Effects of
DL
-methionine hydroxyanalogue (MHA)
or
DL
-methionine (
DL
-Met) on N-retention
in broiler chickens and pigs
Andrea RoÈmer, Hj. Abel
*Institut fuÈr Tierphysiologie und TierernaÈhrung, Kellnerweg 6, 37077 GoÈttingen, Germany
Received 3 July 1998; received in revised form 17 February 1999; accepted 23 June 1999
Abstract
Methionine hydroxyanalogue (MHA) was evaluated for metabolic equivalence compared toDL
-methionine in practical diets for broiler chickens and pigs. Diets calculated to be deficient in methionine, 2.1 and 1.9 g kgÿ1in diets for chicks and pigs, respectively, were supplemented with
MHA1or with molar equivalents ofDL-methionine from suboptimal to optimal methionine feeding
level. A polynomial regression model was used to describe N-retention in response to the DL
-methionine orDL-MHA supplemented diets. Both supplements showed equal effects on N-balances
of chickens and pigs. N-retention (as proportion of N-intake) was 0.56 and 0.54 in chickens and 0.51 and 0.54 in pigs forDL-Met andDL-MHA, respectively.# 1999 Elsevier Science B.V. All
rights reserved.
Keywords: Chickens; Pigs; N-balance trials; Methionine hydroxyanalogue utilization
1. Introduction
Methionine-deficient diets for broilers and pigs can be supplemented with DL -methionine or withDL-methionine hydroxyanalogue. Metabolic equivalence of these two sources of methionine is considered controversial, discrepancies being attributed to their absorptive and enzymatic characteristics in metabolism (Knight and Dibner, 1984; Knight et al., 1997). The utilization of MHA may also be influenced by the experimental diet used, i.e. synthetic or practical based feed mixtures (Saunderson, 1985) as well as by the
81 (1999) 193±203
*Corresponding author. Tel.: +551/393359; fax: +551/393343. 1Alimet1
a registered trademark of Monsanto Inc.
ratio of mono- to di-, tri- and polymeric acids of the MHA-product (Boebel and Baker, 1982). Furthermore, it is possible that the amount of supplemented methionine mainly within the suboptimal supplementation level could cause interferences with absorption mechanisms (Brachet and Puigserver, 1987; Baker and Boebel, 1980) and therefore be responsible for discrepancies between the results of several studies. Both, equivalent (Garlich, 1985; Waldroup et al., 1981; Knight and Dibner, 1984; Chung and Baker, 1992 and Stockland et al., 1992) and lower growth rates and feed conversion efficiencies (Schutte and De Jong, 1996; Boebel and Baker, 1982; Huyghebaert, 1993; Van Weerden et al., 1992; Steinhart and Kirchgeûner, 1985) have been shown in broiler chickens and pigs. However, comparisons between MHA or DL-Met for N-retentions in broilers and pigs have not yet been conducted. The present investigation compares the effects of increasing supplemental levels of eitherDL-Met orDL-MHA in methionine-deficient basal diets on N-retention in broiler chickens and growing pigs.
2. Material and methods
2.1. Animals and diet
2.1.1. Experiment 1
Male broiler chickens were obtained from a commercial hatchery (provenance Lohmann) at one day of age and offered a commercial starter diet ad libitum. At 14 days of age, the chicks were assigned individually to metabolism cages. Two supplements,DL -Met and MHA, each were fed at four increasing levels. At each supplemental level nine birds were fed DL-Met, nine other birds MHA and a further six birds received the unsupplemented basal diet. Each experimental period lasted for 10 days, including five days of adjustment and five days of collection. The basal mixture consisted per kg air dry matter of 510 g wheat, 400 g field beans (white flowered), 50 g soya bean meal, 10 g vitamins and 30 g minerals. It was calculated to contain per kg DM: 2.3 g methionine; 3.9 g cystine; 11.0 g lysine±HCl; 7.4 g threonine, 16.3 g arginine and 12.2 MJ MEN-corr..
Increasing amounts of DL-Met or DL-MHA2 were supplemented in the experimental groups. Four supplemental levels of each methionine source were tested on a molar equivalent basis by adding 0.6, 1.2, 1.8 and 2.4 gDL-Met orDL-MHA-equivalents (termed `Met 1±4' and `MHA 1±4' in the tables). Experimental diets were offered on an ad libitum basis and individual feed consumption of the birds was determined daily. Within the collection period, total amounts of excreta were collected daily. The excreta were weighed and kept frozen (ÿ208C) until analysis.
2.1.2. Experiment 2
N-balance trials were conducted on 32 crossbred barrows (provenance HuÈlsenberg). The trial period lasted for 10 days, including five days of adjustment and five days of collection. The animals were housed individually in metabolism cages. A complete diet for growing pigs was formulated according to the feeding standards (GfE, 1987)
2
DL-MHA free acid, liquid with 120 g water per kg.
consisting per kg air dry matter of 397.2 g wheat, 200 g barley, 370 g field beans (coloured flowered), 2.0 g lysine±HCl; 0.5 g threonine, 0.3 g tryptophane and 30 g mineral±vitamin premix. It was calculated to contain per kg DM: 11.1 g lysine; 1.9 g methionine; 6.5 g threonine; 2.3 g tryptophane; and 14.4 MJ ME. Three supplementation levels of each methionine source were tested by adding 0.8; 1.2 and 1.6 gDL-Met orDL -MHA-equivalents on a molar basis (termed `Met 1±3' and `MHA 1±3' in the tables). Four pigs were fed the basal diet; at supplemental levels 1 and 2, five pigs received the diet withDL-Met or with MHA, respectively, at supplemental level 3 four pigs were fed the DL-Met and four others the MHA diet. Equal amounts of feed adjusted to metabolic body weight (kg0.75) were given twice daily. No feed refusals were encountered. Total amounts of faeces and urine were collected separately and weighed daily. Aliquot samples were taken and kept frozen (ÿ208C) until analysis.
2.2. Chemical analysis
Diets and excreta were analysed in duplicates for dry matter (DM), ash (CA), ether extract (CL) and crude fiber (CF) according to standard Weende analysis methods (Naumann et al., 1976). Nitrogen was determined by the Kjeldahl method. Crude protein (CP; N*6.25) and N-free extracts (NfE) were calculated. Tables 1 and 2 show the analysed nutrient contents of the broiler and pig diets. The contents ofDL-Met and MHA in diets were analysed by high performance liquid chromatography according to Ontiveros et al. (1987). Results are shown in Tables 3 and 4 for broilers and pigs, respectively.
Table 1
Analysed contents of dry matter (g DM) and of crude nutrients (g/kg DM) in diets withDL-Met orDL-MHA supplementations for broilers
Group Parameter
DMa CAb CPc CFd CLe NfEf
Basal diet 902.4 42.7 216.1 54.8 29.5 656.9 Met 1 910.9 43.3 216.1 55.1 28.6 656.9 MHA 1 899.7 43.0 217.4 55.0 29.0 655.6 Met 2 903.0 43.0 217.4 55.3 28.7 655.6 MHA 2 915.0 42.6 215.2 55.0 29.4 657.8 Met 3 887.9 42.5 219.6 54.6 29.9 653.4 MHA 3 918.8 43.3 210.8 55.2 28.5 662.2 Met 4 890.6 43.1 221.1 54.8 29.1 651.9 MHA 4 907.8 43.3 215.5 54.7 29.0 657.5
Table 2
Analysed contents of dry matter (g DM) and of crude nutrients (g/kg DM) in diets withDL-Met orDL-MHA
supplementations for pigs Group Parameter
DMa CAb CPc CFd CLe NfEf
Basal diet 871.6 54.9 192.6 57.2 22.5 672.8 Met 1 873.3 56.6 192.2 55.9 22.1 673.2 MHA 1 873.6 56.1 192.8 57.0 23.8 670.3 Met 2 872.8 54.5 192.5 54.9 22.0 676.1 MHA 2 873.7 52.2 192.7 57.9 21.9 675.3 Met 3 873.2 56.4 192.5 60.9 23.0 667.2 MHA 3 872.9 56.1 192.5 59.6 22.7 669.1
aDry matter.
Analysed contents ofDL-Met and MHA and of total methionine equivalents in diets for broilers (g/kg DM)
Group No. of animals (n) DL-MHA DL-Met Total
Analysed contents ofDL-Met and MHA and of total methionine equivalents in diets for pigs (g/kg DM)
Group No. of animals (n) DL-MHA DL-Met Total
2.3. Statistical analysis
Data of N-balance trials were analysed by Student'st-test. The effect of DL-Met and MHA intake on N-retentions in chickens and pigs was estimated using a polynomial regression model with the equation:
Y abxcx2
where Y= N-retention of chickens or pigs, a= intercept, which was set constant as a common starting point,b andc= curvature steepness coefficients,xandx2= amount of total methionine intake with eitherDL-Met orDL-MHA supplementations.
For pigs the results of urine N-excretions were estimated separately using a hyperbola (one site binding) regression model with the following equation:
Y BminX KdX
where Y= average urine N-excretion of pigs, Bmin= minimum plateau value of
N-excretion,Kd= curvature steepness coefficient,X= amount of total methionine intake.
The regression analysis was performed with the program Graph Pad Prism (Vers. 10, 1980).
3. Results
3.1. Experiment 1
The initial and final body weights and weight gains of the broiler chickens are shown in Table 5. The average daily body weight gain of broiler chickens was 44 g for the basal
Table 5
Body weight and weight gain of broiler chickens during N-balance trials (g,x,s)
Group n Initial body weight Final body weight Weight gain
x s x s x s
Basal 6 442 7 781 35 339 31
Met 1 6 441 7 822 30 381 33
MHA 1 9 441 10 808 53 367 54
Basal 6 414 14 770 67 356 63
Met 2 9 413 17 877 49 464 45
MHA 2 9 412 14 883 49 471 41
Basal 6 469 12 810 62 341 63
Met 3 9 471 8 944 42 473 40
MHA 3 9 471 17 927 60 456 51
Basal 6 453 29 804 57 351 40
Met 4 9 451 25 924 65 473 46
diet and supplementation level 1 and 61 g for supplementation levels 2±4 with a standard deviation of 5 g for both. Feed conversion ratio and results of N-balances are compiled in Table 6.
Feed conversion ratio was significantly poorer in the basal diet group compared to the supplemented groups. Within the supplemented groups, supplementation levels 2±4 showed better feed conversion ratios than supplementation level 1. Feed conver-sion ratios were not different between MHA and DL-Met groups. Furthermore, N-retentions (as proportion of N-intake) were not different between the supplementa-tion sources.
The regression analysis (Fig. 1(a)) showed no significant difference between the effects of the two supplementation sources on N-retention.
3.2. Experiment 2
The initial and final body weights and weight gains of the pigs are shown in Table 7. The average daily body weight gain was 575 g with a standard deviation of 103 g and without any significant variation between groups. Results of the N-balance trials are shown in Table 8.
N-retentions (as proportion of N-intake) showed no differences between the supplementation sources. The highest N-excretions in urine were measured in the basal diet group. Groups with MHA supplementations showed lower urine-N excretions compared toDL-Met supplemented groups. N-retention was low in the basal diet group and increased to similar levels in all supplemented groups. The results of regression analysis (Fig. 1(b)) showed no significant differences between the supplementation sources.
Table 6
Feed conversion ratio and N-balances in broiler chicks (x,s)
Group Feed conversion Intake Excreta Retention Retentiona ratio (g/g) (g N/animal/day)
Basal diet 1.83 0.12 2.97 0.43 1.64 0.30 1.33 0.18 0.45 0.039 Met 1 1.69 0.11 2.49 0.16 1.18 0.10 1.32 0.08 0.53 0.018
4. Discussion
The aim of the study was to compare the effects of DL-Met and DL-MHA supplementations on N-retentions in broiler chickens and growing pigs from suboptimal to optimal methionine supplementation conditions. For that reason, methionine-deficient basal diets based on high contents of field beans were formulated. Compared to the official feeding standards the Met:ME(g/Mj), Met ratio in the basal diet was reduced by
42% with broilers (NRC, 1994) and by 40% with pigs (GfE, 1987).
The basal diets were supplemented by adding molar equivalent doses of eitherDL-Met orDL-MHA. MHA was assumed to be completely utilizable for the animals, irrespective of composition concerning mono-, di- and polymer proportions. Results of feed analysis (Tables 3 and 4) indicated good agreements of the calculated to the analysed methionine contents for DL-Met. In diets for broilers the analysis of DL-MHA contents indicated within supplementation levels 3 and 4 higher equivalent levels compared toDL-Met; diets for pigs showed good agreements betweenDL-Met andDL-MHA contents.
Comparing the effects ofDL-Met andDL-MHA results for chickens show similar weight gains and feed conversions over the whole range from suboptimal to optimal supply for both methionine sources, confirming observations of other researchers (Garlich, 1985; Waldroup et al., 1981 and Knight and Dibner, 1984). Only few results concerning the effects ofDL-Met andDL-MHA supplementation on N-retention in broiler chickens have been reported. Compared to DL-Met equal (Han et al., 1990) or lower N-balances (Rostagno and Barbosa, 1995) were determined for MHA.
Table 7
Body weight and weight gain of pigs during N-balance trials (kg;x,s)
Group n Initial body weight Final body weight Weight gain
Basal 4 29.4 34.5 5.2
Group Intake Faeces Urine Retention Retentiona
(g N/animal/day)
Basal diet 32.72 5.49 7.93 1.37 11.29 4.79 13.51 0.38 0.42 0.068 Met 1 34.41 3.17 8.22 1.22 9.07 2.58 17.12 2.45 0.50 0.073 MHA 1 32.87 1.75 7.94 0.98 6.73 1.82 18.20 0.97 0.55 0.028 Met 2 34.59 3.34 7.65 1.12 8.98 0.62 17.95 2.15 0.52 0.025 MHA 2 34.34 34.34 7.93 0.94 8.18 1.52 18.23 1.93 0.53 0.042 Met 3 34.08 2.65 7.85 1.02 8.54 0.34 17.69 1.91 0.52 0.025 MHA 3 33.93 3.37 8.28 1.44 7.09 0.95 18.56 1.60 0.55 0.010
xMet (1±3) 34.38 2.86 7.91 1.07 8.89ab 1.50 17.58 2.06 0.51 0.046
xMHA (1±3) 33.76 2.70 8.04 1.04 7.40bb 1.50 18.32 1.47 0.54 0.030
aAs proportion of N-intake.
bMeans within a column without common letters differ (p0.05).
A direct comparison of the two methionine sources on N-retentions can only be done, if similar amounts of both supplements are consumed by the animals. Fig. 1(a) shows N-retentions of broiler chickens on base of the actual DL-Met and DL-MHA intake. N-retentions ofDL-MHA groups showed higher standard deviations thanDL-Met groups. The estimation of the regression curves resulted in somewhat higher N-retentions for DL-Met compared to MHA supplementations. However, the difference was not significant.
As in broiler chickens there were also no differences for the effects of the two methionine sources on weight gain and feed conversion ratios in pigs. This result confirms earlier studies (Walz and Pallauf, 1996; Chung and Baker, 1992; Reifsnyder et al., 1984), reporting equal effects of DL-Met and DL-MHA on growth performance in pigs.
In contrast to the results of chicks the calculated regression curve for N-retentions in pigs showed somewhat higher efficiencies withDL-MHA than withDL-Met supplementa-tions. However, again the difference between the two curves was not significant. Regression curves for the effect ofDL-Met andDL-MHA on urine N-excretions of pigs are shown in Fig. 2. Compared to DL-Met supplementations urine N-excretions were significantly lower with MHA supplementations, indicating the efficient utilization of the hydroxy analogue in N-metabolism of pigs. Lower urine N-excretion may also reduce the potential of ammonia nitrogen losses in pig husbandry (Kirchgeûner and Roth, 1993).
5. Conclusion
In conclusion there was equal utilization of MHA andDL-Met for each supplementation level in pigs. Moreover, results indicate similar utilization of both sources of methionine in growing chickens. Supplementation of methionine-deficient diets for pigs with MHA
instead ofDL-methionine may lower urine N-excretion of the animals thus reducing the ammonia-N-emission potential of livestock.
Acknowledgements
We want to thank Dr. Barbara Rischkowsky for critical reading of the manuscript.
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