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Estimation of Early Growth Rate in the Chicken
238
ARIYOSHI ET AL.
separation and quantitative estimation of starch and amylopectin in potato starch. J. Am. Chem. Soc. 65: 1154-1157. Official and Tentative Methods of Analysis of the Association of Official Agricultural Chemists. Assoc, of Official Agricultural Chemists, Wash-
ington, B.C., 1940. Smith, B. W., and J. H. Roe, 1949. A photometric method for the determination of alpha amylase in blood and in urine with use of the starch-iodine color. J. Biol. Chem. 179: 53-59.
Estimation of Early Growth Rate in the Chicken C. W.
ROBERTS
Poultry Genetics Laboratory, The University of British Columbia, Vancouver 8, B.C., Canada (Received for publication July 18, 1963)
T
HE asymetrical sigmoid curve reflects the growth response in poultry as well as in most vertebrate species. Brody (1945) pointed out the difficulties in assuming the linearity of body weight increments when in fact the biological data clearly shows the dependence upon a nonlinear function. His solution to the problem of this non-linearity in the gain of body weight, during the accelerating growth phase, was based on a logarithmic function, which resulted in two distinct estimates of growth rate. When this procedure was applied to chicks, one estimate of growth rate was made for the interval between hatching and three weeks of age and a different estimate of growth rate was made covering the period from three to ten weeks of age. However, the shape of the asymetrical growth curve suggests that one function may describe the accelerating growth phase. This function should reflect growth as being linear from conception to puberty: a measurable period in poultry for each individual from hatching to approximately 7 or 8 weeks of age. This paper shows the reasons why, describes the methods for, and indicates the results of calculating a single estimate of an individual's growth rate within the accelerative phase of growth.
MATERIALS AND METHODS
Two Leghorn lines: a commercial strain (MH) and a strain developed at the University of British Columbia (UBC), a synthetic broiler line (S) and a New Hampshire line (CNH) were utilized in this study. The MH, UBC and CNH lines have been closed populations since 1958, 1927 and 1951 respectively. The MH and UBC lines have been random bred since 1959, while the CNH line has not been subjected to any selection program since 1951. The S line was recently developed from the random matings of the following types of broiler lines: a White New Hampshire, a White Cornish and a White Plymouth Rock. One hundred and twenty baby chicks from each of the four lines were banded and reared in two Jamesway battery brooders. The chicks were randomized into the brooders so that each battery level, with the dividing partitions removed, contained 60 chicks from each line. The random assignment of line to battery level was restricted in that only one line could appear at a given level. When the chicks were 2 weeks of age the sample size of the lines within each battery was randomly reduced to 50 chicks. During the third week of the experiment the birds were subjected to an
EARLY GROWTH RATE
239
of age. The slight advantage of the average hatching weight noted for the females of the MH and S lines disappeared at 1 Weeks week of age for the S females, and at 2 CNH Avg. MH UBC S of age weeks of age for the MH females. Males These averages were arithmetically H 41.8 41.8' 43.8 40.1 41.9 1 78.9 83.8 99.9 83.5 86.5 plotted from hatching to 10 weeks of age 2 139.8 155.1 192.1 155.1 160.5 3 209.0 240.8 310.3 251.9 253.0 (Figure 1). The accelerative phase of 4 275.4 312.6 432.9 346.8 341.9 5 355.0 412.1 568.6 469.5 451.3 growth, as discussed by Brody, was ap6 468.4 556.9 768.3 635.8 607.4 7 588.8 688.4 978.0 810.0 766.3 parent and the lines seemed to have en8 721.5 829.4 1,185.9 1,009.7 936.6 9 825.3 953.8 1,401.2 1,172.4 1,088.2 tered the inhibited growth phase by the 10 924.4 1,058.0 1,563.2 1,339.5 1,221.3 seventh or eighth week. The differential Females H 42.6 40.4 44.7 37.6 41.3 rates of growth for the lines as well as the 1 79.5 80.7 97.4 76.6 83.5 2 138.6 146.9 184.2 137.0 151.7 sexes within a line were evident. 3 203.2 219.2 289.6 218.8 232.0 4 265.7 289.5 400.7 294.7 312.6 5 The data was then replotted on a semi336.6 372.6 512.3 392.5 403.5 6 434.2 490.9 686.4 532.5 536.0 7 log scale, after Brody (1945), (Figure 2). 535.1 596.1 856.8 663.2 662.8 8 643.4 711.5 1,022.2 813.9 797.7 9 From hatching to 10 weeks of age a smooth 730.3 818.3 1,187.3 944.8 920.2 10 807.6 899.2 1,316.8 1,067.8 1,022.8 decelerating curve was apparent for each line and for each sex within a line. This abnormal environmental condition in that result would seem to question the desirthe temperature and the humidity were ex- ability of calculating from a logarithmic cessively high for a four day period. At six function a single estimate of growth rate weeks of age all of the birds were sexed which would reflect linearly over the first and moved to eight floor brooding houses. 3 or 4 weeks of growth. These graphed reThe rerandomization of each line was such sults also do not show any change in the that any single house contained one-half curve that may be associated with the onof the male and one-half of the female set of the decelerating growth phase which sample from each battery. A standard was indicated in Figure 1. Since the chick starter ration and water were fed ad graphed results in Figure 2 show that the libitum throughout the test period. age of the bird has a contributory effect on Individual body weights, recorded in body weight, the average body weights of grams, were taken at hatching and at each sex of the four lines were replotted weekly intervals thereafter up to 10 weeks on a log X log scale (Figure 3), with the of age. When the birds were 10 weeks of time axis calibrated as weeks of age from age the data on 40 males and 40 females conception. from each line were drawn at random for The graphs for the males and the feanalysis, with the restriction that each sex males of each line seemed to show that an was to have equal representation from each approach to linearity was measurable up battery. to 7 or 8 weeks of age. This change in the curve approximately corresponds to their DERIVATION AND ESTIMATION OF respective inflection points in Figure 1. GROWTH RATE The weekly average body weights for Therefore, it may be possible to measure each sex of the four lines are shown in the rate of change in body weight, relative Table 1. In general the males weighed more to body weight and relative to time, for than the females from hatch to 10 weeks each individual in the study by the apTABLE 1.—Average body weights in grams of the males and females of the MH, V .B.C., S and CNH lines from hatching to 10 weeks of age
BODY WEIGHT ( G R A M S
240
C. W. ROBERTS
I2O0
-
1000
-
X
/
800
/V /p', x /
/? 40 0
X /
//
*
'<>•
200
UBC
MH
tf
^
0 1600 /
1
1
•
/
-
1200
X
/
-
X
p /
?
GHT
/ / 800
UJ
.600
BODY
1
X
1000
5
i
-
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i
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*
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rt"
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—
400
y
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-
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* *
10
CNH
I
I
I
1
1
2
4
6
8
10
WEEKS
OF AGE
FIG. 1. Average body weights of the male and female MH, UBC, S and CNH lines, from hatch to 10 weeks of age.
plication of the power function y = at"; where y is equal to the body weight of an individual at time t, a is equal to the body weight of that individual at time o and b represents the growth rate of the individual. When an individual is weighed at two different times prior to puberty the growth rate, b, may be estimated for that time interval. The models depicting the body
weights of the i th individual at two different times would be: for
t
jme j . yn = aitibbii
and for time 2: y=at
b i
241
EARLY GROWTH R A T E
T h e ratio obtained b y dividing these two weights would be:
Solving for b i :
log
vi2 ^ a;t2bi yn
bi = -
a ; ti b i
log
and this will reduce t o :
~yn~ -yu. " t2
-
. ti. This calculated bi value (a pure number) may then be defined as the growth rate of
_y
WEEKS
OF
AGE
FIG. 2. Average body weights of male and female MH, UBC, S and CNH lines from hatch to 10 weeks of age.
242
C. W. ROBERTS
IOOO 800
$
f*
-
7
x ?' 16 x.-
-
600
r
400
/
200 /
/
1
8
7 >v
I 3
7
9 II 13
WEEKS OF A8E
I 3
UBC i
i
7
i
i
i
9 II 13
FROM CONCEPTION
FIG. 3. Average body weights of the rriale and female MH, UBC, S and CNH lines from hatch to 10 weeks of age.
243
EARLY GROWTH RATE TABLE 2.—The average weekly growth rates for the MH, U.B.C., S and CNH lines from hatching to 10 weeks of age Lines
Growth period
MH
UBC
S
H-l 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10
2.19 2.53 2.15 1.75 1.85 2.30 2.04 2.00 1.51 1.21
2.41 2.73 2.30 1.75 1.96 2.48 1.97 1.91 1.61 1.10
2.79 2.90 2.58 2.09 1.96 2.48 2.19 1.82 1.90 1.31
CNH Average 2.51 2.68 2.61 1.99 2.19 2.61 2.19 2.26 1.71 1.52
2.48 2.73 2.40 1.95 2.01 2.48 2.12 2.00 1.71 1.31
the i th individual between time 1 and 2. A series of weekly growth rates may be calculated for the i th individual from a corresponding weekly series of body weights. These independently estimated weekly growth rates when averaged should provide a single estimate of growth rate for the i th individual throughout the accelerating growth phase. Weekly growth rate estimates were calculated for each individual in the study. Table 2 shows the average weekly growth rate and the average "7 week" growth rate of the four lines under study. The diversity of the average weekly growth rates is not unexpected since three changes in the environment occurred during the test. The first week's average chick growth rate (2.48 was undoubtedly affected by the stress of hatching, banding, weighing, and the bird's adjustment to the environmental conditions of the battery brooder. Hatching weights would also be influenced by time of hatch and the length of the drying period. The average growth rate during the fourth week (1.95) and seventh week (2.12) was probably influenced, in turn, by the ventilation difficulties and the transfer of birds from the batteries to the floor pens. An increase in the weekly growth rate follows each of the aforementioned
environmental effects, with the exception of a slight drop in the rate of growth during the eighth week for the MH and UBC chicks. The S line showed an increase in their growth rate one week following the transfer to the floor pens while the CNH had an increase in growth rate in the eighth week. When the major environmental changes that existed in this experiment are superimposed on the calculated weekly growth rates there seems to be a close agreement which tends to explain a portion of the week to week diversity in the average weekly growth rate. The rapid decline in the average weekly growth rate after the birds reached 7 weeks of age (2.00, 1.71 and 1.31 for the eighth, ninth, and tenth weeks) would appear to represent the expected change if at this time the birds had passed beyond puberty and these weekly estimates of growth rate were made during the decelerating phase of growth. The coefficient of variation of the seven weekly growth rates were calculated in order to check the uniformity of the weekly variances as well as ascertain if this statistic would provide an indication when the weekly growth rate estimates could be considered non-linear. Table 3 shows the coefficient of variation by sex for each of the TABLE 3.—The coefficient of variation (C.V.) and the average weekly growth rates (b) for the two sexes in each of the ten growth periods Growth period (weeks)
Males
Females
C.V.
b
C.V.
b
H-l 1-2 2-3 3^: 4-5 5-6 6-7 7-8 8-9 9-10
17.54 9.70 12.46 18.25 14.95 15.51 15.20 24.36 28.78 33.02
2.51 2.78 2.51 1.95 2.07 2.55 2.19 2.09 1.71 1.31
16.92 8.70 13.64 18.50 16.94 14.83 17.19 20.48 22.74 31.48
2.44 2.68 2.33 1.95 1.91 2.42 2.04 1.91 1.61 1.21
244
C. W. ROBERTS
ten growth periods. The uniformity of this statistic for each of the sexes throughout the first seven growth periods indicates that the variability of the weekly estimates of growth rate is quite similar with the single exception of the variability during the second growth period. In this period the males and females had their highest growth rate: males (2.78) and females (2.68), in addition, they had the lowest coefficient of variation, for the males (9.70) and the females (8.70). This may indicate that the exceptional growth during this period was greatly influenced by the environment, such as those previously mentioned factors which could influence the growth rate during the first week, and were believed to have resulted in an adverse environmental situation. For both sexes the coefficients of variation for the last three growth periods were higher than any of the previous weeks, and in addition, from the eighth to the tenth week the coefficient of variation rapidly increased: males (24.36 to 33.02) and the females (20.48 to 31.48). The increase in the coefficients of variation of the eighth week's estimate of growth rate would appear to be associated with the onset of puberty. The subsequent increases in the coefficients of variation would seem to infer that the estimates of growth rate, made during the latter periods, were in fact estimates within the decelerating phase of growth. Based on the graphic interpretation and the results of the coefficients of variation of the weekly growth rates, it was assumed that the weekly series of individual body weights, from hatch to 7 weeks of age, when expressed in the framework of the power function, would approximate linearity up to 7 weeks, and that the average of the weekly growth rates would provide a meaningful estimate of the individual's
growth rate for this 7 week period. Furthermore, it was assumed that the distribution of this trait, 7 week growth rate, was such that all of the conditions necessary for statistical analysis would be satisfied. GROWTH RATE AND BODY WEIGHT ANALYSIS
The following model was assumed to describe the sources of variance in each of the seven analyses of variance of weekly growth rate from hatch to 7 weeks of age: biiki = M+gi+dj+(gd) ij -|-s k -|-(gs)i k + (ds)jk+ (gds)ij k -l- eijki-
The line effect: g (i = 1-4), the battery effect: d (j = 1-2) and the sex effect: s (k = 1-2) were each assumed to be the result of a fixed effect. The residual effect associated with the measurement of the weekly growth of the individuals within a line, battery, and sex: e (1 = 1-20) was assumed to be of a random nature. The TABLE 4.—The average weekly growth rates of the males and females of the four lines from hatching to 7 weeks of age MH
UBC
S
CNH Average
H-1 1-2 2-3 3-4 4-5 5-6 6-7
2.21 2.56 2.19 1.80 1.91 2.36 2.19
Males 2.41 2.86 2.76 2.92 2.40 2.65 1.70 2.18 2.07 2.01 2.55 2.55 2.04 2.27
2.55 2.78 2.65 2.09 2.25 2.55 2.27
2.51 2.78 2.51 1.95 2.07 2.55 2.19
Average
2.17
2.26
2.49
2.45
2.37
H-1 1-2 2-3 3-4 4-5 5-6 6-7
2.18 2.48 2.11 1.75 1.79 2.16 1.97
Females 2.41 2.71 2.68 2.85 2.19 2.47 1.80 2.09 1.91 1.85 2.36 2.48 1.81 2.12
2.46 2.61 2.58 1.95 2.13 2.61 2.12
2.44 2.68 2.33 1.95 1.91 2.42 2.04
Average
2.06
2.17
2.37
2.35
2.25
Line average
2.12
2.22
2.43
2.40
2.31
245
EARLY GROWTH RATE
TABLE 5.—The sums of squares for the sources of variance, of the weekly analyses of variance of growth rate from hatching to 7 weeks of age expressed as a percentage of the total sums of squares Source of variance Batteries (B) Sex (S) BXS Lines (L) LXB LXS LXSXB Individuals within L, S & B Total
Weekly growth periods di. 1-2
H-l 1 1 1 3 3 3 3 304 319
Total sum of squares
2-3
3^
4-5
5-6
6-7
2.52** 0.21 3.78** 0.73 1 3.63** 5.96** 0.32 1.81** 0.09 25.44** 26.60** 30.19** 0.61 2.12* 2.15* 0.42 0.78 0.47 0.64 0.34 0.12
1.46** 4.00** 0.02 5.86** 3.44** 1.12 15.24** 18.30** 1.42 1.50 0.74 0.23 0.38 1.53
6.07** 2.19** 0.03** 10.71** 2.52* 1.62 1.06
68.06 100.0
62.20 100.0
60.81 100.0
74.76 100.0
70.00 100.0
75.80 100.0
82.20 100.0
58.35
20.98
33.61
61.10
33.87
46.37
40.20
0.56** 7.54** 0.14 8.96** 0.38 0.10 0.12
* Significant P < . 0 5 ** Significant P < . 0 1 1 Approaching significance
uniqueness of the lines, the definite environmental limitation of the two batteries, and the restriction of the sexes indicated the estimates of these effects can be considered fixed, however, since each of the weekly growth rate estimates were made on individuals that were drawn at random from the tested population, the estimate associated with this component should also be random. The model which was assumed to describe the sources of variance associated with the analysis of 7 week growth rate (Table 6) was, bijkim = {A+gi+dj + (gd) i j + s k + (gs) j k
utilized a similar model and those assumptions which were applied to the analysis of weekly growth rate. The multiple linear regression of hatching weight and 7 week growth rate on 7 week body weight was determined (after Snedecor, 1956). The multiple correlation index (R 2 ) and the partial regression coefficients as well as their standard partial equivalents were ascertained (Table 9). GROWTH RATE AND BODY WEIGHT RESULTS
The seven average weekly growth rates of the males and females for each line, as
+ (ds) j k +(gds) i j k +fij k i + e ijklm-
The line, battery and sex effects are similar to those which have already been defined. The effect related to the measurement of 7 week growth rate of the 1th individual within a line, battery and sex: f (1 = 1-20) and the residual effect of the measurement of weekly growth rate within the 1th individual: e (m = 1-7) were assumed to be random. The series of weekly body weights were also analysed (Table 7). This analysis
TABLE 6.--The
analysis of variance of 7 week growth rate
Source of variation Batteries (B) Sex (S) BXS Lines (L) LXB LXS LXBXS Individuals within L, B. & S Measurements within individuals Total
d.f.
Sums of squares
l l l 3 3 3 3 304 1,920 2,239
0.003 7.439** 0.022 38.442** 0.344 0.023 0.083 20.882 392.266 459.503
** Significant at P<.01.
Percent sums of squares <0.01 1.62 <0.01 8.37 0.08 <0.01 0.02 4.54 85.37
246
C. W. ROBERTS TABLE 7.—The sums of squares for the sources of variation, of the weekly analyses of variance of body weight from hatching to 7 weeks of age, expressed as a percentage of the total sums of squares
Source of variation (B) Sex (S) BXS Lines (L) LXB LXS LXSXB Individuals within L, S & B Total ' Total sum of squares
Weeks of age d.f. H 1 1 1 3 3 3 3 304 319
0.02 0.39 0.01 21.19** 0.25 2.94** 1.07
1
2
3.80** 0.94** 1.82** 3.31** 0.16 0.67* 51.56** 60.93** 0.38 0.41 1.46* 1.55** 0.49 0.09
3
4
0.41* 1.45** 5.80** 4.87** 0.36* 0.02 64.12** 68.00** 0.51 0.74* 1.47** 1.35** 0.07 0.25
5
6
7
0.90** 7.30** <0.01 66.00** 0.35 1.48** 0.33
0.18 8.53** <0.01 68.94** 0.28 1.06** 0.26
0.25* 10.50** 0.02 68.74** 0.21 1.17** 0.21
23.63 100.0
20.73 100.0
74.12 100.0
40.32 100.0
32.10 100.0
27.26 100.0
23.32 100.0
18.90 100.0
5,745
39,192
189,196
605,848
1,407,555 2,506,773 4,777,412 8,166,033
* Significant at P < . 0 5 . ** Significant at P < . 0 1 .
well as their 7 week average growth rates, are shown in Table 4. The average weekly growth rates, as well as the 7 week growth rate, of the males were greater than that of the females. There was not an appreciable difference between the 7 week growth rates of the two heavy lines: S (2.43) and CNH (2.40), and only a slight difference between the Leghorn lines: MH (2.12) and UBC (2.22). A difference in the 7 week growth rates of the heavy and Leghorn lines is apparent. The analysis of variance of weekly growth rates (Table 5) is recorded as the sums of squares for the sources of variation expressed as a percentage of the total sums of squares. A highly significant difference in the growth rates of the lines (L) was present in each of the seven growth periods. With the exception of the growth rate in the third and seventh growth period, a highly significant difference between the two batteries (B) was measurable. The difference in the growth rate of the sexes (S) approached significance during the first week of growth, and was highly sig-
nificant for the rest of the growth periods with the single exception of the fourth growth period. A first order interaction (B X S) was evident in the second and fourth growth period (P < .01), also another first order interaction ( L X B ) was present in the second, third, and sixth growth period ( P < . 0 5 ) . The remaining interactions ( L X S and L X S X B ) were not in evidence. When the sums of squares of the weekly analysis of variance of growth rate are expressed as a percentage of the total sums of squares, a comparison of the independent analyses may be made for a particular source of variance, especially since the different weekly growth rate analyses are made on the same individuals. The percentage values associated with lines shows an increase for the first three growth periods (25.44% to 30.19%). This is followed by a sharp decline in the fourth period (15.24%), which is probably related to the previously mentioned and demonstrated environmental influence. The slight increase observed in the fifth period
247
EARLY GROWTH RATE
(18.30%) is followed by a consistent decrease in these values. The percentage values associated with the individuals within L, S and B showed that the error terms contained a large proportion of the total sums of squares, and these values reflected the aforementioned changes which occurred in the lines. The remaining sources of variance did not show any sequential changes in their percentage values that could be associated with time nor did they show any apparent correlation with any other source of variation. The magnitude of the percentage sums of squares associated with individuals seems to indicate that, under the conditions of this experiment, weekly growth rate was greatly influenced by the environment. However early growth rate, in this instance up to the third week, may have been more influenced by line differences than was the growth rate in the later periods. The analysis of 7 week growth rate is presented in Table 6. Highly significant differences existed in the 7 week growth rate of the sexes as well as that of the
lines. These results agree with those of Table 5 in that the weekly growth rates also had a consistent effect due to lines and sexes. The analysis of 7 week growth rate also indicated that the effects associated with battery differences as well as those effects related to the first and second order interactions were negligible. These results do not agree completely with the weekly growth rate analysis, especially if one considers the main effect associated with batteries. In the weekly growth rate analysis (Table 5) highly significant differences in growth rate were measurable between the two batteries in 5 out of the 7 weekly test periods, while in the analysis of 7 week growth rate there was not any indication of a differential response between the two batteries. This obvious disagreement necessitated a more comprehensive study of the available data. Accordingly the series of weekly body weights were analysed (Table 7), and were recorded as the percentage of the total sums of squares. From hatching to 7 weeks of age the
TABLE 8.—The average body weights and growth rates for the chickens reared in two batteries from hatch to 7 weeks of age Body weight Weeks of age
Battery 1
2
Growth rate Difference
Growth
(2-1)
periods
1
2
H-1
2.39
2.56
+0.17
1-2
2.75
2.66
-0.09
2-3
2.41
2.38
-0.03NS
3-4
1.83
2.00
+0.17
4-5
2.03
1.95
-0.08
5-6
2.55
2.36
-0.19
6-7
2.07
2.12
+0.05NS
Average
2.29
2.29
0.00
H
41.5
41.7
0.2 N S
1
82.9
87.2
4.3
2
153.7
158.4
4.7
3
239.7
245.3
5.6
4
319.3
335.3
16.0
5
419.0
435.8
16.8
6
566.5
576.8
10.3 NS
7
706.6
722.5
16.9
Battery
Difference (2-1)
248
c. w. rABLE 9.—:The
based on
Population Sex Males Females Lines MH UBC S CNH
midtiph? linear regression analyses Partial regression coefficients (b) and standard partial regression coefficients (b)'
Average
Multiple linear
ROBERTS
7 week. growth rate
Multiple correlation index
7 week body weight
Hatching weight
(grams) 714.6
(grams) 41.6
2.29
(b)* 15.5
0.41
0>0
(b)* 853.5
(b') 0.93
(R2) 0.88
766.3 662.8
41.9 41.3
2.35 2.24
13.5 16.3
0.31 0.56
904.4 802.6
0.92 0.95
0.86 0.90
561.9 642.2 917.4 736.6
42.2 41.1 44.2 38.8
2.11 2.22 2.44 2.40
6.5 10.2 10.9 15.3
0.44 0.42 0.42 0.53
495.1 709.3 837.4 726.4
0.98 0.90 0.90 0.82
0.71 0.83 0.71 0.80
7 week growth rate
Hatching weight
All of the partial regression coefficients were highly significant (P<.01).
main effects associated with lines (L) were highly significant. The difference between the sexes (S) was measurable from 1 to 7 weeks of age (P < .01). These results are in close agreement with the weekly growth rate analysis (Table 5). The analysis of the weekly body weights showed that the first order interaction L X S was highly significant in each body weight analysis from hatching to 7 weeks of age, with the single exception of the lowered probability level at one week of age ( P < . 0 5 ) . This L X S interaction was unexpected in view of the fact that a comparable effect was completely lacking in the weekly growth rate analysis (Table S) as well as the analysis of 7 week growth rate (Table 6). The ability to detect this interaction when considering body weight and the inability of finding a similar response when considering growth rate strongly suggests that growth rate may be considered a distinct statistic, even though it is basically calculated from body weight. The presence of the L X S interaction also suggests a relatively consistent degree of non-linearity in the relationship between line and sex, with respect to body weight.
The lack of this effect after the application of the power function would seem to indicate this non-linearity is associated with the constant a in the power function, and may well mean that further study will indicate that some biological meaning can be associated with this constant. The remaining first order interactions in the body weight analysis do not seem to be related to those first order interactions in the weekly growth rate analysis, and the subsequent 7 week growth rate analysis does not show any indication of the presence of any additional interaction, as evidenced by the percentage sums of squares values. It seems reasonable to assume that those effects, when significant, may either be attributable to sampling errors or as being induced by small weekly battery environmental differences. Differences in the average body weights of the birds in the two batteries were measurable from 1 to 7 weeks of age with the single exception of the nonsignificant result at 6 weeks. Table 8 shows the weekly average body weights and growth rates of the chicks in each battery as well as the weekly difference between these batteries.
EARLY GROWTH RATE
249
The 7 week growth rate for the birds in battery difference because the growth dureach battery (2.29) confirms the analytical ing the seventh week again resulted in a result of a nonsignificant difference between significant difference of the average body batteries for the experimental period (Ta- weights in the two batteries (16.9 grams). ble 6). However in terms of weekly body With respect to the two batteries, the weight, significant differences existed for differences in the chick's average body all but one week throughout the test pe- weights was directly attributable to two riod. The nonsignificant battery differences weekly growth periods and may have been of the hatching weights indicates the ef- influenced by a third. The major changes fectiveness of the original randomization occurred during the first week and the of the birds in the batteries. The apparently fourth week of growth and culminated at 7 contradictory, significant differences in the weeks of age in a significant 16.9 gram difweekly growth rates attributable to battery ferential in favor of battery # 2 . effects is resolved as the non-directional There is no apparent reason why battery influence of weekly growth rates between # 2 would provide a better environment the two batteries. The birds in battery # 1 than battery # 1 , especially for only 2 out had a superior growth rate during 4 growth of the 7 weekly growth periods. If a supeperiods while the chicks in battery # 2 rior battery condition existed it would seem were superior in their growth rate for the more reasonable to assume that the results remaining periods. These results would would be in evidence during the other peseem to indicate that in this experiment riods. The specific lack of a consistent dithe weekly growth rate was not depressed rectional difference in weekly growth rate by a specific battery effect. in favor of the second battery coupled with The difference in the weekly average the fact that only two major changes ocbody weights of the birds in the two bat- curred which resulted in the difference of teries shows that the first week's growth the average body weights in the two batrate in battery # 2 (2.56) resulted in a teries would seem to indicate that the difhighly significant difference in 1 week ferences in the average weekly growth rates body weight (4.3 grams). The growth rate of the two batteries could be considered one for the next two weeks was high in battery of a random environmental effect. This may # 1 (2.75 and 2.41 respectively) but did be the best explanation of why the avernot effectively change the original body age 7 week growth rates of the two batterweight increment. The growth rate of the ies was the same yet the differential weekly birds in battery # 2 during the fourth week growth rates of the birds in the two bat(2.00) resulted in an additional increase teries resulted in significant differences in in the difference between the two batteries average body weights for all but one week (16.0 grams). The growth rate for the next of the experiment. This interpretation may 2 weeks was again in favor of battery # 1 partially explain why many experiments, (2.03 and 2.55 respectively). During the even though they are conducted under relasixth week the growth rate of the birds in tively uniform conditions, result in unexbattery # 1 apparently reduced the differ- plained and unrepeatable pen or battery ential between the two batteries (10.3 effects. grams). However this nonsignificant differThe percentage of the total sums of ence, in all likelihood still represents a true squares for weekly body weights (Table
250
C. W. ROBERTS
7) may be compared for any particular source of variance. The sums of squares associated with sex and line differences both show an increase in their percentage values which appeared to be related to age. In the estimation of sex differences this increase (0.39% to 13.68%) was evenly spread out over the 7 weeks, even though a slight drop was noted in the fourth week. This general increase in the proportionality would seem to correspond to the general divergence of the average male and female body weights from hatch to 7 weeks of age (Table 1 and Figure 1). The percentage increase for the lines appears to be restricted between hatching and 4 weeks of age (21.19% to 68.00%). Beyond this time little if any change is noted. This corresponds to the fairly rapid growth of the lines in which small differences in hatching weights are magnified rather quickly up to 4 weeks of age and thereafter these differences in the lines are proportionately uniform (Table 1). The percentage values associated with battery differences directly reflect those growth rate differences observed in Table 8. The increase in the differences of the average body weights between the two batteries observed following the growth rate during the first and fourth week (Table 8) can be associated with the higher percentage values observed at 1 and 4 weeks of age (3.80% and 1.45% respectively). Each of the remaining first and second order interactions are relatively uniform, for the most part nonsignificant, occur at a low percentage level and do not show any obvious time effects. In view of the results obtained with the separate analyses associated with growth rates and the subsequent analyses associated with body weights, it was deemed necessary to establish what relationship existed between the following traits: hatch-
ing weight, 7 week growth rate and 7 week body weight. If the assumption that the power function will reflect an estimate of growth rate which approaches linearity is valid the multiple linear regression of hatching weight and 7 week growth rate on 7 week body weight should have a relatively high multiple correlation index (R 2 ). Consequently the aforementioned multiple linear regression was determined for the entire population, for the two sexes, and for each individual line. The partial regression coefficients and their standard partial equivalents as well as the associated R2 values for each analysis are presented in Table 9. The multiple linear regression equation explains approximately 88% of the variability in 7 week body weight of the total population. When the males and females are considered separately 86% and 90% of the variability in 7 week body weight is accounted for by the regression equation. The analysis explains 71%, 83%, 71% and 80% of the variability in 7 week body weight of the MH, UBC, S and CNH lines respectively. In each analysis the multiple linear regression equation as well as the associated partial regression coefficients were highly significant. The relative importance of the two traits, hatching weight and 7 week growth rate as affecting 7 week body weight is indicated by the magnitude of their standard partial regression coefficients. In general the contributions of 7 week growth rate was more than twice the contribution of hatching weight to the dependent trait, 7 week body weight. The assumption that the trait approaches linearity appears to be valid although the overall decrease in the average weekly growth rates, from the first to the seventh week of growth (2.48 to 2.00), indicates that some non-linearity is present (Table 2). The cause and the amount of
EARLY GROWTH RATE
this non-linearity as well as the degree to which this influences the estimate of growth rate, will have to be ascertained. Further experiments to answer some of these questions are now in progress. DISCUSSION AND SUMMARY
The weekly average body weights for each sex within a line were plotted on an arithmetic graph, on a semi-log graph, and on a log X log graph. The accelerative phase of growth was apparent in the arithmetic graphs. The graphs also showed that the birds were entering the inhibited phase of growth by the seventh or eighth week. When the series of body weights were replotted on a semi-log basis a smooth decelerating curve was noted in all cases. These curves did not show any changes which could be associated with the onset of pubertal growth and they questioned the desirability of calculating a single estimate of a chick's growth rate for the first 3 or 4 weeks after hatching. When the weekly average body weights were plotted on a log X log scale, with the time axis calibrated as weeks of age from conception, the resultant graph indicated that an approach to linearity was obtained up to 7 or 8 weeks of age. Therefore, the power function y = atb was used to calculate the weekly growth rate of each individual in the study. The weekly growth rate as well as the coefficient of variation of the values was determined. The weekly growth rates reflected some environmental changes that occurred from week to week while the coefficient of variation indicated that the variance of the weekly growth rates was relatively uniform up until the seventh growth period. During the eighth growth period and the subsequent weeks the coefficient of variation rapidly increased, thereby giving some indication that these
251
latter stages could be considered as being in the decelerative growth phase and would not be expected to reflect linearity. Based on the graphic analyses and the evidence associated with the coefficients of variation, it was assumed that the weekly series of body weights for each individual from hatch to 7 weeks of age, when expressed in the framework of the power function, would approximate linearity up to 7 weeks and that the average of these weekly growth rates would provide a meaningful estimate of the individual's growth rate for this 7 week period. The weekly growth rates, the 7 week growth rates and the series of body weights from hatch to 7 weeks of age were subjected to the analysis of variance. The multiple linear regression of hatching weight, 7 week growth rate on 7 week body weight was also determined. Differences were measurable in the weekly growth rates of the lines, of the birds in the two batteries tested and in the weekly growth rates of the two sexes. The analysis of 7 week growth rate showed that only the line and sex effect provided the significant contributions. Sex and line differences were also present in the analysis of the body weights. These were measurable at 1 week of age for the sexes and at hatching for the lines. In addition, a line by sex interaction was consistently present from hatching to 7 weeks of age. This same interaction was completely lacking in any growth rate analysis. Differences in the body weights of the birds in the two batteries were also measurable for 6 out of 7 weeks. The data indicated that the nondirectional but significant battery influence on weekly growth rates produced by chance a 16 gram difference between the two batteries, even though the average 7 week average growth rate for the birds in
252
C. W. ROBERTS
each battery was the same. This difference was directly related to two and possibly three growth periods. The multiple linear regression accounted for a high degree of the variance of 7 week body weight. For the population the multiple correlation index (R 2 ) was 0.88. When the sexes were tested separately, the R2 value for the males was 0.86 and the females 0.90. The R2 values for the lines under study were 0.71 (MH),0.83 (UBC), 0.71 (S) and 0.80 (CNH). The standard partial regression coefficients indicated that the contribution of hatching weight was one-half that of 7 week growth rate when both of these statistics were related to 7 week body weight.
ACKNOWLED GMENTS
The author wishes to thank the American Poultry and Hatchery Federation, Kansas City, Missouri, the National Research Council of Canada, and the British Columbia Department of Agriculture, Victoria, B. C. for the financial assistance to conduct this study. The author is also indebted to Mr. H. W. Ellis, Superintendent of the Poultry Farm, for his contributions to the study. REFERENCES Brody, S., 1945. Bioenergetics and Growth. Reinhold Pub. Corp., New York, N.Y. Snedecor, G. W., 19S6. Statistical Methods. Sth ed., Iowa State College Press, Ames, Iowa.
Further Studies on the Influence of Trans-2Phenylcyclopropylamine (Tranylcypromine) on Growth Responses of Broilers THEODORE ELLISON, JOHN F. PAULS AND GEORGE C. SCOTT Research and Development Division, Smith Kline and French Laboratories, Philadelphia 1, Pennsylvania (Received for publication July 24, 1963)
T
RANYLCYPROMINE ('Parnate,' SK&F trans-385), a potent inhibitor of monoamine oxidase, has been reported to have shown a significant increase on the rate of gain of broiler cockerels (Ellison et al., 1963). These growth responses occurred within a fairly narrow dose range and well below the minimum therapeutic level considered necessary to produce overt pharmacologic action. In this study further data on the nutritional influence of tranylcypromine on gain and feed efficiency are reported using two strains of broiler cockerels. EXPERIMENTAL PROCEDURES
The studies reported herein were conducted in a controlled-environment room.
The room temperature was maintained at 90° ± 2°F. for the first week and was then decreased 5° per week for the next three weeks. The relative humidity was maintained at approximately 50% and artificial illumination (fluorescent) was kept constant 24 hours a day during the entire fourweek period of each study. The birds were raised in compartmented poultry batteries with raised wire floors and individual feed and water pans. Ledbrest X Pilch cockerels were used in the first experiment while Vantress X Arbor Acre broiler cockerels were used in the second trial. One-day-old chicks were fed a basal ration ad libitum for one week prior to selection for each study. At the end of this week, culling on both weight extremes
ARIYOSHI ET AL.
separation and quantitative estimation of starch and amylopectin in potato starch. J. Am. Chem. Soc. 65: 1154-1157. Official and Tentative Methods of Analysis of the Association of Official Agricultural Chemists. Assoc, of Official Agricultural Chemists, Wash-
ington, B.C., 1940. Smith, B. W., and J. H. Roe, 1949. A photometric method for the determination of alpha amylase in blood and in urine with use of the starch-iodine color. J. Biol. Chem. 179: 53-59.
Estimation of Early Growth Rate in the Chicken C. W.
ROBERTS
Poultry Genetics Laboratory, The University of British Columbia, Vancouver 8, B.C., Canada (Received for publication July 18, 1963)
T
HE asymetrical sigmoid curve reflects the growth response in poultry as well as in most vertebrate species. Brody (1945) pointed out the difficulties in assuming the linearity of body weight increments when in fact the biological data clearly shows the dependence upon a nonlinear function. His solution to the problem of this non-linearity in the gain of body weight, during the accelerating growth phase, was based on a logarithmic function, which resulted in two distinct estimates of growth rate. When this procedure was applied to chicks, one estimate of growth rate was made for the interval between hatching and three weeks of age and a different estimate of growth rate was made covering the period from three to ten weeks of age. However, the shape of the asymetrical growth curve suggests that one function may describe the accelerating growth phase. This function should reflect growth as being linear from conception to puberty: a measurable period in poultry for each individual from hatching to approximately 7 or 8 weeks of age. This paper shows the reasons why, describes the methods for, and indicates the results of calculating a single estimate of an individual's growth rate within the accelerative phase of growth.
MATERIALS AND METHODS
Two Leghorn lines: a commercial strain (MH) and a strain developed at the University of British Columbia (UBC), a synthetic broiler line (S) and a New Hampshire line (CNH) were utilized in this study. The MH, UBC and CNH lines have been closed populations since 1958, 1927 and 1951 respectively. The MH and UBC lines have been random bred since 1959, while the CNH line has not been subjected to any selection program since 1951. The S line was recently developed from the random matings of the following types of broiler lines: a White New Hampshire, a White Cornish and a White Plymouth Rock. One hundred and twenty baby chicks from each of the four lines were banded and reared in two Jamesway battery brooders. The chicks were randomized into the brooders so that each battery level, with the dividing partitions removed, contained 60 chicks from each line. The random assignment of line to battery level was restricted in that only one line could appear at a given level. When the chicks were 2 weeks of age the sample size of the lines within each battery was randomly reduced to 50 chicks. During the third week of the experiment the birds were subjected to an
EARLY GROWTH RATE
239
of age. The slight advantage of the average hatching weight noted for the females of the MH and S lines disappeared at 1 Weeks week of age for the S females, and at 2 CNH Avg. MH UBC S of age weeks of age for the MH females. Males These averages were arithmetically H 41.8 41.8' 43.8 40.1 41.9 1 78.9 83.8 99.9 83.5 86.5 plotted from hatching to 10 weeks of age 2 139.8 155.1 192.1 155.1 160.5 3 209.0 240.8 310.3 251.9 253.0 (Figure 1). The accelerative phase of 4 275.4 312.6 432.9 346.8 341.9 5 355.0 412.1 568.6 469.5 451.3 growth, as discussed by Brody, was ap6 468.4 556.9 768.3 635.8 607.4 7 588.8 688.4 978.0 810.0 766.3 parent and the lines seemed to have en8 721.5 829.4 1,185.9 1,009.7 936.6 9 825.3 953.8 1,401.2 1,172.4 1,088.2 tered the inhibited growth phase by the 10 924.4 1,058.0 1,563.2 1,339.5 1,221.3 seventh or eighth week. The differential Females H 42.6 40.4 44.7 37.6 41.3 rates of growth for the lines as well as the 1 79.5 80.7 97.4 76.6 83.5 2 138.6 146.9 184.2 137.0 151.7 sexes within a line were evident. 3 203.2 219.2 289.6 218.8 232.0 4 265.7 289.5 400.7 294.7 312.6 5 The data was then replotted on a semi336.6 372.6 512.3 392.5 403.5 6 434.2 490.9 686.4 532.5 536.0 7 log scale, after Brody (1945), (Figure 2). 535.1 596.1 856.8 663.2 662.8 8 643.4 711.5 1,022.2 813.9 797.7 9 From hatching to 10 weeks of age a smooth 730.3 818.3 1,187.3 944.8 920.2 10 807.6 899.2 1,316.8 1,067.8 1,022.8 decelerating curve was apparent for each line and for each sex within a line. This abnormal environmental condition in that result would seem to question the desirthe temperature and the humidity were ex- ability of calculating from a logarithmic cessively high for a four day period. At six function a single estimate of growth rate weeks of age all of the birds were sexed which would reflect linearly over the first and moved to eight floor brooding houses. 3 or 4 weeks of growth. These graphed reThe rerandomization of each line was such sults also do not show any change in the that any single house contained one-half curve that may be associated with the onof the male and one-half of the female set of the decelerating growth phase which sample from each battery. A standard was indicated in Figure 1. Since the chick starter ration and water were fed ad graphed results in Figure 2 show that the libitum throughout the test period. age of the bird has a contributory effect on Individual body weights, recorded in body weight, the average body weights of grams, were taken at hatching and at each sex of the four lines were replotted weekly intervals thereafter up to 10 weeks on a log X log scale (Figure 3), with the of age. When the birds were 10 weeks of time axis calibrated as weeks of age from age the data on 40 males and 40 females conception. from each line were drawn at random for The graphs for the males and the feanalysis, with the restriction that each sex males of each line seemed to show that an was to have equal representation from each approach to linearity was measurable up battery. to 7 or 8 weeks of age. This change in the curve approximately corresponds to their DERIVATION AND ESTIMATION OF respective inflection points in Figure 1. GROWTH RATE The weekly average body weights for Therefore, it may be possible to measure each sex of the four lines are shown in the rate of change in body weight, relative Table 1. In general the males weighed more to body weight and relative to time, for than the females from hatch to 10 weeks each individual in the study by the apTABLE 1.—Average body weights in grams of the males and females of the MH, V .B.C., S and CNH lines from hatching to 10 weeks of age
BODY WEIGHT ( G R A M S
240
C. W. ROBERTS
I2O0
-
1000
-
X
/
800
/V /p', x /
/? 40 0
X /
//
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'<>•
200
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MH
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-
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-
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.600
BODY
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WEEKS
OF AGE
FIG. 1. Average body weights of the male and female MH, UBC, S and CNH lines, from hatch to 10 weeks of age.
plication of the power function y = at"; where y is equal to the body weight of an individual at time t, a is equal to the body weight of that individual at time o and b represents the growth rate of the individual. When an individual is weighed at two different times prior to puberty the growth rate, b, may be estimated for that time interval. The models depicting the body
weights of the i th individual at two different times would be: for
t
jme j . yn = aitibbii
and for time 2: y=at
b i
241
EARLY GROWTH R A T E
T h e ratio obtained b y dividing these two weights would be:
Solving for b i :
log
vi2 ^ a;t2bi yn
bi = -
a ; ti b i
log
and this will reduce t o :
~yn~ -yu. " t2
-
. ti. This calculated bi value (a pure number) may then be defined as the growth rate of
_y
WEEKS
OF
AGE
FIG. 2. Average body weights of male and female MH, UBC, S and CNH lines from hatch to 10 weeks of age.
242
C. W. ROBERTS
IOOO 800
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f*
-
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x ?' 16 x.-
-
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r
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FROM CONCEPTION
FIG. 3. Average body weights of the rriale and female MH, UBC, S and CNH lines from hatch to 10 weeks of age.
243
EARLY GROWTH RATE TABLE 2.—The average weekly growth rates for the MH, U.B.C., S and CNH lines from hatching to 10 weeks of age Lines
Growth period
MH
UBC
S
H-l 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10
2.19 2.53 2.15 1.75 1.85 2.30 2.04 2.00 1.51 1.21
2.41 2.73 2.30 1.75 1.96 2.48 1.97 1.91 1.61 1.10
2.79 2.90 2.58 2.09 1.96 2.48 2.19 1.82 1.90 1.31
CNH Average 2.51 2.68 2.61 1.99 2.19 2.61 2.19 2.26 1.71 1.52
2.48 2.73 2.40 1.95 2.01 2.48 2.12 2.00 1.71 1.31
the i th individual between time 1 and 2. A series of weekly growth rates may be calculated for the i th individual from a corresponding weekly series of body weights. These independently estimated weekly growth rates when averaged should provide a single estimate of growth rate for the i th individual throughout the accelerating growth phase. Weekly growth rate estimates were calculated for each individual in the study. Table 2 shows the average weekly growth rate and the average "7 week" growth rate of the four lines under study. The diversity of the average weekly growth rates is not unexpected since three changes in the environment occurred during the test. The first week's average chick growth rate (2.48 was undoubtedly affected by the stress of hatching, banding, weighing, and the bird's adjustment to the environmental conditions of the battery brooder. Hatching weights would also be influenced by time of hatch and the length of the drying period. The average growth rate during the fourth week (1.95) and seventh week (2.12) was probably influenced, in turn, by the ventilation difficulties and the transfer of birds from the batteries to the floor pens. An increase in the weekly growth rate follows each of the aforementioned
environmental effects, with the exception of a slight drop in the rate of growth during the eighth week for the MH and UBC chicks. The S line showed an increase in their growth rate one week following the transfer to the floor pens while the CNH had an increase in growth rate in the eighth week. When the major environmental changes that existed in this experiment are superimposed on the calculated weekly growth rates there seems to be a close agreement which tends to explain a portion of the week to week diversity in the average weekly growth rate. The rapid decline in the average weekly growth rate after the birds reached 7 weeks of age (2.00, 1.71 and 1.31 for the eighth, ninth, and tenth weeks) would appear to represent the expected change if at this time the birds had passed beyond puberty and these weekly estimates of growth rate were made during the decelerating phase of growth. The coefficient of variation of the seven weekly growth rates were calculated in order to check the uniformity of the weekly variances as well as ascertain if this statistic would provide an indication when the weekly growth rate estimates could be considered non-linear. Table 3 shows the coefficient of variation by sex for each of the TABLE 3.—The coefficient of variation (C.V.) and the average weekly growth rates (b) for the two sexes in each of the ten growth periods Growth period (weeks)
Males
Females
C.V.
b
C.V.
b
H-l 1-2 2-3 3^: 4-5 5-6 6-7 7-8 8-9 9-10
17.54 9.70 12.46 18.25 14.95 15.51 15.20 24.36 28.78 33.02
2.51 2.78 2.51 1.95 2.07 2.55 2.19 2.09 1.71 1.31
16.92 8.70 13.64 18.50 16.94 14.83 17.19 20.48 22.74 31.48
2.44 2.68 2.33 1.95 1.91 2.42 2.04 1.91 1.61 1.21
244
C. W. ROBERTS
ten growth periods. The uniformity of this statistic for each of the sexes throughout the first seven growth periods indicates that the variability of the weekly estimates of growth rate is quite similar with the single exception of the variability during the second growth period. In this period the males and females had their highest growth rate: males (2.78) and females (2.68), in addition, they had the lowest coefficient of variation, for the males (9.70) and the females (8.70). This may indicate that the exceptional growth during this period was greatly influenced by the environment, such as those previously mentioned factors which could influence the growth rate during the first week, and were believed to have resulted in an adverse environmental situation. For both sexes the coefficients of variation for the last three growth periods were higher than any of the previous weeks, and in addition, from the eighth to the tenth week the coefficient of variation rapidly increased: males (24.36 to 33.02) and the females (20.48 to 31.48). The increase in the coefficients of variation of the eighth week's estimate of growth rate would appear to be associated with the onset of puberty. The subsequent increases in the coefficients of variation would seem to infer that the estimates of growth rate, made during the latter periods, were in fact estimates within the decelerating phase of growth. Based on the graphic interpretation and the results of the coefficients of variation of the weekly growth rates, it was assumed that the weekly series of individual body weights, from hatch to 7 weeks of age, when expressed in the framework of the power function, would approximate linearity up to 7 weeks, and that the average of the weekly growth rates would provide a meaningful estimate of the individual's
growth rate for this 7 week period. Furthermore, it was assumed that the distribution of this trait, 7 week growth rate, was such that all of the conditions necessary for statistical analysis would be satisfied. GROWTH RATE AND BODY WEIGHT ANALYSIS
The following model was assumed to describe the sources of variance in each of the seven analyses of variance of weekly growth rate from hatch to 7 weeks of age: biiki = M+gi+dj+(gd) ij -|-s k -|-(gs)i k + (ds)jk+ (gds)ij k -l- eijki-
The line effect: g (i = 1-4), the battery effect: d (j = 1-2) and the sex effect: s (k = 1-2) were each assumed to be the result of a fixed effect. The residual effect associated with the measurement of the weekly growth of the individuals within a line, battery, and sex: e (1 = 1-20) was assumed to be of a random nature. The TABLE 4.—The average weekly growth rates of the males and females of the four lines from hatching to 7 weeks of age MH
UBC
S
CNH Average
H-1 1-2 2-3 3-4 4-5 5-6 6-7
2.21 2.56 2.19 1.80 1.91 2.36 2.19
Males 2.41 2.86 2.76 2.92 2.40 2.65 1.70 2.18 2.07 2.01 2.55 2.55 2.04 2.27
2.55 2.78 2.65 2.09 2.25 2.55 2.27
2.51 2.78 2.51 1.95 2.07 2.55 2.19
Average
2.17
2.26
2.49
2.45
2.37
H-1 1-2 2-3 3-4 4-5 5-6 6-7
2.18 2.48 2.11 1.75 1.79 2.16 1.97
Females 2.41 2.71 2.68 2.85 2.19 2.47 1.80 2.09 1.91 1.85 2.36 2.48 1.81 2.12
2.46 2.61 2.58 1.95 2.13 2.61 2.12
2.44 2.68 2.33 1.95 1.91 2.42 2.04
Average
2.06
2.17
2.37
2.35
2.25
Line average
2.12
2.22
2.43
2.40
2.31
245
EARLY GROWTH RATE
TABLE 5.—The sums of squares for the sources of variance, of the weekly analyses of variance of growth rate from hatching to 7 weeks of age expressed as a percentage of the total sums of squares Source of variance Batteries (B) Sex (S) BXS Lines (L) LXB LXS LXSXB Individuals within L, S & B Total
Weekly growth periods di. 1-2
H-l 1 1 1 3 3 3 3 304 319
Total sum of squares
2-3
3^
4-5
5-6
6-7
2.52** 0.21 3.78** 0.73 1 3.63** 5.96** 0.32 1.81** 0.09 25.44** 26.60** 30.19** 0.61 2.12* 2.15* 0.42 0.78 0.47 0.64 0.34 0.12
1.46** 4.00** 0.02 5.86** 3.44** 1.12 15.24** 18.30** 1.42 1.50 0.74 0.23 0.38 1.53
6.07** 2.19** 0.03** 10.71** 2.52* 1.62 1.06
68.06 100.0
62.20 100.0
60.81 100.0
74.76 100.0
70.00 100.0
75.80 100.0
82.20 100.0
58.35
20.98
33.61
61.10
33.87
46.37
40.20
0.56** 7.54** 0.14 8.96** 0.38 0.10 0.12
* Significant P < . 0 5 ** Significant P < . 0 1 1 Approaching significance
uniqueness of the lines, the definite environmental limitation of the two batteries, and the restriction of the sexes indicated the estimates of these effects can be considered fixed, however, since each of the weekly growth rate estimates were made on individuals that were drawn at random from the tested population, the estimate associated with this component should also be random. The model which was assumed to describe the sources of variance associated with the analysis of 7 week growth rate (Table 6) was, bijkim = {A+gi+dj + (gd) i j + s k + (gs) j k
utilized a similar model and those assumptions which were applied to the analysis of weekly growth rate. The multiple linear regression of hatching weight and 7 week growth rate on 7 week body weight was determined (after Snedecor, 1956). The multiple correlation index (R 2 ) and the partial regression coefficients as well as their standard partial equivalents were ascertained (Table 9). GROWTH RATE AND BODY WEIGHT RESULTS
The seven average weekly growth rates of the males and females for each line, as
+ (ds) j k +(gds) i j k +fij k i + e ijklm-
The line, battery and sex effects are similar to those which have already been defined. The effect related to the measurement of 7 week growth rate of the 1th individual within a line, battery and sex: f (1 = 1-20) and the residual effect of the measurement of weekly growth rate within the 1th individual: e (m = 1-7) were assumed to be random. The series of weekly body weights were also analysed (Table 7). This analysis
TABLE 6.--The
analysis of variance of 7 week growth rate
Source of variation Batteries (B) Sex (S) BXS Lines (L) LXB LXS LXBXS Individuals within L, B. & S Measurements within individuals Total
d.f.
Sums of squares
l l l 3 3 3 3 304 1,920 2,239
0.003 7.439** 0.022 38.442** 0.344 0.023 0.083 20.882 392.266 459.503
** Significant at P<.01.
Percent sums of squares <0.01 1.62 <0.01 8.37 0.08 <0.01 0.02 4.54 85.37
246
C. W. ROBERTS TABLE 7.—The sums of squares for the sources of variation, of the weekly analyses of variance of body weight from hatching to 7 weeks of age, expressed as a percentage of the total sums of squares
Source of variation (B) Sex (S) BXS Lines (L) LXB LXS LXSXB Individuals within L, S & B Total ' Total sum of squares
Weeks of age d.f. H 1 1 1 3 3 3 3 304 319
0.02 0.39 0.01 21.19** 0.25 2.94** 1.07
1
2
3.80** 0.94** 1.82** 3.31** 0.16 0.67* 51.56** 60.93** 0.38 0.41 1.46* 1.55** 0.49 0.09
3
4
0.41* 1.45** 5.80** 4.87** 0.36* 0.02 64.12** 68.00** 0.51 0.74* 1.47** 1.35** 0.07 0.25
5
6
7
0.90** 7.30** <0.01 66.00** 0.35 1.48** 0.33
0.18 8.53** <0.01 68.94** 0.28 1.06** 0.26
0.25* 10.50** 0.02 68.74** 0.21 1.17** 0.21
23.63 100.0
20.73 100.0
74.12 100.0
40.32 100.0
32.10 100.0
27.26 100.0
23.32 100.0
18.90 100.0
5,745
39,192
189,196
605,848
1,407,555 2,506,773 4,777,412 8,166,033
* Significant at P < . 0 5 . ** Significant at P < . 0 1 .
well as their 7 week average growth rates, are shown in Table 4. The average weekly growth rates, as well as the 7 week growth rate, of the males were greater than that of the females. There was not an appreciable difference between the 7 week growth rates of the two heavy lines: S (2.43) and CNH (2.40), and only a slight difference between the Leghorn lines: MH (2.12) and UBC (2.22). A difference in the 7 week growth rates of the heavy and Leghorn lines is apparent. The analysis of variance of weekly growth rates (Table 5) is recorded as the sums of squares for the sources of variation expressed as a percentage of the total sums of squares. A highly significant difference in the growth rates of the lines (L) was present in each of the seven growth periods. With the exception of the growth rate in the third and seventh growth period, a highly significant difference between the two batteries (B) was measurable. The difference in the growth rate of the sexes (S) approached significance during the first week of growth, and was highly sig-
nificant for the rest of the growth periods with the single exception of the fourth growth period. A first order interaction (B X S) was evident in the second and fourth growth period (P < .01), also another first order interaction ( L X B ) was present in the second, third, and sixth growth period ( P < . 0 5 ) . The remaining interactions ( L X S and L X S X B ) were not in evidence. When the sums of squares of the weekly analysis of variance of growth rate are expressed as a percentage of the total sums of squares, a comparison of the independent analyses may be made for a particular source of variance, especially since the different weekly growth rate analyses are made on the same individuals. The percentage values associated with lines shows an increase for the first three growth periods (25.44% to 30.19%). This is followed by a sharp decline in the fourth period (15.24%), which is probably related to the previously mentioned and demonstrated environmental influence. The slight increase observed in the fifth period
247
EARLY GROWTH RATE
(18.30%) is followed by a consistent decrease in these values. The percentage values associated with the individuals within L, S and B showed that the error terms contained a large proportion of the total sums of squares, and these values reflected the aforementioned changes which occurred in the lines. The remaining sources of variance did not show any sequential changes in their percentage values that could be associated with time nor did they show any apparent correlation with any other source of variation. The magnitude of the percentage sums of squares associated with individuals seems to indicate that, under the conditions of this experiment, weekly growth rate was greatly influenced by the environment. However early growth rate, in this instance up to the third week, may have been more influenced by line differences than was the growth rate in the later periods. The analysis of 7 week growth rate is presented in Table 6. Highly significant differences existed in the 7 week growth rate of the sexes as well as that of the
lines. These results agree with those of Table 5 in that the weekly growth rates also had a consistent effect due to lines and sexes. The analysis of 7 week growth rate also indicated that the effects associated with battery differences as well as those effects related to the first and second order interactions were negligible. These results do not agree completely with the weekly growth rate analysis, especially if one considers the main effect associated with batteries. In the weekly growth rate analysis (Table 5) highly significant differences in growth rate were measurable between the two batteries in 5 out of the 7 weekly test periods, while in the analysis of 7 week growth rate there was not any indication of a differential response between the two batteries. This obvious disagreement necessitated a more comprehensive study of the available data. Accordingly the series of weekly body weights were analysed (Table 7), and were recorded as the percentage of the total sums of squares. From hatching to 7 weeks of age the
TABLE 8.—The average body weights and growth rates for the chickens reared in two batteries from hatch to 7 weeks of age Body weight Weeks of age
Battery 1
2
Growth rate Difference
Growth
(2-1)
periods
1
2
H-1
2.39
2.56
+0.17
1-2
2.75
2.66
-0.09
2-3
2.41
2.38
-0.03NS
3-4
1.83
2.00
+0.17
4-5
2.03
1.95
-0.08
5-6
2.55
2.36
-0.19
6-7
2.07
2.12
+0.05NS
Average
2.29
2.29
0.00
H
41.5
41.7
0.2 N S
1
82.9
87.2
4.3
2
153.7
158.4
4.7
3
239.7
245.3
5.6
4
319.3
335.3
16.0
5
419.0
435.8
16.8
6
566.5
576.8
10.3 NS
7
706.6
722.5
16.9
Battery
Difference (2-1)
248
c. w. rABLE 9.—:The
based on
Population Sex Males Females Lines MH UBC S CNH
midtiph? linear regression analyses Partial regression coefficients (b) and standard partial regression coefficients (b)'
Average
Multiple linear
ROBERTS
7 week. growth rate
Multiple correlation index
7 week body weight
Hatching weight
(grams) 714.6
(grams) 41.6
2.29
(b)* 15.5
0.41
0>0
(b)* 853.5
(b') 0.93
(R2) 0.88
766.3 662.8
41.9 41.3
2.35 2.24
13.5 16.3
0.31 0.56
904.4 802.6
0.92 0.95
0.86 0.90
561.9 642.2 917.4 736.6
42.2 41.1 44.2 38.8
2.11 2.22 2.44 2.40
6.5 10.2 10.9 15.3
0.44 0.42 0.42 0.53
495.1 709.3 837.4 726.4
0.98 0.90 0.90 0.82
0.71 0.83 0.71 0.80
7 week growth rate
Hatching weight
All of the partial regression coefficients were highly significant (P<.01).
main effects associated with lines (L) were highly significant. The difference between the sexes (S) was measurable from 1 to 7 weeks of age (P < .01). These results are in close agreement with the weekly growth rate analysis (Table 5). The analysis of the weekly body weights showed that the first order interaction L X S was highly significant in each body weight analysis from hatching to 7 weeks of age, with the single exception of the lowered probability level at one week of age ( P < . 0 5 ) . This L X S interaction was unexpected in view of the fact that a comparable effect was completely lacking in the weekly growth rate analysis (Table S) as well as the analysis of 7 week growth rate (Table 6). The ability to detect this interaction when considering body weight and the inability of finding a similar response when considering growth rate strongly suggests that growth rate may be considered a distinct statistic, even though it is basically calculated from body weight. The presence of the L X S interaction also suggests a relatively consistent degree of non-linearity in the relationship between line and sex, with respect to body weight.
The lack of this effect after the application of the power function would seem to indicate this non-linearity is associated with the constant a in the power function, and may well mean that further study will indicate that some biological meaning can be associated with this constant. The remaining first order interactions in the body weight analysis do not seem to be related to those first order interactions in the weekly growth rate analysis, and the subsequent 7 week growth rate analysis does not show any indication of the presence of any additional interaction, as evidenced by the percentage sums of squares values. It seems reasonable to assume that those effects, when significant, may either be attributable to sampling errors or as being induced by small weekly battery environmental differences. Differences in the average body weights of the birds in the two batteries were measurable from 1 to 7 weeks of age with the single exception of the nonsignificant result at 6 weeks. Table 8 shows the weekly average body weights and growth rates of the chicks in each battery as well as the weekly difference between these batteries.
EARLY GROWTH RATE
249
The 7 week growth rate for the birds in battery difference because the growth dureach battery (2.29) confirms the analytical ing the seventh week again resulted in a result of a nonsignificant difference between significant difference of the average body batteries for the experimental period (Ta- weights in the two batteries (16.9 grams). ble 6). However in terms of weekly body With respect to the two batteries, the weight, significant differences existed for differences in the chick's average body all but one week throughout the test pe- weights was directly attributable to two riod. The nonsignificant battery differences weekly growth periods and may have been of the hatching weights indicates the ef- influenced by a third. The major changes fectiveness of the original randomization occurred during the first week and the of the birds in the batteries. The apparently fourth week of growth and culminated at 7 contradictory, significant differences in the weeks of age in a significant 16.9 gram difweekly growth rates attributable to battery ferential in favor of battery # 2 . effects is resolved as the non-directional There is no apparent reason why battery influence of weekly growth rates between # 2 would provide a better environment the two batteries. The birds in battery # 1 than battery # 1 , especially for only 2 out had a superior growth rate during 4 growth of the 7 weekly growth periods. If a supeperiods while the chicks in battery # 2 rior battery condition existed it would seem were superior in their growth rate for the more reasonable to assume that the results remaining periods. These results would would be in evidence during the other peseem to indicate that in this experiment riods. The specific lack of a consistent dithe weekly growth rate was not depressed rectional difference in weekly growth rate by a specific battery effect. in favor of the second battery coupled with The difference in the weekly average the fact that only two major changes ocbody weights of the birds in the two bat- curred which resulted in the difference of teries shows that the first week's growth the average body weights in the two batrate in battery # 2 (2.56) resulted in a teries would seem to indicate that the difhighly significant difference in 1 week ferences in the average weekly growth rates body weight (4.3 grams). The growth rate of the two batteries could be considered one for the next two weeks was high in battery of a random environmental effect. This may # 1 (2.75 and 2.41 respectively) but did be the best explanation of why the avernot effectively change the original body age 7 week growth rates of the two batterweight increment. The growth rate of the ies was the same yet the differential weekly birds in battery # 2 during the fourth week growth rates of the birds in the two bat(2.00) resulted in an additional increase teries resulted in significant differences in in the difference between the two batteries average body weights for all but one week (16.0 grams). The growth rate for the next of the experiment. This interpretation may 2 weeks was again in favor of battery # 1 partially explain why many experiments, (2.03 and 2.55 respectively). During the even though they are conducted under relasixth week the growth rate of the birds in tively uniform conditions, result in unexbattery # 1 apparently reduced the differ- plained and unrepeatable pen or battery ential between the two batteries (10.3 effects. grams). However this nonsignificant differThe percentage of the total sums of ence, in all likelihood still represents a true squares for weekly body weights (Table
250
C. W. ROBERTS
7) may be compared for any particular source of variance. The sums of squares associated with sex and line differences both show an increase in their percentage values which appeared to be related to age. In the estimation of sex differences this increase (0.39% to 13.68%) was evenly spread out over the 7 weeks, even though a slight drop was noted in the fourth week. This general increase in the proportionality would seem to correspond to the general divergence of the average male and female body weights from hatch to 7 weeks of age (Table 1 and Figure 1). The percentage increase for the lines appears to be restricted between hatching and 4 weeks of age (21.19% to 68.00%). Beyond this time little if any change is noted. This corresponds to the fairly rapid growth of the lines in which small differences in hatching weights are magnified rather quickly up to 4 weeks of age and thereafter these differences in the lines are proportionately uniform (Table 1). The percentage values associated with battery differences directly reflect those growth rate differences observed in Table 8. The increase in the differences of the average body weights between the two batteries observed following the growth rate during the first and fourth week (Table 8) can be associated with the higher percentage values observed at 1 and 4 weeks of age (3.80% and 1.45% respectively). Each of the remaining first and second order interactions are relatively uniform, for the most part nonsignificant, occur at a low percentage level and do not show any obvious time effects. In view of the results obtained with the separate analyses associated with growth rates and the subsequent analyses associated with body weights, it was deemed necessary to establish what relationship existed between the following traits: hatch-
ing weight, 7 week growth rate and 7 week body weight. If the assumption that the power function will reflect an estimate of growth rate which approaches linearity is valid the multiple linear regression of hatching weight and 7 week growth rate on 7 week body weight should have a relatively high multiple correlation index (R 2 ). Consequently the aforementioned multiple linear regression was determined for the entire population, for the two sexes, and for each individual line. The partial regression coefficients and their standard partial equivalents as well as the associated R2 values for each analysis are presented in Table 9. The multiple linear regression equation explains approximately 88% of the variability in 7 week body weight of the total population. When the males and females are considered separately 86% and 90% of the variability in 7 week body weight is accounted for by the regression equation. The analysis explains 71%, 83%, 71% and 80% of the variability in 7 week body weight of the MH, UBC, S and CNH lines respectively. In each analysis the multiple linear regression equation as well as the associated partial regression coefficients were highly significant. The relative importance of the two traits, hatching weight and 7 week growth rate as affecting 7 week body weight is indicated by the magnitude of their standard partial regression coefficients. In general the contributions of 7 week growth rate was more than twice the contribution of hatching weight to the dependent trait, 7 week body weight. The assumption that the trait approaches linearity appears to be valid although the overall decrease in the average weekly growth rates, from the first to the seventh week of growth (2.48 to 2.00), indicates that some non-linearity is present (Table 2). The cause and the amount of
EARLY GROWTH RATE
this non-linearity as well as the degree to which this influences the estimate of growth rate, will have to be ascertained. Further experiments to answer some of these questions are now in progress. DISCUSSION AND SUMMARY
The weekly average body weights for each sex within a line were plotted on an arithmetic graph, on a semi-log graph, and on a log X log graph. The accelerative phase of growth was apparent in the arithmetic graphs. The graphs also showed that the birds were entering the inhibited phase of growth by the seventh or eighth week. When the series of body weights were replotted on a semi-log basis a smooth decelerating curve was noted in all cases. These curves did not show any changes which could be associated with the onset of pubertal growth and they questioned the desirability of calculating a single estimate of a chick's growth rate for the first 3 or 4 weeks after hatching. When the weekly average body weights were plotted on a log X log scale, with the time axis calibrated as weeks of age from conception, the resultant graph indicated that an approach to linearity was obtained up to 7 or 8 weeks of age. Therefore, the power function y = atb was used to calculate the weekly growth rate of each individual in the study. The weekly growth rate as well as the coefficient of variation of the values was determined. The weekly growth rates reflected some environmental changes that occurred from week to week while the coefficient of variation indicated that the variance of the weekly growth rates was relatively uniform up until the seventh growth period. During the eighth growth period and the subsequent weeks the coefficient of variation rapidly increased, thereby giving some indication that these
251
latter stages could be considered as being in the decelerative growth phase and would not be expected to reflect linearity. Based on the graphic analyses and the evidence associated with the coefficients of variation, it was assumed that the weekly series of body weights for each individual from hatch to 7 weeks of age, when expressed in the framework of the power function, would approximate linearity up to 7 weeks and that the average of these weekly growth rates would provide a meaningful estimate of the individual's growth rate for this 7 week period. The weekly growth rates, the 7 week growth rates and the series of body weights from hatch to 7 weeks of age were subjected to the analysis of variance. The multiple linear regression of hatching weight, 7 week growth rate on 7 week body weight was also determined. Differences were measurable in the weekly growth rates of the lines, of the birds in the two batteries tested and in the weekly growth rates of the two sexes. The analysis of 7 week growth rate showed that only the line and sex effect provided the significant contributions. Sex and line differences were also present in the analysis of the body weights. These were measurable at 1 week of age for the sexes and at hatching for the lines. In addition, a line by sex interaction was consistently present from hatching to 7 weeks of age. This same interaction was completely lacking in any growth rate analysis. Differences in the body weights of the birds in the two batteries were also measurable for 6 out of 7 weeks. The data indicated that the nondirectional but significant battery influence on weekly growth rates produced by chance a 16 gram difference between the two batteries, even though the average 7 week average growth rate for the birds in
252
C. W. ROBERTS
each battery was the same. This difference was directly related to two and possibly three growth periods. The multiple linear regression accounted for a high degree of the variance of 7 week body weight. For the population the multiple correlation index (R 2 ) was 0.88. When the sexes were tested separately, the R2 value for the males was 0.86 and the females 0.90. The R2 values for the lines under study were 0.71 (MH),0.83 (UBC), 0.71 (S) and 0.80 (CNH). The standard partial regression coefficients indicated that the contribution of hatching weight was one-half that of 7 week growth rate when both of these statistics were related to 7 week body weight.
ACKNOWLED GMENTS
The author wishes to thank the American Poultry and Hatchery Federation, Kansas City, Missouri, the National Research Council of Canada, and the British Columbia Department of Agriculture, Victoria, B. C. for the financial assistance to conduct this study. The author is also indebted to Mr. H. W. Ellis, Superintendent of the Poultry Farm, for his contributions to the study. REFERENCES Brody, S., 1945. Bioenergetics and Growth. Reinhold Pub. Corp., New York, N.Y. Snedecor, G. W., 19S6. Statistical Methods. Sth ed., Iowa State College Press, Ames, Iowa.
Further Studies on the Influence of Trans-2Phenylcyclopropylamine (Tranylcypromine) on Growth Responses of Broilers THEODORE ELLISON, JOHN F. PAULS AND GEORGE C. SCOTT Research and Development Division, Smith Kline and French Laboratories, Philadelphia 1, Pennsylvania (Received for publication July 24, 1963)
T
RANYLCYPROMINE ('Parnate,' SK&F trans-385), a potent inhibitor of monoamine oxidase, has been reported to have shown a significant increase on the rate of gain of broiler cockerels (Ellison et al., 1963). These growth responses occurred within a fairly narrow dose range and well below the minimum therapeutic level considered necessary to produce overt pharmacologic action. In this study further data on the nutritional influence of tranylcypromine on gain and feed efficiency are reported using two strains of broiler cockerels. EXPERIMENTAL PROCEDURES
The studies reported herein were conducted in a controlled-environment room.
The room temperature was maintained at 90° ± 2°F. for the first week and was then decreased 5° per week for the next three weeks. The relative humidity was maintained at approximately 50% and artificial illumination (fluorescent) was kept constant 24 hours a day during the entire fourweek period of each study. The birds were raised in compartmented poultry batteries with raised wire floors and individual feed and water pans. Ledbrest X Pilch cockerels were used in the first experiment while Vantress X Arbor Acre broiler cockerels were used in the second trial. One-day-old chicks were fed a basal ration ad libitum for one week prior to selection for each study. At the end of this week, culling on both weight extremes