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Inheritance and Relationships of Linear Type Traits for Age Groups of Holsteins1
Inheritance and Relationships of Linear Type Traits for Age Groups of Holsteins I D. A . L A W S T U E N 2 and L. B. H A N S E N
Department of Animal Science University of Minnesota St. Paul 55108 L. P. J O H N S O N 3
Holstein Association Brattleboro, VT 05301 ABSTRACT
Routine classifications from the linear type trait program of the Holstein Association were analyzed separately for age groups. Inheritance of linear type traits and their genetic and phenotypic relationships were evaluated. Estimates of genetic and phenotypic parameters were compared to other studies with experimental classifications from the Holstein Association and with data from artificial insemination organizations across age groups. Evaluation of sires for type traits across age groups may not properly rank sires if ages of daughters differ for sires. Future genetic evaluations of t y p e by the Holstein Association will consider only classifications of cows closest to 30 mo, so heritabilities for linear type traits for only 2 yr olds from this study may have application. Some linear type traits are very similar genetically. Stature has substantial genetic association with final score as subjectively assigned by classifiers. INTRODUCTION
Linear type traits replaced the previous categorical type traits (1, 2) for the classification program ¢of the Holstein Association (HA) on January 1, 1983. Fifteen linear traits are
Received August 6, 1986. Accepted December 29, 1986. 1Scientific Journal Series Paper 15014, Minnesota Agricultural Experiment Station. 2Present address: Eastern AI Cooperative, P.O. Box 518, Ithaca, NY 14851. 3Present address: Wisconsin DHI, 5301 Tokay Blvd., Madison, Wl 53711. 1987 J Dairy Sci 70:1027-1035
routinely scored and summarized for sire evaluation (4). Thompson et al. (11) gave advantages o f linear scoring over categorical scoring of t y p e traits: 1) traits are scored individually, 2) scores cover a biological range, 3) a wide range of numerical scores is used, 4) degree rather than desirability is recorded, and 5) the scoring allows analyses with continuous scale. Vinson et al. (12) found that an experimental HA linear system for t y p e traits with a 50-point scale distinguished differences of body measurements with reasonable accuracy. Working with data from the same experimental linear system, Lucas et al. (5) reported that classifiers largely ignored effects o f age and stage of lactation when scoring linearly. Type data of breed associations and A1 organizations have been used to estimate heritabilities of linear type traits and their genetic relationships. In all cases, studies have been across age groups of cows with adjustment for age. Experimental data were examined by Thompson et al. (11) for linear type traits scored by HA classifiers with a 50-point scale and collected adjunct to a previous categorical system of the HA. Heritabilities from the experimental data of Thompson et al. (11) were estimated across ages of cows and have been used for HA genetic evaluations of linear t y p e traits. Heritabilities of traits from HA data (11) were usually lower than for corresponding traits scored on a 50-point linear scale for the Mating Appraisal for Profit Program (MAP) of Midwest Breeders Cooperative (10). Schaeffer et al. (7) evaluated a 9-point scale for the linear t y p e traits program o f Select Sires, Inc. and for 8 of 12 type traits heritabilities were intermediate between estimates from MAP (10) and HA experimental scoring (11). Beginning January 1987, only classifications closest to 30 m o of age for cows are to be used
1027
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LAWSTUEN ET AL.
for HA genetic evaluations of type. Previously, only most recent classifications of cows were summarized. The change will result in classifications of 2-yr-olds contributing most data for genetic evaluations. Mixed model procedures for HA type evaluations require prior estimates of heritability for linear type traits. These may differ for age groups. The objectives of this study were to determine the inheritance of, and relationships among, HA linear type traits as routinely scored by classifiers for different ages of cows.
MATERIALS AND METHODS
The HA provided 126,394 classifications of cows from its linear type trait program. Data were from January 1983 through May 1985 and from 10 states: AR, IL, IA, KS, MN, MO, NE, ND, OK, and SD. Fifteen traits routinely scored for the HA program are listed in Table 1. The linear system of scoring has a continuous scale of 50 points that describes the biological degree displayed by cows for each trait. Preliminary edits removed daughters of sires with registration numbers less than 1200000, cows coded not in condition (NIC) on classification day, and classifications with obvious errors in data entry. The 114,287 remaining classifications were divided into five age groups: 2 yr (24 to 35 mo on classification day), 3 yr
(36 to 47 mo), 4 yr (48 to 59 mo), 5 yr (60 to 71 mo), and aged (i>72 mo). The 2-yr-old cows in the study averaged near 30 too, and this age coincides with the critical age designated by HA for evaluations beginning January 1987. Only classifications closest to 30 mo for cows will be evaluated by HA. One classification per cow was allowed for each age group with the earliest retained. Cows scored by classifiers with less than 500 classifications were excluded to ensure that classifiers were experienced and proficient with linear scoring. Sires needed 25 daughters within age groups to minimize instances when all daughters of a sire were scored by a single classifier. This restriction should have eliminated most natural service sires. Table 2 has the edited (46.6% of original data) distribution of 58,942 classifications for age groups by herds, sires, and classifiers. The linear model chosen for analysis of each age group separately included effects of classifier, period nested within classifier, herd nested within period and classifier, stage of lactation, age (days within age group, linear and quadratic), and sire. Period was defined as four consecutive 6-mo intervals (January 1983 to December 1984) followed by a 5-too interval (January 1985 to May 1985) and accounted for probable trends from training and familiarity of classifiers with linear scoring. Herds may have
TABLE 1. Definition of linear type traits.
Trait
Scores approaching 50
Scores approaching 1
Stature Strength Body depth Angularity Rump angle Rump length Rump width Rear legs side view Foot angle Fore udder attachment Rear udder height Rear udder width Udder support Udder depth Teat placement
Tall Strong Deep Sharp Sloped Long Wide Sickle Steep Strong High Wide Strong ShalIow Close
Short Frail Shallow Coarse High pins Short Narrow Posty Low Loose Low Narrow Broken Deep Wide
Journal of Dairy Science Vol. 70, No. 5, 1987
LINEAR TYPE TRAITS FOR AGE GROUPS
1029
TABLE 2. Distribution of classifications for age groups.
Cows Herds S~es Classifiers
2 yr
3 yr
4 yr
14,786 3016 142 15
20,407 3450 167 17
12,605 2843 126 15
been evaluated more than once; however, the restriction of one classification per cow within age group permitted herd to be nested within period and classifier. Herds are defined by classifier, so consideration of year-seasons was not applicable. Stage of lactation was partitioned into 9 30-d intervals with 10th interval for cows in milk > 270 d. Effects in the model were fixed except sire and residual, which were assumed random. Classifer, period (classifier), and herd (period/ classifier) were sequentially absorbed. Analysis of variance and covariance was with least squares procedures. Components of variance and covariance were obtained by Method 3 (3). Standard errors o f heritabilities (8) and genetic correlations (9) were approximated. RESULTS A N D DISCUSSION
Unadjusted means and standard deviations of linear type traits and final score for age groups are in Table 3. Means for 2-yr scores ranged from 20.4 (rump width) to 29.8 (udder depth) and for aged cows from 20.5 (udder depth) to 34.1 (body depth). Older cows have survived culling for low production, so it is logical that they rate high for angularity. Often means from Thompson et al. (11) were intermediate between 2-yr-old cow scores and aged cow scores from this study. Means for many traits increased with age. This m a y be due to actual biological development of cows but also probably is because older cows result from some selection for type traits among cows. Udder traits, notably udder depth, behaved differently with older cows displaying the physical effects of production over time. Means for linear type traits with intermediate optimums, rump angle and rear legs, changed
5 yr 7616 2271 88 13
Aged 3528 1433 50 9
little across age groups. Standard deviations were similar to those for the experimental system for linear scoring (11). Results of analyses of variance for 2-yr-old cows are in Table 4. Absorbed effects of classifier, period (classifier), and herd (period/ classifier) were highly significant (P<.01) from tests o f sequential sums of squares for all age groups and traits except rump angle of aged cows (P<.05). Error mean squares for 2-yr-old cow type traits and final score were lower than for all corresponding traits across ages of Thompson et al. (11). Stage of lactation was significant (P< .05) for all traits of 2-yr-old cows except foot angle. This is in agreement (11) and disagreement (5) with previous studies with HA experimental linear data. Linear partial regressions on age (days within age group) were significant for 7 of the 15 traits and final score. Quadratic effects of age (days) were significant for only four traits. Only tests of significance for 2-yrolds are discussed for clarity of presentation, because significance of effects was similar for older age groups.
Heritabilities
Sire was significant (P<.01) for all linear type traits and final score of all age groups. Heritabilities from sire and residual variances are in Table 5. Estimates for 2-yr-olds were near (~ .05) estimates from Thompson et al. (11) across ages except for the following: angularity was much higher (.33 versus .16), rump angle was somewhat higher (.23 versus .17), and rear udder height was somewhat lower (.15 versus .22). Heritabilities were typically smaller than those reported from AI data (7, 10). Final score Journal of Dairy Science Vol. 70, No. 5, 1987
~o
TABLE 3. Unadjusted m e a n s and standard deviations o f linear t y p e traits for age groups. e~
Trait
2 yr
3 yr
4 yr
5 yr
Aged
Range of SD X1
SD
Stature Strength Body depth Angularity R u m p angle R u m p length R u m p width Rear legs side view Foot angle Fore udder a t t a c h m e n t Rear udder height Rear udder width Udder support Udder depth Teat placement
24,6 20.7 22,5 27,6 26.4 24.3 20.4 26.3 24.2 24.6 24.1 22.5 28.0 29.8 25.0
27.8 24.1 26.3 28.4 25.4 27.2 23.4 27.1 23.9 25,1 25.6 24.3 27.4 27.5 24.8
30.2 27.1 29.6 29.9 24.9 29.4 26.0 27.7 24.0 25.1 26,8 26.0 26.9 24.7 24.7
31.3 29.1 31.9 31.1 24.7 30.6 27,3 27.8 24,1 25,1 27,3 26.7 26.3 22,1 24.6
32.3 30.9 34.1 33.0 24.3 31.7 28,1 27.6 24.6 25.7 28.4 27.7 26.4 20.5 25.0
7.2--7.4 6.1-6.9 6.0--6.3 6.9-7.6 5.2-5.5 5.2-5.4 5.7--6.4 5.9--6.7 6.6--6.7 7,0-8.6 7.3-8.4 6,9-7.7 6,2-7.6 5.7-6,4 6.1--6.8
26.3 28.3 2 2916 24.8 ...2 25.1 26.6 22.33 28.5 25.2 26.0 29.5 29.1 25.6
6,1 6.0
Final score
78.2
79,3
80.8
81.9
83.6
4.5-4.7
.
O
O
xO 0~ ~q
1
Means from 50 to 99 linear scale m i n u s 50 points.
a Experimental project (11) did not include b o d y d e p t h or r u m p length. 3 Heel depth.
Thompson et al. (I1)
.
615 6.2 614 6.7 6.1 6.9 7.0 6.7 6.3 5.2 7.4 .
.
.
.
LINEAR TYPE TRAITS FOR AGE GROUPS
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TABLE 4. Tests of significance and error mean squares from analysis of variance for 2-yroold cows) Trait
Stage
Age
Stature Strength Body depth Angularity Rump angle Rump length Rump width Rear legs side view Foot angle Fore udder attachment Rear udder height Rear udder width Udder support Udder depth Teat placement rear view
* ** ** ** ** ** * **
** * **
Final score
*
** ** ** ** ** **
Age z
*
** **
*
**
**
*
*
**
**
Sire
MS
** ** ** ** ** ** ** ** ** ** ** ** ** ** **
34.97 25.60 24.74 33.56 23.81 18.36 23.65 37.20 31.69 40.35 37.65 34.34 30.23 21.09 30.43
**
12.71
1Absorbed effects of classifier, period (classifier), and herd (period/classifier) were significant (P<.O1) for all traits from tests of sequential sums of squares. *P<.05. **P<.01.
h a d h i g h e s t h e r i t a b i l i t y for 2-yr-olds (.21), b u t all e s t i m a t e s f o r age g r o u p s were l o w e r t h a n f r o m data a n a l y z e d similarly (11) w i t h ages c o m b i n e d (.28). E s t i m a t e s for each age g r o u p e x c e p t 2-yr-olds were significantly ( P < . 0 5 ) d i f f e r e n t f r o m t h e earlier e s t i m a t e for final score. F o r s o m e traits, p o i n t e s t i m a t e s o f herit a b i l i t y varied c o n s i d e r a b l y for age groups, b u t d i f f e r e n c e s were n o t statistically significant (P> .05). E s t i m a t e s for a n g u l a r i t y d r o p p e d f r o m 2-yr-olds (.33) to aged (.23). E s t i m a t e s for rear u d d e r h e i g h t increased m a r k e d l y w i t h age group, suggesting t h a t d i f f e r e n c e s a m o n g d a u g h t e r s o f sires were m o r e d i f f i c u l t t o d e t e c t at y o u n g e r ages for t h a t p a r t i c u l a r trait. Heritabilities for 2-yr-olds f r o m this s t u d y m a y b e m o s t a p p r o p r i a t e for H A g e n e t i c e v a l u a t i o n s o f o n l y classifications closest t o 30 m o . Before J a n u a r y 1987, g e n e t i c e v a l u a t i o n s o f H A used o n l y m o s t r e c e n t classification o f cows. Classifications closest t o 30 m o are relatively u n s e l e c t e d c o m p a r e d w i t h m o s t recent classifications, b e c a u s e only cows t h a t have survived selection in h e r d s are rescored. C o m p a r i s o n o f surviving old d a u g h t e r s o f old bulls w i t h u n s e l e c t e d y o u n g d a u g h t e r s o f
y o u n g e r bulls m a y b e p r o b l e m a t i c . Sires m a y n o t b e p r o p e r l y r a n k e d for t r a n s m i t t i n g abilities if sires have n o n u n i f o r m age d i s t r i b u t i o n s o f d a u g h t e r s at classification.
Relationships of Traits
P h e n o t y p i c c o r r e l a t i o n s a m o n g individual t y p e t r a i t s ( e x c l u d i n g final score) for 2-yr-olds in T a b l e 6 were m o s t l y positive b u t r a n g e d f r o m .72 ( s t r e n g t h a n d b o d y d e p t h ) to - . 1 4 (rear legs side view a n d f o o t angle). S t a t u r e a n d b o d y d e p t h (.62), s t a t u r e a n d r u m p l e n g t h (.54), a n d rear u d d e r h e i g h t a n d rear u d d e r w i d t h (.71) also h a d p h e n o t y p i c c o r r e l a t i o n s g r e a t e r t h a n .50. T a b l e 6 has genetic c o r r e l a t i o n s f o r 2-yr-olds a n d t h e y usually were o f t h e same sign as corresponding phenotypic correlations but of g r e a t e r m a g n i t u d e . A p p r o x i m a t e s t a n d a r d errors o f genetic c o r r e l a t i o n s are in T a b l e 7. G e n e t i c c o r r e l a t i o n s were f r o m .93 ( s t r e n g t h and body depth) to -.25 (angularity and udder d e p t h ) . S t a t u r e a n d r u m p l e n g t h (.91), rear u d d e r h e i g h t a n d rear u d d e r w i d t h (.89), b o d y d e p t h a n d r u m p l e n g t h (.78), s t a t u r e a n d b o d y d e p t h (.78), a n d fore u d d e r a t t a c h m e n t a n d Journal of Dairy Science Vol. 70, No. 5, 1987
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LAWSTUEN ET AL.
TABLE 5. Heritabilities of linear type traits and final score for age groups. 1 Thompson et al. (11) 2
2 yr
3 yr
Stature
32 (4)
35 (4)
Strength
22 (3)
Body depth Angularity
Trait
4 yr
5 yr
Aged
36 (4)
30 (4)
37 (6)
23 (7)
24 (3)
22 (3)
22 (3)
32 (5)
13 (5)
...3
35 (4)
28 (3)
25 (4)
38 (6)
18 (6)
16 (2)
33 (4)
26
27
23
23
(3)
(4)
(4)
(6)
Rump angle
17 (3)
23 (3)
24 (3)
27 (4)
29 (5)
25 (7)
Rump length
...3
15 (2)
20 (3)
21 (3)
21 (4)
14 (5)
Rump width
26 (3)
27 (4)
24 (3)
22 (3)
27 (5)
21 (6)
Rear legs side view
15 (2)
16 (2)
16 (2)
15 (3)
22 (4)
15 (5)
Foot angle
154 (2)
11 (2)
13 (2)
12 (2)
16 (3)
13 (5)
Fore udder attachment
15 (2)
15 (2)
16 (2)
15 (3)
14 (3)
9 (4)
Rear udder height
22 (3)
15 (2)
18 (2)
21 (3)
26 (5)
31 (8)
Rear udder width
15 (2)
18 (3)
12 (2)
15 (2)
19 (4)
18 (6)
Udder support
12 (2)
11 (2)
13 (2)
11 (2)
13 (3)
6 (4)
Udder depth
26 (3)
23 (3)
21 (3)
23 (3)
25 (5)
11 (4)
Teat placement
23 (3)
18 (3)
17 (2)
18 (3)
15 (3)
11 (4)
Final score
28 (3)
21 (3)
18 (2)
18 (3)
21 (4)
14 (5)
(%)
Approximate standard errors in parentheses. a Estimated across age groups from experimental project. 3 Experimental project (11) did not include body depth or rump length. 4 Heel depth.
u d d e r d e p t h (.77) all h a d g e n e t i c c o r r e l a t i o n s g r e a t e r t h a n .75. P h e n o t y p i c c o r r e l a t i o n s were similar to T h o m p s o n et al. (11), b u t g e n e t i c c o r r e l a t i o n s s o m e t i m e s differed. S t a t u r e a n d a n g u l a r i t y departed considerably (.36 versus - . 0 4 ) . Similarly, r u m p angle was positively c o r r e l a t e d Journal of Dairy Science Vol. 70, No. 5, 1987
w i t h m o s t traits, w h e r e a s T h o m p s o n et al. (11) f o u n d negative g e n e t i c c o r r e l a t i o n s . E n v i r o n m e n t a l c o r r e l a t i o n s ( T a b l e 7) usually were smaller t h a n c o r r e s p o n d i n g p h e n o t y p i c a n d g e n e t i c c o r r e l a t i o n s a n d were f r o m .67 (rear u d d e r h e i g h t a n d rear u d d e r w i d t h ) to --.20 ( r u m p angle a n d fore u d d e r a t t a c h m e n t ) .
LINEAR TYPE TRAITS FOR AGE GROUPS
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Strength and b o d y depth (.64) and stature and b o d y depth (.54) also had environmental correlations greater than .50. Rear legs side view and foot angle had correlations of - . 1 4 (phenotypic) and - . 3 9 (genetic), suggesting that cows with steep foot angles have straighter rear legs, which might be expected. Strength and b o d y depth were closely related phenotypically (.72) and genetically (.93) and had similar correlations with other traits• Association with angularity was the exception, because estimates were near zero for strength and moderately positive for b o d y depth. The high genetic correlation (.93) for strength and b o d y depth may indicate that many of the same genes affect these two traits. Udder traits had mutually close relationships. Rear udder height and rear udder width had a genetic correlation of .89 and may indicate another case where many of the same genes may be important for two traits. Genetic correlations were also substantial for fore udder attachment and udder depth (.77), udder support and teat placement (.70), fore udder attachment and teat placement (.59), fore udder attachment and udder support (.50), and udder support and udder depth (.47). Udder support is important to dairy producers so that udders do not become too deep and so that distance between front teats does not become too wide. Gain from scoring udder support is not obvious, however, because udder support (h 2 = .11) is essentially an indicator trait for two traits, udder depth (h 2 = .23) and teat placement (h 2 = .18), which are also scored and have higher heritabilities. Strongest genetic association of udder and nonudder traits was rear udder width and angularity (.42). This is not surprising because cows that look like they milk heavily should have fuller rear udders. Rump angle followed for genetic association with udder traits. Udders with strong fore udder attachments and that were shallow were associated genetically (.36 and .35) with sloping rumps. Udder depth was the udder trait most related to stature genetically (.29); taller cows have longer legs so that udders should be farther from the ground. Correlations with Final Score
The
first row (phenotypic) and column Journal of Dairy Science Vol. 70, No. 5, 1987
1034
LAWSTUEN ET AL.
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(genetic) of Table 6 have correlations of individual type traits with final score. All correlations were positive except for two traits with intermediate optimums; rump angle ( - . 1 5 ) and rear legs side view ( - . 0 4 ) had negative phenotypic correlations with final score. Rear legs side view and final score were not related genetically (.00). Rear udder width (.52), rear udder height (.49), and fore udder attachment (.49) had greatest phenotypic association with final score. These traits also had most environmental relationship (Table 7) with final score (.49). Stature (.69), rump length (.68), rear udder width (.65), and body depth (.63) had largest genetic correlations with final score. The two traits with highest genetic correlations with final score for 2-yr-olds were stature (.69) and rump length (.68). Both these traits may be of questionable ecomomic benefit (6); yet sire groups of tall, long 2-yr-olds subjectively received higher final scores from classifiers. In addition to having substantial genetic association with rump length (.91), stature was closely related to strength (.70) and body depth (.78). Strength and body depth were also closely associated with rump length (.73 and .78) and rump width (.72 and .73). This indicates that tall, long 2-yr-olds receive high final scores and that they also are strong and deep and have wide rumps. Obviously, the question then arises: are these the proper traits to emphasize from 2-yr-olds for optimum lifetime performance?
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Sire and cow evaluations for type by the HA will be mostly from classifications of 2-yr-olds in the future. Estimates of heritability for linear type traits of 2-yr-olds were near (-+ .05) earlier estimates across ages except that angularity (.33) and rump angle (.23) were higher and rear udder height (.15) was lower. Heritabilities of 2-yr-olds from this study may be applicable for HA genetic evaluations of classifications closest to 30 mo. Some linear type traits for 2-yr-olds were very similar genetically. Examples were: 1) strength and body depth, 2) rear udder height and rear udder width, and 3) stature and rump length. Separate scoring for these pairs of traits may be of questionable benefit to dairy pro-
LINEAR TYPE TRAITS FOR AGE GROUPS ducers. F u r t h e r m o r e , scoring c o w s for u d d e r s u p p o r t , an i n d i c a t o r trait, m a y n o t be justified b e c a u s e d i r e c t selection for u d d e r d e p t h a n d t e a t p l a c e m e n t s h o u l d be m o r e successful. C o n s i d e r a b l e e m p h a s i s is placed u p o n s t a t u r e w h e n classifiers subjectively assign final score for 2-yr-olds. R e s e a r c h is n e e d e d to d e t e r m i n e t h e c o n t r i b u t i o n o f linear t y p e traits o f 2yr-olds t o d u r a b i l i t y and l i f e t i m e p e r f o r m a n c e o f cows. ACKNOWLEDGMENT
Data a n d financial s u p p o r t f r o m t h e H o l s t e i n A s s o c i a t i o n w e r e greatly a p p r e c i a t e d .
REFERENCES
1 Cassell, B. G., J. M. White, W. E. Vinson, and R. H. Kliewer. 1973. Genetic and phenotypic relationship among type traits in Holstein-Friesian cattle. J. Dairy Sci. 56:1171. 2 Hay, G. M., J. M. White, W. E. Vinson, and R. H. Kliewer. 1983. Components of genetic variation for descriptive type traits of Holsteins. J. Dairy Sci. 66:1962. 3 Henderson, C. R. 1953. Estimation of variance and covariance components. Biometrics 9: 226. 4 Holstein-Friesian Association of America. 1984.
103 5
Linear-Holstein Association linear classification program. Brattleboro, VT. 5 Lucas, J. L., R. E. Pearson, W. E. Vinson, and L. P. Johnson. 1984. Experimental linear descriptive type classification. J. Dairy Sci. 67:1767. 6 Mahoney, C. B., L. B. Hansen, C. W. Young, G. D. Marx, and J. K. Reneau. 1986. Health care of Holsteins selected for large or small body size. J. Dairy Sci. 69:3131. 7 Schaeffer, G. B., W. E. Vinson, R. E. Pearson, and R. G. Long. 1985. Genetic and phenotypic relationships among type traits scored linearly in Holsteins. J. Dairy Sci. 68:2984. 8 Swiger, L. A., W. R. Harvey, D. O. Everson, and K. R. Gregory. 1964. The variance of intra-class correlation involving groups with one observation. Biometrics 20: 818. 9 Tallls, G. M. 1959. Sampling errors of genetic correlation coefficients calculated from analysis of variance and covariance. Aust. J. Stat. 1 : 35. 10 Thompson, J. R., A. E. Freeman, D. J. Wilson, C. A. Chapin, and P. J. Berger. 1981. Evaluation of a linear type program in Holsteins. J. Dairy Sci. 64:1610. 11 Thompson, J. R., K. L. Lee, A. E. Freeman, and L. P. Johnson. 1983. Evaluation of a linearized type appraisal system for Holstein cattle. J. Dairy Sci. 66:325. 12 Vinson, W. E., R. E. Pearson, and L. P. Johnson. 1982. Relationships between linear descriptive type traits and body measurements. J. Dairy Sci. 65:995.
Journal of Dairy Science Vol. 70, No. 5, 1987
Department of Animal Science University of Minnesota St. Paul 55108 L. P. J O H N S O N 3
Holstein Association Brattleboro, VT 05301 ABSTRACT
Routine classifications from the linear type trait program of the Holstein Association were analyzed separately for age groups. Inheritance of linear type traits and their genetic and phenotypic relationships were evaluated. Estimates of genetic and phenotypic parameters were compared to other studies with experimental classifications from the Holstein Association and with data from artificial insemination organizations across age groups. Evaluation of sires for type traits across age groups may not properly rank sires if ages of daughters differ for sires. Future genetic evaluations of t y p e by the Holstein Association will consider only classifications of cows closest to 30 mo, so heritabilities for linear type traits for only 2 yr olds from this study may have application. Some linear type traits are very similar genetically. Stature has substantial genetic association with final score as subjectively assigned by classifiers. INTRODUCTION
Linear type traits replaced the previous categorical type traits (1, 2) for the classification program ¢of the Holstein Association (HA) on January 1, 1983. Fifteen linear traits are
Received August 6, 1986. Accepted December 29, 1986. 1Scientific Journal Series Paper 15014, Minnesota Agricultural Experiment Station. 2Present address: Eastern AI Cooperative, P.O. Box 518, Ithaca, NY 14851. 3Present address: Wisconsin DHI, 5301 Tokay Blvd., Madison, Wl 53711. 1987 J Dairy Sci 70:1027-1035
routinely scored and summarized for sire evaluation (4). Thompson et al. (11) gave advantages o f linear scoring over categorical scoring of t y p e traits: 1) traits are scored individually, 2) scores cover a biological range, 3) a wide range of numerical scores is used, 4) degree rather than desirability is recorded, and 5) the scoring allows analyses with continuous scale. Vinson et al. (12) found that an experimental HA linear system for t y p e traits with a 50-point scale distinguished differences of body measurements with reasonable accuracy. Working with data from the same experimental linear system, Lucas et al. (5) reported that classifiers largely ignored effects o f age and stage of lactation when scoring linearly. Type data of breed associations and A1 organizations have been used to estimate heritabilities of linear type traits and their genetic relationships. In all cases, studies have been across age groups of cows with adjustment for age. Experimental data were examined by Thompson et al. (11) for linear type traits scored by HA classifiers with a 50-point scale and collected adjunct to a previous categorical system of the HA. Heritabilities from the experimental data of Thompson et al. (11) were estimated across ages of cows and have been used for HA genetic evaluations of linear t y p e traits. Heritabilities of traits from HA data (11) were usually lower than for corresponding traits scored on a 50-point linear scale for the Mating Appraisal for Profit Program (MAP) of Midwest Breeders Cooperative (10). Schaeffer et al. (7) evaluated a 9-point scale for the linear t y p e traits program o f Select Sires, Inc. and for 8 of 12 type traits heritabilities were intermediate between estimates from MAP (10) and HA experimental scoring (11). Beginning January 1987, only classifications closest to 30 m o of age for cows are to be used
1027
1028
LAWSTUEN ET AL.
for HA genetic evaluations of type. Previously, only most recent classifications of cows were summarized. The change will result in classifications of 2-yr-olds contributing most data for genetic evaluations. Mixed model procedures for HA type evaluations require prior estimates of heritability for linear type traits. These may differ for age groups. The objectives of this study were to determine the inheritance of, and relationships among, HA linear type traits as routinely scored by classifiers for different ages of cows.
MATERIALS AND METHODS
The HA provided 126,394 classifications of cows from its linear type trait program. Data were from January 1983 through May 1985 and from 10 states: AR, IL, IA, KS, MN, MO, NE, ND, OK, and SD. Fifteen traits routinely scored for the HA program are listed in Table 1. The linear system of scoring has a continuous scale of 50 points that describes the biological degree displayed by cows for each trait. Preliminary edits removed daughters of sires with registration numbers less than 1200000, cows coded not in condition (NIC) on classification day, and classifications with obvious errors in data entry. The 114,287 remaining classifications were divided into five age groups: 2 yr (24 to 35 mo on classification day), 3 yr
(36 to 47 mo), 4 yr (48 to 59 mo), 5 yr (60 to 71 mo), and aged (i>72 mo). The 2-yr-old cows in the study averaged near 30 too, and this age coincides with the critical age designated by HA for evaluations beginning January 1987. Only classifications closest to 30 mo for cows will be evaluated by HA. One classification per cow was allowed for each age group with the earliest retained. Cows scored by classifiers with less than 500 classifications were excluded to ensure that classifiers were experienced and proficient with linear scoring. Sires needed 25 daughters within age groups to minimize instances when all daughters of a sire were scored by a single classifier. This restriction should have eliminated most natural service sires. Table 2 has the edited (46.6% of original data) distribution of 58,942 classifications for age groups by herds, sires, and classifiers. The linear model chosen for analysis of each age group separately included effects of classifier, period nested within classifier, herd nested within period and classifier, stage of lactation, age (days within age group, linear and quadratic), and sire. Period was defined as four consecutive 6-mo intervals (January 1983 to December 1984) followed by a 5-too interval (January 1985 to May 1985) and accounted for probable trends from training and familiarity of classifiers with linear scoring. Herds may have
TABLE 1. Definition of linear type traits.
Trait
Scores approaching 50
Scores approaching 1
Stature Strength Body depth Angularity Rump angle Rump length Rump width Rear legs side view Foot angle Fore udder attachment Rear udder height Rear udder width Udder support Udder depth Teat placement
Tall Strong Deep Sharp Sloped Long Wide Sickle Steep Strong High Wide Strong ShalIow Close
Short Frail Shallow Coarse High pins Short Narrow Posty Low Loose Low Narrow Broken Deep Wide
Journal of Dairy Science Vol. 70, No. 5, 1987
LINEAR TYPE TRAITS FOR AGE GROUPS
1029
TABLE 2. Distribution of classifications for age groups.
Cows Herds S~es Classifiers
2 yr
3 yr
4 yr
14,786 3016 142 15
20,407 3450 167 17
12,605 2843 126 15
been evaluated more than once; however, the restriction of one classification per cow within age group permitted herd to be nested within period and classifier. Herds are defined by classifier, so consideration of year-seasons was not applicable. Stage of lactation was partitioned into 9 30-d intervals with 10th interval for cows in milk > 270 d. Effects in the model were fixed except sire and residual, which were assumed random. Classifer, period (classifier), and herd (period/ classifier) were sequentially absorbed. Analysis of variance and covariance was with least squares procedures. Components of variance and covariance were obtained by Method 3 (3). Standard errors o f heritabilities (8) and genetic correlations (9) were approximated. RESULTS A N D DISCUSSION
Unadjusted means and standard deviations of linear type traits and final score for age groups are in Table 3. Means for 2-yr scores ranged from 20.4 (rump width) to 29.8 (udder depth) and for aged cows from 20.5 (udder depth) to 34.1 (body depth). Older cows have survived culling for low production, so it is logical that they rate high for angularity. Often means from Thompson et al. (11) were intermediate between 2-yr-old cow scores and aged cow scores from this study. Means for many traits increased with age. This m a y be due to actual biological development of cows but also probably is because older cows result from some selection for type traits among cows. Udder traits, notably udder depth, behaved differently with older cows displaying the physical effects of production over time. Means for linear type traits with intermediate optimums, rump angle and rear legs, changed
5 yr 7616 2271 88 13
Aged 3528 1433 50 9
little across age groups. Standard deviations were similar to those for the experimental system for linear scoring (11). Results of analyses of variance for 2-yr-old cows are in Table 4. Absorbed effects of classifier, period (classifier), and herd (period/ classifier) were highly significant (P<.01) from tests o f sequential sums of squares for all age groups and traits except rump angle of aged cows (P<.05). Error mean squares for 2-yr-old cow type traits and final score were lower than for all corresponding traits across ages of Thompson et al. (11). Stage of lactation was significant (P< .05) for all traits of 2-yr-old cows except foot angle. This is in agreement (11) and disagreement (5) with previous studies with HA experimental linear data. Linear partial regressions on age (days within age group) were significant for 7 of the 15 traits and final score. Quadratic effects of age (days) were significant for only four traits. Only tests of significance for 2-yrolds are discussed for clarity of presentation, because significance of effects was similar for older age groups.
Heritabilities
Sire was significant (P<.01) for all linear type traits and final score of all age groups. Heritabilities from sire and residual variances are in Table 5. Estimates for 2-yr-olds were near (~ .05) estimates from Thompson et al. (11) across ages except for the following: angularity was much higher (.33 versus .16), rump angle was somewhat higher (.23 versus .17), and rear udder height was somewhat lower (.15 versus .22). Heritabilities were typically smaller than those reported from AI data (7, 10). Final score Journal of Dairy Science Vol. 70, No. 5, 1987
~o
TABLE 3. Unadjusted m e a n s and standard deviations o f linear t y p e traits for age groups. e~
Trait
2 yr
3 yr
4 yr
5 yr
Aged
Range of SD X1
SD
Stature Strength Body depth Angularity R u m p angle R u m p length R u m p width Rear legs side view Foot angle Fore udder a t t a c h m e n t Rear udder height Rear udder width Udder support Udder depth Teat placement
24,6 20.7 22,5 27,6 26.4 24.3 20.4 26.3 24.2 24.6 24.1 22.5 28.0 29.8 25.0
27.8 24.1 26.3 28.4 25.4 27.2 23.4 27.1 23.9 25,1 25.6 24.3 27.4 27.5 24.8
30.2 27.1 29.6 29.9 24.9 29.4 26.0 27.7 24.0 25.1 26,8 26.0 26.9 24.7 24.7
31.3 29.1 31.9 31.1 24.7 30.6 27,3 27.8 24,1 25,1 27,3 26.7 26.3 22,1 24.6
32.3 30.9 34.1 33.0 24.3 31.7 28,1 27.6 24.6 25.7 28.4 27.7 26.4 20.5 25.0
7.2--7.4 6.1-6.9 6.0--6.3 6.9-7.6 5.2-5.5 5.2-5.4 5.7--6.4 5.9--6.7 6.6--6.7 7,0-8.6 7.3-8.4 6,9-7.7 6,2-7.6 5.7-6,4 6.1--6.8
26.3 28.3 2 2916 24.8 ...2 25.1 26.6 22.33 28.5 25.2 26.0 29.5 29.1 25.6
6,1 6.0
Final score
78.2
79,3
80.8
81.9
83.6
4.5-4.7
.
O
O
xO 0~ ~q
1
Means from 50 to 99 linear scale m i n u s 50 points.
a Experimental project (11) did not include b o d y d e p t h or r u m p length. 3 Heel depth.
Thompson et al. (I1)
.
615 6.2 614 6.7 6.1 6.9 7.0 6.7 6.3 5.2 7.4 .
.
.
.
LINEAR TYPE TRAITS FOR AGE GROUPS
1031
TABLE 4. Tests of significance and error mean squares from analysis of variance for 2-yroold cows) Trait
Stage
Age
Stature Strength Body depth Angularity Rump angle Rump length Rump width Rear legs side view Foot angle Fore udder attachment Rear udder height Rear udder width Udder support Udder depth Teat placement rear view
* ** ** ** ** ** * **
** * **
Final score
*
** ** ** ** ** **
Age z
*
** **
*
**
**
*
*
**
**
Sire
MS
** ** ** ** ** ** ** ** ** ** ** ** ** ** **
34.97 25.60 24.74 33.56 23.81 18.36 23.65 37.20 31.69 40.35 37.65 34.34 30.23 21.09 30.43
**
12.71
1Absorbed effects of classifier, period (classifier), and herd (period/classifier) were significant (P<.O1) for all traits from tests of sequential sums of squares. *P<.05. **P<.01.
h a d h i g h e s t h e r i t a b i l i t y for 2-yr-olds (.21), b u t all e s t i m a t e s f o r age g r o u p s were l o w e r t h a n f r o m data a n a l y z e d similarly (11) w i t h ages c o m b i n e d (.28). E s t i m a t e s for each age g r o u p e x c e p t 2-yr-olds were significantly ( P < . 0 5 ) d i f f e r e n t f r o m t h e earlier e s t i m a t e for final score. F o r s o m e traits, p o i n t e s t i m a t e s o f herit a b i l i t y varied c o n s i d e r a b l y for age groups, b u t d i f f e r e n c e s were n o t statistically significant (P> .05). E s t i m a t e s for a n g u l a r i t y d r o p p e d f r o m 2-yr-olds (.33) to aged (.23). E s t i m a t e s for rear u d d e r h e i g h t increased m a r k e d l y w i t h age group, suggesting t h a t d i f f e r e n c e s a m o n g d a u g h t e r s o f sires were m o r e d i f f i c u l t t o d e t e c t at y o u n g e r ages for t h a t p a r t i c u l a r trait. Heritabilities for 2-yr-olds f r o m this s t u d y m a y b e m o s t a p p r o p r i a t e for H A g e n e t i c e v a l u a t i o n s o f o n l y classifications closest t o 30 m o . Before J a n u a r y 1987, g e n e t i c e v a l u a t i o n s o f H A used o n l y m o s t r e c e n t classification o f cows. Classifications closest t o 30 m o are relatively u n s e l e c t e d c o m p a r e d w i t h m o s t recent classifications, b e c a u s e only cows t h a t have survived selection in h e r d s are rescored. C o m p a r i s o n o f surviving old d a u g h t e r s o f old bulls w i t h u n s e l e c t e d y o u n g d a u g h t e r s o f
y o u n g e r bulls m a y b e p r o b l e m a t i c . Sires m a y n o t b e p r o p e r l y r a n k e d for t r a n s m i t t i n g abilities if sires have n o n u n i f o r m age d i s t r i b u t i o n s o f d a u g h t e r s at classification.
Relationships of Traits
P h e n o t y p i c c o r r e l a t i o n s a m o n g individual t y p e t r a i t s ( e x c l u d i n g final score) for 2-yr-olds in T a b l e 6 were m o s t l y positive b u t r a n g e d f r o m .72 ( s t r e n g t h a n d b o d y d e p t h ) to - . 1 4 (rear legs side view a n d f o o t angle). S t a t u r e a n d b o d y d e p t h (.62), s t a t u r e a n d r u m p l e n g t h (.54), a n d rear u d d e r h e i g h t a n d rear u d d e r w i d t h (.71) also h a d p h e n o t y p i c c o r r e l a t i o n s g r e a t e r t h a n .50. T a b l e 6 has genetic c o r r e l a t i o n s f o r 2-yr-olds a n d t h e y usually were o f t h e same sign as corresponding phenotypic correlations but of g r e a t e r m a g n i t u d e . A p p r o x i m a t e s t a n d a r d errors o f genetic c o r r e l a t i o n s are in T a b l e 7. G e n e t i c c o r r e l a t i o n s were f r o m .93 ( s t r e n g t h and body depth) to -.25 (angularity and udder d e p t h ) . S t a t u r e a n d r u m p l e n g t h (.91), rear u d d e r h e i g h t a n d rear u d d e r w i d t h (.89), b o d y d e p t h a n d r u m p l e n g t h (.78), s t a t u r e a n d b o d y d e p t h (.78), a n d fore u d d e r a t t a c h m e n t a n d Journal of Dairy Science Vol. 70, No. 5, 1987
1032
LAWSTUEN ET AL.
TABLE 5. Heritabilities of linear type traits and final score for age groups. 1 Thompson et al. (11) 2
2 yr
3 yr
Stature
32 (4)
35 (4)
Strength
22 (3)
Body depth Angularity
Trait
4 yr
5 yr
Aged
36 (4)
30 (4)
37 (6)
23 (7)
24 (3)
22 (3)
22 (3)
32 (5)
13 (5)
...3
35 (4)
28 (3)
25 (4)
38 (6)
18 (6)
16 (2)
33 (4)
26
27
23
23
(3)
(4)
(4)
(6)
Rump angle
17 (3)
23 (3)
24 (3)
27 (4)
29 (5)
25 (7)
Rump length
...3
15 (2)
20 (3)
21 (3)
21 (4)
14 (5)
Rump width
26 (3)
27 (4)
24 (3)
22 (3)
27 (5)
21 (6)
Rear legs side view
15 (2)
16 (2)
16 (2)
15 (3)
22 (4)
15 (5)
Foot angle
154 (2)
11 (2)
13 (2)
12 (2)
16 (3)
13 (5)
Fore udder attachment
15 (2)
15 (2)
16 (2)
15 (3)
14 (3)
9 (4)
Rear udder height
22 (3)
15 (2)
18 (2)
21 (3)
26 (5)
31 (8)
Rear udder width
15 (2)
18 (3)
12 (2)
15 (2)
19 (4)
18 (6)
Udder support
12 (2)
11 (2)
13 (2)
11 (2)
13 (3)
6 (4)
Udder depth
26 (3)
23 (3)
21 (3)
23 (3)
25 (5)
11 (4)
Teat placement
23 (3)
18 (3)
17 (2)
18 (3)
15 (3)
11 (4)
Final score
28 (3)
21 (3)
18 (2)
18 (3)
21 (4)
14 (5)
(%)
Approximate standard errors in parentheses. a Estimated across age groups from experimental project. 3 Experimental project (11) did not include body depth or rump length. 4 Heel depth.
u d d e r d e p t h (.77) all h a d g e n e t i c c o r r e l a t i o n s g r e a t e r t h a n .75. P h e n o t y p i c c o r r e l a t i o n s were similar to T h o m p s o n et al. (11), b u t g e n e t i c c o r r e l a t i o n s s o m e t i m e s differed. S t a t u r e a n d a n g u l a r i t y departed considerably (.36 versus - . 0 4 ) . Similarly, r u m p angle was positively c o r r e l a t e d Journal of Dairy Science Vol. 70, No. 5, 1987
w i t h m o s t traits, w h e r e a s T h o m p s o n et al. (11) f o u n d negative g e n e t i c c o r r e l a t i o n s . E n v i r o n m e n t a l c o r r e l a t i o n s ( T a b l e 7) usually were smaller t h a n c o r r e s p o n d i n g p h e n o t y p i c a n d g e n e t i c c o r r e l a t i o n s a n d were f r o m .67 (rear u d d e r h e i g h t a n d rear u d d e r w i d t h ) to --.20 ( r u m p angle a n d fore u d d e r a t t a c h m e n t ) .
LINEAR TYPE TRAITS FOR AGE GROUPS
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Strength and b o d y depth (.64) and stature and b o d y depth (.54) also had environmental correlations greater than .50. Rear legs side view and foot angle had correlations of - . 1 4 (phenotypic) and - . 3 9 (genetic), suggesting that cows with steep foot angles have straighter rear legs, which might be expected. Strength and b o d y depth were closely related phenotypically (.72) and genetically (.93) and had similar correlations with other traits• Association with angularity was the exception, because estimates were near zero for strength and moderately positive for b o d y depth. The high genetic correlation (.93) for strength and b o d y depth may indicate that many of the same genes affect these two traits. Udder traits had mutually close relationships. Rear udder height and rear udder width had a genetic correlation of .89 and may indicate another case where many of the same genes may be important for two traits. Genetic correlations were also substantial for fore udder attachment and udder depth (.77), udder support and teat placement (.70), fore udder attachment and teat placement (.59), fore udder attachment and udder support (.50), and udder support and udder depth (.47). Udder support is important to dairy producers so that udders do not become too deep and so that distance between front teats does not become too wide. Gain from scoring udder support is not obvious, however, because udder support (h 2 = .11) is essentially an indicator trait for two traits, udder depth (h 2 = .23) and teat placement (h 2 = .18), which are also scored and have higher heritabilities. Strongest genetic association of udder and nonudder traits was rear udder width and angularity (.42). This is not surprising because cows that look like they milk heavily should have fuller rear udders. Rump angle followed for genetic association with udder traits. Udders with strong fore udder attachments and that were shallow were associated genetically (.36 and .35) with sloping rumps. Udder depth was the udder trait most related to stature genetically (.29); taller cows have longer legs so that udders should be farther from the ground. Correlations with Final Score
The
first row (phenotypic) and column Journal of Dairy Science Vol. 70, No. 5, 1987
1034
LAWSTUEN ET AL.
k
I
(genetic) of Table 6 have correlations of individual type traits with final score. All correlations were positive except for two traits with intermediate optimums; rump angle ( - . 1 5 ) and rear legs side view ( - . 0 4 ) had negative phenotypic correlations with final score. Rear legs side view and final score were not related genetically (.00). Rear udder width (.52), rear udder height (.49), and fore udder attachment (.49) had greatest phenotypic association with final score. These traits also had most environmental relationship (Table 7) with final score (.49). Stature (.69), rump length (.68), rear udder width (.65), and body depth (.63) had largest genetic correlations with final score. The two traits with highest genetic correlations with final score for 2-yr-olds were stature (.69) and rump length (.68). Both these traits may be of questionable ecomomic benefit (6); yet sire groups of tall, long 2-yr-olds subjectively received higher final scores from classifiers. In addition to having substantial genetic association with rump length (.91), stature was closely related to strength (.70) and body depth (.78). Strength and body depth were also closely associated with rump length (.73 and .78) and rump width (.72 and .73). This indicates that tall, long 2-yr-olds receive high final scores and that they also are strong and deep and have wide rumps. Obviously, the question then arises: are these the proper traits to emphasize from 2-yr-olds for optimum lifetime performance?
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.< Journal of Dairy Science Vol. 70, No. 5, 1987
Sire and cow evaluations for type by the HA will be mostly from classifications of 2-yr-olds in the future. Estimates of heritability for linear type traits of 2-yr-olds were near (-+ .05) earlier estimates across ages except that angularity (.33) and rump angle (.23) were higher and rear udder height (.15) was lower. Heritabilities of 2-yr-olds from this study may be applicable for HA genetic evaluations of classifications closest to 30 mo. Some linear type traits for 2-yr-olds were very similar genetically. Examples were: 1) strength and body depth, 2) rear udder height and rear udder width, and 3) stature and rump length. Separate scoring for these pairs of traits may be of questionable benefit to dairy pro-
LINEAR TYPE TRAITS FOR AGE GROUPS ducers. F u r t h e r m o r e , scoring c o w s for u d d e r s u p p o r t , an i n d i c a t o r trait, m a y n o t be justified b e c a u s e d i r e c t selection for u d d e r d e p t h a n d t e a t p l a c e m e n t s h o u l d be m o r e successful. C o n s i d e r a b l e e m p h a s i s is placed u p o n s t a t u r e w h e n classifiers subjectively assign final score for 2-yr-olds. R e s e a r c h is n e e d e d to d e t e r m i n e t h e c o n t r i b u t i o n o f linear t y p e traits o f 2yr-olds t o d u r a b i l i t y and l i f e t i m e p e r f o r m a n c e o f cows. ACKNOWLEDGMENT
Data a n d financial s u p p o r t f r o m t h e H o l s t e i n A s s o c i a t i o n w e r e greatly a p p r e c i a t e d .
REFERENCES
1 Cassell, B. G., J. M. White, W. E. Vinson, and R. H. Kliewer. 1973. Genetic and phenotypic relationship among type traits in Holstein-Friesian cattle. J. Dairy Sci. 56:1171. 2 Hay, G. M., J. M. White, W. E. Vinson, and R. H. Kliewer. 1983. Components of genetic variation for descriptive type traits of Holsteins. J. Dairy Sci. 66:1962. 3 Henderson, C. R. 1953. Estimation of variance and covariance components. Biometrics 9: 226. 4 Holstein-Friesian Association of America. 1984.
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Journal of Dairy Science Vol. 70, No. 5, 1987