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The Use of Part Records on Age at First Egg and Survivors Egg Production to Estimate Means, Heritabilities and Genetic Correlations1
THE USE OF PART RECORDS ON AGE AT FIRST EGG AND SURVIVORS EGG PRODUCTION TO ESTIMATE MEANS, HERITABILITIES AND GENETIC CORRELATIONS1 T. B. KINNEY, JR. AND P. C. LOWE United Slates Department of Agriculture and Purdue University Agricultural Experiment Station, Lafayette, Indiana 47907 (Received for publication August 4, 1967)
Journal Paper No. 3139 of the Purdue University Agricultural Experiment Station. 1 This investigation was conducted as a portion of the cooperative research of the NC-47 Regional Poultry Breeding Project entitled "Evaluation of Breeding Systems for Chickens."
ones. Oliver et al. (1956) recognized three day per week trapnesting as a cause of bias in the estimation of age at maturity. It would appear that the correlation between age at maturity and egg production might be biased downward since the upward bias in sexual maturity will be greater for the poor producers than for the better layers. It was the purpose of this study to compare estimates of the means, heritabilities and genetic correlations for days of age at first egg, survivor egg production to 300 or 450 days from three and five day trapnest records with that of the full record taken from 7 day trapnest records. The data utilized in this study were obtained over a four year period from a total of 717 progeny of 32 sires and 211 dams. The birds were trapnested seven days per week. Three and five day trapnest records and age at sexual maturity were obtained by assuming the first three or five days of each week to be trap days. The weighted means for age at first egg, survivor egg production to 300 days of age and 450 days of age as estimated by three, five and seven day trapnest records are presented in Table 1. The estimate of days to
TABLE 1.—Means and standard errors for age at maturity, 300 and 450 day production based on three, five and seven day trapnest records Number of trap days per week Trait 5-Day
3-Day Age at Sex. Mat. 300-Day Production 450-Day Production
179.6+ .68 56.2+ .63 123.1±1.07
181.8+.71 34.0+.38 74.5+.65
1593
7-Day 178.5+ .67 74.5+ .65 169.3 + 1.49
Downloaded from http://ps.oxfordjournals.org/ at University of Queensland on June 23, 2015
Many investigators have reported a high positive correlation between the full egg production record and any of its parts. Olsen (1939) suggested that one day per week trapnest records, throughout the production period were adequate for the estimation of annual egg production. Schnetzler (1948) suggested that four, five or six day per week trapnesting was sufficiently accurate for estimation of egg production in breeding programs. Nordskog (1948), Wheat and Lush (1961) and others have investigated the use of part records on the estimation of breeding values for egg production. Another economic trait of interest to poultry breeders is age at first egg. Estimates of this trait will always be biased upward when estimated from part records simply because the chance of missing the first egg on a three- or five-day trap is much greater for poor layers than for good
1S94
RESEARCH NOTES
. ' spectively.
J
When one estimates genetic parameters from part records he is hopefully obtaining reliable estimates of the parameters for a complete (seven day) record. If the purpose of the estimate is to simply categorize the heritabilities or genetic correlations as high, medium or low, then a considerable difference in the point estimates would be of little consequence. If, however, the estimates are to be used for prediction, index calculation or some other specific genetic evaluation, unbiasedness and accuracy are critical. The results of this study indicate that there is no significant difference between
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Downloaded from http://ps.oxfordjournals.org/ at University of Queensland on June 23, 2015
sexual maturity (181.8) is significantly larger for the three day trap record than for the seven-day trap record (178.5). The difference of approximately three days is probably of little practical significance. The estimate based on a five day trapnest record does not differ significantly from the estimates based on three day or seven day trapnest records. Estimates of heritabilities and genetic correlations were obtained by pooling sums of squares and cross products from nested analyses of variance and covariance conducted on data from each of the four years. These estimates are presented in Table 2. No significant difference between the heritability or genetic correlation estimates from the three, five or seven day trapnest records were found. For each of the three traits, the genetic correlations between estimates of the trait obtained from three, five and seven-day records are close to one. Of particular interest are the estimated genetic correlations between days of age at sexual maturity and survivor production to 300 and 450 days. There is little difference in the estimates of the genetic correlation between age at sexual maturity and production to either 300 or 450 days of age for the three, five and seven day records re-
RESEARCH NOTES
ACKNOWLEDGMENT
The authors wish to express appreciation to Dr. A. B. Stephenson of the Department of Poultry Science, University of Missouri
for providing the basic data utilized in this study. REFERENCES Nordskog, A. W., 1948. Periodical trapnesting and family selection for egg production. Poultry Sci. 27: 713-718. Oliver, M. M., B. B. Bohren and V. L. Anderson, 1956. Heritability and selection efficiency of several measures of egg production. Poultry Sci. 36:395-402. Olsen, M. W., 1939. The value of periodical trapnesting. Poultry Sci. 18: 232-235. Schnetzler, E. E., 1941. Accuracy of short-internal trap-nesting of the fowl. Poultry Sci. 2 1 : 551555. Wheat, J. D., and Lush, J. L., 1961. Accuracy of partial trapnest records. 1. Repeatability of daily egg records. Poultry Sci. 40: 399-406.
DIFFERENTIATION OF AVIAN THROMBOCYTES FROM LEUKOCYTES BY USE OF GIEMSA'S STAIN T. K. S. MUKKUR AND R. E. BRADLEY Department of Veterinary Science, University of Florida, Gainesville, Florida 32603 (Received for publication August 15, 1967)
In the course of investigation of the leukocytic response to artificial infections with Eimeria tenella in chickens, considerable difficulty was encountered in the differentiation of thrombocytes from small lymphocytes. Initially blood films for differential counting were prepared in the conventional manner and stained by Wright's Method, as described by Lucas and Jamroz (1961). In the microscopic examination of films stained by this method, monocytes, large lymphocytes, and polymorphonuclear cells were easily distinguished. However, thrombocytes and small lymphocytes were often confused, in spite of close adherence to the diagnostic criteria for these cells as set forth by Lucas and Jamroz (1961). In view of the unsatisfactory results with Florida Agricultural Experiment Stations Journal Series No. 2741.
Wright's stain, an alternate method was sought. The high degree of cellular differentiation reported for Giemsa's stain when used for blood parasites led to the investigation of the use of this method as a routine blood film-staining procedure. Blood films were prepared within 30 minutes of collection from samples obtained by cardiac puncture of experimental chickens (28-83 days of age), using EDTA as an anticoagulant. After fixation in methyl alcohol for five minutes, films were airdried and then immersed in an aqueous solution of Giemsa's stain (1:50 in distilled water; pH 7.0) for 8 hours. Upon completion of the staining time, the films were washed with tap water, plotted dry on bibulous paper, and examined under the microscope by the use of an oil immersion objective (970 X magnification).
Downloaded from http://ps.oxfordjournals.org/ at University of Queensland on June 23, 2015
heritability or genetic correlation estimates for days to first egg and survivor production to 300 or 450 days of age as estimated from three, five or seven day per week trapnest records. However, the standard errors of heritability or genetic correlation estimates obtained in this study are very large. Further study with a larger volume of data seems justified in order to more critically determine the reliability of parameter estimates obtained from part records.
1595
Journal Paper No. 3139 of the Purdue University Agricultural Experiment Station. 1 This investigation was conducted as a portion of the cooperative research of the NC-47 Regional Poultry Breeding Project entitled "Evaluation of Breeding Systems for Chickens."
ones. Oliver et al. (1956) recognized three day per week trapnesting as a cause of bias in the estimation of age at maturity. It would appear that the correlation between age at maturity and egg production might be biased downward since the upward bias in sexual maturity will be greater for the poor producers than for the better layers. It was the purpose of this study to compare estimates of the means, heritabilities and genetic correlations for days of age at first egg, survivor egg production to 300 or 450 days from three and five day trapnest records with that of the full record taken from 7 day trapnest records. The data utilized in this study were obtained over a four year period from a total of 717 progeny of 32 sires and 211 dams. The birds were trapnested seven days per week. Three and five day trapnest records and age at sexual maturity were obtained by assuming the first three or five days of each week to be trap days. The weighted means for age at first egg, survivor egg production to 300 days of age and 450 days of age as estimated by three, five and seven day trapnest records are presented in Table 1. The estimate of days to
TABLE 1.—Means and standard errors for age at maturity, 300 and 450 day production based on three, five and seven day trapnest records Number of trap days per week Trait 5-Day
3-Day Age at Sex. Mat. 300-Day Production 450-Day Production
179.6+ .68 56.2+ .63 123.1±1.07
181.8+.71 34.0+.38 74.5+.65
1593
7-Day 178.5+ .67 74.5+ .65 169.3 + 1.49
Downloaded from http://ps.oxfordjournals.org/ at University of Queensland on June 23, 2015
Many investigators have reported a high positive correlation between the full egg production record and any of its parts. Olsen (1939) suggested that one day per week trapnest records, throughout the production period were adequate for the estimation of annual egg production. Schnetzler (1948) suggested that four, five or six day per week trapnesting was sufficiently accurate for estimation of egg production in breeding programs. Nordskog (1948), Wheat and Lush (1961) and others have investigated the use of part records on the estimation of breeding values for egg production. Another economic trait of interest to poultry breeders is age at first egg. Estimates of this trait will always be biased upward when estimated from part records simply because the chance of missing the first egg on a three- or five-day trap is much greater for poor layers than for good
1S94
RESEARCH NOTES
. ' spectively.
J
When one estimates genetic parameters from part records he is hopefully obtaining reliable estimates of the parameters for a complete (seven day) record. If the purpose of the estimate is to simply categorize the heritabilities or genetic correlations as high, medium or low, then a considerable difference in the point estimates would be of little consequence. If, however, the estimates are to be used for prediction, index calculation or some other specific genetic evaluation, unbiasedness and accuracy are critical. The results of this study indicate that there is no significant difference between
O 13
| §2^ 21 av Q 2 S?| ^ g •§ g> 13 o |1|
II
"g f §^ Hi.§ aa &•%
| .•§> '-§ 'g T <^ g H
Downloaded from http://ps.oxfordjournals.org/ at University of Queensland on June 23, 2015
sexual maturity (181.8) is significantly larger for the three day trap record than for the seven-day trap record (178.5). The difference of approximately three days is probably of little practical significance. The estimate based on a five day trapnest record does not differ significantly from the estimates based on three day or seven day trapnest records. Estimates of heritabilities and genetic correlations were obtained by pooling sums of squares and cross products from nested analyses of variance and covariance conducted on data from each of the four years. These estimates are presented in Table 2. No significant difference between the heritability or genetic correlation estimates from the three, five or seven day trapnest records were found. For each of the three traits, the genetic correlations between estimates of the trait obtained from three, five and seven-day records are close to one. Of particular interest are the estimated genetic correlations between days of age at sexual maturity and survivor production to 300 and 450 days. There is little difference in the estimates of the genetic correlation between age at sexual maturity and production to either 300 or 450 days of age for the three, five and seven day records re-
RESEARCH NOTES
ACKNOWLEDGMENT
The authors wish to express appreciation to Dr. A. B. Stephenson of the Department of Poultry Science, University of Missouri
for providing the basic data utilized in this study. REFERENCES Nordskog, A. W., 1948. Periodical trapnesting and family selection for egg production. Poultry Sci. 27: 713-718. Oliver, M. M., B. B. Bohren and V. L. Anderson, 1956. Heritability and selection efficiency of several measures of egg production. Poultry Sci. 36:395-402. Olsen, M. W., 1939. The value of periodical trapnesting. Poultry Sci. 18: 232-235. Schnetzler, E. E., 1941. Accuracy of short-internal trap-nesting of the fowl. Poultry Sci. 2 1 : 551555. Wheat, J. D., and Lush, J. L., 1961. Accuracy of partial trapnest records. 1. Repeatability of daily egg records. Poultry Sci. 40: 399-406.
DIFFERENTIATION OF AVIAN THROMBOCYTES FROM LEUKOCYTES BY USE OF GIEMSA'S STAIN T. K. S. MUKKUR AND R. E. BRADLEY Department of Veterinary Science, University of Florida, Gainesville, Florida 32603 (Received for publication August 15, 1967)
In the course of investigation of the leukocytic response to artificial infections with Eimeria tenella in chickens, considerable difficulty was encountered in the differentiation of thrombocytes from small lymphocytes. Initially blood films for differential counting were prepared in the conventional manner and stained by Wright's Method, as described by Lucas and Jamroz (1961). In the microscopic examination of films stained by this method, monocytes, large lymphocytes, and polymorphonuclear cells were easily distinguished. However, thrombocytes and small lymphocytes were often confused, in spite of close adherence to the diagnostic criteria for these cells as set forth by Lucas and Jamroz (1961). In view of the unsatisfactory results with Florida Agricultural Experiment Stations Journal Series No. 2741.
Wright's stain, an alternate method was sought. The high degree of cellular differentiation reported for Giemsa's stain when used for blood parasites led to the investigation of the use of this method as a routine blood film-staining procedure. Blood films were prepared within 30 minutes of collection from samples obtained by cardiac puncture of experimental chickens (28-83 days of age), using EDTA as an anticoagulant. After fixation in methyl alcohol for five minutes, films were airdried and then immersed in an aqueous solution of Giemsa's stain (1:50 in distilled water; pH 7.0) for 8 hours. Upon completion of the staining time, the films were washed with tap water, plotted dry on bibulous paper, and examined under the microscope by the use of an oil immersion objective (970 X magnification).
Downloaded from http://ps.oxfordjournals.org/ at University of Queensland on June 23, 2015
heritability or genetic correlation estimates for days to first egg and survivor production to 300 or 450 days of age as estimated from three, five or seven day per week trapnest records. However, the standard errors of heritability or genetic correlation estimates obtained in this study are very large. Further study with a larger volume of data seems justified in order to more critically determine the reliability of parameter estimates obtained from part records.
1595