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Heritabilities and Genetic Correlations of Conformation and Plumage Characteristics in Pheasant (Phasianus colchicus)
Heritabilities and Genetic Correlations of Conformation and Plumage Characteristics in Pheasant (Phasianus colchicus) R. RIZZI,1 S. CEROLINI, 2 C. MANTOVANI, G. PAGNACCO, M. G. MANGIAGALLI, and L. G. CAVALCHINI Istituto di Zootecnica, Facolta di Medicina Veterinaria, Via Celoria 10, 20133 Milano, Italy and Istituto per la Difesa e la Valorizzazione del Germoplasma Animale, Consiglio Nazionale delle Richerche, Via Celoria 10, 20133, Milano, Italy ABSTRACT Data were obtained from 588 pedigreed pheasants of an unselected population. Body weight, shank length (SL), plumage measurements, and plumage score were analyzed to estimate heritabilities and genetic and phenotypic correlations. All measurements were made at 28 and 120 d of age. The h 2 estimates (sire component) were the following: .27 and .30 for BW at 28 (BW28) and at 120 d (BW120), respectively; .34 and .79 for SL at 28 (SL28) and at 120 d (SL120), respectively; .30 and .13 for rectrices length (RL) at 28 (RL28) and at 120 d (RL120), respectively; .14 for primary remex at 28 d (PR); .21 for primary remex 1 at 28 d (PR1); .23 for secondary remiges length (SRL); .34 for body weight gain (BWG); .35 for shank length gain (SLG). Negative genetic correlations between BW and SL with plumage traits at 120 d were found. The magnitude of heritability indicates that selection for BW is possible but the negative association with plumage traits must be carefully considered. The improvement of housing conditions could lead to birds with a well-developed plumage, because environment influenced variability of plumage traits. (Key words: pheasant, heritability, genetic correlations, body weight, plumage) 1994 Poultry Science 73:1204-1210
INTRODUCTION There is limited information on genetic aspects of BW in pheasants. Heritability is within the range of numerous estimates found for this trait in chickens (Chambers, 1990), Japanese quail (Marks, 1990), ducks (Veremeenko, 1991), and turkeys (Toelle et al, 1990). Kassid et al. (1981) estimated heritability for BW at 1 d, 4 wk, 8 wk, 12 wk, and 18 wk, respectively, in a population of pheasants divergently selected for high and low 12-wk BW. Heritability estimates were .29, .44, .41, .20, and .33 for
Received for publication December 1, 1993. Accepted for publication April 21, 1994. ! To whom correspondence should be addressed. 2 Istituto per la Difesa e la Valorizzazione del Germoplasma Animale.
birds of the low-weight line and .47, .64, .66, .77, and .63 for those of the highweight line. Petitjean et al. (1990) reported the heritability for BW at 18 wk to be .63. In a population of pheasants selected for slow feathering, Hussein (1985) found heritability for BW to be .22, .16, and .10 at 4, 8, and 12 wk, respectively. Heritability was higher in pheasants selected for rapid plumage, being .53, .66, and .73 at 4, 8, and 12 wk, respectively. As reported by Marks (1990), the moderate to high heritability estimates for BW in pheasants suggest high genetic variability, and therefore a marked response to selection would be expected. Although genetic aspects of feather color in pheasants have been well studied, very little information is available on genetic parameters for feather structure, distribution, or growth (Somes, 1990).
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GENETIC VARIATION OF PHEASANTS
Hussein (1985) found that early feather coverage is more heritable than slower feather coverage, with heritabilities of .6 and .11, respectively. Because BW and plumage development are very important factors when pheasants are raised for release on h u n t i n g preserves, it is useful to know the heritability and genetic relationships between these two characteristics in order to design optimal breeding strategies. The purpose of the present study was to estimate heritability and genetic correlations between some conformation traits and some characteristics of plumage in pheasants under game farm conditions. MATERIALS AND METHODS Fifty-five m a l e a n d 120 female pheasants (Phasianus colchicus mongolicus) were housed in individual cages at 37 wk of age. At housing, the photoperiod was 11 h light (L):13 h dark (D), the light was increased at a rate of 1 h / w k to reach 14L: 10D by 40 wk of age. Pheasants were provided ad libitum access to a commercial feed for breeders with 22% CP and 2,833 kcal ME/kg. The 1st wk of housing was considered as acclimatization and no records were taken. Egg production of each female was recorded daily. Semen samples were collected on a biweekly basis, according to the technique described by Lake and Stewart (1978). At 45 wk of age, the 27 best semen-producing males were chosen and mated by artificial insemination to 108 females (4 females randomly assigned to each male). Female pheasants laying no or few eggs were excluded from the study. Individual semen samples were diluted 1:2 with a .9% NaCl solution and inseminated soon after collection. Inseminations were performed biweekly from 45 to 50 wk of age. Eggs were collected from 46 to 50 wk of age and stored at 13 to 15 C until incubation. The laying date and parents' number were marked on each egg. Eggs were set at 48 and 50 wk to produce progeny from two hatches. At hatch, pedigreed chicks were wingbanded and housed on deep litter in a windowless house from 1 to 45 d of age at a housing density of .062 m 2 per bird.
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Room temperature was kept between 25 and 27 C by gas overheaters. Artificial light was supplied for 16 h / d (16L:8D). At 45 d of age the pheasants were debeaked, fitted with spectacles to discourage aggression, and were allowed access to an outdoor aviary with no overheaters and illuminated by natural light. The housing density was .3 m 2 per bird. At 60 d of age the pheasants were transferred to a larger outdoor aviary with natural vegetation and at the density of 1 m 2 per bird. Pheasants were fed a starter ration (27.5% CP and 3,197 kcal ME/kg) from 1 to 17 d of age, a grower ration (26% CP and 3,015 kcal ME/kg) from 18 to 60 d, and a finisher ration (23.5% CP and 3,064 kcal ME/kg) from 61 to 120 d. Feed and water were supplied for ad libitum consumption. Individual records were obtained both at 28 and at 120 d for BW (BW28 and BW120), shank length (SL28 and SL120), and rectrices length (RL28 and RL120). Body weight gain (BWG) and SL gain (SLG) during 28 to 120 d were calculated as the difference between the two measurements. Secondary remiges length (SRL) was measured at 120 d of age. Juvenile molt was evaluated at 28 d by scoring the development of the primary remiges (PR) 8 to 10 with a scale from 1 to 4 (1 = absent, 2 = present, 3 = average length, 4 = longer than average). Postjuvenile molt was evaluated by estimating the replacement of primary remex 1 (PR1) at 28 d with a score system from 1 to 5 (1 = presence of old primary, 2 = absence of the same, 3 = presence of the new remex, 4 = long, 5 = very long). All the evaluations were performed by the same person. The PR1 and PR scores were transformed to square roots because there were significant departures from normality with respect to skewness and kurtosis. However, original data were used for statistical analysis because heritability estimates and genetic correlations were not different from those based on transformed data. Statistical Analysis Variance and covariance components were estimated for each trait using the
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TABLE 1. Number of observations, means, standard errors, and coefficients of variation for traits in male and female pheasants Males
Females
Trait1
n
5c
SE
CV
n
X
SE
CV
BW28, g SL28, cm RL28, cm BW120, g SL120, cm RL120, cm SRL, cm BWG, g SLG, cm
311 312 311 311 312 307 309 310 312
174.0 4.4 6.3 1,362.0 8.0 34.7 9.0 1,188.0 3.7
39.0 .4 1.0 110.0 .3 10.1 1.9 99.5 .5
22.6 10.0 16.5 8.1 3.9 9.8 20.1 8.4 12.3
277 276 276 276 277 258 277 276 276
161.0 4.3 6.2 1,000.0 7.0 26.9 8.2 838.8 2.7
31.9 .4 1.1 91.0 .3 2.7 1.8 97.0 .4
19.8 8.7 17.4 9.1 4.2 10.1 21.4 10.4 15.5
!BW28 = 28-d body weight; SL28 = 28-d shank length; RL28 = 28-d rectrices length; BW120 = 120-d body weight; SL120 = 120-d shank length; RL120 = 120-d rectrices length; SRL = secondary remiges length; BWG = 28- to 120-d body weight gain; SLG = 28- to 120-d shank length gain.
than at 120 d in both sexes. The BW28 in males and SRL in females were the most variable traits with CV of 22.6 and 21.4, respectively. The CV for RL28 was also high in both sexes. Y Means for BW were in good agreement ijkim = M + Hi + SXj + s k with the observations in an unselected line + did + eijklm of Mongolian ring-necked pheasants from where Yi^m = the individual observations Woodard et al. (1977). Variability in BW for trait y; yt. = the overall mean for trait y; H ; decreased with the age in both sexes. Males = the fixed effect of i* hatch; SXj = the fixed had higher CV for BW and SL at both ages, effect of j * sex; sk = the random effect of k* but lower CV for BWG and SLG than females. sire; dy = the random effect of 1th dam The CV for plumage measurements were mated to k* sire; e^^m = the random error all higher in females. The mean for RL120 in associated with measurement of each in- males was 34.7 cm. Meriggi (1992) reported dividual. The error was assumed to be slightly lower values for the same trait randomly and independently distributed, measured in male wild pheasants. with mean of zero and a variance of
restricted maximum-likelihood method from Varcomp procedure of SAS® software (SAS Institute, 1985). The data set was analyzed with the following model:
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GENETIC VARIATION OF PHEASANTS
TABLE 2. Frequency of the pheasants in each class of score to evaluate growing primary remiges 8 to 10 (PR) and primary remex 1 (PR1) at 28 d by sex PR Score1 Sex
1
Males Females Total
2 3 3 6
40 40 80
Sex
1
2
Males Females Total
114 94 208
161 136 297
3 89 88 177 PR1 Score2 3
4
Total
180 145 325
312 278 588
4
26 25 51
4 8 12
5
Total
7 13 20
312 278 588
*PR (Primary Remiges 8 to 10) score 1 = absent; 2 = present; 3 = average length; 4 = longer than average. 2 PR1 (Primary Remex 1) score: 1 = presence of old primary; 2 = absence of the same; 3 = presence of new remex; = long; 5 = very long.
selected for slow feathering. Kassid et al. (1981) reported higher estimates for BW28 in lines selected for both low and high 12-wk BW, whereas heritability for BW120 in a line selected for low-BW was similar to the one found in the present study. The BW120 was found to be highly heritable by Petitjean et al. (1990) in a pheasant population selected for reproductive performances and the estimate closely agreed with that reported by Kassid et al (1981) for pheasants selected for high-BW. A heritability of .34 was obtained for BWG, which is lower than most estimates reported for chickens (Chambers, 1990). Heritabilities for BW reported in this study was obtained in an unselected population of pheasants and were similar to those found in pheasant lines selected for low BW or for slow feathering. Moderate heritabilities at 28 and 120 d suggest that selection for increased BW in pheasants can be successful at early ages. Genetic variability for SL was higher at 120 d than at 28 d, as sire component heritabilities were .79 and .34, respectively. Estimates were consistent with those reported for this trait at 59 d in chicken (Ricard and Rouvier, 1968) and at different ages in turkeys (Havenstein et al, 1988a; Buss, 1990). The lower heritability of SL28 suggests that SL at earlier ages can be influenced by maternal effects such as egg size, egg composition, and incubation environment. Because the heritability for SL120 is high, this trait may be a useful tool
for selection, especially if correlated with the traits that are of interest for the breeder. Heritabilities for RL28 and RL120 were .30 and .13, respectively. In the pheasant, the growth of juvenile rectrices begins at 12 d of age and is completed at about 60 d of age. The molt takes place at about 75 d of age (Delacour, 1982). The molting process in birds is under the influence of several factors; thyroid hormone and sex steroids control the molt in opposite directions,
TABLE 3. Heritability estimates and standard errors from sire (h*), dam (h\), and sire plus dam components (h*d) of variance Trait1
H
BW28 SL28 RL28 PR PR1 BW120 SL120 RL120 SRL BWG SLG
.27 .34 .30 .14 .21 .30 .79 .13 .23 .34 .35
»&
* ± ± ± ± ± ± ± ± ± ± ±
.11 .17 .17 .11 .12 .14 .25 .09 .12 .17 .16
.51 .54 .70 .43 .21 .40 .08 .16 .43 .38 .25
± .19 ± .19 ± .21 ± .16 ± .16 ± .17 ± .11 ± .15 ± .17 ± .18 ± .16
.39 .44 .50 .18 .32 .35 .44 .14 .33 .36 .30
± ± ± ± ± ± ± ± ± ± ±
.09 .11 .11 .07 .09 .14 .14 .09 .09 .10 .11
1 BW28 = 28-d body weight; SL28 = 28-d shank length; RL28 = 28-d rectrices length; PR = primary remiges 8 to 10; PR1 = primary remex 1; BW120 = 120-d body weight; SL120 = 120-d shank length; RL120 = 120-d rectrices length; SRL = secondary remiges length; BWG = 28- to 120-d body weight gain; SLG = 28- to 120-d shank length gain.
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TABLE 4. Genetic (rG) and phenotypic (rP) correlation estimates based on the sire components of variance and covariance for conformation and plumage traits1 Trait 2 BW28 SL28 RL28 PR1 PR BW120 SL120 RL120 SRL BWG SLG
BW28 1.09 .83 .56 .67 .40 .24 .29 -.06 .06 -1.04
SL28
RL28
PR1
.67
.61 .67
.64 .63 .69
.76 .50 .63 .58 .33 .20 .10 .18 -.76
.53 .67 .41 .14 .21 .04 .03 -.64
.49 .21 .04 .16 .20 .02 -.45
PR .93 .79 .66 .74 -.00 .12 .19 .13 .11 -.52
BW120
SL120
RL120
SRL
BWG
SLG
.23 1.55 .21 -.46 .17
.20 .48 -.04 .80 .07 .79
-1.25 -.67 -.41 -.68 -.38 -.67 .39
.71 -.22 -.51 -.41 .11 -1.56 .15 .58
-.10 -.60 -1.11 -.66 -.10 .93 .78 -.08 -1.89
1.48 -.43 -.66 -.33 -.43 1.37 -.56 .55 .35 .15
.39 .47 .14 .94 .17
.13 .04 .69 .38
.16 .41 -.11
.05 -.06
-.35
1
The rG are above and rP are below diagonal. 2 BW28 = 28-d body weight; SL28 = 28-d shank length; RL28 = 28-d rectrices length; PR = primary remiges 8 to 10; PR1 = primary remex 1; BW120 = 120-d body weight; SL120 = 120-d shank length; RL120 = 120-d rectrices length; SRL = secondary remiges length; BWG = 28- to 120-d body weight gain; SLG = 28- to 120-d shank length gain.
whereas growth hormone seems to have a negative effect on the new growth of feathers (Ringer, 1965; Sauveur, 1988). The difference in heritability values could be interpreted as being due to physiological changes occurring from 28 to 120 d. Also, the low heritability of RL120 suggests a strong influence of environment on this trait. Selection for RL28 should be successful because of the moderate heritability of the trait, but probably improvement in the desired length of rectrices at 120 d may be accomplished by altering environmental conditions. Housing conditions seem to influence the completeness of plumage because the heritabilities of PR, PR1, and SRL tend to be low to moderate in magnitude, being .14, .21, and .23, respectively. Craig and Muir (1989) and Gerken and Petersen (1992) reported higher heritabilities for plumage condition score in chickens and in quail. Heritability estimates based on dam and sire plus dam components of variance were higher than corresponding estimates from paternal half-sibs correlations. With the exception of SL120 and SLG, the maternal components were higher than paternal components. On the other hand, the PR1 sire and dam components were very similar in magnitude. In chickens, heritability estimates for BW are low if based on the sire component, higher if based on the dam component, and intermediate when based
on full-sib correlation (Chambers, 1990). A similar pattern was found for BW, carcass and organ measurements, and behavioral traits in quail (Toelle et al, 1991; Gerken and Petersen, 1992) and BW and carcass measurements in turkeys (Havenstein et al, 1988b). The dam component includes maternal effects and additive sex-linked genetic effects, whereas sire-dam interactions involve nonadditive genetic effects. All these effects are likely responsible for higher heritabilities of BW and plumage characteristics in pheasants when the dam component is included, as is the case in poultry (Chambers, 1990). Genetic and Phenotypic Correlations The genetic and phenotypic correlations between traits derived from sire variance and covariance components are given in Table 4. Most phenotypic correlations were positive. Only SLG showed a negative relationship with all traits except BW120 and SL120. Correlations involving RL120 and SRL tended to be low. Generally, phenotypic correlations of traits at 28 d with traits at 120 d were positive but low. Many of the genetic correlations were negative and seven of them were outside the range of -1 and 1. However, the genetic correlations between BW and feathering traits measured at 28 d were high and positive. Traits RL28, PR, and PR1 were negatively associated with RL120 and SRL.
GENETIC VARIATION OF PHEASANTS
Correlation of PR with SRL was positive but very low. Body weight and SL measured at the same age had positive, genetic correlations as reported for chickens (Chambers, 1990) and turkeys (Havenstein et al, 1988a). Toelle et al. (1991) reported a high and positive correlation between BW and shank weight in quail. Also, selection for a rapid growth should increase body size because of high and positive correlations between BWG and BW120 and SL120. Genetic correlation estimates among traits at 28 d and plumage traits at 120 d are interesting because early selection for welldeveloped adult plumage would be successful if correlations are high and positive. On the contrary, it appears from this study that selection for plumage traits at 28 d will not improve the plumage at 120 d. The positive and high correlation between BW28 and SRL indicates that selection for BW28 could lead to better plumage development. It would be more interesting to know the relation between BW28 and RL120, as the former can be measured easily and the latter represents a very important trait for breeders, but this genetic correlation does not indicate that mis would be a desirable approach. Shank length at 28 d was negatively correlated to RL120 and SRL. Shank length measurement can be used in chickens as an alternative to weighing to determine body size (Lerner, 1946). The use of SL as predictor of adult plumage suggests that as the size of pheasant is increased by selection, the development of the plumage decreases. Genetic correlation between BW120 and RL120 was negative and high in magnitude, but RL120 and SRL were positively correlated. Although the phenotypic correlations between plumage traits at 28 d and the same at 120 d were positive, these same negative genetic correlations suggest that selection of pheasants with a welldeveloped plumage at 28 d would not be successful in obtaining birds with the desired plumage at market age. Also, selection for increased BW will lead to poorer plumage. Negative correlations among feather score and some measures of egg production in hens were found by Craig and Muir (1989), but estimates were low and not significant.
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Rectrices length at 120 d was negatively associated with the precocity of juvenile and postjuvenile molts as indicated by negative genetic correlations with PR and PR1. Genetic correlations among traits measured at 28 d and BWG and SLG were all negative. The correlation between BWG and RL120 was negative but very low, whereas the correlation with SRL was out of the acceptable range. These results and other negative genetic correlations between BW and SL and plumage traits suggest that rapid growth could be detrimental for plumage. The results obtained in the present study indicate that heritability of BW and BWG in pheasants was moderate. As in chickens and other galliforms, selection to increase or decrease these traits in pheasants could be successful. It must be pointed out that if the pheasant is too heavy it tends to stay on the ground, whereas if it is too light it makes a difficult target and it represents a poor "game-bag" for the hunter. These aspects must be considered when selecting for increased weight in pheasants reared for hunting preserves. Traits concerning plumage showed low to moderate heritability estimates. Because environment greatly influences these traits, the improvement of housing and rearing management could lead to birds with a well developed plumage at market age. Genetic correlations between measurements concerning body size and plumage traits were negative. It appears therefore that selection for increased body size leads to pheasants with poorer plumage. From the present study it appears that plumage traits can be improved, albeit slowly, with family selection and progeny tests, careful control of management, and low selection emphasis on BW.
REFERENCES Becker, W. A., 1968. Estimation of variance components and heritability. Pages 7-59 in: Manual of Procedures in Quantitative Genetics. 2nd ed. The Program in Genetics. Washington State University, Puyallup, WA. Buss, E. G., 1990. Genetics of growth and meat production in turkeys. Pages 645-675 in: Poultry Breeding and Genetics. R. D. Crawford, ed. Elsevier, Amsterdam, The Netherlands. Chambers, J. R., 1990. Genetics of growth and meat production in chickens. Pages 599-643 in: Poultry
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Poultry Breeding and Genetics. R. D. Crawford, Breeding and Genetics. R. D. Crawford, ed. ed. Elsevier, Amsterdam, The Netherlands. Elsevier, Amsterdam, The Netherlands. Craig, J. V., and W. M. Muir, 1989. Fearful and Meriggi, A., 1992. Fagiano comune, Phasianus colchicus. Pages 824-840 in: Aves: Gavidae-Phasianidae. associated responses of caged white leghorn Vol. XXIX, P. Brichetti and P. De Franceschi, ed. hens: genetic parameter estimates. Poultry Sci. 68: Calderini, Bologna, Italy. 1040-1046. Delacour, J., 1982. The true pheasants. Genus Phasia- Petitjean, M., N. Bencheikh, and G. Malineau, 1990. Etude de la variabilite criteres de la croissance et nus. Pages 262-299 in: The Pheasants in the de la fertility chez le faisan commun. Pages World. SPUR Publications, ed. Triplegate Ltd. 158-164 in: Control of Fertility in Domestic Birds. and Saiga Publishing Co. Ltd., Hindhead, EnJ. P. Brillard, ed. Nouzilly, France. gland. Gerken, M., and J. Petersen, 1992. Heritabilities for Ricard, F. H., and R. Rouvier, 1968. £tude des mesures de conformation du poulet. Ann. Zootech. 17: behavioral and production traits in Japanese 445-458. quail (Cotumix coturnix) bidirectionally selected for dustbathing activity. Poultry Sci. 71:779-788. Ringer, R. K., 1965. Thyroids. Pages 592-648 in: Avian Physiology. P. D. Sturkie, ed. Cornell University Havenstein, G. B., K. E. Nestor, V. D. Toelle, and W. L. Press, New York, NY. Bacon, 1988a. Estimates of genetic parameters in turkeys. 1. Body weight and skeletal characteris- SAS Institute, 1985. SAS® User's Guide Statistics. Version 5 Edition. SAS Institute Inc., Cary, NC. tics. Poultry Sci. 67:1378-1387. Havenstein, G. B., V. D. Toelle, K. E. Nestor, and W. L. Sauver, B., 1988. Mues naturelles et mues provoqu£es. Pages 89-103 in: Reproduction des Volailles et Bacon, 1988b. Estimates of genetic parameters in Production d'Oeufs. Institut National de la turkeys. 1. Body weight and carcass characterisRecherche Agronomique, Paris France. tics. Poultry Sci. 67:1388-1399. Somes, Jr., R. G., 1990. Mutations and major variants in Hussein, T. H., 1985. Genetic Parameter Estimates for ring-necked pheasants. Pages 371-380 in: Poultry Feathering and Growth in Ring-Necked Pheasant Breeding and Genetics. R. D. Crawford, ed. (Phasianus colchicus) Population. Ph.D. dissertaElsevier, Amsterdam, The Netherlands. tion, Michigan State University, East Lansing, MI. Toelle, V. D., G. B. Havenstein, K. E. Nestor, and W. L. Kassid, J. F., C. J. Flegal, and R. J. Balander, 1981. Bacon, 1990. Estimates of genetic parameters in Genetics of body weight of ring-necked pheasant turkeys. 3. Sexual dimorphism and its implica(Phasianus colchicus) population. Poultry Sci. 60: tions in selection procedures. Poultry Sci. 69: 1678-1679.(Abstr.) 1634-1643. Lake, P. E., and J. M. Stewart, 1978. Artificial Toelle, V. D., G. B. Havenstein, K. E. Nestor, and W. R. Insemination in Poultry. Bulletin 213. Ministry of Harvey, 1991. Genetic and phenotypic relationAgriculture, Fisheries and Food, ed. Adas, Edinships in Japanese quail. 1. Body weight, carcass burgh, Scotland. and organ measurements. Poultry Sci. 70: Lerner, I. M., 1946. The effect of selection for shank 1679-1688. length on sexual maturity and early egg weight in Veremeenko, R., 1991. Selection in ducks. PtitSingle Comb White Leghorn pullets. Poultry Sci. sevodstvo 12:28-31. 25:204-209. Woodard, A. E., P. Vohra, and R. L. Snyder, 1977. Effect of protein levels in the diet on the growth of Marks, H. L., 1990. Genetics of growth and meat pheasants. Poultry Sci. 56:1492-1500. production in other galliforms. Pages 677-690 in:
INTRODUCTION There is limited information on genetic aspects of BW in pheasants. Heritability is within the range of numerous estimates found for this trait in chickens (Chambers, 1990), Japanese quail (Marks, 1990), ducks (Veremeenko, 1991), and turkeys (Toelle et al, 1990). Kassid et al. (1981) estimated heritability for BW at 1 d, 4 wk, 8 wk, 12 wk, and 18 wk, respectively, in a population of pheasants divergently selected for high and low 12-wk BW. Heritability estimates were .29, .44, .41, .20, and .33 for
Received for publication December 1, 1993. Accepted for publication April 21, 1994. ! To whom correspondence should be addressed. 2 Istituto per la Difesa e la Valorizzazione del Germoplasma Animale.
birds of the low-weight line and .47, .64, .66, .77, and .63 for those of the highweight line. Petitjean et al. (1990) reported the heritability for BW at 18 wk to be .63. In a population of pheasants selected for slow feathering, Hussein (1985) found heritability for BW to be .22, .16, and .10 at 4, 8, and 12 wk, respectively. Heritability was higher in pheasants selected for rapid plumage, being .53, .66, and .73 at 4, 8, and 12 wk, respectively. As reported by Marks (1990), the moderate to high heritability estimates for BW in pheasants suggest high genetic variability, and therefore a marked response to selection would be expected. Although genetic aspects of feather color in pheasants have been well studied, very little information is available on genetic parameters for feather structure, distribution, or growth (Somes, 1990).
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GENETIC VARIATION OF PHEASANTS
Hussein (1985) found that early feather coverage is more heritable than slower feather coverage, with heritabilities of .6 and .11, respectively. Because BW and plumage development are very important factors when pheasants are raised for release on h u n t i n g preserves, it is useful to know the heritability and genetic relationships between these two characteristics in order to design optimal breeding strategies. The purpose of the present study was to estimate heritability and genetic correlations between some conformation traits and some characteristics of plumage in pheasants under game farm conditions. MATERIALS AND METHODS Fifty-five m a l e a n d 120 female pheasants (Phasianus colchicus mongolicus) were housed in individual cages at 37 wk of age. At housing, the photoperiod was 11 h light (L):13 h dark (D), the light was increased at a rate of 1 h / w k to reach 14L: 10D by 40 wk of age. Pheasants were provided ad libitum access to a commercial feed for breeders with 22% CP and 2,833 kcal ME/kg. The 1st wk of housing was considered as acclimatization and no records were taken. Egg production of each female was recorded daily. Semen samples were collected on a biweekly basis, according to the technique described by Lake and Stewart (1978). At 45 wk of age, the 27 best semen-producing males were chosen and mated by artificial insemination to 108 females (4 females randomly assigned to each male). Female pheasants laying no or few eggs were excluded from the study. Individual semen samples were diluted 1:2 with a .9% NaCl solution and inseminated soon after collection. Inseminations were performed biweekly from 45 to 50 wk of age. Eggs were collected from 46 to 50 wk of age and stored at 13 to 15 C until incubation. The laying date and parents' number were marked on each egg. Eggs were set at 48 and 50 wk to produce progeny from two hatches. At hatch, pedigreed chicks were wingbanded and housed on deep litter in a windowless house from 1 to 45 d of age at a housing density of .062 m 2 per bird.
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Room temperature was kept between 25 and 27 C by gas overheaters. Artificial light was supplied for 16 h / d (16L:8D). At 45 d of age the pheasants were debeaked, fitted with spectacles to discourage aggression, and were allowed access to an outdoor aviary with no overheaters and illuminated by natural light. The housing density was .3 m 2 per bird. At 60 d of age the pheasants were transferred to a larger outdoor aviary with natural vegetation and at the density of 1 m 2 per bird. Pheasants were fed a starter ration (27.5% CP and 3,197 kcal ME/kg) from 1 to 17 d of age, a grower ration (26% CP and 3,015 kcal ME/kg) from 18 to 60 d, and a finisher ration (23.5% CP and 3,064 kcal ME/kg) from 61 to 120 d. Feed and water were supplied for ad libitum consumption. Individual records were obtained both at 28 and at 120 d for BW (BW28 and BW120), shank length (SL28 and SL120), and rectrices length (RL28 and RL120). Body weight gain (BWG) and SL gain (SLG) during 28 to 120 d were calculated as the difference between the two measurements. Secondary remiges length (SRL) was measured at 120 d of age. Juvenile molt was evaluated at 28 d by scoring the development of the primary remiges (PR) 8 to 10 with a scale from 1 to 4 (1 = absent, 2 = present, 3 = average length, 4 = longer than average). Postjuvenile molt was evaluated by estimating the replacement of primary remex 1 (PR1) at 28 d with a score system from 1 to 5 (1 = presence of old primary, 2 = absence of the same, 3 = presence of the new remex, 4 = long, 5 = very long). All the evaluations were performed by the same person. The PR1 and PR scores were transformed to square roots because there were significant departures from normality with respect to skewness and kurtosis. However, original data were used for statistical analysis because heritability estimates and genetic correlations were not different from those based on transformed data. Statistical Analysis Variance and covariance components were estimated for each trait using the
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TABLE 1. Number of observations, means, standard errors, and coefficients of variation for traits in male and female pheasants Males
Females
Trait1
n
5c
SE
CV
n
X
SE
CV
BW28, g SL28, cm RL28, cm BW120, g SL120, cm RL120, cm SRL, cm BWG, g SLG, cm
311 312 311 311 312 307 309 310 312
174.0 4.4 6.3 1,362.0 8.0 34.7 9.0 1,188.0 3.7
39.0 .4 1.0 110.0 .3 10.1 1.9 99.5 .5
22.6 10.0 16.5 8.1 3.9 9.8 20.1 8.4 12.3
277 276 276 276 277 258 277 276 276
161.0 4.3 6.2 1,000.0 7.0 26.9 8.2 838.8 2.7
31.9 .4 1.1 91.0 .3 2.7 1.8 97.0 .4
19.8 8.7 17.4 9.1 4.2 10.1 21.4 10.4 15.5
!BW28 = 28-d body weight; SL28 = 28-d shank length; RL28 = 28-d rectrices length; BW120 = 120-d body weight; SL120 = 120-d shank length; RL120 = 120-d rectrices length; SRL = secondary remiges length; BWG = 28- to 120-d body weight gain; SLG = 28- to 120-d shank length gain.
than at 120 d in both sexes. The BW28 in males and SRL in females were the most variable traits with CV of 22.6 and 21.4, respectively. The CV for RL28 was also high in both sexes. Y Means for BW were in good agreement ijkim = M + Hi + SXj + s k with the observations in an unselected line + did + eijklm of Mongolian ring-necked pheasants from where Yi^m = the individual observations Woodard et al. (1977). Variability in BW for trait y; yt. = the overall mean for trait y; H ; decreased with the age in both sexes. Males = the fixed effect of i* hatch; SXj = the fixed had higher CV for BW and SL at both ages, effect of j * sex; sk = the random effect of k* but lower CV for BWG and SLG than females. sire; dy = the random effect of 1th dam The CV for plumage measurements were mated to k* sire; e^^m = the random error all higher in females. The mean for RL120 in associated with measurement of each in- males was 34.7 cm. Meriggi (1992) reported dividual. The error was assumed to be slightly lower values for the same trait randomly and independently distributed, measured in male wild pheasants. with mean of zero and a variance of
restricted maximum-likelihood method from Varcomp procedure of SAS® software (SAS Institute, 1985). The data set was analyzed with the following model:
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GENETIC VARIATION OF PHEASANTS
TABLE 2. Frequency of the pheasants in each class of score to evaluate growing primary remiges 8 to 10 (PR) and primary remex 1 (PR1) at 28 d by sex PR Score1 Sex
1
Males Females Total
2 3 3 6
40 40 80
Sex
1
2
Males Females Total
114 94 208
161 136 297
3 89 88 177 PR1 Score2 3
4
Total
180 145 325
312 278 588
4
26 25 51
4 8 12
5
Total
7 13 20
312 278 588
*PR (Primary Remiges 8 to 10) score 1 = absent; 2 = present; 3 = average length; 4 = longer than average. 2 PR1 (Primary Remex 1) score: 1 = presence of old primary; 2 = absence of the same; 3 = presence of new remex; = long; 5 = very long.
selected for slow feathering. Kassid et al. (1981) reported higher estimates for BW28 in lines selected for both low and high 12-wk BW, whereas heritability for BW120 in a line selected for low-BW was similar to the one found in the present study. The BW120 was found to be highly heritable by Petitjean et al. (1990) in a pheasant population selected for reproductive performances and the estimate closely agreed with that reported by Kassid et al (1981) for pheasants selected for high-BW. A heritability of .34 was obtained for BWG, which is lower than most estimates reported for chickens (Chambers, 1990). Heritabilities for BW reported in this study was obtained in an unselected population of pheasants and were similar to those found in pheasant lines selected for low BW or for slow feathering. Moderate heritabilities at 28 and 120 d suggest that selection for increased BW in pheasants can be successful at early ages. Genetic variability for SL was higher at 120 d than at 28 d, as sire component heritabilities were .79 and .34, respectively. Estimates were consistent with those reported for this trait at 59 d in chicken (Ricard and Rouvier, 1968) and at different ages in turkeys (Havenstein et al, 1988a; Buss, 1990). The lower heritability of SL28 suggests that SL at earlier ages can be influenced by maternal effects such as egg size, egg composition, and incubation environment. Because the heritability for SL120 is high, this trait may be a useful tool
for selection, especially if correlated with the traits that are of interest for the breeder. Heritabilities for RL28 and RL120 were .30 and .13, respectively. In the pheasant, the growth of juvenile rectrices begins at 12 d of age and is completed at about 60 d of age. The molt takes place at about 75 d of age (Delacour, 1982). The molting process in birds is under the influence of several factors; thyroid hormone and sex steroids control the molt in opposite directions,
TABLE 3. Heritability estimates and standard errors from sire (h*), dam (h\), and sire plus dam components (h*d) of variance Trait1
H
BW28 SL28 RL28 PR PR1 BW120 SL120 RL120 SRL BWG SLG
.27 .34 .30 .14 .21 .30 .79 .13 .23 .34 .35
»&
* ± ± ± ± ± ± ± ± ± ± ±
.11 .17 .17 .11 .12 .14 .25 .09 .12 .17 .16
.51 .54 .70 .43 .21 .40 .08 .16 .43 .38 .25
± .19 ± .19 ± .21 ± .16 ± .16 ± .17 ± .11 ± .15 ± .17 ± .18 ± .16
.39 .44 .50 .18 .32 .35 .44 .14 .33 .36 .30
± ± ± ± ± ± ± ± ± ± ±
.09 .11 .11 .07 .09 .14 .14 .09 .09 .10 .11
1 BW28 = 28-d body weight; SL28 = 28-d shank length; RL28 = 28-d rectrices length; PR = primary remiges 8 to 10; PR1 = primary remex 1; BW120 = 120-d body weight; SL120 = 120-d shank length; RL120 = 120-d rectrices length; SRL = secondary remiges length; BWG = 28- to 120-d body weight gain; SLG = 28- to 120-d shank length gain.
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TABLE 4. Genetic (rG) and phenotypic (rP) correlation estimates based on the sire components of variance and covariance for conformation and plumage traits1 Trait 2 BW28 SL28 RL28 PR1 PR BW120 SL120 RL120 SRL BWG SLG
BW28 1.09 .83 .56 .67 .40 .24 .29 -.06 .06 -1.04
SL28
RL28
PR1
.67
.61 .67
.64 .63 .69
.76 .50 .63 .58 .33 .20 .10 .18 -.76
.53 .67 .41 .14 .21 .04 .03 -.64
.49 .21 .04 .16 .20 .02 -.45
PR .93 .79 .66 .74 -.00 .12 .19 .13 .11 -.52
BW120
SL120
RL120
SRL
BWG
SLG
.23 1.55 .21 -.46 .17
.20 .48 -.04 .80 .07 .79
-1.25 -.67 -.41 -.68 -.38 -.67 .39
.71 -.22 -.51 -.41 .11 -1.56 .15 .58
-.10 -.60 -1.11 -.66 -.10 .93 .78 -.08 -1.89
1.48 -.43 -.66 -.33 -.43 1.37 -.56 .55 .35 .15
.39 .47 .14 .94 .17
.13 .04 .69 .38
.16 .41 -.11
.05 -.06
-.35
1
The rG are above and rP are below diagonal. 2 BW28 = 28-d body weight; SL28 = 28-d shank length; RL28 = 28-d rectrices length; PR = primary remiges 8 to 10; PR1 = primary remex 1; BW120 = 120-d body weight; SL120 = 120-d shank length; RL120 = 120-d rectrices length; SRL = secondary remiges length; BWG = 28- to 120-d body weight gain; SLG = 28- to 120-d shank length gain.
whereas growth hormone seems to have a negative effect on the new growth of feathers (Ringer, 1965; Sauveur, 1988). The difference in heritability values could be interpreted as being due to physiological changes occurring from 28 to 120 d. Also, the low heritability of RL120 suggests a strong influence of environment on this trait. Selection for RL28 should be successful because of the moderate heritability of the trait, but probably improvement in the desired length of rectrices at 120 d may be accomplished by altering environmental conditions. Housing conditions seem to influence the completeness of plumage because the heritabilities of PR, PR1, and SRL tend to be low to moderate in magnitude, being .14, .21, and .23, respectively. Craig and Muir (1989) and Gerken and Petersen (1992) reported higher heritabilities for plumage condition score in chickens and in quail. Heritability estimates based on dam and sire plus dam components of variance were higher than corresponding estimates from paternal half-sibs correlations. With the exception of SL120 and SLG, the maternal components were higher than paternal components. On the other hand, the PR1 sire and dam components were very similar in magnitude. In chickens, heritability estimates for BW are low if based on the sire component, higher if based on the dam component, and intermediate when based
on full-sib correlation (Chambers, 1990). A similar pattern was found for BW, carcass and organ measurements, and behavioral traits in quail (Toelle et al, 1991; Gerken and Petersen, 1992) and BW and carcass measurements in turkeys (Havenstein et al, 1988b). The dam component includes maternal effects and additive sex-linked genetic effects, whereas sire-dam interactions involve nonadditive genetic effects. All these effects are likely responsible for higher heritabilities of BW and plumage characteristics in pheasants when the dam component is included, as is the case in poultry (Chambers, 1990). Genetic and Phenotypic Correlations The genetic and phenotypic correlations between traits derived from sire variance and covariance components are given in Table 4. Most phenotypic correlations were positive. Only SLG showed a negative relationship with all traits except BW120 and SL120. Correlations involving RL120 and SRL tended to be low. Generally, phenotypic correlations of traits at 28 d with traits at 120 d were positive but low. Many of the genetic correlations were negative and seven of them were outside the range of -1 and 1. However, the genetic correlations between BW and feathering traits measured at 28 d were high and positive. Traits RL28, PR, and PR1 were negatively associated with RL120 and SRL.
GENETIC VARIATION OF PHEASANTS
Correlation of PR with SRL was positive but very low. Body weight and SL measured at the same age had positive, genetic correlations as reported for chickens (Chambers, 1990) and turkeys (Havenstein et al, 1988a). Toelle et al. (1991) reported a high and positive correlation between BW and shank weight in quail. Also, selection for a rapid growth should increase body size because of high and positive correlations between BWG and BW120 and SL120. Genetic correlation estimates among traits at 28 d and plumage traits at 120 d are interesting because early selection for welldeveloped adult plumage would be successful if correlations are high and positive. On the contrary, it appears from this study that selection for plumage traits at 28 d will not improve the plumage at 120 d. The positive and high correlation between BW28 and SRL indicates that selection for BW28 could lead to better plumage development. It would be more interesting to know the relation between BW28 and RL120, as the former can be measured easily and the latter represents a very important trait for breeders, but this genetic correlation does not indicate that mis would be a desirable approach. Shank length at 28 d was negatively correlated to RL120 and SRL. Shank length measurement can be used in chickens as an alternative to weighing to determine body size (Lerner, 1946). The use of SL as predictor of adult plumage suggests that as the size of pheasant is increased by selection, the development of the plumage decreases. Genetic correlation between BW120 and RL120 was negative and high in magnitude, but RL120 and SRL were positively correlated. Although the phenotypic correlations between plumage traits at 28 d and the same at 120 d were positive, these same negative genetic correlations suggest that selection of pheasants with a welldeveloped plumage at 28 d would not be successful in obtaining birds with the desired plumage at market age. Also, selection for increased BW will lead to poorer plumage. Negative correlations among feather score and some measures of egg production in hens were found by Craig and Muir (1989), but estimates were low and not significant.
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Rectrices length at 120 d was negatively associated with the precocity of juvenile and postjuvenile molts as indicated by negative genetic correlations with PR and PR1. Genetic correlations among traits measured at 28 d and BWG and SLG were all negative. The correlation between BWG and RL120 was negative but very low, whereas the correlation with SRL was out of the acceptable range. These results and other negative genetic correlations between BW and SL and plumage traits suggest that rapid growth could be detrimental for plumage. The results obtained in the present study indicate that heritability of BW and BWG in pheasants was moderate. As in chickens and other galliforms, selection to increase or decrease these traits in pheasants could be successful. It must be pointed out that if the pheasant is too heavy it tends to stay on the ground, whereas if it is too light it makes a difficult target and it represents a poor "game-bag" for the hunter. These aspects must be considered when selecting for increased weight in pheasants reared for hunting preserves. Traits concerning plumage showed low to moderate heritability estimates. Because environment greatly influences these traits, the improvement of housing and rearing management could lead to birds with a well developed plumage at market age. Genetic correlations between measurements concerning body size and plumage traits were negative. It appears therefore that selection for increased body size leads to pheasants with poorer plumage. From the present study it appears that plumage traits can be improved, albeit slowly, with family selection and progeny tests, careful control of management, and low selection emphasis on BW.
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