileal digestibility and may overestimate the amount of amino acids available for protein syn- thesis. Microbial fermentation and protein syn- thesis in the large intestine also modify the amino acid composition of faeces as compared with the undigested dietary protein residue (Mason 1984). Protein evaluation system currently used in Fin- land is based on the apparent faecal digestibility of protein and the total amount of amino acids in the diet (Salo et al. 1990). In feed tables used in Denmark apparent faecal digestibility of each amino acid is calculated from the total content of amino acids and the faecal digestibility of nitro- gen (Andersen and Just 1983). Recently pub- lished Dutch feed tables also report the apparent ileal digestibility coefficents of amino acids (CVB 1991). Many authors have concluded that amino acid digestibilities measured at the terminal ileal are the most appropriate (e.g. Tanksley and Knabe 1984, Sauer and Ozimek 1986). How- ever, Batterham et al. (1990a, 1990b) have que- ried the validity of measuring the ileal digestibil- ity of some heat-treated feedstuffs. Only a few experiments have been conducted to compare the faecal or ileal digestibility values with animal performance responses (Just et al. 1985, Dierick et al. 1988, Wiseman et al. 1991), and they give no clear answer as to which method is the most reliable for practical diet formulation. In 1992, the Ministry of Agriculture and For- estry set up a project to update Finnish feed tables for farm animals. As part of the project, the different protein evaluation systems for grow- ing pigs were studied. The investigation reported in this paper compares a number of these sys- tems as predictors of performance and carcass parameter responses. Material and methods Protein evaluation systems Four protein evaluation systems were select- ed; apparent digestible crude protein, total amino acids (lysine, methionine and threonine), appar- ent faecal digestible amino acids and apparent ileal digestible amino acids. The apparent faecal digestible crude protein content of the diet was calculated from the analysed crude protein con- tent of the dietary ingredients and the apparent faecal digestibility values taken from the feed tables currently used in Finland (Salo et al. 1990). The total content of amino acids in the diet was calculated from the analysed amino acid content of the feed ingredients. The appar- ent faecal digestible amino acid content was cal- culated from the amino acid content and the table values of the apparent faecal digestibility of crude protein in dietary ingredients (Salo et al. 1990). The apparent ileal digestible amino acid content was calculated using the digestibility co- efficients reported in the Dutch feeding tables (CVB 1991). Data set The data were collected from feeding trials con- ducted on growing pigs at the Swine Research Station of the Agricultural Research Centre of Finland in 1986-92. Five feeding trials compris- ing 23 treatments and 604 pigs were chosen for the investigation (Table 1). In the experiments different protein sources were compared, feeding was restricted (calculated equal energy intake), the amino acid composition of feed ingredients in the experimental diets was analysed and the use of synthetic amino acids in the diets was limited. One treatment mean served as an experi- mental unit. In all experiments the control diet consisted of barley, soyabean meal and a mixture of minerals and vitamins. The experimental diets comprised mainly domestic protein ingredients, e.g. rape- seed meal, meat and bone meal, peas, skim milk 430 Agricultural Science in Finland 3 (1994) Table 1. Description of data set. Experiment Treatments Animals Feeding scale Reference I. Fish meal exp., 1986 SBM 20% 112, 1.2-3.0FU/d Valaja et al. (1992) SBM 16/FM 2.7% 28/trm SBM 10/FM 6.5% FM 13% 2. Meat and bone meal exp., 1987 SBM 16.5% 140, 1.2-2.8 FU/d Alaviuhkola (1989) SBM 10/MBM (Plant 1) 7.5% SBM 3/MBM (Plant 1) 15% 28/trm SBM 10/MBM (Plant 2) 7.5% SBM 3/MBM (Plant 2) 15% 3. Domestic protein sources exp, 1, 1988 SBM 14/FM 2% RSM 22/P 11% 144, 1.2-2.8 FU/d Suomi and Immonen (1989) 24/trm RSM 18/P9/MBM 3% RSM 18/P9/PY 2% RSM 18.7/P 9.3/MBM 2/MP 0.5% RSM 15.3/P 7.7/MBM 3/PY 2/MP 0.5% 4. Domestic protein sources exp. 2, 1989 SBM 14/FM 2% RSM 22/P 11 % 48, 1.2-2.8 FU/d Suomi and Immonen (1989) 12/trm RSM 18/P9/MBM 3% RSM 15.3/P 7.7/MBM 3/PY 2/MP 0.5% 5. Rapeseed meal exp., 1992 SBM 22.5%, SBM 14.9% 160, 1.2-2.9 FU/d Siljander-Rasi (1993) SBM 15.1/RSM 7.6%,58M 9.9/RSM 5% SBM 7.6/RSM 15.1%,SBM 5.0/RSM 9.9% 40/trm RSM 22.6%, RSM 14.9% SBM = soyabean meal, RSM = rapeseed meal, P = peas, MBM = meat and bone meal, FM = fish meal, PY = pekilo yeast and MP = milk powder. powder and pekilo yeast except in experiment 1, where Norwegian fish meal was used. The nitro- gen content of the dietary ingredients was deter- mined by the Kjeldahl method, and amino acids were analysed by high performance liquid chro- matography (HPLC) after hydrolysis with 6 N HCI at 110°C for 20 h. The mean content of digestible crude protein, lysine, methionine and threonine was in the range 118-139,6.5-8.9, 1.4- 3.1 and 3.7-6.2 g/kg feed in the five experiments, respectively (Table 2). The data set contained the treatment means of feed consumption, days in experiment, and performance and carcass com- position results including daily gain (DG), feed conversion ratio (FCR), back fat (BF) and side fat (SF) thickness, and per cent lean in valuable cuts (LVC) and in whole carcass (LC). The mean DG, FCR, BF, SF, LVC and LC of the experi- ments were in the range 807-875 g, 2.61-2.96 FU/kg, 22.3-25.4 mm, 15.5-19.3 mm, 78.7- 80.8% and 49.9-54.5%, respectively. The daily intake of digestible crude protein or essential ami- no acids (lysine, methionine and threonine) was calculated from the protein and amino acid com- position of the diets and feed consumption of the pigs. 431 Agricultural Science in Finland 3 (1994) Table 2. Mean dietary digestible crude protein, lysine, methionine and threonine contents and performance data of the experiments. Experiment DCP LYS MET THR DG FCR BE SF LVC LC g/kg g/kg g/kg g/kg g/day FU/kg mm mm % % 1. Fish meal 139 8.9 3.1 6.2 875 2.61 22.3 15.5 80,6 50.2 2. Meat and bone meal 136 6.5 1.8 5.4 811 2.96 25.4 19.3 78.7 49.9 3. Domestic protein sources 1 126 6.8 1.4 3.7 807 2.65 24.2 16.4 80.4 51.3 4. Domestic protein sources 2 130 6.6 1.4 6.2 819 2.62 24.4 17.8 79.7 50.7 5. Rapeseed meal 1, diet 1 136 8.7 1.9 6.1 844 2.72 23.7 16.8 80.8 54.5 diet 2 118 7.1 1.8 5.0 DCP = digestible crude protein, LYS = lysine, MET = methionine, THR = threonine, DG = daily gain, FCR = feed conversion ratio, BF = back fat, SF = side fat, LVC = lean in valuable cuts and LC = lean in carcass. 1.The experiment was divided into two periods, weeks 1-5 and weeks 6 to slaughter, with different diets. Performance and carcass parameter data are the means of the whole experiment. Analysis of data Statistical analysis of the data was performed us- ing the SAS statistical package (SAS 1990). Pear- son’s linear correlation coefficients were calcu- lated with the CORR procedure between the di- gestible crude protein or different amino acid in- takes and the performance or carcass parameters. Linear regression equations were calculated with the REG procedure, using the digestible crude protein or amino acid intakes as independent var- iables and the different performance and carcass parameters as dependent variables. The signifi- cance of the coefficients of correlations and re- gressions was tested with a t test (H0 : the coeffi- cient of regression or correlation = 0). Partial correlation coefficients were calculated with the CANCORR procedure between the protein or ami- no acid intakes and the LVC or LC in order to eliminate the effect of year from the correlations, because the carcass dissection procedure was changed at the beginning of 1989, resulting in an average 2% increase in carcass lean content. The year effect was partialled out of the correlations with the PARTIAL statement. The year of the experiment was included in the regression mod- els where appropriate. Criteria for evaluation of systems were: significance of the coefficients of regression and correlation, and the fit of the re- gression models evaluated with the coefficients of determination (R 2 ). Results Correlations The correlation matrix revealed large differences in the significance of the correlations between the digestible crude protein or differently assayed amino acid intakes and the performance and car- cass parameters (Table 3). There was no connec- tion between digestible crude protein intake and the performance or carcass parameters of the pigs. Significant correlations were found between amino acid intakes and the performance and carcass com- position data although the differences in the power of correlations were quite small between the dif- ferent amino acid intakes. However, amino acid intakes, especially that of lysine, which were calculated using ileal digestibility coefficients tended to correlate with the performance of the pigs better than did total or faecal digestible amino acid intakes. FCR correlated significantly with ileal digestible lysine intake (r = -0.505, p < 0.05) and digestible crude protein intake (r = -0.431, p < 0.05). BF and SF also correlated significantly with ileal digestible lysine intakes (BF, r = -0.731, P < 0.001; SF, r = -0.700, p< 0.001); the correlations with total and faecal digestible lysine intakes were lower although sig- nificant (total lysine; BF, r = -0.687, p < 0.001; SF, r = -0.564, p < 0.01 and faecal digestible lysine; BF. r = -0.626, p < 0.01; SF, r = -0.490, p < 0.05). 432 Agricultural Science in Finland 3 (1994) Table 3. Correlation matrix between daily protein or amino acid intake and performance data (5 feeding trials, n = 23, except for ileal amino acid intake n = 20). DG FCR BF SF LVC LC 3 g/day FU/kg mm % %mm Protein intake (g/day) Digestible crude protein 0.190 0.431’ Total amino acids -0.085 0.188 -0.093 0.150 lysine 0.808"‘ -0.302 -0.68V" -0.564" 0.612" 0.606" methionine 0.683’” -0.065 -0.418’ -0.272 0.321 0.384" threonine 0.571” 0.038 -0.214 0.120 -0.079 -0.143 Faecal digestible amino acids' lysine 0.812"* -0.263 -0.626" -0.490* 0.574" 0.606" methionine 0.687*" -0.095 -0.414* -0.274 0.324 0.373° threonine 0.671"* -0.035 -0.316 0.016 0.072 0.018 Ileal digestible amino acids 2 lysine 0.867'" -0.505' -0.731'" -0.700"' 0.646" 0.627" methionine 0.731'" -0.265 -0.500' -0.445' 0.385° 0.407° threonine 0.706'" -0.151 -0.341 -0.088 0.085 0.037 DCP = digestible crude protein, LYS = lysine, MET = methionine, THR = threonine, DG = daily gain, FCR = feed conversion ratio, BF = back fat, SF = side fat, LVC = lean in valuable cuts and LC = lean in carcass. 1. coefficients from Salo et al. (1990) 2. coefficients from CVB (1991). 3. calculated as partial correlations. Statistical significances =p < 0.10; ’=p < 0.05; p < 0.01; ’" = p < 0,001. The highest correlations were found between daily lysine intakes and DG (r = 0.808-0.867, p < 0.001). Methionine and threonine intakes also paralleled DG but the correlations were lower than those between lysine intake and DG (me- thionine: r = 0.683-0.731, p < 0.001; threonine: r = 0.571-0.706, p < 0.01 (faecal) and p < 0.001 (ileal)). Daily lysine intakes also correlated well with other performance and carcass parameters except with FCR, whereas the correlations between methionine or threonine intakes and the perform- ance and carcass parameters were clearly lower. Regression equations Since performance responses are a consequence of protein and amino acid intake it was logical to try and fit the data to the regression equations. Only the regression equations calculated for di- gestible crude protein and different lysine intakes are presented (Table 4) because the coefficients of determinations and regressions were extreme- ly low for methionine and threonine intakes ex- cept in the case of DG, where R 2 was 0.467, 0.471 and 0.535 or 0.326, 0.450 and 0.499 with total, apparent faecal and ileal digestible methio- nine and threonine intakes, respectively. The year of the experiment was also included in the equa- tionsfor LVC and LC, where it had a significant effect. The regression equations for digestible crude protein and different lysine intakes were general- ly in agreement with the coefficients of correla- tion. The coefficients of regression calculated for digestible crude protein intake were very low and differed significantly from zero only for FCR (p < 0.05), where the coefficient of determina- tion was quite low, 0.185. The best fit for the regression equations was found between the ileal digestible lysine intakes and performance re- 433 Agricultural Science in Finland 3 (1994) Table 4. Coeffients of regression for performance and carcass data calculated as a function of daily protein or amino acid intakes (xl) (g/day). Experimental year (x2) was included in the regression equation where significant. Digestible protein (g/day) Total lysine (g/day) Faecal dig. lysine (g/day) Ileal dig. lysine (g/day) XI Year R 2 xl Year R 2 xl Year R 2 xl Year R 2 (x2) (x2) (x2) (x 2) Daily gain, g/day 0.332 - 0,036 11.6’' FCR, FU/kg 0.004’ - 0.185 -0.022 Back fat, mm -0.006 - 0.007 -0.387’' Side fat, mm 0.017 - 0.035 -0.417" Lean in valuable cuts, % -0.016 - 0.081 0.238’ 0.095“ Lean in carcass, % 0.008 0.795’’’ 0.780 0.216” 0,783’ 0.653 11.8'” - 0.65912.7" 0.091 -0.019 - 0.069 -0.037' 0.472 -0.356" - 0.392 -0.429" 0.319 -0.365' - 0.239 -0.521" 0.751 0.255 0.534 0.485 0.331 0.221* 0.198° 0.2870.299” 0.178” 0.466 0,851 0.219" 0.796”* 0.8500.241" 0.774*" 0.865 Statistical significance: o = p < 0.10;' =p < 0.05; "= p < 0.01; "’=p < 0.001. FCR = feed conversion ratio. sponses. Only ileal digestible lysine intake paral- leled FCR (p < 0.05), but R 2 was quite low (0.255). Ileal digestible lysine intake also explained well the variations in BF and SF (R 2 = 0.534 and 0.485), and the coefficients of regression were highly significant (p < 0.001). Total lysine intake produced a highly significant coefficient of re- gression with BF (p < 0.001), but a less signifi- cant coefficient with SF (p < 0.01). In both cases, the coefficients of regression for faecal digesti- ble lysine intake were lower (BF, p < 0.01; SF, p < 0.05). The coefficient of regression for ileal digestible lysine intake was higher with LVC (p < 0.01) than was that for total or faecal digest- ible lysine intake (p < 0.05) and the coefficient of determination changed from 0.331 to 0.287 and 0.466 with total, faecal and ileal digestible lysine intakes, respectively. The best fit for the regression equations was found between the dif- ferent lysine intakes and DG, where the coeffi- cients of regression were highly significant (p < 0.001). However, R 2 tended to increase from total to ileal digestible intake (0.653, 0.659 and 0.751 for the total, faecal and ileal digestible in- takes, respectively). Discussion Calculations reported here were based on the as- sumption that the daily intake of protein and amino acids in the diets was below that required to meet the animal’s potential daily body protein deposi- tion, such that the performance responses were linearly related to the changes in intake. How- ever, in four of the five experiments the content of digestible crude protein per unit of energy in the diets was in balance, and in these experi- ments the performance responses could not be related to the amount of digestible crude protein in the diets. This explains the poor correlations and regressions of digestible crude protein in- take. In the case of the daily intake of lysine, the studies of Hanrahan (1989) and Madsen et al. (1991) confirm the validity of the assumption of a linear response. In all diets, lysine was the first limiting amino acid, and it resulted in a better fit to the regressions and higher correlations than did methionine or threonine intake. According to Wang and Fuller (1990), nitrogen retention is very closely related to the intake of the digestible first limiting amino acid. In theory, digestibilities measured at the end of the ileum should give reliable estimates of the digestibility of nitrogen and single amino acids in feeds since only the amino acids ab- sorbed before the ileo-caecal junction are avail- able for protein synthesis, and the nitrogen ab- sorbed from the large intestine is of no nutri- tive value to the animal (Zebrowska 1973). In the present calculations, ileal digestible amino acid intake was more closely related to the 434 Agricultural Science in Finland 3 (1994) performance of the pigs than was digestible crude protein or total or faecal digestible amino acid intakes. This is consistent with the results of Just et al. (1985), who found a slightly high- er correlation of ileal digestible crude protein and amino acids with deposited protein than with crude protein and amino acids disappearing in the whole digestive tract. The results obtained by Dierick et al. (1988) gave even stronger evi- dence for the superiority of ileal over faecal di- gestibility values, as significant correlations of DG or FCR were found with ileal digestible pro- tein (r = 0.76 for DG and -0.87 for FCR) but not with faecal digestible protein (r = 0.34 for DG and -0.65 for FCR). Comparing diet formula- tions based on either the crude protein or the total or ileal digestible amino acid content, Tanks- ley and Knabe (1984) noted that the perform- ance of pigs improved when ileal digestible ami- no acids were used. Low et al. (1982) and Moughan and Smith (1985) also concluded that ileal digestibility is a good predictor of pig re- sponses to the diets used. It is nonetheless evident that in some feeds the ileal digestibility values fail to improve the diet formulation. Batterham et al. (1990a, 1990b) observed that in certain heat-treated feeds, e.g. cottonseed meal and meat and bone meal, the ileal digestibility of lysine only accounts for some of the reduced availability. In the experiment of Wiseman et al. (1991), the formulation of diets containing heat-treated fish meals based on the ileal or faecal digestibility coefficients of amino acids did not fully account for differences in the performance of the pigs compared with those fed untreated fish meal. The authors suggested that the absorbed amino acids were partly in an una- vailable form for the animals. Moughan et al. (1991) also observed that the formulation of a barley, fish meal, and meat and bone meal diet based on the ileal digestibility of amino acids leads to overestimation of actual pig perform- ance. In the present investigation, only the diets of the experiment 2 contained high amounts of heat-treated meat and bone meals and this did not affect the results. Batterham (1992) sug- gested that amino acid availabilities could be measured with the slope-ratio assay instead of ileal digestibility assays. However, the method appears to be rather unreliable in practice (Moughan 1991). Here, the faecal digestible amino acid content calculated from crude protein digestibility failed to show any improvement over the total amino acid content in BF and SF measurements. The calculation method is not appropriate in diet for- mulation since the relationship between the di- gestibility of nitrogen and an amino acid can vary from one feed to another (Jorgensen et al. 1984, Wiseman et al. 1991). Laplace et al. (1989) also found that the source of fibre in the diet had a significant negative interaction with the overall digestibility of amino acids and that additive ef- fects occurred at the end of the small intestine. In addition, the mean ileal digestibilities of essen- tial amino acids in soyabean meal, sunflower meal, fish meal, and meat and bone meal were found to be 12.7% units lower than the mean faecal di- gestibility values (JORGENSEN et al. 1984). Knabe et al. (1989) pointed out that amino acid digest- ibilities could be predicted more precisely from ileal nitrogen digestibility than from the faecal nitrogen digestibility, but that neither ileal nor faecal nitrogen digestibility could be used with a high degree of certainty for predicting ileal ami- no acid digestibilities. Conway et al. (1990) like- wise concluded that the requirement for threo- nine should be related to ileal digestibility and not to faecal digestibility. However, Jorgensen et al. (1985) found correlations ranging from 0.46 to 0.73 between overall crude protein digestibili- ty and ileal digestibility of cystine, threonine, me- thionine and lysine. The very low correlations of amino acid intake with FCR came as a surprise. However, Batter- ham et al. (1981) suggested that FCR should be calculated on a carcass basis in order to elimi- nate the effect of gut fill from the results. Differ- ences in gut fill are evident, especially in the cases of high fibre diets. This may have been the case in experiment 5, where rapeseed meal was included in the diets. The positive correlation be- tween daily digestible crude protein intake and FCR was the result of the generally higher FCR 435 Agricultural Science in Finland 3 (1994) in experiment 2, which had a biasing effect on the correlation. According to this study, the apparent ileal di- gestible amino acid intake is a better predictor of performance and carcass responses than is either total or apparent faecal digestible amino acid in- take. This is in agreement with the theory of the site of digestion processes and the results of most earlier experiments conducted on the same topic. The cost and laboriousness of ileal digestibility assays make them difficult to use as a routine procedure. Consequently, future research should aim to develop cheaper methods, e.g. in vitro assays, to predict the digestibility values of the feeds used in diet formulation. Acknowledgements. The author is grateful to the Swine Research Station of the Agriculture Research Centre for providing the data for the investigation. Financial support was received from the Ministry of Agriculture and Forest- ry- References Alaviuhkola, T. 1989. Lihaluurehujauho sikojen rehuna. Lihayhtymän tiedotuslehti 2: 15-16. Andersen, P.E. & Just, A. 1983. 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Tutkimus oli osa maa- ja metsätalousministeriön käynnistämää rehutaulukoiden uudistusprojektia. Aineistoksi valittiin viisi lihasikojen ruo- kintakoetta Maatalouden tutkimuskeskuksen sikatalouden tutkimusasemalta. Rehun koostumustietojen sekä kirjalli- suudesta saatujen sulavuuskertoimien perusteella lasket- tiin ruokintaryhmien päivittäinen sulavan raakavalkuaisen ja tärkeimpien välttämättömien aminohappojen, lysiinin, metioniinin ja treoniinin, kokonaissaanti sekä ko. amino- happojen kokonaissulava tai ohutsuolessa sulava osuus. Valkuaisen ja aminohappojen saanteja verrattiin ruokinta- ryhmien tuotantotuloksiin (päiväkasvu ja rehuhyötysuh- de) ja teuraslaatuparametreihin (selkä-ja kylkisilavan pak- suus, koko ruhon sekä sen arvokkaiden osien lihaprosent- ti). Päivittäisellä sulavan raakavalkuaisen saannilla ei pys- tytty selittämään eroja sikojen tuotantotuloksissa tai teu- raslaadussa. Osa syynä tähän oli, että neljässä kokeessa viidestä oli ruokintaryhmien sulavan raakavalkuaisen saanti tasattu. Aminohappojen, erityisesti lysiinin, päivittäiset saannit selittivät varsin hyvin tuotantotulosten muutoksia. Korrelaatiokertoimet olivat suurimpia eri tavoin laskettu- jen lysiinin saantien sekä päiväkasvun välillä. Ohutsuo- lessa sulava aminohappojen saanti selitti kokonais- tai son- tasulavaa saantia paremmin tuotantotulosten ja teuraspa- rametrien muutokset. Ero oli suurin rehuhyötysuhteessa sekä selkä- ja kylkisilavan paksuudessa. Myös regressio- yhtälöihin ohutsuolisulavan lysiinin saanti sopi paremmin kuin lysiinin kokonais- tai kokonaissulava saanti. Ohut- suolessa sulavan lysiinin saanti selitti paremmin rehuhyöty- suhteen, selkä- ja kylkisilavan paksuuden sekä ruhon ar- vokkaiden osien lihaprosentin muutoksia verrattuna lysii- nin kokonais- tai kokonaissulavaan saantiin (selkäsilavan paksuudessa ainestaan kokonaissulavan lysiinin saanti hei- kompi). Selvitys vahvistaa käytännössä ohutsuolisulavuus- kertoimien paremmuuden rehujen valkuaisen laadun ar- vioimisessa. 437 Agricultural Science in Finland 3 (1994)