84 Acta argiculturae Slovenica, Supplement 5, 84–88, Ljubljana 2016
24th Int. Symp. “Animal Science Days”, Ptuj, Slovenia, Sept. 21st−23rd, 2016.
COBISS: 1.08
Agris category code: L01
 
THE FREEZING POINT OF BULK TANK MILK IN SLOVENIA 1
Anita ULE 2, Helena PREPADNIK 3, Marija KLOPČIČ 4
The freezing point of bulk tank milk in Slovenia
 
1 This article is part of a Master Science Thesis entitled »Analysis of the factors that affect the freezing point of milk«, issued by Helena Prepadnik, supervisor Assist. 
Prof. Marija Klopčič, Ph. D.
2 University of Ljubljana, Biotechnical Faculty, Department of Animal Science, Groblje 3, SI-1230 Domžale, Slovenia, e-mail: Anita.Ule@bf.uni-lj.si
3 Chamber of Agriculture and Forestry of Slovenia – Regional office Celje, Extension Service Celje, Trnoveljska cesta 1, SI-3000 Celje, Slovenia, 
e-mail: Helena.Prepadnik@ce.kgzs.si
4 Same address as 2, e-mail: Marija.Klopcic@bf.uni-lj.si
ABSTRACT
The purpose of this paper was to determine effects on freezing point of milk in bulk tank. The analysis included 
90,579 milk bulk samples from Štajerska region between 2008 and 2013. The statistical model included milk purchaser, 
herd size, breed, interaction between pipeline material and milking system, calving interval, culling rate, milk cooling 
system, season, fat/protein ratio, production intensity and protein, lactose, and urea content as fixed effects. All effects 
significantly affected freezing point of bulk tank milk. The statistical model explained 32 % of the variance. The aver-
age value of freezing point was −0.5209 °C. The permissible value of −0,515 was exceeded by 5.7 % of the samples. In 
summer an increased freezing point and lower protein content was recorded. The estimated regression coefficient for 
protein was 0.0069 °C/%.
Key words: cattle, dairy cows, milk, freezing point, protein content, season effect
ell, 1989; Kirst et al., 2000; Golc-Teger et al., 2005; Henno 
et al., 2008; Hanuš et al., 2010; Hanuš et al., 2011).
Several studies (Rohm et al., 1991; Wiedemann 
et al., 1993a; Elchner et al., 1997; Golc-Teger et al., 2005; 
Henno et al., 2008; Sala et al., 2010) reported more prob-
lems with freezing point in early summer caused by 
changes in temperature, increase in water intake, and 
transition from winter diet on fresh green fodder and 
grazing. Rohm et al. (1991) found that milk freezing 
point during winter was on average of 0.0008 °C lower 
than during summer. Furthermore, the freezing point 
can also depends on milk composition. Sala et al. (2010) 
presented that a decrease of protein for 0.1 % cause an 
increase of freezing point for 0.002 °C in cows aged up 
to six years.
Moreover, Hanuš et al. (2011) supported that milk 
freezing point was improved with higher protein content. 
Babnik et al. (2010) studied relationship between fat and 
1 INTRODUCTION
The freezing point of milk is the temperature where 
milk changes from liquid to solid. It is rather constant 
and the freezing point of bulk tank milk is therefore used 
to determine whether water has been added. Milk has a 
lower freezing point than water and ranges from 0.520 °C 
to 0.560 °C. Higher freezing point of milk often demon-
strate the falsification of milk with water. For example, 
1 % of additional water increases the milk freezing point 
app. for 0.005 °C (Bajt et al., 1998).
Nevertheless, higher freezing points can also oc-
cur on farms where no water was added, due to cow re-
lated factors like breed, stage of lactation, health (masti-
tis), due to environment like climate, seasonal as well as 
weather changes, and technological solutions as feeding 
regime, water intake, milking system, storage time, and 
milk temperature (Buchberger and Graml, 1988; Mitch-
Acta agriculturae Slovenica, Supplement 5 – 2016 85
THE FREEZING POINT OF BULK TANK MILK IN SLOVENIA
protein ratio (F/P) and milk freezing point. Milk with 
F/P ratio below 1.1, reflecting a poor structured diet, has 
significantly higher freezing point while with F/B ratio 
above 1.5 has lower freezing point. Knowing effects on 
milk freezing point, farmers can avoid problems in de-
livering quality milk in terms of suitable freezing point 
(Babnik and Verbič, 2006; Buchberger, 2000).
Main goal of the research was to determine the most 
important effects on the freezing point of bulk tank milk 
on dairy farms in Štajerska region of Slovenia.
2 MATERIALS AND METHODS
Data on bulk milk samples from Štajerska region 
was obtained from the records of the quality control of 
milk delivered to the Dairies Celeia and Ljubljanske mle-
karne between 2008 and 2013, and from Cattle Business 
Association (GPZ z.o.o.). Information about herd size, 
breed, calving interval, and culling rate were provided 
by Central cattle breeding database on the base of milk 
recording data. Information on the farming system were 
obtained from questionnaires filled out by respondents 
farmers. All together, 90,579 records from 608 farms 
were used in statistical analysis.
The statistical model includes milk purchaser (Oi), 
herd size (Vj), breed (Bk), interaction between pipeline 
material and milking system (CMlm), calving interval 
(Dn), culling rate (Zo), milk cooling system (Hp), sea-
son as year-month interaction (Sr), F/P ratio (Rs), milk 
production intensity (It), and protein (x1ijklmnoprst), lactose 
(x2ijklmnoprst), urea (x3ijklmnoprst) content as fixed effects. Fat 
content and somatic cell count were not significant and 
therefore were not included in the model.
yijklmnoprst = μ + Oi + Vj + Bk + CMlm + Dn + Zo + Hp + Sr  
+ Rs + It + b1(x1ijklmnoprst − x−1) + b2i(x2ijklmnoprst − x−2) 
+ b3(x3ijklmnoprst − x−3) +eijklmnoprst
Data were analyzed by GLM procedure with statisti-
cal package SAS® software (SAS Inst., Inc., 2011). 
3 RESULTS AND DISCUSSION
Average freezing point of bulk tank milk was 
−0.5209 °C (Fig. 1) with standard deviation of 0.0046 °C 
and very close to reference value of −0.520 °C shown 
as solid line on Figure  1. Tolerance for freezing point 
of milk is set at −0.515 °C (dashed line). Whenever the 
freezing point is higher, milk price is reduced. In the pre-
sent study, the freezing point exceeded tolerance value in 
5.7 % of cases, 28.8 % of the samples were found between 
the reference value of 0.520 °C and a tolerance value of 
−0.515 °C. Two third (65.5  %) of milk samples could 
be considered as normal. The sharp drop in frequency 
at tolerance value of −0.515 °C can be a consequence of 
removed low quality milk in order to keep higher prices.
The statistical model used in this research, explained 
32 % of total variance and all effects included in the mod-
el showed significant influence on freezing point. 
Seasonal trends of protein content and freezing 
points of milk for all included years are presented in 
Figure 2. In summertime, freezing point increased and 
exceeded the average value of −0.5209 °C from May to 
October in almost all years. The highest average freez-
ing point was found in July (0.5197 °C). The opposite 
trends were observed between freezing point and protein 
content. Protein content was low during summer and 
both results were related to environment temperature, 
feed and water intake as well as feed quality. Higher milk 
freezing point values during summer was also reported 
from Austria (Rohm et al., 1991), previous researches 
from Slovenia (Golc-Teger et al., 2005), Romania (Sala 
et al., 2010), and Estonia (Henno et al., 2008).
The highest freezing point of milk (Table 1) were 
Figure 1: Distribution of milk freezing point
Acta agriculturae Slovenica, Supplement 5 – 201686
A. ULE et al.
observed by the purchaser 1 (−0.5199 °C). In smaller 
(1.0 to 15.9 cows) and larger herds (>26 cows), there is 
a slightly higher freezing point of milk (0.5212 °C). Also 
Wiedmann et al. (1993a, 1993b) indicate that the freez-
ing point of milk in herds with 10 or fewer cows was 
higher (−0.511 °C).
It was found in our study that herds, with more than 
70 % of Holstein Friesians cows, had the lowest freezing 
point which is just the opposite to other studies (Babnik 
et al., 2010; Buchberger, 1986; Henno et al., 2008). Pos-
sible explanation of this discrepancy in results might be 
in statistical model we used for analysing the influence 
of different parameters on freezing point, as milk com-
ponents were include in the model. Herds with Holstein 
Friesians cows had lower freezing point of milk then 
other breeds probably as consequence of better feeding 
regime. Milk freezing point was the same in herds with 
Brown and Simmental cows, where herds were much 
smaller and cows were fed with less balanced feeding 
ratios. The worst results were obtained in mixed herds 
(with different breeds) where feed ratio for dairy cows 
were not well enough.
The milking system might cause deviation in milk 
freezing points (Table 1). Lower milk freezing point was 
obtained on farms with bucket milking systems. Milk 
from farms with pipeline milking system had better 
freezing point than milk obtained from farms with milk-
ing parlor. Higher freezing point of bulk milk was found 
in farms with milking robot. Kirst et al. (2000) explained 
that milk freezing point was gradually increasing when 
hand milking was replaced by milking machine, due to 
residual water in the equipment and pipelines. Rasmus-
sen et al. (2002) and De Koning et al. (2003) agreed that 
the milk freezing point was increased by introduction of 
robot milking.
Health status of milking animals has a significant 
impact on the quality of milk. Sick animal can reduce 
feed intake which consequently affects the composition 
of milk and freezing point of milk (Babnik and Verbič, 
2006). In our analysis herds which replaced more than 
Figure 2: Least square means for freezing points (solid lines) and averages for protein contents (dotted lines) of bulk milk samples by years
Figure 3: A share of observations for milk protein content and the relation between the protein content and milk freezing point
Acta agriculturae Slovenica, Supplement 5 – 2016 87
THE FREEZING POINT OF BULK TANK MILK IN SLOVENIA
Effects Level LSM SEE
Milk purchaser 1 −0.5199 0.00006
2 −0.5213 0.00009
3 −0.5227 0.00007
Herd size 1–15.9 −0.5212 0.000066
16–25.9 −0.5215 0.000068
more 26 −0.5212 0.000069
Breed Brown −0.5213 0.000082
Simmental −0.5213 0.000081
Holstein Friesian −0.5216 0.000077
Mixed herds −0.5210 0.000077
Season 68 classes
Interaction between pipeline  
material and milking system
1 −0.5223 0.000337
2 −0.5224 0.000065
3 −0.5208 0.000117
4 −0.5215 0.000062
5 −0.5204 0.000070
6 −0.5225 0.000066
7 −0.5216 0.000088
8 −0.5212 0.000127
Calving interval (days) 340–400 −0.5213 0.000068
401–420 −0.5215 0.000067
421–440 −0.5216 0.000069
441–460 −0.5210 0.000069
< 461 −0.5211 0.000071
Culling rate < 30 % −0.5212 0.000070
> 30 % −0.5214 0.000062
Milk cooling system Bulk tank −0.5210 0.000066
Tank −0.5215 0.000062
Other −0.5215 0.000095
Fat/protein ratio < 1.5 −0.5216 0.000130
1.1–1.5 −0.5215 0.000048
> 1.1 −0.5208 0.000093
Production intensity Top 25 % herds −0.5211 0.000067
25 % good herds −0.5217 0.000069
25 % lower average −0.5214 0.000068
Bottom 25 % herds −0.5210 0.000068
Regression coefficient SEE
Protein content −0.0069 0.00009
Lactose content Milk purchaser 1 −0.0122 0.00015
Milk purchaser 2 −0.0196 0.00074
Milk purchaser 3 −0.0150 0.00037
Urea content −0.0002 0.00000
Table 1: Least square means (LSM) and regression coefficient for freezing points with standard errors of estimates (SEE) for studied 
effects (except seasonal effect)
Acta agriculturae Slovenica, Supplement 5 – 201688
A. ULE et al.
30  % of the animals had higher freezing point of milk 
(0.5212 °C).
We found higher freezing point values in milk of top 
25 % and 25 % of the worst herds regarding milk yield. 
Slaghuis (2001) reported that a higher milk yield may 
contribute to increase freezing point of the milk. On the 
other hand, Wiedman et al. (1993b) reported that freez-
ing point of milk more often increased in small herds 
with low milk yield per cow.
Protein content in bulk milk was on average 
3.34 ± 0.20 % (Fig. 3) with most observations between 
2.8 and 3.9  %. Results indicate that the freezing point 
decreases for 0.00069 °C (Fig. 3), when protein content 
increases by 0.1 %. The estimated regression coefficient 
of −0.00086 °C per 0.1 %, calculated by the Babnik et al. 
(2010) is in accordance with our results. By increasing 
the protein content of milk decreases milk freezing point, 
as expected. Buchberger (2000) indicated that reduction 
of protein content for 0.1 % leads to an increase of freez-
ing point for 0.002 °C.
4 CONCLUSIONS
All fixed effects in the statistical model had sig-
nificant effect on milk freezing point. In summer, milk 
freezing point was higher. The opposite trends were 
observed between freezing point and protein content. 
Protein content was low during summer. When protein 
content increased for 0.1 % the freezing point decreased 
for 0.00069 °C. For a more detailed analysis of the factors 
affecting the freezing point of milk, we would need data 
of individual cows.
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