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Within herd estimates of heritabilities for six hoof characteristics and impact of dispersion of discrete severity scores on estimates
ELSEVIER
LivestockProductionScience44 (1995) 107-l 14
Within herd estimates of he&abilities for six hoof characteristics and impact of dispersion of discrete severity scores on estimates Y.C. Huang ‘, R.D. Shanks * Department of Animal Sciences, University of Illinois. Urbana, IL, USA
Accepted6 July 1995
Abstract Heritabilities and repeatabilities of six hoof traits were estimated from 10 years of routine hoof trimming data of a research dairy herd. Heritabilities were estimated by DFFCEMLwith an animal model on original scores and Snell transformed scores. A sire threshold model was also tested, but was numerically unstable due to the small number of observations per sire. Estimated heritabilities based on 3821 records of the transformed scores were 0.05, 0.12, 0.06, 0.14, 0.02 and 0.08 for corkscrew claw, heel erosion, interdigital dermatitis, laminitis, sole ulcers and white line separation, respectively; and repeatabilities were 0.17, 0.19. 0.15, 0.19, 0.14 and 0.14, respectively. Highly consistent results were estimated from original scores. Low he&abilities with a relatively large proportion of permanent environmental variance to additive genetic variance implied that response to selection for a single score of corkscrew claw, interdigital dermatitis and sole ulcers would be small. Large proportions of environmental variances were consistent with two hypotheses: ( 1) corkscrew claw may be influenced by other diseases or inappropriate hoof care and (2) interdigital dermatitis or sole ulcers affect some cows repeatedly. He&abilities of heel erosion and laminitis were more than 10% and improvement by traditional quantitative methods should be possible. Kevwordx Dairy cattle; Hoof trait; Variancecomponent;Threshold
1. Introduction
Lameness is undoubtedly an important cause of economic loss in the dairy industry. Whitaker et al. ( 1983) estimated the annual incidence of lameness in dairy cattle in the United Kingdom to be 25%. Wells ( 1993) reported a 13.7% (summer) and 16.7% (spring) prevalence of lameness in 17 Minnesota or Wisconsin dairy herds. Whitaker et al. (1983) estimated that average annual financial loss due to hoof problems in the United * Correspondingauthor. ’ Present address: Department of Animal Breeding, Taiwan Livestock Research Institute, 112 Farm Road, Hsinhua. Taiwan 71210, ROC. 0301.6226/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDIO301-6226(95)00061-5
Kingdom was approx. & 1175 ( = & 1 to 1.4 US dollars in 1983-1984) per year in a 100 cow herd. One of the reasons for few estimates of heritability is constraints on the measurements. Hoof conditions hidden under the mud of claws inhibited accurate examination without skillful trimming, and severity of disorders are difficult to judge objectively. Unlike other production traits, few large data sets were available. In addition, trimming is a labor intensive and time-consuming job, and hoof growth and wear rate has its own limitations (Hahn et al., 1986), which implies that trimming can only occur a few times a year. Dempster and Lemer ( 1950) derived formula for transformation of heritability between outward scale and underlying score for binary traits. A generalized
108
Y.C. Huang and R.D. Shanks /Livestock Production Science 44 (1995) 107-114
transformation formula for two or more categories was extended by Gianola ( 1979). Although heritabilities of outward scale were always smaller than the underlying score (Gianola and Norton, 1981), determining magnitude of changes between heritabilities for underlying and transformed scores under different score dispersions for each trait would be useful for interpreting heritabilities. Objectives were (1) to estimate heritabilities and repeatabilities of hoof traits by linear and threshold models and (2) to evaluate effects of score dispersion on estimates of heritabilities.
2. Materials and methods Ten years of claw disorders were recorded from 1983 through 1992 in the University of Illinois dairy herd by Lowell R. Hanson of CLC, Inc. Each year cows were trimmed during three seasons, approximately March, July and November. Totally, 4722 trimmings were recorded from 1239 cows of five breeds, Ayrshire, Brown Swiss, Guernsey, Holstein and Jersey. The terminology for different claw disorders is still not very consistent in different countries. Weaver et al. ( 198 1) suggested standard Latin terminology to avoid confusion, but adoption was not complete. English equivalent terminologies of Latin listed by Weaver ( 1986) will be applied in this paper. Descriptions follow. ( 1) Corkscrew claw (CC) is a screw like rotation of the tip of the claw in an upward and inward direction. The sole of the claw becomes oblique and the weight of the cow is consequently born on the outer wall of the claw. (2) Heel erosion (HE) appears as black marks, circular craters or deep terraces in the plantar/ palmar convexity of the heel. As the condition advances, the lines of erosion form a dramatic, dark ‘V’ pointing dorsally. Gradually heel horn is lost (Greenough, 1987b). (3) Interdigital dermatitis (ID) is an acute or chronic inflammation of the skin between the claws without extension to the subcutaneous tissues (Greenough et al., 1981). (4) Laminitis (LA) is a disturbance of the sensitive laminae, sensitive tissue between horny wall and pedal bone of the hooves that may be subclinical, subacute, acute or chronic, and results in degenerative changes that affect the sensitive and horny laminae of the foot (Greenough, 1987a).
(5) Sole ulcers (SU) display tenderness and evidence of hemorrhage, usually in the axial part of sole-horn junction of the lateral claw of the hind leg (Greenough et al., 1981). (6) White line separation (WLS) is an avulsion or separation of the wall of the hoof from the sole (Greenough, 1987~). Scores of 1 (excellent) to 5 (severe), indicated relative degree of the phenotype departing from ideal shape of claw. For example, with corkscrew claw or white line separation, scores indicated degree of claw rotation and degree of hoof wall separation. In heel erosion, interdigital dermatitis, laminitis or sole ulcers, scores indicated relative severity of lesions of the disorders. For the purpose of estimation of repeatability and adjusting for age effect, records from cows with only a single record or lack of a birth date were deleted; 814 cows from 197 sires and 665 dams had 3821 records used for linear animal model estimation. Original scores and normality transformed scores were both analyzed by the linear model. Transformation was based on the method of Snell ( 1964). The purpose of transformation was to improve potential that residuals follow assumption of a normal distribution. Estimates of variance components were obtained by restricted maximum likelihood (REML) using a derivative-free algorithm, fitting an animal model which incorporated available pedigree information (Meyer, 1989). Permanent environmental effects were taken into account by including two random effects, animal and permanent environmental effects. The linear model for the six traits was: =~+Bi+Yrj+S,+T,+M,+b,(D,) Yijkln*nopq +A, + Pp + + eijklnznopq ( 1) where Yijkimnomis the evaluated score of the disorder for a cow of breed i ( Ayrshire, Brown Swiss, Guernsey, Holstein or Jersey), in year j ( < 1985 to 1993), of trimming month k (March, July, November), with previous trimming interval 1 (1 day to 4 months vs. no previous trimming or greater than 4 months interval) and months postpartum m at age at trimming (0,). A, is animal effect of animal 0, 1 to H; Pp is permanent environmental effect of cow p, 1 to G, where G of H animals have records. Meyer’s 1993 version 2.1 DFREML was used to estimate variance components. After estimation of the variance components, heritabilities (h^*) and repeatabilities (fi) were estimated as follows:
Y.C. Huang and R.D. Shanks/Livestock Production Science 44 (1995) 107-114
h*2=8,2/(8,T+6;,+cF,2) R=(s~+~~~)/(8,2+~~~+8e2)
(2)
(4)
@( Xp + Zp) was standard normal cumulative probability at (Xp + Zp) where X was incidence matrix for fixed effects, Z was incidence matrix for random effects, and p and p were coefficients for estimation. A different way of representing the threshold model was to take the inverse mapping (‘link function’ or @ ‘), to both sides of Eq. 4 to obtain Eq. 5. The assumption was that the dependent variable (@-I (E( yi 1p) ) or liability) could not be measured directly but was expressed as the number of standard deviations of a standard normal distribution. The range of liability was from - x to x. @-‘(E(Y;~P))
=XP+ZP
(5)
Due to numerical difficulties related to optimization of the nonlinear objective function in the threshold model, no equivalent animal model with permanent environmental effects generated a stable analysis and, therefore, a sire model was used. Sires were required to have at least two daughters with one record each. Misztal’s 1991 CMMAT2 program with EM algorithms was used for estimation of variance components (Misztal et al., 1989; Misztal, personal communication) . Due to few observations with scores greater than one for sole ulcers and interdigital dermatitis, scores greater than one were merged creating a binary response for both traits. Heritability was estimated as follows: P=46:/(6;+6,2)
Heritability of outward scale (hi) was estimated as:
(Gianola,
1979)
(3)
where &z, S& and &z were the estimates of the animal, permanent environmental and residual variance components, respectively. A threshold model, probit-normal model (Searle et al., 1992)) was Eq. 4 with the same fixed effects as Eq. 1, except for three changes: ( 1) that covariate of age was grouped into three categories ( 1 to 2, 3 and r4 years old) ; (2) random effects were different because animal effect was replaced by sire effect; and (3) no permanent environmental effect was used for estimating parameters. E(YiIP)=@(XP+ZP
109
(6)
where Bf and Bz are estimates of sire and residual variance components, respectively.
( 1 - rr;) - 2#&z-jcicj~in;]
(7)
where: h2 is heritability of underlying scale; zi are ordinates of a standard normal density function; m equals number of categories; Ci and Cj are outward scores for category group i or j; rri and n; are probabilities of phenotypic response for category group i or j. Based on Eq. 7, transformation of heritability from underlying scale into outward scale was simulated for four different scoring methods and six distributions of hoof traits. The four scoring methods simulated different distances between scores. Equal distance scoring was first method: C, = i, where i was element of {i ( 1,2,3,4,5) Second and third methods scoring: C,=4*(log
(8)
were reduced distance
i/log 5) + 1
(9)
and C,=5-4*
Exp(i-5)+1.
(10)
Increased distance scoring was fourth method: Ci=4*
Exp(i-5)
+ 1,
(11)
The objective of simulation was to study response of heritability under different scoring systems, particularly when the assumption of equal distance between scores was not realistic.
3. Results and discussion Fig. 1 contained the frequency of scores for corkscrew claw (CC), heel erosion (HE), interdigital dermatitis (ID), laminitis (LA), sole ulcers (SU) and white line separation (WLS) in linear and threshold models. Scores of each trait were distributed differently. Interdigital dermatitis and sole ulcers had a large incidence of score 1,78 and 85% of observations. Data used in threshold analyses had similar distribution as for linear model analyses but fewer observations were in each score. In order to keep the same range of scores, 1 (excellent) and 5 (severe) were not changed after
110
8 B %
Y.C.Huang and R. D. Shanks /Livestock
HE
1500
LA 1000
Production Science 44 (I 995) 107-I 14
nando ( 1981) compared different scaling procedures and found estimations from Snell transformations and original scores were similar with beef type data. Low heritability with a relatively large proportion of permanent environmental variance was observed for corkscrew claw, interdigital dermatitis and sole ulcers (ai < o&). Response to selection would be small if selection was only based on a single score. Two hypotheses were consistent with these results: (1) corkscrew claw was influenced by inappropriate hoof care or side effect of other diseases and (2) interdigital dermatitis or sole ulcers affected some cows repeatedly. Comparing studies from Europe, estimated heritabilities based on original scores of heel erosion, interdigital dermatitis, laminitis, and sole ulcers ranged widely from 0.1 to 0.3 in German Fleckvieh and Holstein Friesian breeds (Politiek et al., 1986; Smit et al., 1986; Distl et al., 1990). The European her&abilities exceeded those estimated in this study. However, direct interpretations among results were difficult, because different scoring systems and estimation methods were used in the different studies. Due to the sparse density in contingency table (scores by (fixed+random) effects), the threshold model did not behave well for interdigital dermatitis and sole ulcers. Solutions were cycling and did not converge in the threshold model. Final estimates were based on fourth decimal convergence of sire variance components. From studies of other threshold models, high correlations (0.99) were found between corresponding threshold and linear models (Jensen, 1986; Meijering and Gianola, 1985; Weller and Ron, 1992). Higher heritability was estimated more often by threshold than linear models (Weller and Ron, 1992; Weller
: Heel erosion : Interdlgital dermatltls Lamlnltls : Sole uIC*rs
:
E 1
500 0
CC
HE
ID
LA SU WLS
Llnaar model (3821 Ohs.)
CC
HE
ID
LA SU WLS
Threshold model (865 Obs.)
Fig. 1. Distribution of frequency for scores of six discrete hoof traits in linear and threshold models.
Snell transformation (Tong et al., 1977). The Snell transformed scores of corkscrew claw and laminitis were only slightly different from original scores (Table 1). Estimated variance components, heritabilities and repeatabilities for six traits for linear and threshold models were listed in Table 2. Results of both models were similar, although some assumptions were different. The original scores were analyzed with linear model under the assumption that scores 1 to 5 were equally spaced and represented measurements of a continuous distribution corresponding to degrees away from excellent characteristics of hoof. The transformed scores assumed that corresponding residuals more closely followed the normal distribution. Schaeffer and Wilton ( 1975) argued that because BLUP is similar to the GSK procedure proposed by Grizzle et al. ( 1969) for categorical data analysis, BLUP should be justified and sufficient for interpretation of categorical data. FerTable 1 Normality transformed scores ’ Traits
Corkscrew claw (CC) Heel erosion (HE) Interdigital dermatitis (ID) Laminitis (LA) Sole ulcers (SU) White line separation ( WLS)
Original scores 1
2
3
4
5
1 1 1 1 1 1
2.21 2.43 2.58 2.25 3.14 2.5 1
3.22 3.10 3.18 3.24 3.44 3.21
4.06 3.13 3.90 3.99 3.84 3.87
5 5 5 5 5 5
a Snell transformation (Snell, 1964), score1 and 5 not changed. Original score 1 was excellent and 2 to 5 were subjective evaluation of deviation from excellent.
111
Y.C. Huang and R.D. Shanks /Livestock Production Science 44 (1995) 107-114 Table 2 Estimates of variance and genetic parameters from univariate analyses for linear and threshold models Disorders
Model a
Corkscrew claw
SCOrC
Parameters b
V.
VF-
V,
h2
R
0.593 0.67 1
0.054
0.179
0.052
0.170
Linear Linear Thresh
Original Snell Underlying
0.039 0.042 0.037
0.090 0.095
Heel erosion
Linear Linear Thresh
Original Snell Underlying
0.234 0.213 0.150
0.126 0.122
Interdigital dermatitis
Linear Linear Thresh ’
Original Snell Underlying
0.058 0.052 0.131
Laminitis
Linear Linear Thresh
Original Snell Underlying
Sole ulcers
Linear Linear Thresh ’
White ine separation
Linear Linear Thresh
0.036
_
1.511 1.423
0.125 0.121 0.144
0.193 0.190
0.087 0.085
0.698 0.759
0.069 0.058 0.127
0.172 0. I53
0.152 0.145 0.138
0.066 0.051
0.907 0.847
0.135 0.139 0.133
0.193 0.187 _
Original Snell Underlying
0.029 0.030 0.024
0.132 0.141
0.995 1.063
0.025 0.025 0.024
0.139 0.138 _
Original Snell Underlying
0.125 0.125 0.156
0.106 0.087
I.331 1.348
0.080 0.080 0.150
0.148 0.136
’ Linear, linear model(n = 3821); Thresh, threshold model(n = 655), V, = 1.O and V. = I .O estimated by 4*V,; Original, original score; Snell, Snell transformed score; Underlying, underlying score. h V., V,, V., h’ and R: additive variance, permanent environmental variance, residual variance, heritability and repeatability. ’ Scores above 2 merged as one category.
-c=4(Log
‘-C=i
i/Log q+i
*C=4Exp(i-5)+1
+C=5-4Exp(l-i)
0.5
Distribution of Distribution of heel erosion interdigital dermatitis
Distribution of corkscrew claw i _ +C=4Exp(i-5!‘1
0.1 I
;I
rd
o_ol,
!
I,,,
,,I
.l -2.3.4.5
1
.l
I
I,,
-2.3.4.5
h* of underlying Equal
distance
I I I I ‘,
.l
1,
/,
-2.3.4.5
scale
score(i)
Fig. 2. Different scoring systems for transforming distance scores.
one to five equal
Fig. 3. Transformation of he&abilities from underlying scale to outward scale for corkscrew claw, heel erosion and interdigital dermatitis.
Y.C.Huang and R.D. Shanks /Livestock Production Science 44 (1995) 107-114
112 -c=4(Log
--C=,
I/Log q+1 Distribution
o.ol,
I,,
.l
I
I
I
-2.3.4.5
of
I
/
I
*C=4Exp(l-5)+1
Distribution sole ulcers
I
/
/
.l
I,
I
I,,
-2.3.4.5
h2 of underlying
+-C=S-Exp(l-I)
Distribution white line separation
of
I1
I!
1
.l
I
!
of
tion for summarizing and comparing parameters from studies where linear or threshold models were applied separately. Another possible usefulness was in situations where the underlying scale was considered for selection but parameters were not available. Under distributions of the six traits, equal distance scoring had higher he&abilities than from reduced (10) or increased distance scoring ( 11). The results were consistent with those of Gianola and Norton ( 1981)) although their transformations were based on maximization of heritability. High similarity between results of the second scoring method (9) and equal distance scoring (8) implied that slight changes from linear scores, would not appreciatively change estimations of heritabilities.
! I ! 1 I
.2.3.4.6
scale
Fig. 4. Transformation of he&abilities from underlying scale to outward scale for laminitis, sole ulcers and white line separation
et al., 1988; Weller and Gianola, 1989; Jamrozik et al., 1991a, 1991b). Consistent results did not occur in this study of six hoof traits. Small sample size and sire as the only random effects in the threshold model were suspected as the main causes of the differences. Interpretation will primarily be drawn from results of the linear model. In the disorders studied, the assumption of linear scoring distance was not very realistic. Fig. 2 illustrates four examples of possible scoring systems. Using frequency distribution of six hoof traits and four scoring systems, outward heritabilities were calculated by Eq. 7 for different heritabilities. If skewness of data was extreme, e.g., interdigital dermatitis and sole ulcers, outward heritability was only about half of the underlying heritability. If transformed scores did not linearly increase but followed one of the other functions in Fig. 2, lower heritability was expected (Figs. 3 and 4). In the majority of applications where scores linearly increase, heritability of outward scale can be used to approximate the heritability of the underlying scale based on Eq. 7 and frequency distribution of scores (outward scale). From Table 2 and Figs. 3 and 4, estimated heritabilities on underlying scale for six traits ranged from 0.1 to 0.3 and were approximated from outward scale. These results provided useful informa-
4. Conclusions Numerical instability of estimation of variance components was observed for threshold models. Based on results of linear models with original scores and Snell transformed scores, heel erosion and laminitis had heritabilities greater than 0.1. Selection to improve these two traits would be possible. Repeatabilities of all six hoof traits were greater than 0.14. Corkscrew claw, interdigital dermatitis and sole ulcers had larger proportions of permanent environmental variance than additive genetic variance. Heritabilities on outward scale of traits with highly skewed distributions were smaller than those more centrally distributed.
Acknowledgements
This research was supported by Regional research project S-25 1, Genetic enhancement of health and survival of dairy cattle. First author received financial support from National Science Council, ROC for his first 3 years of study. We thank Lowell Hanson for recording claw disorders. Karin Meyer for use of her DFREML program, Tianlin Wang for use of his DF-REML program for proof checking of estimates and Ignacy Misztal for use of his CMMAT2 program. References Dempster, E.R. and Lemer, I.M., 1950. Heritability of threshold characters. Genetics, 35: 212-236.
Y.C. Huang and R.D. Shrinks /Livestock Production Science 44 (1995) 107-114
Distl, 0.. Koom, D.S., McDaniel, B.T., Peterse, D., Politiek, R.D. and Reurink, A., 1990. Claw traits in cattle breeding programs: Report of the EAAP working group ‘Claw Quality in Cattle’. Livest. Prod. Sci., 25: I-13. Fernando, R.L., 1981. Scaling ordered categorical variables in relation to sire evaluation for frame score at weaning in Angus cattle. MS thesis, University of Illinois, Urbana, pp. 90-92. Gianola, D., 1979. Heritability of polychotomous characters. Genetics, 93: 1051-1055. Gianola, D. and Norton, H.W., 1981. Scaling threshold characters. Genetics, 99: 357-364. Greenough, P.R., MacCallum, F.J. and Weaver. A.D., 1981. Lameness in Cattle. John Wright & Sons Ltd., Bristol, UK, pp. 151227. Greenough, P.R., 1987a. An illustrated compendium of bovine lameness: part I. Mod. Vet. Pratt., 68: 6-9. Greenough, P.R., 1987b. An illustrated compendium of bovine lameness: part 2. Mod. Vet. Pratt., 68: 94-97. Greenough, P.R., 1987~. An illustrated compendium of bovine lameness: part 3. Mod. Vet. Pratt., 68: 148-152. Grizzle, J.E., Starmer, CF. and Koch, G.G., 1969. Analysis of categorical data by linear models. Biometrics, 25: 489-504. Hahn. M.V., McDaniel, B.T. and Wilk. J.C., 1986. Rates of hoof growth and wear in Holstein cattle. J. Dairy Sci., 69: 2148-2156. Jamrozik, J., Schaeffer, L.R., Bumside, E.B. and Sullivan, B.P., 199la. Estimates of he&abilities of Canadian Holstein conformation traits by threshold model. Can. J. Anim. Sci., 71: 629632. Jamrozik, J., Schaeffer, L.R., Burnside, E.B. and Sullivan, B.P., I99 1b. Threshold models applied to Holstein conformation traits. J. Dairy Sci., 74: 31963201. Jensen, J., 1986. Sire evaluation for type traits with linear and nonlinear procedures, Livest. Prod. Sci., 15: 165-171. Meijering, A. and Gianola, D., 1985. Linear versus nonlinear methods of sire evaluation for categorical traits: a simulation study. Genet. Sel. Evol., 17: 115-132. Meyer, K., 1989. Restricted maximum likelihood to estimate variance components for animal models with several random effects using a derivative-free algorithm. Genet. Sel. Evol., 21: 317340. Misztal, I., Gianola, D. and Foulley, J.L., 1989. Computing aspects of a nonlinear method of sire evaluation for categorical data. J. Dairy Sci., 72: 1557-1568.
Politiek, R.D., Distl, O., Fjeldaas, T., Heeres, J., McDaniel, B.T., Nielsen, E., Peterse, D.J., Reurink, A. and Strandberg, P., 1986. Importance of claw quality in cattle: review and recommendations to achieve genetic improvement. Report of the EAAP working group on ‘Claw Quality in Cattle’. Livest. Prod. Sci., 15: 133-152. Schaeffer, L.R. and Wilton, J.W., 1975. Methods of sire evaluation for calving ease. J. Dairy Sci., 59: 544-551. Searle, S.R., Casella, G. and McCulloch, C.E., 1992. Variance Components. John Willey & Sons Inc., New York, pp. 367-377. Smit, H., Verbeek, B., Peterse, D.J., Jansen, J., McDaniel, B.T. and Politiek, R.D., 1986b. Genetic aspects of claw disorders, claw measurements and ‘type’ scores for feet in Friesian cattle. Livest. Prod. Sci., 15: 205-217. Snell, E.J., 1964. A scaling procedure for ordered categorical data. Biometrics, 20: 592607. Tong, A.K.W., Wihon, J.W. and Schaeffer, L.R., 1977. Application of a scoring procedure and transformations to dairy type classification and beef ease of calving categorical data. Can. J. Anim. Sci., 57: l-5. Weaver, A.D., Andersson, L., Laistre Banting, A.D.E., Demerzis, P.N., Knezevic, P.F., Peterse, D.J. and Sankovic, F., 1981. Review of disorders of the ruminant digit with proposals for anatomical and pathological terminology and recording. Vet. Rec., 108: 117-120. Weaver, A.D., 1986. Bovine Surgery and Lameness. Blackwell Scientific Publications, Oxford, UK, pp. 175-225. Weller, J.I., Misztal, I. and Gianola, D., 1988. Genetic analysis of dystocia and calf mortality in Israeli-Holsteins by threshold and linear models. J. Dairy Sci., 71: 2491-2501. Weller, J.I. and Gianola, D., 1989. Models for genetic analysis of dystocia and calf mortality. J. Dairy Sci., 72: 2633-2643. Weller, J.I. and Ron, M., 1992. Genetic analysis of fertility traits in Israeli Holsteins by linear and threshold models. J. Dairy Sci., 75: 2541-2548. Wells, S.J., Trent, A.M., Marsh, W.E. and Robinson, R.A., 1993. Prevalence and severity of lameness in lactating dairy cows in a sample of Minnesota and Wisconsin herds. J. Am. Vet. Med. Assoc., 202: 78-82. Whitaker, D.A., Kelly, J.M. and Smith, E.J., 1983. Incidence of lameness in dairy cows. Vet. Rec., 113: 60-62.
Huang, Y.C. et Shanks, R.D., 1995. Estimations entre troupeau des her&abilitib pour six characteristiques estimations de la dispersion de leurs scores disc&es de severhe. Liuest. Prod. Sci., 44: 107-l 14. Les heretabilites exp&imentale
et repetabilites
113
de six traits des pieds sont estimes pour donnees provenant
des pieds et l’impacte
sur ses
du soin habitue1 des pieds dans un troupeau
de vaches laitieres au tours de dix ans. Les heretabilites sont estim& par DFREML avec un mod&e animal sur les scores originaux
et transform& d’apres Snell. Un modele seuil pour patemite est evahu? mais est instable numeriquement par cause de paucite d’observations pour chaque p&e. Les heretabilites estim& pour 3821 fiches de scores transform& sont 0.05, 0.12, 0.06, 0.14, 0.02, et 0.08 pour la griffe de tourbillon, l’erosion du talon, la dermatite interdig&%, le fourbure cbronique, la contusion de la sole, et la maladie de la ligne blanche; les repetabilitds
sont 0.17, 0.19, 0.15, 0.19, 0.14 et 0.14. Resultats estim& d’apr&s scores originaux y sont fort consistants.
Les petits heretabilitt%
avec une grande variance permanente environmentale par rapport a la variance additive genetique impliquent que la mponse de selection pour un score individuel de la griffe de tourbillon, la dermatite interdigit& et la contusion de la sole semi petit. Les proportions grandes de variances
114
Y.C.Huang and R.D. Shanks/Livestock
Production Science 44 (1995) 107-114
environmentales sont consistants avec deux hypotheses: ( 1) la griffe de tourbillon est influenc& par d’autres maladies ou le soin inapportun des pieds et (2) la dermitite interdigitee ou la contusion de la sole affecte cettaines vaches a plusietus reprises. Les h&&abilites de l’erosion du talon et de la fourbure chronique sont sup&ems a 10% et leur am6lioration par m6thodes quantitatives traditionelles est possible.
Kurzfassung Huang, Y.C. und Shanks, R.D., 1995. Innerhalb-Herden-Schtzung der Heritabilitat fur sechs Klauenmerkmrde und der EinfluB der Verteilung diskreter Befahsklassen auf die Schatzwerte. Liuest Prod. Sci., 44: 107-l 14. Heritabilitaten und Wiederholbarkeiten fur sechs Klauenmerkmale wurden anhand von Daten gesch&t, die iJber einen Z&mum von 10 Jahren bei der Klauenpflege einer Versuchsmilchrinderherde erhoben wurden. Heritabilitaten wurden iiber ein Tiermodell mit DFREML einmal anhand der Originaldaten und einmal anhand transformierter Daten (Snell) gesch&zt. Es wurde auBerdem ein Vater-Schwellenwettmodell getestet, das sich aber aufgrund der geringen Anzahl von Beobachtungen pro Vaterals numerisch instabil envies. Die Schatzung der Heritabilmten beruht auf 3821 Beobachtungen und betrug 0.05 Rir das Merkmal Korkenzieher-KJauen, 0.12 fur Ballenhomfaule, 0.06 fur Dermatitis interdigitalis, 0.14 fur Klauenrehe, 0.02 fur Sohlengeschwtire und 0.08 fiir das Merkmal Spalt in der we&n Linie. Die geschatzten Wiederholbarkeiten der Merkmale lagen bei 0.17, 0.19, 0.15, 0.19, 0.14 und 0.14. Die Ergebnisse, die auf den Originaldaten basierten, waren hoch konsistent. Niedrige Heritabilitaten in Verbindung mit einer im Vergleich zur additiv genetischen Varianz gerhrgen permanten Umweltvarianz fiihrten zu der SchluBfolgerung, da8 eine Selektion auf die Merkmale Korkenzieher-KJauen, Dermatitis interdigitalis und Sohlengeschwtire mu getinge Erfolge zeigen wiirde. Durch den grol3en Anteil der Umweltvarianz kam es einmal zur der Schlu8foJgerung, da8 Korkenzieher-Klauen durch andere Krankheiten oder durch ungentigende Klauenpflege verursacht wurden, und zum anderen zu der Annahme, da8 Dermatitis interdigitalis und Sohlengeschwtire bei einigen Kiihen wiederholt auftraten. Die Heritabilititen der Merkmale Ballenhomfaule und Klauenrehe betrugen mehr als 10% und lassen einde Verbessenmg mit herkijmmlichen Zuchtmethoden als mijglich erscheinen.
LivestockProductionScience44 (1995) 107-l 14
Within herd estimates of he&abilities for six hoof characteristics and impact of dispersion of discrete severity scores on estimates Y.C. Huang ‘, R.D. Shanks * Department of Animal Sciences, University of Illinois. Urbana, IL, USA
Accepted6 July 1995
Abstract Heritabilities and repeatabilities of six hoof traits were estimated from 10 years of routine hoof trimming data of a research dairy herd. Heritabilities were estimated by DFFCEMLwith an animal model on original scores and Snell transformed scores. A sire threshold model was also tested, but was numerically unstable due to the small number of observations per sire. Estimated heritabilities based on 3821 records of the transformed scores were 0.05, 0.12, 0.06, 0.14, 0.02 and 0.08 for corkscrew claw, heel erosion, interdigital dermatitis, laminitis, sole ulcers and white line separation, respectively; and repeatabilities were 0.17, 0.19. 0.15, 0.19, 0.14 and 0.14, respectively. Highly consistent results were estimated from original scores. Low he&abilities with a relatively large proportion of permanent environmental variance to additive genetic variance implied that response to selection for a single score of corkscrew claw, interdigital dermatitis and sole ulcers would be small. Large proportions of environmental variances were consistent with two hypotheses: ( 1) corkscrew claw may be influenced by other diseases or inappropriate hoof care and (2) interdigital dermatitis or sole ulcers affect some cows repeatedly. He&abilities of heel erosion and laminitis were more than 10% and improvement by traditional quantitative methods should be possible. Kevwordx Dairy cattle; Hoof trait; Variancecomponent;Threshold
1. Introduction
Lameness is undoubtedly an important cause of economic loss in the dairy industry. Whitaker et al. ( 1983) estimated the annual incidence of lameness in dairy cattle in the United Kingdom to be 25%. Wells ( 1993) reported a 13.7% (summer) and 16.7% (spring) prevalence of lameness in 17 Minnesota or Wisconsin dairy herds. Whitaker et al. (1983) estimated that average annual financial loss due to hoof problems in the United * Correspondingauthor. ’ Present address: Department of Animal Breeding, Taiwan Livestock Research Institute, 112 Farm Road, Hsinhua. Taiwan 71210, ROC. 0301.6226/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDIO301-6226(95)00061-5
Kingdom was approx. & 1175 ( = & 1 to 1.4 US dollars in 1983-1984) per year in a 100 cow herd. One of the reasons for few estimates of heritability is constraints on the measurements. Hoof conditions hidden under the mud of claws inhibited accurate examination without skillful trimming, and severity of disorders are difficult to judge objectively. Unlike other production traits, few large data sets were available. In addition, trimming is a labor intensive and time-consuming job, and hoof growth and wear rate has its own limitations (Hahn et al., 1986), which implies that trimming can only occur a few times a year. Dempster and Lemer ( 1950) derived formula for transformation of heritability between outward scale and underlying score for binary traits. A generalized
108
Y.C. Huang and R.D. Shanks /Livestock Production Science 44 (1995) 107-114
transformation formula for two or more categories was extended by Gianola ( 1979). Although heritabilities of outward scale were always smaller than the underlying score (Gianola and Norton, 1981), determining magnitude of changes between heritabilities for underlying and transformed scores under different score dispersions for each trait would be useful for interpreting heritabilities. Objectives were (1) to estimate heritabilities and repeatabilities of hoof traits by linear and threshold models and (2) to evaluate effects of score dispersion on estimates of heritabilities.
2. Materials and methods Ten years of claw disorders were recorded from 1983 through 1992 in the University of Illinois dairy herd by Lowell R. Hanson of CLC, Inc. Each year cows were trimmed during three seasons, approximately March, July and November. Totally, 4722 trimmings were recorded from 1239 cows of five breeds, Ayrshire, Brown Swiss, Guernsey, Holstein and Jersey. The terminology for different claw disorders is still not very consistent in different countries. Weaver et al. ( 198 1) suggested standard Latin terminology to avoid confusion, but adoption was not complete. English equivalent terminologies of Latin listed by Weaver ( 1986) will be applied in this paper. Descriptions follow. ( 1) Corkscrew claw (CC) is a screw like rotation of the tip of the claw in an upward and inward direction. The sole of the claw becomes oblique and the weight of the cow is consequently born on the outer wall of the claw. (2) Heel erosion (HE) appears as black marks, circular craters or deep terraces in the plantar/ palmar convexity of the heel. As the condition advances, the lines of erosion form a dramatic, dark ‘V’ pointing dorsally. Gradually heel horn is lost (Greenough, 1987b). (3) Interdigital dermatitis (ID) is an acute or chronic inflammation of the skin between the claws without extension to the subcutaneous tissues (Greenough et al., 1981). (4) Laminitis (LA) is a disturbance of the sensitive laminae, sensitive tissue between horny wall and pedal bone of the hooves that may be subclinical, subacute, acute or chronic, and results in degenerative changes that affect the sensitive and horny laminae of the foot (Greenough, 1987a).
(5) Sole ulcers (SU) display tenderness and evidence of hemorrhage, usually in the axial part of sole-horn junction of the lateral claw of the hind leg (Greenough et al., 1981). (6) White line separation (WLS) is an avulsion or separation of the wall of the hoof from the sole (Greenough, 1987~). Scores of 1 (excellent) to 5 (severe), indicated relative degree of the phenotype departing from ideal shape of claw. For example, with corkscrew claw or white line separation, scores indicated degree of claw rotation and degree of hoof wall separation. In heel erosion, interdigital dermatitis, laminitis or sole ulcers, scores indicated relative severity of lesions of the disorders. For the purpose of estimation of repeatability and adjusting for age effect, records from cows with only a single record or lack of a birth date were deleted; 814 cows from 197 sires and 665 dams had 3821 records used for linear animal model estimation. Original scores and normality transformed scores were both analyzed by the linear model. Transformation was based on the method of Snell ( 1964). The purpose of transformation was to improve potential that residuals follow assumption of a normal distribution. Estimates of variance components were obtained by restricted maximum likelihood (REML) using a derivative-free algorithm, fitting an animal model which incorporated available pedigree information (Meyer, 1989). Permanent environmental effects were taken into account by including two random effects, animal and permanent environmental effects. The linear model for the six traits was: =~+Bi+Yrj+S,+T,+M,+b,(D,) Yijkln*nopq +A, + Pp + + eijklnznopq ( 1) where Yijkimnomis the evaluated score of the disorder for a cow of breed i ( Ayrshire, Brown Swiss, Guernsey, Holstein or Jersey), in year j ( < 1985 to 1993), of trimming month k (March, July, November), with previous trimming interval 1 (1 day to 4 months vs. no previous trimming or greater than 4 months interval) and months postpartum m at age at trimming (0,). A, is animal effect of animal 0, 1 to H; Pp is permanent environmental effect of cow p, 1 to G, where G of H animals have records. Meyer’s 1993 version 2.1 DFREML was used to estimate variance components. After estimation of the variance components, heritabilities (h^*) and repeatabilities (fi) were estimated as follows:
Y.C. Huang and R.D. Shanks/Livestock Production Science 44 (1995) 107-114
h*2=8,2/(8,T+6;,+cF,2) R=(s~+~~~)/(8,2+~~~+8e2)
(2)
(4)
@( Xp + Zp) was standard normal cumulative probability at (Xp + Zp) where X was incidence matrix for fixed effects, Z was incidence matrix for random effects, and p and p were coefficients for estimation. A different way of representing the threshold model was to take the inverse mapping (‘link function’ or @ ‘), to both sides of Eq. 4 to obtain Eq. 5. The assumption was that the dependent variable (@-I (E( yi 1p) ) or liability) could not be measured directly but was expressed as the number of standard deviations of a standard normal distribution. The range of liability was from - x to x. @-‘(E(Y;~P))
=XP+ZP
(5)
Due to numerical difficulties related to optimization of the nonlinear objective function in the threshold model, no equivalent animal model with permanent environmental effects generated a stable analysis and, therefore, a sire model was used. Sires were required to have at least two daughters with one record each. Misztal’s 1991 CMMAT2 program with EM algorithms was used for estimation of variance components (Misztal et al., 1989; Misztal, personal communication) . Due to few observations with scores greater than one for sole ulcers and interdigital dermatitis, scores greater than one were merged creating a binary response for both traits. Heritability was estimated as follows: P=46:/(6;+6,2)
Heritability of outward scale (hi) was estimated as:
(Gianola,
1979)
(3)
where &z, S& and &z were the estimates of the animal, permanent environmental and residual variance components, respectively. A threshold model, probit-normal model (Searle et al., 1992)) was Eq. 4 with the same fixed effects as Eq. 1, except for three changes: ( 1) that covariate of age was grouped into three categories ( 1 to 2, 3 and r4 years old) ; (2) random effects were different because animal effect was replaced by sire effect; and (3) no permanent environmental effect was used for estimating parameters. E(YiIP)=@(XP+ZP
109
(6)
where Bf and Bz are estimates of sire and residual variance components, respectively.
( 1 - rr;) - 2#&z-jcicj~in;]
(7)
where: h2 is heritability of underlying scale; zi are ordinates of a standard normal density function; m equals number of categories; Ci and Cj are outward scores for category group i or j; rri and n; are probabilities of phenotypic response for category group i or j. Based on Eq. 7, transformation of heritability from underlying scale into outward scale was simulated for four different scoring methods and six distributions of hoof traits. The four scoring methods simulated different distances between scores. Equal distance scoring was first method: C, = i, where i was element of {i ( 1,2,3,4,5) Second and third methods scoring: C,=4*(log
(8)
were reduced distance
i/log 5) + 1
(9)
and C,=5-4*
Exp(i-5)+1.
(10)
Increased distance scoring was fourth method: Ci=4*
Exp(i-5)
+ 1,
(11)
The objective of simulation was to study response of heritability under different scoring systems, particularly when the assumption of equal distance between scores was not realistic.
3. Results and discussion Fig. 1 contained the frequency of scores for corkscrew claw (CC), heel erosion (HE), interdigital dermatitis (ID), laminitis (LA), sole ulcers (SU) and white line separation (WLS) in linear and threshold models. Scores of each trait were distributed differently. Interdigital dermatitis and sole ulcers had a large incidence of score 1,78 and 85% of observations. Data used in threshold analyses had similar distribution as for linear model analyses but fewer observations were in each score. In order to keep the same range of scores, 1 (excellent) and 5 (severe) were not changed after
110
8 B %
Y.C.Huang and R. D. Shanks /Livestock
HE
1500
LA 1000
Production Science 44 (I 995) 107-I 14
nando ( 1981) compared different scaling procedures and found estimations from Snell transformations and original scores were similar with beef type data. Low heritability with a relatively large proportion of permanent environmental variance was observed for corkscrew claw, interdigital dermatitis and sole ulcers (ai < o&). Response to selection would be small if selection was only based on a single score. Two hypotheses were consistent with these results: (1) corkscrew claw was influenced by inappropriate hoof care or side effect of other diseases and (2) interdigital dermatitis or sole ulcers affected some cows repeatedly. Comparing studies from Europe, estimated heritabilities based on original scores of heel erosion, interdigital dermatitis, laminitis, and sole ulcers ranged widely from 0.1 to 0.3 in German Fleckvieh and Holstein Friesian breeds (Politiek et al., 1986; Smit et al., 1986; Distl et al., 1990). The European her&abilities exceeded those estimated in this study. However, direct interpretations among results were difficult, because different scoring systems and estimation methods were used in the different studies. Due to the sparse density in contingency table (scores by (fixed+random) effects), the threshold model did not behave well for interdigital dermatitis and sole ulcers. Solutions were cycling and did not converge in the threshold model. Final estimates were based on fourth decimal convergence of sire variance components. From studies of other threshold models, high correlations (0.99) were found between corresponding threshold and linear models (Jensen, 1986; Meijering and Gianola, 1985; Weller and Ron, 1992). Higher heritability was estimated more often by threshold than linear models (Weller and Ron, 1992; Weller
: Heel erosion : Interdlgital dermatltls Lamlnltls : Sole uIC*rs
:
E 1
500 0
CC
HE
ID
LA SU WLS
Llnaar model (3821 Ohs.)
CC
HE
ID
LA SU WLS
Threshold model (865 Obs.)
Fig. 1. Distribution of frequency for scores of six discrete hoof traits in linear and threshold models.
Snell transformation (Tong et al., 1977). The Snell transformed scores of corkscrew claw and laminitis were only slightly different from original scores (Table 1). Estimated variance components, heritabilities and repeatabilities for six traits for linear and threshold models were listed in Table 2. Results of both models were similar, although some assumptions were different. The original scores were analyzed with linear model under the assumption that scores 1 to 5 were equally spaced and represented measurements of a continuous distribution corresponding to degrees away from excellent characteristics of hoof. The transformed scores assumed that corresponding residuals more closely followed the normal distribution. Schaeffer and Wilton ( 1975) argued that because BLUP is similar to the GSK procedure proposed by Grizzle et al. ( 1969) for categorical data analysis, BLUP should be justified and sufficient for interpretation of categorical data. FerTable 1 Normality transformed scores ’ Traits
Corkscrew claw (CC) Heel erosion (HE) Interdigital dermatitis (ID) Laminitis (LA) Sole ulcers (SU) White line separation ( WLS)
Original scores 1
2
3
4
5
1 1 1 1 1 1
2.21 2.43 2.58 2.25 3.14 2.5 1
3.22 3.10 3.18 3.24 3.44 3.21
4.06 3.13 3.90 3.99 3.84 3.87
5 5 5 5 5 5
a Snell transformation (Snell, 1964), score1 and 5 not changed. Original score 1 was excellent and 2 to 5 were subjective evaluation of deviation from excellent.
111
Y.C. Huang and R.D. Shanks /Livestock Production Science 44 (1995) 107-114 Table 2 Estimates of variance and genetic parameters from univariate analyses for linear and threshold models Disorders
Model a
Corkscrew claw
SCOrC
Parameters b
V.
VF-
V,
h2
R
0.593 0.67 1
0.054
0.179
0.052
0.170
Linear Linear Thresh
Original Snell Underlying
0.039 0.042 0.037
0.090 0.095
Heel erosion
Linear Linear Thresh
Original Snell Underlying
0.234 0.213 0.150
0.126 0.122
Interdigital dermatitis
Linear Linear Thresh ’
Original Snell Underlying
0.058 0.052 0.131
Laminitis
Linear Linear Thresh
Original Snell Underlying
Sole ulcers
Linear Linear Thresh ’
White ine separation
Linear Linear Thresh
0.036
_
1.511 1.423
0.125 0.121 0.144
0.193 0.190
0.087 0.085
0.698 0.759
0.069 0.058 0.127
0.172 0. I53
0.152 0.145 0.138
0.066 0.051
0.907 0.847
0.135 0.139 0.133
0.193 0.187 _
Original Snell Underlying
0.029 0.030 0.024
0.132 0.141
0.995 1.063
0.025 0.025 0.024
0.139 0.138 _
Original Snell Underlying
0.125 0.125 0.156
0.106 0.087
I.331 1.348
0.080 0.080 0.150
0.148 0.136
’ Linear, linear model(n = 3821); Thresh, threshold model(n = 655), V, = 1.O and V. = I .O estimated by 4*V,; Original, original score; Snell, Snell transformed score; Underlying, underlying score. h V., V,, V., h’ and R: additive variance, permanent environmental variance, residual variance, heritability and repeatability. ’ Scores above 2 merged as one category.
-c=4(Log
‘-C=i
i/Log q+i
*C=4Exp(i-5)+1
+C=5-4Exp(l-i)
0.5
Distribution of Distribution of heel erosion interdigital dermatitis
Distribution of corkscrew claw i _ +C=4Exp(i-5!‘1
0.1 I
;I
rd
o_ol,
!
I,,,
,,I
.l -2.3.4.5
1
.l
I
I,,
-2.3.4.5
h* of underlying Equal
distance
I I I I ‘,
.l
1,
/,
-2.3.4.5
scale
score(i)
Fig. 2. Different scoring systems for transforming distance scores.
one to five equal
Fig. 3. Transformation of he&abilities from underlying scale to outward scale for corkscrew claw, heel erosion and interdigital dermatitis.
Y.C.Huang and R.D. Shanks /Livestock Production Science 44 (1995) 107-114
112 -c=4(Log
--C=,
I/Log q+1 Distribution
o.ol,
I,,
.l
I
I
I
-2.3.4.5
of
I
/
I
*C=4Exp(l-5)+1
Distribution sole ulcers
I
/
/
.l
I,
I
I,,
-2.3.4.5
h2 of underlying
+-C=S-Exp(l-I)
Distribution white line separation
of
I1
I!
1
.l
I
!
of
tion for summarizing and comparing parameters from studies where linear or threshold models were applied separately. Another possible usefulness was in situations where the underlying scale was considered for selection but parameters were not available. Under distributions of the six traits, equal distance scoring had higher he&abilities than from reduced (10) or increased distance scoring ( 11). The results were consistent with those of Gianola and Norton ( 1981)) although their transformations were based on maximization of heritability. High similarity between results of the second scoring method (9) and equal distance scoring (8) implied that slight changes from linear scores, would not appreciatively change estimations of heritabilities.
! I ! 1 I
.2.3.4.6
scale
Fig. 4. Transformation of he&abilities from underlying scale to outward scale for laminitis, sole ulcers and white line separation
et al., 1988; Weller and Gianola, 1989; Jamrozik et al., 1991a, 1991b). Consistent results did not occur in this study of six hoof traits. Small sample size and sire as the only random effects in the threshold model were suspected as the main causes of the differences. Interpretation will primarily be drawn from results of the linear model. In the disorders studied, the assumption of linear scoring distance was not very realistic. Fig. 2 illustrates four examples of possible scoring systems. Using frequency distribution of six hoof traits and four scoring systems, outward heritabilities were calculated by Eq. 7 for different heritabilities. If skewness of data was extreme, e.g., interdigital dermatitis and sole ulcers, outward heritability was only about half of the underlying heritability. If transformed scores did not linearly increase but followed one of the other functions in Fig. 2, lower heritability was expected (Figs. 3 and 4). In the majority of applications where scores linearly increase, heritability of outward scale can be used to approximate the heritability of the underlying scale based on Eq. 7 and frequency distribution of scores (outward scale). From Table 2 and Figs. 3 and 4, estimated heritabilities on underlying scale for six traits ranged from 0.1 to 0.3 and were approximated from outward scale. These results provided useful informa-
4. Conclusions Numerical instability of estimation of variance components was observed for threshold models. Based on results of linear models with original scores and Snell transformed scores, heel erosion and laminitis had heritabilities greater than 0.1. Selection to improve these two traits would be possible. Repeatabilities of all six hoof traits were greater than 0.14. Corkscrew claw, interdigital dermatitis and sole ulcers had larger proportions of permanent environmental variance than additive genetic variance. Heritabilities on outward scale of traits with highly skewed distributions were smaller than those more centrally distributed.
Acknowledgements
This research was supported by Regional research project S-25 1, Genetic enhancement of health and survival of dairy cattle. First author received financial support from National Science Council, ROC for his first 3 years of study. We thank Lowell Hanson for recording claw disorders. Karin Meyer for use of her DFREML program, Tianlin Wang for use of his DF-REML program for proof checking of estimates and Ignacy Misztal for use of his CMMAT2 program. References Dempster, E.R. and Lemer, I.M., 1950. Heritability of threshold characters. Genetics, 35: 212-236.
Y.C. Huang and R.D. Shrinks /Livestock Production Science 44 (1995) 107-114
Distl, 0.. Koom, D.S., McDaniel, B.T., Peterse, D., Politiek, R.D. and Reurink, A., 1990. Claw traits in cattle breeding programs: Report of the EAAP working group ‘Claw Quality in Cattle’. Livest. Prod. Sci., 25: I-13. Fernando, R.L., 1981. Scaling ordered categorical variables in relation to sire evaluation for frame score at weaning in Angus cattle. MS thesis, University of Illinois, Urbana, pp. 90-92. Gianola, D., 1979. Heritability of polychotomous characters. Genetics, 93: 1051-1055. Gianola, D. and Norton, H.W., 1981. Scaling threshold characters. Genetics, 99: 357-364. Greenough, P.R., MacCallum, F.J. and Weaver. A.D., 1981. Lameness in Cattle. John Wright & Sons Ltd., Bristol, UK, pp. 151227. Greenough, P.R., 1987a. An illustrated compendium of bovine lameness: part I. Mod. Vet. Pratt., 68: 6-9. Greenough, P.R., 1987b. An illustrated compendium of bovine lameness: part 2. Mod. Vet. Pratt., 68: 94-97. Greenough, P.R., 1987~. An illustrated compendium of bovine lameness: part 3. Mod. Vet. Pratt., 68: 148-152. Grizzle, J.E., Starmer, CF. and Koch, G.G., 1969. Analysis of categorical data by linear models. Biometrics, 25: 489-504. Hahn. M.V., McDaniel, B.T. and Wilk. J.C., 1986. Rates of hoof growth and wear in Holstein cattle. J. Dairy Sci., 69: 2148-2156. Jamrozik, J., Schaeffer, L.R., Bumside, E.B. and Sullivan, B.P., 199la. Estimates of he&abilities of Canadian Holstein conformation traits by threshold model. Can. J. Anim. Sci., 71: 629632. Jamrozik, J., Schaeffer, L.R., Burnside, E.B. and Sullivan, B.P., I99 1b. Threshold models applied to Holstein conformation traits. J. Dairy Sci., 74: 31963201. Jensen, J., 1986. Sire evaluation for type traits with linear and nonlinear procedures, Livest. Prod. Sci., 15: 165-171. Meijering, A. and Gianola, D., 1985. Linear versus nonlinear methods of sire evaluation for categorical traits: a simulation study. Genet. Sel. Evol., 17: 115-132. Meyer, K., 1989. Restricted maximum likelihood to estimate variance components for animal models with several random effects using a derivative-free algorithm. Genet. Sel. Evol., 21: 317340. Misztal, I., Gianola, D. and Foulley, J.L., 1989. Computing aspects of a nonlinear method of sire evaluation for categorical data. J. Dairy Sci., 72: 1557-1568.
Politiek, R.D., Distl, O., Fjeldaas, T., Heeres, J., McDaniel, B.T., Nielsen, E., Peterse, D.J., Reurink, A. and Strandberg, P., 1986. Importance of claw quality in cattle: review and recommendations to achieve genetic improvement. Report of the EAAP working group on ‘Claw Quality in Cattle’. Livest. Prod. Sci., 15: 133-152. Schaeffer, L.R. and Wilton, J.W., 1975. Methods of sire evaluation for calving ease. J. Dairy Sci., 59: 544-551. Searle, S.R., Casella, G. and McCulloch, C.E., 1992. Variance Components. John Willey & Sons Inc., New York, pp. 367-377. Smit, H., Verbeek, B., Peterse, D.J., Jansen, J., McDaniel, B.T. and Politiek, R.D., 1986b. Genetic aspects of claw disorders, claw measurements and ‘type’ scores for feet in Friesian cattle. Livest. Prod. Sci., 15: 205-217. Snell, E.J., 1964. A scaling procedure for ordered categorical data. Biometrics, 20: 592607. Tong, A.K.W., Wihon, J.W. and Schaeffer, L.R., 1977. Application of a scoring procedure and transformations to dairy type classification and beef ease of calving categorical data. Can. J. Anim. Sci., 57: l-5. Weaver, A.D., Andersson, L., Laistre Banting, A.D.E., Demerzis, P.N., Knezevic, P.F., Peterse, D.J. and Sankovic, F., 1981. Review of disorders of the ruminant digit with proposals for anatomical and pathological terminology and recording. Vet. Rec., 108: 117-120. Weaver, A.D., 1986. Bovine Surgery and Lameness. Blackwell Scientific Publications, Oxford, UK, pp. 175-225. Weller, J.I., Misztal, I. and Gianola, D., 1988. Genetic analysis of dystocia and calf mortality in Israeli-Holsteins by threshold and linear models. J. Dairy Sci., 71: 2491-2501. Weller, J.I. and Gianola, D., 1989. Models for genetic analysis of dystocia and calf mortality. J. Dairy Sci., 72: 2633-2643. Weller, J.I. and Ron, M., 1992. Genetic analysis of fertility traits in Israeli Holsteins by linear and threshold models. J. Dairy Sci., 75: 2541-2548. Wells, S.J., Trent, A.M., Marsh, W.E. and Robinson, R.A., 1993. Prevalence and severity of lameness in lactating dairy cows in a sample of Minnesota and Wisconsin herds. J. Am. Vet. Med. Assoc., 202: 78-82. Whitaker, D.A., Kelly, J.M. and Smith, E.J., 1983. Incidence of lameness in dairy cows. Vet. Rec., 113: 60-62.
Huang, Y.C. et Shanks, R.D., 1995. Estimations entre troupeau des her&abilitib pour six characteristiques estimations de la dispersion de leurs scores disc&es de severhe. Liuest. Prod. Sci., 44: 107-l 14. Les heretabilites exp&imentale
et repetabilites
113
de six traits des pieds sont estimes pour donnees provenant
des pieds et l’impacte
sur ses
du soin habitue1 des pieds dans un troupeau
de vaches laitieres au tours de dix ans. Les heretabilites sont estim& par DFREML avec un mod&e animal sur les scores originaux
et transform& d’apres Snell. Un modele seuil pour patemite est evahu? mais est instable numeriquement par cause de paucite d’observations pour chaque p&e. Les heretabilites estim& pour 3821 fiches de scores transform& sont 0.05, 0.12, 0.06, 0.14, 0.02, et 0.08 pour la griffe de tourbillon, l’erosion du talon, la dermatite interdig&%, le fourbure cbronique, la contusion de la sole, et la maladie de la ligne blanche; les repetabilitds
sont 0.17, 0.19, 0.15, 0.19, 0.14 et 0.14. Resultats estim& d’apr&s scores originaux y sont fort consistants.
Les petits heretabilitt%
avec une grande variance permanente environmentale par rapport a la variance additive genetique impliquent que la mponse de selection pour un score individuel de la griffe de tourbillon, la dermatite interdigit& et la contusion de la sole semi petit. Les proportions grandes de variances
114
Y.C.Huang and R.D. Shanks/Livestock
Production Science 44 (1995) 107-114
environmentales sont consistants avec deux hypotheses: ( 1) la griffe de tourbillon est influenc& par d’autres maladies ou le soin inapportun des pieds et (2) la dermitite interdigitee ou la contusion de la sole affecte cettaines vaches a plusietus reprises. Les h&&abilites de l’erosion du talon et de la fourbure chronique sont sup&ems a 10% et leur am6lioration par m6thodes quantitatives traditionelles est possible.
Kurzfassung Huang, Y.C. und Shanks, R.D., 1995. Innerhalb-Herden-Schtzung der Heritabilitat fur sechs Klauenmerkmrde und der EinfluB der Verteilung diskreter Befahsklassen auf die Schatzwerte. Liuest Prod. Sci., 44: 107-l 14. Heritabilitaten und Wiederholbarkeiten fur sechs Klauenmerkmale wurden anhand von Daten gesch&t, die iJber einen Z&mum von 10 Jahren bei der Klauenpflege einer Versuchsmilchrinderherde erhoben wurden. Heritabilitaten wurden iiber ein Tiermodell mit DFREML einmal anhand der Originaldaten und einmal anhand transformierter Daten (Snell) gesch&zt. Es wurde auBerdem ein Vater-Schwellenwettmodell getestet, das sich aber aufgrund der geringen Anzahl von Beobachtungen pro Vaterals numerisch instabil envies. Die Schatzung der Heritabilmten beruht auf 3821 Beobachtungen und betrug 0.05 Rir das Merkmal Korkenzieher-KJauen, 0.12 fur Ballenhomfaule, 0.06 fur Dermatitis interdigitalis, 0.14 fur Klauenrehe, 0.02 fur Sohlengeschwtire und 0.08 fiir das Merkmal Spalt in der we&n Linie. Die geschatzten Wiederholbarkeiten der Merkmale lagen bei 0.17, 0.19, 0.15, 0.19, 0.14 und 0.14. Die Ergebnisse, die auf den Originaldaten basierten, waren hoch konsistent. Niedrige Heritabilitaten in Verbindung mit einer im Vergleich zur additiv genetischen Varianz gerhrgen permanten Umweltvarianz fiihrten zu der SchluBfolgerung, da8 eine Selektion auf die Merkmale Korkenzieher-KJauen, Dermatitis interdigitalis und Sohlengeschwtire mu getinge Erfolge zeigen wiirde. Durch den grol3en Anteil der Umweltvarianz kam es einmal zur der Schlu8foJgerung, da8 Korkenzieher-Klauen durch andere Krankheiten oder durch ungentigende Klauenpflege verursacht wurden, und zum anderen zu der Annahme, da8 Dermatitis interdigitalis und Sohlengeschwtire bei einigen Kiihen wiederholt auftraten. Die Heritabilititen der Merkmale Ballenhomfaule und Klauenrehe betrugen mehr als 10% und lassen einde Verbessenmg mit herkijmmlichen Zuchtmethoden als mijglich erscheinen.