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Cluj Vet J 2022, 27, 2 http://clujveterinaryjournal.ro 

Article 

Hoop structure for horses during winter season: controlling 

the low critical temperature 

 
Ioan HUTU1,2, Bianca LUNGU2*, Gabriel OTAVA1,2 , Iuliu TORDA2, Simona MARC1,2, Oana BOLDURA1,2, Calin 
MIRCU 1,2 

 

1 University of Life Science “The King Michael I” – Faculty of Veterinary Medicine, Timisoara, RO 
2 Horia Cernescu Research Unit – USV Timisoara, RO 
*Correspondence: bianca.lungu@fmvt.ro 

Abstract: Hoop barns, the low input housing structures, can be used in housing horses during fall and winter seasons. One of the 
hoop structures issue is the level of temperature, which is close to environmental temperature. The aim of this study is to show some 
technological measures which can overcome the weaknesses of hoop structures such as: feeding strategy, water system and body 
warming of horses using IR film. The control variable was the skin temperature of six horses, repeatedly measured with FLIR® 
thermo camera during several levels of environmental temperature. In the study, by using IR heating film at outside temperatures 
such as 0, -5 and -10°C,  the body temperature measured in three body regions (neck, shoulder point and internal angle of eyes) did 
not differed significant (F=0.167 at p =0.847): without IR heating system, differences were observed (F= 8.905 at p =0.000). Moreover, 
in low BCS’s animals, below -10°C environmental temperature, in absence of IR heating and if less fiber was present in the diet, low 
critical temperature signs were observed. In conclusion the hoop structure can be used successfully in horses even when outside 
temperatures are below low critical temperature of horses if certain conditions are assigned such as: water at 10-15°C, additional hay 
for fiber, with or without infrared heating. 

Keywords: hoop structures, low temperature, horse 
 

1. Introduction 
 
Hoop structures have been used as effective alternative housing for grow-finish 

swine in the United States, Canada and Australia for over 30 years [4]. In Romania a hoop 
structure was studied [6,7,9,10,11, 13] and has been operable at Banat University – Horia 
Cernescu Research Unit since 2012. Hoop structures offer a distinct advantage for animal 
production due to the substantially smaller capital investment, relative to a conventional 
confinement building along with substantial reductions in energy operating cost.  

Energy use is reduced because these structures are not heated or mechanically ven-
tilated. In cold seasons, horses utilize the low energy consumption systems - IR heat pan-
els to increase the thermal comfort. During warm seasons, structures with a north/south 
long axis orientation in open areas, will experience substantial natural air flow for venti-
lation. In addition, the high arch-shape of the structure creates a “chimney effect” that 
facilitates natural air flow. Furthermore, hoop structures are also versatile buildings that 
are easily converted to facilities for other types of livestock or for feed or equipment stor-
age if a farmer decide to discontinue swine production and focus on other enterprises [9].   

Finnish researchers investigated the respiratory health effects of loose indoor/out-
door group housing on weanling foals in cold Scandinavian winters (below −20°C in Fin-
land for several consecutive weeks during the winter season) and they found that, gener-
ally, the foals did very well in this environment. The general conclusion was that keeping 
weanling horses in cold loose housing systems does not seem to increase the occurrence 

Received: 06.10.2022 

Accepted: 27.10.2022 

Published: 15.11.2022 

DOI: 10.52331/cvj.v27i2.39 

 

 

 

Copyright:© 2022 by the authors. 

Submitted for possible open access 

publication under the terms and 

conditions of the Creative Commons 

Attribution (CC BY) license 

(http://creativecommons.org/licenses

/by/4.0/). 

https://doi.org/10.52331/cvj.v27i2.39


Cluj Vet J 2022, 27, 2 2 of 24 
 

 
of respiratory diseases, but special attention should be focused on ventilation, air quality 
and feeding-practices [12].  

The specific objective of this report was to establish baseline conditions and expecta-
tions for keeping horses in hoop systems in Romania during the winter season of the year 
by using IR heating film panels. 

 
2. Materials and Methods 

Animals and data collection: six horses (Thoroughbreds, Romanian sport horse and Arabian breeds) 
weighing 580.83±17.14 kg were obtained from private owners on November 2018 by Research Contract 
no. 6944 from 25.09.2013 and placed in the ruminants hoop structure at the Horia Cernescu Research Unit, 
infrastructure of Life Science University “King Michael I” Timisoara, RO. The group consisted of 4 females 
and 2 males which were placed in individual pens inside the hoop structure after deworming based on 
fecal analysis. The horses were acclimated to their new location for 15 days. No haircuts were performed 
during the trial, but one physiological change was observed - an increase in density and length of the 
horse's coat. On the fifteenth day, horses were weighed and scored for body condition scoring. Subse-
quently, horses were weighed and scored for BCS every month considering the Henneke’s scale [5] for 
jumping horses. Inside and outside temperature and humidity of hoop were continuously monitored us-
ing a multi-functional wireless digital device Weather Station PCE-FWS 20. The FLIR (E50 Multi-Spectral 
Imaging Dynamic, MSX®, Wilsonville, Oregon, USA). A thermocamera was used for collecting the external 
body temperature of horses several times, when environmental temperature was in the limits established 
by the study. The body temperature was taken in three points (neck, head – internal angle of eyes and 
point of shoulder – figure 2) during the trial period (December and January) depending on the inside tem-
perature inside the hoop: at 0.0±2.0°C, at -5.0±2.0°C, and -10.0±2.0°C.  

Feed: Feed consisted of two intakes of 2.0 kg of washed oats and three intakes of 3.0 kg of grasses hay 
(less than 2% of their body weight in hay per day), 40 ml of corn oil daily, salt, vitamins A, D, E and 2:1 
calcium-phosphorus mixture. For medical reason, during January one horse received just 1.25 kg of grasses 
hay per intake. Composition of the feed was analyzed by Foss InfraXact® (Hillerød 3400, DK), NIR equip-
ment. Feed was stored in bags in the hoop structure and feeders were filled manually after weighing using 
Ranger Mate (American Calan, Northwood, New Hampshire, USA). Each pen was equipped with one nip-
ple/cup water fountain and one feeder. In order to prevent freezing of pipes, a heating cable was used – 
the temperature was set to 10-15°C.  

Housing: The Experimental Unit – hoop structure used for this trial has a total exterior dimension of 
12 X 36 m and has concrete flooring, although it was primary designed for heifers and redesigned for 
horses’ during the trial (figure 1). The primary design feature of these types of structures consists of uni-
formly spaced metal arches which are covered with a tightly woven plastic tarpaulin which is stretched 
out over the arches. The arches are attached to the top of vertical posts. These posts serve as the foundation 
of the structure. The tarp is stretched by means of small winches attached to the exterior surface of the 
posts. The interior of the posts is faced with wooden boards or sheet material to create a wall of 1.75 meters 
in height. The arched ends of the structure are typically covered with similar plastic canvass material with 
some type of roll-up doorway. The end-walls are often partially or completely opened during warm 
weather to increase air flow and reduce internal structure temperature and totally closed during the cold 
season. During winter, the one side inlet (15 cm x 36m) and top outlet 30cm x 36 m) were completely open 
in order to stimulate the air flow and to avoid the formation of condensation drops. The six horses were 
housed in the hoop structure, one per pen. Each of the six pens in which horses were housed measured 
3.6 X 5.50 m. This offered 23.76 m2 per animal which is more than the recommendation on horse housing 
for research purposes – [4,8]. Each of the 6 pens were equipped with one heating panel (handmade - two 
rows of 2 m2 of heating film, power 200W/m2, with long-wave infrared radiation, of 4 µm ÷14 µm anchored 
in arch ceiling structure, parallel with floor, at 3.5 meters high (figure 1). 

 



Cluj Vet J 2021, 27, 2 3 of 24 
 

  
(a) (b) 

Figure 1. Normal (a) and FLIR thermocamera (b) imagines of trial place – six pens in hoop structure each with one IR 
heating panel suspended in arches of ceiling (Hutu, 2018). 

Statistical Analysis: Analysis of external body temperature of horses were performed using one-way 
Analysis of Variance (ANOVA) for temperature of three body regions in presence or absence of IR heating 
panels. All data comparing body temperatures in case of using/not using IR heating was analyzed using 
two-sample Student’s t-tests. For lower number of data, the Wilcoxon Signed Ranks Test was used. 

3. Results and Discussion 
 

Body weight was in average 580.83±17.14 kg at the beginning of the study (November 2018) and 
585.83±18.09 kg at the end, on 31th of January 2019. The easy training activities were done during the study. 
In those conditions, even if the temperature in the hoop was lower, horses became heavier - but the difference 
between the start and finish of the trial cannot be statistically sustained (Z=-0.843 at p = 0.339 - Wilcoxon 
Signed Ranks Test). 

Body condition scoring was in average adequate for jumping horse (BCS = 5.54±0.12). BSC was assessed 
three times: during the accommodation period, at the end of December and at the end of January. Major 
differences were not observed during the study period (p=0.317, Wilcoxon test): in average BCS was 5.41±0.24 
at the beginning of the study (November 2018), 5.58±0.20 in December and 5.62±0.22 at the end of the study 
period (January 2019).  

Temperature and Humidity: The inside temperature was higher (+1.56 оC at p< 0.001) and humidity in-
dex was lower (-0.49% at p< 0.001) than outside measurements. There was a strong correlation between in-
side and outside temperature (r = 0.925 at p < 0.01) and humidity index (r = 0.829 at p< 0.01). There were no 
clinical signs of low critical temperature among horses even though daily minimum temperatures often ex-
ceeded -10.0o C during January, with one exception. One horse that scored 4.5 in BCS had horripilation, 
muscle contractions, reduced blood flow at the level of the extremities such as ears, muzzle and legs as a 
sign of cold stress. As a preventive measure, horses that are body clipped or with low BCS will benefit from 
a blanket. Blankets are also beneficial for short term, in extremely cold, wet weather [3]. 

External body temperature of horses was measured in three body regions, with and without IR heating 
film, at outside temperatures such as 0, -5 and -10°C. Without IR heating panels, at previously mentioned 
environmental temperature, the body temperature measured was 18.28±0.74оC, 18.90±0.72оC and 
22.19±0.65оC – in the study, the differences were significant (F= 8.905 at p =0.000). When measured in each 
body region (middle of neck, shoulder point and internal angle of eyes) the temperature was well differen-
tiated (F=38.34, p=0.000): 17.79±0.38оC for neck region, 18.09±0.63оC for shoulder point and 23.49±0.50оC for 
internal angle of eyes. The variability between several body regions is normal and was reported by several 
authors [1]. 



Cluj Vet J 2022, 27, 2 4 of 24 
 

 
With IR heating panels on, the body temperature meas-

ured was 19.99±0.85оC, 19.34±0.76оC and 19.61 ±0.78оC – in 
the study, the differences did not differ significantly 
(F=0.167 at p =0.847). It appears clearly that IR body heating 
panels reduce the variability of body part temperature and 
the influence of external negative temperature of the envi-
ronment. Measured in each body region (neck, shoulder 
point and internal angle of eyes) the temperature was well 
differentiated (F=36.46, p=0.000): 17.79±0.37оC for neck re-
gion, 17.92±0.65оC for shoulder point and 23.23±0.46оC for 
internal angle of eyes). Because the aim of using IR heating 
film is body’s warming and not to heat the air of the stable, 
IR panel heating film had a lower electricity power con-
sumption - for one horse the electrical power consumption 
is 0.4 kWh (1.44 MJ). For all six pens the electricity con-
sumption was 2.4 kWh (8.64 MJ) which is similar with a 
domestic air heater.  

The FLIR thermocamera used for collecting the exter-
nal body temperature worked pretty well in cold climate, 
like other authors suggested [2]. 

The low critical temperature's signs were observed at 
environmental temperature below -10°C in one horse– it 
was the case of a horse that had a lower BCS’s, in absence of IR heating and with less fiber in the diet – 
because of colic prevention measure. Horses increase body metabolism through various physiological mech-
anisms. Bacterial fermentation of forage in the hind gut of the horse is one of them – by this, horses can 
generate a tremendous amount of heat. As a result, horses can tolerate much colder weather than humans. 
Practically, the addition of fiber to the diet will increase heat from fermentation. 

 
In conclusion of the study, the hoop structure can be used successfully in horses, even when outside 

temperatures are below the low critical temperature of horses, if certain conditions are fulfilled such as: 
water at 10-15°C, feed rich in fiber and BSC in optimum ranges. 

 

5. Conclusions 
Hoop structures can be used for housing horses during the winter season, if an increased diet of grass 

hay is provided. Increasing the external temperature by using panels with long-wave infrared radiation of 4 
µm ÷14 µm does increase thermal comfort and will facilitate the housing of horses in extremely cold envi-
ronments. Because the aim of body warming by IR heating film is not to heat the air of the stable, IR panels 
had a lower electricity power consumption - for one horse the electrical power consumption is 0.4 KW/hour. 
Low body condition score imposes the increase of grass hay intake, use of a blanket, or IR heating systems 
in order to avoid the clinical signs of low critical temperature in the hoop structure. 
 

Author Contributions: “Conceptualization, I.H. and C.M.; methodology, G.O.; validation, O.B investigation, L.B and 
I.T.; writing—original draft preparation, I.H.; writing—review and editing, S.M.; visualization, C.M.; funding acquisi-
tion, I.H. All authors have read and agreed to the published version of the manuscript”. 

Funding: The research was financed by Extension Unit, ONG, in Research Contract no 6944 from 25.09.2013 - Analysis 
and testing of the infrastructure for the maintenance and exploitation of horses.  

Institutional Review Board Statement:  

The study was conducted according to the guidelines of the Low 43 11.04.2014 and approved by the Ethics Committee 
of Horia Cernescu Researh Unit, protocol code POUEX1.1 from 27.05.2016. 

Acknowledgments: The authors acknowledge to the Faculty of Veterinary Medicine students (Gabriel Terei, Bibart 
Alexandru, Balint Andras, Balint Szillard and Halil Fahmawi coordinated by PhD Irina Patras) for their volunteer activ-
ities, to the Banat’s University horse jumping team (Lupu Andreea and Rusu Adelina whith Mary, Popescu Teodora 

 

Figure 2. FLIR® IR image with temperature 

spot on "point of shoulder".  



Cluj Vet J 2021, 27, 2 5 of 24 
 

with Gordon, Marza-Rizac Laura with F-Rock, Moaca Marius with Afrodita, Galeancu Stefan whith Navaro) and to 
trainers Olimpia Rusu and Bogdan Biris for collaboration and giving horse during trial period.  

Conflicts of Interest: “The authors declare no conflict of interest.”  

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https://doi.org/10.1016/C2018-0-04639-3
https://doi.org/10.1016/C2018-0-04639-3

	1. Introduction
	2. Materials and Methods
	3. Results and Discussion
	5. Conclusions
	References

