the effect of grazing on cow mortality in danish dairy herds

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Preventive Veterinary Medicine 100 (2011) 237–241 Contents lists available at ScienceDirect Preventive Veterinary Medicine j ourna l ho me pag e: ww w.elsevi er.com/locate/prev etmed Short communication The effect of grazing on cow mortality in Danish dairy herds E. Burow , P.T. Thomsen, J.T. Sørensen, T. Rousing Aarhus University, Department of Animal Health and Bioscience, Blichers Allé 20, P.O. Box 50, 8830 Tjele, Denmark a r t i c l e i n f o Article history: Received 22 September 2010 Received in revised form 1 April 2011 Accepted 2 April 2011 Keywords: Death Pasture Confinement Animal health Cattle a b s t r a c t The effect of summer grazing in large Danish dairy herds and certain management char- acteristics of grazing were studied for their impact on dairy cow mortality. Mortality data (from the Danish Cattle Database) from 391 Danish dairy herds (>100 cows) were com- bined with information from a questionnaire survey of grazing procedures on these herds in 2008. In all, 131 of the herds were identified as summer grazing and 260 as zero-grazing herds. The mortality was affected by an interaction of summer grazing and milking system. The risk of a cow dying was reduced to 46% in a grazing compared to a zero-grazing herd having automatic milking system. In traditional milking system, mortality was reduced to 75% in grazing compared to zero-grazing herds. Within the grazing herds, the risk of mor- tality decreased with increasing number of hours on pasture during the season. Free access between barn and pasture was associated with increased cow mortality. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Cows’ grazing during summer is in general associated with good animal welfare by the public (Ellis et al., 2009). However, the knowledge of effects of grazing on the wel- fare of cows is still scarce. Some studies have demonstrated a positive effect on, e.g. lameness, leg injuries (Haskell et al., 2006; Olmos et al., 2009) and clinical mastitis (Washburn et al., 2002). In contrast, the incidence of hoof treatments was found to be increased for grazing compared to zero- grazing (meaning all-year-round-indoor-kept) dairy cows (Mortensen and Kjeldsen, 2004) and the cow’s body con- dition and mean body weight were found to decrease after turn-out to pasture (Washburn et al., 2002; Boken et al., 2005; Hernandez-Mendo et al., 2007). A study in Danish dairy herds in 2001 revealed that the mortality was reduced in herds with summer graz- ing compared to zero-grazing herds (Thomsen et al., 2006). Since 2001 the herd size has almost doubled (Danish Cattle Federation, 2010) and the proportion of tie-stall herds has Corresponding author. Tel.: +45 89 99 13 45; fax: +45 89 99 15 25. E-mail address: [email protected] (E. Burow). decreased from 60% in 2000 (Thomsen et al., 2006) to 23% in 2010 (Lauritsen, U., RYK–Livestock Registration and Milk Recording, personal communication, 07.05.2010). The increase in herd size requires not only changes in the barn but also a different pasture management strategy. Larger herds are less likely to be sent out to pasture (Mortensen and Kjeldsen, 2004). The objective of this study was to evaluate the effect of grazing on dairy cow mortality in large Danish dairy herds. The hypotheses were that cow mortality is lower in grazing than zero-grazing herds and that specific characteristics of grazing management have an impact on mortality. 2. Materials and methods 2.1. Selection of herds The target population was Danish dairy herds with more than 100 cows. The study sample was based on responses from a questionnaire survey of grazing procedures on Dan- ish dairy farms. The survey was carried out in 2009 by the Danish Cattle Federation and Aarhus University to find barriers and opportunities in grazing cattle. A total of 812 Danish dairy herds with more than 100 cows were ran- 0167-5877/$ see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.prevetmed.2011.04.001

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Page 1: The effect of grazing on cow mortality in Danish dairy herds

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Preventive Veterinary Medicine 100 (2011) 237– 241

Contents lists available at ScienceDirect

Preventive Veterinary Medicine

j ourna l ho me pag e: ww w.elsev i er .com/ locate /prev etmed

hort communication

he effect of grazing on cow mortality in Danish dairy herds

. Burow ∗, P.T. Thomsen, J.T. Sørensen, T. Rousingarhus University, Department of Animal Health and Bioscience, Blichers Allé 20, P.O. Box 50, 8830 Tjele, Denmark

r t i c l e i n f o

rticle history:eceived 22 September 2010eceived in revised form 1 April 2011ccepted 2 April 2011

eywords:

a b s t r a c t

The effect of summer grazing in large Danish dairy herds and certain management char-acteristics of grazing were studied for their impact on dairy cow mortality. Mortality data(from the Danish Cattle Database) from 391 Danish dairy herds (>100 cows) were com-bined with information from a questionnaire survey of grazing procedures on these herdsin 2008. In all, 131 of the herds were identified as summer grazing and 260 as zero-grazingherds. The mortality was affected by an interaction of summer grazing and milking system.

eathastureonfinementnimal healthattle

The risk of a cow dying was reduced to 46% in a grazing compared to a zero-grazing herdhaving automatic milking system. In traditional milking system, mortality was reduced to75% in grazing compared to zero-grazing herds. Within the grazing herds, the risk of mor-tality decreased with increasing number of hours on pasture during the season. Free accessbetween barn and pasture was associated with increased cow mortality.

. Introduction

Cows’ grazing during summer is in general associatedith good animal welfare by the public (Ellis et al., 2009).owever, the knowledge of effects of grazing on the wel-

are of cows is still scarce. Some studies have demonstrated positive effect on, e.g. lameness, leg injuries (Haskell et al.,006; Olmos et al., 2009) and clinical mastitis (Washburnt al., 2002). In contrast, the incidence of hoof treatmentsas found to be increased for grazing compared to zero-

razing (meaning all-year-round-indoor-kept) dairy cowsMortensen and Kjeldsen, 2004) and the cow’s body con-ition and mean body weight were found to decrease afterurn-out to pasture (Washburn et al., 2002; Boken et al.,005; Hernandez-Mendo et al., 2007).

A study in Danish dairy herds in 2001 revealed thathe mortality was reduced in herds with summer graz-

ng compared to zero-grazing herds (Thomsen et al., 2006).ince 2001 the herd size has almost doubled (Danish Cattleederation, 2010) and the proportion of tie-stall herds has

∗ Corresponding author. Tel.: +45 89 99 13 45; fax: +45 89 99 15 25.E-mail address: [email protected] (E. Burow).

167-5877/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.prevetmed.2011.04.001

© 2011 Elsevier B.V. All rights reserved.

decreased from 60% in 2000 (Thomsen et al., 2006) to23% in 2010 (Lauritsen, U., RYK–Livestock Registration andMilk Recording, personal communication, 07.05.2010). Theincrease in herd size requires not only changes in the barnbut also a different pasture management strategy. Largerherds are less likely to be sent out to pasture (Mortensenand Kjeldsen, 2004).

The objective of this study was to evaluate the effect ofgrazing on dairy cow mortality in large Danish dairy herds.The hypotheses were that cow mortality is lower in grazingthan zero-grazing herds and that specific characteristics ofgrazing management have an impact on mortality.

2. Materials and methods

2.1. Selection of herds

The target population was Danish dairy herds with morethan 100 cows. The study sample was based on responsesfrom a questionnaire survey of grazing procedures on Dan-

ish dairy farms. The survey was carried out in 2009 bythe Danish Cattle Federation and Aarhus University to findbarriers and opportunities in grazing cattle. A total of 812Danish dairy herds with more than 100 cows were ran-
Page 2: The effect of grazing on cow mortality in Danish dairy herds

238 E. Burow et al. / Preventive Veterinary Medicine 100 (2011) 237– 241

Table 1List of herd level explanatory variables included in a study of cow mortality in grazing (N = 131) vs. zero-grazing (N = 260) Danish dairy herds and theirdescriptive characteristics (data from 2008).

Explanatory variables N Descriptive characteristics of herds p-Valued

Grazing Zero-grazing

Energy corrected milk yield/cow-year (mean kg ± SD) 375 9126 ± 1204 9544 ± 902 <0.001Somatic cell count (mean 1000 cells/ml) 376 301 ± 86 297 ± 82 0.546Herd size in cow-years (mean ± SD) 390 154 ± 51 182 ± 78 <0.001Breed: Danish Holsteina (%) 223 74 (56.5%) 149 (57.3%) 0.813Breed: Jerseya (%) 34 10 (7.6%) 24 (9.2%)Breed: otherb (%) 134 47 (35.9%) 87 (33.5%)Milking system: automatic (%) 90 18 (13.7%) 72 (27.7%) 0.002Milking system: traditional (%) 301 113 (86.3%) 188 (72.3%)Barn system: cubicle loose housing (%)c 341 111 (84.7%) 230 (88.8%) 0.003Barn system: deep litter (%)c 16 12 (9.2%) 4 (1.5%)Barn system: tie-stalls (%)c 8 2 (1.5%) 6 (2.3%)Barn system: several systems (%)c 25 6 (4.6%) 19 (7.3%)Flooring: slatted (%)c 269 87 (67.4%) 182 (70.8%) 0.788Flooring: solid concrete (%)c 41 15 (11.6%) 26 (10.1%)Flooring: several or other system (%)c 76 27 (20.9%) 49(19.1%)Grouping (Splitting of herd): yes (%)c 76 16 (12.2%) 60 (23.3%) 0.009Grouping (Splitting of herd): no (%)c 313 115 (87.8%) 198 (76.7%)Farmer’s attitude tw. grazing: positive (%) 219 121 (93.1%) 98 (38.3%) <0.001Farmer’s attitude tw. grazing: negative (%) 134 4 (3.1%) 130 (50.8%)Farmer’s attitude tw. grazing: ‘indifferent’ or ‘don’t know’ (%) 33 5 (3.9%) 28 (10.9%)

a Herds with at least 90% cows of this breed.

ariable.

b Herds with less than 90% Danish Holstein or Jersey cows.c Related only to lactating cows.d t-Test per continuous variable or pearson chi-square per categorical v

domly selected for this survey. The questionnaire (a copyis accessible via corresponding author) was sent by mailto the selected farmers. Farmers that did not respond tothe first letter received one reminder by mail three weekslater. A total of 401 farmers answered the questionnaire(response rate 49.4%) and represented the target popu-lation with regard to housing, management procedure,breed, milk yield and somatic cell count.

2.2. Data collection

Information on breed, milk yield, somatic cell count,herd size, milking system (Table 1), organic/conventionalproduction method and deaths originated from the Dan-ish Cattle Database and considered the status in the periodfrom 1st January to 31st December 2008.

Further herd information on barn system, flooring,grouping, grazing management as well as attitude of thefarmers (Table 1) originated from the questionnaire. Itincluded in total 58 questions about management, housingand grazing practices in 2008 with specific sections aboutheifers and cows as well as questions on the attitudes andfuture plans of the farmers regarding grazing. The ques-tions considered were of closed or semi-closed type givinginformation on a categorical scale level.

2.3. Data editing

The 401 herds that responded were divided into twogroups based on the grazing practices in 2008. Grazing

herds were defined as herds using summer pasture forall their lactating cows. Zero-grazing herds were definedas those not being on pasture, neither with lactating nordry cows. Herds that did not meet the definitions were

excluded from the study: two herds for having less than100% of the lactating cows on pasture, five herds with onlydry cows on pasture and three herds with only an exer-cise area. Thus, the final dataset included 391 herds, ofwhich 131 herds were defined as grazing herds and 260as zero-grazing herds (Table 1).

All farmers were asked in the survey for their level ofagreement with eleven statements on, e.g. cow health andmanagement regarding use of grazing. Possible answersfor each statement were either high degree, some degreeor absolutely no degree of agreement or ‘don’t know’. Thefirst two levels were aggregated to ‘positive’, the third levelwas termed ‘negative’ and the fourth level ‘indifferent’. Thefarmers’ answers to the 11 questions were summarised inone measure ‘positive’, ‘negative’ or ‘indifferent’ based onthe majority of his answers. If an equal number of ‘positive’and ‘negative’ answers were given, it was assessed as being‘indifferent’.

As part of the questionnaire, the farmers from the 131grazing herds were asked about their pasture manage-ment/procedures in relation to lactating cows in 2008.Based on these answers, four variables describing thegrazing system were defined (Table 2). These variablesdescribed ‘track distance’ and ‘free access’ between barnand pasture, duration of seasonal stay (‘time’) and ‘wateraccess’ on pasture. ‘Track distance’ distinguishes between1: ≤200 m and 2: >200 m length. ‘Free access’ means opengate between barn and pasture to 1: ‘high degree’ or 2: ‘noor some degree’. ‘Time’ was based on information aboutdaily grazing hours (1: 0, 2: 1–<6 (estimated mean 4 h),

3: 6–10 (estimated mean 7 h), 4: >10 h (estimated mean12 h)) in June, August and October. A fictive sum of hoursper day on pasture in each of the three months times 30days per month was calculated. The sum was categorised
Page 3: The effect of grazing on cow mortality in Danish dairy herds

E. Burow et al. / Preventive Veterinary

Table 2Categories of explanatory variables for grazing management in a studyof cow mortality in 131 Danish grazing herds based on a survey of theyear 2008 (deviation from 131 in the sum of herds per variable is due tomissing values).

Explanatory variables Definition ofclassification

N study herds

‘Time’ on pasture in June,August and/or October

1: 120–360 h 29

2: 420–570 h 383: 630 h 334: 720–1080 h 29

‘Track distance’ 1: ≤200 m distance 972: >200 m distance 32

‘Free access’ between barnand pasture

1: Yes 93

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‘Water access’ on pasture 0: No or low degree 341: Yes 1030: No 25

nto the four ‘time’ levels 1: ‘short period, few daily hours’120–360 h), 2: ‘medium period, medium daily’ (420–570),: ‘long period, medium daily’ (630), 4: ‘long period, manyaily’ (720–1080) containing approximately equal num-ers of herds. ‘Water access’ on pasture was either 1: ‘yes’r 0: ‘no’.

.4. Statistical analysis

The effect of grazing on cow mortality was analysed.he outcome variable was herd level annual mortality ratenumber of cows dying per 100 cows per year) in 2008.

ortality included both euthanized cows and cows dyingnassisted, but not cows slaughtered.

In a first analysis of the entire dataset, risk factorsor mortality rate in grazing vs. zero-grazing herds werevaluated. In a second analysis of a subset of the data,ossible differences within grazing herds were evaluated.oth analyses were carried out using negative binomialegression (PROC GENMOD procedure in SAS Version 9.2).n the analysis of grazing vs. zero-grazing, mortality rate

as the outcome and grazing plus all herd level variablesisted in Table 1 were the explanatory variables (their dif-

erence between grazing and zero-grazing was tested byhi-square- or t-test). The effect on mortality rate of graz-ng management described by the variables presented inable 2 was evaluated for grazing herds only. All variables

able 3ariables with significant effect (p < 0.05) in a study of cow mortality incidence

008 (369 degrees of freedom).a

Parameter N herds Memo

Energy corrected milk yield/cow-year (1000 kgincrease)

Somatic cell count (100,000 cells/ml increase)

Grazing system × Milking system

Grazing vs. zero-grazing in traditional milking system 113 vs. 188 5.1Grazing vs. zero-grazing in automatic milking system 18 vs. 72 2.8Automatic vs. traditional milking system in grazing

system18 vs. 113 2.8

Automatic vs. traditional milking system in zero-grazing system

72 vs. 188 5.9

a A likelihood ratio test comparing the large model to the final model resulted

Medicine 100 (2011) 237– 241 239

listed in Table 1 were also included in the second analy-sis. Both analyses were carried out according to a strategydescribed by Hosmer and Lemeshow (1989). At first theassociation between single risk factors and the outcomevariable was screened by univariable analyses. Only vari-ables with p < 0.5 were considered in the initial model. Themodel was reduced using backward elimination (p < 0.05as threshold). The resulting model was expanded by allpossible two-way interactions (large model), reduced bybackward elimination (p < 0.05 as threshold) and checkedfor confounding (20% threshold for change in the estimateof the variable of interest). Since the variation of mor-tality rate decreased with increasing herd size, an offsetstatement for the log-transformed variable ‘herd size’ wasincluded to control for this variance difference. The finalmodel was the one with the smallest Akaike informationcriterion among those models derived from the large model(Burnham and Anderson, 2002).

3. Results

Descriptive characteristics of the 391 herds are shownin Table 1. Grazing herds were on average smaller and hadlower mean milk yield per cow-year but similar somaticcell counts compared to zero-grazing herds. Automaticmilking was used in twice as many zero-grazing herds com-pared to grazing herds. Among the grazing herds 35.9%were organic.

Mean annual mortality rate was 5.6 (standard devia-tion (SD) 3.5) in all 391 herds. In the 131 grazing and260 zero-grazing herds, the mean annual mortality rateswere 4.8 (SD 3.8) and 6.0 (SD 3.3; p = 0.11), respectively.The final model included the explanatory variables milkyield, somatic cell count, grazing, milking system and theinteraction between grazing and milking system (Table 3).The mortality incidence rate was lowest in herds with thecombination of grazing and automatic milking system andhighest in herds with zero-grazing and traditional milk-ing system. A high milk yield in a herd was associated withreduced mortality; a high somatic cell count with increasedmortality.

‘Time’ on pasture had a significant effect on the mortal-ity rate (Table 4). Increasing the grazing time from few tomany hours decreased the risk of mortality significantly.‘Free access’ to pasture significantly increased the mortal-

rate in 131 grazing compared to 260 zero-grazing herds in Denmark in

an %rtality

Ratio of mortalityincidence rate

95% confidencelimits

p-Value type III

0.88 0.83 0.93 <0.0001

1.23 1.15 1.32 <0.0001<0.0001

vs. 6.0 0.75 0.66 0.85 vs. 5.9 0.46 0.33 0.64 vs. 5.1 0.54 0.40 0.75

vs. 6.0 0.88 0.76 1.01

in p = 0.9482.

Page 4: The effect of grazing on cow mortality in Danish dairy herds

240 E. Burow et al. / Preventive Veterinary Medicine 100 (2011) 237– 241

Table 4Variables with significant effect (p < 0.05) in a study of cow mortality incidence rate in 131 Danish grazing herds in the year 2008 (111 degrees of freedom).a,b

Parameter Level N herds Mean %mortality

Ratio of mortalityincidence rate

95% confidencelimits

p-Valuetype III

Milking system Automatic vs. traditional 17 vs. 112 2.8 vs. 5.1 0.53 0.37 0.75 0.0004‘Free access’ between

barn and pastureYes vs. no or to low degree 93 vs. 34 5.2 vs. 3.6 1.42 1.10 1.84 0.0079

‘Time’ on pasture inJune, August and/orOctober

420–570 vs. 120–360 h 38 vs. 29 4.6 vs. 5.2 0.83 0.63 1.11

630 h vs. 120–360 h 33 vs. 29 4.6 vs. 5.2 0.74 0.55 1.01 0.0008720–1080 vs. 120–360 h 29 vs. 29 4.7 vs. 5.2 0.50 0.35 0.70

Energy corrected milkyield

1000 kg increase 0.87 0.79 0.96 0.0073

ormatioesulted

Somatic cell count 100,000 cells/ml increase

a The survey response of 129 of the grazing herds offered sufficient infb A likelihood ratio test comparing the large model to the final model r

ity compared to no or low degree of ‘free access’. ‘Trackdistance’ and ‘water access’ did not show a significanteffect. None of the tested interactions were statisticallysignificant.

4. Discussion

In the analysis, the estimated mortality in grazing herdswas significantly reduced compared to zero-grazing herds(interaction with milking system). An effect of grazing lead-ing to an odds ratio of cow mortality of 0.8 compared tozero-grazing herds was found in Danish herds in 2001 byThomsen et al. (2006).

An increase in herd level milk yield in a herd was asso-ciated with a reduced mortality rate, which corresponds tofindings in previous studies (Smith et al., 2000; Thomsenet al., 2006). Further, the association of increasing somaticcell count with increasing mortality in the present studywas in agreement with previous findings (Thomsen et al.,2006; Dechow and Goodling, 2008).

‘Time’ on and ‘free access’ to pasture showed a signif-icant effect on mortality while ‘track distance’ and ‘wateraccess’ did not. The more hours cows stayed on pasture,the lower the mortality. This finding emphasizes the basi-cally positive effect of grazing from the first analysis. It isrelevant to further examine whether the longest possiblestay on pasture has a positive effect on mortality under allcircumstances or that it, e.g. depends on individual cowcharacteristics. It is also an open question which ‘underly-ing factors’ actually lead to a lower mortality rate when thecows spend more time on pasture.

‘Free access’ between barn and pasture for the cowswas associated with increased mortality. It could have beenexpected that ‘free access’ would allow a cow to choosewhat is individually advantageous. However, one couldspeculate that cows that could benefit most from going onpasture may rarely voluntarily choose to go. With regardto, e.g. metabolic health, exercise would be good for cows(Adewuyi et al., 2005), but it may be necessary to forcethem to go. Further, cows that prefer staying inside being

somehow weak or physically and/or behaviourally chal-lenged, e.g. after birth and regrouping or due to disease,may in many cases not be offered additional or fresh feedand bedding in the barn since farmers expect the cows to

1.35 1.19 1.55 <0.0001

n to study the impact of the certain grazing parameters on mortality.in p = 0.5476.

find these resources outside. The positive effect of no ‘freeaccess’ between barn and pasture may be due to the factthat the farmer watches the cows at least twice daily dur-ing driving (and thus be able to identify, e.g. lame cows) andmakes sure that all cows actually do reach the pasture or– as an alternative – houses weak cows deliberately insidein hospital pens where offering at least food and water tothese cows.

5. Conclusion

Mortality is lower in Danish summer grazing dairy herdscompared to zero-grazing herds. The more time the cowsspend on pasture, the lower the mortality. No ‘free access’between barn and pasture leads to a decrease in mortality.

Conflict of interest statement

The authors declare that they have no conflicts of inter-est regarding the present study and manuscript.

Acknowledgements

The study is part of the project Afgræsning- også en del affremtidens kvægbrug and supported by funds from AarhusUniversity, Stiftelsen Hofmansgave and Mælkeafgifts-fonden. The study sponsors were not involved in studydesign, analysis and interpretation of results.

The authors wish to thank the Knowledge Centre forAgriculture/Cattle for providing access to data from theDanish Cattle Database. The authors also wish to thankTroels Kristensen, Department of Agroecology and Envi-ronment, Aarhus University, for making data available fromthe survey of grazing procedures in Danish dairy herds andUlrich Halekoh, Department of Genetics and Biotechnol-ogy, Aarhus University, for advice on the statistical analysis.

References

Adewuyi, A.A., Gruys, E., Van Eerdenburg, F.J.C.M., 2005. Non esterifiedfatty acids (NEFA) in dairy cattle. A review. Vet. Quart. 27, 117–126.

Boken, S.L., Staples, C.R., Sollenberger, L.E., Jenkins, T.C., Thatcher, W.W.,2005. Effect of grazing and fat supplementation on production andreproduction of Holstein cows. J. Dairy Sci. 88, 4258–4272.

Page 5: The effect of grazing on cow mortality in Danish dairy herds

erinary

B

Df.

D

E

H

H

E. Burow et al. / Preventive Vet

urnham, K.P., Anderson, D.R., 2002. Model selection and multimodelinference: A practical information-theoretic approach. Springer, NewYork, p. 60ff., 70ff.

anish Cattle Federation, 2010. Figures on Danish Cattle 2009.,http://www.landbrugsinfo.dk/kvaeg/filer/kvaegbruget tal2009eng.pd

echow, C.D., Goodling, R.C., 2008. Mortality, culling by sixty days in milk,and production profiles in high- and low-survival Pensylvania herds.J. Dairy Sci. 91, 4630–4639.

llis, K.A., Billington, K., McNeil, B., McKeegan, D.E.F., 2009. Public opin-ion on UK milk marketing and dairy cow welfare. Anim. Welfare 18,267–282.

askell, M.J., Rennie, L.J., Bowell, V.A., Bell, M.J., Lawrance, A.B., 2006. Hous-

ing system, milk production, and zero-grazing effects on lameness andleg injury in dairy cows. J. Dairy Sci. 89, 4259–4266.

ernandez-Mendo, O., Von Keyserlingk, M.A.G., Veira, D.M., Weary, D.M.,2007. Effects of pasture on lameness in dairy cows. J. Dairy Sci. 90,1209–1214.

Medicine 100 (2011) 237– 241 241

Hosmer, D.W., Lemeshow, S., 1989. Applied Logistic Regression. Wiley,New York, p. 301.

Mortensen, B.Ø., Kjeldsen, A.M., 2004. Afgræsningens betydning fordanske malkekøers sundhed. Dansk Landbrugsrådgivning, Lands-centret, KvægInfo 1374., http://li.lr.dk/applikationer/kate/viskategori.asp?ID=ka004000080001300&nodoclimit=1.

Olmos, G., Boyle, L., Hanlon, A., Patton, J., Murphy, J.J., Mee, J.F., 2009.Hoof disorders, locomotion ability and lying times of cubicle-housedcompared to pasture-based dairy cows. Livest. Sci. 125, 199–207.

Smith, J.W., Ely, L.O., Chapa, A.M., 2000. Effect of region, herd size, and milkproduction on reasons cows leave the herd. J. Dairy Sci. 83, 2980–2987.

Thomsen, P.T., Kjeldsen, A.M., Sørensen, J.T., Houe, H., Ersbøll, A.K., 2006.

Herd-level risk factors for the mortality of cows in Danish dairy herds.Vet. Rec. 158, 622–626.

Washburn, S.P., White, S.L., Green, J.T., Benson, G.A., 2002. Reproduction,mastitis and body condition of seasonally calved Holstein and Jerseycows in confinement or pasture systems. J. Dairy Sci. 85, 105–111.