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Genetic Changes in Efficiency of Feed Utilization of Chicks Maintaining Body Weight Constant
1146
ANDREWS, SEAY, HARRIS JR. , AND NELSON
carcasses as affected by cage rearing. Poultry Sci. 51: 1837-1838. Nelson, G. S., L. D. Andrews and G. C. Harris, Jr., 1973. Mechanized cage system for growing broilers. Arkansas Farm Res. XXII, No. 4. Peterson, R. A., M. A. Hellickson, W. D. Wagner and A. D. Longhouse, 1971. The effect of humidity and flooring type on body weight and the severity of keel bursae in broilers. Poultry Sci. 50: 285-287.
Wagner, W. D., R. A. Peterson, M. A. Hellickson and A. D. Longhouse, 1969. Humidity and flooring type effect on severity of breast blisters and moisture content of fecal material from broilers. Poultry Sci. 48: 1888. Winget, C. M., A. H. Smith and C. F. Kelly, 1959. The effect of body weight on joint and skin disorders of domestic birds. Poultry Sci. 37: 1253-1254.
R. A. GUILL AND K. W. WASHBURN
Department of Poultry Science, University of Georgia, Athens, Georgia 30602 (Received for publication September 20, 1973)
ABSTRACT Selection based on individual feed conversion ratio was made for three generations in a chicken population previously selected for rate of growth and for one generation in a randombred population which had not been selected for rate of growth. Two sets of high (HL) and two sets of low (LL) feed conversion ratio lines were selected in each population: one set selected so that body weight was constant over generations (HLWK, LLWK), while in the other set (HLWV, LLWV) body weight was allowed to vary. In the three generations of selection in the chicken population the units of feed required for a unit of gain was increased .12 in the HLWV line over that of non-selected controls and .08 in the HLWK line. In the low feed conversion ratio lines the units of feed required for a unit of gain was decreased .11 in the LLWK line and .07 in the LLWV line. In both low lines more progress was made in females than in males. In the randombred stock, which had no previous selection for growth, as much progress in lowering the feed conversion ratio was made in one generation of selection as was made in three generations in the broiler population (decreased .12 in the LLWK and .13 in the LLWV) with no sex difference in response. The realized heritabilities for feed conversion for the lines selected from the broiler population were .20, .21, .33 and .26 for the LLWV, LLWK, HLWV, HLWK, respectively. In the lines selected from the randombred population the realized heritabilities were .56, .45, .35 and .31, respectively. The magnitude of the heritability values obtained indicate that even in lines previously selected for growth there is sufficient variation in efficiency of feed utilization to allow progress in selection without further change in body weight. POULTRY SCIENCE 53: 1146-1154, 1974
S
OME basis of genetic control for effi-
fifty years progress in cattle breeding. The
ciency of feed utilization has been report-
mean heritability estimates for feed lot gain
ed for a number of species. Thomas et al.
and efficiency were .45 and .39, respectively.
(1958) reported a sire component heritability
Craft (1958) compiled a composite of fifty
estimate for 4-8 week feed conversion in
years research in swine breeding. The average
chickens of .24 and .36 for males and females,
heritability estimates for growth rate and
respectively, and a combined sex component
efficiency were .29 and .31, respectively.
of .51. Wilson (1969) calculated sire and dam component heritability estimates of .69 and
Sutherland et al.
(1970) selecting three
separate lines of mice for growth rate, found
.79 for feed consumption, .81 and .89 for
similar response in all three lines through nine
daily gain and .34 and .50 for feed efficiency.
generations. In generation 10-21, the lines
Warwick (1958) prepared a composite of
were selected for correlated responses; one
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Genetic Changes in Efficiency of Feed Utilization of Chicks Maintaining Body Weight Constant
GENETIC CHANGES IN FEED EFFICIENCY
or experimental differences. Fox and Bohren (1954) found a correlation between gain and efficiency of +.60 and concluded there is little justification for commercial breeders to select on the basis of food requirements. Wilson (1969) reported a phenotypic correlation of -.52 (difference in sign is due to arrangement of traits in the ratio) between efficiency and consumption. Similar high correlations between gain and feed efficiency have been reported for steers (Winters and McMahon, 1933; Fitzhugh and Cartwright, 1971), swine (Dickerson and Grimes, 1947), and mice (Sutherland et al., 1970). The objectives of this study were to determine if the efficiency of feed utilization could be changed without an associated change in growth rate or body size and to compare the genetic variability for efficiency in populations differing in growth rate. MATERIALS AND METHODS Selection for feed conversion ratio (units feed/unit gain) was conducted for three generations in a broiler grandparent line which had been previously selected for growth rate and for one generation in a randombred line (Hess, 1962) which had not been selected for growth rate since its construction. Selection was for individual feed conversion ratio (units feed required for 1 unit gain) between four and eight weeks of age for the broiler population and from 5-9 weeks in the randombred population. The individual cages and feeding methods have been previously described by Guill and Washburn (1972). The parent stock of each line was subdivided into five separate lines which were maintained as closed populations. The five lines were: low line weight variable (LLWV), low line weight constant (LLWK), high line weight variable (HLWV), and high line weight constant (HLWK), and control. The weight variable lines (WV) were selected solely on the basis of their feed conversion ratio. The weight constant (WK) lines were selected for
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for efficiency of feed utilization, one for feed consumption and one for growth rate. The line selected for efficiency made faster advances in efficiency from generation 10-21 while all three lines made similar advancement in gain on test. Pooled heritability estimates for all lines and sexes were .27 for efficiency and .24 for rate of gain. Feed conversion is influenced by a large number of physiological and environmental factors which sometimes are confounded with genetic differences. Often differences between genetic stocks in growth rate and efficiency may simply be due to difference in appetite as shown by Siegel and Wisman (1966) in their studies of the physiological basis of differences in high and low growth lines of chickens. A similar explanation was proposed by Timon and Eisen (1970) in studying the differences in lines of mice selected for post-weaning gain. However, differences in appetite may not always be the explanation for differences in growth rate and efficiency. Proudman et al. (1970) found no difference in feed conversion of chickens selected for high growth rate whether they were fed ad libitum, or restricted in body weight to that of the low line, or restricted in feed consumption to that consumed by the low line. Improvement in efficiency of feed utilization has usually been brought about as a growth correlated trait although the association between feed efficiency, feed consumption and growth are complex and not easily understood. Hess et al. (1941) found a strong correlation between the efficiency of purebred progeny and crossbred progeny produced by the same sire and concluded that the efficiency of feed utilization was inherited. Hess and M l (1948), in reviewing previous information concerning the genetic basis for efficiency, noted an inherent difference in efficiency of feed utilization between individuals that could not be explained on the basis of body weight, rate of gain,
1147
1148
R. A. GUILL AND K. W. WASHBURN
.14 .12 .10 .08 .06 •04 + .02
-.02 .04 .06 .08 .10 .12 .14
LLWV • — • LLWK • • HLWV • - - • HLWK*- - •
SI
S2
S3
GENERATIONS
FIG. 1. Response to selection for divergence in feed conversion ratio in broiler base population (expressed as deviation from control, sexes combined). LLWV = Low conversion ratio, weight variable HLWV = High conversion ratio, weight variable LLWK = Low conversion ration, weight constant HLWK = High conversion ratio, weight constant
feed conversion with the restriction that body weight changes be minimal from generation to generation. This was done by first ranking all individuals of a population by weight (sexes separate). This ranking was divided into groups of 5 individuals. One individual was then selected from each group of 5 individuals. In this way, the range of body weights was evenly distributed over the population selected for feed conversion ratio. The controls for the broiler line consisted of 40 paired matings reproduced each generation and reared intermingled with the lines. The AC and ARB randombred line eggs were obtained from the populations maintained at
RESULTS AND DISCUSSION The response to selection for divergence in feed conversion using the broiler base population is shown in Figure 1. The progress for sexes combined was relatively high in the HLWV line the first generation (.095 increase in units feed/unit gain); but in the second generation it was increased only .020 with no further progress in the third generation. Progress in the HLWK line was less than in the HLWV the first generation (.040 increase in conversion ratio); but in the second generation progress continued to increase to a conversion ratio of .085. However, in the third generation no progress was made in this line for a total increase in units feed required/unit of gain of .075 for the HLWK as compared to .115 for the HLWV line. The units feed required/unit gain for sexes combined was decreased .03 in the LLWV line in the first generation and .04 in the
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z o
the Southern Regional Poultry Genetics Laboratory. The parent populations consisted of 432 birds to which a selection pressure of 90% in males and 70% in females was applied for each line. In the subsequent generations feed conversions were obtained for a total of 864 birds of the five lines and a selection pressure of 95% applied to the males and 70% applied to the females. At hatching, chicks were banded according to their respective lines, vaccinated for Marek's disease, reared in litter covered pens for 25 to 32 days of age. At this time, the chicks were placed in the individual cages and given a three-day adjustment period before being placed on test. Body weights and feed consumption were determined at 2-week intervals. Realized heritability estimates on all selected generations were determined and heritability by regression of offspring on midparent was determined for the S 2 and S 3 of the commercial broiler lines.
GENETIC CHANGES IN FEED EFFICIENCY
HLWV HLWV HLWK HLWK
rf* £ . - - • $ g) g tf* * - - - • $ » •
.14 .12
/
.10 .08
/
.06 .04
+
.02
/
/
-*•--_,
/
/ /
/
/*'
/
""--•
.•^
_-•
^\^^-— " '•*~~^^~~~^^
^-~~~~~^~^^^
~ /' 'i^~^ ~ * ez^^ •c
*"*;=^
~ .02 .06
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.08 .10 .12
LLWV LLWV LLWK LLWK
<* O % O 0?» O $ O
D 0 0 O
XX^^^--^
.14
S2
with no progress in the third generation. A slight decrease (0.025) in feed required was noted in the second generation of the LLWV males, while in the third generation the progress in the males of LLWK line had approached that of the females. In the high feed conversion ratio lines, more rapid progress was made in the males than in the females. In the HLWV line, the units feed required /unit gain in the males was increased to 0.14 the first generation, with no subsequent improvement. The HLWV females made progress for the first and second generations to an increase of 0.11 feed with no progress for the third generation. Although the males of the HLWK line made faster progress than the females of that line,
S3
GENERATION
FIG. 2. Sex effect on response to selection for divergence in feed conversion ratio in broiler base population (expressed as deviations from controls). LLWV = Low conversion ratio, weight variable HLWV = High conversion ratio, weight variable LLWK = Low conversion ratio, weight constant HLWK = High conversion ratio, weight constant second generation with slight progress in the third generation for a total decrease of .07 units feed required/unit gain in the three generations of selection. In the LLWK line the units feed required/unit gain was decreased by .025 the first generation, .045 the second generation and .040 the third generation for a total decrease of .10 in three generations of selection. The response of the sexes was quite different for the lines selected for low or high feed conversion values (Figure 2). No progress in decreasing the feed conversion was made in the first generation in males of either low line, while in the females it was decreased .05 in the LLWK and .06 in the LLWV lines the first generation. Similar progress (decrease of .06 units) was made in both the female lines the second generation
-
z o o s o
-
/ •^
_
/ \
m
~~-///
„
„
^
~-^r--
LLWV LLWK - HLWV HLWK
. •——• • • •——•
m
i
i
i
SI
S2
S3
GENERATIONS
FIG. 3. Percent deviation from control in body weight each generation for lines selected for divergence in feed conversion ratio. LLWV = Low conversion ratio, weight variable HLWV = High conversion ratio, weight variable LLWK = Low conversion ratio, weight constant HLWK = High conversion ratio, weight constant
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.04
1149
1150
R. A. GUILL AND K. W. WASHBURN
GENERATIONS
FIG. 4. Response to selection for divergence in feed conversion ratio in randombred population (expressed as deviation from control, sexes combined). LLWV = Low conversion ratio, weight variable HLWV = High conversion ratio, weight variable LLWK = Low conversion ratio, weight constant HLWK = High conversion ratio, weight constant both sexes continued to make progress for all three generations. These results indicate that faster initial gains in improvement of efficiency of feed utilization can be made in females than in males of broiler lines which have been previously selected for growth. This may be associated with the more intense selection pressure that is usually applied in males for growth and other traits. This would tend to decrease the number of loci not fixed, reducing the overall variability of the population. Body weight of the various lines did not change significantly from generation to generation compared to the non-selected control
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si
P
line (Figure 3). Although the LLWV was the only line that was consistently (3%) higher in each generation, there was no significant difference in any line for any generation. Since the change in body weight in all lines over each generation was negligible, the weight variable and weight constant lines can be considered replicate lines. Figure 4 shows the response to selection for feed conversion, sexes combined, in one generation of a randombred population. The feed conversion ratio of the HLWK line increased .055 units, while that of the HLWV increased .080 units. This did not differ significantly from the progress made in one generation of the broiler high lines. The feed conversion ratio of the LLWK decreased to . 125 below that of the control and the LLWV decreased to .130 below the control lines. Both the low lines of the randombred population made significantly more progress in one generation of selection than did the broiler low lines. In fact, more progress was made in decreasing the feed conversion ratio in the randombred line in one generation than in 3 generations of selection in the broiler type stock. Presented in Tables 1 and 2 are summaries of body weights, feed conversion ratios and feed consumption. The results of some studies (Siegel and Wisman, 1966) indicated it might be difficult to conduct accurate experiments on growth rate or efficiency of feed utilization due to the high correlation of both traits with appetite. Thus, selection would be of those individuals with large appetites in addition to or instead of those that actually have the genetic make-up for larger growth or better feed conversion. In the present study, selection for feed conversion ratio in the broiler population for three generations resulted in a significant change in both high lines and between both low lines compared to the control line. However, there were no significant changes in body weight, rate of gain or appetite in
1151
GENETIC CHANGES IN FEED EFFICIENCY
the selected lines compared to controls. The mean change in 8-week body weight after 3 generations was +9 gms. in the lines selected for low feed conversion ratio. The mean change in 4-8 week gain after three generations was +6 gms for the lines selected for low feed conversion ratio and - 4 2 gms. in the lines selected for high feed conversion ratio. The mean change in 4-8 week feed
consumption after three generations was - 2 7 gms. in the line selected for low feed conversion ratio and +51 gms. in the line selected for high feed conversion ratio (Table 1). In the one generation of selection for feed conversion ratio in the randombred population, the weight (compared to controls) was decreased 9 gms. in the line selected for low conversion ratio and decreased 109 gms. in
s, LLWV
s2 LLWV LLWV LLWK LLWK C 8 C 9 HLWV HLWV HLWK HLWK
3 9 3 9
8 9 3 9
s, LLWV LLWV LLWK LLWK C 8 C 9 HLWV HLWV HLWK HLWK
3 9 3 9
3 9 3 9
Wt. 4 wks.
Wt. 8 wks.
4-8 wk. feed conv.
4-8 wks. gain
4-8 wk. feed cons.
482 408 430 378 466 395 471 405 459 401
1537 1202 1408 1131 1485 1170 1463 1156 1469 1193
2.36 2.51 2.36 2.52 2.36 2.57 2.50 2.62 2.40 2.61
1055 794 978 753 1019 775 992 751 1010 792
2490 1993 2308 1898 2405 1992 2480 1968 2424 2067
546 432 500 438 510 431 519 419 529 431
1571 1227 1517 1231 1518 1189 1470 1155 1466 1169
2.16 2.25 2.15 2.22 2.19 2.33 2.33 2.41 2.30 2.39
1025 795 1017 793 1008 758 951 736 937 738
2214 1789 2187 1760 2208 1766 2216 1774 2155 1764
468 357 430 357 447 384 467 403 438 408
1440 1116 1358 1074 1371 1104 1392 1134 1323 1108
2.10 2.18 2.05 2.15 2.15 2.27 2.27 2.38 2.22 2.35
972 759 928 717 924 720 925 731 885 700
2041 1655 1902 1535 1987 1634 2100 1738 1965 1645
LLWV = low line weight variable; LLWK = low line weight constant; HLWV • high line weight variable; HLWK = high line weight constant; S = selected generation; C = control.
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TABLE 1.—Summary of 4 to 8 week weights (gms.), 4 to 8 week feed conversion, 4 to 8 week gain (gms.), 4 to 8 week feed consumption (gms.) of broiler stock
1152
R. A. GUILL AND K. W. WASHBURN
TABLE 2.—Summary of S, randombred population for 5-9 week weights (gms.), 5-9 week feed conversion ratio, 5-9 week gain (gms.), 5-9 week feed consumption (gms.)
Lines
6 9
Dev. from cont.
Wt. 9 wks.
Dev. from cont.
5-9 wk. feed conv.
Dev. from cont.
5-9 wk. gain
Dev. from cont.
5-9 wk. feed cons.
Dev. from cont.
530 433 535 451 547 483 521 417 504 437
-17 -50 -12 -32
1340 1073 1422 1092 1350 1118 1269 987 1240 1013
-10 -45 +72 -26
2.36 2.48 2.33 2.52 2.46 2.64 2.56 2.70 2.53 2.68
-.10 -.16 -.13 -.12
810 640 887 641 803 635 748 570 736 556
+07 +05 +84 +06
1912 1587 2067 1615 1975 1676 1915 1539 1862 1490
-63 -89 +92 -61
-26 -66 -43 -46
-81 -131 -110 -105
+ + + +
.10 .06 .07 .04
-55 -65 -67 -79
-60 -137 -113 -186
LLWV = low line weight variable; LLWK = low line weight constant; HLWV = high line weight variable; HLWK = high line weight constant; S = selected generation; C = control. the line selected for high feed conversion ratio. The 4-8 week gain was increased an average of 26 gms. in the low line and decreased 64 gms in the high line. Consumption for this period was decreased 30 gms. in the low line and 124 gms. in the high line. Wilson (1969), using the same randombred base population that we used, concluded that selection for improved feed conversion would produce a bird that gained slower, consumed less feed but converted feed to body tissue somewhat more efficiently than those birds produced by selection for gain. In our study, the one generation of selection for improved feed conversion in the randombred population produced progeny that ate slightly less feed with a more efficient conversion ratio. However, the line selected for poor feed conversion also ate less feed than controls. The gain in body weight of the low lines were slightly higher but the differences were not significant while the high lines were significantly lower in body weight gain. Estimates of realized heritability for 4-8 week feed conversion are presented in Table 3 for the commercial broiler and randombred stocks. Realized heritability estimates, adjusted for control, were calculated by the formula:
The progeny control average minus the parent control average compensated for environmental or replicate differences. This gave somewhat lower heritability estimates but was considered more accurate. The unweighted mean realized heritability for the Sj randombred lines was .42 compared to .26 for the S, of the lines selected from the commercial broiler stock. This indicates that a greater amount of variability for feed conversion was present in stocks which had not been selected for growth rate than in the commercial broilers selected for growth rate. However, this greater heritability may be a reflection of more variability in growth rate not separable from feed conversion. The heritability for decreasing the feed conversion ratio (which could be accomplished by increasing growth rate if variability was present in a population) was greater (.50) than was that of increasing the ratio (.33). The converse was true in the realized heritability of the S, commercial broiler stock. The mean realized h2 of the two low lines was .13 compared to .38 for the two high lines. This difference is primarily due to the complete lack of response of the low line males in the first generation. In the second generation, the realized h 2
(Progeny x — Parent x) - (Progeny Control x — Parent Control x) (Selected Parent x - Parent x)
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LLWV LLWV LLWK LLWK C 3 C 9 HLWV HLWV HLWK HLWK
Wt. 5 wks.
1153
GENETIC CHANGES IN F E E D EFFICIENCY
TABLE 3.—Realized heritability for randombred and selected broiler lines ARB-AC
s,
Commercial
Broiler
Stock
s,
S2 .25 .37 .32 .41
s3
Unweighted means .20 .21 .33 .26
.22 .14 .56 LLWV .15 .12 .45 LLWK .17 .50 .35 HLWV .11 .27 .31 HLWK Unweighted .25 .16 .34 .26 .42 mean LLWV = low weight variable; LLWK = low line weight constant; HLWV = high line weight variable; HLWK = high line weight constant; S = selected generation.
TABLE 4. Heritability by regression of offspring on mid-parent of selected broiler lines.
Hatch Hatch Hatch Hatch
1 1 2 2
Combined
.30 .28 .35 .39 .33
.23 .36 .29 .32 .30
to selection would be expected in males than in females of growth-selected lines. REFERENCES Craft, W. A., 1958. Fifty years of progress in swine breeding. J. Animal Sci. 17: 960-980. Dickerson, G. E., and J. C. Grimes, 1947. Effectiveness of selection for efficiency of gain in Duroc swine. J. Animal Sci. 6: 265-287. Fitzhugh, H. A., Jr., and T. C. Cartwright, 1971. Variation in post-weaning weight gains of steers independent of appetite. J. Animal Sci. 32: 832-839. Fox, T. W., and B. B. Bohren, 1954. An analysis of feed efficiency among breeds of chickens and its relationship to rate of growth. Poultry Sci. 33: 549-561. Guill, R. A., and K. W. Washburn, 1972. Cages and feed troughs for individual broiler feed consumption experiments. Poultry Sci. 51: 1047-1048. Hess, C. W., 1962. Randombred populations of the southern regional poultry breeding project. Wld.'s Poultry Sci. J. 18(2): 147-152. Hess, C. W., T. C. Byerly and M. A. Jull, 1941. The efficiency of feed utilization by Barred Plymouth Rock and crossbred broilers. Poultry Sci. 20: 210-216. Hess, C. W., and M. A. Jull, 1948. A study of the inheritance of feed utilization efficiency in the growing domestic fowl. Poultry Sci. 27: 24-39. Proudman, J. A., W. J. Mellen andD. L. Anderson, 1970. Utilization of feed in fast- and slow-growing lines of chickens. Poultry Sci. 49: 961-972. Siegel, P. B., and E. L. Wisman, 1966. Selection for body weight at eight weeks of age. 6. Changes in appetite and feed utilization. Poultry Sci. 45: 13911397. Sutherland, T. M., P. E. Biondini, L. H. Haverland, D. Pettus and W. B. Owens, 1970. Selection for rate of gain, appetite and efficiency of feed utilization in mice. J. Animal Sci. 31: 1049-1057. Thomas, C. H., W. L. Blow, C. C. Cockerham and
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of both broiler lines was similar. The h2 of all lines in the third generation decreased. If the mean realized heritabilities of the two populations (.42 and .25, Table 3) are combined with those obtained by regression of offspring (x = .31, shown in Table 4) the mean h2 obtained is .32. It may vary depending on sex, previous selection for growth, whether selection is for high or low efficiency and amount of selection applied. Heritability estimates presented by Thomas et al. (1958) and Wilson (1969) for 4-8 week feed conversion in broilers were .31 and .34, respectively, for sire component and .55 and .50, respectively, for dam component. The heritability of the sire component corresponds with the realized heritability in generation 1 and 2 of this study and heritability by regression of offspring on mid-parent in generation 2 and 3 of this study. The magnitude of the heritability values obtained indicate that even in lines previously selected for growth there is sufficient variation in efficiency of feed utilization to allow progress in selection without further change in body weight. However, faster response
1154
R. A. GUILL AND K. W. WASHBURN
E. W. Glazener, 1958. The heritability of body weight, gain, feed consumption and feed conversion in broilers. Poultry Sci. 37: 862-869. Timon, V. M., and E. J. Eisen, 1970. Comparisons of ad libitumand restricted feeding of mice selected and unselected for post-weaning gain. I. Growth, feed consumption and feed efficiency. Genetics, 64: 41-57.
Warwick, E. J., 1958. Fifty years of progress in breeding beef cattle. J. Animal Sci. 17: 922-943. Wilson, S. P., 1969. Genetic aspects of feed efficiency in broilers. Poultry Sci. 48: 487-495. Winters, L. M., and J. McMahon, 1933. Efficiency variation in steers. Minnesota Agr. Exp. Sta. Tech. Bull. 94: 1-28.
W A Y N E L . BACON, MARGERY A . MUSSER AND KEITH I. BROWN
Department of Poultry Science, Ohio Agricultural Research and Development Center, Wooster, Ohio 44691 (Received for publication September 24, 1973)
ABSTRACT Free fatty acid (FFA) concentrations in blood plasma from immature, laying and broody turkey hens were re-examined following removal of phospholipids. A mean value of .21 ± .02 (A. equiv./ml. plasma of FFA was found for immature hens and as they were stimulated into egg production, and no systematic increase was noted. Broody hens had the same concentration as laying and immature hens. Neutral lipid levels (mainly triglyceride) increased from about 3.5 mg./ml. plasma to about 18-25 mg./ml. plasma as the hens reached sexual maturity, then plateaued until a broody period began when they dropped to concentrations comparable to those in immature hens. No correlation was found between FFA and neutral lipid concentrations. Although FFA concentration is much lower than previously reported, 14% of the total daily amount cleared was calculated to be sufficient to account for egg yolk neutral lipid. The remaining 86% would be available for other metabolic functions. POULTRY SCIENCE 53: 1154-1160, 1974
INTRODUCTION
P
LASMA free fatty acid (FFA) levels in chickens have been reported to increase from about 0.3 JJL. equiv. per ml. in non-laying pullets to about 1.0 to 2.0 |JL. equiv. per ml. in laying hens (Heald and Badman, 1963). In this study, FFA levels were determined by the titrimetric method of Dole and Meinertz (1960). A similar study has recently appeared for turkeys (Bajpayee and Brown, 1972). Prior to exposing immature birds to stimulatory lighting, plasma FFA concentration was 1.14 ± .20 |JL. equiv. per ml. After 21 days of stimulatory lighting, FFA concentration had almost doubled to 2.15 ± .11 (ju equiv. per ml. These authors used the method of Kvam
et al. (1964) to determine plasma FFA. This method is based on forming the copper salts of fatty acids (FA) and then colorimetrically determining the amount of copper associated with the fatty acids after they are extracted. The effect of fasting and gonadotrophin injection on plasma FFA levels was studied by Heald and Rookledge (1964). They observed that fasting caused an increase in plasma FFA in normal cocks, but a decrease in plasma FFA in laying hens when initial FFA levels were high and an increase when initial levels were low. Their method of determining FFA was based on the titrimeteric method of Dole and Meinertz (1960). When pituitary powder was injected during four-day starvation of laying hens, plasma FFA levels were maintained, as were plasma total lipids.
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Plasma Free Fatty Acid and Neutral Lipid Concentrations in Immature, Laying and Broody Turkey Hens
ANDREWS, SEAY, HARRIS JR. , AND NELSON
carcasses as affected by cage rearing. Poultry Sci. 51: 1837-1838. Nelson, G. S., L. D. Andrews and G. C. Harris, Jr., 1973. Mechanized cage system for growing broilers. Arkansas Farm Res. XXII, No. 4. Peterson, R. A., M. A. Hellickson, W. D. Wagner and A. D. Longhouse, 1971. The effect of humidity and flooring type on body weight and the severity of keel bursae in broilers. Poultry Sci. 50: 285-287.
Wagner, W. D., R. A. Peterson, M. A. Hellickson and A. D. Longhouse, 1969. Humidity and flooring type effect on severity of breast blisters and moisture content of fecal material from broilers. Poultry Sci. 48: 1888. Winget, C. M., A. H. Smith and C. F. Kelly, 1959. The effect of body weight on joint and skin disorders of domestic birds. Poultry Sci. 37: 1253-1254.
R. A. GUILL AND K. W. WASHBURN
Department of Poultry Science, University of Georgia, Athens, Georgia 30602 (Received for publication September 20, 1973)
ABSTRACT Selection based on individual feed conversion ratio was made for three generations in a chicken population previously selected for rate of growth and for one generation in a randombred population which had not been selected for rate of growth. Two sets of high (HL) and two sets of low (LL) feed conversion ratio lines were selected in each population: one set selected so that body weight was constant over generations (HLWK, LLWK), while in the other set (HLWV, LLWV) body weight was allowed to vary. In the three generations of selection in the chicken population the units of feed required for a unit of gain was increased .12 in the HLWV line over that of non-selected controls and .08 in the HLWK line. In the low feed conversion ratio lines the units of feed required for a unit of gain was decreased .11 in the LLWK line and .07 in the LLWV line. In both low lines more progress was made in females than in males. In the randombred stock, which had no previous selection for growth, as much progress in lowering the feed conversion ratio was made in one generation of selection as was made in three generations in the broiler population (decreased .12 in the LLWK and .13 in the LLWV) with no sex difference in response. The realized heritabilities for feed conversion for the lines selected from the broiler population were .20, .21, .33 and .26 for the LLWV, LLWK, HLWV, HLWK, respectively. In the lines selected from the randombred population the realized heritabilities were .56, .45, .35 and .31, respectively. The magnitude of the heritability values obtained indicate that even in lines previously selected for growth there is sufficient variation in efficiency of feed utilization to allow progress in selection without further change in body weight. POULTRY SCIENCE 53: 1146-1154, 1974
S
OME basis of genetic control for effi-
fifty years progress in cattle breeding. The
ciency of feed utilization has been report-
mean heritability estimates for feed lot gain
ed for a number of species. Thomas et al.
and efficiency were .45 and .39, respectively.
(1958) reported a sire component heritability
Craft (1958) compiled a composite of fifty
estimate for 4-8 week feed conversion in
years research in swine breeding. The average
chickens of .24 and .36 for males and females,
heritability estimates for growth rate and
respectively, and a combined sex component
efficiency were .29 and .31, respectively.
of .51. Wilson (1969) calculated sire and dam component heritability estimates of .69 and
Sutherland et al.
(1970) selecting three
separate lines of mice for growth rate, found
.79 for feed consumption, .81 and .89 for
similar response in all three lines through nine
daily gain and .34 and .50 for feed efficiency.
generations. In generation 10-21, the lines
Warwick (1958) prepared a composite of
were selected for correlated responses; one
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Genetic Changes in Efficiency of Feed Utilization of Chicks Maintaining Body Weight Constant
GENETIC CHANGES IN FEED EFFICIENCY
or experimental differences. Fox and Bohren (1954) found a correlation between gain and efficiency of +.60 and concluded there is little justification for commercial breeders to select on the basis of food requirements. Wilson (1969) reported a phenotypic correlation of -.52 (difference in sign is due to arrangement of traits in the ratio) between efficiency and consumption. Similar high correlations between gain and feed efficiency have been reported for steers (Winters and McMahon, 1933; Fitzhugh and Cartwright, 1971), swine (Dickerson and Grimes, 1947), and mice (Sutherland et al., 1970). The objectives of this study were to determine if the efficiency of feed utilization could be changed without an associated change in growth rate or body size and to compare the genetic variability for efficiency in populations differing in growth rate. MATERIALS AND METHODS Selection for feed conversion ratio (units feed/unit gain) was conducted for three generations in a broiler grandparent line which had been previously selected for growth rate and for one generation in a randombred line (Hess, 1962) which had not been selected for growth rate since its construction. Selection was for individual feed conversion ratio (units feed required for 1 unit gain) between four and eight weeks of age for the broiler population and from 5-9 weeks in the randombred population. The individual cages and feeding methods have been previously described by Guill and Washburn (1972). The parent stock of each line was subdivided into five separate lines which were maintained as closed populations. The five lines were: low line weight variable (LLWV), low line weight constant (LLWK), high line weight variable (HLWV), and high line weight constant (HLWK), and control. The weight variable lines (WV) were selected solely on the basis of their feed conversion ratio. The weight constant (WK) lines were selected for
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for efficiency of feed utilization, one for feed consumption and one for growth rate. The line selected for efficiency made faster advances in efficiency from generation 10-21 while all three lines made similar advancement in gain on test. Pooled heritability estimates for all lines and sexes were .27 for efficiency and .24 for rate of gain. Feed conversion is influenced by a large number of physiological and environmental factors which sometimes are confounded with genetic differences. Often differences between genetic stocks in growth rate and efficiency may simply be due to difference in appetite as shown by Siegel and Wisman (1966) in their studies of the physiological basis of differences in high and low growth lines of chickens. A similar explanation was proposed by Timon and Eisen (1970) in studying the differences in lines of mice selected for post-weaning gain. However, differences in appetite may not always be the explanation for differences in growth rate and efficiency. Proudman et al. (1970) found no difference in feed conversion of chickens selected for high growth rate whether they were fed ad libitum, or restricted in body weight to that of the low line, or restricted in feed consumption to that consumed by the low line. Improvement in efficiency of feed utilization has usually been brought about as a growth correlated trait although the association between feed efficiency, feed consumption and growth are complex and not easily understood. Hess et al. (1941) found a strong correlation between the efficiency of purebred progeny and crossbred progeny produced by the same sire and concluded that the efficiency of feed utilization was inherited. Hess and M l (1948), in reviewing previous information concerning the genetic basis for efficiency, noted an inherent difference in efficiency of feed utilization between individuals that could not be explained on the basis of body weight, rate of gain,
1147
1148
R. A. GUILL AND K. W. WASHBURN
.14 .12 .10 .08 .06 •04 + .02
-.02 .04 .06 .08 .10 .12 .14
LLWV • — • LLWK • • HLWV • - - • HLWK*- - •
SI
S2
S3
GENERATIONS
FIG. 1. Response to selection for divergence in feed conversion ratio in broiler base population (expressed as deviation from control, sexes combined). LLWV = Low conversion ratio, weight variable HLWV = High conversion ratio, weight variable LLWK = Low conversion ration, weight constant HLWK = High conversion ratio, weight constant
feed conversion with the restriction that body weight changes be minimal from generation to generation. This was done by first ranking all individuals of a population by weight (sexes separate). This ranking was divided into groups of 5 individuals. One individual was then selected from each group of 5 individuals. In this way, the range of body weights was evenly distributed over the population selected for feed conversion ratio. The controls for the broiler line consisted of 40 paired matings reproduced each generation and reared intermingled with the lines. The AC and ARB randombred line eggs were obtained from the populations maintained at
RESULTS AND DISCUSSION The response to selection for divergence in feed conversion using the broiler base population is shown in Figure 1. The progress for sexes combined was relatively high in the HLWV line the first generation (.095 increase in units feed/unit gain); but in the second generation it was increased only .020 with no further progress in the third generation. Progress in the HLWK line was less than in the HLWV the first generation (.040 increase in conversion ratio); but in the second generation progress continued to increase to a conversion ratio of .085. However, in the third generation no progress was made in this line for a total increase in units feed required/unit of gain of .075 for the HLWK as compared to .115 for the HLWV line. The units feed required/unit gain for sexes combined was decreased .03 in the LLWV line in the first generation and .04 in the
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z o
the Southern Regional Poultry Genetics Laboratory. The parent populations consisted of 432 birds to which a selection pressure of 90% in males and 70% in females was applied for each line. In the subsequent generations feed conversions were obtained for a total of 864 birds of the five lines and a selection pressure of 95% applied to the males and 70% applied to the females. At hatching, chicks were banded according to their respective lines, vaccinated for Marek's disease, reared in litter covered pens for 25 to 32 days of age. At this time, the chicks were placed in the individual cages and given a three-day adjustment period before being placed on test. Body weights and feed consumption were determined at 2-week intervals. Realized heritability estimates on all selected generations were determined and heritability by regression of offspring on midparent was determined for the S 2 and S 3 of the commercial broiler lines.
GENETIC CHANGES IN FEED EFFICIENCY
HLWV HLWV HLWK HLWK
rf* £ . - - • $ g) g tf* * - - - • $ » •
.14 .12
/
.10 .08
/
.06 .04
+
.02
/
/
-*•--_,
/
/ /
/
/*'
/
""--•
.•^
_-•
^\^^-— " '•*~~^^~~~^^
^-~~~~~^~^^^
~ /' 'i^~^ ~ * ez^^ •c
*"*;=^
~ .02 .06
\
O s \ .
.08 .10 .12
LLWV LLWV LLWK LLWK
<* O % O 0?» O $ O
D 0 0 O
XX^^^--^
.14
S2
with no progress in the third generation. A slight decrease (0.025) in feed required was noted in the second generation of the LLWV males, while in the third generation the progress in the males of LLWK line had approached that of the females. In the high feed conversion ratio lines, more rapid progress was made in the males than in the females. In the HLWV line, the units feed required /unit gain in the males was increased to 0.14 the first generation, with no subsequent improvement. The HLWV females made progress for the first and second generations to an increase of 0.11 feed with no progress for the third generation. Although the males of the HLWK line made faster progress than the females of that line,
S3
GENERATION
FIG. 2. Sex effect on response to selection for divergence in feed conversion ratio in broiler base population (expressed as deviations from controls). LLWV = Low conversion ratio, weight variable HLWV = High conversion ratio, weight variable LLWK = Low conversion ratio, weight constant HLWK = High conversion ratio, weight constant second generation with slight progress in the third generation for a total decrease of .07 units feed required/unit gain in the three generations of selection. In the LLWK line the units feed required/unit gain was decreased by .025 the first generation, .045 the second generation and .040 the third generation for a total decrease of .10 in three generations of selection. The response of the sexes was quite different for the lines selected for low or high feed conversion values (Figure 2). No progress in decreasing the feed conversion was made in the first generation in males of either low line, while in the females it was decreased .05 in the LLWK and .06 in the LLWV lines the first generation. Similar progress (decrease of .06 units) was made in both the female lines the second generation
-
z o o s o
-
/ •^
_
/ \
m
~~-///
„
„
^
~-^r--
LLWV LLWK - HLWV HLWK
. •——• • • •——•
m
i
i
i
SI
S2
S3
GENERATIONS
FIG. 3. Percent deviation from control in body weight each generation for lines selected for divergence in feed conversion ratio. LLWV = Low conversion ratio, weight variable HLWV = High conversion ratio, weight variable LLWK = Low conversion ratio, weight constant HLWK = High conversion ratio, weight constant
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.04
1149
1150
R. A. GUILL AND K. W. WASHBURN
GENERATIONS
FIG. 4. Response to selection for divergence in feed conversion ratio in randombred population (expressed as deviation from control, sexes combined). LLWV = Low conversion ratio, weight variable HLWV = High conversion ratio, weight variable LLWK = Low conversion ratio, weight constant HLWK = High conversion ratio, weight constant both sexes continued to make progress for all three generations. These results indicate that faster initial gains in improvement of efficiency of feed utilization can be made in females than in males of broiler lines which have been previously selected for growth. This may be associated with the more intense selection pressure that is usually applied in males for growth and other traits. This would tend to decrease the number of loci not fixed, reducing the overall variability of the population. Body weight of the various lines did not change significantly from generation to generation compared to the non-selected control
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si
P
line (Figure 3). Although the LLWV was the only line that was consistently (3%) higher in each generation, there was no significant difference in any line for any generation. Since the change in body weight in all lines over each generation was negligible, the weight variable and weight constant lines can be considered replicate lines. Figure 4 shows the response to selection for feed conversion, sexes combined, in one generation of a randombred population. The feed conversion ratio of the HLWK line increased .055 units, while that of the HLWV increased .080 units. This did not differ significantly from the progress made in one generation of the broiler high lines. The feed conversion ratio of the LLWK decreased to . 125 below that of the control and the LLWV decreased to .130 below the control lines. Both the low lines of the randombred population made significantly more progress in one generation of selection than did the broiler low lines. In fact, more progress was made in decreasing the feed conversion ratio in the randombred line in one generation than in 3 generations of selection in the broiler type stock. Presented in Tables 1 and 2 are summaries of body weights, feed conversion ratios and feed consumption. The results of some studies (Siegel and Wisman, 1966) indicated it might be difficult to conduct accurate experiments on growth rate or efficiency of feed utilization due to the high correlation of both traits with appetite. Thus, selection would be of those individuals with large appetites in addition to or instead of those that actually have the genetic make-up for larger growth or better feed conversion. In the present study, selection for feed conversion ratio in the broiler population for three generations resulted in a significant change in both high lines and between both low lines compared to the control line. However, there were no significant changes in body weight, rate of gain or appetite in
1151
GENETIC CHANGES IN FEED EFFICIENCY
the selected lines compared to controls. The mean change in 8-week body weight after 3 generations was +9 gms. in the lines selected for low feed conversion ratio. The mean change in 4-8 week gain after three generations was +6 gms for the lines selected for low feed conversion ratio and - 4 2 gms. in the lines selected for high feed conversion ratio. The mean change in 4-8 week feed
consumption after three generations was - 2 7 gms. in the line selected for low feed conversion ratio and +51 gms. in the line selected for high feed conversion ratio (Table 1). In the one generation of selection for feed conversion ratio in the randombred population, the weight (compared to controls) was decreased 9 gms. in the line selected for low conversion ratio and decreased 109 gms. in
s, LLWV
s2 LLWV LLWV LLWK LLWK C 8 C 9 HLWV HLWV HLWK HLWK
3 9 3 9
8 9 3 9
s, LLWV LLWV LLWK LLWK C 8 C 9 HLWV HLWV HLWK HLWK
3 9 3 9
3 9 3 9
Wt. 4 wks.
Wt. 8 wks.
4-8 wk. feed conv.
4-8 wks. gain
4-8 wk. feed cons.
482 408 430 378 466 395 471 405 459 401
1537 1202 1408 1131 1485 1170 1463 1156 1469 1193
2.36 2.51 2.36 2.52 2.36 2.57 2.50 2.62 2.40 2.61
1055 794 978 753 1019 775 992 751 1010 792
2490 1993 2308 1898 2405 1992 2480 1968 2424 2067
546 432 500 438 510 431 519 419 529 431
1571 1227 1517 1231 1518 1189 1470 1155 1466 1169
2.16 2.25 2.15 2.22 2.19 2.33 2.33 2.41 2.30 2.39
1025 795 1017 793 1008 758 951 736 937 738
2214 1789 2187 1760 2208 1766 2216 1774 2155 1764
468 357 430 357 447 384 467 403 438 408
1440 1116 1358 1074 1371 1104 1392 1134 1323 1108
2.10 2.18 2.05 2.15 2.15 2.27 2.27 2.38 2.22 2.35
972 759 928 717 924 720 925 731 885 700
2041 1655 1902 1535 1987 1634 2100 1738 1965 1645
LLWV = low line weight variable; LLWK = low line weight constant; HLWV • high line weight variable; HLWK = high line weight constant; S = selected generation; C = control.
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TABLE 1.—Summary of 4 to 8 week weights (gms.), 4 to 8 week feed conversion, 4 to 8 week gain (gms.), 4 to 8 week feed consumption (gms.) of broiler stock
1152
R. A. GUILL AND K. W. WASHBURN
TABLE 2.—Summary of S, randombred population for 5-9 week weights (gms.), 5-9 week feed conversion ratio, 5-9 week gain (gms.), 5-9 week feed consumption (gms.)
Lines
6 9
Dev. from cont.
Wt. 9 wks.
Dev. from cont.
5-9 wk. feed conv.
Dev. from cont.
5-9 wk. gain
Dev. from cont.
5-9 wk. feed cons.
Dev. from cont.
530 433 535 451 547 483 521 417 504 437
-17 -50 -12 -32
1340 1073 1422 1092 1350 1118 1269 987 1240 1013
-10 -45 +72 -26
2.36 2.48 2.33 2.52 2.46 2.64 2.56 2.70 2.53 2.68
-.10 -.16 -.13 -.12
810 640 887 641 803 635 748 570 736 556
+07 +05 +84 +06
1912 1587 2067 1615 1975 1676 1915 1539 1862 1490
-63 -89 +92 -61
-26 -66 -43 -46
-81 -131 -110 -105
+ + + +
.10 .06 .07 .04
-55 -65 -67 -79
-60 -137 -113 -186
LLWV = low line weight variable; LLWK = low line weight constant; HLWV = high line weight variable; HLWK = high line weight constant; S = selected generation; C = control. the line selected for high feed conversion ratio. The 4-8 week gain was increased an average of 26 gms. in the low line and decreased 64 gms in the high line. Consumption for this period was decreased 30 gms. in the low line and 124 gms. in the high line. Wilson (1969), using the same randombred base population that we used, concluded that selection for improved feed conversion would produce a bird that gained slower, consumed less feed but converted feed to body tissue somewhat more efficiently than those birds produced by selection for gain. In our study, the one generation of selection for improved feed conversion in the randombred population produced progeny that ate slightly less feed with a more efficient conversion ratio. However, the line selected for poor feed conversion also ate less feed than controls. The gain in body weight of the low lines were slightly higher but the differences were not significant while the high lines were significantly lower in body weight gain. Estimates of realized heritability for 4-8 week feed conversion are presented in Table 3 for the commercial broiler and randombred stocks. Realized heritability estimates, adjusted for control, were calculated by the formula:
The progeny control average minus the parent control average compensated for environmental or replicate differences. This gave somewhat lower heritability estimates but was considered more accurate. The unweighted mean realized heritability for the Sj randombred lines was .42 compared to .26 for the S, of the lines selected from the commercial broiler stock. This indicates that a greater amount of variability for feed conversion was present in stocks which had not been selected for growth rate than in the commercial broilers selected for growth rate. However, this greater heritability may be a reflection of more variability in growth rate not separable from feed conversion. The heritability for decreasing the feed conversion ratio (which could be accomplished by increasing growth rate if variability was present in a population) was greater (.50) than was that of increasing the ratio (.33). The converse was true in the realized heritability of the S, commercial broiler stock. The mean realized h2 of the two low lines was .13 compared to .38 for the two high lines. This difference is primarily due to the complete lack of response of the low line males in the first generation. In the second generation, the realized h 2
(Progeny x — Parent x) - (Progeny Control x — Parent Control x) (Selected Parent x - Parent x)
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LLWV LLWV LLWK LLWK C 3 C 9 HLWV HLWV HLWK HLWK
Wt. 5 wks.
1153
GENETIC CHANGES IN F E E D EFFICIENCY
TABLE 3.—Realized heritability for randombred and selected broiler lines ARB-AC
s,
Commercial
Broiler
Stock
s,
S2 .25 .37 .32 .41
s3
Unweighted means .20 .21 .33 .26
.22 .14 .56 LLWV .15 .12 .45 LLWK .17 .50 .35 HLWV .11 .27 .31 HLWK Unweighted .25 .16 .34 .26 .42 mean LLWV = low weight variable; LLWK = low line weight constant; HLWV = high line weight variable; HLWK = high line weight constant; S = selected generation.
TABLE 4. Heritability by regression of offspring on mid-parent of selected broiler lines.
Hatch Hatch Hatch Hatch
1 1 2 2
Combined
.30 .28 .35 .39 .33
.23 .36 .29 .32 .30
to selection would be expected in males than in females of growth-selected lines. REFERENCES Craft, W. A., 1958. Fifty years of progress in swine breeding. J. Animal Sci. 17: 960-980. Dickerson, G. E., and J. C. Grimes, 1947. Effectiveness of selection for efficiency of gain in Duroc swine. J. Animal Sci. 6: 265-287. Fitzhugh, H. A., Jr., and T. C. Cartwright, 1971. Variation in post-weaning weight gains of steers independent of appetite. J. Animal Sci. 32: 832-839. Fox, T. W., and B. B. Bohren, 1954. An analysis of feed efficiency among breeds of chickens and its relationship to rate of growth. Poultry Sci. 33: 549-561. Guill, R. A., and K. W. Washburn, 1972. Cages and feed troughs for individual broiler feed consumption experiments. Poultry Sci. 51: 1047-1048. Hess, C. W., 1962. Randombred populations of the southern regional poultry breeding project. Wld.'s Poultry Sci. J. 18(2): 147-152. Hess, C. W., T. C. Byerly and M. A. Jull, 1941. The efficiency of feed utilization by Barred Plymouth Rock and crossbred broilers. Poultry Sci. 20: 210-216. Hess, C. W., and M. A. Jull, 1948. A study of the inheritance of feed utilization efficiency in the growing domestic fowl. Poultry Sci. 27: 24-39. Proudman, J. A., W. J. Mellen andD. L. Anderson, 1970. Utilization of feed in fast- and slow-growing lines of chickens. Poultry Sci. 49: 961-972. Siegel, P. B., and E. L. Wisman, 1966. Selection for body weight at eight weeks of age. 6. Changes in appetite and feed utilization. Poultry Sci. 45: 13911397. Sutherland, T. M., P. E. Biondini, L. H. Haverland, D. Pettus and W. B. Owens, 1970. Selection for rate of gain, appetite and efficiency of feed utilization in mice. J. Animal Sci. 31: 1049-1057. Thomas, C. H., W. L. Blow, C. C. Cockerham and
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of both broiler lines was similar. The h2 of all lines in the third generation decreased. If the mean realized heritabilities of the two populations (.42 and .25, Table 3) are combined with those obtained by regression of offspring (x = .31, shown in Table 4) the mean h2 obtained is .32. It may vary depending on sex, previous selection for growth, whether selection is for high or low efficiency and amount of selection applied. Heritability estimates presented by Thomas et al. (1958) and Wilson (1969) for 4-8 week feed conversion in broilers were .31 and .34, respectively, for sire component and .55 and .50, respectively, for dam component. The heritability of the sire component corresponds with the realized heritability in generation 1 and 2 of this study and heritability by regression of offspring on mid-parent in generation 2 and 3 of this study. The magnitude of the heritability values obtained indicate that even in lines previously selected for growth there is sufficient variation in efficiency of feed utilization to allow progress in selection without further change in body weight. However, faster response
1154
R. A. GUILL AND K. W. WASHBURN
E. W. Glazener, 1958. The heritability of body weight, gain, feed consumption and feed conversion in broilers. Poultry Sci. 37: 862-869. Timon, V. M., and E. J. Eisen, 1970. Comparisons of ad libitumand restricted feeding of mice selected and unselected for post-weaning gain. I. Growth, feed consumption and feed efficiency. Genetics, 64: 41-57.
Warwick, E. J., 1958. Fifty years of progress in breeding beef cattle. J. Animal Sci. 17: 922-943. Wilson, S. P., 1969. Genetic aspects of feed efficiency in broilers. Poultry Sci. 48: 487-495. Winters, L. M., and J. McMahon, 1933. Efficiency variation in steers. Minnesota Agr. Exp. Sta. Tech. Bull. 94: 1-28.
W A Y N E L . BACON, MARGERY A . MUSSER AND KEITH I. BROWN
Department of Poultry Science, Ohio Agricultural Research and Development Center, Wooster, Ohio 44691 (Received for publication September 24, 1973)
ABSTRACT Free fatty acid (FFA) concentrations in blood plasma from immature, laying and broody turkey hens were re-examined following removal of phospholipids. A mean value of .21 ± .02 (A. equiv./ml. plasma of FFA was found for immature hens and as they were stimulated into egg production, and no systematic increase was noted. Broody hens had the same concentration as laying and immature hens. Neutral lipid levels (mainly triglyceride) increased from about 3.5 mg./ml. plasma to about 18-25 mg./ml. plasma as the hens reached sexual maturity, then plateaued until a broody period began when they dropped to concentrations comparable to those in immature hens. No correlation was found between FFA and neutral lipid concentrations. Although FFA concentration is much lower than previously reported, 14% of the total daily amount cleared was calculated to be sufficient to account for egg yolk neutral lipid. The remaining 86% would be available for other metabolic functions. POULTRY SCIENCE 53: 1154-1160, 1974
INTRODUCTION
P
LASMA free fatty acid (FFA) levels in chickens have been reported to increase from about 0.3 JJL. equiv. per ml. in non-laying pullets to about 1.0 to 2.0 |JL. equiv. per ml. in laying hens (Heald and Badman, 1963). In this study, FFA levels were determined by the titrimetric method of Dole and Meinertz (1960). A similar study has recently appeared for turkeys (Bajpayee and Brown, 1972). Prior to exposing immature birds to stimulatory lighting, plasma FFA concentration was 1.14 ± .20 |JL. equiv. per ml. After 21 days of stimulatory lighting, FFA concentration had almost doubled to 2.15 ± .11 (ju equiv. per ml. These authors used the method of Kvam
et al. (1964) to determine plasma FFA. This method is based on forming the copper salts of fatty acids (FA) and then colorimetrically determining the amount of copper associated with the fatty acids after they are extracted. The effect of fasting and gonadotrophin injection on plasma FFA levels was studied by Heald and Rookledge (1964). They observed that fasting caused an increase in plasma FFA in normal cocks, but a decrease in plasma FFA in laying hens when initial FFA levels were high and an increase when initial levels were low. Their method of determining FFA was based on the titrimeteric method of Dole and Meinertz (1960). When pituitary powder was injected during four-day starvation of laying hens, plasma FFA levels were maintained, as were plasma total lipids.
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Plasma Free Fatty Acid and Neutral Lipid Concentrations in Immature, Laying and Broody Turkey Hens