LIBRARY,
*A & M COLLEGE,
campus,

A40-240-6M-L1S0

TEXAS AGRICULTURAL EXPERIMENT STATION
A. B. CONNER, DIRECTOR

COLLEGE STATION, BRAZOS COUNTY, TEXAS

ABEULLETIN NO. 583 MARCH 1940

I

DIVISION OF POULTRY HUSBANDRY
DIVISION OF CHEMISTRY '

Requirements of Chickens for Vitamin A
When Fed as Carotene

 

AGRICULTURAL AND MECHANICAL COLLEGE OF TEXAS
T. O. WALTON, President

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The vitamin A potency in the form of carotene required by
chicks and laying hens was studied in eleven experiments. Pullets
require more carotene than chicks and laying hens more than
growing pullets. Suitable quantities 0f vitamin A resulted in
larger growth and lower mortality for growing chicks than
lower quantities. Suitable quantities for laying hens resulted in
larger numbers 0f eggs, a longer productive period as well as
longer life, larger percentages of hatchable eggs and less defec-
tive chicks hatched, than when insufficient quantities were fed.

For growing chicks up to the age of 12 weeks, 180 micrograms
of carotene per 100 grams of feed (300 U. S. P. units) is recom-
mended. This provides a margin of safety over the minimum
of 125 to 150 micrograms of carotene per 100 grams of feed
which the experiments indicate would be satisfactory. Carotene
dissolved in oil seems to be equally as suitable as carotene in
alfalfa leaf meal.

For pullets during the period of from 12 weeks to the begin-
ning of the laying period, not less than 200 micrograms of caro-
tene per 100 grams of feed (333 U. S. P. units) is recommended.
This affords a margin of safety over the minimum of 150 to 175
micrograms which appears to furnish sufficient vitamin A potency
for growth, but which is too low for satisfactory egg production.

For laying hens not less than 500 micrograms of carotene per
100 grams of feed (833 U. S. P. units) is recommended, thus
allowing a margin of safety over the minimum of 450 micrograms
indicated as satisfactory. When the eggs are to be used for hatch-
ing, not less than 600 micrograms of carotene per 100 grams of
feed (1,000 U. S. P. units) is recommended, thus allowing a margin
of safety over the minimum of 550 micrograms. If eggs high in
vitamin A potency are desired, still larger quantities of carotene
must be fed.

In some of the experiments, the chickens did well on smaller
amounts of carotene than here recommended but in other experi-
ments, higher quantities were found to be needed, and it was
thought best to make recommendations on the safe side.

TABLE OF CONTENTS

Page
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Previous recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 6
Vitamin A requirements for growing chicks . . . . . . . . . . . . . . . . . . . . . . . . .. 7

Comparison of carotene fed in alfalfa leaf meal with carotene in
Wesson oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  11

Requirements of pullets from 12 weeks to 20 months, through the

laying periods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 13
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2O
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 21

 

BULLETIN NO. 583 i MARCH 1940

REQUIREMENTS OF CHICKENS FOR VITAMIN A
WHEN FED AS CAROTENE

By Ross M. Sherwood, Chief, Division of Poultry Husbandry
and G. S. Fraps, Chief, Division of Chemistry

The exact vitamin A requirements for chickens have not yet been agreed
upon, although considerable work has now been done on this subject by a
number of investigators. The requirements are different according to the
object of feeding the chickens. If the chickens are grown for broilers, the
quantity needed is that which will give the most economical growth with
sufficiently good health to avoid financial losses by death or unsatisfactory
appearance of the chickens. If the pullets are to be kept for production
of eggs or for breeding purposes, additional quantities may be needed for
storage or to insure more vigorous health, which may result in longer life.

Vitamin A potency may be supplied by vitamin A as such, which occurs
as a colorless compound in fish oils, by carotene, which occurs as a yellow
compound in alfalfa and other green feeds, or by cryptoxanthin, which
occurs as a yellow compound in yellow corn. In northern states, fish oils
are fed to supply vitamin D and they furnish vitamin A incidentally, and
are an important source of vitamin A potency. In the south, the abundant
sunshine supplies the needed vitamin D potency, except for battery brooder
chicks, and the most important sources of vitamin A potency are carotene
in green colored feeds or cryptoxanthin in yellow corn. According to Record
and associates (10) the same number of international units have the same
effect on chickens whether fed as vitamin A or as carotene. One inter-
national unit is defined as equal to 0.6 micrograms of carotene, 1.0 U. S. P.
unit, and approximately .08 Sherman-Munsell (S. M.) unit. The value of
a Sherman-Munsell unit may vary from 0.5 to 1.5 (7a).

This is fifth in a series of publications on the vitamin A requirements
of poultry on a joint project of the Division of Poultry Husbandry and the
Division of Chemistry of the Texas Agricultural Experiment Station. It
has been previously shown (15) that laying pullets raised on the same
ration lived from 34 to over 199 days on a ration low in vitamin A, indicat-
ing wide variations in the vitamin A stored by the birds or wide differences
in resistance to a deficiency. Pullets receiving 270 Sherman-Munsell units
were heavier in weight than those receiving 120 units and laid more eggs.
The vitamin A potency of the eggs, as measured by biological methods,
decreased from 20 S. M. units per gram of yolk at the beginning to 5 to 8
units at the end of the period of 6% months. In subsequent work (16)
fowls receiving 444 S. M. units of vitamin A potency laid about 15% more
eggs than those in groups receiving lower quantities. The vitamin A
potency of the eggs declined regularly from 20-22 S. M. units per gram
at the beginning of the experiment to 6 units for pullets receiving 224

6 BULLETIN NO. 583, TEXAS AGRICULTURAL EXPERIMENT STATION

units per day, 12 units for those receiving 336 units per day and 15
units for those receiving 444 units S. M. per day. When allowance was
made for the vitamin A stored by the pullets, from 4.0 to 5.7 units of
vitamin A in the feed was required for 1 unit in the eggs.

In a third publication (17) the vitamin A content of the yolks (10 to 16
S. M. units at first) decreased to 5, 6, and 9 units with pullets receiving
150, 254, and 330 S. M. units per day, respectively. The apparent per-
centage of vitamin A potency recovered in the eggs ranged from 8 to
39% and averaged 25%, but the recovery of vitamin A potency fed, when
the storage in the body was allowed for, was 3.8 to 4.4 units in the feed
for one in the egg. yolk, or 25% utilization. The process of molting
seemed to require much vitamin A. The quantity of vitamin A required
for laying birds would be greater if the eggs are desired to have a high
potency of vitamin A.

In a fourth publication (18) it was pointed out that both the vitamin A
potency of the feed of the hen laying eggs from which chicks were hatched
and also the vitamin A potency fed the chicks must be adequate, if good
results are to be obtained. Chicks hatched from eggs laid by hens receiving
265 S. M. units per day had low vitality. The mortality of the chicks in
this work ranged from 64% for chicks from hens receiving 265 S. M. units
per day or 325 S. M. units per 100 grams of feed to 39% for chickens
from hens receiving 539 units per day or 325 S. M. units per 100 grams
of feed. The vitamin A potency required by chicks is higher for those
hatched from eggs laid by hens receiving low amounts of vitamin A than
those fed more liberal amounts. In fact, high quantities of vitamin A
potency (300 S. M. units per day) did not overcome the influence of a low
vitamin content of the feed of the mother hen.

In previous work on vitamin A, the chief attention has been given to
the requirements for growth up to 12 weeks and requirements during the
laying period. The requirements of pullets from the period of 12 weeks
until the time of laying has been given little or no attention. It is during
this period, however, that the prospective layer has opportunity to store
vitamin A to prevent losses that might occur from high mortality and to
provide for the more heavy requirements for laying.

The work here presented deals with the vitamin A potency requirements
for growth and for egg production and the effect of the quantity of
vitamin A potency fed from 12 weeks to time of laying upon the health
and mortality of the chickens. The vitamin A potency was fed in the
form of carotene. A

Previous recommendations

Vitamin A requirements for growing chicks have been estimated at 150
U. S. P. units per 100 grams of feed by Ringrose and Norris (12), 1,332
U. S. P. units by Schroeder and co-workers (14), 264 U. S. P. units by
Wilson and co-workers (21), 50 to 100 micrograms of carotene or 80 to

REQUIREMENTS OF CHICKENS FOR VITAMIN A 7

160 U. S. P. units of vitamin A by Record and associates (10), 175 Sherman-
Munsell units by Bearse and co-workers (2), 93 U. S. P. units by Frohring
and Wyeno (6), 520 micrograms of carotene by Hinshaw and Lloyd (7),
100 to 150 Sherman-Munsell units by Sherwood and Fraps (18) for chicks
hatched from eggs produced by hens receiving adequate supplies of vitamin
A and larger quantities for chicks hatched from eggs of hens receiving a
diet low in vitamin A. According to Norris (8), 150 U. S. P. units per
100 grams of feed are sufficient for good growth and freedom from
symptoms of deficiency of vitamin A, but in order to allow for storage
so that the pullets can enter the productive stage with adequate reserves
of vitamin A, 300 to 400 U. S. P. units are recommended. Obviously the
higher quantity is not needed if the chickens are eaten and not saved
for production of eggs. Titus (19) suggested 320 U. S. P. units per 100
grams of feed for growing chicks.

For laying hens, Record and associates (11) estimate that leghorn
pullets require 350 to 400 U. S. P. units of vitamin A per 100 grams of feed,
while Russell (13) found 485 U. S. P. units give a satisfactory result.
Sherwood and Fraps (17) estimated 300 Sherman-Munsell units per 100
grams of feed were required to maintain hens in good health with heavy
egg production and 750 Sherman-Munsell units to produce eggs with sat-
isfactory amounts of vitamin A. Bearse and associates (3) reported 500
S. M. units and Titus and associates (19) reported that 1,000 to 1,110
U. S. P. units were necessary for high producing hens and suggested 720
U. S. P. units for laying hens and 1,040 I. U. units for breeding stock,
both allowing margins for safety. Norris (8) states that 400 to 500 U. S. P.
units of vitamin A are sufficient to maintain hens in good health and
enable them to produce eggs which hatch a normal number of usable
chickens. Almquist and Mecchi (1) reported that about 440 U. S. P. units
per 100 grams of feed was required for laying hens. Williams and asso~
ciates (20) found that the equivalent of 240 Sherman-Munsell units or
333 U. S. P. units were required per hen per day.

Vitamin A requirements of growing chicks

With young cockerels there is a distinct increase in the rate of
g growth at about eight to twelve weeks of age. At this time both the
 primary sexual organs and the secondary sexual characters develop rapidly.
Following this there is a decrease in rate of growth followed again by a
slight increase as the cockerels approach twenty-two to twenty-four weeks
of age. With pullets there are two distinct periods of more rapid growth,
one at the age of twelve to eighteen Weeks, and the other just when the
birds begin to lay. A

L

A number of experiments are reported in this bulletin. In all the
experiments, alfalfa leaf meal was used, the carotene content was deter-
mined by analysis by Dr. A. R. Kemmerer or S. M. Greenberg, and the
quantity of alfalfa leaf meal included in the rations was calculated from
' the analyses. In experiments 34, 35 and 39, dehydrated alfalfa leaf meal

 

8

Table 1.

(Sufficient alfalfa leaf meal was used in place 0f white corn or kafir to give

desired carotene content.)

BULLETIN NO. 583, TEXAS AGRICULTURAL EXPERIMENT STATION

Percentages of ingredients of mixtures used in various chick experim (It

Percentages of ingredients used

Ingredients of mixture Experiments
Experiments 68. 7, 0*. Experiments
34. 35, 39 84A*, 848* 59 and 6O
Meat and bone scraps, 50% protein . . . . . . . . 6.0 4.0 6.0

Cottonseed meal. 43% protein . . . . . . . . . . . . . 6.0 2.0 6.0

Dried skimmed milk . . . . . . . . . . . . . . . . . . . . . . 6.0 6.0 6.

Soybean oil meal, 41 % protein . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.0 . . . . . . . . . . . . . .

Wheat gray shorts . . . . . . . . . . . . . . . . . . . . . . . . 20.0 20.0 20.

Ground whole oats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.0 . . . . . . . . . . . . . .

Ground white corn . . . . . . . . . . . . . . . . . . . . . . . 59.37 . . . . . . . . . . . . . . 5 .37

Ground kafir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54.62 . . . . . . . . . . . . . .

Chick size oyster shell . . . . . . . . . . . . . . . . . f . . 1.5 1.5 .5

Salt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 .0 0.5 1.0

Vitamin A free fortified cod liver oil . . . . . . . . 0.13 0.38 0.13

*Chicks on Experiment 80. 84A, and 84B had access to sunlight, and the 38% fortified cod

liver oil was not used in place of kafir.

Table 2. Gains in live weight of growing chicks on various levels of carotene
Weight of cockerels in grams Weight of pullets in grams
Micrograms of carotene

for 100 grams of feed Mean of Mean of
Exp. 34 Exp. 35 Exp. 39 three ex- Exp. 35 Exp. 39 two ex-
periments periments

50 . . . . . . . . . . . . . . . . . . . . . . . . .. 627.4 671.6 656.8 651.9 490.9 495.1 493.0

75 . . . . . . . . . . . . . . . . . . . . . . . . .. 731.8 611.3 633.2 658.8 519.2 519.1 519.2

100 . . . . . . . . . . . . . . . . . . . . . . . . .. 744.4 652.1 665.8 687.4 614.1 550.1 582.1

125 . . . . . . . . . . . . . . . . . . . . . . . . .. 721.5 712.3 661.5 698.4 599.4 550.8 575.1

150 . . . . . . . . . . . . . . . . . . . . . . . . .. 771.6 741.5 730.6 747.9 589.4 576.5 583.0

175 . . . . . . . . . . . . . . . . . . . . . . . . .. 787.6 625.1 676.8 696.5 573.5 539.6 556.6
Table 3. Per cent mortality and vitamin A deficiency of growing chicks on various levels
of carotene

Per cent of chicks showing vitamin A
Per cent mortality deficiency at the end of the experiments
Micrograms of

carotene for Mean of Mean of
100 grams of feed Exp. 34 Exp. 35 Exp. 39 three ex- Exp. 34 Exp. 35 Exp. 39 three ex-
periments periments

50 . . . . . . . . . . . . . . .. 27.1 41.7 33.3 34.0 12.5 16.7 19.1 16.1

75 . . . . . . . . . . . . . . .. 33.3 27.7 34.0 31.7 8.3 10.6 17.0 12.0

100 . . . . . . . . . . . . . . .. 9.8 16.7 17.8 14.8 3.9 4.8 8.9 5.9

125 . . . . . . . . . . . . . . .. 10.6 29.3 28.8 22.9 8.5 7.3 26.9 14.2

150 . . . . . . . . . . . . . .. 14.9 16.3 14.3 15.2 4.3 10.2 12.2 8.9

175 . . . . . . . . . . . . . . .. 12.8 8.1 25.5 15.5 13.2 10.8 17.0 13.7

REQUIREMENTS OF CHICKENS FOR VITAMIN A 9

was used to supply 50, 75, 100, 125, 150 and 175 micrograms of carotene
per 100 grams of feed, respectively. Table 1 shows the feeds used. In
experiment 34, the number of cockerels used 0n each vitamin level was
52, in experiments 35 and 39, the total number of mixed cockerels and
pullets was 52 per group. These experiments began with day-old chicks
and continued for twelve weeks.

As shown in Table 2, the cockerels required 150 micrograms of carotene

per 100 grams of feed for best gains. The pullets required from 100 to

150 micrograms of carotene for 100 grams of feed.

The data for mortality and for indications of vitamin A deficiency at
the close of the experiment are given in Table 3. The lowest mortality is
at 100, 150, and 175 in the three experiments with the average lowest
mortality at 100 micrograms of carotene in 100 grams of feeds. The dif-
ference between 14.3 per cent at 150 units and 17.8 per cent at 100 micro-
grams in experiment 39, is within the limits of error. In this experiment
100 micrograms seem to be sufficient. The percentage of chicks with vita-
min deficiency at the end of the experiment is lowest at 100 micrograms
per 100 grams of feed. The latter data show more variability than the
gains in weight. Some of this variability may be the result of leucosis.
Losses known to occur from this disease are not included in this ‘data.
However, there may have been mild cases of leucosis that were not iden-
tified but which weakened the chicks and caused them to die, apparently
from vitamin A deficiency, and these deaths might not have occurred had
not leucosis been present. According to this experiment, from 100 to 150
micrograms of carotene seems desirable. Chicks fed 50 to 75 micrograms
had higher mortality and more cases of vitamin A deficiency symptoms
than those fed higher quantities.

Another series of five experiments was conducted with 75, 100, and
125 micrograms of carotene from alfalfa per 100 grams of feed. The basal
ration is given in Table 1. Ground kafir was replaced by the alfalfa leaf
meal in suflicient quantities to provide the quantities of carotene desired.
The gains in weight are presented in Table 4. The highest gains in weight
by both the cockerels and the pullets were made on 125 micrograms of
carotene per 100 grams of feed, with the exception of experiment 77, in
which the highest gains of both pullets and cockerels were made with
100 micrograms, and experiment 80, in which the highest gain of the
pullets was made with 75 micrograms. The average gains for the cockerels
are appreciably different, but the differences in average weights of the
pullets (616.2, 617.9, and 626.2 grams) were not great, but would be greater
if experiment 77 was excluded. In this series of experiments, 125 micro-
grams per 100 grams was required by both cockerels and pullets. With
the exception of experiment 84A, the chicks on these experiments made
better gains than those in the preceding section. The chickens in experi-
ment 84B were New Hampshires, while all of the others were single-
combed white leghorns. There were 52 chickens on each carotene level in
all of the experiments of this series except experiments 84A and 84B in
which there were 26 chickens on each level.

10

Table 4.

BULLETIN NO. 583, TEXAS AGRICULTURAL EXPERIMENT STATION

Gain in live weight of growing chicks on 3 levels of carotene

Gain in live weight in grams

Micrograms of l

 

 

 

 

 

 

 

 

 

 

 

carotene per 100
grams of feed Exp. 68 Exp. 77 Exp. 80 Exp. 84a Exp. 84b Mean
Cockerels

75 . . . . . . . . . . . . . . . .. 878.3 811.8 772.0 535.9 692.9 738.2

100 . . . . . . . . . . . . . . . .. 851.5 840.4 711.0 501.7 722.6 725.
125 . . . . . . . . . . . . . . . . . 968.7 820.6 790.8 577.5 750.2 781.6

Pullets
75 . . . . . . . . . .. . . . . .. 679.5 709.7 657.4 464.6 569.7 616.2
100 . . . . . . . . . . . . . . . .. 690.8 720.4 628.1 473.2 576.8 617.9
125 . . . . . . . . . . . . . . . .. 761.9 675.1 646.2 482. 5 565.1 626. 2
Table 5. Percentage of mortality of growing chicks on 3 levels of carotene
Per cent mortality
Micrograms of
carotene per 100

grams of feed Exp. 68 Exp. 77 Exp. 80 Exp. 84a Exp. 84b Mean

75 . . . . . . . . . . . . . . . .. 15.4 13.5 23.1 l 1.9 0.0 10.8

100 . . . . . . . . . . . . . . . .. 11.5 15.4 7.7 11.5 11.5 11.5

125 . . . . . . . . . . . . . . . .. 11.5 15.4 19.2 3.8 11.5 12.3

Table 6.

Gains in live weight of growing chicks on 3 levels of carotene

Micrograms of carotene per

Gains of cockerels in grams

Gains of pullets in grams

100 grams of feed

Exp. 59 Exp. 60 Mean Exp. 59 Exp. 60 Mean

75 550.9 532.9 541.9 _ 448.2 489.7 469.0

Alfalfa leaf meal 125 536.8 499.6 518.2 470.0 414.9 442.5
150 573 .0 535.2 554.1 496.8 425.6 461.2

75 504.4 465.8 485.1 509.4 427.0 468.0

Carotene in oil 125 501.5 515.1 508.3 465.3 452.4 458.9
150 493.1 513.4 503.3 500.2 424.8 462.5

75 . . . . . . . . . . . . . . . . . . . . 56. 8 . . . . . . . . . . . . . . . . . . . . 1.0

Differences in favor of alfalfa 125 . . . . . . . . . . . . . . . . . . .. 9.9 . . . . . . . . . . . . . . . . . . .. -—16.4

leaf meal

150 . . . . . . . . . . . . . . . . . . .. 50.8 . . . . . . . . . . . . . . . . . . .. — 1.3

REQUIREMENTS OF CHICKENS FOR VITAMIN A 11

The mortality is given in Table 5. The lowest mortality was with 100
micrograms in two experiments, and 75 micrograms in three experiments,
but the significance of these differences is questionable.

In the first series of three experiments, the cockerels required 150
micrograms of carotene per 100 grams of feed for the best gain in weight,
while in the second series of experiments, 125 micrograms of carotene
was sufficient, though higher quantities were not tested.

We conclude, from the data just presented, that 125 to 150 micrograms
of carotene per 100 grams of feed, gives satisfactory results with growing
chickens up to the age of twelve weeks. Since 0.6 microgram of carotene
equals either 1 international unit or 1 U. S. P. unit, these chicks would
require 210 to 250 U. S. P. units of vitamin A per 100 grams of feed. The
faster growing breeds of chickens appear to require more carotene.

Comparison of carotene fed in alfalfa leaf meal with
carotene in wesson oil

Since the alfalfa leaf meal might possibly supply some other ingredient
besides carotene which would affect the results, two experiments were
conducted in which carotene dissolved in Wesson oil was compared with
carotene in alfalfa leaf meal. Crystallized carotene was dissolved in a
small quantity of chloroform and made up to the desired volume with
wesson oil (purified cottonseed oil). Fresh solutions were made and mixed
with the feed every two weeks. The rations used in these experiments
are given in Table 1. The ground white corn was replaced by the alfalfa
leaf meal or the carotene dissolved in oil in such quantities as to give
75, 125, and 150 micrograms of carotene per 100 grams.

Table 6 shows that the cockerels on the rations containing alfalfa leaf
meal averaged 9.9 to 56.8 grams higher gains than the rations containing
carotene in oil. With the pullets there were also slight differences in
favor of the carotene in oil over the alfalfa leaf meal.

The mortality (Table 7) was lower in the group receiving the alfalfa
leaf meal than in the group receiving carotene in oil. However, the per-

Table 7. Mortality and vitamin A deficiency of growing chicks on 3 levels of carotene

_ Percentage of chicks showing
Per cent mortality deficiency at close of experiments

Micrograms of carotene
pel- 100 grams of teed
Exp. 59 Exp. 60 Mean Exp. 59 Exp. 60 Mean

76 7.69 7.69 7.69 82.70 16.88 24.04

Alfalfa leaf meal 126 8 .86 8 .86 8 .86 8 .86 19 .28 11.64
160 1.92 8.86 ' 2.89 6.77 8.86 4.81

76 9.62 18.88 11.48 17.81 24.44 20.88

Carotene in oil 125 3.85 11.36 7.61 9.62 9.09 9.36
160 6.77 11.86 8.67 7.69 18.64 10.67

12 BULLETIN NO. 583, TEXAS AGRICULTURAL EXPERIMENT STATION

Table 8. Developing pullets used to make up groups for the following year for Experiments

     

35 and 39
Micrograms of carotene per 100 grams of feed
5O 75 100 125 150 175
Number of pullets alive at 12 weeks __
of age . . . . . . . . . . . . . . . . . . . . .. 31 38 42 32 39 35
Number placed 0n experiment fol-
lowing . . . . . . . . . . . . . . . . . . . . . . 17 2O 2O 2O 2O 20
Per cent placed 0n experiment fol-
lowing . . . . . . . . . . . . . . . . . . . . .. 54.8 52.6 47.6 62.5 51.3 57.1

Table 9. Summary of experiment on laying pullets fed various levels of caroteme

_ Average feed
Micrograms of Number of Mortality, Number of per bird Average
carotene per blI'_(1S _at per cent eggs laid per month, weight,
100 grams of feed beginning per bird grams grams
50 . . . . . . . . . . . . . . . . .. 17 100.0 1.1 1590.3 830.5

75 . . . . . . . . . . . . . . . . .. 20 100.0 15.9 1688.4 1034.8

100 . . . . . . . . . . . . . . . . . . 20 80.0 59.0 2141.8 1329.7

125 . . . . . . . . . . . . . . . . .. 20 85.0 46.6 1973.7 1165.6

150 . . . . . . . . . . . . . . . . .. 20 90.0 61.2 2317.7 1347.1

175 . . . . . . . . . . . . . . . . .. 20 70.0 80.4 2141.3 1213.9

Table 10. Number of laying pullets which died each month on various levels of carotene

Micrograms of carotene per 100 grams of feed
50 75 100 125 150 175
Number birds at beginning . . . . . . . . 17 20 2O 20 20 20

July 11-31 . . . . . . . . . . . . . . . . . . . . . . 0 3 1 0 O O

August . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4 4 1 1 1

September . . . . . . . . . . . . . . . . . . . . . . . 6 1 O 0 1 0

October . . . . . . . . . . . . . . . . . . . . . . . . . 3 3 1 4 1 1

November . . . . . . . . . . . . . . . . . . . . . . . 1 0 2 2 0 0

December . . . . . . . . . . . . . . . . . . . . . . . All dead 2 0 1 4 3

January . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2 1 0 2

February . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 1 1 1 1

March . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2 3 1 O

April . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 0 1 3 4

May . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 0 2 2 2

June . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . All dead 3 1 4 0

July 1-11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 0 0 0

Number remaining at close . . . . . . . . 0 0 4 3 2 6

Per cent mortality . . . . . . . . . . . . . . . 100.0 100.0 80 O 85.0 9O 0 70.0

REQUIREMENTS OF CHICKENS FOR VITAMIN A 13

centage of chicks showing vitamin A deficiency at the close of the experi-
ment was as high with those receiving alfalfa leaf meal as those receiving
carotene in oil. There appears to be no significant difierence in the effec-
tiveness of carotene in alfalfa leaf meal as compared with crystallized
carotene dissolved in oil. This is in agreement with Record and associates
(10). On the other hand, alfalfa contains xanthophyll, and Peterson and
associates (9) report that chicks that had shown vitamin A deficiency
as a result of depletion, revived in three to seven days after 20 micro-
grams per 100 grams of feed of a crystalline xanthophyll mixture had
been added.

Requirements of pullets from 12 weeks to 20 months, through
the laying periods

The pullets used in experiments 35 and 39 (Tables 1, 2, and 3) were
continued on the same feeds (see Table 1) in order to ascertain their
requirements at later stages of development.

Forty-nine days after the chicks in experiment 35 had reached twelve
weeks of age and nineteen days after the chicks in experiment 39 had
reached that age, arrangements were made to continue the work for one
year longer. The equipment was of limited size, and it was impossible to
carry more than twenty pullets in a pen. For that reason, 20 good pullets
were placed in each group with the exception of the group receiving 50
micrograms, for which only seventeen satisfactory pullets were available.
The pullets discarded were weaker birds than those that were continued
on the experiment.

Table 8 shows the percentage of the pullets remaining at the close of
the chick-growing experiment that were used in the work the following
year.

According to the data summarized in Table 9, none of the 6 levels of
carotene from 50 to 175 micrograms per 100 grams were high enough for
good results. Egg production increased with the increased quantities of
carotene fed with all groups except for the group receiving 125 micro-
grams. eNo reason is known for the poorer performance of this group
as compared with the others. The mortality was lower as the carotene
increased and the weights of the birds increased in the first 3 groups.
The mortality is given in Table 10. The length of life of the pullets is
longer when they received larger quantities of carotene than when smaller
quantities were fed.

The average monthly feed consumption and the monthly weights were
influenced greatly by the individuality of the birds remaining alive in the
groups each month.

In another experiment (Experiment 19), hens were fed for a period of
twenty months on 200, 300, and 400 micrograms of carotene per 100 grams
of feed in the ration shown in Table 11. The data are given in Table 12.
The mortality was high in all groups as shown also in Tables 12 and 13; it

14 BULLETIN NO. 583, TEXAS AGRICULTURAL EXPERIMENT STATION

Table 11. Percentages of ingredients of mixtures used in experiments with laying hens

(Sufficient alfalfa leaf meal was used in place of corn to give the desired carotene content)

   

Percentage ingredients used
Feeds _
Experiment Experiment Experiment
19 2 4
Meat and bone scrafis, 50% protein . . . . . . . . . . . . . . 7.0 8 0 10 0

Dried skimmed mil . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.0 . . . . . . . . . . . . . . . . . . . . . . . .

Dried whey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.0 3.0

Salt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 .0 0.5 0.5

Chick size oyster shell . . . . . . . . . . . . . . . . . . . . . . . . . . 4.0 . . . . . . . . . . . . 1 .0

Wheat ray shorts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.0 10.0 10.0

Wheat ran . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 10.0 10.0 10.0

Ground whole oats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.0 10.0 10.0

Ground white oats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 .0 59.5 55.5

Table 12. Summary for Experiment 19 on laying hens fed 3 levels of carotene

Percent Number Average
Micrograms of _ mortality of feed eaten Average
carotene per Time Number at of eggs laid per hen weight,
100 grams of feed beginning original per hen per month. grams
number grams
First '
year 20 80.0 50.0 1864.9 1308.0
Following
200 8 months 4 15.0 36.9 1936.5 1350.6
Mean or No. at end
total 1 95 .0 86.9 1900.7 1329.3
First
year 20 55 .0 74. 6 2286 .3 1497. 2
Following
300 8 months 9 30.0 45.4 2222.3 1463.2
Mean or No. at end
total 3 85 .0 120.0 2254.3 1480.2
First
year 20 50 .0 107.3 2378.9 1433. 9
_ Following
400 8 months 10 25.0 60.4 2260.3 1376.4
Mean or No. at end
total 5 75.0 167.7 2319.6 1405.2

was 80% for the first year in the group on the 10W level of 200 micro-
grams per 100 grams of feed, 55% on 300 micrograms, and 50% for 400
micrograms. During the last eight months of the experiment, the hens on
the higher levels of carotene were sufficiently depleted to cause a high
mortality in those lots also. At the end of 20 months, the total mortality
was 95, 85, and 75% respectively for the 3 groups. Egg production and
feed consumption increased as the carotene in the feed increased. The
number of eggs produced was 86.8 with the hens on 200 micrograms, 120
with hens on 300 micrograms, and 167.7 for hens on 400 micrograms.
The average weight was less for the birds on the low carotene levels than
for those on the two higher levels.

REQUIREMENTS OF CHICKENS FOR VITAMIN A 15

Table 13 shows the number by months of birds which died in the
different groups. It shows clearly that the mortality was high during the
first year with the birds on the low level of carotene and that the birds
on the higher levels lived longer but died later as their reserve of vitamin A
became depleted. Probably the quantity of eggs produced affected the
vitamin A depletion and the resulting mortality. None of these levels
of carotene were high enough for good results over a long period of time.

Two additional experiments were made. Table 11 shows the ingredients
of the feed for experiment 62. A summary of the data is given in Table 14.
The birds on experiment 62 were on experiment for two years. The groups
received 150, 225, and 300 micrograms of carotene per 100 grams of feed.
The egg production, body weight, and hatchability as shown in Table 14
are closely related to the carotene intake, but the results indicate that
the highest amount (300 micrograms) is not sufiicient for good results
over a long period of time. This is also shown in the mortality (Table 15).

The birds on experiment 94 received 200, 400, and 600 micrograms of
carotene per 100 grams of feed. The ingredients of the ration are given
in Table 11. Table 16 summarizes the data, while Table 17 shows the
relative length of life. The egg production and hatchability was closely
related to the carotene intake. When the eggs were incubated, as seen

Table l3. Number of hens which died each month on 3 levels of carotene

Micrograms of carotene
per 100 grams of feed
200 300 400
Number at beginning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 20 20 20
First Year
November . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . O O 0

December . _ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 1 2

January . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2 O

February . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . O 1 2

March . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2 O

April . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 0 O

May . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 O 1

June . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1 1

July . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1 2

August...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1 1 O

September . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 1

October . . . . . . . . . . . . . . . . . . . . . i . . . . . . . . . . . . . . . . . . . . . . . 1 O 1

Total-—1 year . . . . . . . . . . . . . . . . _ . . . . . . . . . . . . . . .. 16 11 1O
Following Eight Months
November . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 O

December . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 O 1

January . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i . . . . . 1 2 O

February . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 0 1

March . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . O 1 1

April . . . . . . J , . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . 0 1 0

Nlay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . O O 2

June . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 1 O

Total—8 months . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 6 5

Total—20 months . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 17 15

Table 14. Summary of Experiment 62 on hens fed 3 levels of carotene

91

F d Hatchability Test
ee
Micrograms _ required Average Embryonic Crippled Vigorous Vigorous
0f carotene Number Mortality per hen hen Average Number Infertile mortality chicks of chicks of chicks of
per 100 grams at per cent per weight eggs _ 0f eggs 0f fertile fertile fertile total
0f feed start month grams per hen eggs per cent eggs eggs eggs eggs
grams per cent per cent per cent per cent
1937——38
150 . . . . . . . . . .. 34 76.5 2089.5 1304.2 58.9 78 23.1 40.0 5.0 55.0 42.4
225 . . . . . . . . . .. 36 72.2 2245.8 1283.2 79.8 158 17.1 19.9 2.3 77.8 64.6
300 . . . . . . . . . .. 34 61.8 2224.6 1283.6 84.3 175 31.4 10.8 .8 88.3 60.5
1938-—39 ,
150 . . . . . . . . . .. 8 62.5 2245.4 1267.8 56.8 115 28.7 30.5 11.0 58.5 41.8
225 . . . . . . . . . .. 10 40.0 2510.6 1271.8 63.9 158 32.9 23.6 2.8 73.6 49.4
300 . . . . . . . . . .. 13 61.5 2160.2 1348.0 51.3 126 12.7 11.8 6.4 81.8 71.4

NOLLVLS lNSWIHHJXE "IVHILLTIIOIHOV SVXELL ‘$89 'ON NLLEFYIIIH

REQUIREMENTS OF CHICKENS FOR VITAMIN A 17

in Tables 14 and 16, there were more dead embryos and crippled chicks
from the eggs produced 0n the lower‘ levels than on the higher ones.
From 400 to 600 micrograms of carotene per 100 grams of feed seems
to be required by hens to be used for chick production.

Table 18 summarizes the egg production of all of the experiments on
the different levels of carotene. The different levels do not give the same
number of eggs in all of the experiments, but in each experiment the
production of eggs is closely related to the carotene intake.

These experiments indicate that 550 micrograms or more of carotene
(920 U. S. P. units of vitamin A) per 100 grams of feed is necessary for
hens producing eggs high in vitamin A potency or for hatching. In

Table 15. Number of birds which died each month on 3 levels of car0tene—
Experiment 62

 

 

Micrograms of carotene
per 100 grams of feed
150 225 300
First Year
Number birds at beginning . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 36 34

November . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 0 0

December . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 1 0

January . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 6 2

February . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 O 2

blarch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 6 4

April . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 0 0

May . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _ . . . . . . . . . . . . . . 3 l’ 5

June . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3 1

July. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 5 1

August . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3 4

September . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 O 2

October . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 O

Total mortality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 26 21

Total deficient from vitamin A . . . . . . . . . . . . . . . . . . . 16 16 10

Per cent deficient from vitamin A . . . . . . . . . . . . . . . . 47 1 44.4 29 4

Number at close . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 1O 13
Second Year
Number at beginning . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . .. 8 1O 13

November . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . O 2 0

December . . . . . . . . . . . . O 0 2

January . . . . . . . . . . . . . . 0 0 1

February . . . . . . . . . . . . . O O 2

March . . . . . . . . . . . . . . . 1 0 1

April . . . . . . . . . . . . _ . . . O 1 O

l\Iay . . . . . . . . . . . . . . . . . . . . . . . . . O 0 O

June . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 0 0

July . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 0 1

August . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 0 1

September . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . O 1 O

Total mortality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4 8

Total deficient from vitamin A . . . . . . . . . . . . . . . . . . . O 2 4

Per cent deficient from vitamin A . . . . . . . . . . . . . . . . 0 20.0 30.8

Number birds at close . . . . . . . . . . . . . . . . . . . . . . . . . . 3 6 5

Table 16. Summary for Experiment 94 on laying hens fed 3 levels of carotene
Hatchability Test
Feed
Micrograms _ required Average Embryonic Crippled Vigorous Vigorous
of carotene Number Mortality per hen hen Average Number mortality chicks 0f chicks 0f chicks of
per 100 grams at per cent per Weight eggs of 0f fertile fertile fertile total
of feed start month grams per hen eggs eggs eggs eggs
grams per cent per cent per cent per cent
200 . . . . . . . . . .. 33 27.3 2306.2 1319.9 81.4 670 5 7.4 72.1 53.5
400 . . . . . . . . . .. 33 33.3 2481.3 1340.9 94.9 837 1.5 1 2 2.6 82.2 64.5
600 . . . . . . . . . .. 33 33.3 2595.3 1333.7 116.4 996 5.4 1 3 3.4 85.3 72.2

SI

NOLLVLS LNHWIHEIJXEI TVHILIFIIIOIHOV SVXELL ‘£89 'ON NILEFYIIIH

REQUIREMENTS OF CHICKENS FOR VITAMIN A 19

order to provide a factor of safety, at least 600 micrograms of carotene
(1,000 U. S. P. units) are recommended. If the eggs are not to be hatched
and the vitamin A content of the eggs is not important, 450 micrograms
of carotene (750 U. S. P. units) per 100 grams of feed or more seems to
be required. In order to provide a factor of safety, 500 micrograms (833
U. S. P. units) are recommended. These figures are in agreement with the
findings of some of the other workers.

Table 17. Number of hens which died each month on 3 levels of carotene~
Experiment 94
hlicrograms of carotene
per 100 grams of feed
200 400 600
Number at beginning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 33 33

December . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . O 0 O

January . . . . . . . . . . . . . . . . . . . . . . . . . . ; . . . . . . . . . . . . . . . . . . 1 O 0

February . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 1

March . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 1

April . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 2

May . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 5 1

June . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 2*

July . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 3 O

August . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 0

September . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2 1

Total mortality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 15 8*

Number vitamin A deficient . . . . . . . . . . . . . . . . . . .. 6 5 0

Per cent vitamin A deficient . . . . . . . . . . . . . . . . . . . . . 18.2 15.2 0

Number of birds at close . . . . . . . . . . . . . . . . . . . . . . . . 18 18 19*

*Six other birds were killed accidentally on June 28th.

Table 18. Summary of relation of amount of carotene fed laying hensltflnumber of eggs laid
l
_ Experiment 19 Experiment 62 _
Micrograms of Experi- .__?_— Experi-
carotene per 100 Following ments IIIBHl 94
grams of feed First eight 35 and 39 First Second
year months
50 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

75 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

100 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

125 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

150 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

175 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

200 . . . . . . . . . . . . . . . . . 50 37

225 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

300 . . . . . . . . . . . . . . . . _ 75 45

400 . . . . . . . . . . . . . . . . . 107 60

600 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

 

2O BULLETIN NO. 583, TEXAS AGRICULTURAL EXPERIMENT STATION

SUMMARY

The 8 experiments on growing chicks indicate that 125 to 150 micrograms
of carotene (210 to 250 U. S. P. units of vitamin A) per 100 grams of
feed gives satisfactory results in health and growth up to twelve weeks

of age. In order to provide a factor of safety, 180 micrograms of carotene i

per 100 grams of feed are recommended for growing chicks up to 12
weeks of age. This is equivalent to 300 U. S. P. units per 100 grams of
feed. Fast growing chicks appear to require more carotene than slow
growing ones.

When alfalfa leaf meal and crystallized carotene dissolved in oil were
compared in 2 experiments as sources of carotene for growing chicks,
slight differences in gains in weight and mortality were found in favor
of the alfalfa leaf meal although it is doubtful whether these differences
are significant.

Four experiments were made on pullets from 12 to 20 weeks old to
the end of their profitable existence. The mortality of pullets grown on
50, 75, 100, 125, 150, and 175 micrograms of carotene per 100 grams of
feed during the period from July 11 to November 1 was 94, 55, 30, 25,
15, and 10 per cent respectively. From July 11 to the following July 11,
the mortality was 100, 100, 80, 85, 90, and '70 per cent respectively. This
data would indicate that 150 and 175 micrograms of carotene per 100
grams of feed furnish the requirements for growth but are far too low
for satisfactory egg production and long life. Allowing a factor of safety,
it is recommended that pullets be fed rations containing not less than
200 micrograms carotene per 100 grams of feed (333 U. S. P. units), from
12 weeks of age until they begin to lay.

Experiments with 200, 400, and 600 micrograms of carotene per gram
of feed indicate that not less than 450 micrograms of carotene (750 U. S. P.
units of vitamin A) per 100 grams of feed is needed for good egg pro-
duction. In order to provide a factor of safety, not less than 500 micro-
grams of carotene per 100 grams of feed is recommended (833 U. S. P.
units). When the eggs are to be used for hatching or a market where
the vitamin A content of the eggs is important, 550 or more micrograms
of carotene (920 U. S. P. units of vitamin A) per 100 grams of feed is
required. In order to provide a factor of safety, not less than 600 micro-
grams of carotene per 100 grams of feed (1,000 U. S. P. units) is recom-
mended for hens producing eggs for hatching.

In some of the experiments, the chickens did well on smaller amounts
than here recommended, but it was thought best to be on the safe side.

REQUIREMENTS OF CHICKENS FOR VITAMIN A 21

REFERENCES

Almquist, H. _J., and Mecchi, E. 1939. Vitamin A requirements of laying hens.
Poultry Sci. 18:129.

Bearse, Gordon E., and_Miller, M. Wayne. 1937. The vitamin A requirements of white
leghorn pullets during the growing period. Poultry Sci. 16:34.

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