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Comparisons of sorghum grain (milo)and maize as the principal cereal grainsource in poultry rationsS. Bornstein a & Bianka Lipstein aa Division of Poultry Science , The Volcani Institute of AgriculturalResearch , Rehovot, IsraelPublished online: 08 Nov 2007.

To cite this article: S. Bornstein & Bianka Lipstein (1971) Comparisons of sorghum grain (milo) andmaize as the principal cereal grain source in poultry rations, British Poultry Science, 12:1, 1-13,DOI: 10.1080/00071667108415848

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Br. Poult. Sci,, 12: 1-13. 1971 Longman: printed in Great Britain

COMPARISONS OF SORGHUM GRAIN (MILO)AND MAIZE AS THE PRINCIPAL CEREAL GRAIN

SOURCE IN POULTRY RATIONS

4. THE RELATIVE CONTENT OF AVAILABLE SULPHURAMINO ACIDS IN MILO AND MAIZE 1

S. BORNSTEIN AND BIANKA LIPSTEINDivision of Poultry Science, The Volcani Institute of Agricultural Research,

Rehovot, Israel

Received for publication 13th April 1970

SYNOPSIS

Three trials were performed with chicks from 5-8 to 22-29 d of age in orderto compare the relative content of available sulphur amino acids (SAA) in maizeand in milo grains, and to determine whether or not milo was a poorer source thanmaize in any additional amino acid. The cereal grains were substituted for eachother on an isonitrogenous basis in grain-soyabean meal diets, their crude proteincontent ranging from 16-6 to 17-8 per cent, and these diets were control-fed inuniform quantities. The maize and milo diets of each trial were supplementedwith three common levels of DL-methionine, and with a fourth level which wascalculated to be in excess of the SAA requirement. The relative available SAAcontent of the grains was estimated by using the regression equations for the bestfitting lines to calculate the amounts of added methionine required with the twodiets to obtain a certain common weight gain. The difference between these twoquantities was then related to the dietary cereal protein.

In all trials linear graded responses were obtained to increments of DL-methionine, with both maize and milo diets, and the differences in chick performancebetween these two dietary cereals were eliminated once methionine supplementationwas high enough. Thus, under the conditions of this study, SAA were the firstand only limiting amino acids for both types of diet.

The calculated differences in SAA between maize and milo protein were 1·53,1·31 and 0·96 percentage points for trials 1·3, respectively. Since milo proteinthus contained, on an average, 1·27 percentage points less available SAA thanmaize protein, which can be assumed to contain 3-89 per cent SAA, the estimatedavailable SAA content of milo protein was 2·62 per cent.

INTRODUCTION

In a previous report of this series (Bornstein, Lipstein and Bartov, 1968) the onlyconsistent and significant effect due to the source of cereal grains in all-vegetable

1 Contribution from The Volcani Institute of Agricultural Research, Bet Dagan, Israel. 1970 seriesno. 1704-E.

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2 S. BORNSTEIN AND BIANKA UPSTEIN

layer diets was the reduction in egg size due to milo. Fish meal supplementa-tion of milo diets equalised egg weights, and it was suggested that this effect offish meal was due mainly to the methionine it supplied. Additional experimentsconducted since have confirmed this assumption (unpublished data). However,when the sulphur amino acids (SAA) contents of the milo and maize diets used

TABLE I

Summary of published reports on the methionine and cystine levels {per cent) of milo and maize

Milo Maize

Authors

Block and Weiss (1956)Vavich et al. (1959)Almquist (1962)Combs and Nicholson

(1962)Deyoe and Shellenberger

(1965)Combs et al. (1965)Hubbell (1965)

Waggle et al. (1966)

Waggle and Deyoe (1966)Hubbell (1967)Cromwell et al. (1967)

Waggle etal. (1967a)

Waggle et al. (19674)

Combs and Nott (1967)Virupaksha and Sastry

(1968)Drews et al. (1969)Anderson and Warnick

(1969)Blair and Waring (1969)Hubbell (1969)

1 Total sulphur amino

1 "Protein Methionine Cystine

IO-O1 0 5IO-O

IO-O

10-43

9 0

/ 7-9\n-8

9 99 0

f 8-3\ 10-5f 9-i-ho-6L l I - 2

IO-O

f 8-6\lI-2

. . .

10-09-29 0

acids (g/16

0-16

0 1 8

0-16

0-137...

0-160-090-14O-I20-16

0-140-16O-II0-140-140 1 30-090-22

. . .

0-160 1 30-16

0 1 5

0 1 5

...

0-105. . .

0 1 7O-II0 1 8

. . .

0 1 5

0-17O-2I0-14O l 80-160-160-150-15

. . .

0-21O-O38

0 1 9

SAA1

3 '3 33 3

3-i

2-32. . .

3-662-532-71

3-44

3-743522-743-022-682 92-78329

...

3 7

3-88

g nitrogen); where necessary

Protein

9-0...9-o

8 9

...8-98-8...

...8-99 1. . .

. . .

. . .

. . .9-2

. . .89

9 08-68 9

Methionine

0 1 8

0 1 8

0 1 8

. . .o-i962

0-18. . .

. . .0 1 80-15

. . .

. . .0-21*

. . .

0-14

0-21O l 8O l 8

calculated from the

Cystine

0-16. . .

0-17

. . .

. . .0-16

. . .

. . .0-160-14

. . .

0-16. . .

0-14

0-160-03*0-16

original

SAA

378...

389

3-82

...

...386

...

...3823 ' 9

...

...

...

...4-02

. . .

. . .

3>5

4-1

382

data bythe present authors.

8 Determined available methionine.* Probably due to a large loss of cystine on hydrolysis.

in these trials were calculated, on the basis of the estimated values of that time(Table 1), they did not differ markedly. Such small differences should not beable to account for a significant effect on egg size, unless the additional explanationof differential availability was invoked, a possibility also suggested by Bressani,Aguirre and Scrimshaw (1959).

The purpose of the present study was, therefore, to test the possibility of alower availability of SAA in milo, relative to maize, by means of growth tests withchicks. A secondary objective was to determine whether or not the amino acidcomposition of milo was limited in an additional amino acid other than SAA,compared with the pattern of maize.

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AVAILABLE SULPHUR AMINO ACIDS IN MILO AND MAIZE 3

While the experiments described here were in progress, some reports werepublished attributing to milo a lower methionine or SAA content than had beenpreviously assumed (Deyoe and Shellenberger, 1965; Waggle, Parrish and Deyoe,1966; Waggle, Deyoe and Smith, 1967; Combs and Nott, 1967), as detailed inTable 1. Moreover, Bragg, Ivy and Stephenson (1967) reported that the retentionvalues of methionine and cystine in sorghum approached 100 per cent.

In 77 samples of sorghum grain evaluated by Waggle and Deyoe (1966),the concentration of cystine was always equal to or greater than that of methionine.The variation in the methionine/cystine ratio among different diets (Bornstein andLipstein, 1966) makes it advisable to consider SAA rather than methionine values,even though methionine supplementation is used to increase SAA levels.

GENERAL PROCEDURE

Commercial, i-d-old, broiler-type chicks (males of a heavy White Rock strain)were allocated at random to the compartments (two compartments per storey) of

TABLE 2

Composition (in per cent) of the main dietary ingredients

Trial Nutrient

Crude proteinCrude fat

Crude proteinCrude fat

Crude protein

Maize

8-54-0

9-i3-9

8-2

1 Not assayed.

Milo

972-9

9-530

9 0

Soyabeanmeal

47-01-7

44-8...x

45-0

the two upper storeys of three-storey thermostatically controlled electric batterybrooders (measuring 70 x 300 cm). They were fed a milo starting diet, low inmethionine, for 5 or 8 d (according to the trial). At the end of this preliminaryperiod, the chicks were weighed individually, and those in the middle two-thirdsof the weight distribution were divided into groups of 20, equally balanced accordingto individual weights. The groups (compartments) were assigned to the dietarytreatments (2 or 3 replicate groups per treatment) in such a way that no tworeplicates of a given treatment appeared in the same battery, deck level or side ofbattery.

The protein and fat contents of the principal ingredients are given in Table 2and the composition of the experimental diets in Table 3. The milo diet containingthe lowest methionine supplementation served as the common pre-experimentaldiet. The grain-soyabean diets, containing either maize or milo, were maintainedisonitrogenous, but no attempt was made to also equalise their energy content.They were formulated to ensure that, for a given dietary protein level, an equivalentquantity of cereal protein was supplied by either maize or milo, and glucose wasadded to the milo diets to make up the difference.

The maize- and milo-diets of each trial were supplemented with three equal

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4 S. BORNSTEIN AND BIANKA LIPSTEIN

levels of DL-methionine. Besides these three common supplements, each diet wasfortified with a fourth level, calculated to be in excess of the SAA requirement(in order to ascertain whether milo was limited by a second amino acid, in com-parison with maize). These eight diets were fed for a 17 to 2 2-d period (according tothe trial) to duplicate (trial 1) or triplicate (trials 2 and 3) groups of 20 birds each.

All trials involved pair-feeding. The experimental lots were fed a quantityequal to 90-95 per cent of the average amount of the milo diet with the lowest levelof methionine supplementation consumed freely during the previous 24 hours bythe control group.

TABLE 3

Composition of chick diets (per cent)

Trial I Trial 2 Trial 3

Ingredients

MaizeMiloGlucoseSoyabean mealConstant ingredients 1

Protein levels

Total content (assayed)Cereal-derived (calc.)

660...

26-08-o

18-15-6

\

58-08 0

26-08 0

181

5-6

r

6g-0......

23-08-0

i6-7

6-3

...660

3-023-0

8 0

1 7 06-3

65-0

• ••27-0

8 0

17-45-3

...5906 0

27-08 0

17-85-3

1 Soya soapstock (acidulated), 4^0; dicalcium phosphate, 2-0; limestone, 1-25; mineral supplement2,0-4; vitamin supplement2, 0-3; vitamin B12 supplement (3 mg/kg), 0-05.

2 Detailed composition described in another report (Bornstein and Lipstein, 1963).

In trials 2 and 3 an attempt was made to use apparent nitrogen retention asan additional parameter of the chicks' response to methionine supplementation, andin the latter trial this opportunity was utilised to determine the metabolisable energy(ME) of the diets. The procedures used have been described previously (Lipsteinand Bornstein, 1968).

The results were subjected to standard analyses of variance (Snedecor, 1956),and significant differences to Duncan's multiple range test (1955). All interpreta-tions of data are based on the 1 per cent level of probability.

EXPERIMENTAL METHODS AND RESULTS

Trial 1. This trial was started with 430 chicks, hatched in January 1967.The experimental period started at 5 d of age—when 320 chicks were selected anddistributed into 16 lots, as described before—and lasted for 17 d. The two basaldiets used are presented in Table 3. They were supplemented with three commonlevels of methionine: 100, 600 and 1100 mg/kg, and with a fourth unequal level:2600 and 3100 mg/kg for the diets based on maize and milo, respectively. Duringthe first 2 d of the experiment these eight diets were fed ad libitum (but in measuredquantities) to duplicate groups; thereafter, they were pair-fed to those groupsreceiving the milo-based diet with the lowest methionine supplementation. Thelatter, too, were pair-fed during the last 4 d of the trial, in order to equalise foodintake of all treatments.

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AVAILABLE SULPHUR AMINO ACIDS IN MILO AND MAIZE 5

During the first 2 d of the trial, while all diets were fed ad libitum, the chickstended to consume more of the diets containing milo than those containing maize,and more of the diets containing the higher levels of methionine supplementation.

The growth performance of the chicks is summarised in Table 4. The improve-ment of the diets based on maize due to methionine supplementation was ratherlimited and not statistically significant and practically ceased beyond the addedlevel of 0-06 per cent, whereas the chicks fed the milo diets responded very noticeablyto the DL-methionine, even beyond the o-11 per cent level. The growth ratesobtained with the maize-based diets containing o-oi and 0-06 per cent addedmethionine were numerically better than those due to the milo diets fortified with0-06 and o-11 per cent methionine, respectively, but the latter diet yielded greaterweight gains than the maize diet containing o-oi per cent DL-methionine.

When the weight gains during the 5 to 22-d age period (j) are plotted againstsupplementary methionine (#), expressed as mg/kg, separately for each type of

TABLE 4

Effect of two types of cereal grain and four levels of methionine supplementationon the growth rate of chicks1 (trial i)

Added methionine(percent) ooi 006 o-n 031 0̂ 26

Cereal grain Milo Maize Milo Maize Milo Maize Milo Maize

Weight gain (g)5-15 d 103 112 109 113 in 112 114 1145-22 d 222c2 239ab 234bc 245ab 242ab 24^ab 247ab 248a

1 Averages of duplicate groups of 20 chicks each.2 Any two mean values not having a common letter differ significantly (P<O'Oi).

cereal diet, linear relationships are obtained for the first three supplementationlevels; the fourth level was excessive (intentionally). The regression equationsfor the maize and milo diets were, respectively,

y = 239-13 + 0-007*y = 220-70 + 0-020X

With the fourth (excessive) levels of DL-methionine, the difference betweenmaize and milo diets practically disappeared (Table 4).

Trial 2. This experiment was started with 700 chicks, hatched in August1967. At 7 d of age 540 of them were allocated to 27 groups, as described before.The trial lasted 18 days. The diets fed, to triplicate lots, were the maize and milodiets described in Table 3, each supplemented with three common levels of methi-onine and one unequal one (Table 5). The milo diet with the lowest level of DL-methionine was used in two different treatments: once as the ad libitum controlfor the pair-feeding, and the second time as an experimental one (being pair-fed,to the first, like all the other experimental diets). After the chicks had been on theexperimental diets for 15 d, droppings were collected quantitatively for nitrogenbalance assays.

During the first 24 h of the experimental period, while group weights were

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6 S. BORNSTEIN AND BIANKA LIPSTEIN

still uniform and all diets were fed ad libitum, the composition of the diets appearedto have a marked effect on appetitite: food intake ranged from 360 g to 407 gper 20 chicks (averages of 3 replicates) for the milo diets containing the lowest andhighest levels of DL-methionine, respectively; and from 393 g to 403 g for thecorresponding maize diets.

TABLE 5

Effect of four levels of methionine supplementation of equivalent maize and milo dietson the performance of chicks1 (trial s)

Added methionine(per cent)

Cereal grain

Weight gain (g)8-18 d8-26 d

Food intake (g)8-26 d

Nitrogen retention(per cent)

Milo2

138

309

609

o-oiA

Milo

134b3

284c

572

52-OC

Maize

I38ab

572

58-2ab

0-05A

r •*Milo Maize

I37ab 140a29obc 2g8ab

572 572

56-8ab 5g-6a

0-09A

( \

Milo Maize

I37ab 141a

572 572

57-4ab 58-6ab

0-30

Milo

I38ab

572

55-2abc

0-25

Maize

141a300a

572

59-oab

1 Averages of 3 replicates of 20 chicks each.2 The chicks of this treatment were fed ad libitum, whereas those of all the other treatments were

pair-fed.3 See footnote 2 to Table 4.

The results obtained during the entire experimental period are summarisedin Table 5. The improvement of the maize diets due to DL-methionine supple-mentation was limited to the 0-05 per cent level. An approximate difference of0-08 per cent available natural SAA is indicated between the unsupplementedmaize and milo diets.

When the weight gains during the 8 to 26-d age period (y) are plotted againstlevels of added methionine (#), expressed as mg/kg, a linear correlation is obtainedfor the first three supplementation levels, whereas the fourth level is excessive(intentionally). The respective regression equations for the maize and milo dietswere:

y = 292-92 + 0-0075*y = 283-50 + 0-011*

The effects of type of cereal and methionine supplementation on apparentnitrogen retention were both significant, by analysis of variance. The data ofTable 5 indicate that methionine supplementation of the maize diet affected thisparameter only very slightly, but its improvement with the milo diets approachedlinearity when plotted against the first three levels of DL-methionine expressed aslogarithms. However, the highest level of added methionine appeared to depressnitrogen retention slightly, although this was not reflected in weight gain.

Trial 3. Seven hundred chicks, hatched in March 1968, were allocated to27 groups of 20 chicks each at 7 d of age, as described before. The experimentalperiod lasted 22 d. The basal maize and milo diets are presented in Table 3 andtheir methionine supplementations in Table 6. Each of these diets was pair-fed

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AVAILABLE SULPHUR AMINO ACIDS IN MILO AND MAIZE 7

to triplicate groups having free access to the milo diet with the lowest level ofDL-methionine. After 10 d on the experimental diets, droppings were collected fordetermination of the apparent nitrogen retention and of the ME of four diets.

TABLE 6

Effect of two types of cereal grain and four levels of methionine supplementationon the performance of chicks1 {trial 3)

Added methionine(per cent)

Cereal grain

Weight gain (g)7-22 d7-29 d

Food intake (g)7-29 d

Nitrogen retention(per cent)

ME of diets (kcal/g)

Milo2

183276

675

0-005

Milo

157c3

247d

610

5 5 ' o b

Maize

I72ab261bed

610

58-gab

0-045A

Milo

168b259cd

610

6o-2a285

Maize

I73aba66bc

610

61-4a2-90

I-3 See footnotes to Table 5.

0095A

Milo

I76ab26gabc

610

59-9a

Maize

181a276ab

610

61-ga

0305

Milo

180a285a

610

6o-7a2-93

0-205

Maize

182a283a

610

62-5a2-86

During the first 24 h of the experiment, while all diets were fed ad libitum,the composition of the diets (i.e. their relative methionine deficiency) appeared tohave a decided effect on food intake: average consumption (3 replicate groups)per 20 chicks ranged from 343 g to 397 g for the milo diets with lowest and highestlevels of added methionine, respectively, and from 363 g to 380 g for the corre-sponding maize diets.

A summary of the results of this trial is presented in Table 6. Linear relation-ships exist between the first three methionine increments (x) and the weight gains(j) of the chicks fed the maize and milo diets during the 7 to 29-d period; therespective regression equations are:

y = 259-54 + o-oi 7*y = 246-58 + 0-024*

The fourth supplementary levels were purposely excessive and resulted inequal growth rates with the maize and milo diets.

According to the data of Table 6, comparisons of growth rates due to maizeand milo diets containing various levels of DL-methionine appear to indicate that thedifference in natural available SAA between unsupplemented maize and milo dietsamounts to between 0-04 and 0-05 per cent, and should be less than 0-09 per cent.

Apparent nitrogen retention was significantly affected by type of cereal andmethionine increments (according to analysis of variance) but only one significantimprovement was caused by DL-methionine (according to the range test).

DISCUSSION

Considering their importance, chick bioassays to determine the availabilityof methionine from different natural sources have been described by relatively few

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8 S. BORNSTEIN AND BIANKA LIPSTEIN

investigators (Ousterhout, Grau and Lundholm, 1959; Guttridge, Lewis andMorgan, 1961; Guttridge and Lewis, 1964; Miller, Carpenter and Morgan, 1965;Combs, Bossard and Childs, 1965, 1968; Harwood and Shrimp ton, 1969). Thesetests usually involved foodstuffs of rather high protein content, supplying a majorproportion of the total dietary methionine.

In the present study, on the other hand, the contribution of protein by thetest ingredients (maize and milo) was too low for an acceptable bioassay withoutfortification with a protein supplement, because in such tests the protein must behigh enough to support satisfactory growth (Uwaegbute and Lewis, 1966a;Woodham, 1968; Fisher and Griminger, 1969). Consequently, the soyabean mealused contributed about two-thirds of the SAA in the unsupplemented basal milodiets and almost three-fifths of the SAA in the maize diets. It thus supplied somuch ingredient-SAA from a source other than the test cereals as to endangerdiscrimination between the latter and between the levels of methionine increments.

Variations in food consumption, whether due to amino acid deficiency, im-balance or both, or to differences in the palatability, energy content or both ofthe diets, cause differential intakes of amino acids, thus confounding the effect ofdifferent dietary amino acid levels. Several of the authors mentioned at thebeginning of the discussion, as well as Carpenter, March, Milner and Campbell(1963) and Uwaegbute and Lewis (19660), have pointed out the importance ofconsidering quantitative consumption in chick bioasays.

In the present study the effect of methionine deficiency and/or amino acidimbalance on appetitite was very pronounced, even during the first 24 h ofthe experiments, while group weights were still uniform and all diets were fedad libitum. The cumulative effect during an entire experiment, and the influenceof such an effect on the final results, are easily imagined. As a solution, it has beenproposed to express growth as a function of food intake (Uwaegbute and Lewis,1966a) or of amino acid intake (Carpenter et al., 1963; Combs et al., 1965, 1968).Only Campbell (1966) mentions " paired " or controlled feeding, but thinks thatthis " would greatly complicate the experiments and would also bring some separateproblems of interpretation ".

Admittedly, controlled feeding is a rather laborious method, but experienceat this institute has shown that the accuracy of growth tests can be rather amazing,once the effects of differential food intake (due to nutritional treatments or environ-mental conditions) have been eliminated. The total food consumption of thecontrol-fed chicks reached 94 and 90 per cent of that of the chicks fed ad libitumin trials 2 (Table 5) and 3 (Table 6), respectively. For the diets containing thehigher levels of supplementary methionine, this restriction was more severe thanis apparent from these percentages, considering the relatively small appetite of thechicks fed the methionine-deficient milo diet.

In all three trials linear graded responses were obtained to increments of addedmethionine, with both maize and milo diets (Figure 1). Moreover, in two out ofthree trials the differences in chick performance between maize and milo dietsdisappeared once methionine supplementation was high enough. It can be assumed,therefore, that in each trial the difference in weight gain at any common methionineincrement is the direct result of the difference in ingredient-derived available SAAbetween the two types of basal diets.

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AVAILABLE SULPHUR AMINO ACIDS IN MILO AND MAIZE 9

The regression lines obtained for the maize and milo diets of the same trialare not parallel (Figure i), and they approach the single and common requirementlevel at different rates, in spite of equal methionine supplementation. At leasttwo explanations can be offered for this phenomenon: (i) total dietary SAA wereunequal to begin with, since maize contains more SAA (Table i) and maize diets

300 —

290 —

2201—

200 400 600 800 1000Methionine supplementation (mg/kg)

FIG. I.—Graded responses to supplementary methionine by chicks fed isonitrogenous maize or milo diets.The lines are based on regression equations (see text), calculated from three levels of supplementation.Stippled lines indicate the weight gain of each trial used to compare the requirements of these twodifferent diets for added methionine.

had a higher grain portion (Table 3); and (2) methionine supplementation notonly increased dietary SAA levels, but simultaneously improved amino acid balance,and with it the biological value of the cereal protein, hence the rate of improvement(slope of the regression lines) is higher with milo than with maize diets. Accordingly,the results of comparisons are affected by the choice of the weight gain level. Thepoints, in common to all three trials, at which the differences in available SAA

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10 S. BORNSTEIN AND BIANKA LIPSTEIN

content between the maize and milo diets were measured (by means of regressionequations), were the weight gains obtained with the maize diets supplemented withioo mg/kg methionine, the first increment in trials i and 2 (Figure i) .

The results of trial i (Table 4) seem to indicate that the difference in SAAcontent between the basal maize and milo diets (Table 3) exceeds 0-05 per centbut ought to be less than o-io per cent. By means of regression equations for thebest fitting lines it can be calculated that the addition of 100 mg/kg DL-methionineto the maize diet resulted in a weight gain of 240 g, and that such a gain could beobtained with the milo diet by a methionine supplementation of 955 mg/kg, adifference of about 0-085 per cent available SAA between these two diets.

The data presented in Table 5 might be construed as indicating that in trial 2there existed an approximate difference of 0-08 per cent available SAA betweenthe maize and milo diets. Repeating the calculations of the preceding paragraphwith regard to trial 2, a difference of about 0-083 per cent is obtained.

From the weight gains attained in trial 3 (Table 6) it appears that the differ-ence between maize and milo diets in available SAA might be 0-04-0-05 per cent.According to the calculations used for the previous trials, this difference amountsto approximately 0-051 percentage points.

Since each trial involved pair-feeding of isonitrogenous diets containingidentical quantities of soyabean meal (Table 3), the differences in available SAAbetween the maize and milo diets, detailed in the previous paragraphs, can onlybe the result of the differential SAA content of the cereal proteins derived fromthese two types of grain. In trials 1, 2 and 3 the dietary cereal protein concentra-tions were 5-6, 6-3 and 5-3 per cent, respectively, hence milo protein contained1'53> I ' 3 I a n d 0-96 percentage points, respectively, less available SAA than didmaize protein; or an average difference of 1-27 percentage points in favour ofmaize protein on the basis of the three trials combined.

According to Table 1, the protein, methionine and cystine analyses of maizeare rather uniform, with only two out of twelve authors reporting exceptionallylow methionine values. Averaging the SAA values of eight reports (two of themdid not present data for cystine), a mean of 3-89 per cent SAA is obtained for maizeprotein (with maize grains containing 8-9 per cent protein). Subtracting from thisestimated value the above-mentioned 1-27 per cent, it appears justified to assumethat milo protein contains about 2-62 per cent available SAA. Applying this levelto milo grain samples of 9-0 and io-o per cent protein, their respective content ofavailable SAA would then be 0-24 and 0-26 per cent.

The above SAA contents of milo protein compares reasonably well with thevalues of Deyoe and Shellenberger (1965), Waggle and Deyoe (1966), Waggleet al. (1967^) and Combs and Nott (1967), as cited in Table 1. All of them arelower than usually reported in food ingredients' composition tables. Investigationsof previous years were carried out with sorghum grain largely from pure strains,and therefore may not be characteristic for the presently grown hybrids, sinceDeyoe and Shellenberger (1965) noted highly significant hybrid effects.

The linear correlations between protein and methionine content in sorghumgrain have been worked out by Waggle and Deyoe (1966), who reported that themethionine concentration in the protein was relatively unaffected by the proteincontent of the grain.

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AVAILABLE SULPHUR AMINO ACIDS IN MILO AND MAIZE II

Since excess DL-methionine in milo diets supported a growth rate equal tothat of maize, there is no indication, under the conditions of this study, of anadditional limiting amino acid in milo, in comparison to maize, when fed togetherwith soyabean meal. Thus it appears justified to conclude that in grain-soyabeandiets maize and milo proteins are of equal nutritional value, once the latter has beensupplemented with methionine.

According to the assayed ME content of the diets used in trial 3 (Table 6),there is no difference between the energy value of 65 per cent maize and that of59 per cent milo plus 6 per cent glucose (Table 3). Since milo was reported tocontain 3-34 kcal/g (Combs and Nott, 1967) and glucose 3-31 kcal/g (Morris, 1968),it appears that the ME contents of maize and milo are practically identical, inspite of the slight difference between them in fat content (Table 2; Bornstein andBartov, 1967a). This is in full agreement with previous observations, in whichthe energy contents of maize and milo diets were evaluated comparatively in termsof food utilisation (Bornstein and Bartov, 1967a, b; Bornstein et al., 1968).

It has been suggested that nitrogen retention data are more reliable thanlive-weight gain, since the former are more closely related to the fate of ingestedamino acids (Uwaegbute and Lewis, 1966a, c). Under the experimental conditionsof trials 2 and 3 this did not seem to be the case (Tables 5 and 6), especially wherethe highest methionine increments were concerned. Uwaegbute and Lewis (19666),too, appeared to have obtained a decrease in nitrogen retention when the lysinedose exceeded the potential assay range. This divergence between weight gainand nitrogen retention data might possibly be the result of changes in body com-position when the former approaches or reaches maximal rate.

The data of this study may be assumed to indicate a relatively low SAA contentof milo grains, rather than a low availability of amino acids. Combs and Nicholson(1962) and Combs and Nott (1967) estimated the relative amino acid availabilityof milo as 100 per cent.

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