- Email: [email protected]
The Correlation Between Growth Rate and Male Fertility and Some Observations on Selecting for Male Fertility in Broiler Stocks
248
S. T.
MCCREADY AND F.
than at normal p H and p H 5.0, although the amount of SSP was not always greater. The greater emulsifying efficiency of dark meat over light meat, indicated in this study and reported previously in the literature, could be related to the higher p H of normal dark meat. Results indicated that p H was more important in emulsifying capacity than was the percentage of SSP extracted from meat tissues. REFERENCES
CUNNINGHAM
turkeys, hens, and broilers, and dark meat tissues of ducks. Food Technol. 21: 1141-1142. Hudspeth, J. P., and K. N. May, 1969. Emulsifying capacity of salt-soluble proteins of poultry meat. II. Heat, gizzard and skin from broilers, turkeys, hens and ducks. Food Technol. 23 : 373-374. Parkes, M. R., and K. N. May, 1968. Effect of freezing, evaporation and freeze-drying on emulsifying capacity of salt-soluble protein. Poultry Sci. 47: 1236-1240. Saffle, R. L., and J. W. Galbreath, 1964. Quantitative determination of salt-soluble protein in various types of meats. Food Technol. 18: 1943-1944. Swift, C. E., C. Lockett and A. J. Fryar, 1961. Comminuted meat emulsions—the capacity of meats for emulsifying fat. Food Technol. 15: 468-473. Swift, C. E., and W. L. Sulzbacher, 1963. Comminuted meat emulsions: Factors affecting meat proteins as emulsion stabilizers. Food Technol. 17: 224-226. Weinberg, B., and D. Rose, 1960. Changes in protein extractability during tenderization of chicken breast muscle. Food Technol. 14: 376379.
The Correlation Between Growth Rate and Male Fertility and Some Observations on Selecting for Male Fertility in Broiler Stocks M.
SOLLER 1 AND S.
RAPPAPORT
The Volcani Institute of Agricultural Research, Rehovot, Israel (Received for publication August 5, 1970)
E
V E R decreasing fertility has been a disturbing concomitant of the intense and successful selection for rapid growth-rate in broiler stocks of poultry (Parker, 1961; Soller et al., 1965a). A possible explanation for this phenomenon m a y be Lerner's (1954) suggestion t h a t stringent one-way selection for a polygenic trait other t h a n fitness, b y disturbing t h e co-adaptation of the gene pool, m a y generate negative genetic correla1
Present address: Dept. of Biology, Roosevelt University, Chicago, Illinois.
tions between the trait under selection and fitness components. Such negative genetic correlations have, in fact, been reported in broiler stocks of poultry. T h u s Siegel (1963) found t h a t selection for growth-rate decreased semen motility, while Soller et al. (1965 b) and R a p p a p o r t and Soller (1966) found negative genetic correlations between growth-rate and semen motility and between growth-rate and mating activity, respectively. Studies on the genetic correlation between growthrate and fertility itself, however, do not appear to have been published.
Downloaded from http://ps.oxfordjournals.org/ by guest on April 30, 2015
Association of Official Agricultural Chemists, 1960. Official Methods of Analysis of The Association of Official Agricultural Chemists. Ninth Edition. Hanson, L. J., 1960. Emulsion formulation in finely comminuted sausage. Food Technol. 14: 565-569. Helmer, R. L., and R. L. Saffle, 1963. Effect of chopping temperature on the stability of sausage emulsions. Food Technol. 17: 1195-1197. Hudspeth, J. P., and K. N. May, 1967. A study of the emulsifying capacity of salt-soluble proteins of poultry meat. I. Light and dark tissues of
E.
249
BROILER STOCK SELECTION
TABLE 1.—Farms, years and number ofmales j'or which data were obtained, Type of data Farm
M M Y Y 1
Year
1964 1964 1964 1965
Breed
Rock Cornish Cornish Cornish
Sets1
Individual weight
Progeny test
Fertility
Hatchability
Semen motility
(no.)
(no.)
(no.)
(no.)
(no.)
(no.)
7 1 6 7
207 20 122 138
207
207 20 122 138
122 138
86 20 122 138
See text.
DATA AND METHODS D a t a from a number of sources were examined in order to provide information on t h e parameters of interest. These data and the methods used to analyze t h e m will now be described according to the particular parameter studied. The correlations between growth-rate, fertility and semen quality were examined in three sets of d a t a obtained from progeny testing programs involving broiler line males. For most of these males, individual body weight, fertility and progeny test results were available, and for some of 2 Masuot Yitzchak Poultry Breeding Farm, Masuot Yitzchak, Israel (Farm M), andYavne Poultry Breeding Farm, Kibbutz Yavne, Israel (Farm Y).
them semen motility scores and hatchability were available as well. Table 1 shows the farms, years and the numbers of males for which the various sorts of d a t a were obtained. At each farm the males were tested in sets of 20-30 at a time. T h e number of such sets is also shown in Table 1. Progeny tests were carried out by placing each of the males to be tested at a particular time in a separate single-male pen with 15 White Rock females. Two or three hatches were raised from each pen, each hatch including eggs collected over a two-week period. T h e males were t h e n removed and another set of males introduced into the pens, for a total of 6-7 sets of males tested on each group of pens, at which time the females were replaced. Chicks were wing-banded by sires, raised intermingled, and weighed at 8-9 weeks of age. Live-weight for age was taken as a measure of growth-rate. Generally 100150 offspring were raised for each sire. Progeny test results were calculated in t h e following manner: the mean weight of the male offspring of each male in each hatch was expressed as a deviation from the mean weight of all the male birds weighed in t h a t hatch, similarly for the female offspring. Since t h e number of offspring included in each sex-hatch deviation varied considerably, t h e weighted mean 3 5
It would have been more proper to calculate the
Downloaded from http://ps.oxfordjournals.org/ by guest on April 30, 2015
T h e purpose of this investigation, based on d a t a obtained from two commercial breeding farms, 2 was to study the genetic correlation between growth-rate and fertility, and to provide additional information on the genetic correlation between growth rate and semen motility. T h e d a t a also enabled information to be gathered on the relative importance of sire and pen effects in determining family differences in fertility. These parameters are of interest from the point of view of selecting for improved male fertility. Some provisional estimates of the probable effects of such selection schemes are also provided.
250
M . SOLLER AND S. RAPPAPOET
(TA) weighted mean of the male and female deviations separately, and then give equal weight to the two sexes by using the unweighted mean of these deviations. However, with roughly equal numbers of male and female offspring, and with male and female deviations of distinctly the same order of magnitude, we would not expect the progeny test results obtained with this procedure to differ to any appreciable extent from those calculated as above.
r' = rAVWh? 2
(1)
where hf and hg> , refer respectively, to the heritability of fertility and to the regression of progeny test results on breeding value for growth-rate. Other studies of these data have shown that kg>2, is equal to 0.54 (Soller and Rappaport, 1971).
Downloaded from http://ps.oxfordjournals.org/ by guest on April 30, 2015
of these deviations was used in order to ing on the particular set of families) were avoid undue influence of a single extreme raised from each family, each hatch included the eggs collected during a twodeviation based on few offspring. The individual weight of each sire was week period. Fertility for each pen in expressed as a deviation from the mean each hatch was determined by candling weight of the hatch in which he was raised. after 7-days of incubation. The fertility Fertility was determined by candling at data from each set of families was then 7-days, hatchability as the percent of submitted to a one-way analysis of varichicks hatched out of total eggs set. Semen ance by families, and the between family 2 motility was scored visually on a scale of (oy ) and within family (i.e., between0-7. Each male tested for semen motility hatch within family) component of variwas scored three times and the average ance (ay?) obtained. Since the sires were score was used in all subsequent calcula- kept in the same pens throughout, the between family component included the tions. 2 The correlation coefficients between the between sire component \"2>2 for each year and farm for which data ay 2 + (Tw2 were available. The correlation between fertility and The genetic correlation between fertility hatchability was calculated for those males and growth-rate and the heritability of ferfor which both sorts of information were tility could not be directly calculated from available. the data. However, since the environThe repeatability of fertility was esti- mental correlation between sire fertility mated from data provided by a family and offspring growth-rate must necessarily selection program for White Rock broilers be equal to zero, we have the following at Farm M. Four sets of families were relationship between the phenotypic cortested, each set including 12-24 families. relation of sire fertility and offspring Each family consisted of 15 females and growth rate (/) and the genetic correlaone male. Ten to fifteen hatches (depend- tion between fertility and growth-rate
BROILER STOCK SELECTION
Thus (1) reduces to _
rxi is the regression of index value on trait (X) value, and is equal to
r'
bx2xbY
0.735
vx —
where AG is the genetic value of the selected individuals, rA is the genetic correlation between the two traits under consideration, and X and F , as subscripts, refer to the trait under direct selection and the trait under indirect selection, respectively. I n the case of selecting sequentially for one trait and then the other, the direct and indirect effects were simply added. Selection indices were calculated according to the method described by Hazel (1943). Index superiority of the selected animals was converted to trait superiority (AP) b y t h e relation „
where,
oi2 is the variance of index values, and is equal to bx2ox2 + br2(7Y2 + 2rAbxbY
Number
Individual weight
Offspring weight
M Y
207 260
-0.04 -0.01
-0.16 -0.07
rxiarii
Downloaded from http://ps.oxfordjournals.org/ by guest on April 30, 2015
A knowledge of thephenotypiccorrelation, r', therefore, does give some notion of the possible range within which the genetic correlation and heritability fall. Also, the term rA hf1 appears as a unit in the biometric equations showing the effect of selection for growth on fertility, Hence an unequalified estimate of this effect, a t least, can be obtained. The effect of selection for growth and fertility. T h e direct effect of selection for growth and fertility on these traits was obtained by the usual methods (see, e.g., Falconer, 1960). T h e indirect effect of selection for one trait, on the other was obtained from the relation AGx = AGyrA^/h^hY1
251
252
M . SOLLER AND S. RAPPAPORT TABLE 3.—Correlation between semen motility and fertility, individual and of spring growth-rate Correlations with semen motility Breed
Number FertilityJ
White Rock 86 Cornish 20
0.04 0.09
lndi
?^™1 weight
Offspring weight
-0.12 -0.21
-0.09
The correlation between hatchability and fertility for 260 males at the Y farm was 0.85. This indicates that 7-day fertility is the most important determinant of hatchability of all eggs set. Pen effects and the repeatability of fertility. Table 4 shows the within family and (2) r = rA\/K + V + rE between family variance components for where r, rA and h2/ are as previously de- the four sets of M farm families. The nned, and h2g is the heritability of growth- within family components from each set rate. Noting that the average phenotypic are similar in magnitude and it would correlation between growth-rate of pro- seem reasonable to pool them. The begeny and fertility was —0.12, we have, tween family components are consistent by (1) r J i W = ; — -16. Other studies of in three of the four family groups, but these data (Soller and Rappaport, 1971) extremely large in the second set of famihave shown that A92 = 0.27. Substituting lies tested. This is primarily due to one these values in (2) we see that TE is not family in that set that was maintained far from zero; perhaps slightly positive. over the course of the hatching season in This would be in accord with Lerner's spite of a very low fertility. It would seem hypothesis, which implies that the nega- permissible, therefore, to eliminate this tive correlation between growth-rate and set of families. When this is done, the fertility would not be due to a direct pooled variance components are effect of larger size itself, but to a disrup153 tion of normal genetic relationships. Hence larger size due to environmental °r 173 factors should not be reflected in decreased fertility. TABLE 4.—Within family and between family components of variance for fertility Table 3 shows the correlation between semen motility and fertility, individual Components of variance growth and of spring growth-rate. The corHatches Set Families per family Within Between relations between fertility and motility family (ov2) family (o-f2) were positive, though low. Those between (no.) (no.) motility and growth-rate were negative. 24 10 1 275.1 249.0 These results confirm those found pre18 2 7 136.4 882.0 23 11 133.5 142.7 3 viously by Siegel (1963) and by Soller et 12 4 8 70.3 116.6 al. (1965 b).
Downloaded from http://ps.oxfordjournals.org/ by guest on April 30, 2015
than they would have been in an unselected population. Appropriate correction can be made by the method described in Cohen (1957). The corrected correlations are equal to —0.067 and —0.017 for the M and Y farms, respectively. The pooled correlation is —0.04. This enables us to obtain some estimate of the relative magnitude, at least, of the environmental correlation, YE, between growth-rate and fertility, i.e., of the degree to which environmental factors affecting 8-week body weight also affect mature-male fertility. The phenotypic correlation, r, between the growth-rate of a sire himself and his fertility is equal to
253
BROILER STOCK SELECTION TABLE 5.—Within pen and between pen components of variance for fertility Within pen Farm Y Y M
Between pen
d.f.
Variance component
d.f.
Variance component
101 98 70
115 96 225
23 23 46
14 35 33
The genetic correlation between fertility and growth-rate and the heritability of fertility. Heritability has often been found to be equal to 1/2-2/3 of the repeatability. In our case the repeatability of fertility was found to be 0.42. Hence we might expect the heritability of fertility to be somewhere between 0.21 and 0.28, say, 0.25. Substituting this value in rAhf = —0.16, gives rA= —0.3. Other possible, though less likely sets of values would be, V = 0.1,rA=-0.5;andV = 0 . 5 , ^ = - 0 . 2 .
The results of this study and of others in the literature indicate that a negative genetic correlation exists between growthrate and fertility in broiler stocks. As a result, selection for increased growth-rate alone, necessarily results in decreased fertility. While this decrease in fertility may be palliated to some extent by suitable management, it may be more appropriate to counter the indirect deleterious effect of selection for growth-rate on fertility by direct selection for fertility. Such a program might involve the following sort of procedure: Mass selection of males on the basis of body weight at 8-9 weeks of age; testing the fertility of the selected males in a natural mating situation; followed by a final selection on the basis of fertility alone, or on the basis of fertility plus the growth-rate of the progeny produced in the course of the fertility test. I t is of great practical interest to estimate the effect of such programs on fertility and growth. At the present time this cannot be done in an exact way since estimates are not available for three crucial parameters: the heritability of fertility; its genetic correlation with growth rate; and the genetic correlation between fertility in a single-male pen situation and fertility in a flock mating situation. With respect to the last named parameter, the fact that males of heavy Cornish strains when tested individually are less fertile than White Rock males, and to a degree that more or less compares to the difference between breeds in flock matings (Soller et al., 1965 a) seems to indicate that the decrease in fertility associated with increased growth-rate is expressed on an individual basis as well as a flock mating basis. This lends some support to the converse proposition—that increased individual fertility will result in increased flock fertility. It is clear, however, that
Downloaded from http://ps.oxfordjournals.org/ by guest on April 30, 2015
The proportion of the total variance due to family effects was thus 0.53. Table 5 shows the between pen and within pen components of variance calculated as described above. The between pen component obtained from the M farm data was 33. The between sire component can now be estimated by subtracting the between pen component from the between family component to give <7„2 = 140. The repeatability of a sire fertility record based on one hatch is thus 0.42. Furthermore, the small value of the between pen component indicates that systematic differences between pens will not be a serious source of error in evaluatmg male fertility. These results indicate that a fairly reliable estimate of a sire's fertility in natural mating (single pen) can be obtained from a relatively short testing period in one pen. The between-pen component calculated from the Y farm data were similar to those obtained from the M farm. The within-pen component, however, was somewhat smaller.
DISCUSSION
254
M . SOLXER AND S. RAPPAPORT
W
A
- - - - -
--
-
Soller and Rappaport (1971). In computing the relative economic value of one gram of increased 8-week body weight compared to a one percent increase in fertility, the following factors were taken into account: (1) only half the increase in growth will be reflected in the offspring of male-line broiler males, whereas all of the fertility increase will be obtained in the eggs they fertilize; (2) the value of increased growth-rate comes as a result of decreased growing time to reach a given market weight, and (3) it takes about 150 hatching eggs to get 100 8-week broilers. Under Israeli conditions an extra chick due to increased fertility is worth 0.50 IL (Israeli pounds), an extra gram of growth returns growing time savings of 0.00075 IL. The relative economic value of the two traits under these conditions is 1:20 (growth-fertility). Since economic values can be expected to vary from place to place and from time to time, results, when dependent on economic values are also given for the case of relative economic value equal to 1:10. In this way the general effect of changes in economic value can be determined. Considering now, a broiler stock characterized by the parameters given in Table 6, Table 7 shows the genetic values
TABLE 6.—Genetic parameters used in calculating the effect of selection on growth and fertility Parameter
Symbol
Estimate
hg2
0.25
2 Regression of progeny test for growth-rate on breeding value h g ' for growth-rate
0.50
Heritability of growth rate
2
Heritability of fertility
hf
Genetic correlation of fertility and growth-rate
rA
.
0.10 —0.5
0.25
0.50
—0.3 —0.2
Genetic standard deviations Growth-rate
og
Progeny test for growth-rate
Fertility
<,i
150 gram 50 gram 14%
for growth and fertility of males chosen by: (1) selection for growth-rate alone, at a proportion selected of 0.025; (2) selection for fertility alone, at a proportion selected of 0.25; (3) selection for growth rate at a proportion selected of 0.10, followed by selection for fertility at a proportion selected of 0.25; and (4) selection for growth-rate at a proportion selected of 0.10, followed by testing the selected males for fertility, progeny testing the males on the basis of their fertility-test offspring, and selecting them (at a proportion selected of 0.25) on the basis of an index combining progeny test and fertility test results. Since this selection index will depend in part on the relative economic value of the two traits, index selection gains are shown for relative economic values of 1:10 and 1:20. As can be expected, selection of males for growth alone produces the greatest increase in growth-rate and the greatest decrease in fertility, while the converse is true of selection for fertility alone. Selection for growth followed by selection for fertility alone or by index selection for fertility and progeny growth give similar results, except that the second procedure provides somewhat more growth and less fertility than the first.
Downloaded from http://ps.oxfordjournals.org/ by guest on April 30, 2015
improvement of single male pen fertility may proceed via biological pathways that are irrelevant to the improvement of multiple male pen fertility. I t is nevertheless possible, by using the range of estimates of heritability and genetic correlation obtained above, and by restricting the argument to a single male situation, to obtain some approximate estimates of the possible effects of such programs, and to compare the relative effectiveness of various sorts of programs. Table 6 shows values of the various parameters that were used in this study. The growth-rate narameters came from
255
BROILER STOCK SELECTION TABLE 7.—Expected genetic value Jor growth-rate and fertility of males and females selected under various breeding programs1 Expected genetic value2 Growth-rate Fertility
Breeding program
(%)
(gm.) Males Mass selection for growth alone Mass selection for fertility alone Mass selection for growth followed by mass selection for fertility Mass selection for growth followed by index selection: for fertility and progeny test for growth
87 -14 54
(85) (72)
Females Mass selection for growth alone 1 2
70 66
-2.6 4.2
(8.4)
(-0.3)
2.2
(6.4)
(65) (63)
(-2.4) (-1.3)
1.2 1.8
(5.8) (6.2)
47
-1.4
See text for details Estimates in parentheses were calculated for h 2 f=0.1 and h2f = 0.5, respectively.
It should be noted that a presentation in terms of genetic superiority of selected males exaggerates the differences between the programs. Genetic change in the population as a whole will be equally determined by selection of females, and this part of the program will be identical for all of the procedures described. Table 7 also shows the genetic values for growth and male fertility of females selected on the basis of growth-rate alone at a proportion selected of 0.25 Considering, the effects of both male and female selection, it can be seen that if the heritability of fertility is low, the only procedure that prevents any decline in fertility is selecting males for fertility alone. However, if the heritability of fertility is moderately high (0.25, or more), all of the selection schemes involving fertility can maintain fertility along with increased growth gains. It is instructive in deciding upon field programs to compare the relative economic genetic values of the males that
would be selected by each procedure. These are shown in Table 8. The most striking conclusion of Table 8 is that under all conditions, selection for growth TABLE 8.—Economic value of males selected
under various breeding programs1
Breeding program
Economic value2 of selected males '8
Relative economic value (growth:fertility),1:10 Mass selection for growth alone
(1.00)
0.73
(0.49)
Mass selection for fertility alone
(0.05)
0.34
(0.57)
Mass selection for growth followed by mass selection for fertility
(0.8.3)
0.91
(0.96)
Mass selection for growth followed by index selection: for fertility and progeny test for growth
(1.00)
1.00
(1.00)
Relative economic value (growth:fertility), 1:20 Mass selection for growth alone
(0.72)
0.35
(0.19)
Mass selection for fertility alone
(0.41)
0.70
(0.83)
Mass selection for growth followed by mass selection for fertility
(0.98)
0.97
(0.97)
Mass selection for growth followed by index selection: for fertility and progeny test for growth
(1.00)
1.00
(1.00)
1 2
See text for details. Relative to index selected males (mass selection for growth followed by index selection for fertility and progeny test for growth). 3 Values in parentheses calculated forh2f = 0.1 andh2f =0.5., respectively.
Downloaded from http://ps.oxfordjournals.org/ by guest on April 30, 2015
Relative economic value (growth: fertility) 1:10 1:20
1.7)
(
256
M . SOLLEE AND S. RAPPAPORT
alone, followed by selection for fertility alone will give close to optimal results. In fact, if the diluting effect of the female side selections, and the increased generation interval required by progeny testing for growth-rate are taken into consideration, this procedure may be even more effective than selection for growth followed by index selection for growth and fertility. In contrast, selection for growthrate or for fertility alone can, under certain circumstances, give far from optimum results.
It is concluded that a program of mass selection for growth-rate, followed by a fertility test of the selected roosters in a single-pen mating situation, and a further selection on the basis of fertility will give close to optimum gains in economic value.
The authors wish to thank A. Ben Dov of Masuot Yitzchak Poultry Breeding Farm, and B. Eckert of Kibbutz Yavne Poultry Breeding Farm for their cooperation in making available the data on which this study was based. They also wish to thank A. Genizi for his guidance in the statistical analyses. REFERENCES Cohen, A. C , 1957. Restriction and selection in multinomial distribution. Ann. Math. Stat. 28: 731-741. Falconer, D. S., 1960. Introduction to Quantitative Genetics. The Ronald Press Co., New York. Hazel, L. N., 1943. The genetic basis for constructing selection indexes. Genetics, 28: 476-490. Lemer, I. M., 1954. Genetic Homeostasis. Oliver and Boyd, Edinburgh. Parker, J. E., 1961. Observations on the low fertility problem in Cornish cockerels. Poultry Sci. 40: 1214-1219. Rappaport, S., and M. Soller, 1966. Mating behavior, fertility and rate-of-gain in Cornish males. Poultry Sci. 45: 997-1003. Siegel, P. B., 1963. Selection for body weight at 8 weeks of age. 2. Correlated responses of feathering, body weight, and reproductive characteristics. Poultry Sci. 42: 895-905. Soller, M., H. Schindler and S. Bornstein, 1965a. Semen characteristics, failure of insemination and fertility in Cornish and White Rock males. Poultry Sci. 44: 424-432. Soller, M., N. Snapir and H. Schindler, 1965b. Heritability of semen quality, concentration and motility in White Rock roosters and their genetic correlation with rate of gain. Poultry Sci. 44: 1527-1529. Soller, M., and S. Rappaport, 1971. Interaction and pen effects in evaluating broiler sires. To be published.
APRIL 14-16. SYMPOSIUM ON PEST CONTROL STRATEGIES FOR THE FUTURE OF THE AGRICULTURAL BOARD, DIVISION OF BIOLOGY AND AGRICULTURE, NATIONAL ACADEMY OF SCIENCES, AUDITORIUM, NATIONAL ACADEMY OF SCIENCES, 2101 CONSTITUTION AVE., N.W., WASHINGTON, D.C. 20418.
Downloaded from http://ps.oxfordjournals.org/ by guest on April 30, 2015
SUMMARY The relationship between growth-rate and fertility was studied in White Rock and Cornish roosters. The correlation between individual growth-rate and fertility was —0.04, that between progeny test for growth-rate and fertility was —0.12. The genetic correlation between growth-rate and fertility was thus negative, while the environmental correlation was zero or slightly positive. The correlations between semen motility and fertility were positive, though low, those between semen motily and growth-rate were negative. The correlation between fertility and hatchability was 0.85. Repeatability of a fertility test based on the performance of a rooster in one pen for one hatch was 0.42.
ACKNOWLEDGMENT
S. T.
MCCREADY AND F.
than at normal p H and p H 5.0, although the amount of SSP was not always greater. The greater emulsifying efficiency of dark meat over light meat, indicated in this study and reported previously in the literature, could be related to the higher p H of normal dark meat. Results indicated that p H was more important in emulsifying capacity than was the percentage of SSP extracted from meat tissues. REFERENCES
CUNNINGHAM
turkeys, hens, and broilers, and dark meat tissues of ducks. Food Technol. 21: 1141-1142. Hudspeth, J. P., and K. N. May, 1969. Emulsifying capacity of salt-soluble proteins of poultry meat. II. Heat, gizzard and skin from broilers, turkeys, hens and ducks. Food Technol. 23 : 373-374. Parkes, M. R., and K. N. May, 1968. Effect of freezing, evaporation and freeze-drying on emulsifying capacity of salt-soluble protein. Poultry Sci. 47: 1236-1240. Saffle, R. L., and J. W. Galbreath, 1964. Quantitative determination of salt-soluble protein in various types of meats. Food Technol. 18: 1943-1944. Swift, C. E., C. Lockett and A. J. Fryar, 1961. Comminuted meat emulsions—the capacity of meats for emulsifying fat. Food Technol. 15: 468-473. Swift, C. E., and W. L. Sulzbacher, 1963. Comminuted meat emulsions: Factors affecting meat proteins as emulsion stabilizers. Food Technol. 17: 224-226. Weinberg, B., and D. Rose, 1960. Changes in protein extractability during tenderization of chicken breast muscle. Food Technol. 14: 376379.
The Correlation Between Growth Rate and Male Fertility and Some Observations on Selecting for Male Fertility in Broiler Stocks M.
SOLLER 1 AND S.
RAPPAPORT
The Volcani Institute of Agricultural Research, Rehovot, Israel (Received for publication August 5, 1970)
E
V E R decreasing fertility has been a disturbing concomitant of the intense and successful selection for rapid growth-rate in broiler stocks of poultry (Parker, 1961; Soller et al., 1965a). A possible explanation for this phenomenon m a y be Lerner's (1954) suggestion t h a t stringent one-way selection for a polygenic trait other t h a n fitness, b y disturbing t h e co-adaptation of the gene pool, m a y generate negative genetic correla1
Present address: Dept. of Biology, Roosevelt University, Chicago, Illinois.
tions between the trait under selection and fitness components. Such negative genetic correlations have, in fact, been reported in broiler stocks of poultry. T h u s Siegel (1963) found t h a t selection for growth-rate decreased semen motility, while Soller et al. (1965 b) and R a p p a p o r t and Soller (1966) found negative genetic correlations between growth-rate and semen motility and between growth-rate and mating activity, respectively. Studies on the genetic correlation between growthrate and fertility itself, however, do not appear to have been published.
Downloaded from http://ps.oxfordjournals.org/ by guest on April 30, 2015
Association of Official Agricultural Chemists, 1960. Official Methods of Analysis of The Association of Official Agricultural Chemists. Ninth Edition. Hanson, L. J., 1960. Emulsion formulation in finely comminuted sausage. Food Technol. 14: 565-569. Helmer, R. L., and R. L. Saffle, 1963. Effect of chopping temperature on the stability of sausage emulsions. Food Technol. 17: 1195-1197. Hudspeth, J. P., and K. N. May, 1967. A study of the emulsifying capacity of salt-soluble proteins of poultry meat. I. Light and dark tissues of
E.
249
BROILER STOCK SELECTION
TABLE 1.—Farms, years and number ofmales j'or which data were obtained, Type of data Farm
M M Y Y 1
Year
1964 1964 1964 1965
Breed
Rock Cornish Cornish Cornish
Sets1
Individual weight
Progeny test
Fertility
Hatchability
Semen motility
(no.)
(no.)
(no.)
(no.)
(no.)
(no.)
7 1 6 7
207 20 122 138
207
207 20 122 138
122 138
86 20 122 138
See text.
DATA AND METHODS D a t a from a number of sources were examined in order to provide information on t h e parameters of interest. These data and the methods used to analyze t h e m will now be described according to the particular parameter studied. The correlations between growth-rate, fertility and semen quality were examined in three sets of d a t a obtained from progeny testing programs involving broiler line males. For most of these males, individual body weight, fertility and progeny test results were available, and for some of 2 Masuot Yitzchak Poultry Breeding Farm, Masuot Yitzchak, Israel (Farm M), andYavne Poultry Breeding Farm, Kibbutz Yavne, Israel (Farm Y).
them semen motility scores and hatchability were available as well. Table 1 shows the farms, years and the numbers of males for which the various sorts of d a t a were obtained. At each farm the males were tested in sets of 20-30 at a time. T h e number of such sets is also shown in Table 1. Progeny tests were carried out by placing each of the males to be tested at a particular time in a separate single-male pen with 15 White Rock females. Two or three hatches were raised from each pen, each hatch including eggs collected over a two-week period. T h e males were t h e n removed and another set of males introduced into the pens, for a total of 6-7 sets of males tested on each group of pens, at which time the females were replaced. Chicks were wing-banded by sires, raised intermingled, and weighed at 8-9 weeks of age. Live-weight for age was taken as a measure of growth-rate. Generally 100150 offspring were raised for each sire. Progeny test results were calculated in t h e following manner: the mean weight of the male offspring of each male in each hatch was expressed as a deviation from the mean weight of all the male birds weighed in t h a t hatch, similarly for the female offspring. Since t h e number of offspring included in each sex-hatch deviation varied considerably, t h e weighted mean 3 5
It would have been more proper to calculate the
Downloaded from http://ps.oxfordjournals.org/ by guest on April 30, 2015
T h e purpose of this investigation, based on d a t a obtained from two commercial breeding farms, 2 was to study the genetic correlation between growth-rate and fertility, and to provide additional information on the genetic correlation between growth rate and semen motility. T h e d a t a also enabled information to be gathered on the relative importance of sire and pen effects in determining family differences in fertility. These parameters are of interest from the point of view of selecting for improved male fertility. Some provisional estimates of the probable effects of such selection schemes are also provided.
250
M . SOLLER AND S. RAPPAPOET
(TA) weighted mean of the male and female deviations separately, and then give equal weight to the two sexes by using the unweighted mean of these deviations. However, with roughly equal numbers of male and female offspring, and with male and female deviations of distinctly the same order of magnitude, we would not expect the progeny test results obtained with this procedure to differ to any appreciable extent from those calculated as above.
r' = rAVWh? 2
(1)
where hf and hg> , refer respectively, to the heritability of fertility and to the regression of progeny test results on breeding value for growth-rate. Other studies of these data have shown that kg>2, is equal to 0.54 (Soller and Rappaport, 1971).
Downloaded from http://ps.oxfordjournals.org/ by guest on April 30, 2015
of these deviations was used in order to ing on the particular set of families) were avoid undue influence of a single extreme raised from each family, each hatch included the eggs collected during a twodeviation based on few offspring. The individual weight of each sire was week period. Fertility for each pen in expressed as a deviation from the mean each hatch was determined by candling weight of the hatch in which he was raised. after 7-days of incubation. The fertility Fertility was determined by candling at data from each set of families was then 7-days, hatchability as the percent of submitted to a one-way analysis of varichicks hatched out of total eggs set. Semen ance by families, and the between family 2 motility was scored visually on a scale of (oy ) and within family (i.e., between0-7. Each male tested for semen motility hatch within family) component of variwas scored three times and the average ance (ay?) obtained. Since the sires were score was used in all subsequent calcula- kept in the same pens throughout, the between family component included the tions. 2 The correlation coefficients between the between sire component \
BROILER STOCK SELECTION
Thus (1) reduces to _
rxi is the regression of index value on trait (X) value, and is equal to
r'
bx2xbY
0.735
vx —
where AG is the genetic value of the selected individuals, rA is the genetic correlation between the two traits under consideration, and X and F , as subscripts, refer to the trait under direct selection and the trait under indirect selection, respectively. I n the case of selecting sequentially for one trait and then the other, the direct and indirect effects were simply added. Selection indices were calculated according to the method described by Hazel (1943). Index superiority of the selected animals was converted to trait superiority (AP) b y t h e relation „
where,
oi2 is the variance of index values, and is equal to bx2ox2 + br2(7Y2 + 2rAbxbY
Number
Individual weight
Offspring weight
M Y
207 260
-0.04 -0.01
-0.16 -0.07
rxiarii
Downloaded from http://ps.oxfordjournals.org/ by guest on April 30, 2015
A knowledge of thephenotypiccorrelation, r', therefore, does give some notion of the possible range within which the genetic correlation and heritability fall. Also, the term rA hf1 appears as a unit in the biometric equations showing the effect of selection for growth on fertility, Hence an unequalified estimate of this effect, a t least, can be obtained. The effect of selection for growth and fertility. T h e direct effect of selection for growth and fertility on these traits was obtained by the usual methods (see, e.g., Falconer, 1960). T h e indirect effect of selection for one trait, on the other was obtained from the relation AGx = AGyrA^/h^hY1
251
252
M . SOLLER AND S. RAPPAPORT TABLE 3.—Correlation between semen motility and fertility, individual and of spring growth-rate Correlations with semen motility Breed
Number FertilityJ
White Rock 86 Cornish 20
0.04 0.09
lndi
?^™1 weight
Offspring weight
-0.12 -0.21
-0.09
The correlation between hatchability and fertility for 260 males at the Y farm was 0.85. This indicates that 7-day fertility is the most important determinant of hatchability of all eggs set. Pen effects and the repeatability of fertility. Table 4 shows the within family and (2) r = rA\/K + V + rE between family variance components for where r, rA and h2/ are as previously de- the four sets of M farm families. The nned, and h2g is the heritability of growth- within family components from each set rate. Noting that the average phenotypic are similar in magnitude and it would correlation between growth-rate of pro- seem reasonable to pool them. The begeny and fertility was —0.12, we have, tween family components are consistent by (1) r J i W = ; — -16. Other studies of in three of the four family groups, but these data (Soller and Rappaport, 1971) extremely large in the second set of famihave shown that A92 = 0.27. Substituting lies tested. This is primarily due to one these values in (2) we see that TE is not family in that set that was maintained far from zero; perhaps slightly positive. over the course of the hatching season in This would be in accord with Lerner's spite of a very low fertility. It would seem hypothesis, which implies that the nega- permissible, therefore, to eliminate this tive correlation between growth-rate and set of families. When this is done, the fertility would not be due to a direct pooled variance components are effect of larger size itself, but to a disrup153 tion of normal genetic relationships. Hence larger size due to environmental °r 173 factors should not be reflected in decreased fertility. TABLE 4.—Within family and between family components of variance for fertility Table 3 shows the correlation between semen motility and fertility, individual Components of variance growth and of spring growth-rate. The corHatches Set Families per family Within Between relations between fertility and motility family (ov2) family (o-f2) were positive, though low. Those between (no.) (no.) motility and growth-rate were negative. 24 10 1 275.1 249.0 These results confirm those found pre18 2 7 136.4 882.0 23 11 133.5 142.7 3 viously by Siegel (1963) and by Soller et 12 4 8 70.3 116.6 al. (1965 b).
Downloaded from http://ps.oxfordjournals.org/ by guest on April 30, 2015
than they would have been in an unselected population. Appropriate correction can be made by the method described in Cohen (1957). The corrected correlations are equal to —0.067 and —0.017 for the M and Y farms, respectively. The pooled correlation is —0.04. This enables us to obtain some estimate of the relative magnitude, at least, of the environmental correlation, YE, between growth-rate and fertility, i.e., of the degree to which environmental factors affecting 8-week body weight also affect mature-male fertility. The phenotypic correlation, r, between the growth-rate of a sire himself and his fertility is equal to
253
BROILER STOCK SELECTION TABLE 5.—Within pen and between pen components of variance for fertility Within pen Farm Y Y M
Between pen
d.f.
Variance component
d.f.
Variance component
101 98 70
115 96 225
23 23 46
14 35 33
The genetic correlation between fertility and growth-rate and the heritability of fertility. Heritability has often been found to be equal to 1/2-2/3 of the repeatability. In our case the repeatability of fertility was found to be 0.42. Hence we might expect the heritability of fertility to be somewhere between 0.21 and 0.28, say, 0.25. Substituting this value in rAhf = —0.16, gives rA= —0.3. Other possible, though less likely sets of values would be, V = 0.1,rA=-0.5;andV = 0 . 5 , ^ = - 0 . 2 .
The results of this study and of others in the literature indicate that a negative genetic correlation exists between growthrate and fertility in broiler stocks. As a result, selection for increased growth-rate alone, necessarily results in decreased fertility. While this decrease in fertility may be palliated to some extent by suitable management, it may be more appropriate to counter the indirect deleterious effect of selection for growth-rate on fertility by direct selection for fertility. Such a program might involve the following sort of procedure: Mass selection of males on the basis of body weight at 8-9 weeks of age; testing the fertility of the selected males in a natural mating situation; followed by a final selection on the basis of fertility alone, or on the basis of fertility plus the growth-rate of the progeny produced in the course of the fertility test. I t is of great practical interest to estimate the effect of such programs on fertility and growth. At the present time this cannot be done in an exact way since estimates are not available for three crucial parameters: the heritability of fertility; its genetic correlation with growth rate; and the genetic correlation between fertility in a single-male pen situation and fertility in a flock mating situation. With respect to the last named parameter, the fact that males of heavy Cornish strains when tested individually are less fertile than White Rock males, and to a degree that more or less compares to the difference between breeds in flock matings (Soller et al., 1965 a) seems to indicate that the decrease in fertility associated with increased growth-rate is expressed on an individual basis as well as a flock mating basis. This lends some support to the converse proposition—that increased individual fertility will result in increased flock fertility. It is clear, however, that
Downloaded from http://ps.oxfordjournals.org/ by guest on April 30, 2015
The proportion of the total variance due to family effects was thus 0.53. Table 5 shows the between pen and within pen components of variance calculated as described above. The between pen component obtained from the M farm data was 33. The between sire component can now be estimated by subtracting the between pen component from the between family component to give <7„2 = 140. The repeatability of a sire fertility record based on one hatch is thus 0.42. Furthermore, the small value of the between pen component indicates that systematic differences between pens will not be a serious source of error in evaluatmg male fertility. These results indicate that a fairly reliable estimate of a sire's fertility in natural mating (single pen) can be obtained from a relatively short testing period in one pen. The between-pen component calculated from the Y farm data were similar to those obtained from the M farm. The within-pen component, however, was somewhat smaller.
DISCUSSION
254
M . SOLXER AND S. RAPPAPORT
W
A
- - - - -
--
-
Soller and Rappaport (1971). In computing the relative economic value of one gram of increased 8-week body weight compared to a one percent increase in fertility, the following factors were taken into account: (1) only half the increase in growth will be reflected in the offspring of male-line broiler males, whereas all of the fertility increase will be obtained in the eggs they fertilize; (2) the value of increased growth-rate comes as a result of decreased growing time to reach a given market weight, and (3) it takes about 150 hatching eggs to get 100 8-week broilers. Under Israeli conditions an extra chick due to increased fertility is worth 0.50 IL (Israeli pounds), an extra gram of growth returns growing time savings of 0.00075 IL. The relative economic value of the two traits under these conditions is 1:20 (growth-fertility). Since economic values can be expected to vary from place to place and from time to time, results, when dependent on economic values are also given for the case of relative economic value equal to 1:10. In this way the general effect of changes in economic value can be determined. Considering now, a broiler stock characterized by the parameters given in Table 6, Table 7 shows the genetic values
TABLE 6.—Genetic parameters used in calculating the effect of selection on growth and fertility Parameter
Symbol
Estimate
hg2
0.25
2 Regression of progeny test for growth-rate on breeding value h g ' for growth-rate
0.50
Heritability of growth rate
2
Heritability of fertility
hf
Genetic correlation of fertility and growth-rate
rA
.
0.10 —0.5
0.25
0.50
—0.3 —0.2
Genetic standard deviations Growth-rate
og
Progeny test for growth-rate
Fertility
<,i
150 gram 50 gram 14%
for growth and fertility of males chosen by: (1) selection for growth-rate alone, at a proportion selected of 0.025; (2) selection for fertility alone, at a proportion selected of 0.25; (3) selection for growth rate at a proportion selected of 0.10, followed by selection for fertility at a proportion selected of 0.25; and (4) selection for growth-rate at a proportion selected of 0.10, followed by testing the selected males for fertility, progeny testing the males on the basis of their fertility-test offspring, and selecting them (at a proportion selected of 0.25) on the basis of an index combining progeny test and fertility test results. Since this selection index will depend in part on the relative economic value of the two traits, index selection gains are shown for relative economic values of 1:10 and 1:20. As can be expected, selection of males for growth alone produces the greatest increase in growth-rate and the greatest decrease in fertility, while the converse is true of selection for fertility alone. Selection for growth followed by selection for fertility alone or by index selection for fertility and progeny growth give similar results, except that the second procedure provides somewhat more growth and less fertility than the first.
Downloaded from http://ps.oxfordjournals.org/ by guest on April 30, 2015
improvement of single male pen fertility may proceed via biological pathways that are irrelevant to the improvement of multiple male pen fertility. I t is nevertheless possible, by using the range of estimates of heritability and genetic correlation obtained above, and by restricting the argument to a single male situation, to obtain some approximate estimates of the possible effects of such programs, and to compare the relative effectiveness of various sorts of programs. Table 6 shows values of the various parameters that were used in this study. The growth-rate narameters came from
255
BROILER STOCK SELECTION TABLE 7.—Expected genetic value Jor growth-rate and fertility of males and females selected under various breeding programs1 Expected genetic value2 Growth-rate Fertility
Breeding program
(%)
(gm.) Males Mass selection for growth alone Mass selection for fertility alone Mass selection for growth followed by mass selection for fertility Mass selection for growth followed by index selection: for fertility and progeny test for growth
87 -14 54
(85) (72)
Females Mass selection for growth alone 1 2
70 66
-2.6 4.2
(8.4)
(-0.3)
2.2
(6.4)
(65) (63)
(-2.4) (-1.3)
1.2 1.8
(5.8) (6.2)
47
-1.4
See text for details Estimates in parentheses were calculated for h 2 f=0.1 and h2f = 0.5, respectively.
It should be noted that a presentation in terms of genetic superiority of selected males exaggerates the differences between the programs. Genetic change in the population as a whole will be equally determined by selection of females, and this part of the program will be identical for all of the procedures described. Table 7 also shows the genetic values for growth and male fertility of females selected on the basis of growth-rate alone at a proportion selected of 0.25 Considering, the effects of both male and female selection, it can be seen that if the heritability of fertility is low, the only procedure that prevents any decline in fertility is selecting males for fertility alone. However, if the heritability of fertility is moderately high (0.25, or more), all of the selection schemes involving fertility can maintain fertility along with increased growth gains. It is instructive in deciding upon field programs to compare the relative economic genetic values of the males that
would be selected by each procedure. These are shown in Table 8. The most striking conclusion of Table 8 is that under all conditions, selection for growth TABLE 8.—Economic value of males selected
under various breeding programs1
Breeding program
Economic value2 of selected males '8
Relative economic value (growth:fertility),1:10 Mass selection for growth alone
(1.00)
0.73
(0.49)
Mass selection for fertility alone
(0.05)
0.34
(0.57)
Mass selection for growth followed by mass selection for fertility
(0.8.3)
0.91
(0.96)
Mass selection for growth followed by index selection: for fertility and progeny test for growth
(1.00)
1.00
(1.00)
Relative economic value (growth:fertility), 1:20 Mass selection for growth alone
(0.72)
0.35
(0.19)
Mass selection for fertility alone
(0.41)
0.70
(0.83)
Mass selection for growth followed by mass selection for fertility
(0.98)
0.97
(0.97)
Mass selection for growth followed by index selection: for fertility and progeny test for growth
(1.00)
1.00
(1.00)
1 2
See text for details. Relative to index selected males (mass selection for growth followed by index selection for fertility and progeny test for growth). 3 Values in parentheses calculated forh2f = 0.1 andh2f =0.5., respectively.
Downloaded from http://ps.oxfordjournals.org/ by guest on April 30, 2015
Relative economic value (growth: fertility) 1:10 1:20
1.7)
(
256
M . SOLLEE AND S. RAPPAPORT
alone, followed by selection for fertility alone will give close to optimal results. In fact, if the diluting effect of the female side selections, and the increased generation interval required by progeny testing for growth-rate are taken into consideration, this procedure may be even more effective than selection for growth followed by index selection for growth and fertility. In contrast, selection for growthrate or for fertility alone can, under certain circumstances, give far from optimum results.
It is concluded that a program of mass selection for growth-rate, followed by a fertility test of the selected roosters in a single-pen mating situation, and a further selection on the basis of fertility will give close to optimum gains in economic value.
The authors wish to thank A. Ben Dov of Masuot Yitzchak Poultry Breeding Farm, and B. Eckert of Kibbutz Yavne Poultry Breeding Farm for their cooperation in making available the data on which this study was based. They also wish to thank A. Genizi for his guidance in the statistical analyses. REFERENCES Cohen, A. C , 1957. Restriction and selection in multinomial distribution. Ann. Math. Stat. 28: 731-741. Falconer, D. S., 1960. Introduction to Quantitative Genetics. The Ronald Press Co., New York. Hazel, L. N., 1943. The genetic basis for constructing selection indexes. Genetics, 28: 476-490. Lemer, I. M., 1954. Genetic Homeostasis. Oliver and Boyd, Edinburgh. Parker, J. E., 1961. Observations on the low fertility problem in Cornish cockerels. Poultry Sci. 40: 1214-1219. Rappaport, S., and M. Soller, 1966. Mating behavior, fertility and rate-of-gain in Cornish males. Poultry Sci. 45: 997-1003. Siegel, P. B., 1963. Selection for body weight at 8 weeks of age. 2. Correlated responses of feathering, body weight, and reproductive characteristics. Poultry Sci. 42: 895-905. Soller, M., H. Schindler and S. Bornstein, 1965a. Semen characteristics, failure of insemination and fertility in Cornish and White Rock males. Poultry Sci. 44: 424-432. Soller, M., N. Snapir and H. Schindler, 1965b. Heritability of semen quality, concentration and motility in White Rock roosters and their genetic correlation with rate of gain. Poultry Sci. 44: 1527-1529. Soller, M., and S. Rappaport, 1971. Interaction and pen effects in evaluating broiler sires. To be published.
APRIL 14-16. SYMPOSIUM ON PEST CONTROL STRATEGIES FOR THE FUTURE OF THE AGRICULTURAL BOARD, DIVISION OF BIOLOGY AND AGRICULTURE, NATIONAL ACADEMY OF SCIENCES, AUDITORIUM, NATIONAL ACADEMY OF SCIENCES, 2101 CONSTITUTION AVE., N.W., WASHINGTON, D.C. 20418.
Downloaded from http://ps.oxfordjournals.org/ by guest on April 30, 2015
SUMMARY The relationship between growth-rate and fertility was studied in White Rock and Cornish roosters. The correlation between individual growth-rate and fertility was —0.04, that between progeny test for growth-rate and fertility was —0.12. The genetic correlation between growth-rate and fertility was thus negative, while the environmental correlation was zero or slightly positive. The correlations between semen motility and fertility were positive, though low, those between semen motily and growth-rate were negative. The correlation between fertility and hatchability was 0.85. Repeatability of a fertility test based on the performance of a rooster in one pen for one hatch was 0.42.
ACKNOWLEDGMENT