Wheat Middlings as an Alternate Feedstuff for Laying Hens

Wheat Middlings as an Alternate Feedstuff for Laying Hens

METABOLISM AND NUTRITION Wheat Middlings as an Alternate Feedstuff for Laying Hens YISHENG BAI, M. L. SUNDE, and M. E. COOK Departments of Nutritional...

569KB Sizes 0 Downloads 58 Views

METABOLISM AND NUTRITION Wheat Middlings as an Alternate Feedstuff for Laying Hens YISHENG BAI, M. L. SUNDE, and M. E. COOK Departments of Nutritional and Poultry Sciences, University of Wisconsin, Madison, Wisconsin 53706 ABSTRACT Three long-term experiments were conducted to evaluate the possibility of using wheat middlings (WM) for laying hens and to study the responses of six strains of commercial laying hens fed WM diet. In Experiment 1, 320 layers maintained in floor pens were fed diets containing 45% WM with .25 or .75% salt, or 89% WM with .25% or 1.5% salt. Salt supplementation did not show any beneficial effect on egg production. Hen-day egg production by hens fed the 45% WM diet was significantly higher for hens fed 45% WM than for those fed the 89% WM diet (79 versus 67.5%, 44-wk period). Feed, limestone, and water intakes were increased by the 89% WM diet. Yolk color, Haugh units, hen livability, and reproductive parameters were not different among the dietary treatments. In Experiments 2 and 3, laying hens from six commercial strains (four strains each experiment, 240 hens per strain) were maintained in laying cages in each year, and fed either a corn and soybean meal (CSM) or a 25% WM diet. Results show that neither diet nor strain had effects on hen-day egg production; however, egg weights from Strains A, C, and F were heavier than those from Strains 6, D, and E. Feed intakes and feed utilizations were similar among the strains. The 25% WM diet increased egg weight, feed intake, and feed utilization compared with the CSM diet. Livability of hens was 93.8 to 97.5% and was not affected by either strain or diet. It is concluded that commercial strains of laying hens can be fed diets containing 25 to 45% WM and still have normal hen-day egg production although feed utilization will be poorer. (Key words: laying hen, wheat middlings, strains, hen-day egg production, performance) 1992 Poultry Science 71:1007-1014

INTRODUCTION

production dropped during Periods 5 to 8, which occurred during cold weather conThe feeding of wheat middlings (WM) ditions. However, it was believed that to commercial laying hens has been stud- other factors besides temperature were ied for 7 yr. Previous results (Patterson et also involved in the depressed egg proah, 1988) demonstrated that WM could be duction. Salt was considered as a possible used in laying hen diets at certain levels to factor because Slinger et ah (1950) reported obtain satisfactory egg production without that high fiber-low energy grains, wheat reducing feed utilization. Furthermore, by-product, and cellulose, increased the with as high as 89% WM as the sole salt requirement up to 2% of the diet to protein and energy source, hen-day egg obtain maximum chick growth. Therefore, production reached a peak of 85%, with an the objective of the first experiment in the average of 66% (during a 44-wk laying current study was to study the effect of period). Results of 2 yr (Experiments 1 and salt supplementation of high WM diets on 2, Patterson et ah, 1988) showed that egg performance of laying hens. Patterson et ah (1988) did not find significant differences in percentage of hen-day egg production, feed intake, and Received for publication June 26, 1991. feed utilization between laying hens fed Accepted for publication February 12, 1992. 1007

1008

BAI ET AL.

2 consecutive days in each period, and average water intake was also obtained during the same time. The water intake was obtained every 24 h by measuring the disappearance of water from a preweighed water jug hung above a water cup connected with a plastic tube in each pen. Reproductive performance, including fertility, hatchability, percentage hatch, and chick growth rate, were evaluated in Experiment 1 as described previously (Patterson et al, 1988). This was done to assure that the dietary treatments did not induce any nutritional deficiencies. Dietary treatments were 89% WM plus 1.5 or .25% salt (89% WM), and 45% WM plus .75% or .25% salt (45% WM). The basal diet compositions are shown in Table 1. In Experiments 2 and 3, as in Experiment 1, day-old chicks were obtained from a primary breeder 1 and raised to 18 wk of age. Then a total of 960 pullets from the four commercial strains (A, B, C, and D in Experiment 2, and A, B, E, and F in Experiment 3, 240 per strain) were randomly assigned into laying cages (three birds per cage with floor space of 30.5 x 45.7 cm). Ten adjacent cages were assigned as an experimental unit (eight replicates per strain). Periods were divided as that in Experiment 1 with a starting age of 19 wk, but averages reported for the measured parameters began at 23 wk of age except feed intake, which began at 19 wk of age. The experiments were divided into two MATERIALS AND METHODS phases. In Phase 1 (19 to 34 wk), the diet The general experimental design for contained 17% CP (Table 1) and in Phase 2 Experiment 1 was the same as that (35 to 66 wk in Experiment 2 and 35 to 62 described in detail previously (Patterson et wk in Experiment 3) the diet contained ah, 1988). Briefly, 40 birds at 18 wk of age 15% CP. Dietary treatments were a CSM were housed in each floor pen (355 x 233 or a 25% WM diet. These two experiments cm), with two pens per dietary treatment. were designed with 2 x 4 factorial arThe experimental diets were fed to the rangements of treatments (two diets by birds at 23 wk of age, and hen-day egg four strains). production, feed intake, and limestone As in the previous experiments, diets intake were determined at the end of each were formulated to meet or exceed Naof 11 28-day periods. tional Research Council (NRC, 1984) nutriHaugh units (Haugh, 1937), egg yolk ent recommendations for laying hens excolor (Heiman and Carver, 1935), and egg cept for ME and calcium; the latter was weight were measured from the eggs met by providing limestone grits in sepacollected from individual hens laid during rate containers in each floor pen (Experiment 1) or by supplying 3.4 g of limestone grits per hen per day (supplied once a week, in Experiments 2 and 3). The 1 Shaver Poultry Breeding Farms Ltd., Cambridge, specifications of WM were described in ON, N1R 5V9, Canada.

the diet containing 20 or 25% WM and the control diet. In addition, reports have demonstrated different performances of various strains or breeds in response to feed restrictions (Leclercq, 1975; Renden, 1987). Leclercq (1975) reported that about 20% feed restriction resulted in decreased egg numbers produced by two commercial Rhode Island Red strains, but egg weight was decreased only for Cross 1, and not Cross 2. They reported that the difference in egg weight between the strains was due to the different egg production. In the current study, the diet with 25% WM contains approximately 88% of the ME of the corn and soybean meal (CSM) diet by calculation. The bulky volume of the WM diet limits the feed intake of laying hens such that various strains may respond differently to the ME restriction. The objectives of the second and third experiments of the current study were to investigate genetic variations in performance of six strains (A, B, C, and D in Experiment 2, and A, B, E, and F in Experiment 3) of commercial Leghorn laying hens fed the diets containing 25% WM. Such information may assist in selecting strains of layers that could perform well in geographical locations with limited grains but abundant supplies of grain by-products.

PERFORMANCE OF LAYING HENS FED WHEAT MIDDLINGS TABLE 1. Composition of experimental diets Ingredients and analysis

Experiment 1 45% WM

89% WM

1009

1

Experiments 2 and 3 WM (PI)

CSM (P2)

WM (P2)

67.32 19.47

.50 1.004

40.68 20.21 25.00 3.00 1.45 6.70 1.21 .10 .15 .50 1.00

.50 1.00

47.30 14.38 25.00 3.00 1.18 6.89 .50 .10 .15 .50 1.00

17.00 2,750 3.00 .43 .63 .92

17.00 2,415 3.00 .43 .66 1.04

15.00 2,775 3.00 .37 .56 .76

15.00 2,440 3.00 .37 .61 .88

CSM (PI) CO

35.02 9.00 45.00 3.00 1.20 5.80

Yellow corn Soybean meal

WM Alfalfa meal Dicalcium phosphate Limestone Animal fat

Met Lys Salt Premix Calculated analysis: CP ME, kcal/kg Calcium Available phosphorus Met + Cys Lys

.10 .13 .25 .50 3 15.13 2,227 2.58 .30 .64 .79

60.45 25.39 88.95 3.00 1.00 6.00 .10 .20 .25 .50 14.77 1,643 2.63 .30 .68 .80

3.00 157 6.66 1.37 .06

3.00 1.30 6.85 .51 .05

WM = wheat middlings; CSM = corn and soybean meal; PI = Phase 1 (Weeks 19 to 34); P2 = Phase 2 (Weeks 35 to 66 in Experiment 2, and Weeks 35 to 62 in Experiment 3). 2 The soybean meal contained 48% CP in Experiment 1, and 44% CP in Experiments 2 and 3. Premix supplied the following per kilogram of diet in Experiment 1: vitamin A, 4,000 IU; cholecalciferol, 1,400 IU; vitamin E, 12.4 mg; riboflavin, 1.7 mg; vitamin B ^ 7.3 |ig; iron, 42 mg; zinc, 36 mg. 4 Premix supplied the following per kilogram of diet of Experiments 2 and 3: vitamin A, 12,000 IU; cholecalciferol, 1500 IU; vitamin E, 25 mg; menadione sulfate, .5 mg; riboflavin, 3.97 mg; folacin, .25 mg; niacin, 39.5 mg; calcium pantothenate, 4.5 mg; vitamin Bj2, 8 ug; choline chloride, 396 mg; manganese, 44 mg; zinc, 32 mg; lincomycin, 3.97 mg.

detail previously (Patterson et ah, 1988). All diets were fed crumbled. Cage egg production was recorded daily. Feed intake was measured at the end of each period. At the beginning and end of each experiment, individual laying-hen body weight was measured. Statistical Analysis The data obtained from Experiment 1 were analyzed by one-way ANOVA based on each period or average of the experiment, and only the latter is presented in this paper. The data obtained from Experiments 2 and 3 were analyzed by two-way ANOVA based on each period or average of entire experiments (SAS Institute, 1985). Means of each diet, main effects of diet and strain, and interactions between diet and strain were separated by the least significant difference method. Percentage data were transformed using arc sine of square root of

percentage prior to the ANOVA (SAS Institute, 1985), however, percentage values are reported for ease of data interpretation. RESULTS AND DISCUSSION Salt supplementation did not benefit any production parameters for either WM diet; however, it increased water intake at both WM levels and increased limestone intake with the 89% WM diet (Table 2). The water intake difference is in agreement with that previously reported (Patterson et ol., 1988). In the present experiment, only those birds fed the 89% WM diet with 1.50% salt produced extremely wet Utter that required frequent changing. When hens were 46 wk old, salt was reduced to 1.0% of the diet due to the poor litter condition. Even with the reduced salt level, average daily water intake of the hens fed the 89% WM diet was still 30% higher than that of laying

1010

BAI ET AL.

TABLE 2. Effects of wheat middling (WM) diets on parameters measured in Experiment l 1 Hen-day egg production

Treatment WM

Salt

89 89 45 45 SEM

25 150 .25 .75

(%)

67.0" 68.2" 80.03 78.1a

Egg weight

Feed per Feed 12 eggs intake

(g) 58.0 58.5 59.0 59.0 35

(kg) 3.01a 3.05a 2.13" 2.1l" .10

— (gram 168a 174a 142" 137" 1.32

Water intake2

Limestone intake

per hen per day) — 6.5b 349.0 455.0 7.4a 259.0 5.6C 285.0 52c .16

Yolk color3

Haugh units4

7.1 7.0 7.3 7.4 .14

82^ 83.1 83.8 83.9 .80

a-c

Means within a column with no common superscripts are significantly different (P < .05). ^Experiment 1 conducted during laying hens' age of 23 to 66 wk. No replicate for water intake, only means of each treatment are presented here. 3 Heiman and Carver (1935). 4 Haugh (1937).

hens fed the 89% WM with .25% salt. Salt at .75% level increased water intake by 10% compared with .25% salt with the 45% WM diet. At the .25% salt level, laying hens fed the 89% WM diet consumed 35% more water daily than those fed the 45% WM diet. Higher hen-day egg production was obtained in the present experiment than in the previous ones with similar dietary treatments. Feed intake of laying hens fed the 45% WM diet also was greater than that reported by Patterson et al. (1988). One finding of the present experiment was that the laying hens fed the 89% WM diet consumed more supplemental limestone grits (provided for ad libitum consumption) than those fed the 45% WM diet, suggesting that a supplemental calcium level higher than that recommended by the NRC (1984) should be considered when diets contain high levels of WM. Egg weights, yolk color, and Haugh units were similar regardless of the dietary treatments (Table 2). Fertility, hatchability, and percentage hatch, as well as chick growth rate, livability, and nutritional deficiency symptoms were not significantly different among dietary treatments in Experiment 1 (data not shown). These results demonstrated that WM can be used as a feed ingredient for laying hens at 45% with satisfactory hen-day egg production but with a poorer feed utilization. Similar performances (patterns of henday egg production, egg weight, daily

feed intake, and feed utilization) were obtained from Experiments 2 and 3. Only selected parameters are shown in Figures 1 to 4, and the averages of these parameters from both experiments are presented in Table 3. The yearly average hen-day egg production was not affected by either strain or diet (Table 3). However, in Experiment 3, Strains A and F produced more eggs (P < .05) than Strains B and E in Period 3 (Weeks 23 to 26), suggesting that Strains A and F reached their egg production peak earlier than the other two strains (data not shown). Egg production was

4

5

6

7

Period (28-day)

FIGURE 1. Main effect of diet on hen-day egg production of laying hens fed corn and soybean meal (CSM) or 25% wheat middling (WM) diets in Experiment 3. No significant difference was found during all periods except for Periods 6 to 8, in which hen-day egg production was lower from laying hens fed the 25% WM than from hens fed the CSM diet (P < .05).

PERFORMANCE OF LAYING HENS FED WHEAT MIDDLINGS 68 66 64 62 60 58 56 54 52 50

1011

68-1

666462-

I

60 5856 54 52 50

4

5

6

7

10

11

12

1

4

Period (28-day)

66 -J 64.

A

A

A

A

__^

^ S S — ^

CM CO

A

O
bv

FIGURE 3. Main effect of diets on egg weights from different strains of laving hens fed corn and soybean meal (CSM) or 25% wheat middling (WM) diets in Experiment 3. There was no significant difference during Periods 2 to 4, and after Period 4, egg weights from laying hens fed the WM diet were significantly heavier than those fed the CSM diet (P < .01).

Byr-

A ^

58.

a

56

""D



Strain A

°—

Strain B

D

A V 54

5 6 7 Period (28-day)

cy

52 50 2

3

4

7 5 6 Period (28-day)

8

9

10

11

FIGURE 2. Main effect of strain on egg weights of laying hens fed corn and soybean meal (CSM) or 25% wheat middling (WM) diets, a) Experiment 2. Egg weights from Strains A and C were significantly heavier than those of Strains B and D except that egg weights of Strain C were lower than those of Strain A during Periods 2 and 4 (P < .01). b) Experiment 3. Means at same period with different letters are significantly different (P < .01).

depressed by the WM diet as compared with the CSM diet in Periods 6 to 8 (Figure 1). The reason for this decrease in production is not known. Egg weight (size) is a very important economic trait of laying hens. The price difference per dozen between large and medium eggs varies with the season. Medium and small eggs produced early in the egg production cycle are usually not profitable, nor are extra large eggs produced later in the production cycle. The present results (Table 3, Figure 2a,b) showed that strains of laying hens differed significantly in overall egg weight and also varied at certain times during the egg laying cycle, suggesting that one strain

might be more profitable than another. In Experiment 2, the eggs produced by Strains A and C were significantly heavier than those produced by Strains B and D (Table 3). In Experiment 3, the eggs produced by Strains A and F were heavier than those laid by Strains B and E. The changes of egg weight with the strains and different egg production periods in Experiments 2 and 3 are shown in Figure 2a,b. Strains A and C consistently laid bigger eggs than the other strains. The dietary treatments in both Experiments 2 and 3 had no effect on egg weight during

4

5 6 7 Period (28-day)

FIGURE 4. Main effect of diet on feed intake (grams per hen per day) of laying hens fed corn and soybean meal (CSM) or 25% wheat middling (WM) diets in Experiment 3. The WM diet resulted in a significantly higher feed intake than the CSM diet in each period (P < .01).

1012

BAI FT AL. TABLE 3. Average results of six strains and two diets on measures of production in Experiments (Exp) 2 and 3

Diet2

Hen-day egg E production Strain SS weight Exp 2 Exp 3 Exp 2 Exp 3 Exp 2 Exp 3

CSM A A CSM B B CSM C CSM D CSM E CSM F WM A A WM B B WM C WM D WM E WM F Main effect of diets CSM WM SEM of variation Strain Diet Strain by diet

77.4 76.1 77.3 78.1 75.7 78.6 77.8 77.0

(%) 81.6 81.5 83.5 81.4 81.2 82.9

62.9 61.3 63.2 61.9

79.9 80.1 77.2 77.3

.66 .94 .19

82.0 81.0

.54 .21 .14

- - (g per heni per day) •• — (kg:kg eggs) — 107 2.14 2.21 109 106 104 2.19 2.26 108 2.12 109 2.11 106 2.25 106 2.20 120 115 2.30 2.34 117 112 2.26 2.30 117 Z26 115 2.30 112 2.42 115 2.43

(g) 61.0 58.4

65.5 62.9 63.9 62.1

58.6 60.7 62.6 593 59.7 61.5

62.3B 63.6A .23 .0001 .0001 .20

Feed utilization Exp 2 Exp 3

Feed intake Exp 2 Exp 3

59.8B 60.8A .13 .0001 .0001 .30

108B 117A .78

2.14B 2.28A .02

107B 113A .59

.12 .0001 .15

.13 .0001 .49

2.23B 2.37A .02

.35 .001 .15

.34 .0001 .08

'TMeans within each column with no common superscripts are significantly different (P ^ .001). A11 parameters are the average of Periods 2 to 12 (23 to 66 wk) in Exp 2 and Periods 2 to 11 (23 to 62 wk) in Exp 3, except feed intake, which is the average of 12 periods (18 to 66 wk) in Exp 2 and the average of 11 periods (18 to 62 wk) in Exp 3. ^ S M = corn-soybean meal diet; WM = 25% wheat middlings diet. 1

Periods 2 to 4, but laying hens fed the 25% WM diet produced heavier eggs than those fed the CSM diet after Period 4 (Figure 3). When yearly egg mass production (kilograms of egg per hen) was calculated (data not shown), Strains A and C produced more egg mass compared with Strains B and D in Experiment 2. In Experiment 3, Strain A produced the most egg mass, which was significantly more than Strains B and E; Strain F was intermediate. Diet had no effect on this parameter in both experiments (data not shown). The strain difference data suggest that an international poultry breeding company may want to select different strains of laying hens depending on whether their market is based on the weight of eggs or on dozens. Feed intake (grams per hen per day) for the hens of the different strains in each

experiment was not significantly different (Table 3). As expected, laying hens fed the 25% WM diet had significantly higher feed intake compared with those fed the CSM diet (Table 3 and Figure 4). No differences were found in feed utilization among the four strains of laying hens when this

TABLE 4. Initial and final body weights and hen livability rate of Experiment 1

WM

Salt

89 89 45 45 SEM

.25 1.50 .25 .75

Body• weight 66 wk 18 wk 1,176 1,176 1,189 1,207 13

(g) U09b l,628 ab 1,680s l,671a 21

Livability - (%) 93.8 90.0 95.0 96.4

a/b Means within each column with no common superscripts are significantly different (P < .05).

1013

PERFORMANCE OF LAYING HENS FED WHEAT MIDDLINGS

TABLE 5. Main effect of strains and diets on initial and final body weights and laying hen livability rate of Experiments (Exp) 2 and 3 1 Main effect of strain Exp 2

Exp 3

Livability

66 wk BW f»

A B C D

A B

Experiment 3

Experiment 2 18 wk BW l,139 b l,134 b l,143 b l,168 a

(%) 97.5 97.1 96.7 97.1

vg; 2,013" 1.946b l,991 a l,978 a b

E F SEM Main effect of diets CSM WM SEM

8

16 1,874 1,888 11

18 wk BW

62 wk BW

Livability

l,225 a l,181 b

(g) l,850 a b l,872 a

(%) 93.8 94.6

l,226 a l,182 b 7

l,862 a l,812 b 15

97.1 96.2

l,835 b l,863 a 10

96.3 95.0

96.3 97.5

ab

' Means within each column and main effect with no common superscripts are significantly different (P <

.05).

*CSM = corn soybean meal diet; 25% WM = diet containing 25% wheat middlings.

parameter is expressed as kilograms of kilogram of eggs) had probability values feed per kilogram of eggs (Table 3). The of .15 or .08 for Experiments 2 and 3, feed utilization of laying hens fed the 25% respectively. WM diet was poorer than those fed the Initial and final body weights and hen CSM, as would be expected due to the low livability from these experiments are preME of the WM diet. There were no sented in Tables 4 and 5. Laying hens fed significant interactions of strain and diet the 89% WM diet with .25% salt had lower found for the parameters measured (Table final body weight compared with those 3). The interactions of diets and strains for fed the 45% WM diets with either level of feed utilization (kilograms of feed per supplemental salt (Table 4). Livability was

TABLE 6. Calculated daily amino acids and crude protein intakes (grams per hen per day) of laying hens fed corn-soybean meal (CSM) or 25% wheat middling (WM) diet in the 2nd and 11th 28-day period Period 2 (23 to It > wk)

Period 11 (59 to 62 wk)

Amino acids and protein

CSM

WM

WMfSM1

CSM

WM

WMrCSM

Met + Cys Lys Arg Gly Ser His Ue Leu Cys Phe Tyr Thr Trp Val CP

.55 .80 .02 .73 .78 .37 .75 1.40 .24 .78 .54 .63 20 .82 15.92

.58 .89 1.04 .77 .77 .38 .71 1.29 .26 .74 .51 .61 .20 .81 16.53

1.05 1.11 1.02 1.06 .99 1.03 .95 .92 1.08 .95 .94 .97 1.00 .98 1.04

.60 .82 1.08 .78 .83 .39 .80 158 .26 .84 .61 .68 2\ .89 16.13

.73 1.02 1.23 .93 .91 .46 .83 1.60 .32 .89 .64 .74 23 .98 17.99

1.21 1.24 1.14 1.19 1.10 1.18 1.04 1.01 1.23 1.06 1.05 1.09 1.10 1.10 1.12

WMCSM = ratios between the two diets.

1014

BAI ET AL.

not significantly different among the treat- increased the intake of vitamins and ments. The body weights of Strain D at 18 minerals. Therefore, egg weight was inwk of age were significantly heavier than creased in Phase 2, probably because of those of the other strains in Experiment 2, the increased intake of amino acids and and the body weights of Strains A and E CP. In summary, including WM in laying at age of 18 w k were heavier than those of Strains B and F in Experiment 3 (Table 5). hen diets resulted in reasonable to excelLaying hens fed the 25% WM diet had lent hen-day egg production with inhigher final body weights than those fed creased feed intake and increased egg the CSM diet in both experiments but it weight (Experiments 2 and 3). All strains was significant only in Experiment 3. tested responded to the WM diet similarLivability was excellent in all treatments ly. Six strains of laying hens showed and was not significantly different among similar hen-day egg production, but strains or between diets in Experiments 2 strains differed in egg weight, and consequently producers should select strains and 3. To determine why the egg weight was depending on whether eggs are sold by higher in Phase 2 of each year for the the dozen or by case weight. laying hens fed the 25% WM diets in Experiments 2 and 3 (Table 3 and Figure REFERENCES 3), daily consumption of amino acids and CP for Period 2 (Weeks 23 to 26, repre- Haugh, R. R., 1937. The Haugh unit for measuring egg quality. U.S. Egg Poultry Mag. 43(9): senting Phase 1) and for Period 11 (Weeks 552-555, 572-573. 59 to 62, representing Phase 2) of Experi- Heiman, V., and J. S. Carver, 1935. The yolk color index. U.S. Egg Poult. Mag. 42(8):40-42. ment 2 were calculated by multiplying the amino acid content of the two diets with Leclercq, B., 1975. Energy requirements of avian species. Page 133 in: Nutrient Requirements of feed intake, as shown in Table 6. The Poultry and Nutritional Research. C. Fisher and ratios of each amino acid and CP between K. N. Boorman, ed. Butterworths, London, the two diets were approximately equal to England. 1 in Period 2 but were greater than 1 in National Research Council, 1984. Nutrient Requirements of Poultry. 8th rev. ed. National AcaPeriod 11. Both diets were formulated to demic Press. Washington, DC. contain the same percentage of CP; the Patterson, P. H., M. L. Sunde, E. M. Schieber, and W. lower levels of ME of the 25% WM diet W. White, 1988. Wheat middling as an alternate feedstuff for laving hens. Poultry Sci. 67: resulted in an increased feed intake. The 1329-1337. ME consumption (kilocalories per hen per Renden, J. A., 1987. Egg production efficiency in day) was similar between the CSM and dwarf lines selected for high and low body the 25% WM diets (259 versus 246 in weights as influenced by feed restriction. Poultry Sci. 66:1085-1089. Period 2 and 289 versus 275 in Period 11, respectively). The increments of feed in- SAS Institute, 1985. SAS® User's Guide. Version 5 Edition. SAS Institute Inc., Cary, NC. take of laying hens fed the 25% WM diet Slinger, S. J., W. F. Peper, and I. Motzok, 1950. over those fed the CSM diet were similar Factors affecting the salt requirements of chickin both periods, which proportionally ens. Poultry Sci. 29:780.(Abstr.)