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The influence of relative birth weight and certain other factors on calving performance in Swedish dairy cattle breeds
Animal Reproduction Science, 15 (1987) 81-93
81
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
The Influence of R e l a t i v e Birth Weight and Certain Other Factors on Calving P e r f o r m a n c e in S w e d i s h D a i r y Cattle B r e e d s
BRITT BERGLUND and JAN PHILIPSSON
Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, S750 07 Uppsala (Sweden) (Accepted 21 April 1987 )
ABSTRACT Berglund, B. and Philipsson, J., 1987. The influence of relativebirth weight and certain other factorson calvingperformance in Swedish dairy cattlebreeds.Anita. Reprod. Sci., 15: 81-93. The influence of relativebirth weight and certain other factors on calving performance was investigated under controlled environmental conditions in the same herd over a 7-year period. Altogether 493 calvings from firstto sixth parity for 159 cows were included. The cows were of Swedish Friesianand Swedish Red and White breeds,a crossbredgroup between these two breeds, and of Jersey breed. Weight of calfexpressed as a percentage of the dam's weight justafter calving was the main cause of the breed differencesdemonstrated for calvingperformance. The dam's weight itselfdid not have much influenceon the calvingscorewhen effectsof breed, cow, parity,and sex of the calf were considered simultaneously. A curvilinearrelationshipwas shown between the birth weight of the calfand the dam's weight. Within breed, relativebirth weight increased with increasing gestationlength,which alsoincreasedthe riskof difficultcalving.The Jersey breed had no difficult calvings.Relative birth weights for Jersey were 1-1.5 percentage units lighterthan for the other breeds, while Friesiansand crosseswith thisbreed, which had the highest relativebirth weights, had most problems, especiallyat firstcalving.The frequency of attitudesof calves other than the anterior normal presentation was alsohighest for Friesiansat firstcalving.Relative birth weight decreased with increasingparity in allbreeds, due to a largerweight gain of dams compared with the calves.Calving performance was to some extent repeatable from firstto subsequent parturitions (range 0.08-0.13) but not to such an extent that any selectionof individualcows based on earlierresultswould be worthwhile. The corresponding values for gestationlength were 0.23-0.27. In general,repeatabilityestimates for birth weight were high and for relativebirth weight they ranged between 0.32 and 0.52.Signs of imminent calving (congestion of vulva and udder, relaxation of pelvicligaments) were of limitedpredictivevalue for calvingdifficulties.Various external body measurements (hip width, thurl width and rump length) were also of limited value in accounting for calvingdifficulties,especiallywhen birth weight was available.
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© 1987 Elsevier Science Publishers B.V.
82
INTRODUCTION In view of decreasing cow populations, larger herds and increasing labour costs, the importance of ease of calving and of liveborn calves increases. Extensive studies have therefore been undertaken and breeding programs have been developed for dairy breeds in order to reduce calf losses. Philipsson (1976a) studied calving traits and their implications in Swedish cattle of mainly Friesian breed in a large number of herds. In a recent crossbreeding experiment in Denmark ( Christensen et al., 1984) calving traits were examined for purebred Red Danish, Danish Friesian and Finnish Ayrshire and crosses between these breeds. A recent broad study of dystocia in dairy cattle, with particular attention to some causes of variation and sire evaluation methods for categorical traits, was recently published by Meijering {1986 ). Generally speaking, a substantial genetic variation in calving performance and stillbirth has been documented and the causes of problems at parturition relates to both maternal and calf factors, such as breed and parity of dam and sex and weight of calf. Heterosis seems to be positive for viability but less important for dystocia. Most of the studies referred to consisted of field recordings made under farm conditions on large populations. The accuracy of various measurements could vary a great deal under such circumstances and some parameters could even have been impossible to obtain. The present investigation was undertaken to study the entire parturition process in greater detail in the two principal dairy breeds in Sweden, Swedish Friesian (SLB) and Swedish Red and White (SRB), a crossbred group between these two breeds ( SRB × SLB), and in Jersey ( SJB ), under controlled environmental conditions. The cows were observed during repeated calvings over a 7-year period. In a previous study (Berglund et al., 1987), various signs of imminent calving and of the process of parturition were investigated. In the present study the intention was to study, in greater detail, certain factors affecting calving difficulty which could be related to variations found earlier, e.g. among breeds and parities, and to obtain estimates of the repeatability of calving difficulty. MATERIAL AND METHODS
Animals and registrations The data and animals used were the same as described in detail in Berglund et al. (1987). For each calving, a special calving report was used, containing information about age, weight, parity and breed of dam, breeding and calving dates, sire of calf, single or twin birth, extent of help needed at parturition, veterinary assistance, reason for assistance, sex, weight and presentation of calf, viability, congenital defects ( if any) and retained placenta.
83 Calving difficulty was given a numerical score based on the extent of assistance required. Dystocia scores were recorded as (1) easy calving (unobserved successful calving or unassisted), (2) normal calving (assistance of one person required), (3) difficult calving (assistance of more than one person required), and (4) very difficult calving (veterinary assistance required). The total number of parturitions in the four different classes are shown in Table 1. An attempt was made to allow sufficient time for animals to calve naturally prior to intervention. Veterinary assistance was sought when indicated. Guidelines for this procedure were described in Berglund et al. (1987). All parturitions that resulted in a twin birth or in a calf with visible congenital defects were omitted from the material. Gestation periods of less than 260 days were considered to lie outside of the normal range and were excluded. The cows were weighed after delivery of the placenta or else within 24 h. The cow's external body dimensions ( hip width, thurl width and rump length) were measured about 10 weeks after calving according to procedures described by Philipsson (1976c) and Meijering and Postma (1984). Calves were weighed within 12 h of birth. The relative birth weight was calculated as the proportion between the calf's birth weight and the dam's first weight after calving, expressed as a percentage. The attitudes of calves were recorded under ten different headings, but ultimately grouped into one of three clas~es: anterior normal presentation, posterior normal presentation, or other (presentations, positions or postures). Calves dead at birth or dying within 24 h of birth were considered stillborn and included in the material.
Statistical analysis Continuous traits ( gestation length, birth weight and relative birth weight) and categorical traits (calving difficulty score and attitude of calf) were analysed by Ordinary Least Squares (Harvey, 1977 ). On the assumption of a threshold model, theoretically more satisfactory procedures for categorical traits are available for estimation of variance components (Gianola, 1982; Gianola and Foulley, 1983). Ordinary least-squares procedures applied to linear models of visible scores are, however, often found to be robust and do result in unbiased estimates of fixed effects (Harvey, 1982). However, since calving difficulty was scored in four classes, an attempt was made to provide homogeneous residual variances over subclasses and normally distributed residual deviations. The scores for the whole material were then transformed as follows: by first obtaining the total frequency distribution of the scores, the percentages of records with the different score numbers were applied to a standard normal curve with mean zero and variance one. The heights of the ordinates at the centre of gravity of the areas below the curve corresponding to the cumulative percentage of the scores were then used as normalized scores. In order to obtain positive values only, a common value was
CaNing Normalized score difficulty (z of centre (first class score (raw score) of gravity) set to one)
L
I
:
~ /
1
- 0A.97
1.00
2
+ 0.868
2.37
3
+1,~27
2.92
/+
+2.585
~,.08
Fig. I. Normalizing calving difficulty scores.
added to each normalized score in such a way t h a t class I was given a value of 1, as illustrated in Fig. 1. Attitude of calf was treated as a 0, 1 variable in the analysis of variance, with the normal anterior presentation in the first group and all others grouped together in the second. Factors examined with respect to their effect on calving difficulty, gestation length, birth weight and attitude of calf, were breed, rearing intensity, cow (within breed), parity, sex of calf and season of birth. Relative birth weight was regarded mainly as an independent covariate, but also examined as a dependent variable. The statistical model selected was similar to t h a t in Berglund et al. (1987) as follows: Yijhlm = lt-f'bi + cij + P~ +st + e~jht,.
where Y ijklra = i j k l m t h observation on calving difficulty, gestation length, birth weight, relative birth weight and attitude of calf, respectively /~ = least-squares m e a n bi = fixed effect of ith breed, i = 1-5 cij = random effect o f j t h cow within ith breed with mean = 0 and variance Pk st
= fixed effect of kth parity, k = 1-4 = fixed effect o f / t h sex of calf, l = 1, 2 eijk~m = r a n d o m residual effect with m e a n = 0 and variance a~ In the model for attitude of calf, the interaction between breed and parity was also included. The model was further expanded to include relative birth weight within breed, or cow's weight within breed as independent covariates, as shown in Table 5. All factors and two-factor interactions not included in the final model were found in preliminary analyses to be non-significant (P>~ 0.10). To be able to
85 TABLE 1 Distribution of parturitions according to calving scores and stillbirths Calving score
Number of parturitions
Easy (1) Normal (2) Difficult (3) Very difficult (4)
Frequency (% )
345 98 37 13
70.0 19.9 7.5 2.6
Stillbirths (no.)
(%)
5 4 2 4
1.5 4.1 5.4 30.1
account for individual cow effects, those crossbred dams having progenies with both SRB and SLB sires, respectively, had to be coded as different individuals. RESULTS
AND DISCUSSION
The general frequency of difficult calving was 10.1% for the total material, while 3.0% of the calves were stillborn {Tables 1 and 2). The distribution of these problems by breeds and parities accord with earlier results based on larger populations of field data (Philipsson, 19765). The Jersey breed had no difficult calving (Table 2) among their 100 parturitions. As is well known, Jersey have a low birth weight. Their relative birth weight is, however, also lower compared to the other breeds (Table 3). Their relatively smaller size in relation to the size of dam might also be an explanation for the few malpositions in this breed. All Jersey calvings except one were in the normal anterior position. The more detailed results, distributed by breed and parity are given in Table TABLE2 Distribution of calving difficulty ( % scores 3 + 4) stillbirth ( % ) and abnormal attitude ( % ) according to breed and parity Breed
Parity
Total
1
2
3
>4
Calving difficulty
Stillbirth
Abnormal attitude a
SLB SRB SRB × SLB SJB
30.0 14.7 21.4 0.0
12.1 9.4 8.3 0.0
4.0 15.4 9.1 0.0
7.1 2.6 6.3 0.0
15.5 11.0 12.2 0.0
7.1 3.1 0.0 1.0
11.6 9.4 10.0 1.0
Total
17.0
8.1
8.4
3.3
10.1
3.0
8.3
~Includes posterior normal presentation.
86
TABLE 3 Overall means (2) and standard deviations ( S.D. ) for calving score, gestation length, birth weight and relative birth weight distributed according to parities and breeds Parity
Breed
n
Calving score
Gestation length
Birth weight
Relative birth
(days)
(kg)
weight (%)"
>4
S.D.
2
S.D.
2
S.D.
~
S.D.
SLB SRB (SRB X SLB) SLB ( SRB × SLB) SRB SJB
40 61 12 16 30
2.14 1.59 2.38 1.53 1.32
1.01 0.84 0.81 0.83 0.59
277.8 280.3 278.4 279.4 280.5
4.2 4.0 3.5 3.5 4.1
39.8 35.3 40.7 37.5 23.6
3.5 3.8 3.7 3.9 3.2
8.83 8.22 8.98 8.32 7.31
0.97 0.97 0.94 0.87 1.19
SLB SRB ( SRB × SLB ) SLB (SRB × SLB) SRB SJB
33 53 11 13 25
1.56 1.52 1.47 l.ll 1.05
0.85 0.74 0.82 0.38 0.27
280.0 283.6 281.1 282.7 280.8
4.4 4.3 4.2 4.1 3.0
44.7 39.6 44.2 39.5 24.5
4.9 4.0 6.8 3.7 2.7
8.60 8.30 8.88 7.80 6.89
1.07 0.96 1.28 0.95 0.88
SLB SRB (SRB× SLB) SLB (SRB × SLB) SRB SJB
25 39 -11 11 21
1.40 1.60 1.90 1.30 1.07
0.79 0.93 1.00 0.68 0.30
280.9 283.4 280.2 282.5 282.7
3.8 4.3 3.7 3.3 4.2
44.3 40.8 42.5 44.3 25.8
5.7 5.2 4.0 5.2 2.9
7.81 7.93 7.88 8.34 6.74
1.42 0.98 0.93 0.95 0.93
SLB SRB (SRB X SLB) SLB (SRB X SLB) SRB SJB
14 38 8 8 24
1.51 1.37 1.24 1.17 1.11
0.94 281.4 0 . 7 2 284.4 0.68 282.0 0.48 282.4 0.39 281.4
7.7 5.7 2.6 3.0 4.7
46.5 40.7 45.3 39.1 25.1
6.1 4.5 5.2 3.5 2.5
7.67 7.26 7.99 7.02 6.22
1.20 0.94 0.90 0.84 0.69
aRelative birth weight-- (weight of calf/weight of cow ) • 100. 3 for t h e t r a n s f o r m e d v a l u e s o f c a l v i n g score, g e s t a t i o n length, b i r t h w e i g h t a n d r e l a t i v e b i r t h weight. F o r all b r e e d s e x c e p t S J B , first g e s t a t i o n p e r i o d w a s on average 3 days shorter than second gestation period and, thereafter, minor c h a n g e s in l e n g t h s o c c u r r e d . B i r t h w e i g h t o f calves i n c r e a s e d p r e d o m i n a n t l y f r o m first t o s e c o n d c a l v i n g a n d in g e n e r a l t h e r e l a t i v e b i r t h w e i g h t d e c r e a s e d for all b r e e d s w i t h i n c r e a s i n g p a r i t y n u m b e r . R e s u l t s f r o m a n a l y s e s o f v a r i a n c e are p r e s e n t e d in T a b l e 4. T h e effect of breed, cow, p a r i t y , a n d sex o f c a l f w e r e h i g h l y s i g n i f i c a n t for all t h e s e traits. T h e 3 - 4 k g h e a v i e r c a l v e s a t l a t e r p a r i t i e s v i s - a - v i s t h e first w a s a p p a r e n t l y c o m p e n s a t e d b y a n e v e n l a r g e r r e l a t i v e w e i g h t g a i n of t h e d a m s , since t h e rela t i v e b i r t h w e i g h t d e c r e a s e d b y p a r i t y for all breeds. T h e s a m e f a c t o r s all af-
87 TABLE 4 Resultsof analysesofvariance of calvingscore, gestation length, birth weight,relativebirth weight and attitude of calf (model without covariates) Source of variation
d.f.
Meansquares for Calving score
Breed Cow Parity Sex of calf Breed X Parity Residualb Coefficientof determination¢
4 179 3 1 12
Gestation length
7.879*** 162.340"** 0.720** 25.689*** 2.031"* 248.423*** 3.715"* 147.791"** 0.507 23.4
Birth weight
Relative birth weighta
4235.895*** 24.896*** 485.565*** 615.885"**
33.865*** 1.565"** 16.317"** 25.521"**
14.234
11.494
33.8
82.6
0.584 60.7
Attitude of calf 0.220* 0.094*** 0.257** 0.018.... 0.044* 0.063 17.1
.... ( not significant) P> 0.05; *P < 0.05; **P < 0.01; ***P< 0.001. aRelativebirth weight = (weight of calf/weightof cow) • 100. bd.f. for residual for the variables were 305, 305,302, 300 and 293, respectively. ( n - tl ,, - -D2~j where n=the number of observations, CAdjustedfor degrees of freedom:R~= 1- 1____~) (n-p) p = the number of degrees of freedomin the model. fected attitude of calf, except t h a t sex of calf had no effect. However, the breed and parity interaction was significant in this case, due to the relatively high frequency of attitudes other t h a n the anterior normal presentation among firstcalving Friesians.
Effects of weight of dam and relative birth weight of calf In order to further investigate the causes of the differences found in calving performance between breeds and individual dams, the possible role of an interaction between the dam's weight at calving and the birth weight of the calf was analysed. T h e dam's weight in itself did not greatly influence the calving score, when effects of breed, cow, parity and sex of calf were considered simultaneously. As regards birth weight, the influence of dam weight was considerable. The effect was curvilinear for most breeds, with increasing birth weights with higher dam weights and slightly decreasing birth weights at the highest dam weights. From a comparison of results presented in Tables 4 and 5 it could be concluded t h a t weight of calf, expressed as a percentage of the dam's weight, significantly influenced the calving score and was the main cause of the breed difference demonstrated for calving performance. The mean square for breed dropped by nearly 80% when the relative birth weight was considered. Sex
88 TABLE 5 Results of analyses of variance of calving score, gestation length, birth weight and attitude of calf (model with covariates) Source of variation
d.f.
M e a n squares for Calving score
Breed Cow Parity Sex of calf Breed × Parity Relative birth weight lin. regr. within breed quadr, regr, within breed Weight of cow lin, regr. within breed quadr, regr. within breed Residual a Coefficient of determination b
4 179 3 1 12
1.631" 0.665** 1.519" 2.028*
Gestation length
Birth weight
35.905 .... 23,416"** 328.790*** 25.423 ....
35,806 .... 23.310"** 86.147"** 478.304***
Attitude of calf 0.112 .... 0.097*** 0.309** 0.045 .... 0.134"*
5
1.825
33.619
0.106 n-s-
5
1.996"**
29.894*
0,105 ....
195.149
5
12.830
36.633** 10.358
40.6
84.1
5 0.453 30.3
0.061 19.8
.... (not significant) P > 0.05; * P < 0.05; * * P < 0.01; ***P< 0.001. ad.f. for residual for the variables were 290, 290, 290 and 278, respectively. bAdjusted for degrees of freedom: R~ = 1 - ~( n - l )
'1 - R 2~~ where n = the number of observations, ~
p = the number of degrees of freedom in the model.
effects were also reduced considerably.The coefficient of determination for the model was increased from 23 to 30% by including the relative birth weight. At higher relative birth weights, a slight increase in calving difficulties occurred. At the lowest relativebirth weights, higher scores for calving difficulty were also obtained. This was especially so for both the crossbred groups. In the present study, the more difficult calvings at low relative birth weights could not, however, be attributed to stillborn calves, as there were no stillbirthsin the crossbred groups. Due to the limited numbers of animals in the crossbred groups, the shape of the curves n and especially in the tailends n is,however, more uncertain for these groups. These resultsare in agreement with the study by Pollak and Freeman (1976), where calf size was reported to be an important factor in calving difficulty.
89 TABLE 6 Estimates of cow (a~) and error (a~) variancesand repeatabilities (t) for calvingscores,gestation lengthbirth weightand relativebirth weightafter correctionfor breed,parity and sex of calf Parity
Calvingscore
Gestationlength
Birth weight
a~
a~
a~
a~
t
a~
t
a~
Relative birth weight t
a~
a~
t
1,2 0.060 0.556 0.10 3.857 12.447 0.24 0.314 24.002 0.01 4.928 4.544 0.52 2,3,>4 0.030 0.480 0.06 5.408 14.439 0.27 6.942 18.776 0.27 1.874 3.918 0.32 1,2,3, >4 0.079 0.506 0.13 4.309 14.234 0.23 3.542 24.214 0.13 2.516 4.923 0.34 However, size of dam was not an important factor, although it did affect the size of the calf. The duration of gestation was affected when taking into account the relative birth weight within breed too. When considering the relative birth weight, significant effects of breed or sex of calf could no longer be found. However, individual cow effects remained largely unaffected, whereas parity effects increased. The latter phenomenon means that the within-breed effects are such that the relative birth weight increases with longer gestation periods. At constant relative birth weights, the difference in gestation length between parities is accentuated. The slight curvilinearity for relative birth weight in relation to gestation length might have been due partly to factors such as wrong estrous period given for pregnancy, or to a real change in the proportional increase in live weight between calf and dam relative to gestation length. A non-linear relationship between birth weight (in absolute terms) and gestation length was reported by Burfening et al. (1978). As gestation lengthened, birth weight increased, at a decreasing rate.
Repeatability of calving traits Since calvings were recorded repeatedly for the same dams, it was possible to estimate the repeatability of calving traits as dam traits. The results are shown in Table 6. For calving score the repeatability between first and second calving was estimated as 0.10, among cow calvings 0.06 and for all parturitions 0.13. The corresponding values for gestation length ranged between 0.23 and 0.27. As heritabilities for later lactations are lower, repeatabilities would also be expected to be lower for later lactations. The estimates of repeatability in the present study are in agreement with Thompson and Rege (1984) where repeatabilities of calving difficulty score between first and second parity were 0.16, at second and subsequent parities, 0.10 and for all calvings, 0.14. The values for gestation length also agree with other studies on beef breeds and
Anterior normal presentation Posterior normal presentation Other presentations, positions or postures % Posterior normal and other
Attitude of calf
11
8
9.4
7
5
11.6
173
SRB
99
SLB
Breed
16.7
4
3
35
(SRB× SLB) SLB
4.2
--
2
46
(SRB× SLB) SRB
1.0
11.9
7
12
1
--
140
1
99
SJB
Parity
5.9
6
2
127
2
7.5
6
2
99
3
6.5
4
2
86
>4
40.5
39.5
42.6
16.7
39.1
3.7
4.7
(2)
4.8
6.5
5.4
(S.D.)
% Birth weight veterinary (kg) (all assistance breeds except SJB)
0.2
91.7
% ofall attitudes
8.7
8.2
8.1
1.1
1.3
1.1
Relative birth weight (kg) (all breeds except SJB) (2) (S.D.)
Frequencies and percentages of various attitudes of calves, average percentage of veterinary assistance and average birth weights in attitude classes, distributed by breeds and parity
TABLE 7
91 dairy cows (Bourdon and Brinks, 1982; Polastre et al., 1982). Thus calving performance is to some extent repeatable from first to later parturitions, but not to an extent that any selection of individual cows based on earlier results would be worthwhile. The repeatability of birth weight from first to second calving was unexpectedly low. This was due to a low component of variance between cows. For second and higher calving numbers, a more reasonable repeatability was obtained (r= 0.27) which agrees with repeatability estimates of birth weight reported by Woldehawariat et al. (1977) r=0.27, and Bourdon and Brinks (1982) r--0.22. Repeatability estimates for relative birth weight were rather high, ranging from 0.32 to 0.52. Here the highest value was obtained for first to second calvers. The very low repeatability estimate for birth weight itself for these calving numbers might therefore have been due to a variation in the growth of the dams after first calving.
Signs of imminent calving The results of the same study on the value of various signs of imminent calving for prediction of the time of parturition indicated that a few signs are of importance. The time interval from first determination of a specific sign, to expulsion of the calf was in this study also related to the calving score. However, significant effects were found only for the sign "udder highly distended". A curvilinear relationship was obtained which increased the R 2 value of the model by 4 percentage units.
Attitude of calves An abnormal attitude of the calf is a well documented cause of dystocia. In Table 7 it is shown that an abnormal attitude {including posterior normal presentation) is about twice as common among heifers as among cows. There is a tendency for calves with other abnormal attitudes than a posterior presentation to be rather heavier and have a higher relative birth weight. Friesians and crosses with this breed showed the highest frequency of abnormal attitudes.
Body dimensions of dam In order to study the relationship between dystocia and external body measurements of dam, multiple regressions on the various body measurements of the animal were included in the basic model for dystocia. The analyses were performed for heifers separately and for the whole material, with exclusion of Jerseys as an alternative. The regressions were non-significant, with very small changes in the coefficient of determination by including the body measure-
92
ment covariates. Partial correlations (adjusted for breed, cow, parity and sex of calf) between the body measurements of dams and the score for calving difficulty were also studied. Correlations between calving score and hip width, rump length, thurl width and a ratio of hip width to thurl width did not differ significantly from zero. However, a larger hip width and a larger ratio between hip width and thurl width tended to increase the score for calving difficulty (r=0.21 and r=0.19, respectively). The findings are consistent with results in previous studies on primiparous cows, where simply measurable dam traits such as body weight and body dimensions only have proved to be weakly associated with calving ease (e.g. Hansen, 1975; Hissig and Schlote, 1979; Meijering and Postma, 1984). Simply measurable calf dimensions have also been shown to have limited value when birth weight is obtainable (e.g. Meijering and Postma, 1984). CONCLUSIONS
Large breed differences in calving performance were evident, with Jersey being one extreme and Friesians (purebred and crosses) being the other extreme. Jersey had no difficulties in calving, while Friesians and the crossbred group mated with Friesians had most problems, especially at first calving. This seemed to have been caused mainly by their relatively large calves, with frequent attitudes other than the anterior normal presentation.
REFERENCES Berglund, B., Philipsson,J. and Danell, 0., 1987. External signs of preparation for calving and course of parturitionin Swedish dairy cattlebreeds.Anita. Reprod. Sci.,15: 61-79. Bourdon, R.M. and Brinks,J.S.,1982.Genetic,environmental and phenotypic relationshipsamong gestationlength,birthweight, growth traitsand age at firstcalvingin beef cattle.J. Anim. Sci., 55: 543-553. Burfening, P.J.,Kress, D.D., Friedrich,R.L. and Vaniman, D.D., 1978. Phenotypic and genetic relationshipsbetween calving ease, gestationlength,birth weight and preweaning growth. J. Anita. Sci.,47: 595-600. Christensen, L.G., Barlow, R. and Neimann-S~rensen, A., 1984. Crossbreeding Red Danish, Holstein-Friesianand Finnish Ayrshire Cattle.Performance of foundation females and traitsof foundation and first-generationcalves.Acta Agric. Scand., 34: 463-479. Gianola, D., 1982. Theory and analysisof threshold characters.J. Anim. Sci.,54" 1079-1096. Gianola, D. and Foulley,J.L., 1983. Sire evaluation for ordered categoricaldata with a threshold model. Gdn~t. S~l.Evol.,15: 201-223. Hansen, M., 1975. Calving performance in Danish breeds of dual purpose cattle.Livest.Prod. Sci., 2: 51-58. Harvey, W.R., 1977. User's Guide for LSML76. Mixed model least-squaresand maximum likelihood computer program. Ohio State University,Columbus, OH, 76 pp. Harvey, W.R., 1982. Least-squaresanalysisof discretedata. J. Anita. Sci.,54: 1067-1071.
93 H~ssig, H. and Schlote,W., 1979.Untersuchungen zum Geburtsverlaufbei Fleckviehf~-sen.Ziichtungskunde, 51: 275-288. Meijering,A., 1986. Dystocia in dairy cattlebreeding with specialattentionto sireevaluationfor categoricaltraits.Thesis, Agric. Univ. Wageningen, 179 pp. Meijering, A. and Postma, A., 1984. Morphologic aspects of dystocia in dairy and dual purpose heifers.Can. J. Anita. Sci.,64: 551-562. Philipsson,J., 1976a. Studies on calving difficulty,stillbirthand associatedfactorsin Swedish cattlebreeds.Thesis, Agric. Univ. Uppsala. Philipsson,J., 1976b. Studies on calving difficulty,stillbirthand associatedfactorsin Swedish cattlebreeds.General introductionand breed averages.Acta Agric. Scand., 26: 151-164. Philipsson,J., 1976c. Studies on calving difficulty,stillbirthand associatedfactorsin Swedish cattlebreeds.IV. Relationshipsbetween calvingperformance, precalvingbody measurements and sizeof pelvic opening in Friesianheifers.Acta Agric. Scand., 26:221-229. Polastre,R., Villares,J.B. and Ramos, A., de A., 1982. Par~metros gen~ticose fatoresambientais relacionados corn a dura~o da gesta~o na rata Jersey. (Genetic and environmental factors affectinggestationlength in Jerseys.) Rev. Soc. Bras. Zootec.,11: 668-680. Pollak, E.J. and Freeman, A.E., 1976. Parameter estimation and sireevaluationfor dystociaand calfsizein Holsteins.J. Dairy Sci.,59: 1817-1824. Thompson, J.R. and Rege, J.E.O., 1984. Influence of dam on calving difficultyand early calf mortality.J. Dairy Sci.,67: 847-853. Woldehawariat, G., Talamantes, M.A., Petty, R.R., Jr. and Cartwright,T.C., 1977. A summary of genetic and environmental statisticsf6r growth and conformation characters in young beef cattle,2nd Edn. Texas Agric. Exp. Stn.,Dep. Tech. Rep., No. 103.
81
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
The Influence of R e l a t i v e Birth Weight and Certain Other Factors on Calving P e r f o r m a n c e in S w e d i s h D a i r y Cattle B r e e d s
BRITT BERGLUND and JAN PHILIPSSON
Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, S750 07 Uppsala (Sweden) (Accepted 21 April 1987 )
ABSTRACT Berglund, B. and Philipsson, J., 1987. The influence of relativebirth weight and certain other factorson calvingperformance in Swedish dairy cattlebreeds.Anita. Reprod. Sci., 15: 81-93. The influence of relativebirth weight and certain other factors on calving performance was investigated under controlled environmental conditions in the same herd over a 7-year period. Altogether 493 calvings from firstto sixth parity for 159 cows were included. The cows were of Swedish Friesianand Swedish Red and White breeds,a crossbredgroup between these two breeds, and of Jersey breed. Weight of calfexpressed as a percentage of the dam's weight justafter calving was the main cause of the breed differencesdemonstrated for calvingperformance. The dam's weight itselfdid not have much influenceon the calvingscorewhen effectsof breed, cow, parity,and sex of the calf were considered simultaneously. A curvilinearrelationshipwas shown between the birth weight of the calfand the dam's weight. Within breed, relativebirth weight increased with increasing gestationlength,which alsoincreasedthe riskof difficultcalving.The Jersey breed had no difficult calvings.Relative birth weights for Jersey were 1-1.5 percentage units lighterthan for the other breeds, while Friesiansand crosseswith thisbreed, which had the highest relativebirth weights, had most problems, especiallyat firstcalving.The frequency of attitudesof calves other than the anterior normal presentation was alsohighest for Friesiansat firstcalving.Relative birth weight decreased with increasingparity in allbreeds, due to a largerweight gain of dams compared with the calves.Calving performance was to some extent repeatable from firstto subsequent parturitions (range 0.08-0.13) but not to such an extent that any selectionof individualcows based on earlierresultswould be worthwhile. The corresponding values for gestationlength were 0.23-0.27. In general,repeatabilityestimates for birth weight were high and for relativebirth weight they ranged between 0.32 and 0.52.Signs of imminent calving (congestion of vulva and udder, relaxation of pelvicligaments) were of limitedpredictivevalue for calvingdifficulties.Various external body measurements (hip width, thurl width and rump length) were also of limited value in accounting for calvingdifficulties,especiallywhen birth weight was available.
0378-4320/87/$03.50
© 1987 Elsevier Science Publishers B.V.
82
INTRODUCTION In view of decreasing cow populations, larger herds and increasing labour costs, the importance of ease of calving and of liveborn calves increases. Extensive studies have therefore been undertaken and breeding programs have been developed for dairy breeds in order to reduce calf losses. Philipsson (1976a) studied calving traits and their implications in Swedish cattle of mainly Friesian breed in a large number of herds. In a recent crossbreeding experiment in Denmark ( Christensen et al., 1984) calving traits were examined for purebred Red Danish, Danish Friesian and Finnish Ayrshire and crosses between these breeds. A recent broad study of dystocia in dairy cattle, with particular attention to some causes of variation and sire evaluation methods for categorical traits, was recently published by Meijering {1986 ). Generally speaking, a substantial genetic variation in calving performance and stillbirth has been documented and the causes of problems at parturition relates to both maternal and calf factors, such as breed and parity of dam and sex and weight of calf. Heterosis seems to be positive for viability but less important for dystocia. Most of the studies referred to consisted of field recordings made under farm conditions on large populations. The accuracy of various measurements could vary a great deal under such circumstances and some parameters could even have been impossible to obtain. The present investigation was undertaken to study the entire parturition process in greater detail in the two principal dairy breeds in Sweden, Swedish Friesian (SLB) and Swedish Red and White (SRB), a crossbred group between these two breeds ( SRB × SLB), and in Jersey ( SJB ), under controlled environmental conditions. The cows were observed during repeated calvings over a 7-year period. In a previous study (Berglund et al., 1987), various signs of imminent calving and of the process of parturition were investigated. In the present study the intention was to study, in greater detail, certain factors affecting calving difficulty which could be related to variations found earlier, e.g. among breeds and parities, and to obtain estimates of the repeatability of calving difficulty. MATERIAL AND METHODS
Animals and registrations The data and animals used were the same as described in detail in Berglund et al. (1987). For each calving, a special calving report was used, containing information about age, weight, parity and breed of dam, breeding and calving dates, sire of calf, single or twin birth, extent of help needed at parturition, veterinary assistance, reason for assistance, sex, weight and presentation of calf, viability, congenital defects ( if any) and retained placenta.
83 Calving difficulty was given a numerical score based on the extent of assistance required. Dystocia scores were recorded as (1) easy calving (unobserved successful calving or unassisted), (2) normal calving (assistance of one person required), (3) difficult calving (assistance of more than one person required), and (4) very difficult calving (veterinary assistance required). The total number of parturitions in the four different classes are shown in Table 1. An attempt was made to allow sufficient time for animals to calve naturally prior to intervention. Veterinary assistance was sought when indicated. Guidelines for this procedure were described in Berglund et al. (1987). All parturitions that resulted in a twin birth or in a calf with visible congenital defects were omitted from the material. Gestation periods of less than 260 days were considered to lie outside of the normal range and were excluded. The cows were weighed after delivery of the placenta or else within 24 h. The cow's external body dimensions ( hip width, thurl width and rump length) were measured about 10 weeks after calving according to procedures described by Philipsson (1976c) and Meijering and Postma (1984). Calves were weighed within 12 h of birth. The relative birth weight was calculated as the proportion between the calf's birth weight and the dam's first weight after calving, expressed as a percentage. The attitudes of calves were recorded under ten different headings, but ultimately grouped into one of three clas~es: anterior normal presentation, posterior normal presentation, or other (presentations, positions or postures). Calves dead at birth or dying within 24 h of birth were considered stillborn and included in the material.
Statistical analysis Continuous traits ( gestation length, birth weight and relative birth weight) and categorical traits (calving difficulty score and attitude of calf) were analysed by Ordinary Least Squares (Harvey, 1977 ). On the assumption of a threshold model, theoretically more satisfactory procedures for categorical traits are available for estimation of variance components (Gianola, 1982; Gianola and Foulley, 1983). Ordinary least-squares procedures applied to linear models of visible scores are, however, often found to be robust and do result in unbiased estimates of fixed effects (Harvey, 1982). However, since calving difficulty was scored in four classes, an attempt was made to provide homogeneous residual variances over subclasses and normally distributed residual deviations. The scores for the whole material were then transformed as follows: by first obtaining the total frequency distribution of the scores, the percentages of records with the different score numbers were applied to a standard normal curve with mean zero and variance one. The heights of the ordinates at the centre of gravity of the areas below the curve corresponding to the cumulative percentage of the scores were then used as normalized scores. In order to obtain positive values only, a common value was
CaNing Normalized score difficulty (z of centre (first class score (raw score) of gravity) set to one)
L
I
:
~ /
1
- 0A.97
1.00
2
+ 0.868
2.37
3
+1,~27
2.92
/+
+2.585
~,.08
Fig. I. Normalizing calving difficulty scores.
added to each normalized score in such a way t h a t class I was given a value of 1, as illustrated in Fig. 1. Attitude of calf was treated as a 0, 1 variable in the analysis of variance, with the normal anterior presentation in the first group and all others grouped together in the second. Factors examined with respect to their effect on calving difficulty, gestation length, birth weight and attitude of calf, were breed, rearing intensity, cow (within breed), parity, sex of calf and season of birth. Relative birth weight was regarded mainly as an independent covariate, but also examined as a dependent variable. The statistical model selected was similar to t h a t in Berglund et al. (1987) as follows: Yijhlm = lt-f'bi + cij + P~ +st + e~jht,.
where Y ijklra = i j k l m t h observation on calving difficulty, gestation length, birth weight, relative birth weight and attitude of calf, respectively /~ = least-squares m e a n bi = fixed effect of ith breed, i = 1-5 cij = random effect o f j t h cow within ith breed with mean = 0 and variance Pk st
= fixed effect of kth parity, k = 1-4 = fixed effect o f / t h sex of calf, l = 1, 2 eijk~m = r a n d o m residual effect with m e a n = 0 and variance a~ In the model for attitude of calf, the interaction between breed and parity was also included. The model was further expanded to include relative birth weight within breed, or cow's weight within breed as independent covariates, as shown in Table 5. All factors and two-factor interactions not included in the final model were found in preliminary analyses to be non-significant (P>~ 0.10). To be able to
85 TABLE 1 Distribution of parturitions according to calving scores and stillbirths Calving score
Number of parturitions
Easy (1) Normal (2) Difficult (3) Very difficult (4)
Frequency (% )
345 98 37 13
70.0 19.9 7.5 2.6
Stillbirths (no.)
(%)
5 4 2 4
1.5 4.1 5.4 30.1
account for individual cow effects, those crossbred dams having progenies with both SRB and SLB sires, respectively, had to be coded as different individuals. RESULTS
AND DISCUSSION
The general frequency of difficult calving was 10.1% for the total material, while 3.0% of the calves were stillborn {Tables 1 and 2). The distribution of these problems by breeds and parities accord with earlier results based on larger populations of field data (Philipsson, 19765). The Jersey breed had no difficult calving (Table 2) among their 100 parturitions. As is well known, Jersey have a low birth weight. Their relative birth weight is, however, also lower compared to the other breeds (Table 3). Their relatively smaller size in relation to the size of dam might also be an explanation for the few malpositions in this breed. All Jersey calvings except one were in the normal anterior position. The more detailed results, distributed by breed and parity are given in Table TABLE2 Distribution of calving difficulty ( % scores 3 + 4) stillbirth ( % ) and abnormal attitude ( % ) according to breed and parity Breed
Parity
Total
1
2
3
>4
Calving difficulty
Stillbirth
Abnormal attitude a
SLB SRB SRB × SLB SJB
30.0 14.7 21.4 0.0
12.1 9.4 8.3 0.0
4.0 15.4 9.1 0.0
7.1 2.6 6.3 0.0
15.5 11.0 12.2 0.0
7.1 3.1 0.0 1.0
11.6 9.4 10.0 1.0
Total
17.0
8.1
8.4
3.3
10.1
3.0
8.3
~Includes posterior normal presentation.
86
TABLE 3 Overall means (2) and standard deviations ( S.D. ) for calving score, gestation length, birth weight and relative birth weight distributed according to parities and breeds Parity
Breed
n
Calving score
Gestation length
Birth weight
Relative birth
(days)
(kg)
weight (%)"
>4
S.D.
2
S.D.
2
S.D.
~
S.D.
SLB SRB (SRB X SLB) SLB ( SRB × SLB) SRB SJB
40 61 12 16 30
2.14 1.59 2.38 1.53 1.32
1.01 0.84 0.81 0.83 0.59
277.8 280.3 278.4 279.4 280.5
4.2 4.0 3.5 3.5 4.1
39.8 35.3 40.7 37.5 23.6
3.5 3.8 3.7 3.9 3.2
8.83 8.22 8.98 8.32 7.31
0.97 0.97 0.94 0.87 1.19
SLB SRB ( SRB × SLB ) SLB (SRB × SLB) SRB SJB
33 53 11 13 25
1.56 1.52 1.47 l.ll 1.05
0.85 0.74 0.82 0.38 0.27
280.0 283.6 281.1 282.7 280.8
4.4 4.3 4.2 4.1 3.0
44.7 39.6 44.2 39.5 24.5
4.9 4.0 6.8 3.7 2.7
8.60 8.30 8.88 7.80 6.89
1.07 0.96 1.28 0.95 0.88
SLB SRB (SRB× SLB) SLB (SRB × SLB) SRB SJB
25 39 -11 11 21
1.40 1.60 1.90 1.30 1.07
0.79 0.93 1.00 0.68 0.30
280.9 283.4 280.2 282.5 282.7
3.8 4.3 3.7 3.3 4.2
44.3 40.8 42.5 44.3 25.8
5.7 5.2 4.0 5.2 2.9
7.81 7.93 7.88 8.34 6.74
1.42 0.98 0.93 0.95 0.93
SLB SRB (SRB X SLB) SLB (SRB X SLB) SRB SJB
14 38 8 8 24
1.51 1.37 1.24 1.17 1.11
0.94 281.4 0 . 7 2 284.4 0.68 282.0 0.48 282.4 0.39 281.4
7.7 5.7 2.6 3.0 4.7
46.5 40.7 45.3 39.1 25.1
6.1 4.5 5.2 3.5 2.5
7.67 7.26 7.99 7.02 6.22
1.20 0.94 0.90 0.84 0.69
aRelative birth weight-- (weight of calf/weight of cow ) • 100. 3 for t h e t r a n s f o r m e d v a l u e s o f c a l v i n g score, g e s t a t i o n length, b i r t h w e i g h t a n d r e l a t i v e b i r t h weight. F o r all b r e e d s e x c e p t S J B , first g e s t a t i o n p e r i o d w a s on average 3 days shorter than second gestation period and, thereafter, minor c h a n g e s in l e n g t h s o c c u r r e d . B i r t h w e i g h t o f calves i n c r e a s e d p r e d o m i n a n t l y f r o m first t o s e c o n d c a l v i n g a n d in g e n e r a l t h e r e l a t i v e b i r t h w e i g h t d e c r e a s e d for all b r e e d s w i t h i n c r e a s i n g p a r i t y n u m b e r . R e s u l t s f r o m a n a l y s e s o f v a r i a n c e are p r e s e n t e d in T a b l e 4. T h e effect of breed, cow, p a r i t y , a n d sex o f c a l f w e r e h i g h l y s i g n i f i c a n t for all t h e s e traits. T h e 3 - 4 k g h e a v i e r c a l v e s a t l a t e r p a r i t i e s v i s - a - v i s t h e first w a s a p p a r e n t l y c o m p e n s a t e d b y a n e v e n l a r g e r r e l a t i v e w e i g h t g a i n of t h e d a m s , since t h e rela t i v e b i r t h w e i g h t d e c r e a s e d b y p a r i t y for all breeds. T h e s a m e f a c t o r s all af-
87 TABLE 4 Resultsof analysesofvariance of calvingscore, gestation length, birth weight,relativebirth weight and attitude of calf (model without covariates) Source of variation
d.f.
Meansquares for Calving score
Breed Cow Parity Sex of calf Breed X Parity Residualb Coefficientof determination¢
4 179 3 1 12
Gestation length
7.879*** 162.340"** 0.720** 25.689*** 2.031"* 248.423*** 3.715"* 147.791"** 0.507 23.4
Birth weight
Relative birth weighta
4235.895*** 24.896*** 485.565*** 615.885"**
33.865*** 1.565"** 16.317"** 25.521"**
14.234
11.494
33.8
82.6
0.584 60.7
Attitude of calf 0.220* 0.094*** 0.257** 0.018.... 0.044* 0.063 17.1
.... ( not significant) P> 0.05; *P < 0.05; **P < 0.01; ***P< 0.001. aRelativebirth weight = (weight of calf/weightof cow) • 100. bd.f. for residual for the variables were 305, 305,302, 300 and 293, respectively. ( n - tl ,, - -D2~j where n=the number of observations, CAdjustedfor degrees of freedom:R~= 1- 1____~) (n-p) p = the number of degrees of freedomin the model. fected attitude of calf, except t h a t sex of calf had no effect. However, the breed and parity interaction was significant in this case, due to the relatively high frequency of attitudes other t h a n the anterior normal presentation among firstcalving Friesians.
Effects of weight of dam and relative birth weight of calf In order to further investigate the causes of the differences found in calving performance between breeds and individual dams, the possible role of an interaction between the dam's weight at calving and the birth weight of the calf was analysed. T h e dam's weight in itself did not greatly influence the calving score, when effects of breed, cow, parity and sex of calf were considered simultaneously. As regards birth weight, the influence of dam weight was considerable. The effect was curvilinear for most breeds, with increasing birth weights with higher dam weights and slightly decreasing birth weights at the highest dam weights. From a comparison of results presented in Tables 4 and 5 it could be concluded t h a t weight of calf, expressed as a percentage of the dam's weight, significantly influenced the calving score and was the main cause of the breed difference demonstrated for calving performance. The mean square for breed dropped by nearly 80% when the relative birth weight was considered. Sex
88 TABLE 5 Results of analyses of variance of calving score, gestation length, birth weight and attitude of calf (model with covariates) Source of variation
d.f.
M e a n squares for Calving score
Breed Cow Parity Sex of calf Breed × Parity Relative birth weight lin. regr. within breed quadr, regr, within breed Weight of cow lin, regr. within breed quadr, regr. within breed Residual a Coefficient of determination b
4 179 3 1 12
1.631" 0.665** 1.519" 2.028*
Gestation length
Birth weight
35.905 .... 23,416"** 328.790*** 25.423 ....
35,806 .... 23.310"** 86.147"** 478.304***
Attitude of calf 0.112 .... 0.097*** 0.309** 0.045 .... 0.134"*
5
1.825
33.619
0.106 n-s-
5
1.996"**
29.894*
0,105 ....
195.149
5
12.830
36.633** 10.358
40.6
84.1
5 0.453 30.3
0.061 19.8
.... (not significant) P > 0.05; * P < 0.05; * * P < 0.01; ***P< 0.001. ad.f. for residual for the variables were 290, 290, 290 and 278, respectively. bAdjusted for degrees of freedom: R~ = 1 - ~( n - l )
'1 - R 2~~ where n = the number of observations, ~
p = the number of degrees of freedom in the model.
effects were also reduced considerably.The coefficient of determination for the model was increased from 23 to 30% by including the relative birth weight. At higher relative birth weights, a slight increase in calving difficulties occurred. At the lowest relativebirth weights, higher scores for calving difficulty were also obtained. This was especially so for both the crossbred groups. In the present study, the more difficult calvings at low relative birth weights could not, however, be attributed to stillborn calves, as there were no stillbirthsin the crossbred groups. Due to the limited numbers of animals in the crossbred groups, the shape of the curves n and especially in the tailends n is,however, more uncertain for these groups. These resultsare in agreement with the study by Pollak and Freeman (1976), where calf size was reported to be an important factor in calving difficulty.
89 TABLE 6 Estimates of cow (a~) and error (a~) variancesand repeatabilities (t) for calvingscores,gestation lengthbirth weightand relativebirth weightafter correctionfor breed,parity and sex of calf Parity
Calvingscore
Gestationlength
Birth weight
a~
a~
a~
a~
t
a~
t
a~
Relative birth weight t
a~
a~
t
1,2 0.060 0.556 0.10 3.857 12.447 0.24 0.314 24.002 0.01 4.928 4.544 0.52 2,3,>4 0.030 0.480 0.06 5.408 14.439 0.27 6.942 18.776 0.27 1.874 3.918 0.32 1,2,3, >4 0.079 0.506 0.13 4.309 14.234 0.23 3.542 24.214 0.13 2.516 4.923 0.34 However, size of dam was not an important factor, although it did affect the size of the calf. The duration of gestation was affected when taking into account the relative birth weight within breed too. When considering the relative birth weight, significant effects of breed or sex of calf could no longer be found. However, individual cow effects remained largely unaffected, whereas parity effects increased. The latter phenomenon means that the within-breed effects are such that the relative birth weight increases with longer gestation periods. At constant relative birth weights, the difference in gestation length between parities is accentuated. The slight curvilinearity for relative birth weight in relation to gestation length might have been due partly to factors such as wrong estrous period given for pregnancy, or to a real change in the proportional increase in live weight between calf and dam relative to gestation length. A non-linear relationship between birth weight (in absolute terms) and gestation length was reported by Burfening et al. (1978). As gestation lengthened, birth weight increased, at a decreasing rate.
Repeatability of calving traits Since calvings were recorded repeatedly for the same dams, it was possible to estimate the repeatability of calving traits as dam traits. The results are shown in Table 6. For calving score the repeatability between first and second calving was estimated as 0.10, among cow calvings 0.06 and for all parturitions 0.13. The corresponding values for gestation length ranged between 0.23 and 0.27. As heritabilities for later lactations are lower, repeatabilities would also be expected to be lower for later lactations. The estimates of repeatability in the present study are in agreement with Thompson and Rege (1984) where repeatabilities of calving difficulty score between first and second parity were 0.16, at second and subsequent parities, 0.10 and for all calvings, 0.14. The values for gestation length also agree with other studies on beef breeds and
Anterior normal presentation Posterior normal presentation Other presentations, positions or postures % Posterior normal and other
Attitude of calf
11
8
9.4
7
5
11.6
173
SRB
99
SLB
Breed
16.7
4
3
35
(SRB× SLB) SLB
4.2
--
2
46
(SRB× SLB) SRB
1.0
11.9
7
12
1
--
140
1
99
SJB
Parity
5.9
6
2
127
2
7.5
6
2
99
3
6.5
4
2
86
>4
40.5
39.5
42.6
16.7
39.1
3.7
4.7
(2)
4.8
6.5
5.4
(S.D.)
% Birth weight veterinary (kg) (all assistance breeds except SJB)
0.2
91.7
% ofall attitudes
8.7
8.2
8.1
1.1
1.3
1.1
Relative birth weight (kg) (all breeds except SJB) (2) (S.D.)
Frequencies and percentages of various attitudes of calves, average percentage of veterinary assistance and average birth weights in attitude classes, distributed by breeds and parity
TABLE 7
91 dairy cows (Bourdon and Brinks, 1982; Polastre et al., 1982). Thus calving performance is to some extent repeatable from first to later parturitions, but not to an extent that any selection of individual cows based on earlier results would be worthwhile. The repeatability of birth weight from first to second calving was unexpectedly low. This was due to a low component of variance between cows. For second and higher calving numbers, a more reasonable repeatability was obtained (r= 0.27) which agrees with repeatability estimates of birth weight reported by Woldehawariat et al. (1977) r=0.27, and Bourdon and Brinks (1982) r--0.22. Repeatability estimates for relative birth weight were rather high, ranging from 0.32 to 0.52. Here the highest value was obtained for first to second calvers. The very low repeatability estimate for birth weight itself for these calving numbers might therefore have been due to a variation in the growth of the dams after first calving.
Signs of imminent calving The results of the same study on the value of various signs of imminent calving for prediction of the time of parturition indicated that a few signs are of importance. The time interval from first determination of a specific sign, to expulsion of the calf was in this study also related to the calving score. However, significant effects were found only for the sign "udder highly distended". A curvilinear relationship was obtained which increased the R 2 value of the model by 4 percentage units.
Attitude of calves An abnormal attitude of the calf is a well documented cause of dystocia. In Table 7 it is shown that an abnormal attitude {including posterior normal presentation) is about twice as common among heifers as among cows. There is a tendency for calves with other abnormal attitudes than a posterior presentation to be rather heavier and have a higher relative birth weight. Friesians and crosses with this breed showed the highest frequency of abnormal attitudes.
Body dimensions of dam In order to study the relationship between dystocia and external body measurements of dam, multiple regressions on the various body measurements of the animal were included in the basic model for dystocia. The analyses were performed for heifers separately and for the whole material, with exclusion of Jerseys as an alternative. The regressions were non-significant, with very small changes in the coefficient of determination by including the body measure-
92
ment covariates. Partial correlations (adjusted for breed, cow, parity and sex of calf) between the body measurements of dams and the score for calving difficulty were also studied. Correlations between calving score and hip width, rump length, thurl width and a ratio of hip width to thurl width did not differ significantly from zero. However, a larger hip width and a larger ratio between hip width and thurl width tended to increase the score for calving difficulty (r=0.21 and r=0.19, respectively). The findings are consistent with results in previous studies on primiparous cows, where simply measurable dam traits such as body weight and body dimensions only have proved to be weakly associated with calving ease (e.g. Hansen, 1975; Hissig and Schlote, 1979; Meijering and Postma, 1984). Simply measurable calf dimensions have also been shown to have limited value when birth weight is obtainable (e.g. Meijering and Postma, 1984). CONCLUSIONS
Large breed differences in calving performance were evident, with Jersey being one extreme and Friesians (purebred and crosses) being the other extreme. Jersey had no difficulties in calving, while Friesians and the crossbred group mated with Friesians had most problems, especially at first calving. This seemed to have been caused mainly by their relatively large calves, with frequent attitudes other than the anterior normal presentation.
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93 H~ssig, H. and Schlote,W., 1979.Untersuchungen zum Geburtsverlaufbei Fleckviehf~-sen.Ziichtungskunde, 51: 275-288. Meijering,A., 1986. Dystocia in dairy cattlebreeding with specialattentionto sireevaluationfor categoricaltraits.Thesis, Agric. Univ. Wageningen, 179 pp. Meijering, A. and Postma, A., 1984. Morphologic aspects of dystocia in dairy and dual purpose heifers.Can. J. Anita. Sci.,64: 551-562. Philipsson,J., 1976a. Studies on calving difficulty,stillbirthand associatedfactorsin Swedish cattlebreeds.Thesis, Agric. Univ. Uppsala. Philipsson,J., 1976b. Studies on calving difficulty,stillbirthand associatedfactorsin Swedish cattlebreeds.General introductionand breed averages.Acta Agric. Scand., 26: 151-164. Philipsson,J., 1976c. Studies on calving difficulty,stillbirthand associatedfactorsin Swedish cattlebreeds.IV. Relationshipsbetween calvingperformance, precalvingbody measurements and sizeof pelvic opening in Friesianheifers.Acta Agric. Scand., 26:221-229. Polastre,R., Villares,J.B. and Ramos, A., de A., 1982. Par~metros gen~ticose fatoresambientais relacionados corn a dura~o da gesta~o na rata Jersey. (Genetic and environmental factors affectinggestationlength in Jerseys.) Rev. Soc. Bras. Zootec.,11: 668-680. Pollak, E.J. and Freeman, A.E., 1976. Parameter estimation and sireevaluationfor dystociaand calfsizein Holsteins.J. Dairy Sci.,59: 1817-1824. Thompson, J.R. and Rege, J.E.O., 1984. Influence of dam on calving difficultyand early calf mortality.J. Dairy Sci.,67: 847-853. Woldehawariat, G., Talamantes, M.A., Petty, R.R., Jr. and Cartwright,T.C., 1977. A summary of genetic and environmental statisticsf6r growth and conformation characters in young beef cattle,2nd Edn. Texas Agric. Exp. Stn.,Dep. Tech. Rep., No. 103.