Disease frequencies in Swedish dairy cows. I. Dystocia

Preventive Veterinary Medicine, 4 (1986) 307--316

307

Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

DISEASE FREQUENCIES IN SWEDISH DAIRY COWS. I. DYSTOCIA

P.H. B E N D I X E N , B. V I L S O N , I. E K E S B O a n d D . B . . : ~ S T R A N D '

Swedish University of Agricultural Sciences, Faculty of Veterinary Medicine. Department of Animal Hygiene, 532 O0 Skara (Sweden) 'Swedish Unit,ersity of Agricultural Sciences. Faculty of Agriculture. Department of Economics and Statistics, 750 07 Uppsala (Sweden) ( A c c e p t e d for p u b l i c a t i o n 11 A u g u s t 1 9 8 6 )

ABSTRACT B e n d i x e n , P.H., Vilson, B., E k e s b o , I. a n d • s t r a n d , D.B., 1986. Disease frequencies in Swedish dairy cows. I. Dystocia. Prey. Vet. Med., 4: 3 0 7 - - 3 1 6 . A n e p i d e m i o l o g i c s t u d y of d y s t o c i a i n c i d e n c e in Swedish dairy cows, covering a p p r o x i m a t e l y 140 0 0 0 calvings, is p r e s e n t e d . V a r i o u s risk factors were identified. The Swedish Friesian Breed (SLB) had a higher i n c i d e n c e t h a n the Swedish Red a n d White Breed (SRB), a n d first calving n u m b e r had a higher i n c i d e n c e t h a n s u b s e q u e n t calving n u m b e r s . SLB heifers y o u n g e r t h a n 28 m o n t h s w h e n calving had a higher risk o f d.vstocia t h a n older heifers. S R B heifers y o u n g e r t h a n 26 m o n t h s w h e n calving had a higher risk t h a n older heifers. A n a s s o c i a t i o n b e t w e e n p a r t u r i e n t paresis a n d d y s t o c i a was d e m o n s t r a t e d . Male calves a n d t w i n n i n g increased t h e risk. A r e d u c e d risk d u r i n g p a s t u r e as o p p o s e d to h o u s i n g for cows f r o m tied h e r d s was f o u n d , b u t no d i f f e r e n c e b e t w e e n i n c i d e n c e for cows in tied h e r d s a n d cows in loose h o u s i n g could be d e m o n s t r a t e d . Previous h i s t o r y of dystocia increased t h e risk of r e c u r r e n c e in s u b s e q u e n t calvings and also t h e risk o f being r e m o v e d d u r i n g lactation.

INTRODUCTION

Data about disease occurrence in Swedish dairy cows were collected in Sweden during the period October 1970--September 1974 as a descriptive epidemiologic project for the purpose of identifying risk factors. Identification of risk factors for dystocia and their relative contributions to the cases observed in the field is motivated by the economic consequences of this disease. Both direct losses and longer term costs have been described (Philipsson, 1976b). This paper presents the frequencies of dystocia in the two most c o m m o n dairy breeds in Sweden, Swedish Red and White (SRB) and Swedish Friesian (SLB). The incidence for cows in different housing systems and during housing and pasture is investigated. The frequency of twinning, of dystocia when twinning, and dystocia with respect to sex of the calf is presented. The relationship between parturient paresis and dystocia is analysed, in addition

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308 to the risk of removal of dystocia-positive cows, and the risk of recurrence of dystocia. MATERIALS AND METHODS Study population, data collection, storage and validation have been described previously (Bendixen et al., 1986). The total num ber of calvings was 153 991. SRB account ed for 102 312 and SLB for 34 690 calvings and were the only two breeds included in this study. The n u mb er of heifers calving during the first year of observation on farms that participated for all four years was 5368 and 1962 for SRB and SLB, respectively. These heifers were subjected to special cohort analysis.

Disease incidence The farmers were given the following definitions as a guide to identification of case: Dystocia -- calvings in which assistance was necessary to save the life of the calf or to prevent the cow from suffering; Parturient paresis -cases of paresis occurring in connect i on with calving which could not be related to any other cause. Cumulative incidence, CI, was used as the measure of frequency of both diseases and calculated as the num be r of cows developing the disease divided by the n u mb er of calvings. Incidence density, ID, was used as the measure of removal f r e q u e n c y and calculated as the n u m b e r of cows being removed for any reason during the lactation divided by the sum of cow months during t h at lactation. The accumulated risk for a cow of developing dystocia from the first to the fourth calving was calculated in the c o h o r t by combining subsequent incidences using the m e t h o d of Elveback (1958).

Data analysis The risk ratio, RR, was calculated by dividing the incidence for risk factor positive cows by the incidence for risk factor negative cows, age-adjusted by a modified Mantel-Haenszel procedure (Kleinbaum et al., 1982). Risk difference was calculated by subtracting the cumulative incidence for risk factor negative cows from the cumulative incidence for risk factor positive cows. Recurrence risk ratios were calculated for the second, third, and fourt h lactations in the cohort, as the ratio between the incidence for cows with a previous positive dystocia r e por t and the incidence for cows with no previous history of dystocia. Statistical analysis for differences between risk factor positive and risk factor negative cows was p e r f o r m e d using the X2 test or the Mantel-Haenszel test for a summary X2. Due to the large n u m b e r of calvings, only differences of P < 0 . 0 1 were considered statistically significant.

309

RESULTS AND DISCUSSION In b o t h b r e e d s the incidence of d y s t o c i a was higher in the first calving t h a n in s u b s e q u e n t calvings ( T a b l e I; R R = 1.4 a n d 2.9 for S R B a n d SLB, r e s p e c t i v e l y ) . T h e incidence d e c l i n e d in the s e c o n d and third calvings and rose again f r o m the f o u r t h . This a g e - d e p e n d e n t f r e q u e n c y d i s t r i b u t i o n is in a c c o r d a n c e w i t h t h e findings of D o h o o and Martin ( 1 9 8 4 ) . C o m p a r i s o n bet w e e n b r e e d s s h o w e d t h a t SLB h a d a significantly higher risk of d y s t o c i a t h a n S R B c o w s ( R R = 2.0). In the first calving the risk f o r SLB c o w s was 2.9 t i m e s higher t h a n the risk f o r S R B cows. In s u b s e q u e n t calvings the risk was 1.4. TABLE I Number of dystocia negative and dystocia positive caivings within calving number, cumulative incidence of dystocia (CI %) and ratio between breed incidences (RR SLB/-

SRB) Calving number

SRB Dystocia negative

SLB Dystocia positive

RR SLB/SRB

CI %

Dystocia negative

Dystocia positive

CI %

1 2 3 4 5 6 7 >7 Unknown

29 521 22 862 16 722 11 658 7564 4446 2433 2229 2191

993 512 362 263 199 127 77 81 72

3.25 2.19 2.12 2.21 2.56 2.78 3.07 3.51 3.18

10 674 8028 5467 3360 1956 1088 580 442 1247

1106 287 163 108 54 41 27 16 46

9.39 3.45 2.90 3.11 2.69 3.63 4.45 3.49 3.56

2.9 1.6 1.4 1.4 1.1 1.3 1.5 1.0 1.1

Total

99 626

2686

2.63

32 842

1848

5.33

2.0**

**P
310 TABLE II Number of calvings in heifers according to age when calving (N), cumulative incidence of dystocia (CI %), and ratio between incidence in younger age group(s) and older age groups (RR) Age in months when calving <23.9 24--25.9 26--27.9 28--29.9 30--31.9 32--33.9 34--35.9 >36

SRB

SLB

N

CI %

RR

N

CI %

3463 8606 8773 8909 8469 7375 4880 1853

3.90 2.97 2.62 2.19 2.64 2.24 2.19 3.08

1.5"* 1.2"* 1.1 n.s.

1567 3302 3052 3125 2877 2948 1950 720

8.87 7.42 7.67 6.02 6.74 5.77 4.67 3.75

RR

1.4"*

1.2"* 1.3"* 1.1 n.s.

**P<0.01.

B o t h breeds had a significantly higher risk o f d y s t o c i a during housing periods as o p p o s e d to pasture periods ( T a b l e IV). T h e highest risk o c c u r r e d in first calving ( R R = 1.7 and 1.8 f o r SRB and SLB, respectively). In subseq u e n t calvings no seasonal d i f f e r e n c e c o u l d be d e m o n s t r a t e d in SRB, b u t SLB still had a significantly higher risk o f 1.3 during housing periods. T h e finding o f lower d y s t o c i a i n c i d e n c e during s u m m e r in Holstein-Friesian cows is in a c c o r d a n c e w i t h the o b s e r v a t i o n s of Erb and Martin (1980). L a t e r observations were h o w e v e r u n a b l e t o c o n f i r m this finding ( D o h o o and Martin, 1984). Less intensive surveillance a r o u n d calving d u r i n g the grazing season has been suggested as the r e a s o n for d e c r e a s e d i n c i d e n c e d u r i n g this p e r i o d (Philipsson, 1976a). H o w e v e r , h y p o c a l c a e m i a as a c o m m o n cause of d y s t o c i a (weak labour) and p a r t u r i e n t paresis c o u l d also explain the seasonal p a t t e r n in SRB. Cows o f this b r e e d are very susceptible to p a r t u r i e n t paresis and have a significantly increased risk o f this disease during pasture, with incidences ranging f r o m 8% in third calving t o 30% in sixth calving ( B e n d i x e n et al., 1986). T h u s a beneficial e f f e c t o f p a s t u r e m a n a g e m e n t on t h e risk of dystocia as f o u n d in SLB cows and SRB heifers w o u l d be c o u n t e r b a l a n c e d in SRB cows by their susceptibility to h y p o c a l c a e m i a . No d i f f e r e n c e in d y s t o c i a f r e q u e n c i e s c o u l d be d e m o n s t r a t e d b e t w e e n tied cows and cows in loose housing ( T a b l e V), a finding in a c c o r d a n c e with the o b s e r v a t i o n s o f E k e s b o (1966). T h u s exercise alone as o f f e r e d by loose housing did n o t seem to r e d u c e the incidence of dystocia. SLB had a significantly higher i n c i d e n c e o f twin calvings t h a n SRB (Table VI; R R = 1.3), a n d the risk o f t w i n n i n g increased w i t h age in b o t h breeds. In h u m a n s a similar race d e p e n d e n t variation in t w i n n i n g f r e q u e n c i e s and increased risk of t w i n n i n g in higher ages has been d e s c r i b e d by N y l a n d e r

311

(1975). Twinning significantly increased the risk of dystocia for both SRB and SLB cows (RR = 6.0 and 3.5, respectively). Part of the dystocia incidence in older cows and part of the increased risk for SLB cows when compared with SRB cows might thus be due to the incidence of twin calvings. TABLE IIIa Number of calvings within calving number (N) according to status of parturient paresis, cumulative incidence of dystocia (CI %) and ratio between incidences (RR) in SRB Calving number

Parturient paresis negative

Parturient paresis positive

RR

N

CI %

N

CI %

1 2 3 4 5 6 7 :>7 Unknown

30 490 23 029 15 915 10 191 6061 3446 1872 1789 2069

3.25 2.14 1.90 1.95 2.01 1.92 2.40 3.02 2.90

24 345 1169 1730 1702 1127 638 521 194

8.33 5.80 5.05 3.70 4.52 5.41 5.02 5.18 6.19

2.6 2.7 2.7 1.9 2.3 2.8 2.1 1.7 2.1

Total

94 862

2.46

7450

4.75

2.3**

**P<0.01 (age-adjusted).

TABLE IIIb Number of calvings within calving number (N) according to status of parturient paresis, cumulative incidence of dystocia (CI %) and ratio between incidences (RR) in SLB Calving number

Parturient paresis negative

Parturient paresis positive

N

CI %

N

1 2 3 4 5 6 7 :>7 Unknown

11 762 8238 5379 3120 1709 936 483 368 1206

9.36 3.42 2.83 2.63 2.52 2.67 3.73 3.26 3.48

18 77 251 348 301 193 124 90 87

27.78 6.49 4.38 7.47 3.65 8.29 7.26 4.44 4.60

Total

33 201

5.29

1489

6.11

*

*P< O.01 ( age-adju sted).

RR

CI % 3.0 1.9 1.6 2.8 1.5 3.1 2.0 1.4 1.3 2.1"*

312

TABLE IV Number of calvings (N) within calving number and season, of cows from tied herds with traditional pasture periods during summertime, cumulative incidence of dystocia (CI %), and ratio between seasonal incidences (RR) Calving number

SRB

SLB

Pasture

Housing

Pasture

Housing

N

CI %

N

CI %

RR

N

CI %

1 2 3 4 5 6 7 >7 Unknown

10 066 6075 3657 2329 1409 845 432 413 482

2.35 2.06 2.00 2.02 2.56 3.31 2.31 3.39 2.29

14 921 13 184 10394 7504 5040 3004 1658 1536 1433

3.98 2.31 2.09 2.28 2.64 2.56 3.02 3.32 2.86

1.7 1.1 1.1 1.1 1.0 0.8 1.3 1.0 1.3

3097 1716 1073 564 293 147 94 56 195

6.33 2.51 2.52 3.72 3.07 4.76 1.06 0.00 2.56

Total

25 708

2.26

58 674

2.79

1.3"*

7235

4.27

N

CI %

RR

4355 3577 2586 1682 972 575 295 228 542

11.21 4.19 3.48 3.15 3.19 2.96 3.73 4.39 3.69

1.8 1.7 1.4 0.9 1.0 0.6 3.5 -1.4

14 812

5.87

1.6"*

**P<0.01 (age-adjusted). TABLE V Number of calvings (N) according to housing system, cumulative incidence of dystocia (CI %) and ratio between incidences (RR)

SRB' SLB 2

Loose housing

Tie stalls

RR

N

CI %

N

CI %

8472 7584

2.68 4.55

92 306 26 325

2.63 5.50

1.0 n.s. 1.2 n.s.

'1534 calvings in combined housing systems. 2 781 calvings in combined housing systems.

B o t h b r e e d s h a d a s i g n i f i c a n t l y h i g h e r d y s t o c i a risk f o r m a l e calves ( T a b l e V I I ) . T h e risk o f d i f f e r e n c e , also c a l l e d t h e e x c e s s risk, r e f l e c t s t h e a b s o l u t e r a t e o f d y s t o c i a cases, a t t r i b u t a b l e t o t h e risk f a c t o r . W h e n c o m p a r i n g m a l e calves o f S L B t o m a l e calves o f S R B a r i s k d i f f e r e n c e o f 3 . 6 7 % ( 6 . 4 5 - - 2 . 7 8 ) w a s f o u n d . T h e risk d i f f e r e n c e f o r f e m a l e calves was 1 . 6 2 % ( 3 . 5 3 - - 1 . 9 1 ) . T h u s m a l e calves o f S L B c o n t r i b u t e d t o a larger d e g r e e t o i n c r e a s e d d y s t o c i a f r e q u e n c y i n t h i s b r e e d t h a n f e m a l e calves. C o w s o f b o t h b r e e d s w i t h a p o s i t i v e d y s t o c i a s t a t u s h a d a n e l e v a t e d risk of being r e m o v e d f r o m the herd d u r i n g the l a c t a t i o n w h e n c o m p a r e d to

313 TABLE VI Cumulative incidence of twinning within calving number, cumulative incidence of dystocia (CI %) in twin versus single calvings and ratio between incidences (RR) Calving number

SRB

SLB

SRB dystocia CI %

SLB dystocia CI %

Twin

CI %

Twin negative

Twin positive

RR

Twin negative

Twin positive

RR

1 2 3 4 5 6 7 >7 Unknown

0.51 1.74 2.22 2.79 2.87 2.89 3.44 3.75 1.51

0.73 1.84 3.10 3.25 3.29 4.73 4.13 5.70 1.86

3.17 1.99 1.79 1.85 2.09 2.34 2.57 3.12 2.79

10.97 10.40 12.73 12.69 17.57 13.74 13.95 12.79 20.59

3.5 5.2 7.1 6.9 8.4 5.9 5.4 4.1 7.4

9.09 3.10 2.63 2.82 2.43 3.28 4.48 3.26 3.16

20.93 19.08 10.92 10.71 9.09 9.43 4.00 3.85 8.33

2.3 6.2 4.2 3.8 3.8 2.9 0.9 1.2 2.6

Total

1.83

2.12

2.38

12.92

6.0**

5.05

12.95

3.5**

**P<0.01 (age-adjusted).

TABLE VII Number of calvings according to sex of the calf (N), cumulative incidence of dystocia (CI %), and ratio between incidences (RR) Male calf

SRB l SLB ~

Female calf

RR

N

CI %

N

CI%

52 586 17 583

2.78 6.45

47 437 16 208

1.91 3.35

1.5"* 1.8"*

**P
314 T A B L E VIII N u m b e r of cows being r e m o v e d f r o m t h e h e r d d u r i n g l a c t a t i o n a c c o r d i n g to d y s t o c i a s t a t u s in t h e calving i n i t i a t i n g the l a c t a t i o n (N), a c c u m u l a t e d cow m o n t h s in respective g r o u p s ( H T ) , c a l c u l a t e d i n c i d e n c e d e n s i t y per 1 2 0 0 m o n t h s (ID), a n d age-adjusted r a t i o b e t w e e n r e m o v a l i n c i d e n c e for d y s t o c i a positive a n d d y s t o c i a negative cows ( R R ) D y s t o c i a negative

SRB SLB

D y s t o c i a positive

RR

N

HT

ID

N

HT

ID

20 614 7054

9 4 5 512 297 281

26.16 28.47

902 612

23 921 15 674

45.25 46.85

1.7" 1.8"*

**P<0.01.

T A B L E IX C u m u l a t i v e i n c i d e n c e of first diagnosis of d y s t o c i a (CI %), a c c u m u l a t e d risk (CI a %)~ for first diagnosis of dystocia, a n d r a t i o b e t w e e n i n c i d e n c e of first diagnosis of d y s t o c i a ( R R S R B / S L B ) . F r o m a c o h o r t of heifers calving for the first time d u r i n g the first year of r e p o r t i n g o n farms t h a t p a r t i c i p a t e d for all f o u r years Calving number

1 2 3 4

SRB

SLR

RR SLB/SRB

CI %

CI a %

CI %

CI a %

4.06 1.60 1.92 1.75

5.60 7.41 9.03

12.08 2.42 2.25 1.95

14.21 16.14 17.78

3.0** 1.5 n.s. 1.2 n.s. 1.1 n.s.

**P<0.01. ' Calculated as: 1--( 1--CI, )( 1--CI~ )( 1--CI 3)(1--CI,).

curred in first calving; in s u b s e q u e n t calvings the increased risk was n o t statistically significant in the c o h o r t study. T h e r e c u r r e n c e risk ratio evaluates the h y p o t h e s i s t h a t the disease is a risk f a c t o r for r e c u r r e n c e o f disease. SRB cows with at least o n e positive r e p o r t o f d y s t o c i a had a significantly higher risk o f r e c u r r e n c e of d y s t o c i a in second and third calvings (Table X). T h e elevated risk in f o u r t h calving was based on a small n u m b e r of cows and was n o t statistically significant. SLB cows had a statistically significant higher risk o f r e c u r r e n c e in s e c o n d calving; in third and f o u r t h calvings the risks were n o t significant. Analysis of data f r o m d y n a m i c c o h o r t s has the s h o r t c o m i n g of ignoring disease o c c u r r e n c e in animals in the p e r i o d p r i o r t o their e n t r y in the study. This d i f f i c u l t y is o v e r c o m e by analysis o f f i x e d c o h o r t s o f heifers which provides i n f o r m a t i o n a b o u t the entire disease h i s t o r y . T h e d e m o n s t r a t e d increased r e c u r r e n c e risk ratio in SRB, suggests d y s t o c i a - p r o n e cows to ac-

315 c o u n t f o r an i m p o r t a n t part o f d y s t o c i a cases in higher calving n u m b e r s of the entire d a t a set. T h e possible c o n n e c t i o n o f this finding with the observed a s s o c i a t i o n b e t w e e n d y s t o c i a and p a r t u r i e n t paresis needs to be analysed in f u t u r e studies. TABLE X Ratio between incidence for cows with at least one previous history of dystocia and incidence for cows with no previous history of dystocia (Dystocia recurrence RR). From a cohort of heifers calving for the first time during the first year of reporting on farms that participated for all four years Dystocia recurrence RR

2nd calving 3rd calving 4th calving

SRB

SLB

5.65/1.60 = 3.5** 6.40/1.92 = 3.3** 4.35/1.75 = 2.5 n.s.

6.57/2.42 = 2.7** 3.57/2.25 = 1.6 n.s. 1.45/1.95 = 0.7 n.s.

**P<0.01.

CONCLUSION Seven risk f a c t o r s for d y s t o c i a are identified and can be s u m m a r i z e d as follows. (1) Calving n u m b e r : first calvings have higher risk t h a n s u b s e q u e n t calvings. (2) Age w h e n calving: SRB heifers less than 26 m o n t h s old have higher risk than o l d e r heifers, and SLB heifers less than 28 m o n t h s old have higher risk t h a n older heifers. (3) Breed: SLB have higher risk than SRB. (4) Sex: male calves cause higher incidence o f dystocia. (5) Twinning. (6) Housing p e r i o d : SRB heifers have r e d u c e d risk during pasture, and SLB have red u c e d risk d u r i n g p a s t u r e b o t h in first and s u b s e q u e n t calvings. (7) D y s t o c i a : previous h i s t o r y o f d y s t o c i a increases the risk in s e c o n d and third calvings f o r SRB a n d in s e c o n d calving for SLB.

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Kleinbaum, D.G., Kupper, L.L. and Morgenstern, H., 1982. Epidemiologic Research, Principles and Quantitative Methods. Lifetime Learning Publications, Belmont, CA, p. 345. Nylander, P.P.S., 1975. Factors which influence twinning rates. In: Human Multiple Reproduction. W.B. Saunders Company, pp. 98--I06. Philipsson, J., 1976a. Studies on calving difficulty, stillbirth and associated factors in Swedish cattle breeds. If. Effects of non-genetic factors. Acta Agric. Scand., 26: 165-174. Philipsson, J., 1976b. Studies on calving difficulty, stillbirth and associated factors in Swedish cattle breeds. V. Effects of calving performance and stillbirth in Swedish Friesian Heifers on productivity in the subsequent lactation. Acta Agric. Scand., 26: 230--234.