Simensen et al. Acta Veterinaria Scandinavica 2010, 52:14
http://www.actavetscand.com/content/52/1/14

RESEARCH

Open AccessHousing system and herd size interactions in
Norwegian dairy herds; associations withperformance and disease incidence
Egil Simensen1*, Olav Østerås1, Knut Egil Bøe2, Camilla Kielland1, Lars Erik Ruud2, Geir Næss3

Abstract
Background: According to the Norwegian animal welfare regulations, it has been forbidden to build new tie-stallbarns since the end of 2004. Previous studies have shown that cow performance and health differ between
housing systems. The interaction between housing system and herd size with respect to performance and disease
incidence has not been evaluated.
Methods: Cow performance and health in 620 herds housed in free-stall barns were compared with in 192 herds
housed in tie-stall barns based on a mail survey and data from the Norwegian Dairy Herd Recording and Cattle
Health Systems. The housing systems herds were comparable with respect to herd size (15-55 cows). Associations
between performance/disease incidence and housing system, herd size and year of building the cow barn were
tested in general linear models, and values for fixed herd size of 20 and 50 cows were calculated. On theindividual cow level mixed models were run to test the effect of among others housing system and herd size on
test-day milk yield, and to evaluate lactation curves in different parities. All cows were of the Norwegian Red Breed.
Results: Average milk production per cow-year was 134 kg lower in free-stall herd than in tie-stall herds, but in therange 27-45 cows there was no significant difference in yields between the herd categories. In herds with less than
27 cows there were increasingly lower yields in free-stalls, particularly in first parity, whereas the yields wereincreasingly higher in free-stalls with more than 45 cows.
In free-stalls fertility was better, calving interval shorter, and the incidence rate of teat injuries, ketosis, indigestions,anoestrus and cystic ovaries was lower than in tie-stalls. All of these factors were more favourable in estimated 50cow herds as compared to 20-cow herds. In the larger herd category, bulk milk somatic cell counts were higher,
and the incidence rate of mastitis (all cases) and all diseases was lower.
Conclusion: This study has shown that there is an interaction between housing system and herd size, and that
performance and health is not universally better in small free-stalls than in tie-stalls.

Background
Modern dairy production in large herds most commonly
takes place in free-stall barns. Tie-stalls are, however,still an alternative to consider, particularly in smaller
herds. In Norway tie-stalls constitute the most common
housing system for dairy cows but, according to theNorwegian animal welfare regulations, it has been forbidden to build new tie-stall barns since the end of
2004. A panel appointed by European Food Safety* Correspondence: Egil.Simensen@fjellnett.no1
Norwegian School of Veterinary Science, Department of Production Animal
Clinical Sciences, POB 8146 Dep, 0033 Oslo, Norway

Authority stated that there currently is limited amountof scientific data linking the period per day of being tiedin tie-stalls to the level of disease and overall impact onwelfare, so this should be studied. A minority of thepanel recommended that dairy cattle should not be routinely kept in tie-stalls [1].
Previous studies have shown that performance anddisease incidences vary between free-stalls and tie-stalls.
A higher reproductive performance has been recordedin free-stalls [2-4] whereas milk yield has been reported
to be lower [3-6]. Lower disease incidence rates havebeen recorded in free-stalls, i.e. of mastitis[2,6], teat
injuries [4,7,8] and ketosis[2-4,9], whereas cows in free-© 2010 Simensen et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative
Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, andreproduction in any medium, provided the original work is properly cited.

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stalls have shown poorer claw health [10-12]. Milksomatic cell counts have been found to be higher infree-stalls [5,13] or at the same level in the two housing
categories [2,14]. When comparing housing systems,
results may as well interact with differences in herd size.
However, the interaction between housing system andherd size has not been studied and should be evaluatedfurther.
The purpose of the present paper was to study differences in performance and disease incidences between
free-stall and tie-stall housing for dairy cows in herds
with approximately equal size, and to evaluate the interaction between housing system and herd size. The study
is based on mail survey and data from the Norwegian
Dairy Herd Recording System (NDHRS) and the Norwegian Cattle Health Recording System (NCHRS).

Materials and methods
Data

An overview of types of dairy cow housing systems(free-stalls or tie-stalls) was obtained by the NDHRS
personnel from 11,600 dairy farms, which was 81% of all
farms participating in the NDHRS. Fourteen per cent(1,600) of these farms were confirmed to have a freestall system.
A questionnaire was sent to 2,400 farmers during
March 2006. Of these 1,600 were confirmed as having
free-stall barns and 800, with larger milk quota (morethan 100,000 litres), where type of housing had not been
confirmed. The purpose was to verify type of housing(by the farmer) and to obtain information on year ofbuilding, housing design and management in free-stallsystems as basis for selection of farms for further studies. Questions were of the multiple-choice type, andalternative answers were pre-coded. Completed questionnaire was returned by 1,323 farmers (response rateof 55% after one reminder). Of these were 1036 farms
with free-stalls and 287 with tie-stalls.
The questionnaire data were merged with data fromNDHRS [15], i.e. herd and individual cow level data for2005 and 2006. Herds with barns built in 2005 were notincluded, since these herds were in a transition phasewith respect to production. Furthermore, herds withother breeds than Norwegian Red Breed, an average ofless than 3,500 kg milk per cow, less than 15 cows orless than 100,000 litres milk quota were also excluded.
The maximum herd size was 53.9 cows in tie-stalls and134.5 cows in free-stalls. In order to fit the material to acomparison between herd categories, free-stall herds
with more than 55 cows (30 herds) were also excluded.
The final data set included 620 free-stall herds (average
herd size 26.5 cows, SD 9.4) and 192 tie-stall herds(average herd size 26.6 cows, SD 8.4). The average yearof building or last renovation of the cow barns

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(representing the current building status) was 1984 (SD14.3) for tie-stalls and 1996 (SD 7.2) for free-stalls. The
distribution of herds with respect to herd size and yearof building is shown in Fig. 1.
Comparison between free-stalls and tie-stalls at theherd level was based on NDHRS averages for the calendar year 2005. Studies at the individual cow level were
performed using NDHRS data for 2005 and 2006. This
material included cows that had terminated lactation
during 2006. Cows with lactation periods of more than
483 days were excluded (2.5% of the lactations). Cows
from breeds other than Norwegian Red were also
excluded.
Data extraction from NDHRS

The following data were extracted from NDHRS at herd
level: Milk production per cow-year (estimated at mean
production per 365 days), fertility index, herds meancalving interval, the herds annual geometric mean bulk
tank milk somatic cell count (BMSCC).
The fertility index is defines as:
Fertility status (FS-index): A measure of reproductive
performance calculated according to the following formula:
FS-index [a /b (c 125)]*(e  d)ewhere:
a = non return after 60 days (%) + % of 2 or 3 inseminations in same oestrus period,b = number of services per inseminated cow orheifer,c = average number of days between calving and lastinsemination,d = number of cows culled because of infertility,e = total number of inseminated cows or heifers.
Disease data at herd level were extracted from available calculated herd incidence rates estimated as cows
having at least one event of disease or other events
divided by number of cow years at risk, expressed asincidence rate per 100 cow-years. Separate incidenceswere available for removals, replacements, severe/moderate clinical mastitis, teat injuries, ketosis, milk fever,indigestion, retained placenta, abortion, anoestrus,
metritis, cystic ovaries and all diseases.
At individual cow level, parity and calving interval for
lactations that ended in removal or new calvings in
2006, altogether 26,276 lactations, was extracted.
Furthermore test-days data regarding kg milk and information whether the cow was diseased or not on test-day
were extracted. After removing all cows with otherSimensen et al. Acta Veterinaria Scandinavica 2010, 52:14
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40.00
35.00

% of herds

30.00
25.00
20.00
15.00
10.00
5.00
0.00
15-20

20-25

25-30

30-35

35-40

40-45

45-50

50-55

Herd size (no. of cows)
35.00
30.00

% of herds

25.00
20.00
15.00
10.00
5.00
0.00
-1960

1961-1965

1966-1970

1971-1975

1976-1980

1981-1985

1986-1990

1991-1995

1996-2000

2001-2004

Year of building

Figure 1 Distribution of 620 free-stall and 192 tie-stall herds with respect to herd size (no. of cow-years) and building year of cow
barn (building or last renovation). Black bars indicate free-stalls and white bars indicate tie-stalls.

breeds than NRF, the data set was reduced to 25,898
lactations, of which 38% were cows in first parity, 26%
in second, 18% in third and 19% in higher parities.
Mean lactation length was 293 days (median 342 days,
25% with less than 223 days and 10% with less than 78
days and range 1-483 days). Of the included lactations,
14.5% were second lactation within the same cow. The
test-day data which were extracted from these lactations
included 191,046 observations from 21,235 cows. Afterremoving test-say yields lower than 5 kg and higher
than 60 kg, the final material included 185,272
observations.
Statistical analyses
Herd level models

Statistical analyses were undertaken by means of SAS
statistical package version 9.1 (SAS, Cary, NC, USA).
Tests for herd level differences with respect to continuous variables, i.e. milk production per cow-year, fertility
index, culling rate, calving interval and BMSCC were
undertaken by means of general linear modelling (Proc
GLM) after having tested for outliers and normal distribution. One model was made for each dependent variable separately:Y  a  b* X  e

X consisted of the independent variables stall type (1= tie-stall, 2 = free-stall), herds size (continuous), theinteraction between stall type and herd size and the yearof building/reconstruction (continuous).
Differences between herd disease incidence rates were
tested by means of general modelling (Proc GenMod inSAS) using the log link function and poisson or negative
binomial distribution according to the best fit of themodel assessed by deviance. Number of disease eventsin each herd were estimated from the given incidence
rate and herd size (number of cow-years). Logarithm(Ln) of mean number of cows in the herd during one
year was used as offset variable. If herd size was significantly associated with the outcome the model was
adjusted for herd size. The model fit was evaluated bylog likelihood or deviance. Independent variables were
number of cases with the diseases mastitis, severe/moderate clinical mastitis, teat injuries, ketosis, milk fever,indigestion, retained placenta, abortion, anoestrus,
metritis, cystic ovaries and all diseases. The model was
E(Y) = nl, where l is a function of the predictors. Ln(l)= b 0 + b 1 X where variance = μ+ aμ 2 with a poisson

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distribution a = 1. X consisted of the independent variables stall type (1 = tie-stall, 2 = free-stall), herds size
(continuous), the interaction between stall type andherd size or the year of building/reconstruction(continuous).
In all models at herd level non-significant variables
were removed one by one, first the interaction between
herd size and stall type and thereafter herd size orbuilding year if non-significant. Significance was set at p
≤ 0.05, but the variable was included in the model if p <0.10.
Test-day level model with milk yield as dependent variable

Finally a different test-day models was run using mixed
models with herd as random effect and repeated measurements within lactation, nested within herd, applying
an autoregressive type 1 regression (AR1) matrix. As kg
milk was not log-transformed the model was estimating
the lactation curve parameterized using the Wilmink
equation [16]:Y test-day-milk-yield  a  b1DIM  b 2 ln DIM  b 3X  Z h  Z l  ewhere DIM = days in milk, X = represent all other fixed
affects type of stall (tie- = 1 or free-stall = 2), herd size
(continuous), calving interval and interaction by herd size
and type of stall, herd size and DIM, type of stall andDIM and calving interval and DIM applied, Zh = theherd random effect, Zl = the lactation repeated effectwithin herd using AR(1) correlation matrix, and e = random error effect. As this model has well known interaction between parity and DIM and lnDIM, the model was
stratified on parity both to avoid random effect at individual and the interaction terms (parity and DIM) which
would make the model too complicated to deduce.

Results
Pairwise analyses by means of the analysis of varianceshowed that milk production per cow-year was 134 kg
lower in free-stalls than in tie-stalls, 6943 vs. 7077 kg (p< 0.05). In free-stalls FS-index was higher than in tie-stalls (78.9 vs. 57.2, p < 0.001), calving interval was
lower (369 vs. 384 days, p < 0.001), and the incidence
rate of the following diseases were also lower: teat injuries (1.08 vs. 2.12, p < 0.001), ketosis (1.30 vs. 3.39, p <0.001), indigestions (0.66 vs. 1.46, p < 0.001) and anoestrus (1.19 vs. 2.28, p < 0.002). No difference between
housing systems was found for among others mastitis(all cases) all diseases and BMSCC.
The herd level models included herd size and year ofbuilding of the cow barn in addition to housing system,and the results regarding performance are shown in
Table 1. Estimated means at a fixed herd size of 20 and
50 cows for factors being significantly associated withhousing system and herd size in the models are shownin Fig. 2. Correspondingly, results from the models
regarding disease incidences are shown in Table 2, andmodel estimates for 20- and 50-cow herds are presented
in Fig. 3. The results are summarized in Table 3. Yearof building of the cow barn had no significant associations with disease incidences, but it had a significantly
negative association with calving interval. In free-stalls,
the following factors were significantly different fromtie-stalls: Lower milk yields, higher FS-index, lower calving interval, lower incidence rate of teat injuries, ketosis and anoestrus. Except from anoestrus, all of thesefactors were also associated with herd size, i.e. higher
milk yields and higher FS-index, and lower incidences ofteat injuries and ketosis in 50-cow herds as compared to
20-cow herds. The following significant associations
were found with herd size, but not with type of housing:Higher BMSCC and lower incidences of mastitis (allcases), indigestions and all diseases in the 50-cow
category.
The interaction between housing system and herd sizewith respect to milk production per cow is shown in
Fig. 4. The 95% confidence intervals for milk yield infree-stalls and tie-stalls overlapped in herds from 27 to
45 cows, i.e. there was no significant difference between
housing systems in this range. Outside this range thedifferences were significant. In herds with less than 27

Table 1 Model estimates (with standard error in brackets) from the general linear (GLM) model estimates in 620 freestalls and 192 tie-stalls using Proc GLM in SAS.

Milk per cow-year(kg)
FS status (FS-index)
Calving interval(days)BMSCC (1000/ml)x

Tie-stall

Herd size

7472.1 (277.2)xxx

719.1 (218.9)xx-45.48 (19.04) -21.38 (7.83)xx

0.855 (0.299)xx

95.201 (7.724)xxx-21.278 (1.894)-1.159 (0.536)

0.018 (0.009)x

782.22 (137.43)

11.541 (1.72)xxx

0.913 (0.429)x80.364 (12.740)

3.779 (3.144)ns

2.429 (0.882)

xxx

xxx

= p < 0.05, xx = p < 0.01, xxx = 0.001(Effect of free-stall = 0 in the models).

xxx

Interaction tie-stall herd
sizeYear ofbuilding

Herd size in 2nd
powerIntercept

x

x

xx

-0.214 (0.069)xx-0.014 (0.007)x-0.024 (0.014)0.06

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Milk per cow-year (kg)Calving interval (days)

7400
7300
7200
7100
7000
6900
6800
6700
6600

380
375
370
365
360
355

20 Cows

50 cows

20 Cows

Fertility status (FS-index)

50 cows

Bulk milk cell count (1000/ml)

100
80
60
40
20
0

190
140
90
40

20 Cows

50 cows

20 Cows

50 cows

Figure 2 Expected least squares means from model estimates (Table 1) at a herd size of 20 and 50 cows in 620 free-stall and 192 tiestall herds. Black bars indicate free-stalls and white bars indicate tie-stalls.

cows there were increasingly lower yields in free-stallherds, whereas the yield were increasingly higher infree-stall herds with more than 45 cows.
The mixed models regarding test-day milk yields were
run separately for each parity (1, 2, 3, >3). The lactation
curves based on these models showed that the largest
difference was found between parity 1 and 3. The resultsfrom the test-day models for these parities are shown in
Table 4, and the lactation curves in Fig 5. The results
were in agreement with the herd level model in thatmilk yields were significantly associated with housing
system and herd size. In parity 1 the yields were lower
in free-stalls in the 20-cow herds throughout the wholelactation, whereas they were at the same level in freestalls and tie-stalls in 50-cow herds. In parity 3 theyields were also lower in the 20-cow herds, but the difference in relation to tie-stalls was less than for cows inparity 1. There was a difference in the shape of the lactation curve; yields being higher in the first 60-80 daysof lactation in tie-stalls, and also in the last part of lactation. In the 50-cow herds the yields were higher in freestalls in mid-lactation.

Discussion
The two herd categories differed with respect to year ofbuilding/renovation in that tie-stall buildings were in
average 12 years older than the free-stall buildings. Fourof the tie-stalls and 33 of the free-stalls were built in2004 and were thus in a transition phase that year withrespect to performance and health. We therefore used
NDHRS data for 2005/2006 in the analyses. Other studies [5,17] have shown that cows changing from one
system to another produced less milk the first few
months after the transfer, but recovered after a full year.

Table 2 Model estimates (with standard error in brackets) from the poisson or negative binomial (NB) model
estimates in 620 free-stalls and 192 tie-stalls cows using Proc Genmod in SAS.
Disease event

Intercept

Tie-stall

Herd size

Severe/moderate mastitis-1.8233 (0.0918)xxx

0.0160 (0.0695)-0.0060 (0.0031)0.005

All cases of mastitis-1.2239 (0.0922)xxx-0.3144 (0.2075)-0.0124 (0.0032)xxx

Teat injuries-3.7139 (0.2233)xxx

0.6633 (0.1487)xxx-0.0285 (0.0077)xxx

Ketosis-3.7847 (0.2240)xxx

0.9649 (0.1520)xxx-0.0189 (0.0076)x

1.8793 (0.2907)

Milk fever
Indigestions-2.9452 (0.0391)xxx-4.1680 (0.3249)xxx

0.0702 (0.0782)-0.2089 (0.5558)-0.0303 (0.0115)xx

0.2071 (0.0476)
1.2651 (03637)

Retained placentaxxx-3.3586 (0.0539)-0.0812 (0.1126)

0.6680 (0.1071)

Abortions-6.0659 (0.1622)xxx-0.5325 (0.4113)

PoissonAnoestrus-4.4459 (0.1232)xxx

0.7085 (0.2334)xx

5.8928 (0.8265)

Metritis-4.4742 (0.0859)xxx-0.4554 (0.2016)x

1.1197 (0.3160)

Cystic ovaries-4.8557 (0.1151)xxx-0.4537 (0.2151)x

All diseases-0.4513 (0.0812)xxx-0.0461 (0.0620)

x

xx

xxx

= p < 0.05, = p < 0.01,= 0.001(Effect of free-stall = 0 in the models).

Interaction tie-stall herd size

Dispersion (If NB fit)
0.4254 (0.0379)

0.0121 (0.0072)0.09

0.4188 (0.0325)
1.0733 (0.2602)

0.0391 (0.0189)x3.1334 (0.6429)-0.0062 (0.0028)x

0.4869 (0.0282)

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All cases of mastitis

Ketosis

0,25

0,05
0,04
0,03
0,02
0,01
0

0,2
0,15
0,1
0,05
0

20 cows

20 Cows

50 cows

50 cows

Indigestions

Teat injuries
0,03
0,025
0,02
0,015
0,01
0,005
0

0,025
0,02
0,015
0,01
0,005
0

20 Cows

20 Cows

50 cows

50 cows

All diseases

Anoestrus
0,6
0,5
0,4
0,3
0,2
0,1
0

0,03
0,025
0,02
0,015
0,01
0,005
0

20 Cows

50 cows

20 Cows

50 cows

Figure 3 Expected incidence rates from model estimates (Table 2) at a herd size of 20 and 50 cows in 620 free-stall and 192 tie-stall
herd. Black bars indicate free-stalls and white bars indicate tie-stalls.

Automatic milking may be a confounding factor as it
has been associated with a higher risk for high SCC [5],but in our material only 16 of the farms had automatic
milking.
Usually herd estimates of cow performance are basedon milk production per cow-year or disease incidences
per cow-year as measures of intensity of milk production and disease occurrence at herd level. These measures are used as descriptive statistics, but they could be
biased owing to different combinations of parities andTable 3 Overview of significant associations between
performance/disease incidences and type of housing/herd size (20 and 50 cows) as shown in Table 1 and 2
and Fig. 2 and 3.
Housing system

Herd size

Interactions

Milk per cow-year

xx

x

xx

Fertility status (FS-index)

xxx

x

Calving interval
BMSCC

xxx

x
xx

Teat injuries

xxx

xxx

Ketosisxxx

Mastitis, all cases

different combinations of days in milk. This again could
be due to different removal strategies in different herds.
When analyzing the association between milk yield andhousing system/herd size we therefore used two models.
In addition to the herd level general linear model wealso used individual cow test-day mixed models which
also included calving interval in different parities. The
results from these models confirmed the herd level
result in that milk yields were significantly associatedwith housing system and herd size.
The finding that milk production per cow-year was
lower in free-stalls is in agreement with results fromprevious studies in Norway [3,4] and Finland [5],xxx

Indigestions

xxx

Anoestrus

xx

Metritisx

Cystic ovaries
All diseasesxx = p < 0.05, xx = p < 0.01, xxx = 0.001

xx

Figure 4 Herd milk yields per cow-year and their 95%
confidence intervals in 620 free-stall 192 tie-stalls related toherd size out from the general linear models as shown in Table
1.

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Table 4 Model estimates (with standard error in brackets) from the mixed models (ProcMixed in SAS) regarding testday milk yield for cows in parity 1 (73,878 observations) and parity 3 (31,259 observations).
Parameter

ClassIntercept
Dim (days in milk)

Continuous

Estimate (b), parity 1

Estimate (b), parity 3

10,9556 (0,4407)xxx

19,3046 (1,3906)xxx-0,08280 (0,001694)xxx-0,1511 (0,004225)xxx

xxx

Lndim
Housing (tie-stalls)

Continuous
1

3,2422 (0,09681)
3,9006 (0,6385)xxx

5,0496 (0,2793)xxx
5,4013 (0,9872)xxx

Housing (free-stalls)

2

0

0

Dim*housing

1

0,003912 (0,000921)xxx

0,009284 (0,001902)xxx

Dim*housing

2

0

0

Lndim*housing

1-0,4517 (0,0763)xxx-1,0271 (0,1472)xxx

Lndim*housing

20

CI (calving interval)

Continuous

0,004768 (0,001409)xxx

0,008638 (0,001908)xxx

Dim*CI
Lndim*CI

Continuous
Continuous

0,000043 (0.0000003)
0,0000007 (0,0000002)x

0,000101 (0,0000010)xxx-0,00145 (0,000616)x

Dim* cows (herd no of cow-years)

Continuous-0,00010 (0,000038)xx-0,00018 (0,000079)x

Continuous

xxx

0,02182 (0,006012)xxx

xxx-0,2022 (0,07613)xx

x0,001119 (0,000142)

0,002519 (0,001139)xxx-0,05634 (0,03034)ns

Lndim*cows
Cows

Continuous

Cows*cows

Continuous

xxx

0,02167 (0,003022)-0,04516 (0,01325)

Cows*housing

1-0,05597 (0,02091)

Cows*housing

2

0

x

= p < 0.05, xx = p < 0.01, xxx = 0.001
Random herd effect estimated to 19.0% in parity 1 and 19.8% in parity 3.
Random lactation effect estimated to 3.8% in parity 1 and 2.3% in parity 3.

whereas no difference was found between tie-stalls andloose housing in a large-scale study in Denmark [18].
Our result could indicate that free-stall barns have a lessParity 130

Test-day milk yield kg

25

20

15

10
Tie-stall 20 cows
Free-stall 20 cows
Tie-stall 50 cows

5Free-stall 50 cows

05

14 23 32 41 50 59 68 77 86 95 104 113 122 131 140 149 158 167 176 185 194 203 212 221 230 239 248 257 266 275 284 293 302
Days in milk (DIM)

Parity 3
40

35

Test-day milk yield kg

30

25

20

15
Tie-stall 20 cows

10Free-stall 20 cows
Tie-stall 50 cows
5Free-stall 50 cows

05

14 23 32 41 50 59 68 77 86 95 104 113 122 131 140 149 158 167 176 185 194 203 212 221 230 239 248 257 266 275 284 293 302
Days in milk (DIM)

Figure 5 Lactation curves for cows in parity 1 and 3 frommodel estimates (Table 4) in 662 free-stall and 192 tie-stallherds.

optimal function in smaller herds as other factors
appear to intervene. Cattle are social animals and readily
form dominance hierarchies, especially at areas of accessto feed and water and the best resting area [19]. In general, changes in social strategies are related to variations
in group size [20]. Sheep in larger groups spent lesstime queuing at the feed barrier [21], and in weaned
pigs there were significantly more fights in smallergroups [22]. Among dairy calves increased group size
reduced conflicts, and calves in the larger groups spent
more time feeding [23]. Possibly similar interactions
between group size and social behaviour also take place
among adult cattle. The difference we found in the
shape of the lactation curves, i.e. that yields were lowest
among first parity cows primarily in 20-cow herds (Fig.
5) may indicate that these cows are lower in social rank
and that this has larger consequences in smaller herds.
The design of the cow barns may also be a factor having
effect on cow behaviour, and suboptimal designs (areaper cow, blind alleys, access to drinking water etc.) may
have more unfavourable consequences in small freestalls. Several of the associations recorded regarding performance and disease incidence were less favourable inthe 20-cow herds as compared to the 50-cow herds, andthis also indicates that small free-stalls are functioning
less optimal.
The higher reproductive performance (higher fertility
index, lower calving interval and lower treatments rates
of anoestrus and cystic ovaries) which was found inSimensen et al. Acta Veterinaria Scandinavica 2010, 52:14
http://www.actavetscand.com/content/52/1/14

free-stalls in this study is in agreement with previous
results [2,3,9], and may possibly be related to easier oestrus detection when the cows are allowed to movefreely. However, earlier oestrus detection and higher
conception rates at first service have been observed intie-stall barns as compared to free-stalls [24].
No significant difference between free-stalls and tiestalls was found in average herd incidence rate of mastitis and BMSCC. This is in agreement with previous
findings [3,4,7,25]. In another study, cows in tie-stalls
had lower cell counts, but the proportion of cows having
new high SCC for the first time and the incidence rateof mastitis did not differ between housing systems [5].
Lower mastitis incidence rate in free-stalls was foundbut no difference in somatic cell counts [2,6].
Teat injuries were found to be less frequent in freestalls than in tie-stalls, and this is in accordance withprevious results [4,7,8] Other studies have shown poorer
claw health in free-stalls [10-12], but the present material did not provide sufficient information on claw
health to make a comparison between housing systems
possible.
The incidence rate of ketosis was 2.6 times higher intie-stalls than in free-stalls, and this result is in agreement with previous findings [2-4,9]. The main risk factors for ketosis are related to nutrition and feeding. We
found that the incidence of indigestions was higher intie-stalls and that the shape of the lactation curve differed between herd categories, particularly in the firstand last part of lactation for cows in parity 3 in the 20cow herds. These results indicate that feeding strategies
were different in the two housing categories.

Conclusions
Several of the performance and health related factors
were more favourable in free-stalls than in tie-stalls, andmore so in estimated 50-cow herds as compared to 20cow herds. Milk yields were increasingly lower in freestall herds with less than 27 cows. Our study has shownthat performance and health is not universally better insmall free-stalls than in tie-stalls.
Acknowledgements
The authors would like to thank the participating farmers for their help andsupport during the study. The access to the data was given by the
Norwegian Dairy Herd Recording System (NDHRS) and the Norwegian Cattle
Health Services (NCHS) (for health data) in agreement 3/2006. The study was
financially supported by grants from The Research Council of Norway (15%),
Agricultural Agreement Research Fund (16%) and Foundation for Research
Levy on Agricultural Products (69%).
Author details
1
Norwegian School of Veterinary Science, Department of Production Animal
Clinical Sciences, POB 8146 Dep, 0033 Oslo, Norway. 2Norwegian Universityof Life Sciences, Department of Animal and Aquacultural Sciences, POB 5003,
1432 Ås, Norway. 3North-Trøndelag University College, POB 2501, 7729
Steinkjer, Norway.

Page 8 of 9

Authors’ contributions
ES, KEB and OØ had a central role in initiation of the research programme,
CK, LER and GN carried out the mail survey, OØ performed the statisticalanalyses, and ES was the head writer of the manuscript. All authors haveread and approved the final manuscript.
Competing interests
The authors declare that they have no competing interests.
Received: 6 August 2009
Accepted: 16 February 2010 Published: 16 February 2010
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doi:10.1186/1751-0147-52-14
Cite this article as: Simensen et al.: Housing system and herd sizeinteractions in Norwegian dairy herds; associations with performanceand disease incidence. Acta Veterinaria Scandinavica 2010 52:14.

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