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Comparisons of sorghum grain (milo)and maize as the principal cerealgrain source in poultry rationsS. Bornstein a & Bianka Lipstein aa Division, of Poultry Science , The Volcani Institute ofAgricultural Research , Rehovbt, IsraelPublished online: 08 Nov 2007.

To cite this article: S. Bornstein & Bianka Lipstein (1972) Comparisons of sorghum grain (milo)and maize as the principal cereal grain source in poultry rations, British Poultry Science, 13:1,91-103, DOI: 10.1080/00071667208415920

To link to this article: http://dx.doi.org/10.1080/00071667208415920

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B r . P o u l t . S c i . , 1 3 : 9 1 - 1 0 3 . 1 9 7 2 : • " : . . • • . , . • . • : { • ' . . ' . ''.,. . ••.• L o n g m a n : p r i n t e d i n G r e a t B r i t a i n

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

SOURCE IN POULTRY RATIONS

5. THE EFFECT OF METHIONINE AND LINOLEIC ACIDSUPPLEMENTATIONS ON ALL-VEGETABLE MILO

- LAYER DIETS1

; . ' • • ' : - ( • , ' . ; " . • < : • • . • • • • • - • • • • • - : " • • ' . : , • ! . / • • ' • •

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

Rehovbt, Israel

Received for publication 24th May 1971

SYNOPSIS

Three trials were performed during consecutive years, involving a total of 972Leghorn hens, in order to compare all-vegetable layer diets of marginal protein con-tent based either on milo or on maize as the only cereal grain.

Under the conditions of this study the only consistent, and at times significant,effect due to the source of cereals was the reduction of egg size due to milo. Methio-nine supplementation of milo diets equalised egg weights. The calculated sulphuramino acid requirement for optimal egg size appeared to be about 560 mg/bird d.

Maize contains decidedly higher levels of linoleic acid than milo, especially ona whole grain basis (2.3% as compared with 1.5%); the difference is reflected in thefatty acid pattern of the yolk lipids of eggs produced by hens-fed these diets. Thedietary to yolk linoleic acid ratio appeared to be 1 to 9-10, for dietary levels rangingfrom 1.0 to 1.7%.

Milo-soya diets containing 1.1-1.2% dietary linoleic acid were adequate foroptimal egg size, on the condition that methionine requirements had been met, thatdaily food consumption was not less than 110 g/bird, and that the pre-layer dietshad been rich in linoleic acid. If the pre-layer diets had been composed of practicalingredients relatively low in this essential fatty acid, a minimum level of 1.5-1.6%dietary linoleic acid was indicated. Acidulated soya soapstock proved a practicallinoleic acid supplement.

INTRODUCTION

In a previous study of this series (Bornstein, Lipstein and Bartov, 1968),significantly lower egg size was obtained with milo diets than with those based onmaize. Fish meal supplementation of milo diets tended to equalise egg weightswith those due to maize .diets, and some beneficial effects were also obtained fromadded methionine and acidulated soapstock. It was suggested that in milo-soya diets

1 Contribution from The Volcani Institute of Agricultural Research, Bet Dagan, Israel. 1971 Series,No. 1899-E.

91

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9 2 S. BORNSTEIN AND BIANKA LIPSTEIN

methionine was the first limiting factor, and that linoleic acid was next limiting inincreasing egg size.

The purpose of the present study was to test this hypothesis. These trials wereconducted simultaneously with those on the relative content of available sulphuramino acids (SAA) in milo (Bornstein and Lipstein, 1971); hence, the latter resultswere not yet available for the experiments reported here.

GENERAL PROCEDURE

Housing, record keeping and statistical analyses were the same as described ina previous report (Bornstein and Bartov, 1967). Diets within trials were maintainedisonitrogenous, but no attempt was made to equalise energy content. The pre-experimental layer diets, except for trial 3, contained equal parts of maize and milo,3% fish meal and 1 % acidulated soapstock, as was customary for local practical layerrations. The chicks and pullets were fed commercial diets, based on the same prin-ciples of composition.

Beginning at about 24 weeks of age, when egg production had reached anapproximate level of 10%, a daylength of 11 h was established by artificial illumina-tion, and thereafter it was increased by 30 min twice monthly.

Two consecutive 2-week pre-experimental test periods were employed. Thefirst was concerned with the recording of individual egg production, egg size andbody weight, and on their basis about one-third of the flock with extreme perform-ance values was eliminated from the experiment. The remaining birds were allo-cated to the experimental groups, in a manner to approach similar performance andcomparable within-group variability for all replicate groups. The second test periodwas used to check this allocation and to determine pre-experimental performance.

Lipids from food and egg yolk were extracted and their fatty acid compositionwas determined as previously described (Bornstein et al., 1968).

A single batch of each cereal grain and soybean meal was used throughout theexperiment, after having been analysed in advance, except for trial 2, which wasdivided into two parts.

EXPERIMENTAL METHODS AND RESULTS

Trial 1The purpose of this experiment was to compare (a) all-milo and all-maize as

the cereal portion of the diets (with or without added methionine), and (b) fish mealand methionine (or methionine plus soapstock) as supplements of milo diets. Thecomposition of maize and milo grains used in this trial is presented in Table 1, andTable 2 gives a description of the diets involved. All diets contained a uniformprotein level (14-8-15-0%, averages of the assays of three different mixes per diet).

This trial was performed with 288 S.C. White Leghorn (strain-cross) layinghens, hatched on 23rd May 1966. The first pre-experimental period started whenthe birds were 27 weeks old; the trial itself was begun on 21st November (whendaily egg production per group ranged from 85 to 90%) and was completed on30th April 1967. Four replicate groups of 12 layers each were assigned to each ofthe six dietry treatments, in a manner to minimise potential effects of cage locationwithin the battery shed.

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Cereal grain

Trial no.

Protein (Nx6-25)Ether extract (%)Fatty acid1

' 4161618181818

o2

0

1

01

2

3

COMPARISON OF SORGHUM AND MAIZE

TABLE I

Composition of maize and milo grains used

t1

8-54-1

. . .

ia-9...1-2

26-059-i

0-9

MaizeA

2

9-43-9

13-1o-i2-2

26-557-2

0-9

38-63-9

...12-5

'•924-559-i

2 - 0

fI

9 72-9

. . .

«5-4o-80-4

30-2

53'2...

Milo

2

9-53-0

. . .

'5-3o-8I-O

32-548-8

i-6

93

3

9-1a-9

i-3'5-10-70-9

29-75°-7

i-618

(%/grain) 3-42 2-23 2-30 '•541 Percentage, by weight, of total fatty acids.s Chain length: no. of double bonds.

1-46 1-47

Trial no.

Diet no.

MaizeMiloSoybean mealFish mealPotato starchSoya soapstock (acidulated)DL-methionineConstant ingredients A4

Constant ingredients B5

TABLE 2

Percentage composition of layer diets used

I . 2 1

66-8o...

19-00

2-00. . ....1

12-20

IA

3.41

68-8o17-00

• . •2-00. . .

. . . x

12-20

5

68-8o17-00

. . .

2-000-04

12-20

6

• ••72-00II-OO4-002-00. . .

11-00

f

1,2*

69-25

17-50. . .1-50

. . . 2

. . .

"•75

2A

3,4s

69-2517-50

. . .

I-50

. . . 2

"•75

1

5...

69-1317-50

. . .

1-500-12. . .

"•75

3A

' I , 2 »

65-20

23-00. . .

. . ."O-05. . .

" •75

3,4 s

66-1322-OO

. . .

. . .

. . ."0-12. . .

"•751 Diets 2 and 4 contained 0-04% DL-methionine, the approximate difference between 4% fish meal and

6% soybean meal.2 Diets 2 and 4 contained 0-05 and 0-12% DL-methionine, respectively.8 Diets 2 and 4 contained 1 % soya soapstock, added at the expense of the entire diet.4 Alfalfa meal, 2-50; vitamin supplement,' 0-25; limestone, 7-50; dicalcium phosphate. i-6o; mineral

supplement,4 0-35; (diet 6 contained 7-00, i-oo and 0-25 limestone, dicalcium phosphate and mineral sup-plement, respectively).

5 As in footnote 4, except 7-00, 1-70 and 0-30 of the latter three supplements, respectively.6 Detailed composition of the vitamin and mineral supplements is given in another report (Bornstein

and Lipstein, 1963).

A summary of the results of this trial is presented in Table 3. None of the differ-ences observed in this experiment was significant, probably due to a rather highrate of food consumption, caused by unusually (for this country) cold winter weather.Nevertheless, two trends are apparent, namely the slower rate of egg weight increaseand lower average egg size due to the unsupplemented milo diet. The latter wasmarkedly improved by fish meal or methionine supplementation, eliminating thedifference between milo diets and the unsupplemented maize diet. Body weightgains tend to reflect the energy content of the diets, which (together with rates ofproduction) also influenced daily food consumption and food utilisation.

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S; BORNSTEIN AND BIANKA LIPSTEIN

TABLE. 3

Performance of laying hens fed variously supplemented all-maize and all^milo diets during a 4-month period {trial 1,1966-67)1

- - • ••' -•— -Averages of 4 replicates of i"2 layers each

Cereal grain1

Supplements '-Diet no.2

Hen-day production (%) .Egg weight (g)Egg weight increase3 (g)Initial body weight (g)Weight gain (g) ^Food consumption (g/hen d)Food utilisation (g/egg)Mortality4 (%).

Nonei

. 77-357-5

4-61768

130114148

. 0

MaizeA '

Methionine2

77*558-1

5-21756

143" 5148

2M

rNone

373-856-8

3-61779

139" 3153

4-2

;- Methionine

4

57-74'5 .

1760

1 1 2

1570

Milo

Meth. + Soapstock.'

580-557-5

3-91788

2191 116

1442-1

Fish meal

.•'H'Y''V74-i '58V?:. 4"3-

232in ,150

2 - 1 •.,.

1 None of the differences in this table is significant.2 See Table 2. ' / . ' • ••',".'•",••,„.'.<".3 Difference between pre-experimental egg weight and that after a 2-month experimental period.4 In the absence of culling. Three replicates of every treatment had no mortality at all.

TABLE 4

„ Fatty acid composition of diets and of egg yolk lipid as affected by diets fed in trial 1

• " •• f ,-• - Fattyacid1

14: 0W

CO

«

CO

•••

16: 0

12-712-512-814-3

25-927-726-627-7

16:1 18:0 18:1 18 :2 3 18 :3

Diets. . .o-80-7o-8

Yolk lipid5

4-64-53'94-7

i-92-1

2-52-O

10-3IO-I10-59-2

25-034-923-027-4

42-8B": 46-5AB

42-7B48-3A

56-645-454-950-1

i6-4A •II-2Bi6-2AI0-2B

2-53-05'93-9

• ••.... . .. . .

Each fatty acid expressed as a per-

DietNo.2

3564

1

356*

1 Denoted by carbon chain length and number of double bonds.c e n t a g e o f t o t a l f a t t y a c i d s . ' , •:• •.-_•:. . , . : • . •

2 See Table 2.3 The dietary linoleic acid levels of diets 1, 3 and 5 were 1-75, 1-12 and 2-21%, respectively.4 No attempt was made to detrmine the long-chain polyunsaturated fatty acids offish oil.5 Averages of 4 pooled samples of 5 yolks each, representing 5 different hens per replicate.6 Any two mean values, within one line or column, not having one letter in common, differ significantly;

capital letters used for the 1% level and small letters for the 5% level of probability (Duncan, 1955).

Table 4 presents the fatty acid composition of the diets used and of the yolks ofeggs produced by hens fed these rations. Diets containing either maize or soyasoapstock contained a higher proportion of linoleic acid than the unsupplemented.milo diet, in accordance with the respective composition of maize and milo grains.(Table i ) . These dietary differences are reflected in the composition of the yolklipids, causingthe yolks of milo (or milo plus fish meal) diets to contain significantly,lower levels of linoleic acid than those of the maize diet. The use of 2% dietarysoya soapstock eliminated this difference. . - . \ .'.. . . ..•„.-, •.' .:..;.. •.;.•.

94i

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COMPARISON OF SORGHUM AND MAIZE 95

; The average weights of the eggs used for the above assays were 59-7; 57'6, 58-1and 60-7 g for diets 1,3, 5 and 6, respectively, with a significant difference betweenthe eggs of diets 1 and 3. The percentage shell was very uniform (g'S-o/s) irrespec-tive of dietary treatments. For diets 1, 3 and 6, the albumen and yolk percentageswere also rather uniform (6o-o-6o'3 and 3O-2-3O-7, respectively), but there appearedto exist a slight trend toward an increased proportion of yolk and less albumen(31-3 and 59'4%, respectively) for the milo diet containing soapstock.

Trial 2 •Leghorn hens from the same breeder as in trial 1 and hatched on 22nd May

1967, were used in this trial. Each experimental diet was fed to five replicate groupsof 12 layers, from 15th December 1967 to 22nd April 1968. ! .

TABLE 5

Performance of laying hens fed variously supplemented maize and milo diets duringa 2-month period {trial s)1

'. Averages of 5 replicates of 12 layers each

Cereal gram

Supplements2 ;

Diet no. ; '

Hen-day production (%)Egg weight (g) ;Egg weight increase3 (g)Initial body weight (g)Weight gain (g)Food consumption (g/hen d)Food utilisation (g/egg)Mortality6 (%) .

Maizet

Nonei

82-855-64-6A1

176935

109132

3-3

Methionine2

8i-655-44'3A_

175957

n o134

None3 '80-954-12-6B

'"•• 1 7 5 3

421 0 6131

5-0

MiloA

Methionine4

83-955-84-6A

176878

n o131

3-3

Meth. + Soapstock58o-o55-95-4A

176488

1 0 8

'35'•7

1 Pertaining only to the first half of this trial, from 15th December 1967 to 14th February 1968.2 See Table 2.8 Difference between pre-experimental egg weight and that after a 2-month experimental period.1 See footnote 6 to Table 4. .... .....-"• •... ;5 In the absence of culling, and pertaining to the entire 4-month experimental period. Three replicates

of every treatment had no mortality at all. ••-;.'

The composition of the cereal grains and of the five diets used during the firstpart of the experiment is shown in Tables 1 and 2, respectively; all diets containedI5"3"I5'5% dietary protein. On 14th February 1968 the second part of the trialstarted, involving the following changes: (a) new lots of grains—the maize contain-ing 8*i and 4-3% crude protein and ether extract, respectively, with the correspond-ing values of the milo being 9-0 and 3-7; (b) reduction of dietary protein level" (ofall diets) by o-6 percentage points; and (c) switch-back of four dietary treatments:from diets 1 to 3 and 2 to 4, and vice versa, with only the birds on diet 5 continuingwith the same treatment. The fatty acid composition of food and yolk lipids wasdetermined a few days before this change.

The results of the first 2 months of this experiment are summarised in Table 5.As in the previous trial, the only meaningful effect involved egg size: feeding theunsupplemented milo diet caused a markedly lower average egg weight and a sig-nificantly slower egg weight increase than produced on the maize diets or on thesupplemented milo diets; the latter four diets yielded comparable results.

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96 S. BORNSTEIN AND BIANKA LIPSTEIN

The switch-back and the other changes between the first and second parts ofthis experiment had no marked or consistent effect on the rate of production. Thelatter reached its peak during January; during February and March it decreasedslightly and uniformly.

In contrast, the change in type of cereal had a pronounced effect on egg weights,but this effect was limited to the unsupplemented diets (Figure i) . When the birds

50

Maizea -BMiloA- AMilo + Methionine+ —

Soapstock

Dec. Jan. Feb.MONTH

March AprilJ

FIG. I.—The effect on egg size of methionine supplementation of maize and milo diets of trial 2. On 14thFebruary there was a change in type of cereal, except for the birds being fed the milo diet supplementedwith both methionine and soapstock. For further details see Table 5. Open symbols—unsupplementeddiets; solid symbols—diets supplemented with methionine.

fed the unsupplemented maize diet were changed to the unsupplemented milo diettheir average egg size decreased by 1 -3 g from the first to the second half of February,whereas the opposite change brought about an increase in egg weight by 1*7 g.The egg weights of diets 2, 4 and 5 continued their smooth and uninterrupted ascent(0-4 to o-8 g) irrespective of the cereal change.

The fatty acid composition of the diets in trial 2 and of the egg yolks producedon these diets is described in Table 6. The unsupplemented milo diet contained

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14:0

°-5

...

Fatty acid composition

16:0

14-1

28-327-727-5

(%) of food and egg yolk

Fatty acid1

16 : 1 18 : 0

Diets1-2 p8

1*5 1*1

! • ! 2-O

Yolk lipid5

3-8 io-64-7 io-63-9 10-4

lipids (trial 2)

18: 1

25-529-626-7

44-4b6

47-8a

18 : 2 3

55-65°-352-6

I2-8A6

92B137A

18: 3

2-2

3.6

COMPARISON OF SORGHUM AND MAIZE 97

relatively more oleic and less linoleic acid than did the corresponding maize diet,and the addition of 1*5% soya soapstock increased the relative concentration oflinoleic acid at the expense of oleic acid. On the basis of lipid composition this didnot bring up the linoleic acid level of diet 3 to that of diet 1, but in terms of totaldietary content it exceeded it (due to increased fat content of diet 3). The yolklipid patterns reflect these dietary differences, with significant effects on the linoleicand oleic acids levels of egg yolks of unsupplemented milo and maize diets. Thesedifferences were eliminated by the dietary soapstock.

TABLE 6

Diet

1

35

x> 2 See corresponding footnotes to Table 4.3 The dietary linoleic acid levels of diets 1, 3 and 5 were 1-66, IM6 and 1*95%, respectively.4 The soapstock included in this diet had the following fatty acid composition: 58-2% 18:2, 16-6%

18 : 1, 16-2% 16 : o, 6-o% 18 : 3, and 3-0% 18:0 .5 Averages of 3 pooled samples of 5 yolks each, representing different hens per replicate.6 See corresponding footnote to Table 4.

Trial 3The purpose of this trial was to create nutritional conditions in which linoleic

acid was the only possible limiting factor in the layer diets. With this aim in mindthe dietary protein level was raised and DL-methionine was added. On the otherhand, special but practical-type pre-experimental pullet and layer diets were for-mulated, containing a minimum of linoleic acid.

This trial involved 384 Leghorn hens, hatched on 17th May 1968. At 16 weeksof age, about 2 weeks after the pullets had been housed in their laying cages, thebirds were started on the special pullet diet. The latter was made up of 79, 18 and3% milo, soybean meal and mineral-vitamin supplements, respectively, and con-tained approximately 15*6% protein. Six week later this diet was changed to aspecial layer diet, very similar to experimental diet 3 of this trial (Table 2), exceptfor an additional 2 and 1 percentage points of soybean meal and limestone, respec-tively, at the expense of milo. The trial itself lasted from 20th December 1968 (whenthe production rate of the replicate groups ranged from 80 to 90%) to 28th February1969. Thereafter, egg weights were recorded an additional time, after the birdshad been on a uniform commercial ration for 3 weeks.

Four groups of 24 layers each were assigned, in a systematic manner as to loca-tion, to each of four treatments. The experimental design was a 2 x 2 factorial,with type of cereal grain and absence or addition of 1 % acidulated soya soapstock

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g8 S. BORNSTEIN AND BIANKA LIPSTEIN

being the variables (Table 2). All diets contained a uniform protein level of 16-6%(calculated), with the assays ranging from 16-1 to 16-6%, and the calculated SAAlevel reaching 0-6%. Assays of the yolk fatty acid patterns were performed witheggs collected 2 weeks before the end of the experiment.

Table 7 and Figure 2 summarise the performance data obtained. The only

TABLE 7

Effect of cereal grain and acidulated soya soapstock on the performance of laying hens during a 2^-month period (trial 3)

Averages of 4 replicates of 24 layers each

Maize MiloCereal grain

Supplement1

Diet no.

Hen-day production (%)Egg weight (g)Egg weight increase2 (g)Initial body weight (g)Weight gain (g)Food consumption (g/hen d)Food utilisation (g/egg)Mortality4 (%)

1 See Table 2.2 Difference between pre-experimental weight and that after a 2j-month experimental period.3 See footnote 6 to Table 4.4 In the absence of culling. At least on replicate of every treatment had no mortality at all.

None

i

74-i

57'°3-gab3

1756+ 20

i n

149Q . T

Soapstock

2

72-257-54-8a

1813+ 41

1 1 2

1556-2

None

374-656-4

3-3b

1823— 10

109146

4-2

Soapstock

476-757-'

4-2ab1844- 7109142

2-1

54 —

Dec. Jan. Feb.MONTH

March

FIG. 2.—The effect on egg size of supplementing maize and milo diets with acidulated soya soapstock. Thebirds had been partially depleted of linoloic acid before the start of the experiment (trial 3). Opensymbols—unsupplemented diets; solid symbols—diets supplemented with soapstock.

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COMPARISON OF SORGHUM AND MAIZE 99

consistent dietary effects were those on average egg weight and egg weight increase.The latter was significantly (P<o-O5) influenced by soapstock, but not by type ofcereal grain. Supplementation of the milo diet with i % soapstock brought eggweights up to the unsupplemented maize diet, but the latter, too, was improved bysuch supplementation.

As in the previous trials, the unsupplemented milo diet contained considerablyless linoleic acid than the corresponding maize diet, causing significant differencesin the linoleic acid content of eggs laid by hens fed on these diets (Table 8). Both thetypes of cereal and the supplementary soapstock had a highly significant effect onyolk linoleic acid levels (without interaction), whereas oleic acid levels were affected(P<o*oi) only by the cereal grain.

TABLE 8

Fatty acid composition (%) of food and egg yolk lipids (trial 3)

Dietno.2

12 4

344

1234

x> 2 See corresponding footnotes to Table 4.3 The dietary linoleic acid levels of diets 1, 2, 3 and 4 were 1-53, 2-04, I - I I and 1-63%, respectively.4 The main fatty acids of the soapstock used in this diet were: 58-6, 19-0, 11-8 and 9-1 % of 18 : 2, 18 : 1,

16 : o and 18 : 3, respectively.6 Averages of 4 pooled samples of 5 yolks each, representing different hens per replicate.6 See corresponding footnote to Table 4.

The eggs used for yolk lipid extraction showed relatively small egg weightdifferences, almost parallel to those of Table 7. The average weights of the eggsused were 57-5, 58-0, 57-1 and 57-7 g for diets 1-4, respectively. Percentage yolk ofthese eggs was rather uniform and ranged from 28-8 to 29'4%, without definitetrends.

DISCUSSION

In accord with a previous study (Bornstein et al., 1968), the only consistenteffect on layer performance caused by the source of dietary cereal grain was thereduction in egg size as a result of milo-soya diets. The literature on this subject hasbeen reviewed previously (Bornstein and Bartov, 1967; Bornstein et al., 1968).

The above effect could be best demonstrated by the use of" egg weight increase''during a relatively short period, which proved a better parameter than average eggweight, since (a) it minimised the effect of the variability existing during the pre-experimental period (Edwards and Morris, 1967), (b) it emphasised early egg weight

14: 0

o-6

o-5

0-9I-O

0-4

16 : 0

12-812-813-0n-7

27-526-225-825-2

1 6 :

1-2I-OI-I1-2

Fatty acid1

1 18:0

Diets

'•5o-81-4I-I

Yolk lipid5

3-95-04-9

n-7n-710-912-0

I 8 : i

20-130-525-8

38-9B°39-1B47-oA44-2A

18 : 2 3

56-358-250-552-6

i6-oABi8-oAio-8Gi3-iBC

18:3

3-86-4

3-5

.. .

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changes, and (c) it is not confounded by the flattening of the egg size curve with ageand due to approaching high seasonal temperatures.

Effect of methionine

In trials i and 2 the addition of DL-methionine to the milo-soya diets consistentlyimproved average egg weight and egg weight increase to the level of the maize diets(Tables 3 and 5). In trial 1 the maize diet, too, responded to methionine sup-plementation, further improving egg size. These results are in accordance with ourprevious ones (Bornstein et al., 1968), and with those of Bray (1964), who found agreater response from supplementing a soybean/sorghum protein mixture withmethionine than from supplementing a soybean/maize mixture.

Assuming that the SAA content of soybean protein is 2*96% (Combs andNott, 1967), and that of milo and maize proteins is 2#62 and 3*89%, respectively(Bornstein and Lipstein, 1971), it can be calculated that the unsupplemented maizeand milo diets of trial 1 contained 0-50 and 0-43% SAA, respectively. The corres-ponding values for trial 2 are 0-51 and 0-43%. According to the National ResearchCouncil of America (1966), the SAA requirement for layer diets is 0-53%, and underthe conditions of the previous study (Bornstein et al., 1968) it appeared as if the SAArequirement for maximum egg size ought to be found between 0-49 and 0-52%.

Thus, unsupplemented milo-soybean diets are suboptimal with regard to SAAand hence the response to added methionine. The differential response of the maizediets of trials 1 and 2 to added methionine appears to indicate that the SAA require-ment for maximal egg size under these specific experimental conditions (e.g. foodintake of 110 g/hen day) might be 0-51 %—if the calculated values are correct. As awhole, the results presented in Tables 3 and 5 appear to support the above calculatedSAA values, especially their relatively low level in milo (Bornstein and Lipstein,I970-

Effect of soapstock

Maize contains more oil and this oil has a higher linoleic acid content than milo(Table 1). On the basis of five oil samples each of these two cereals, assayed in thepresent and previous study (Bornstein et al., 1968), their linoleate content rangedfrom 56-8 to 59-1 % and 45-5 to 53-2%, respectively; these levels are higher and lessvariable than those reported by Edwards (1964) for maize and by Chavez, DeMatheu and Reid (1966) for milo. These differences in linoleic acid content becomeeven more pronounced on a whole-grain basis (2#23-2'44 compared with 1 -41-1 g6o%,respectively). Acidulated soya soapstock can be considered a practical and econ-omical source of linoleic acid, containing a concentration of 53"8-58-6% (samples ofboth studies).

The addition of soapstock to milo diets containing DL-methionine gave no eggsize response in trial 1 and only a slight one in trial 2 (Tables 3 and 5, respectively),whereas in trial 3 this supplementation brought about a significant improvement inegg weight increase in diets based on both cereals (Table 7). In our previous ex-periments, too, only slight responses were obtained (Bornstein et al., 1968). Thedifference between the latter experiments and trials 1 and 2 of the present study, onthe one hand, and trial 3, on the other hand, is in the employment of a pre-experi-mental diet low in linoleic acid in the latter trial. Previously, the chicks, pullets

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and layers were fed commercial-type rations rich in linoleic acid up to the start ofthe experiment. Thus the birds entered the experimental period with a largereservoir of linoleate in their adipose tissues. The importance of this reservoir, andthe very long period of time required to deplete laying hens of linoleic acid beforetheir performance is affected, has been stressed by Miller, Menge and Denton(1963), Menge, Calvert and Denton (1965) and Balnave and Brown (1968).

No attempt was made in trial 3 to actually deplete the birds of their linoleicacid reserves by the use of purified diets; instead, the rations used beginning with16 weeks of age contained normal levels of practical food ingredients having relativelylow concentrations of linoleic acid. The importance of supplying milo-soya (andeven maize-soya) layer diets with a linoleic acid supplement, under such circum-stances, is rather obvious (Table 7 and Figure 2).

The differences in egg weights between diets of low and optimal amounts oflinoleic acid might have increased as the laying period advanced, beyond that of therelatively short experimental period of this trial, due to slow further depletion oflinoleic acid reserves in the body (Kivimae, Wadne and Hildingstam, 1970),although other authors emphasise especially the early effect of linoleic acid on eggsize (Shutze, Jensen and McGinnis, 1962; Edwards and Morris, 1967).

Since the study of Jensen, Allred, Fry and McGinnis (1958), there have beenmany reports of the beneficial effect of unsaturated vegetable oils on egg productionand egg size. The literature on this subject was reviewed in our previous report(Bornstein et aL, 1968) as well as by Jensen (1968) and Balnave (1970a). However,there is some doubt as to whether this effect is due to increased energy concentrationof the diet (Blamberg, Bossard and Combs, 1964; Jackson, Kirkpatrick and Fulton,1969) or to the essential fatty acids present in the unsaturated vegetable oils (Shutzeand Jensen, 1963; Edwards and Morris, 1967; Menge, 1968, Kivimae et aL, 1970).The pronounced influence of relatively small amounts of oil (trial 3; Chavez et al.,1966) supports the contention that linoleic acid is responsible for the major part ofthe egg weight effect obtained from feeding these oils.

The above improvement in egg size due to the addition of linoleic acid-containing oils to milo diets (containing adequate levels of SAA) has been reportedalso by Chavez et al. (1966) and Deaton and Quisenberry (1967). A parallel situationhas also been described for layer diets based on wheat (Edwards and Morris, 1967;Balnave, 1970J) or on a combination of wheat, barley and oats (Kivimae et aL,1970). In general, practical diets based on maize do not respond in egg weightsto linoleic acid supplementation, but the improvement of the maize diet used in trial3 is in agreement with the results of Shutze et al. (1962), Chavez et al. (1966) andCooper and Barnett (1968).

It might be useful to attempt an estimate of the dietary linoleic acid require-ment of the hen for maximum egg size on the basis of the data presented in this report.The results of trials 1 and 2 (Tables 3-6) seem to indicate that under the conditionsof these experiments {i.e. large reserves of linoleic acid from previous diets and a lay-ing mash intake of about 110-116 g/bird d), levels of 1-1-1-2% linoleic acid wereadequate. On the other hand, in trial 3 (Tables 7 and 8), in which the birds werefed from 16 to 31 weeks of age commercial-type rations relatively low in dietarylinoleic acid, laying diets containing 1-5 and i*6% linoleic acid (diets 1 and 4)caused greater egg weights than one containing I-I % (diet 3), with a slight trend for

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an additional improvement due to 2-o% dietary linoleic acid (diet 2). Under theconditions of the latter experiment, a dietary level of approximately i«8% linoleicacid might be an acceptable recommendation.

The requirement of dietary linoleic acid for optimum egg weight has beenreported variously within a range of i-o to 2-5% (Shutze et al., 1962; Jensen,Wagstaff, Parks and Martinson, 1964; Marion and Edwards, 1964; Menge, 1968,1970; Kivimae et al. 1970).

Considerable information has been gathered concerning the influence of dietaryfat on fatty acid composition of egg yolk lipids, beginning with the early studies ofCruickshank (1934) and Fisher and Leveille (1957). The level of yolk linoleic acidusually reflects dietary linoleate levels fairly accurately; however, there appears tobe a limit to the percentage of linoleic acid that can be deposited in the egg (Summers,Slinger and Anderson, 1966; Sell, Choo and Kondra, 1968).

The differences in fatty acid patterns between maize and milo (Table 1) werereflected in the lipid composition of the diets, which in turn influenced the yolkfatty acids of eggs laid by hens fed these diets (Tables 4, 6 and 8). The milo-soyadiets (no. 3) of all three trials contained a rather uniform level of I * I % dietarylinoleic acid, and the corresponding yolk lipids were made up of 9-11 % of this fattyacid. The parallel values for the maize diets (no. 1) were 1*5-1 "7 and 13-16%,respectively. The data of Chavez et al. (1966) and Kivimae et al. (1970), too,indicate a 1 to 9-10 ratio for the dietary to yolk linoleic acid relationship.

The results presented here, together with those of previous papers of this series(Bornstein and Bartov, 1967; Bornstein et ah, 1968), indicate that under practicalconditions grain sorghum may be freely substituted for maize in laying hen rations,as long as in formulating these diets proper adjustments are made in xanthophylls,linoleic acid and SAA.

ACKNOWLEDGEMENTS

This study was supported by grants from the Israel Ministry of Agriculture andthe Egg and Poultry Marketing Board. The technical assistance of Mrs MiriamBen-Mosheh is gratefully acknowledged.

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