- Email: [email protected]
The Relation of the Weight of Rhode Island Red Pullets at Four Weeks to their Subsequent Rate of Growth
THE RELATION OF THE WEIGHT OP RHODE ISLAND RED PULLETS AT FOUR W E E K S TO THEIR SUBSEQUENT RATE OF GROWTH D O N A L D C. H E N D E B S O N
(Received for Publication 2-2-28) The degree of relationship that exists between the weight of chickens at an early age and the subsequent rate of grow is an important factor in their early selection. Rate of growth, as used in this article, refers to the increase in weight of a bird relative to the time required to bring the increase. If chickens that are large early in their development continue to hold this advantage tip past the broiler stage we have a basis for the early elimination of the slow growing birds. A larger profit would be obtained through the early disposal of the birds that are below average weight if they could be sold with assurance that if carried along the greater per cent of them would be culled later in the season. At present, many commercial poultrymen follow the practice of disposing of the faster growing cockerels as broilers. If a positive relationship exists between the weight of chickens at an early age and the subsequent rate of increase in .weight, selection of the larger birds at an early age on the basis of weight would shorten the time required to bring the birds to this certain weight. The selected cockerels that are above average weight, if they continue to grow rapidly, would then be marked and kept for breeding purposes. The pullets that are above average weight would then be kept for fall egg production. Kennard 1 has shown that early maturing pullets (Leghorns) are more profitable than slow maturing pullets due to greater egg production and less mortality. More recently Kempster 2 reports that the shorter the time required to bring pullets into laying the higher the records they make. The following study was designed to show the relationship in the rate of growth of pullets by four week periods from four to sixteen weeks and the variability in the rate of growth. i Monthly Bulletin, Ohio Experiment Station. November-December 1921. Vol. VI, No's. 11 and 12, pp. 163-167. 2 Missouri Research Bulletin 78, July 1925. 181
182
POULTRY
SCIENCE
MATERIAL
Two hundred twenty-three single comb Rhode Island Red female chicks hatched and raised during the summer of 1925 by the division of poultry husbandry of the University of Illinois, were used in this study. These chicks were obtained from the matings of cockerels and pullets. All obviously weak chicks were eliminated at the time of hatching. Those kept were marked with individual wing bands. TABLE I HATCHING DATES
Hatching dates March 12 March 19 March 26 April 2 April 9
Number of chicks 52 33 41 39 58 223
All weights were taken at four, eight, twelve and sixteen weeks from the time of hatching. Where possible, the weighings were made between six and seven o'clock in the morning. Peed and water were withheld until after weighing. The crops were empty and the weighings made on the different dates were comparable for each period. As the chick increases in weight the capacity of the crop increases proportionately and the weight of the chick after feetling would be correspondingly greater for each successive period if feed and water were not withheld. The individual weight of chicks was obtained in grams and the data recorded to the nearest five grams for the first weighing and to the nearest ten grams for the following weighings. The hatching dates and the number of female chicks studied are given in Table I. DISCUSSION
,
The coefficients of variability, which are the best measures of the amount of variation, do not indicate any significant differences between the different groups. Jull 3 in a study of the sex growth curve in Barred Plymouth Rock chicks reports that the variability in the weekly mean weight for female chicks increases from the first to the fourth week, after which it rea Sci. Agr. pp. 58-65. 1923. •
GROWTH OF RHODE ISLAND
RED PULLETS
183
mains fairly constant u p to a n d including the twelfth week. J u l l also concludes t h a t the difference in the average weight of female and male chicks is not significant at any weekly period from hatching to eight weeks. T h a t is, the growth curve of pullets a n d cockerels is similar. The p o u l t r y m a n would not be able to divide his hatches of chicks into the two sexes at four weeks on the basis of weight. Mean weight
Jt weeks 150.24 ± 1.53
TABLE II 8 weeks 12 weeks 16 weeks 453.18 ± 4.96 797.08 ± 8.75 1083.32 ± 11.05
Range 60 —240 170 —710 280 —1230 Standard deviation • 33.96 ± 1.08 109.95 ± 3.51 193.80 ± 6.19 CoefC. of variability 22.6 ± .76 24.2 ± .82 24.3 ± .82
410
—1580
233.56 ±
7.81
22.5 ±
.75
This study indicates t h a t after the chick has passed the initial period of slow growth immediately after hatching, the amount of variation in weight within the groups from four to sixteen weeks, as measured by the s t a n d a r d deviation, increases in proportion to the increase in weight. The amount of variation in weight within a g r o u p is in almost exact proportion t o the increase in weight. The amount of variation relative to the mean weight for each period is therefore practically constant, as indicated by the coefficients of variability given in Table I I . The difference of four weeks, in the time of hatching p a r t l y accounts for the r a n g e in the weight of chicks at eight, twelve, and sixteen weeks since the growth of late hatched chicks is slower t h a n is the growth of early hatched chicks. This would make a higher coefficient of variability a t the later ages t h a n would be found in a n y single hatch. The relationship of the weights a t different ages d u r i n g the period of r a p i d growth, since the variation relative to the mean weight is constant, is an index of the r a t e growth. . I n computing the correlations, the female chicks a t each age were divided into classes on the basis of weight. I n selecting class intervals two objects were in m i n d ; viz. to secure practically the same n u m b e r of classes a n d to have class intervals t h a t were multiples of the same number. The class intervals used were fifteen grams or multiples of fifteen grams. The class
184
POULTRY
SCIENCE
interval for the weight at four weeks was fifteen grams, at eight weeks forty-five grams, at twelve weeks seventy-five grams, a n d a t sixteen weeks n i n e t y grams. Using the range in weight of chicks as given in the second line of Table I I and the class intervals of fifteen, forty-five, seventy-five a n d ninety grams for the weights at four, eight, twelve, and sixteen weeks we have twelve classes at four weeks, thirteen classes each at eight a n d twelve weeks, and fourteen classes at sixteen weeks. Latimer* in a s t u d y of Leghorn chickens found a correlation of .1042 ± .0344 between the hatching weight a n d the thirtyfive day weight in female chicks. I n this study the writer considered only the correlation of the weight of chicks a t four weeks of age with the weights at eight, twelve, a n d sixteen weeks since these correlations show the relationship t h a t exists between the weight of chicks at a n early age and the subsequent rate of growth. The correlation of the weights of chicks at eight weeks with the weights at twelve and sixteen weeks, and the weight at twelve weeks with the weight a t sixteen weeks, as given in the fourth, fifth, and sixth lines of Table I I I , are included to complete the series h u t are not considered in the conclusions. TABLE III Coefficients of Correlation Four and eight weeks Four and twelve weeks Four and sixteen weeks Eight and twelve weeks Eight and sixteen weeks Twelve and sixteen weeks
82 ± 74 ± 71 ± ± 87 ± 94 ±
.015 .020 .022 .010 .011 .005
Table I I I shows the degree of relationship in the weight of female Rhode Island R e d Chicks for four p e r i o d s ; namely, at four, eight, twelve, a n d sixteen weeks of age. The correlations are highly significant. The correlations of the weights of chicks at four a n d eight weeks, .82 ± .015, at four a n d twelve weeks, .74 ± .020, a n d at four a n d sixteen weeks, .71 ± .022 are from thirty-five to fifty times as g r e a t as their probable errors. If these results are to be taken as conclusive, a p o u l t r y m a n could divide a g r o u p of four week old chicks into the r a p i d and slow * American Naturalist Vol. LVIII, pp. 278-282.
GROWTH
OF RHODE
ISLAND
RED
PULLETS
185
growing classes on the basis of their relative weights. The female chicks that are above average weight at four weeks of age hold this advantage at eight, twelve and sixteen weeks. Conversely, the female chicks that are below average weight at four weeks of age are below average weight at eight, twelve and sixteen weeks of age. CONCLUSIONS
The variation in the weight of chicks relative to the mean weight remains nearly constant from four to sixteen weeks. The correlation of the weights of female chicks at four weeks and the weights at eight, twelve and sixteen weeks are positive and show that the chicks that are relatively large at four weeks are relatively large at eight, twelve and sixteen weeks, respectively.
(Received for Publication 2-2-28) The degree of relationship that exists between the weight of chickens at an early age and the subsequent rate of grow is an important factor in their early selection. Rate of growth, as used in this article, refers to the increase in weight of a bird relative to the time required to bring the increase. If chickens that are large early in their development continue to hold this advantage tip past the broiler stage we have a basis for the early elimination of the slow growing birds. A larger profit would be obtained through the early disposal of the birds that are below average weight if they could be sold with assurance that if carried along the greater per cent of them would be culled later in the season. At present, many commercial poultrymen follow the practice of disposing of the faster growing cockerels as broilers. If a positive relationship exists between the weight of chickens at an early age and the subsequent rate of increase in .weight, selection of the larger birds at an early age on the basis of weight would shorten the time required to bring the birds to this certain weight. The selected cockerels that are above average weight, if they continue to grow rapidly, would then be marked and kept for breeding purposes. The pullets that are above average weight would then be kept for fall egg production. Kennard 1 has shown that early maturing pullets (Leghorns) are more profitable than slow maturing pullets due to greater egg production and less mortality. More recently Kempster 2 reports that the shorter the time required to bring pullets into laying the higher the records they make. The following study was designed to show the relationship in the rate of growth of pullets by four week periods from four to sixteen weeks and the variability in the rate of growth. i Monthly Bulletin, Ohio Experiment Station. November-December 1921. Vol. VI, No's. 11 and 12, pp. 163-167. 2 Missouri Research Bulletin 78, July 1925. 181
182
POULTRY
SCIENCE
MATERIAL
Two hundred twenty-three single comb Rhode Island Red female chicks hatched and raised during the summer of 1925 by the division of poultry husbandry of the University of Illinois, were used in this study. These chicks were obtained from the matings of cockerels and pullets. All obviously weak chicks were eliminated at the time of hatching. Those kept were marked with individual wing bands. TABLE I HATCHING DATES
Hatching dates March 12 March 19 March 26 April 2 April 9
Number of chicks 52 33 41 39 58 223
All weights were taken at four, eight, twelve and sixteen weeks from the time of hatching. Where possible, the weighings were made between six and seven o'clock in the morning. Peed and water were withheld until after weighing. The crops were empty and the weighings made on the different dates were comparable for each period. As the chick increases in weight the capacity of the crop increases proportionately and the weight of the chick after feetling would be correspondingly greater for each successive period if feed and water were not withheld. The individual weight of chicks was obtained in grams and the data recorded to the nearest five grams for the first weighing and to the nearest ten grams for the following weighings. The hatching dates and the number of female chicks studied are given in Table I. DISCUSSION
,
The coefficients of variability, which are the best measures of the amount of variation, do not indicate any significant differences between the different groups. Jull 3 in a study of the sex growth curve in Barred Plymouth Rock chicks reports that the variability in the weekly mean weight for female chicks increases from the first to the fourth week, after which it rea Sci. Agr. pp. 58-65. 1923. •
GROWTH OF RHODE ISLAND
RED PULLETS
183
mains fairly constant u p to a n d including the twelfth week. J u l l also concludes t h a t the difference in the average weight of female and male chicks is not significant at any weekly period from hatching to eight weeks. T h a t is, the growth curve of pullets a n d cockerels is similar. The p o u l t r y m a n would not be able to divide his hatches of chicks into the two sexes at four weeks on the basis of weight. Mean weight
Jt weeks 150.24 ± 1.53
TABLE II 8 weeks 12 weeks 16 weeks 453.18 ± 4.96 797.08 ± 8.75 1083.32 ± 11.05
Range 60 —240 170 —710 280 —1230 Standard deviation • 33.96 ± 1.08 109.95 ± 3.51 193.80 ± 6.19 CoefC. of variability 22.6 ± .76 24.2 ± .82 24.3 ± .82
410
—1580
233.56 ±
7.81
22.5 ±
.75
This study indicates t h a t after the chick has passed the initial period of slow growth immediately after hatching, the amount of variation in weight within the groups from four to sixteen weeks, as measured by the s t a n d a r d deviation, increases in proportion to the increase in weight. The amount of variation in weight within a g r o u p is in almost exact proportion t o the increase in weight. The amount of variation relative to the mean weight for each period is therefore practically constant, as indicated by the coefficients of variability given in Table I I . The difference of four weeks, in the time of hatching p a r t l y accounts for the r a n g e in the weight of chicks at eight, twelve, and sixteen weeks since the growth of late hatched chicks is slower t h a n is the growth of early hatched chicks. This would make a higher coefficient of variability a t the later ages t h a n would be found in a n y single hatch. The relationship of the weights a t different ages d u r i n g the period of r a p i d growth, since the variation relative to the mean weight is constant, is an index of the r a t e growth. . I n computing the correlations, the female chicks a t each age were divided into classes on the basis of weight. I n selecting class intervals two objects were in m i n d ; viz. to secure practically the same n u m b e r of classes a n d to have class intervals t h a t were multiples of the same number. The class intervals used were fifteen grams or multiples of fifteen grams. The class
184
POULTRY
SCIENCE
interval for the weight at four weeks was fifteen grams, at eight weeks forty-five grams, at twelve weeks seventy-five grams, a n d a t sixteen weeks n i n e t y grams. Using the range in weight of chicks as given in the second line of Table I I and the class intervals of fifteen, forty-five, seventy-five a n d ninety grams for the weights at four, eight, twelve, and sixteen weeks we have twelve classes at four weeks, thirteen classes each at eight a n d twelve weeks, and fourteen classes at sixteen weeks. Latimer* in a s t u d y of Leghorn chickens found a correlation of .1042 ± .0344 between the hatching weight a n d the thirtyfive day weight in female chicks. I n this study the writer considered only the correlation of the weight of chicks a t four weeks of age with the weights at eight, twelve, a n d sixteen weeks since these correlations show the relationship t h a t exists between the weight of chicks at a n early age and the subsequent rate of growth. The correlation of the weights of chicks at eight weeks with the weights at twelve and sixteen weeks, and the weight at twelve weeks with the weight a t sixteen weeks, as given in the fourth, fifth, and sixth lines of Table I I I , are included to complete the series h u t are not considered in the conclusions. TABLE III Coefficients of Correlation Four and eight weeks Four and twelve weeks Four and sixteen weeks Eight and twelve weeks Eight and sixteen weeks Twelve and sixteen weeks
82 ± 74 ± 71 ± ± 87 ± 94 ±
.015 .020 .022 .010 .011 .005
Table I I I shows the degree of relationship in the weight of female Rhode Island R e d Chicks for four p e r i o d s ; namely, at four, eight, twelve, a n d sixteen weeks of age. The correlations are highly significant. The correlations of the weights of chicks at four a n d eight weeks, .82 ± .015, at four a n d twelve weeks, .74 ± .020, a n d at four a n d sixteen weeks, .71 ± .022 are from thirty-five to fifty times as g r e a t as their probable errors. If these results are to be taken as conclusive, a p o u l t r y m a n could divide a g r o u p of four week old chicks into the r a p i d and slow * American Naturalist Vol. LVIII, pp. 278-282.
GROWTH
OF RHODE
ISLAND
RED
PULLETS
185
growing classes on the basis of their relative weights. The female chicks that are above average weight at four weeks of age hold this advantage at eight, twelve and sixteen weeks. Conversely, the female chicks that are below average weight at four weeks of age are below average weight at eight, twelve and sixteen weeks of age. CONCLUSIONS
The variation in the weight of chicks relative to the mean weight remains nearly constant from four to sixteen weeks. The correlation of the weights of female chicks at four weeks and the weights at eight, twelve and sixteen weeks are positive and show that the chicks that are relatively large at four weeks are relatively large at eight, twelve and sixteen weeks, respectively.