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The Effect of Certain Groups of Environmental Factors upon the Expression of Broodiness
T h e Effect of Certain Groups of Environmental Factors upon the Expression of Broodiness WILLIAM H. BURROWS AND THEODORE C. BYERLY1 Bureau of Animal Industry, U. S. Department of Agriculture, Beltsville, Maryland (Received for publication December 27, 1937)
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ROODINESS is, to some extent, a detriment to egg production of chickens even with modern methods of management. The influence of environment on chickens has received considerable attention, but mostly from the standpoint of egg production without particular reference to broodiness. The investigations herein reported were made at the National Agricultural Research Center, Beltsville, Maryland, as exploratory tests of the effects of some environmental factors, physical and psychological, on the expression of broodiness by chickens whose previous records had shown that they possessed various degrees of broodiness. The purpose of these investigations was more to obtain an indication, if possible, of the extent to which broodiness, and incidentally egg production, could be influenced by psychological stimuli than to evaluate any specific stimulus or group of stimuli. The authors realize that some of the data are not as complete as could be desired, but feel that the results, such as they are, carry implications of sufficient importance to justify publication. The literature contains a few reports of work done in this field. Reaumur (1750) recognized the effects of certain environmental factors on the expression of broodiness in chickens. He ad' N o w at the University of Maryland, College Park, Maryland.
vised, as a method of inducing hens and capons to brood chicks, the use of the stimuli produced by the presence of the chicks themselves. Punnett (1923) cited a case in which two "non-broody" hens expressed broodiness. These hens had shown no broodiness in their first two years of life, but when a clutch of eggs was allowed to accumulate in the nest of each, they both became broody, hatched the eggs and raised the chicks. Patel (1936) showed that broodiness in male pigeons (crop gland development) did not occur if the males were isolated as soon as the eggs were laid, but that it did occur if the males were merely restricted from taking part in the incubating of the eggs, yet were where they could observe the females during the incubating period. He called this "psychological broodiness." Punnett (1922) suggested that "factors for high fecundity may themselves inhibit the broody instinct in some cases." From the context it appears that Punnett referred to genetic factors for fecundity rather than environmental factors of a nature to stimulate egg production. Lippincott and Card (1934) wrote: "Increased fecundity seems to have caused longer periods of time to elapse between seasons of broodiness. In general, it may be said that the broodiness of a breed is in inverse proportion to its fecundity."
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EFFECT OF ENVIRONMENTAL FACTORS UPON EXPRESSION OF BROODINESS
The same authors stated that, by regular removal of eggs, Austin increased egg production in wild mallard ducks from 12-18 to 80-100 and Hauke obtained 48 eggs in succession from the common wryneck, and Wenzel obtained 51 eggs in succession from the house sparrow. They suggested that the frequent gathering of eggs had long since reached the limit of its effectiveness. Riddle, Bates, and Lahr (1935) induced broodiness in chickens by the injection of prolactin and made the statement that a hormone had been identified as an essential element in the broody instinct. To sum up, Reaumur, Punnett, and Patel have shown that certain environmental factors can stimulate the expression of broodiness. Lippincott and Card quote evidence of stimulation of egg production by removal of eggs from the nest and Punnett relates that the failure to remove eggs from the nest caused broodiness. Thus, the records present one example of an environmental factor which stimulates broodiness and indirectly decreases egg production; namely, the presence of eggs in the nest. That the removal of this factor results in stimulating egg production and indirectly decreasing broodiness indicates that the recognition and removal of certain stimulating factors for broodiness might be an effective supplementary method of increasing egg production. TO STIMULATE THE EXPRESSION OF BROODINESS Six crossbred hens (Rhode Island Red $ X Barred Rock ? ) were placed in coops with baby chicks. Four of these hens were laying and two were not laying, but were not showing any signs of broodiness. The sides of the coops were covered in such a manner that semi-darkness resulted. This arrengement was used in an effort to eliminate, as far as possible, distracting influences of a visual nature. Sound disturb-
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ances were not controlled, but the place was relatively quiet from 5:00 p.m. to 8:00 a.m. The semi-darkness was presumed to have a sedative effect, but not to reduce visibility beyond a point at which the hens could be stimulated by the sight of baby chicks. The baby chicks were used to furnish active stimuli. Three distinct stimuli were thus introduced. The stimulus through the eye was kept active by movements of the chicks unless the hen chose to hover them. The stimulus through the ear, caused by peeping of chicks, was persistent unless the chicks were hovered. The stimulus through sense of touch was brought about by the burrowing under the hen of the chicks whenever hovering was permitted. These six crossbred hens were submitted to this treatment at 4:00 p.m. and in all instances but one, egg laying ceased abruptly, and that one hen laid on the day following the beginning of treatment; an egg that had been obviously ovulated and on its way through the oviduct before treatment began. One of the non-laying hens showed the typical signs of a full expression of broodiness such as clucking, feeding the chicks, and uttering warning calls when startled, 18 hours after treatment began. The other nonlaying hen showed these signs after three days. The four laying hens showed the full expression of broodiness after one day, one day, three days, and six days, respectively, of the treatment. The hen that became broody in six days was kept broody for two months by simply keeping young chicks with her. In another test two White Leghorn pullets failed to respond to the stimuli and showed some hostility toward the chicks. Such tests were temporarily postponed and attention turned toward increasing the stimulating effect of the environment. Attempts to cause broodiness by sub-
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WILLIAM H. BURROWS AND THEODORE C. BYERLY
jecting the hens to the aforementioned stimuli in the morning were less successful than those in which the hens were started in the evening. It was also noticed that when more light was admitted to some of the coops broodiness did not seem to occur as readily. To facilitate exclusion of light the coops were discarded and a box about 18 inches square and 3 feet high was ventilated with small holes and used for holding hens with chicks. Temperatures around 90°F. and high humidity existed during the following tests: Two White Leghorn hens were tested under these new conditions and were readily stimulated to broodiness. Both of these hens were hovering the chicks on the morning following the application of the stimuli, one of them became actively interested after five days and the other after seven days. The following is taken from the records of one of these tests. Hen 516. Non-broody record. 215 eggs in pullet year. Hen was laying regularly in her second year at time of test. August 16, 1937. Placed in box with chicks at 4:00 p.m. August 17 Passively hovering the chicks. August 18 Clucking. Laid an egg. August 19 Clucking. August 20 Calls chicks and feeds them. Laid an egg. August 23 No eggs since August 20. Hen fully broody and fights to protect chicks. A young Light Sussex pullet of about 20 weeks of age hovered chicks, fed them, and sounded danger warnings after nine days of exposure to the stimuli of chicks in semidarkness. A 12-week-old pullet (Rhode Island Red X Light Sussex) did likewise after 12 days of exposure to similar stimuli.
Neither of these young birds made sounds comparable to those of an adult bird, but they were well understood by the chicks, as was shown by the chicks answering the feed call and crouching when the danger signal was uttered. The pituitaries of hens, made psychologically broody, were implanted on the crops of young pigeons to ascertain the amount of prolactin-like substance in them. In every test, the pituitary of a laying hen was implanted on the opposite side of the pigeon crop. In some instances the tests were made as soon as a full expression of broodiness had been induced and, in others, after the hens had been kept broody for various lengths of time; in one instance this was two months. Contrary to expectations the pituitaries of broody hens, as compared with those of laying hens, showed no indication of an increase in prolactin-like substance. TO INHIBIT THE EXPRESSION OF BROODINESS
Forty hens, progeny of three-way crosses involving Rhode Island Red, White Wyandotte, and Light Sussex were selected for a study of a certain group of environmental factors for inhibiting the expression of broodiness. These birds were two years old at the time of selection and their first year mature body weights averaged 2,090 grams. Only hens whose records showed that they had been broody two or more times were included. Some had been broody as many as five times. These hens were divided into two groups of 20 birds each by random selection without reference to their records. The birds in group 1 were used as test birds and those in group 2 as controls. The birds of group 1 were placed in a laying battery. It was thought that the wirebottomed cages of the battery would simulate the conditions of the usual broody
EFFECT OF ENVIRONMENTAL FACTORS UPON EXPRESSION OF BROODINESS
coop. The battery was on the second floor of a three-story cinder-block building in a room which was well lighted and ventilated. Electric lights furnished additional light by means of a time switch which turned the lights on at 4:00 a.m. and off at 8:00 p.m. thus providing a uniform 16-hour period of light each day. The birds in group 2 were placed in a
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ords were kept of egg production, number of hens expressing broodiness, number of cases of expressed broodiness, number of days of broodiness, and the number of days of pause in laying when that pause extended to five or more days in succession and might be interpreted by some investigators as being a partial expression of broodiness.
TABLE 1.—Broodiness among test birds (group 1) and control birds (group 2) from January 13 to August 31, 1937, as compared to the same period of time in 19361 Group 1 2 1 2 1 2
Year 1937 1937 1936 1936
Number of broody hens
Number of broody cases
Days of broodiness
Days of pause 2
2 9 20 20
2 IS 61 56
164 413 1,098 997
292 748 1,367 1,328
All hens were kept in a long laying house throughout their pullet year. Days of pause were counted only when there were five or more of them in succession.
colony laying house. They were trap-nested and allowed access to a grassy yard with bushes for shade. Broody hens were "broken up" in a broody coop as soon as discovered on nests. No additional light was furnished, therefore the length of day varied with the season. Both groups were fed an all-mash laying diet, but the birds in the batteries received additional amounts of ground limestone and alfalfa leaf meal to compensate for lack of range. Temperatures in the building that contained the test group naturally fluctuated less than for those in the colony house. Throughout the winter months the battery room was kept at 65 degrees, or warmer; but during the summer the temperature rose at times to as high as 92 degrees. However, the battery room was, on the average, cooler than the colony house during the day and warmer at night throughout the summer. Changes from the noonday heat to the cool of the night and from one day to another were much more gradual. Under these two sets of conditions, rec-
Table 1 gives the values for broodiness in group 1 and group 2 during the testing periods from January 13, 1937, to August 31,1937, inclusive, as compared with values taken from a similar period of time during 1936. The record shows that, whereas in 1936 there were fewer broody cases, fewer days of broodiness, and fewer days of pause among the hens of group 2 than among the hens of group 1, in 1937 the reverse is true. During the test period the hens in group 2 exhibited about iy2 times as much broodiness as did the hens in group 1. Table 2 gives the percentage of egg production over the same periods of time. These values are greater for group 1 than for group 2 in the 1936 records as well as in the 1937 records, but the difference between the values for group 1 and group 2 is much greater in the 1937 records than it is in the 1936 records. The data are such as to make it impossible to determine what proportion of additional egg production shown by group 1 in 1937 is due to actual difference in days of broodiness, and how
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WILLIAM H. BURROWS AND THEODORE C. BYERLY
much is due to environmental factors, especially electric lighting, which may have stimulated egg production without actually suppressing broodiness. However, since group 1 produced more eggs per hen than did group 2 during June and August when the broodiness of group 2 was most evident, some of the difference in egg production between the two groups was probably due to the suppression of broodiness. TABLE 2!.—Relative
exert a powerful influence over the processes of the chicken is shown by the fact that hens of a so-called non-broody strain and pullets too young to normally become broody were made broody by them. Certain other conditions have been shown to have a definite inhibiting effect on the expression of broodiness. That the broodiness of broody hens was not entirely inhibited may have been due to a failure to
egg production of test birds (group 1) and control birds (group 2) from January 13 to August 31, 1937, and for the same period of time in 1936
January
February
March
April
May
June
July
August
Average
percent
percent
percent
percent
percent
percent
percent
percent
percent
57.9 22.0
82.9 41.4
76.5 62.3
72.6 69.6
61.6 59.2
65.2 43.8
52.1 50.0
53.5 44.3
65.3 49.0
42.6 40.2
58.8 43.1
66.9 57.2
58.0 50.5
44.7 42.7
35.8 43.2
53.4 54.5
44.0 44.0
50.5 46.9
Group 1937: 1 2 1936: 1 2
The exhibition of broodiness by both groups was less in 1937 than in 1936 and this is what might be expected, since only those birds were chosen for the test which showed more than average broodiness during their pullet year, and extremes usually tend to regress toward the average. The two birds in group 1 that went broody in the batteries, remained broody until the end of the test period. In one case this involved 31 days of broodiness, but in the other it involved 133 days of broodiness; and in both cases the birds were still in a broody condition when the test was stopped. Both of these birds had extremely broody records in their pullet year, but other birds with equally broody first-year records failed to show any broodiness in the battery. DISCUSSION
Data have been presented to show that certain conditions will induce hens to exhibit broodiness. That these conditions
create an environment which was sufficiently free from factors which stimulate broodiness or sufficient in factors which inhibit the expression of broodiness. The pituitaries of the hens that became broody from exposure to external factors did not show, by the pigeon crop test, the presence of more prolactin-like substance than did the pituitaries of birds that were not broody. Burrows and Byerly (1936) found that hens, just becoming broody under normal conditions, showed a marked increase in a prolactin-like substance in their pituitaries, but that those in the later stages of broodiness did not. It appears that prolactin can cause broodiness and either prolactin or some similar substance does bring on broodiness under natural conditions, but it also appears that such a substance is not essential to the broody instinct. This is in agreement with the work of Nobel, Kumpf, and Billings who found that jewel fish could be stimulated to broody behavior by injections of prolactin,
EFFECT OF ENVIRONMENTAL FACTORS UPON EXPRESSION OF BROODINESS
corpus luteum extract, thyroid, and 5 percent phenol solution, whereas injections of saline had no such effect, but disagrees with Riddle's conclusion. Moreover, in most of Riddle's experiments three or more days were required to cause nesting and usually one more day was required to cause clucking even with relatively large doses of prolactin. Broodines induced by psychological stimuli can occur in too short a time to suppose it to be the secondary effect of a primary stimulation of the pituitary to the production of prolactin. A classification of the various factors, that might form a part of the chicken's environment, into those that stimulate broodiness and those that do not would seem to be desirable. Many such factors have already been evaluated as to their favorable influence on egg preduction, but while it is true that some factors, favorable to egg production, decrease broodiness, this may not be true in every instance. Although the environment of the 20 hens in the battery was composed of a variety of factors such as were available, and therefore not as ideal as could have been desired, certain factors present gave reason to expect results similar to those obtained. The laying cages, in addition to resembling broody coops in construction, automatically removed the eggs as soon as they were laid. Food and water were always in sight so that as soon as the egg was laid the attention of the bird was diverted from that process to other things—usually it was water. It is assumed that the 16-hour lighting had a stimulating effect upon egg production and indirectly some inhibitory influence on broodiness; since in attempting to induce the expression of broodiness it was found that light does inhibit the expression of broodines and that the lack of light stimulates it. No attempt was made to control temperature and humidity.
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It seems pertinent here to raise the question as to how much of broodiness can exist in hens and exert an unfavorable influence on egg production without any outward exhibition in the form of nesting or clucking. How much are vaguely expressed conditions such as winter pause, pause between clutches, rest periods, and nonproductive days of the intermittent layers, and lack of persistence due to broodiness which is not so expressed as to be recognized? It is possible that a sort of partlyexpressed broodines may account for more of these non-productive periods than is usually thought. The results of these tests would seem to indicate that no single environment will reveal to .the best advantage the broodiness and egg-producing abilities of a hen. The records of the hens in group 1 show, to a fair degree at least, their egg-producing abilities, but are obviously false if considered for broodiness, whereas records for hens kept under conditions conducive to broodiness would not show their true production abilities. In selecting for high production and non-broodiness, progress might be expedited if hens, after having been selected for high production, in an environment conducive to laying, were submitted to a more or less broody environment and the broody birds then culled. The hens in group 1 layed an average of 34 eggs per hen more in 7^4 months than the hens in group 2. SUMMARY Hens of broody and non-broody strains and pullets, too young to become broody in a natural way, were made to express broodiness by the application of physical and psychological stimuli. Temperatures about 90°F., darkness, and the presence of chicks formed the most potent combination of stimuli. Low temperatures and even a small
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WILLIAM H. BURROWS AND THEODORE C. BYERLY
amount of light reduced the effectiveness of the environment in inducing broodiness. The hens and pullets performed all the duties of caring for chicks after being stimulated to broodiness. The time required for the stimuli to be effective varied from 18 hours to 12 days and, although some of this variation was apparently due to differences in degrees of darkness and temperature of the environment, White Leghorn hens were definitely slower to respond than the crossbred hens used in the tests. Hens kept in a standard type colony house without artificial light showed 2^2 times as much broodiness as hens kept in a battery in a large cinder-block building with artificial light to give a uniform 16hour day. Moderate temperature, slow temperature changes, light, wire floor of cages, feeding habits, and quick, automatic removal of eggs in batteries constituted a group of environmental factors which decreased the expression of broodiness. The hens in the battery laid an average of 34 eggs more than the hens in the colony house during the 7^2 months of the test and at least a part of this increase may be at-
tributed to the suppression of broodiness. No evidence of an increase in prolactinlike substance was found in the pituitaries of "psychologically broody" hens when these were implanted, opposite those of laying hens, on the crop glands of 6-8 week old pigeons. REFERENCES
Burrows, W. H., and T. C. Byerly, 1936. Studies of prolactin in the fowl pituitary. I. Broody hens compared with laying hens and males. Proc. Soc. Exp. Biol, and Med. 34:841-844. Lippincott, W. A., and L. E. Card, 1934. Poultry production, pp. 21-22. Lea and Febiger, Philadelphia, Pa. Noble, G. K., K. F . Kumpf, and V. N. Billings, 1936. The induction of brooding behavior in jewel fish. Anat. Record, Sup. No. 1, Vol. 67 :S0. Patel, M. D., 1936. The physiology of the formation of pigeon milk. Physiol. Zool. 9:129-152. Punnett, R. C , 1923. Heredity in poultry, p. 179. Macmillan & Co., New York, N.Y. Reaumur, Rene Antoine Ferschault, de, 1750. The art of hatching and bringing up domestic fowl at any time of the year, either by means of the heat of hotbeds or that of common fire. C. Davis, London, p. 283. Riddle, Oscar, Robert W. Bates, and Earnest L. Laher, 1935. Prolactin induces broodiness in fowl. Amer. Jour. Physiol. 111:352-360.
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ROODINESS is, to some extent, a detriment to egg production of chickens even with modern methods of management. The influence of environment on chickens has received considerable attention, but mostly from the standpoint of egg production without particular reference to broodiness. The investigations herein reported were made at the National Agricultural Research Center, Beltsville, Maryland, as exploratory tests of the effects of some environmental factors, physical and psychological, on the expression of broodiness by chickens whose previous records had shown that they possessed various degrees of broodiness. The purpose of these investigations was more to obtain an indication, if possible, of the extent to which broodiness, and incidentally egg production, could be influenced by psychological stimuli than to evaluate any specific stimulus or group of stimuli. The authors realize that some of the data are not as complete as could be desired, but feel that the results, such as they are, carry implications of sufficient importance to justify publication. The literature contains a few reports of work done in this field. Reaumur (1750) recognized the effects of certain environmental factors on the expression of broodiness in chickens. He ad' N o w at the University of Maryland, College Park, Maryland.
vised, as a method of inducing hens and capons to brood chicks, the use of the stimuli produced by the presence of the chicks themselves. Punnett (1923) cited a case in which two "non-broody" hens expressed broodiness. These hens had shown no broodiness in their first two years of life, but when a clutch of eggs was allowed to accumulate in the nest of each, they both became broody, hatched the eggs and raised the chicks. Patel (1936) showed that broodiness in male pigeons (crop gland development) did not occur if the males were isolated as soon as the eggs were laid, but that it did occur if the males were merely restricted from taking part in the incubating of the eggs, yet were where they could observe the females during the incubating period. He called this "psychological broodiness." Punnett (1922) suggested that "factors for high fecundity may themselves inhibit the broody instinct in some cases." From the context it appears that Punnett referred to genetic factors for fecundity rather than environmental factors of a nature to stimulate egg production. Lippincott and Card (1934) wrote: "Increased fecundity seems to have caused longer periods of time to elapse between seasons of broodiness. In general, it may be said that the broodiness of a breed is in inverse proportion to its fecundity."
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EFFECT OF ENVIRONMENTAL FACTORS UPON EXPRESSION OF BROODINESS
The same authors stated that, by regular removal of eggs, Austin increased egg production in wild mallard ducks from 12-18 to 80-100 and Hauke obtained 48 eggs in succession from the common wryneck, and Wenzel obtained 51 eggs in succession from the house sparrow. They suggested that the frequent gathering of eggs had long since reached the limit of its effectiveness. Riddle, Bates, and Lahr (1935) induced broodiness in chickens by the injection of prolactin and made the statement that a hormone had been identified as an essential element in the broody instinct. To sum up, Reaumur, Punnett, and Patel have shown that certain environmental factors can stimulate the expression of broodiness. Lippincott and Card quote evidence of stimulation of egg production by removal of eggs from the nest and Punnett relates that the failure to remove eggs from the nest caused broodiness. Thus, the records present one example of an environmental factor which stimulates broodiness and indirectly decreases egg production; namely, the presence of eggs in the nest. That the removal of this factor results in stimulating egg production and indirectly decreasing broodiness indicates that the recognition and removal of certain stimulating factors for broodiness might be an effective supplementary method of increasing egg production. TO STIMULATE THE EXPRESSION OF BROODINESS Six crossbred hens (Rhode Island Red $ X Barred Rock ? ) were placed in coops with baby chicks. Four of these hens were laying and two were not laying, but were not showing any signs of broodiness. The sides of the coops were covered in such a manner that semi-darkness resulted. This arrengement was used in an effort to eliminate, as far as possible, distracting influences of a visual nature. Sound disturb-
325
ances were not controlled, but the place was relatively quiet from 5:00 p.m. to 8:00 a.m. The semi-darkness was presumed to have a sedative effect, but not to reduce visibility beyond a point at which the hens could be stimulated by the sight of baby chicks. The baby chicks were used to furnish active stimuli. Three distinct stimuli were thus introduced. The stimulus through the eye was kept active by movements of the chicks unless the hen chose to hover them. The stimulus through the ear, caused by peeping of chicks, was persistent unless the chicks were hovered. The stimulus through sense of touch was brought about by the burrowing under the hen of the chicks whenever hovering was permitted. These six crossbred hens were submitted to this treatment at 4:00 p.m. and in all instances but one, egg laying ceased abruptly, and that one hen laid on the day following the beginning of treatment; an egg that had been obviously ovulated and on its way through the oviduct before treatment began. One of the non-laying hens showed the typical signs of a full expression of broodiness such as clucking, feeding the chicks, and uttering warning calls when startled, 18 hours after treatment began. The other nonlaying hen showed these signs after three days. The four laying hens showed the full expression of broodiness after one day, one day, three days, and six days, respectively, of the treatment. The hen that became broody in six days was kept broody for two months by simply keeping young chicks with her. In another test two White Leghorn pullets failed to respond to the stimuli and showed some hostility toward the chicks. Such tests were temporarily postponed and attention turned toward increasing the stimulating effect of the environment. Attempts to cause broodiness by sub-
326
WILLIAM H. BURROWS AND THEODORE C. BYERLY
jecting the hens to the aforementioned stimuli in the morning were less successful than those in which the hens were started in the evening. It was also noticed that when more light was admitted to some of the coops broodiness did not seem to occur as readily. To facilitate exclusion of light the coops were discarded and a box about 18 inches square and 3 feet high was ventilated with small holes and used for holding hens with chicks. Temperatures around 90°F. and high humidity existed during the following tests: Two White Leghorn hens were tested under these new conditions and were readily stimulated to broodiness. Both of these hens were hovering the chicks on the morning following the application of the stimuli, one of them became actively interested after five days and the other after seven days. The following is taken from the records of one of these tests. Hen 516. Non-broody record. 215 eggs in pullet year. Hen was laying regularly in her second year at time of test. August 16, 1937. Placed in box with chicks at 4:00 p.m. August 17 Passively hovering the chicks. August 18 Clucking. Laid an egg. August 19 Clucking. August 20 Calls chicks and feeds them. Laid an egg. August 23 No eggs since August 20. Hen fully broody and fights to protect chicks. A young Light Sussex pullet of about 20 weeks of age hovered chicks, fed them, and sounded danger warnings after nine days of exposure to the stimuli of chicks in semidarkness. A 12-week-old pullet (Rhode Island Red X Light Sussex) did likewise after 12 days of exposure to similar stimuli.
Neither of these young birds made sounds comparable to those of an adult bird, but they were well understood by the chicks, as was shown by the chicks answering the feed call and crouching when the danger signal was uttered. The pituitaries of hens, made psychologically broody, were implanted on the crops of young pigeons to ascertain the amount of prolactin-like substance in them. In every test, the pituitary of a laying hen was implanted on the opposite side of the pigeon crop. In some instances the tests were made as soon as a full expression of broodiness had been induced and, in others, after the hens had been kept broody for various lengths of time; in one instance this was two months. Contrary to expectations the pituitaries of broody hens, as compared with those of laying hens, showed no indication of an increase in prolactin-like substance. TO INHIBIT THE EXPRESSION OF BROODINESS
Forty hens, progeny of three-way crosses involving Rhode Island Red, White Wyandotte, and Light Sussex were selected for a study of a certain group of environmental factors for inhibiting the expression of broodiness. These birds were two years old at the time of selection and their first year mature body weights averaged 2,090 grams. Only hens whose records showed that they had been broody two or more times were included. Some had been broody as many as five times. These hens were divided into two groups of 20 birds each by random selection without reference to their records. The birds in group 1 were used as test birds and those in group 2 as controls. The birds of group 1 were placed in a laying battery. It was thought that the wirebottomed cages of the battery would simulate the conditions of the usual broody
EFFECT OF ENVIRONMENTAL FACTORS UPON EXPRESSION OF BROODINESS
coop. The battery was on the second floor of a three-story cinder-block building in a room which was well lighted and ventilated. Electric lights furnished additional light by means of a time switch which turned the lights on at 4:00 a.m. and off at 8:00 p.m. thus providing a uniform 16-hour period of light each day. The birds in group 2 were placed in a
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ords were kept of egg production, number of hens expressing broodiness, number of cases of expressed broodiness, number of days of broodiness, and the number of days of pause in laying when that pause extended to five or more days in succession and might be interpreted by some investigators as being a partial expression of broodiness.
TABLE 1.—Broodiness among test birds (group 1) and control birds (group 2) from January 13 to August 31, 1937, as compared to the same period of time in 19361 Group 1 2 1 2 1 2
Year 1937 1937 1936 1936
Number of broody hens
Number of broody cases
Days of broodiness
Days of pause 2
2 9 20 20
2 IS 61 56
164 413 1,098 997
292 748 1,367 1,328
All hens were kept in a long laying house throughout their pullet year. Days of pause were counted only when there were five or more of them in succession.
colony laying house. They were trap-nested and allowed access to a grassy yard with bushes for shade. Broody hens were "broken up" in a broody coop as soon as discovered on nests. No additional light was furnished, therefore the length of day varied with the season. Both groups were fed an all-mash laying diet, but the birds in the batteries received additional amounts of ground limestone and alfalfa leaf meal to compensate for lack of range. Temperatures in the building that contained the test group naturally fluctuated less than for those in the colony house. Throughout the winter months the battery room was kept at 65 degrees, or warmer; but during the summer the temperature rose at times to as high as 92 degrees. However, the battery room was, on the average, cooler than the colony house during the day and warmer at night throughout the summer. Changes from the noonday heat to the cool of the night and from one day to another were much more gradual. Under these two sets of conditions, rec-
Table 1 gives the values for broodiness in group 1 and group 2 during the testing periods from January 13, 1937, to August 31,1937, inclusive, as compared with values taken from a similar period of time during 1936. The record shows that, whereas in 1936 there were fewer broody cases, fewer days of broodiness, and fewer days of pause among the hens of group 2 than among the hens of group 1, in 1937 the reverse is true. During the test period the hens in group 2 exhibited about iy2 times as much broodiness as did the hens in group 1. Table 2 gives the percentage of egg production over the same periods of time. These values are greater for group 1 than for group 2 in the 1936 records as well as in the 1937 records, but the difference between the values for group 1 and group 2 is much greater in the 1937 records than it is in the 1936 records. The data are such as to make it impossible to determine what proportion of additional egg production shown by group 1 in 1937 is due to actual difference in days of broodiness, and how
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WILLIAM H. BURROWS AND THEODORE C. BYERLY
much is due to environmental factors, especially electric lighting, which may have stimulated egg production without actually suppressing broodiness. However, since group 1 produced more eggs per hen than did group 2 during June and August when the broodiness of group 2 was most evident, some of the difference in egg production between the two groups was probably due to the suppression of broodiness. TABLE 2!.—Relative
exert a powerful influence over the processes of the chicken is shown by the fact that hens of a so-called non-broody strain and pullets too young to normally become broody were made broody by them. Certain other conditions have been shown to have a definite inhibiting effect on the expression of broodiness. That the broodiness of broody hens was not entirely inhibited may have been due to a failure to
egg production of test birds (group 1) and control birds (group 2) from January 13 to August 31, 1937, and for the same period of time in 1936
January
February
March
April
May
June
July
August
Average
percent
percent
percent
percent
percent
percent
percent
percent
percent
57.9 22.0
82.9 41.4
76.5 62.3
72.6 69.6
61.6 59.2
65.2 43.8
52.1 50.0
53.5 44.3
65.3 49.0
42.6 40.2
58.8 43.1
66.9 57.2
58.0 50.5
44.7 42.7
35.8 43.2
53.4 54.5
44.0 44.0
50.5 46.9
Group 1937: 1 2 1936: 1 2
The exhibition of broodiness by both groups was less in 1937 than in 1936 and this is what might be expected, since only those birds were chosen for the test which showed more than average broodiness during their pullet year, and extremes usually tend to regress toward the average. The two birds in group 1 that went broody in the batteries, remained broody until the end of the test period. In one case this involved 31 days of broodiness, but in the other it involved 133 days of broodiness; and in both cases the birds were still in a broody condition when the test was stopped. Both of these birds had extremely broody records in their pullet year, but other birds with equally broody first-year records failed to show any broodiness in the battery. DISCUSSION
Data have been presented to show that certain conditions will induce hens to exhibit broodiness. That these conditions
create an environment which was sufficiently free from factors which stimulate broodiness or sufficient in factors which inhibit the expression of broodiness. The pituitaries of the hens that became broody from exposure to external factors did not show, by the pigeon crop test, the presence of more prolactin-like substance than did the pituitaries of birds that were not broody. Burrows and Byerly (1936) found that hens, just becoming broody under normal conditions, showed a marked increase in a prolactin-like substance in their pituitaries, but that those in the later stages of broodiness did not. It appears that prolactin can cause broodiness and either prolactin or some similar substance does bring on broodiness under natural conditions, but it also appears that such a substance is not essential to the broody instinct. This is in agreement with the work of Nobel, Kumpf, and Billings who found that jewel fish could be stimulated to broody behavior by injections of prolactin,
EFFECT OF ENVIRONMENTAL FACTORS UPON EXPRESSION OF BROODINESS
corpus luteum extract, thyroid, and 5 percent phenol solution, whereas injections of saline had no such effect, but disagrees with Riddle's conclusion. Moreover, in most of Riddle's experiments three or more days were required to cause nesting and usually one more day was required to cause clucking even with relatively large doses of prolactin. Broodines induced by psychological stimuli can occur in too short a time to suppose it to be the secondary effect of a primary stimulation of the pituitary to the production of prolactin. A classification of the various factors, that might form a part of the chicken's environment, into those that stimulate broodiness and those that do not would seem to be desirable. Many such factors have already been evaluated as to their favorable influence on egg preduction, but while it is true that some factors, favorable to egg production, decrease broodiness, this may not be true in every instance. Although the environment of the 20 hens in the battery was composed of a variety of factors such as were available, and therefore not as ideal as could have been desired, certain factors present gave reason to expect results similar to those obtained. The laying cages, in addition to resembling broody coops in construction, automatically removed the eggs as soon as they were laid. Food and water were always in sight so that as soon as the egg was laid the attention of the bird was diverted from that process to other things—usually it was water. It is assumed that the 16-hour lighting had a stimulating effect upon egg production and indirectly some inhibitory influence on broodiness; since in attempting to induce the expression of broodiness it was found that light does inhibit the expression of broodines and that the lack of light stimulates it. No attempt was made to control temperature and humidity.
329
It seems pertinent here to raise the question as to how much of broodiness can exist in hens and exert an unfavorable influence on egg production without any outward exhibition in the form of nesting or clucking. How much are vaguely expressed conditions such as winter pause, pause between clutches, rest periods, and nonproductive days of the intermittent layers, and lack of persistence due to broodiness which is not so expressed as to be recognized? It is possible that a sort of partlyexpressed broodines may account for more of these non-productive periods than is usually thought. The results of these tests would seem to indicate that no single environment will reveal to .the best advantage the broodiness and egg-producing abilities of a hen. The records of the hens in group 1 show, to a fair degree at least, their egg-producing abilities, but are obviously false if considered for broodiness, whereas records for hens kept under conditions conducive to broodiness would not show their true production abilities. In selecting for high production and non-broodiness, progress might be expedited if hens, after having been selected for high production, in an environment conducive to laying, were submitted to a more or less broody environment and the broody birds then culled. The hens in group 1 layed an average of 34 eggs per hen more in 7^4 months than the hens in group 2. SUMMARY Hens of broody and non-broody strains and pullets, too young to become broody in a natural way, were made to express broodiness by the application of physical and psychological stimuli. Temperatures about 90°F., darkness, and the presence of chicks formed the most potent combination of stimuli. Low temperatures and even a small
330
WILLIAM H. BURROWS AND THEODORE C. BYERLY
amount of light reduced the effectiveness of the environment in inducing broodiness. The hens and pullets performed all the duties of caring for chicks after being stimulated to broodiness. The time required for the stimuli to be effective varied from 18 hours to 12 days and, although some of this variation was apparently due to differences in degrees of darkness and temperature of the environment, White Leghorn hens were definitely slower to respond than the crossbred hens used in the tests. Hens kept in a standard type colony house without artificial light showed 2^2 times as much broodiness as hens kept in a battery in a large cinder-block building with artificial light to give a uniform 16hour day. Moderate temperature, slow temperature changes, light, wire floor of cages, feeding habits, and quick, automatic removal of eggs in batteries constituted a group of environmental factors which decreased the expression of broodiness. The hens in the battery laid an average of 34 eggs more than the hens in the colony house during the 7^2 months of the test and at least a part of this increase may be at-
tributed to the suppression of broodiness. No evidence of an increase in prolactinlike substance was found in the pituitaries of "psychologically broody" hens when these were implanted, opposite those of laying hens, on the crop glands of 6-8 week old pigeons. REFERENCES
Burrows, W. H., and T. C. Byerly, 1936. Studies of prolactin in the fowl pituitary. I. Broody hens compared with laying hens and males. Proc. Soc. Exp. Biol, and Med. 34:841-844. Lippincott, W. A., and L. E. Card, 1934. Poultry production, pp. 21-22. Lea and Febiger, Philadelphia, Pa. Noble, G. K., K. F . Kumpf, and V. N. Billings, 1936. The induction of brooding behavior in jewel fish. Anat. Record, Sup. No. 1, Vol. 67 :S0. Patel, M. D., 1936. The physiology of the formation of pigeon milk. Physiol. Zool. 9:129-152. Punnett, R. C , 1923. Heredity in poultry, p. 179. Macmillan & Co., New York, N.Y. Reaumur, Rene Antoine Ferschault, de, 1750. The art of hatching and bringing up domestic fowl at any time of the year, either by means of the heat of hotbeds or that of common fire. C. Davis, London, p. 283. Riddle, Oscar, Robert W. Bates, and Earnest L. Laher, 1935. Prolactin induces broodiness in fowl. Amer. Jour. Physiol. 111:352-360.