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Effects of discontinuity on heritabilities and phenotypic correlations for classified type characteristics in Japanese black heifers
Livestock Production Science, 10 (1983) 611--616
611
Elsevier Science Publishers B.V., Amsterdam - - P r i n t e d in The Netherlands
Short Communication EFFECTS OF DISCONTINUITY ON HERITABILITIES AND PHENOTYPIC CORRELATIONS FOR CLASSIFIED TYPE CHARACTERISTICS IN JAPANESE BLACK HEIFERS
HIROAKI IWAISAKI
Department of Animal Science, College of Agriculture, Kyoto University, Kyoto-shi 606 (Japan) (Accepted 26 May 1983)
ABSTRACT
Iwaisaki, H., 1983. Effects of discontinuity on heritabilities and phenotypic correlations for classified type characteristics in Japanese Black heifers. Livest. Prod. Sci., 10: 611--616. The data on classified t y p e characteristics of 1692 Japanese Black breeding heifers were analyzed to investigate the effects of discontinuity and to estimate the heritabilities and phenotypic correlations in the underlying continuous scale. The parameters in an outward scale were computed with the equally-spaced scoring, employing mixed-model least squares procedures, and then those were adjusted for the effects of discontinuity. The effects of discontinuity for the classified type characteristics were generally minor in this applied work.
INTRODUCTION
A program to classify beef production characteristics in breeding cattle was carried o u t b y The Wagyu Cattle Registry Association of Japan. The main purpose was to investigate the usefulness of the b o d y characteristics as an indicator of carcass merit. Sasaki et al. (1976b), using descriptively coded data, have estimated genetic and phenotypic parameters in an outward scale. Assigning outward scores, however, may cause an environmental measurem e n t error, in other words, the effects of discontinuity on the parameters. In this context, this paper investigates the magnitude o f the effects of discontinuity on heritabilities of, and phenotypic correlations among classified t y p e characteristics and presents the adjusted estimates. MATERIALS
AND METHODS
The data utilized were records on descriptive type classification for 1692 Japanese Black breeding heifers, which were collected by The Wagyu Cattle Registry Association in 1973 and 1974. These records were much the same,
0301-6226/83/$03.00
© 1983 Elsevier Science Publishers B.V.
612 but slightly (about 350) more than those used by Sasaki et al. (1976a, b). The heifers consisted of sets of 93 sires from five prefectures. Of the many characteristics studied previously (Sasaki et al., 1976a) the main fifteen were included, and the equally spaced scoring was adopted under the assumption of the classes being ordered according to relative merit. Raw data on the outward scale were analyzed by a mixed-model, leastsquares analysis of variance procedure, using the LSML76 Program (Harvey, 1977). The factors considered in the model were prefectures, sires within prefectures (random), years, prefecture × year interactions, age of month at classification as a covariate and residuals (random). The discrete estimates of heritability and phenotypic correlation within subclass were computed from paternal half-sister correlations. Then, the discrete ones were adjusted as follows for the effects of discontinuity by the methodology of Vinson et al. (1976) h2u ' = 5 2
2 am /(Z Zim)2 i
Puv = PmnOmOn/[(Z Zim)(2; Zin)] i
i
where, h2u: heritability of the underlying continuous phenotype, h ~ : heritability of the discrete phenotype, Puv: correlation between the continuous phenotypes, Pmn: correlation between the discrete phenotypes, am and an: standard deviation on the discrete phenotypes, Zim and Zin: height of the ordinate of the normal curve at the threshold point (i). The standard deviations of outward phenotypes, am and an, were computed from the sire and residual variance component estimates. Additionally, the values of heights of the normal curve, Zim and Zin, were totally determined by the category frequencies adjusted for the fixed effects, performing a least-squares analysis on each frequency. The genetic correlations were not included in this paper because the correlation between the underlying variables is directly estimated as that from multinomial phenotypes of related individuals (Vinson et al., 1976; Gianola, 1982). RESULTS AND DISCUSSION Adjusted heritabilities and phenotypic correlations in comparison with those observed are presented in Tables I and II, respectively. Observed heritability estimates remained generally unchanged from those found by Sasaki et al. (1976b) and were sizeable to moderate. These were comparable to the findings with the scoring in relation to ideal type for the U.S. Holsteins (Cassell et al., 1973; Thompson et al., 1981), in which Thompson et al. (1981) indicated that such estimates were slightly lower than those with the ordered evaluation and linear scoring. The heritabilities observed in this and the above mentioned studies were all based on the equally-spaced scoring. On this point, the observed heritabil-
613 TABLE I Heritability estimates adjusted for discontinuity in comparison with observed estimates Characteristics
Condition Stature Proportions Hair Skin Chest Shoulder (rear view) Back Loin Rib Belly
Rump (rear view) Thigh (side view) Udder Teats
Heritability
Observed*
Adjusted
0.18 b 0.10a 0.12 a 0.23 b 0.34 d 0.13 a 0.15 a 0.13 a 0.09 a 0.26 c 0.14 a 0.23b
0.40 0.10 0.12 0.23 0.34 0.13 0.16 0.14 0.10 0.29 0.16 0.25 0.19 0.32 0.21
0.19 b
0.26 c 0.19 b
* S t a n d a r d error for the observed estimate. a = 0.05, b = 0.06, c = 0.07, a n d d = 0.08.
ity estimate is n o t invariant t o the assigned scores because o f multinomial p h e n o t y p e s (Gianola, 1979). However, it has been suggested by Gianola and N o r t o n (1981) that, in general, equally-spaced scores will result in negligible losses in terms of heritability in comparison with t he " c a n o n i c a l " scaling developed by them. Adjusted heritability estimates f or stature, proportions, hair, and skin remained f u n d am ent al l y unchanged f r o m those previously observed. The classes themselves have been defined in terms o f a one dimensional and o r d er ed c o n c e p t (e.g., very good, good, average, ...), and consequent l y those traits generally followed symmetrical distributions as c o n f i r m e d from the p h e n o t y p i c frequencies f o u n d f or t he classes and the scores. For several characteristics associated with beef t y p e and u d d e r c o n f o r m a t i o n , the effects o f discontinuity were f o u n d t o be existing although their magnitudes were only small to sizeable. As t he num be r s o f classes were almost the same for all o f the traits studied, such results m a y be due to m o r e asymmetrical and skewed distributions f o u n d in practice because o f the m o r e discrete and conceptually co mp licat ed definitions o f classes. Exceptionally, t he effect was larger for co n d itio n because of the distribution with t he large relative skewness value of 11.8. Th e discrepancy bet w e e n the observed and t he adjusted p h e n o t y p i c correlation also showed a t r e nd r a t he r similar t o t he case o f heritabflity.
614
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c~
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u~o~
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c~
0 ~s~qo
~
u~IS N ,0 0 0
-~odo~I
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615
As a whole, the results indicate that heritability and phenotypic correlation estimates in the outward scale for multinomial traits are deflated, but the effects of discontinuity are practically minor for beef type characteristics, agreeing with findings from the U.S. studies for dairy cattle (Cassell et al., 1973; Vinson et al., 1976). ACKNOWLEDGEMENTS
The author is grateful to The Wagyu Cattle Registry Association for providing the data for this study. The author is also indebted to Dr. W.E. Vinson, Virginia Polytechnic Institute and State University, U.S.A. for his valuable suggestion for the analysis, and to Dr. Y. Sasaki and Dr. K. Namikawa for their critical readings of this paper.
REFERENCES Cassell, B.G., White, J.M., Vinson, W.E. and Kliewer, R.H., 1973. Genetic and phenotypic relationships among type traits in Holstein--Friesian cattle. J. Dairy Sci., 56: 1171-1177. Gianola, D., 1979. Heritability o f p o l y c h o t o m o u s characters. Genetics, 93: 1051--1055. Gianola, D., 1982. Theory and analysis of threshold characters. J. Anita. Sci., 54: 1079-1096. Gianola, D. and Norton, H.W., 1981. Scaling threshold characters. Genetics, 99: 357-364. Harvey, W.R., 1977. User's Guide for LSML76. Monograph, Ohio State Univ., Columbus, OH, 76 pp. Sasaki, Y., Iwaisaki, H., Mukai, F. and Namikawa, K., 1976a. Factors affecting descriptive type traits. Jpn. J. Zootech. Sci., 4 7 : 3 5 9 - - 3 7 0 (in Japanese). Sasaki, Y., Iwaisaki, H., Mukai, F. and Namikawa, K., I976b. Inheritance of descriptive type traits based on phenotypic resemblance between half-sib heifers. Jpn. J. Zootech. Sci., 4 7 : 3 7 1 - - 3 7 7 (in Japanese). Thompson, J.R., Freeman, A.E., Wilson, D.J., Chapin, C.A. and Berger, P.J., 1981. Evaluation o f a linear t y p e program in Holsteins. J. Dairy Sci., 64: 1610--1617. Vinson, W.E., White, J.M. and Kliewer, R.H., 1976. Overall classification as a selection criterion for improving categorically scored components of type in Holsteins. J. Dairy Sci., 59: 2104--2121.
RESUME Iwaisaki, H., 1983. Incidence sur les h~ritabilit6s et les correlations phfinotypiques du caract~re discontinu des mesures de conformation chez les g~nlsses Noires Japonaises. Livest. Prod. Sci., 10:611--616 (en anglais).
Les donn~es de conformation lait~re de 1692 g6nisses Noires Japonaises ont ~t~ analys~es pour examiner la mani~re d o n t leur caract~re discontinu peut affecter les estimations d'h~ritabflit~ et de correlation ph~notypiques. Ces param~tres ont fit~ ~valu~s dans le cadre d ' u n module mixte en utilisant soit les notes ~quidistantes de d~part, soit de nouvelles notes obtenues ~ partir de variables continues sous-jacentes. Les differences entre les r~sultats fournls par les deux m~thodes ont ~t~ g~n~ralement mineures.
616 KURZFASSUNG i
Iwaisaki, H., 1983. Der Einfluss von Diskontinuit~it auf die Heritabilit~iten und ph~inotypischen Korrelationen fiir klassifizierte Typmerkmale bei F~irsen der Rasse Japanischer Schwarzvieh. Livest. Prod. Sci., 1 0 : 6 1 1 - - 6 1 6 (auf englisch). Die Daten yon klassifizierten Typmerkmalen yon 1692 Zuchtf~irsen der Rasse Japanischer Schwarzvieh wurden analysiert, um die Auswirkungen der Diskontinuit/it zu untersuchen und um die Hertabilit~ten und ph~'notypischen Korrelationen fiir die zugrundeliegende kontinuierliche Merkmalsverteilung abzusch~itzen. Die Parameter der aufgenommenen Merkmalsskalierung wurden in eine Enteilung nach gleichen Abst~inden iiberfiihrt, wobei die Methode der kleinsten Quadrate im gemischten Modell angewandt wurde. Zus~tzlich erfolgte eine Korrektur nach den Auswirkungen der Diskontinuit~t. Die Auswirkungen der Diskontinuit~it auf die Klassifizierten Typmerkmale waren in dieser angewandten Forschungsarbeit im allgemeinen gering.
611
Elsevier Science Publishers B.V., Amsterdam - - P r i n t e d in The Netherlands
Short Communication EFFECTS OF DISCONTINUITY ON HERITABILITIES AND PHENOTYPIC CORRELATIONS FOR CLASSIFIED TYPE CHARACTERISTICS IN JAPANESE BLACK HEIFERS
HIROAKI IWAISAKI
Department of Animal Science, College of Agriculture, Kyoto University, Kyoto-shi 606 (Japan) (Accepted 26 May 1983)
ABSTRACT
Iwaisaki, H., 1983. Effects of discontinuity on heritabilities and phenotypic correlations for classified type characteristics in Japanese Black heifers. Livest. Prod. Sci., 10: 611--616. The data on classified t y p e characteristics of 1692 Japanese Black breeding heifers were analyzed to investigate the effects of discontinuity and to estimate the heritabilities and phenotypic correlations in the underlying continuous scale. The parameters in an outward scale were computed with the equally-spaced scoring, employing mixed-model least squares procedures, and then those were adjusted for the effects of discontinuity. The effects of discontinuity for the classified type characteristics were generally minor in this applied work.
INTRODUCTION
A program to classify beef production characteristics in breeding cattle was carried o u t b y The Wagyu Cattle Registry Association of Japan. The main purpose was to investigate the usefulness of the b o d y characteristics as an indicator of carcass merit. Sasaki et al. (1976b), using descriptively coded data, have estimated genetic and phenotypic parameters in an outward scale. Assigning outward scores, however, may cause an environmental measurem e n t error, in other words, the effects of discontinuity on the parameters. In this context, this paper investigates the magnitude o f the effects of discontinuity on heritabilities of, and phenotypic correlations among classified t y p e characteristics and presents the adjusted estimates. MATERIALS
AND METHODS
The data utilized were records on descriptive type classification for 1692 Japanese Black breeding heifers, which were collected by The Wagyu Cattle Registry Association in 1973 and 1974. These records were much the same,
0301-6226/83/$03.00
© 1983 Elsevier Science Publishers B.V.
612 but slightly (about 350) more than those used by Sasaki et al. (1976a, b). The heifers consisted of sets of 93 sires from five prefectures. Of the many characteristics studied previously (Sasaki et al., 1976a) the main fifteen were included, and the equally spaced scoring was adopted under the assumption of the classes being ordered according to relative merit. Raw data on the outward scale were analyzed by a mixed-model, leastsquares analysis of variance procedure, using the LSML76 Program (Harvey, 1977). The factors considered in the model were prefectures, sires within prefectures (random), years, prefecture × year interactions, age of month at classification as a covariate and residuals (random). The discrete estimates of heritability and phenotypic correlation within subclass were computed from paternal half-sister correlations. Then, the discrete ones were adjusted as follows for the effects of discontinuity by the methodology of Vinson et al. (1976) h2u ' = 5 2
2 am /(Z Zim)2 i
Puv = PmnOmOn/[(Z Zim)(2; Zin)] i
i
where, h2u: heritability of the underlying continuous phenotype, h ~ : heritability of the discrete phenotype, Puv: correlation between the continuous phenotypes, Pmn: correlation between the discrete phenotypes, am and an: standard deviation on the discrete phenotypes, Zim and Zin: height of the ordinate of the normal curve at the threshold point (i). The standard deviations of outward phenotypes, am and an, were computed from the sire and residual variance component estimates. Additionally, the values of heights of the normal curve, Zim and Zin, were totally determined by the category frequencies adjusted for the fixed effects, performing a least-squares analysis on each frequency. The genetic correlations were not included in this paper because the correlation between the underlying variables is directly estimated as that from multinomial phenotypes of related individuals (Vinson et al., 1976; Gianola, 1982). RESULTS AND DISCUSSION Adjusted heritabilities and phenotypic correlations in comparison with those observed are presented in Tables I and II, respectively. Observed heritability estimates remained generally unchanged from those found by Sasaki et al. (1976b) and were sizeable to moderate. These were comparable to the findings with the scoring in relation to ideal type for the U.S. Holsteins (Cassell et al., 1973; Thompson et al., 1981), in which Thompson et al. (1981) indicated that such estimates were slightly lower than those with the ordered evaluation and linear scoring. The heritabilities observed in this and the above mentioned studies were all based on the equally-spaced scoring. On this point, the observed heritabil-
613 TABLE I Heritability estimates adjusted for discontinuity in comparison with observed estimates Characteristics
Condition Stature Proportions Hair Skin Chest Shoulder (rear view) Back Loin Rib Belly
Rump (rear view) Thigh (side view) Udder Teats
Heritability
Observed*
Adjusted
0.18 b 0.10a 0.12 a 0.23 b 0.34 d 0.13 a 0.15 a 0.13 a 0.09 a 0.26 c 0.14 a 0.23b
0.40 0.10 0.12 0.23 0.34 0.13 0.16 0.14 0.10 0.29 0.16 0.25 0.19 0.32 0.21
0.19 b
0.26 c 0.19 b
* S t a n d a r d error for the observed estimate. a = 0.05, b = 0.06, c = 0.07, a n d d = 0.08.
ity estimate is n o t invariant t o the assigned scores because o f multinomial p h e n o t y p e s (Gianola, 1979). However, it has been suggested by Gianola and N o r t o n (1981) that, in general, equally-spaced scores will result in negligible losses in terms of heritability in comparison with t he " c a n o n i c a l " scaling developed by them. Adjusted heritability estimates f or stature, proportions, hair, and skin remained f u n d am ent al l y unchanged f r o m those previously observed. The classes themselves have been defined in terms o f a one dimensional and o r d er ed c o n c e p t (e.g., very good, good, average, ...), and consequent l y those traits generally followed symmetrical distributions as c o n f i r m e d from the p h e n o t y p i c frequencies f o u n d f or t he classes and the scores. For several characteristics associated with beef t y p e and u d d e r c o n f o r m a t i o n , the effects o f discontinuity were f o u n d t o be existing although their magnitudes were only small to sizeable. As t he num be r s o f classes were almost the same for all o f the traits studied, such results m a y be due to m o r e asymmetrical and skewed distributions f o u n d in practice because o f the m o r e discrete and conceptually co mp licat ed definitions o f classes. Exceptionally, t he effect was larger for co n d itio n because of the distribution with t he large relative skewness value of 11.8. Th e discrepancy bet w e e n the observed and t he adjusted p h e n o t y p i c correlation also showed a t r e nd r a t he r similar t o t he case o f heritabflity.
614
(~I~
app;)
q~Tq~
dmn~t
c~
qT~l
u~o~
"0
0
0 :~PInoqs
c~
0 ~s~qo
~
u~IS N ,0 0 0
-~odo~I
o
0 uo!~puoo e~ 0
m <
"0
<
615
As a whole, the results indicate that heritability and phenotypic correlation estimates in the outward scale for multinomial traits are deflated, but the effects of discontinuity are practically minor for beef type characteristics, agreeing with findings from the U.S. studies for dairy cattle (Cassell et al., 1973; Vinson et al., 1976). ACKNOWLEDGEMENTS
The author is grateful to The Wagyu Cattle Registry Association for providing the data for this study. The author is also indebted to Dr. W.E. Vinson, Virginia Polytechnic Institute and State University, U.S.A. for his valuable suggestion for the analysis, and to Dr. Y. Sasaki and Dr. K. Namikawa for their critical readings of this paper.
REFERENCES Cassell, B.G., White, J.M., Vinson, W.E. and Kliewer, R.H., 1973. Genetic and phenotypic relationships among type traits in Holstein--Friesian cattle. J. Dairy Sci., 56: 1171-1177. Gianola, D., 1979. Heritability o f p o l y c h o t o m o u s characters. Genetics, 93: 1051--1055. Gianola, D., 1982. Theory and analysis of threshold characters. J. Anita. Sci., 54: 1079-1096. Gianola, D. and Norton, H.W., 1981. Scaling threshold characters. Genetics, 99: 357-364. Harvey, W.R., 1977. User's Guide for LSML76. Monograph, Ohio State Univ., Columbus, OH, 76 pp. Sasaki, Y., Iwaisaki, H., Mukai, F. and Namikawa, K., 1976a. Factors affecting descriptive type traits. Jpn. J. Zootech. Sci., 4 7 : 3 5 9 - - 3 7 0 (in Japanese). Sasaki, Y., Iwaisaki, H., Mukai, F. and Namikawa, K., I976b. Inheritance of descriptive type traits based on phenotypic resemblance between half-sib heifers. Jpn. J. Zootech. Sci., 4 7 : 3 7 1 - - 3 7 7 (in Japanese). Thompson, J.R., Freeman, A.E., Wilson, D.J., Chapin, C.A. and Berger, P.J., 1981. Evaluation o f a linear t y p e program in Holsteins. J. Dairy Sci., 64: 1610--1617. Vinson, W.E., White, J.M. and Kliewer, R.H., 1976. Overall classification as a selection criterion for improving categorically scored components of type in Holsteins. J. Dairy Sci., 59: 2104--2121.
RESUME Iwaisaki, H., 1983. Incidence sur les h~ritabilit6s et les correlations phfinotypiques du caract~re discontinu des mesures de conformation chez les g~nlsses Noires Japonaises. Livest. Prod. Sci., 10:611--616 (en anglais).
Les donn~es de conformation lait~re de 1692 g6nisses Noires Japonaises ont ~t~ analys~es pour examiner la mani~re d o n t leur caract~re discontinu peut affecter les estimations d'h~ritabflit~ et de correlation ph~notypiques. Ces param~tres ont fit~ ~valu~s dans le cadre d ' u n module mixte en utilisant soit les notes ~quidistantes de d~part, soit de nouvelles notes obtenues ~ partir de variables continues sous-jacentes. Les differences entre les r~sultats fournls par les deux m~thodes ont ~t~ g~n~ralement mineures.
616 KURZFASSUNG i
Iwaisaki, H., 1983. Der Einfluss von Diskontinuit~it auf die Heritabilit~iten und ph~inotypischen Korrelationen fiir klassifizierte Typmerkmale bei F~irsen der Rasse Japanischer Schwarzvieh. Livest. Prod. Sci., 1 0 : 6 1 1 - - 6 1 6 (auf englisch). Die Daten yon klassifizierten Typmerkmalen yon 1692 Zuchtf~irsen der Rasse Japanischer Schwarzvieh wurden analysiert, um die Auswirkungen der Diskontinuit/it zu untersuchen und um die Hertabilit~ten und ph~'notypischen Korrelationen fiir die zugrundeliegende kontinuierliche Merkmalsverteilung abzusch~itzen. Die Parameter der aufgenommenen Merkmalsskalierung wurden in eine Enteilung nach gleichen Abst~inden iiberfiihrt, wobei die Methode der kleinsten Quadrate im gemischten Modell angewandt wurde. Zus~tzlich erfolgte eine Korrektur nach den Auswirkungen der Diskontinuit~t. Die Auswirkungen der Diskontinuit~it auf die Klassifizierten Typmerkmale waren in dieser angewandten Forschungsarbeit im allgemeinen gering.