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One-Week Body Weight and Bi-Weekly Early Growth Rate as Related to 7-Week Body Weight in the Chicken
AMINO ACID SUPPLEMENTS AND PRODUCTION National Research Council, 1954. Nutrient requirement for domestic animals. No. 1 Nutrient requirements for poultry. National Research Council, 1960. Nutrient requirements for domestic animals. No. 1 Nutrient requirements for poultry.
947
Sunde, M. L., 1962. Amino acids, proteins and stuff. Poultry Sci. 4 1 : 1688. Waibel, P. E., R. C, Fitzsimmons and D. C. Snetsinger, 1961. Amino acid supplementation of corn meal when used as the sole source of protein in laying rations. Poultry Sci. 40: 1466.
One-Week Body Weight and Bi-Weekly Early Growth Rate as Related to 7-Week Body Weight in the Chicken C.
W.
ROBERTS
Poultry Genetics Laboratory, The University of British Columbia, Vancouver 8, B.C., Canada (Received for publication November 16, 1964)
OBERTS (1964) showed that prepubertal weekly growth rate, based on the power function y = atb, approached linearity from hatch to 7 weeks of age. It was further shown, via multiple linear regression, that the combination of the average of these weekly growth rates (7 week growth rate) and hatching weight accounted for 71% to 83% of the variability of 7-week body weight in the four lines studied, but the contribution of hatching weight towards this variability was only one-half that of 7-week growth rate. Therefore it was decided to ascertain if there would be an increase in the proportion of variability accounted for when 1-week body weight was substituted for hatching weight in the aforementioned relationship.
R
ronmental test building. The hatches were arranged so that approximately a 2-week interval occurred between the first two and the latter two hatches. Slightly more than 7 weeks elapsed between the second and the third hatch. Individual body weights were taken at 1, 3, 5 and 7 weeks of age. The sex was recorded and the trial terminated. At 2 weeks of age the birds were given an ocular bronchitis and Newcastle vaccine. The birds were reared on a starter ration whose chief source of grain was Number 1 wheat screenings. Both feed and water were fed ad libitum. The growth rate for the experimental period was based on the average of the bi-weekly growth periods: 1-3, 3-5 and 5-7 weeks. The individual body weights, bi-weekly growth rates and the overall growth rates of each sex were then subjected to analysis.
MATERIALS AND METHODS
The chicks from a single day's collection of eggs from a random-bred population of New Hampshires were used as the experimental material. From each of four hatches 128 straight-run chicks were individually banded, and randomly distributed throughout one-half of eight locations in an envi-
BODY WEIGHT AND GROWTH RATE ANALYSIS The following statistical model was assumed to describe the body weight of each individual at four ages in the four analyses of variance: ySj = n + hi + e^. The hatch effect: h(i = 1 — 4) was assumed
948
C. W. ROBERTS
TABLE 1.—The average body weights in grams of the experiment by sex and hatch
Snedecor, 1956) for the aforementioned traits.
Weeks of Age Hatch
(N) 1
3
5
7
1 2 3 4 Mean
75 76 83 71 76
(Males) 252 544 256 517 262 554 252 523 256 534
886 885 948 897 904
58 59 55 65 237
1 2 3 4 Mean
74 73 78 71 74
(Females) 226 461 229 451 226 460 225 449 226 455
729 758 756 728 743
68 65 66 59 258
to be fixed and the residual effect of individuals within hatches was assumed to be random. The model used to describe each of the three bi-weekly growth periods for each individual was b mn = n + hm + emn. The hatch effect: h(m = 1 — 4 ) was assumed to be fixed and the residual effect assumed to be random. The simple correlations of 7-week body weight with the following traits were calculated for each hatch; 1-week body weight. the three bi-weekly growth rates and the growth rate for the experimental period. In addition the sample partial correlation coefficients were also calculated (after TABLE 2.—The average bi-weekly growth rates and the growth rate for the experimental period by sex and hatch Bi-Weekly Growth Rate 1-3
3-5
5-7
Growth Rate
1 2 3 4 Mean
2.97 3.00 2.84 3.11 2.98
(Males) 2.67 2.44 2.59 2.53 2.56
2.19 2.40 2.41 2.42 2.36
2.61 2.61 2.61 2.68 2.63
1 2 3 4 Mean
2.74 2.80 2.62 2.84 2.75
(Females) 2.47 2.34 2.48 2.40 2.42
2.06 2.34 2.22 2.18 2.20
2.42 2.49 2.44 2.47 2.46
Hatch
BODY WEIGHT AND GROWTH RATERESULTS AND DISCUSSION The average bi-weekly body weights and growth rates for each bi-weekly growth period as well as the growth rate for the experimental period are presented by sex in Tables 1 and 2. The 7-week body weight of the males in hatches 3 and 4 was superior to their contemporaries, while for the females, hatches 2 and 3 were superior (Table 1). The males in hatch 4 and the females in hatches 2 and 4 showed a superior growth rate for the experimental period (Table 2). The analyses of variance (Table 3) of the male and female bi-weekly body weights showed that for males there were highly significant differences among hatches in all but the 3-week age level. The females showed a highly significant difference at 1 week, and not until the seventh week did the hatch effect attain a level of significance (probability < 0.05). The analyses of variance of bi-weekly growth rates (Table 4) indicated highly significant differences existed between hatches for both sexes throughout the three growth periods. The mean of the bi-weekly growth rates deTABLE 3.—Body weight analyses of variance for hatch effects by sex
S.V.
d.f.
Percentage Sums of Squares (Weeks of Age) 1
Hatch Error Total
3 233 236
Hatch Error Total
3 254 257
3
5
7
(Males) 17.6** 2.1 5.8** 82.4 97.9 94.2
6.6** 93.4
(Females) 10.6** 0.7 1.8 89.4 99.3 98.2
3.7* 96.3
* Significant (P<0.05). ** Highly Significant (P<0.01).
949
EARLY GROWTH RATE
creased from the first to the last period: males (2.98 to 2.36), females (2.75 to 2.20) (Table 2). The cause for the reduction of these values is unknown, however, it is suspected that the diet had a considerable influence. It is also suspected that an environmental effect, evidenced by the loss of significance of the hatch effects in the body weight analyses of both sexes at the third week of age, was produced by the subsequent "take" of the vaccination of the birds at 2 weeks of age. The percentage sums of squares for hatches suggested that males recovered more quickly than did the females (Table 3). Possibly sexual dimorphism exists in recovery rates following vaccinations. It is of interest to note the failure of the body weight analysis to distinguish the hatch effects at the beginning and at the end of the highly significant 3 to 5-week growth period of the females. The reduction in the hatch effect percentage sums of squares of the bi-weekly growth periods (Table 4) was not as great as in the body weight analyses (Table 3). This shows that an environmental effect influencing the analysis of growth rate, in one period, is not expressed as severely in the analysis of the following growth rate period, while the same effect measured in terms of body weight is accumulative and could be expected to influence a later analysis. The difference appears to be attributable to the influence on the variability of the error terms. The variability for growth rate of individuals within hatches was not increased as much as the analogous body weight error terms. However, some reduction in the percentage sums of squares for hatches in both analyses is noted for both sexes during the 3 to 5-week growth period. The subsequent increase of these values for the last growth period indicated that some effect had influenced growth. The simple correlation of 7-week body
TABLE 4.—Bi-weekly growth rate analyses of variance for hatch ejects by sex
s.v.
d.f.
Percentage Sums of Squares (Bi-Weekly Periods) 1-3
Hatch Error Total
3 233 236
Hatch Error Total
3 254 257
3-5
5-7
(Males) 15.8** 10.0** 84.2 90.0
11.6** 88.4
(Females) 12.0** 6.0** 88.0 94.0
14.3** 85.7
Highly Significant (P<0.01).
weight with each bi-weekly growth rate and with 1-week body weight are shown in Table 5. With the exception of the males in the first hatch the simple correlations between the first growth period and 7-week body weight of males and females were of the same general magnitude and direction as those between 1-week and 7-week body weight. Furthermore, the correlations between the 3 to 5-week growth period of the males in the latter three hatches and 7-week body weight were of the same general level. The females however, did not reflect the male response for that period. For both sexes the correlations between 7-week body weight and the growth rate between 5 and 7-weeks of age were for the most part low, non-significant and undirectional. This supports an earlier conclusion (Roberts, 1964) that growth rate, although calculated from body weight, is a distinct trait. The simple correlation between the growth rate for the experimental period and 7-week body weight is also presented in Table 5. In general these values were higher and less variable than those using bi-weekly growth rates. Since 7-week body weight has been considered as resulting from the combined traits, 1-week body weight and the three successive bi-weekly growth rates, the
950
C. W. ROBERTS
TABLE 5.—The simple correlation coefficients of the bi-weekly growth rates, the growth rate for the experimental period and 1-week body weight with 7-week body weight, by sex hatch Simple Correlation Hatch
Growth Rate
1-Week Body Weight
(Males) -.06 .29* -.20 .12
.16 .62** .45** .45**
.61** .30* 51** .46**
(Females) -.10 -.23 .17 -.25f
.53** .35** .33** .33**
.53** .48** .66** .45**
Bi-Weekly Period 1-3
3-5
1 2 3 4
.15 .34** .44** .36**
.12 .42** .48** .33**
1 2 3 4
.64** .51** .29* .49**
.24* .17 .04 .29*
5-7
* Significant (P<0.05). ** Highly Significant (P<0.01). f Approaching Significance.
third order sample partial correlation coefficients as well as the multiple correlation coefficient for the aforementioned traits were calculated (Table 6). It is not unexpected that each of these traits was able to successfully account for all of the residual variability of 7-week body weight, when all of the other traits were held constant. Together they were able to explain essentially all of the variation in 7-week body weight. When the growth rate for the experimental period was substituted for the three bi-weekly growth rates (Table 7), the reduction in the multiple correlation coefficient was apTABLE 6.—The sample partial correlation coefficients of the bi-weekly growth rates and 1-week body weight with 7-week body weight, by sex and hatch
proximately .05. The multiple correlation coefficient indicated that over 90 percent of the variability of 7-week body weight was explained by the combination of 1-week body weight and the growth rate for the experimental period. The average sample partial correlation values for the two sexes were of the same magnitude, and showed that each trait explained most of the variability of 7-week body weight, when the other was held constant. It should be pointed out that this high correlative value was achieved in spite of the general decline of bi-weekly growth rates, and possibly in spite of an adverse environmental effect. These results indicate that 7-week body weight can be successfully partitioned into two component traits, and that these two traits combined account for a substantial portion of the total variation of 7-week body weight. The influence of these two traits, growth rate and 1-week body weight, on 7-week body weight can be ascertained for each individual in the test population. Table 8 shows the distribution of individuals above or below the hatch average with respect to TABLE 7.—The sample partial correlation coefficients of the growth rate over the experimental period and 1-week body weight with 7-week body weight, by sex and hatch Sample Partial Correlation Hatch
Growth Rate
Bi -Weekly Period 1-3
1-Week - Body Weight
Multiple Correlation Coefficient
3-5
5-7
.99 1.00 .99 .99
.99 1.00 1.00 1.00
.99 .99 1.00 .99
.99 1.00 1.00 1.00
1 2 3 4
.99 .99 .99 .99
.98 .99 .98 .99
(Males) .95 .99 .97 .98
1 2 3 4
.99 .99 .99 .99
.97 .98 .98 .98
(Females) .96 .97 .98 .96
Multiple Correlation Coefficient
1 2 3 4 Average
.93 .95 .95 .96 .95
(Males) .96 .92 .97 .96 .95
.96 .95 .97 .97 .96
1 2 3 4 Average
.96 .93 .94 .94 .94
(Females) .96 .94 .96 .95 .95
.97 .95 .96 .95 .95
Sample Partial Correlation Hatch
1-Week Body Weight
951
EARLY GROWTH RATE
7-week body weight, 1-week body weight, and growth rate for the experimental period. There were 127 males from the four hatches whose body weights at 7 weeks were above the average of their respective hatches. Of these, 40 had an above average 1-week body weight and an above average growth rate (Group A). However 45 males attained the upper 50 percent level by having only an above average 1-week body weight (Group B), and 42 attained the same level by having only an above average growth rate (Group C). The respective values for the 134 females with above average 7-week body weight were: Group A (46), Group B (52) and Group C (36). Only two males gave incongruous results, in that the calculated values showed that they were below the average 7-week body weight while the other two traits were above average. In one case the values were extremely close to the means of their respective hatches, while in the other case sampling errors appeared to be a factor. While the observed frequencies of Groups A, B and C may provide a tempting measure for speculation it must be remembered that the individuals under test were from a random breeding population of New Hampshires. These birds have been maintained without directional selection for at least 10 years, and the reproductive unit has been from 300 to 600 females. It would be reasonable to expect that in selected populations the frequencies of these three groups would change. However in spite of prior selection for body weight it could be assumed that a significant proportion of the individuals selected had attained the selective level by having either a faster growth rate or an above average 1-week body weight. At this time it can only be speculated as to the effect which the aforementioned individuals would have on the subsequent gain of their progeny as compared to the selection differential. It
TABLE 8.—The distribution of individuals by sex as related to their position above or below the hatch average for each of the following traits: 7-week body weight, 1-week body weight and growth rate for the experimental • 7-Week Body Weight Above Hatch Average Group* A
B
C
D
N
1 2 3 4 Total
10 10 10 10 40
(Males) 14 7 9 14 13 11 9 10 45 42
0 0 0 0 0
127
1 2 3 4 Total
14 12 12 8 46
(Females) 16 9 9 11 16 7 11 9 52 36
0 0 0 0 0
134
7-Week Body Weight Below Hatch Average Group A
B
C
D
N
1 2 3 4 Total
0 2 0 0 2
(Males) 8 9 6 8 3 7 8 15 25 39
10 10 11 13 44
110
1 2 3 4 Total
0 0 0 0 0
(Females) 11 9 9 13 7 12 9 13 36 47
9 11 12 9 41
124
Group A—one-week body weight and growth rate above mean. B—one-week body weight above mean. C—growth rate above mean. D—neither trait above mean.
would be reasonable to assume that a faster rate of progress could be made if those selected individuals were above the average for both of these traits. SUMMARY A total of 495 random bred, New Hampshire chicks from four hatches were evaluated for the following traits: 1, 3, 5 and 7-week body weight, the three biweekly growth rates and the growth rate
952
C. W. ROBERTS
for the experimental period. The simple correlations of 7-week body weight with each of the three bi-weekly growth rates and with growth rates for the experimental period were calculated. In addition the sample partial correlation coefficients were also evaluated for the aforementioned traits. The data showed that 1-week body weight when combined with the growth rate for the experimental period accounted for over 90 percent of the variability of 7-week body weight. Furthermore it was shown that either of these two traits, when the other is held constant, will account for a substantial proportion of the heretofore unexplained residual variation of 7-week body weight.
The influence of the above results on a selection program for body weight was discussed. ACKNOWLED GMENTS The author wishes to thank the National Research Council of Canada for the financial assistance to conduct this study. The author is also indebted to Mr. H. W. Ellis, Superintendent of the Poultry Farm, and Mr. R. Wagner for their contributions to this study. REFERENCES Roberts, C. W., 1964. Estimation of early growth rate in the chicken. Poultry Sci. 43: 238-252. Snedecor, G. W., 1956. Statistical Methods. 5th Ed., Iowa State College Press, Ames, Iowa.
Effect of Processing on Bacteria Associated with Turkey Giblets R. H. SALZER,1 A. A. KRAFT AND J. C. AYRES Department of Dairy and Food Industry, Iowa State University, Ames, Iowa (Received for publication November 23, 1964)
T
HE effect of flowing water in reducing bacterial populations on the surfaces of poultry has been demonstrated by several workers. Gunderson et al. (1946) found that washing birds after they were eviscerated reduced the total bacterial count, but did not eliminate coliforms. According to May (1961), the transfer sta-
Journal Paper No. J-4990 of the Iowa Agricultural and Home Economics Experiment Station, Ames, Iowa. Project No. 1392, Center for Agricultural and Economic Development Cooperating. This investigation was supported in part by PHS research grant EF-00113-10 from the Division of Environmental Engineering and Food Protection, Public Health Service. 'Present address: Kellogg Co., Battle Creek, Mich.
tion for moving chicken carcasses from the picking to the evisceration line was the most consistent source of increases in bacterial counts, probably because there were no hand washing facilities at this station. He also found that final washing by a spray washer after evisceration reduced total counts significantly. Kotula et al. (1962) noted that a significant decrease occurred in bacterial populations on the skin of chickens chilled in a continuous counterflow-tumbler chiller. This was believed to be due to the fact that fresh coolant was added to the chill unit and water overflowed continuously from the chiller, resulting in dilution and removal of bacteria.
947
Sunde, M. L., 1962. Amino acids, proteins and stuff. Poultry Sci. 4 1 : 1688. Waibel, P. E., R. C, Fitzsimmons and D. C. Snetsinger, 1961. Amino acid supplementation of corn meal when used as the sole source of protein in laying rations. Poultry Sci. 40: 1466.
One-Week Body Weight and Bi-Weekly Early Growth Rate as Related to 7-Week Body Weight in the Chicken C.
W.
ROBERTS
Poultry Genetics Laboratory, The University of British Columbia, Vancouver 8, B.C., Canada (Received for publication November 16, 1964)
OBERTS (1964) showed that prepubertal weekly growth rate, based on the power function y = atb, approached linearity from hatch to 7 weeks of age. It was further shown, via multiple linear regression, that the combination of the average of these weekly growth rates (7 week growth rate) and hatching weight accounted for 71% to 83% of the variability of 7-week body weight in the four lines studied, but the contribution of hatching weight towards this variability was only one-half that of 7-week growth rate. Therefore it was decided to ascertain if there would be an increase in the proportion of variability accounted for when 1-week body weight was substituted for hatching weight in the aforementioned relationship.
R
ronmental test building. The hatches were arranged so that approximately a 2-week interval occurred between the first two and the latter two hatches. Slightly more than 7 weeks elapsed between the second and the third hatch. Individual body weights were taken at 1, 3, 5 and 7 weeks of age. The sex was recorded and the trial terminated. At 2 weeks of age the birds were given an ocular bronchitis and Newcastle vaccine. The birds were reared on a starter ration whose chief source of grain was Number 1 wheat screenings. Both feed and water were fed ad libitum. The growth rate for the experimental period was based on the average of the bi-weekly growth periods: 1-3, 3-5 and 5-7 weeks. The individual body weights, bi-weekly growth rates and the overall growth rates of each sex were then subjected to analysis.
MATERIALS AND METHODS
The chicks from a single day's collection of eggs from a random-bred population of New Hampshires were used as the experimental material. From each of four hatches 128 straight-run chicks were individually banded, and randomly distributed throughout one-half of eight locations in an envi-
BODY WEIGHT AND GROWTH RATE ANALYSIS The following statistical model was assumed to describe the body weight of each individual at four ages in the four analyses of variance: ySj = n + hi + e^. The hatch effect: h(i = 1 — 4) was assumed
948
C. W. ROBERTS
TABLE 1.—The average body weights in grams of the experiment by sex and hatch
Snedecor, 1956) for the aforementioned traits.
Weeks of Age Hatch
(N) 1
3
5
7
1 2 3 4 Mean
75 76 83 71 76
(Males) 252 544 256 517 262 554 252 523 256 534
886 885 948 897 904
58 59 55 65 237
1 2 3 4 Mean
74 73 78 71 74
(Females) 226 461 229 451 226 460 225 449 226 455
729 758 756 728 743
68 65 66 59 258
to be fixed and the residual effect of individuals within hatches was assumed to be random. The model used to describe each of the three bi-weekly growth periods for each individual was b mn = n + hm + emn. The hatch effect: h(m = 1 — 4 ) was assumed to be fixed and the residual effect assumed to be random. The simple correlations of 7-week body weight with the following traits were calculated for each hatch; 1-week body weight. the three bi-weekly growth rates and the growth rate for the experimental period. In addition the sample partial correlation coefficients were also calculated (after TABLE 2.—The average bi-weekly growth rates and the growth rate for the experimental period by sex and hatch Bi-Weekly Growth Rate 1-3
3-5
5-7
Growth Rate
1 2 3 4 Mean
2.97 3.00 2.84 3.11 2.98
(Males) 2.67 2.44 2.59 2.53 2.56
2.19 2.40 2.41 2.42 2.36
2.61 2.61 2.61 2.68 2.63
1 2 3 4 Mean
2.74 2.80 2.62 2.84 2.75
(Females) 2.47 2.34 2.48 2.40 2.42
2.06 2.34 2.22 2.18 2.20
2.42 2.49 2.44 2.47 2.46
Hatch
BODY WEIGHT AND GROWTH RATERESULTS AND DISCUSSION The average bi-weekly body weights and growth rates for each bi-weekly growth period as well as the growth rate for the experimental period are presented by sex in Tables 1 and 2. The 7-week body weight of the males in hatches 3 and 4 was superior to their contemporaries, while for the females, hatches 2 and 3 were superior (Table 1). The males in hatch 4 and the females in hatches 2 and 4 showed a superior growth rate for the experimental period (Table 2). The analyses of variance (Table 3) of the male and female bi-weekly body weights showed that for males there were highly significant differences among hatches in all but the 3-week age level. The females showed a highly significant difference at 1 week, and not until the seventh week did the hatch effect attain a level of significance (probability < 0.05). The analyses of variance of bi-weekly growth rates (Table 4) indicated highly significant differences existed between hatches for both sexes throughout the three growth periods. The mean of the bi-weekly growth rates deTABLE 3.—Body weight analyses of variance for hatch effects by sex
S.V.
d.f.
Percentage Sums of Squares (Weeks of Age) 1
Hatch Error Total
3 233 236
Hatch Error Total
3 254 257
3
5
7
(Males) 17.6** 2.1 5.8** 82.4 97.9 94.2
6.6** 93.4
(Females) 10.6** 0.7 1.8 89.4 99.3 98.2
3.7* 96.3
* Significant (P<0.05). ** Highly Significant (P<0.01).
949
EARLY GROWTH RATE
creased from the first to the last period: males (2.98 to 2.36), females (2.75 to 2.20) (Table 2). The cause for the reduction of these values is unknown, however, it is suspected that the diet had a considerable influence. It is also suspected that an environmental effect, evidenced by the loss of significance of the hatch effects in the body weight analyses of both sexes at the third week of age, was produced by the subsequent "take" of the vaccination of the birds at 2 weeks of age. The percentage sums of squares for hatches suggested that males recovered more quickly than did the females (Table 3). Possibly sexual dimorphism exists in recovery rates following vaccinations. It is of interest to note the failure of the body weight analysis to distinguish the hatch effects at the beginning and at the end of the highly significant 3 to 5-week growth period of the females. The reduction in the hatch effect percentage sums of squares of the bi-weekly growth periods (Table 4) was not as great as in the body weight analyses (Table 3). This shows that an environmental effect influencing the analysis of growth rate, in one period, is not expressed as severely in the analysis of the following growth rate period, while the same effect measured in terms of body weight is accumulative and could be expected to influence a later analysis. The difference appears to be attributable to the influence on the variability of the error terms. The variability for growth rate of individuals within hatches was not increased as much as the analogous body weight error terms. However, some reduction in the percentage sums of squares for hatches in both analyses is noted for both sexes during the 3 to 5-week growth period. The subsequent increase of these values for the last growth period indicated that some effect had influenced growth. The simple correlation of 7-week body
TABLE 4.—Bi-weekly growth rate analyses of variance for hatch ejects by sex
s.v.
d.f.
Percentage Sums of Squares (Bi-Weekly Periods) 1-3
Hatch Error Total
3 233 236
Hatch Error Total
3 254 257
3-5
5-7
(Males) 15.8** 10.0** 84.2 90.0
11.6** 88.4
(Females) 12.0** 6.0** 88.0 94.0
14.3** 85.7
Highly Significant (P<0.01).
weight with each bi-weekly growth rate and with 1-week body weight are shown in Table 5. With the exception of the males in the first hatch the simple correlations between the first growth period and 7-week body weight of males and females were of the same general magnitude and direction as those between 1-week and 7-week body weight. Furthermore, the correlations between the 3 to 5-week growth period of the males in the latter three hatches and 7-week body weight were of the same general level. The females however, did not reflect the male response for that period. For both sexes the correlations between 7-week body weight and the growth rate between 5 and 7-weeks of age were for the most part low, non-significant and undirectional. This supports an earlier conclusion (Roberts, 1964) that growth rate, although calculated from body weight, is a distinct trait. The simple correlation between the growth rate for the experimental period and 7-week body weight is also presented in Table 5. In general these values were higher and less variable than those using bi-weekly growth rates. Since 7-week body weight has been considered as resulting from the combined traits, 1-week body weight and the three successive bi-weekly growth rates, the
950
C. W. ROBERTS
TABLE 5.—The simple correlation coefficients of the bi-weekly growth rates, the growth rate for the experimental period and 1-week body weight with 7-week body weight, by sex hatch Simple Correlation Hatch
Growth Rate
1-Week Body Weight
(Males) -.06 .29* -.20 .12
.16 .62** .45** .45**
.61** .30* 51** .46**
(Females) -.10 -.23 .17 -.25f
.53** .35** .33** .33**
.53** .48** .66** .45**
Bi-Weekly Period 1-3
3-5
1 2 3 4
.15 .34** .44** .36**
.12 .42** .48** .33**
1 2 3 4
.64** .51** .29* .49**
.24* .17 .04 .29*
5-7
* Significant (P<0.05). ** Highly Significant (P<0.01). f Approaching Significance.
third order sample partial correlation coefficients as well as the multiple correlation coefficient for the aforementioned traits were calculated (Table 6). It is not unexpected that each of these traits was able to successfully account for all of the residual variability of 7-week body weight, when all of the other traits were held constant. Together they were able to explain essentially all of the variation in 7-week body weight. When the growth rate for the experimental period was substituted for the three bi-weekly growth rates (Table 7), the reduction in the multiple correlation coefficient was apTABLE 6.—The sample partial correlation coefficients of the bi-weekly growth rates and 1-week body weight with 7-week body weight, by sex and hatch
proximately .05. The multiple correlation coefficient indicated that over 90 percent of the variability of 7-week body weight was explained by the combination of 1-week body weight and the growth rate for the experimental period. The average sample partial correlation values for the two sexes were of the same magnitude, and showed that each trait explained most of the variability of 7-week body weight, when the other was held constant. It should be pointed out that this high correlative value was achieved in spite of the general decline of bi-weekly growth rates, and possibly in spite of an adverse environmental effect. These results indicate that 7-week body weight can be successfully partitioned into two component traits, and that these two traits combined account for a substantial portion of the total variation of 7-week body weight. The influence of these two traits, growth rate and 1-week body weight, on 7-week body weight can be ascertained for each individual in the test population. Table 8 shows the distribution of individuals above or below the hatch average with respect to TABLE 7.—The sample partial correlation coefficients of the growth rate over the experimental period and 1-week body weight with 7-week body weight, by sex and hatch Sample Partial Correlation Hatch
Growth Rate
Bi -Weekly Period 1-3
1-Week - Body Weight
Multiple Correlation Coefficient
3-5
5-7
.99 1.00 .99 .99
.99 1.00 1.00 1.00
.99 .99 1.00 .99
.99 1.00 1.00 1.00
1 2 3 4
.99 .99 .99 .99
.98 .99 .98 .99
(Males) .95 .99 .97 .98
1 2 3 4
.99 .99 .99 .99
.97 .98 .98 .98
(Females) .96 .97 .98 .96
Multiple Correlation Coefficient
1 2 3 4 Average
.93 .95 .95 .96 .95
(Males) .96 .92 .97 .96 .95
.96 .95 .97 .97 .96
1 2 3 4 Average
.96 .93 .94 .94 .94
(Females) .96 .94 .96 .95 .95
.97 .95 .96 .95 .95
Sample Partial Correlation Hatch
1-Week Body Weight
951
EARLY GROWTH RATE
7-week body weight, 1-week body weight, and growth rate for the experimental period. There were 127 males from the four hatches whose body weights at 7 weeks were above the average of their respective hatches. Of these, 40 had an above average 1-week body weight and an above average growth rate (Group A). However 45 males attained the upper 50 percent level by having only an above average 1-week body weight (Group B), and 42 attained the same level by having only an above average growth rate (Group C). The respective values for the 134 females with above average 7-week body weight were: Group A (46), Group B (52) and Group C (36). Only two males gave incongruous results, in that the calculated values showed that they were below the average 7-week body weight while the other two traits were above average. In one case the values were extremely close to the means of their respective hatches, while in the other case sampling errors appeared to be a factor. While the observed frequencies of Groups A, B and C may provide a tempting measure for speculation it must be remembered that the individuals under test were from a random breeding population of New Hampshires. These birds have been maintained without directional selection for at least 10 years, and the reproductive unit has been from 300 to 600 females. It would be reasonable to expect that in selected populations the frequencies of these three groups would change. However in spite of prior selection for body weight it could be assumed that a significant proportion of the individuals selected had attained the selective level by having either a faster growth rate or an above average 1-week body weight. At this time it can only be speculated as to the effect which the aforementioned individuals would have on the subsequent gain of their progeny as compared to the selection differential. It
TABLE 8.—The distribution of individuals by sex as related to their position above or below the hatch average for each of the following traits: 7-week body weight, 1-week body weight and growth rate for the experimental • 7-Week Body Weight Above Hatch Average Group* A
B
C
D
N
1 2 3 4 Total
10 10 10 10 40
(Males) 14 7 9 14 13 11 9 10 45 42
0 0 0 0 0
127
1 2 3 4 Total
14 12 12 8 46
(Females) 16 9 9 11 16 7 11 9 52 36
0 0 0 0 0
134
7-Week Body Weight Below Hatch Average Group A
B
C
D
N
1 2 3 4 Total
0 2 0 0 2
(Males) 8 9 6 8 3 7 8 15 25 39
10 10 11 13 44
110
1 2 3 4 Total
0 0 0 0 0
(Females) 11 9 9 13 7 12 9 13 36 47
9 11 12 9 41
124
Group A—one-week body weight and growth rate above mean. B—one-week body weight above mean. C—growth rate above mean. D—neither trait above mean.
would be reasonable to assume that a faster rate of progress could be made if those selected individuals were above the average for both of these traits. SUMMARY A total of 495 random bred, New Hampshire chicks from four hatches were evaluated for the following traits: 1, 3, 5 and 7-week body weight, the three biweekly growth rates and the growth rate
952
C. W. ROBERTS
for the experimental period. The simple correlations of 7-week body weight with each of the three bi-weekly growth rates and with growth rates for the experimental period were calculated. In addition the sample partial correlation coefficients were also evaluated for the aforementioned traits. The data showed that 1-week body weight when combined with the growth rate for the experimental period accounted for over 90 percent of the variability of 7-week body weight. Furthermore it was shown that either of these two traits, when the other is held constant, will account for a substantial proportion of the heretofore unexplained residual variation of 7-week body weight.
The influence of the above results on a selection program for body weight was discussed. ACKNOWLED GMENTS The author wishes to thank the National Research Council of Canada for the financial assistance to conduct this study. The author is also indebted to Mr. H. W. Ellis, Superintendent of the Poultry Farm, and Mr. R. Wagner for their contributions to this study. REFERENCES Roberts, C. W., 1964. Estimation of early growth rate in the chicken. Poultry Sci. 43: 238-252. Snedecor, G. W., 1956. Statistical Methods. 5th Ed., Iowa State College Press, Ames, Iowa.
Effect of Processing on Bacteria Associated with Turkey Giblets R. H. SALZER,1 A. A. KRAFT AND J. C. AYRES Department of Dairy and Food Industry, Iowa State University, Ames, Iowa (Received for publication November 23, 1964)
T
HE effect of flowing water in reducing bacterial populations on the surfaces of poultry has been demonstrated by several workers. Gunderson et al. (1946) found that washing birds after they were eviscerated reduced the total bacterial count, but did not eliminate coliforms. According to May (1961), the transfer sta-
Journal Paper No. J-4990 of the Iowa Agricultural and Home Economics Experiment Station, Ames, Iowa. Project No. 1392, Center for Agricultural and Economic Development Cooperating. This investigation was supported in part by PHS research grant EF-00113-10 from the Division of Environmental Engineering and Food Protection, Public Health Service. 'Present address: Kellogg Co., Battle Creek, Mich.
tion for moving chicken carcasses from the picking to the evisceration line was the most consistent source of increases in bacterial counts, probably because there were no hand washing facilities at this station. He also found that final washing by a spray washer after evisceration reduced total counts significantly. Kotula et al. (1962) noted that a significant decrease occurred in bacterial populations on the skin of chickens chilled in a continuous counterflow-tumbler chiller. This was believed to be due to the fact that fresh coolant was added to the chill unit and water overflowed continuously from the chiller, resulting in dilution and removal of bacteria.