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Does the Growing chick Require Grit?*
DOES THE GROWING CHICK REQUIRE GRIT ?* BY R . M. BETHKE AND D . C. KENNARD
(From the Department of Animal Industry, Ohio Agricultural Experiment Station, Wooster)
EXPERIMENTAL
Experiment 1. Four groups of 18, day old. White Leghorn chicks, hatched from eggs laid by hens which had all received similar nations and management, were placed in our standard * Published with the permission of the Director of the Ohio Agricultural ExpfeTiment Station.
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(Received for PuhUcation 4-19-26) Numerous practices in poultry husbandry are chiefly based on tradition and supposition. However, in consequence of the growing interest in poultry, many of the old traditional beliefs are being put to scientific test and those not supported by natural laws or scientific facts are being gradually abandoned. Since the fowl has no teeth with which to grind its feed, it is generally supposed that, to aid in reducing the feed to fineness in the gizzard, some hard, sharp material commonly termed " g r i t " must be supplied. This general belief, that grit is essential for chickens, appears to be about as firmly established as any that can be cited. In fact, in So far as the writers are aware, the literature reveals no instance of any one questioning the merits of the practice. Poultry writers of the past emphasized the importance of grit being sharp so as to cut or shred the feed material in the gizzard. Accordingly, some stressed the merits of broken chinaware^the knife-like porcelain edges being, presumably, especially eificient. More recently the idea has been advanced that in nature the chicken does not get sharp grit but rounded pebbles such as in coarse sand and fine gravel. The importance of supplying grit to baby chicks is further emphasized by the general recommendation that a drink and coarse sand or a similar material should comprise the "first course" in good chick management; in this way insuring the presence of a grinding mechanism in the gizzard for efficient utilization of subsequent feeds. In order to obtain definite evidence as to the necessity or merits of supplying grit to chicks, the following tests were conducted:
POULTRY
286
SCIENCE
TABLE I RECORDS OF T H E C K I O K S RECEIVING A F I N E AND COAKSE RATION
WITH
AND W I T H O U T
GBIT.
(EXPEBIMENT
1)
Coarse ground Grit ad libitum Age
No. surviving
weelts 0 2 4 6 8 10 12
18 17 17 15 14 13 13
Av. weight gm. 32.5 59.7 90.0 138.3 186.8 259.6 353.0
Age
No grit No. surviving
weeks 0 2 4 6 8 10 12
18 17 17 16 16 16 16
Av. weight gm. 32.5 63.5 101.4 152.5 206.2 271.2 346.6
Fine ground
Age weeks 0 2 4 6 8 10 12
Grit ad libitum Av. No. weight surviving gm. 18 32.5 61.2 16 15 97.6 14 138.2 14 206.0 14 282.1 14 373.5
Age
No grit No. surviving
weeks 0 2 4 6 8 10 12
18 18 16 15 15 14 14
Av. weight gm. 32.5 56.9 98.4 145.0 206.3 284.3 395.3
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laboratory pens of 3 by 6 feet, located in the poultry building, Pine shavings, renewed weekly, were used as litter. In order to determine whether the relative state of fineness of the basal mash had any effect, two of the groups were allowed a rather coarse mash after the first week. One group had free access to granite grit. The other two groups received a ration of identical composition but very finely ground. Granite grit ad libitum was again supplied one of the groups. The basal ration was composed of 56 parts yellow corn, 23.5 parts wheat middlings, 15 parts casein, 2 parts calcium carbonate, 1 part common salt, and 2.5 parts cod-liver oil—with water to drink. In order to insure uniform consumption of the mash in all four groups, the feeding schedule was so arranged that fresh feed was supplied only when complete consumption of the previous feed had occurred. The record of the chicks is given in Table I.
GRIT REQUIREMENTS
287
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The chicks in all four groups did not do as well as was anticipated, compared to previous experiences with this ration. There was a tendency towards constipation which in part might account for the heavy mortality and slow growth. However, aside from this no abnormalities or nutritional disorders were observed. From Table I, it is evident that the birds which received grit ad libitum were no better than the cheek or " n o g r i t " individuals. Likewise, there was no apparent difference between the coarse-mash and fine-mash groups. The slightly better weights in the two fine-mash groups can be accounted for by the relative percentage of cockerels to pullets which was much greater in these groups than in the coarse mash groups. By coincidence, the two groups which received the coarse mash only contained 3 cockerels each. The total feed consumption of the four groups, while low, was comparatively the same. Experiment 2. After the foregoing experiment had been in progress for eight weeks, with no apparent differences between the grit and no grit birds, we had occasion to test the relative merit of dried buttermilk as compared with liquid skimmilk as a part of an otherwise complete ration. Similar rations had in the past produced good livability and growth of chicks when grit was supplied ad libitum. Accordingly, these rations were employed without the supplementary grit. Finally the pullets from both groups were divided and continued on an adequate ration with and without grit. For this purpose, day old, White Leghorn chicks, hatched from eggs laid by the Station flock, were divided into two groups and placed in the experimental pens as before. Pine shavings were used as litter. The only feed allowed was a dry, medium-ground mash fed in open troughs. The ration of Group 1 was composed of 66 parts yellow corn, 28.5 parts wheat middlings, 2 parts calcium carbonate, 1 part common salt, 2.5 parts cod-liver oil, and skimmilk ad libitum. Group 2 received a ration composed of 56 parts yellow corn, 23.5 parts wheat middlings, 15 parts dried buttermilk, 2 parts calcium carbonate, 1 part salt, 2.5 parts cod-liver oil, and water ad libitum. Good livability and growth were obtained in both groups as shown in Table II. The birds in Group 1, which received skim-
288
POULTRY
SCIENCE
TABLE II R E C O B D O F T H E CHICKS R E C E I V I N G A COMPLETE R A T I O N INCLUDING A M I L K S U P P L E M E N T — ^ W I T H O U T ACCESS TO G E I T . ( E X P E R I M E N T 2)
Age weeks 0 2 4 6 8 10 12
GROUP 1
GROUP 2
Liquid sliimmillc ad libitum
Dried buttermilk 15 per cent
No. surviving
Average weiglit
Age
No. surviving
26 26 26 25 25 25 25
gm. 33.0 78.0 161.4 302.6 491.1 716.6 934.2
weeks 0 2 4 6 8 10 12
20 20 20 19 19 19 19
Average weight ~
gm. 33.0 63.0 125.0 218.6 343.0 510.0 704.4
To further substantiate or refute our previous results that the state of division of the feed has no direct relationship to the necessity of grit in the gizzard, the birds in both'|)ens were fed a grain mixture in addition to the mash. The grain mixture was composed of 3 parts coarse cracked corn and 2 parts whole wheat. This was placed before the birds for 30 minutes, daily, in open troughs. The mash composed of 70 parts yellow corn, 20 parts wheat middlings, 4 parts bone ash, 5 parts codliver oil, 1 part salt, and skimmilk ad libitum, remained before them at all times. One pen was given granite grit, while the other received no grit. The records are given in Table I I I .
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milk ad libitum, did remarkably well and were fully two weeks ahead of the dried buttermilk group at the end of the 12th week (Table I I ) . No digestive or nutritional disorders were noted in either group. Altho there was no group receiving grit for direct comparison, the writers believe from past "exp'etieîieés with like rations, that no better results would have:been obtained had grit been supplied. However, in order to secure further evidence on this point, the 20 pullets Wiere divided into two groups at the end of the 12th week and ione given free access to grit and the other, without grit, kept: as a control. Six pullets and 3 cockerels from the skimmilk group and 4 pullets from the buttermilk group were placed in each pen of 5 by 6 feet. Pine shavings were used as litter.
GRIT
REQUIREMENTS
289
TABLE RECORD A F T E B
III
20 P U L L E T S A N D 6 COCKEBELS
(IN TABLE II)
WERE
E Q U A L L Y DIA-IDED I N T O T W O P E N S AND F E D A G R A I N M I X T U R E I N A D D I T I O N TO A M A S H — W I T H A N D W I T H O U T G R I T . (EXPERIMENT 2 CONT'D) No g r i t
Grit ad libiitum Age
No. surviving
Average weight'
Age
gm.
weeks
13 13 13 12'' 12 12 12
949.5 1128.0 1314.8 1479.5 1539.8 1627.5 1616.5
12 14 16 18 19 21 23
weeks
12 14 16 18 19 21 23
No. surviving
Average weight'
13 13 13 13 13 13 13
954.5 1139.7 1333.7 1401.3 1514.6 1581.3 1655.3
gm.
' The cockerel and pullet weights were averaged separately and the two averages combined for a general average. ' One pullet died In the 17th week irom oviduct trovible.
Autopsy examination revealed nothing abnormal. The digestive tracts of the " n o g r i t " birds were normal in all appearances and apparently did not differ from those of the " g r i t " birds. A careful examination of the gizzard showed that the thickness and firmness of the musculature bore no relationship to the presence or absence of grit. The contents of this organ from the grit birds were approximately from one quarter to one third grit. In the " n o g r i t " group it was observed that the gizzards' contents contained a few pieces (from 2 to 10) of hard granular material suggestive of small pebbles. How mu(^h effect the presence of this material might have had upon the validity of the results is debatable. However, it would seem that the grinding action of 10 pebbles is not comparable to a number which comprises 25 to 35 per cent of the gizzard con-
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The birds were continued under this management for eleven weeks when they were killed for autopsy. The birds in both pens made a normal rate of growth with no signs of digestive or nutritional disturbances. Both groups started to lay between the 18th and 19th week. The egg production up to the time of slaughter was the same for both pens, namely 8 eggs per bird. The amounts of mash and grain consumed by each pen were relatively the same.
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tents. We thus feel justified in thinking that if grit is essential in the proper grinding of feed—and indirectly aids digestion— a différence in the behavior of the two corresponding groups of growing chickens should have manifested itself in the course of eleven weeks. However, not knowing definitely how much effect the few pebbles might have had in the " n o g r i t " pen, another test was conducted with two groups of chicks on screens of hardware cloth to safeguard against the possibilities of picking up grit-like material which might be in the litter. Experiment 3. Fifty, day old. White Leghorn chicks from the Station's Poultry plant were divided into two lots of 25 each and placed in the laboratory pens as before. The floor of the pen and brooder were covered with muslin cloth, renewed daily, for the first 2 weeks. After that the chicks were kept off the floor by means of frames covered with % inch mesh hardAvare cloth elevated 3 inches above the floor. In this way there was no possibility of the chicks coming in contact with the floor and litter. Both lots received a medium ground mash of 70 parts yellow corn, 20 parts wheat middlings, 5 parts casein, 2 parts bone ash, 1 part salt, 2 parts cod-liver oil, and skimmilk to drink. In addition, one lot had free access to granite grit. The other, or " n o g r i t " lot serving as a control. The chicks were allowed to continue under the foregoing management until the 10th week, when the cockerels and pullets were separated into separate pens and continued on screens as before (Table I V ) . To make conditions still more drastic as to the necessity of grit for grinding purposes, the medium ground mash was replaced by a coarse mixture in which 20 parts of whole wheat replaced the wheat niiddlings. Two additional parts of bone ash were added to increase the mineral content. The yellow corn was also coarsely ground—approximately the size of whole wheat. Otherwise, the ration was the same as before. , At the end of the 16th week (see Table IV) the cockerels in both lots were killed and a thorough examination made of theii digestive tract. No apparent deviations from normal were observed regardless of whether the bird had access to grit or not. Neither was there any variation in the thickness nor firmness of
GBIT
REQUIREMEVTS
291
TABLE G K I T V E B S U S No
IV
G B I T — ^ W H E N B I B D S A K E Ρ Β Ε Λ Έ Ν Τ Ε Β F É O M COMING IN
CONTACT W I T H F L O O B OK L I T T E R BY M E A N S OF C L O T H AND W I B E SCREENS.
(EXPERIMENT
Grit ad libitum Age
No. surviving
Average weight
weeks 0 2 4 6 8 10 12' 14 16 18= 20' 22 24 28
25 25 25 25 23 23 23 23 21 9 9 9 9 9
gm. 33.0 86.0 143.0 233.8 352.6 575.4 704.1 867.5 1008.3 1036.6 1162.2 1287.5 1360.0 1352.0
3)
Age
No grit No. surviving
Average weight
weeks 0 2 4 6 8 10 12 14 16 18= 20' 22 24 28
25 25 25 24 23 23 22 21 20 10 10 10 9' 9
gm. 32.0 76.0 117.6 201.5 322.6 482.2 607.5 764.0 953.8 1018.5 1215.5 1349.4 1450.0 1445.5
' Cockerel and pullet weights averaged separately and combined for general average. Cockerels were separated from pullets at close of 10th week—and the medium ground mash was replaced by a coarse mash. (See Text). - Pullets only. Cockerels killed for examination at close of 16th week. ' Given one half pint of whole corn daily in addition to coarse mash. * Pullet died from oviduct trouble.
The pullets were continued on the same ration and management. (See Table IV.). The "no g r i t " birds started to lay at the close of the 19th week. One week later the " g r i t " birds started. At this time, the 20th week, one half pint of whole yellow corn was supplied to each group, daily, in addition to the coarse corn-whole wheat mash. The latter was, however, fortified with two additional parts of cod-liver oil in order not to reduce the total anti-rachitic vitamin intake. No digestive or nutritional disorders were observed at any time. At the present writing, both groups are in good condition, and from all
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the gizzard musculature. The gizzard contents from the " g r i t " birds were thoroughly interspersed with granite grit while no grit or granular material was found in the gizzards of the " n o grit ' ' individuals, showing that the screening of the birds from the floor and litter proved effective.
292
POULTRY
SCIENCE
appearances and behavior, alike. The total egg production to date also has been practically the same—namely 120 for the grit group and 126 for the group not receiving grit.
How much grinding action grit will exert in the gizzard of a chicken we are unable to state. However, it is the writers' belief, from the data secured, that the supposed grinding or reducing action has no direct or indirect relation to rate of growth, livability, or well being of a growing chick. If grit, as commonly thought, exerts a grinding action of importance and thereby aids digestion, a différence should have been observed in the response and behavior of the groups of birds which received grit when compared with those Λvhich M^ere denied grit ; especially in case of the groups receiA^ng a coarse feed mixture without grit. In reality, no differences were observed, regard less of the state of fineness of the feed or the presence or ab sence of grit in the ration. (See Tables I, II, III, and IV.) We, accordingly, believe that the grinding action of grit is of minor importance, especially when considered as a factor favoring digestion, and that the quality of the ration in conjunction with
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DISCUSSION
The data herein presented appear to indicate that the generally accepted belief and the common practice of supplying grit to growing chicks is based on theory rather than facts. While there is no evidence that grit or like material is injurious to the chick, there seems to be no benefit derived from it as an aid for grinding purposes. The chicken has a natural craving for most any kind of gritlike material. There appears to be no satisfactory explanation for this manifestation. The accepted theory has been that the grit is required for grinding purposes or "hen's teeth." Grit might also be thought of as partially serving as ballast in the digestive tract and may have some function in that respect, or the craving for grit may be largely a matter of instinct. However, it seems more plausible to believe that the craving for grit by the chicken is prompted by the desire to satisfy its mineral recjuirements. Under natural conditions the chicken is obliged to depend upon grit material for certain essential minerals and may instinctively eat or crave the grit even if adequate minerals are supplied from other sources.
GRIT REQUIREMENTS
293
SUMMARY
No benefit resulted from the use of grit (granite) in the case of baby chicks reared to 12 weeks of age or maturity in the three foregoing experiments. The groups of birds which did not receive grit appeared to utilize coarse ground feeds and whole corn and wheat as effectively as those that had free access to grit. The belief that grit is essential in the gizzard for grinding or reducing purposes in the case of growing chicks appears to be based on theory rather than facts. Grit may, however, serve an important function as a source of essential minerals if the ration is deficient in this respect.
Credit is due Mr. M. C. Kik for his assistance with the experiments herein reported.
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the digestive fluids of the alimentary tir,act are .the factors which determine the rate of growth and well-being .of a chick. It, therefore, appears that grit is not necessary in the dietary of a chick and that its presence in the gizzard is simply an incidental factor. Under natural environment the chicken is probably obliged to eat grit to satisfy its mineral requirements and instinctively clings to the practice under domesticated conditions where minerals are often supplied in the feed mixtures. Although the results of this study are not of great practical value, they, nevertheless, are of interest, in that they call attention to one of a number of traditional theories and practices in connection with poultry keeping which are not necessarily supported by facts.
(From the Department of Animal Industry, Ohio Agricultural Experiment Station, Wooster)
EXPERIMENTAL
Experiment 1. Four groups of 18, day old. White Leghorn chicks, hatched from eggs laid by hens which had all received similar nations and management, were placed in our standard * Published with the permission of the Director of the Ohio Agricultural ExpfeTiment Station.
285
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(Received for PuhUcation 4-19-26) Numerous practices in poultry husbandry are chiefly based on tradition and supposition. However, in consequence of the growing interest in poultry, many of the old traditional beliefs are being put to scientific test and those not supported by natural laws or scientific facts are being gradually abandoned. Since the fowl has no teeth with which to grind its feed, it is generally supposed that, to aid in reducing the feed to fineness in the gizzard, some hard, sharp material commonly termed " g r i t " must be supplied. This general belief, that grit is essential for chickens, appears to be about as firmly established as any that can be cited. In fact, in So far as the writers are aware, the literature reveals no instance of any one questioning the merits of the practice. Poultry writers of the past emphasized the importance of grit being sharp so as to cut or shred the feed material in the gizzard. Accordingly, some stressed the merits of broken chinaware^the knife-like porcelain edges being, presumably, especially eificient. More recently the idea has been advanced that in nature the chicken does not get sharp grit but rounded pebbles such as in coarse sand and fine gravel. The importance of supplying grit to baby chicks is further emphasized by the general recommendation that a drink and coarse sand or a similar material should comprise the "first course" in good chick management; in this way insuring the presence of a grinding mechanism in the gizzard for efficient utilization of subsequent feeds. In order to obtain definite evidence as to the necessity or merits of supplying grit to chicks, the following tests were conducted:
POULTRY
286
SCIENCE
TABLE I RECORDS OF T H E C K I O K S RECEIVING A F I N E AND COAKSE RATION
WITH
AND W I T H O U T
GBIT.
(EXPEBIMENT
1)
Coarse ground Grit ad libitum Age
No. surviving
weelts 0 2 4 6 8 10 12
18 17 17 15 14 13 13
Av. weight gm. 32.5 59.7 90.0 138.3 186.8 259.6 353.0
Age
No grit No. surviving
weeks 0 2 4 6 8 10 12
18 17 17 16 16 16 16
Av. weight gm. 32.5 63.5 101.4 152.5 206.2 271.2 346.6
Fine ground
Age weeks 0 2 4 6 8 10 12
Grit ad libitum Av. No. weight surviving gm. 18 32.5 61.2 16 15 97.6 14 138.2 14 206.0 14 282.1 14 373.5
Age
No grit No. surviving
weeks 0 2 4 6 8 10 12
18 18 16 15 15 14 14
Av. weight gm. 32.5 56.9 98.4 145.0 206.3 284.3 395.3
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laboratory pens of 3 by 6 feet, located in the poultry building, Pine shavings, renewed weekly, were used as litter. In order to determine whether the relative state of fineness of the basal mash had any effect, two of the groups were allowed a rather coarse mash after the first week. One group had free access to granite grit. The other two groups received a ration of identical composition but very finely ground. Granite grit ad libitum was again supplied one of the groups. The basal ration was composed of 56 parts yellow corn, 23.5 parts wheat middlings, 15 parts casein, 2 parts calcium carbonate, 1 part common salt, and 2.5 parts cod-liver oil—with water to drink. In order to insure uniform consumption of the mash in all four groups, the feeding schedule was so arranged that fresh feed was supplied only when complete consumption of the previous feed had occurred. The record of the chicks is given in Table I.
GRIT REQUIREMENTS
287
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The chicks in all four groups did not do as well as was anticipated, compared to previous experiences with this ration. There was a tendency towards constipation which in part might account for the heavy mortality and slow growth. However, aside from this no abnormalities or nutritional disorders were observed. From Table I, it is evident that the birds which received grit ad libitum were no better than the cheek or " n o g r i t " individuals. Likewise, there was no apparent difference between the coarse-mash and fine-mash groups. The slightly better weights in the two fine-mash groups can be accounted for by the relative percentage of cockerels to pullets which was much greater in these groups than in the coarse mash groups. By coincidence, the two groups which received the coarse mash only contained 3 cockerels each. The total feed consumption of the four groups, while low, was comparatively the same. Experiment 2. After the foregoing experiment had been in progress for eight weeks, with no apparent differences between the grit and no grit birds, we had occasion to test the relative merit of dried buttermilk as compared with liquid skimmilk as a part of an otherwise complete ration. Similar rations had in the past produced good livability and growth of chicks when grit was supplied ad libitum. Accordingly, these rations were employed without the supplementary grit. Finally the pullets from both groups were divided and continued on an adequate ration with and without grit. For this purpose, day old, White Leghorn chicks, hatched from eggs laid by the Station flock, were divided into two groups and placed in the experimental pens as before. Pine shavings were used as litter. The only feed allowed was a dry, medium-ground mash fed in open troughs. The ration of Group 1 was composed of 66 parts yellow corn, 28.5 parts wheat middlings, 2 parts calcium carbonate, 1 part common salt, 2.5 parts cod-liver oil, and skimmilk ad libitum. Group 2 received a ration composed of 56 parts yellow corn, 23.5 parts wheat middlings, 15 parts dried buttermilk, 2 parts calcium carbonate, 1 part salt, 2.5 parts cod-liver oil, and water ad libitum. Good livability and growth were obtained in both groups as shown in Table II. The birds in Group 1, which received skim-
288
POULTRY
SCIENCE
TABLE II R E C O B D O F T H E CHICKS R E C E I V I N G A COMPLETE R A T I O N INCLUDING A M I L K S U P P L E M E N T — ^ W I T H O U T ACCESS TO G E I T . ( E X P E R I M E N T 2)
Age weeks 0 2 4 6 8 10 12
GROUP 1
GROUP 2
Liquid sliimmillc ad libitum
Dried buttermilk 15 per cent
No. surviving
Average weiglit
Age
No. surviving
26 26 26 25 25 25 25
gm. 33.0 78.0 161.4 302.6 491.1 716.6 934.2
weeks 0 2 4 6 8 10 12
20 20 20 19 19 19 19
Average weight ~
gm. 33.0 63.0 125.0 218.6 343.0 510.0 704.4
To further substantiate or refute our previous results that the state of division of the feed has no direct relationship to the necessity of grit in the gizzard, the birds in both'|)ens were fed a grain mixture in addition to the mash. The grain mixture was composed of 3 parts coarse cracked corn and 2 parts whole wheat. This was placed before the birds for 30 minutes, daily, in open troughs. The mash composed of 70 parts yellow corn, 20 parts wheat middlings, 4 parts bone ash, 5 parts codliver oil, 1 part salt, and skimmilk ad libitum, remained before them at all times. One pen was given granite grit, while the other received no grit. The records are given in Table I I I .
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milk ad libitum, did remarkably well and were fully two weeks ahead of the dried buttermilk group at the end of the 12th week (Table I I ) . No digestive or nutritional disorders were noted in either group. Altho there was no group receiving grit for direct comparison, the writers believe from past "exp'etieîieés with like rations, that no better results would have:been obtained had grit been supplied. However, in order to secure further evidence on this point, the 20 pullets Wiere divided into two groups at the end of the 12th week and ione given free access to grit and the other, without grit, kept: as a control. Six pullets and 3 cockerels from the skimmilk group and 4 pullets from the buttermilk group were placed in each pen of 5 by 6 feet. Pine shavings were used as litter.
GRIT
REQUIREMENTS
289
TABLE RECORD A F T E B
III
20 P U L L E T S A N D 6 COCKEBELS
(IN TABLE II)
WERE
E Q U A L L Y DIA-IDED I N T O T W O P E N S AND F E D A G R A I N M I X T U R E I N A D D I T I O N TO A M A S H — W I T H A N D W I T H O U T G R I T . (EXPERIMENT 2 CONT'D) No g r i t
Grit ad libiitum Age
No. surviving
Average weight'
Age
gm.
weeks
13 13 13 12'' 12 12 12
949.5 1128.0 1314.8 1479.5 1539.8 1627.5 1616.5
12 14 16 18 19 21 23
weeks
12 14 16 18 19 21 23
No. surviving
Average weight'
13 13 13 13 13 13 13
954.5 1139.7 1333.7 1401.3 1514.6 1581.3 1655.3
gm.
' The cockerel and pullet weights were averaged separately and the two averages combined for a general average. ' One pullet died In the 17th week irom oviduct trovible.
Autopsy examination revealed nothing abnormal. The digestive tracts of the " n o g r i t " birds were normal in all appearances and apparently did not differ from those of the " g r i t " birds. A careful examination of the gizzard showed that the thickness and firmness of the musculature bore no relationship to the presence or absence of grit. The contents of this organ from the grit birds were approximately from one quarter to one third grit. In the " n o g r i t " group it was observed that the gizzards' contents contained a few pieces (from 2 to 10) of hard granular material suggestive of small pebbles. How mu(^h effect the presence of this material might have had upon the validity of the results is debatable. However, it would seem that the grinding action of 10 pebbles is not comparable to a number which comprises 25 to 35 per cent of the gizzard con-
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The birds were continued under this management for eleven weeks when they were killed for autopsy. The birds in both pens made a normal rate of growth with no signs of digestive or nutritional disturbances. Both groups started to lay between the 18th and 19th week. The egg production up to the time of slaughter was the same for both pens, namely 8 eggs per bird. The amounts of mash and grain consumed by each pen were relatively the same.
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POULTRY
SCIENCE
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tents. We thus feel justified in thinking that if grit is essential in the proper grinding of feed—and indirectly aids digestion— a différence in the behavior of the two corresponding groups of growing chickens should have manifested itself in the course of eleven weeks. However, not knowing definitely how much effect the few pebbles might have had in the " n o g r i t " pen, another test was conducted with two groups of chicks on screens of hardware cloth to safeguard against the possibilities of picking up grit-like material which might be in the litter. Experiment 3. Fifty, day old. White Leghorn chicks from the Station's Poultry plant were divided into two lots of 25 each and placed in the laboratory pens as before. The floor of the pen and brooder were covered with muslin cloth, renewed daily, for the first 2 weeks. After that the chicks were kept off the floor by means of frames covered with % inch mesh hardAvare cloth elevated 3 inches above the floor. In this way there was no possibility of the chicks coming in contact with the floor and litter. Both lots received a medium ground mash of 70 parts yellow corn, 20 parts wheat middlings, 5 parts casein, 2 parts bone ash, 1 part salt, 2 parts cod-liver oil, and skimmilk to drink. In addition, one lot had free access to granite grit. The other, or " n o g r i t " lot serving as a control. The chicks were allowed to continue under the foregoing management until the 10th week, when the cockerels and pullets were separated into separate pens and continued on screens as before (Table I V ) . To make conditions still more drastic as to the necessity of grit for grinding purposes, the medium ground mash was replaced by a coarse mixture in which 20 parts of whole wheat replaced the wheat niiddlings. Two additional parts of bone ash were added to increase the mineral content. The yellow corn was also coarsely ground—approximately the size of whole wheat. Otherwise, the ration was the same as before. , At the end of the 16th week (see Table IV) the cockerels in both lots were killed and a thorough examination made of theii digestive tract. No apparent deviations from normal were observed regardless of whether the bird had access to grit or not. Neither was there any variation in the thickness nor firmness of
GBIT
REQUIREMEVTS
291
TABLE G K I T V E B S U S No
IV
G B I T — ^ W H E N B I B D S A K E Ρ Β Ε Λ Έ Ν Τ Ε Β F É O M COMING IN
CONTACT W I T H F L O O B OK L I T T E R BY M E A N S OF C L O T H AND W I B E SCREENS.
(EXPERIMENT
Grit ad libitum Age
No. surviving
Average weight
weeks 0 2 4 6 8 10 12' 14 16 18= 20' 22 24 28
25 25 25 25 23 23 23 23 21 9 9 9 9 9
gm. 33.0 86.0 143.0 233.8 352.6 575.4 704.1 867.5 1008.3 1036.6 1162.2 1287.5 1360.0 1352.0
3)
Age
No grit No. surviving
Average weight
weeks 0 2 4 6 8 10 12 14 16 18= 20' 22 24 28
25 25 25 24 23 23 22 21 20 10 10 10 9' 9
gm. 32.0 76.0 117.6 201.5 322.6 482.2 607.5 764.0 953.8 1018.5 1215.5 1349.4 1450.0 1445.5
' Cockerel and pullet weights averaged separately and combined for general average. Cockerels were separated from pullets at close of 10th week—and the medium ground mash was replaced by a coarse mash. (See Text). - Pullets only. Cockerels killed for examination at close of 16th week. ' Given one half pint of whole corn daily in addition to coarse mash. * Pullet died from oviduct trouble.
The pullets were continued on the same ration and management. (See Table IV.). The "no g r i t " birds started to lay at the close of the 19th week. One week later the " g r i t " birds started. At this time, the 20th week, one half pint of whole yellow corn was supplied to each group, daily, in addition to the coarse corn-whole wheat mash. The latter was, however, fortified with two additional parts of cod-liver oil in order not to reduce the total anti-rachitic vitamin intake. No digestive or nutritional disorders were observed at any time. At the present writing, both groups are in good condition, and from all
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the gizzard musculature. The gizzard contents from the " g r i t " birds were thoroughly interspersed with granite grit while no grit or granular material was found in the gizzards of the " n o grit ' ' individuals, showing that the screening of the birds from the floor and litter proved effective.
292
POULTRY
SCIENCE
appearances and behavior, alike. The total egg production to date also has been practically the same—namely 120 for the grit group and 126 for the group not receiving grit.
How much grinding action grit will exert in the gizzard of a chicken we are unable to state. However, it is the writers' belief, from the data secured, that the supposed grinding or reducing action has no direct or indirect relation to rate of growth, livability, or well being of a growing chick. If grit, as commonly thought, exerts a grinding action of importance and thereby aids digestion, a différence should have been observed in the response and behavior of the groups of birds which received grit when compared with those Λvhich M^ere denied grit ; especially in case of the groups receiA^ng a coarse feed mixture without grit. In reality, no differences were observed, regard less of the state of fineness of the feed or the presence or ab sence of grit in the ration. (See Tables I, II, III, and IV.) We, accordingly, believe that the grinding action of grit is of minor importance, especially when considered as a factor favoring digestion, and that the quality of the ration in conjunction with
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DISCUSSION
The data herein presented appear to indicate that the generally accepted belief and the common practice of supplying grit to growing chicks is based on theory rather than facts. While there is no evidence that grit or like material is injurious to the chick, there seems to be no benefit derived from it as an aid for grinding purposes. The chicken has a natural craving for most any kind of gritlike material. There appears to be no satisfactory explanation for this manifestation. The accepted theory has been that the grit is required for grinding purposes or "hen's teeth." Grit might also be thought of as partially serving as ballast in the digestive tract and may have some function in that respect, or the craving for grit may be largely a matter of instinct. However, it seems more plausible to believe that the craving for grit by the chicken is prompted by the desire to satisfy its mineral recjuirements. Under natural conditions the chicken is obliged to depend upon grit material for certain essential minerals and may instinctively eat or crave the grit even if adequate minerals are supplied from other sources.
GRIT REQUIREMENTS
293
SUMMARY
No benefit resulted from the use of grit (granite) in the case of baby chicks reared to 12 weeks of age or maturity in the three foregoing experiments. The groups of birds which did not receive grit appeared to utilize coarse ground feeds and whole corn and wheat as effectively as those that had free access to grit. The belief that grit is essential in the gizzard for grinding or reducing purposes in the case of growing chicks appears to be based on theory rather than facts. Grit may, however, serve an important function as a source of essential minerals if the ration is deficient in this respect.
Credit is due Mr. M. C. Kik for his assistance with the experiments herein reported.
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the digestive fluids of the alimentary tir,act are .the factors which determine the rate of growth and well-being .of a chick. It, therefore, appears that grit is not necessary in the dietary of a chick and that its presence in the gizzard is simply an incidental factor. Under natural environment the chicken is probably obliged to eat grit to satisfy its mineral requirements and instinctively clings to the practice under domesticated conditions where minerals are often supplied in the feed mixtures. Although the results of this study are not of great practical value, they, nevertheless, are of interest, in that they call attention to one of a number of traditional theories and practices in connection with poultry keeping which are not necessarily supported by facts.