KHẢO SÁT TÌNH HÌNH BỆNH, THIỆT HẠI VÀ PHƯƠNG PHÁP PHÒNG, TRỊ BỆNH ORNITHOBACTERIUM RHINOTRACHEALE (ORT) TRÊN GÀ TẠI CÁC TỈNH PHÍA NAM VIỆT NAM

0KHẢO SÁT TÌNH HÌNH BỆNH, THIỆT HẠI VÀ PHƯƠNG PHÁP PHÒNG, TRỊ BỆNH
ORNITHOBACTERIUM RHINOTRACHEALE (ORT) TRÊN GÀ TẠI CÁC TỈNH
PHÍA NAM VIỆT NAM
SURVEYING THE DISEASE SITUATION, ECONOMIC LOSS, PREVENTION AND
TREATMENT REGIMEN FOR ORNITHOBACTERIUM RHINOTRACHEALE (ORT) IN
CHICKENS IN THE SOUTH OF VIETNAM

Vo Chi Nhan
Phone: 0978.109.120
Email:
Dinh Thuy Phuong Thao
Phone: 0868.189.496
Email:
Derpartment: Animal science and Veterinary medicine
ABSTRACT

The survey was conducted on 863 layer and broiler chicken farms in 5 provinces including Tien
Giang, Long An, Ben Tre, Dong Nai and Ba Ria Vung Tau (BRVT) by directly interviewing farmers
using dedicated questionnaires. The aims of the survey were to overall evaluate the current ORT
epidemiology and losses caused by this disease, as well as ORT treatment regimens applied.
Results from the farm's answers showed that currently, ORT disease was known in 80.76%
of the farms and outbreaks were reported in 64.19% of the farms. Dong Nai
and Tien Giang provinces had particularly high rates of ORT disease. Especially,
this disease occurs popular at 3 - 10 weeks of age. The larger population is, the higher ORT
occurs. The disease outbreaks all year long in 41.4% of the farms and 34% of
farms reported morbidity rate of up to 100%. Many case reports of O. rhinotracheale
infection report a concomitant infection with other respiratory pathogens and that the severity of
lesions is enhanced. When the disease occurs, it took long time to treat this disease. The
duration of treatment ranged from 3-7 days in 45% of the farms to over 7 days
in 40%. Treatment costs depend on the age of the chickens and the average expense treatment for
one chicken was VND 2,460. In addition, despite treatment interventions, birds continued to

suffer and die causing heavy loss to the farms. In 69.96% of the farms, preventive
treatment still mainly based on antibiotics and thus creating high chance of antibiotic resistant
development.


TÓM TẮT
Điều tra được tiến hành trên 863 trại gà thịt và gà đẻ thuộc địa bàn 5 tỉnh Tiền Giang, Long
An, Bến Tre, Đồng Nai và Bà Rịa Vũng Tàu (BRVT) bằng phương pháp phỏng vấn trực tiếp thông
qua bảng câu hỏi được thiết kế sẵn. Điều tra nhằm đánh giá tổng thể thực trạng bệnh ORT, các
thiệt hại của bệnh, cũng như ghi nhận các biện pháp phòng trị ORT mà các trại đang áp dụng. Kết
quả cho thấy bệnh ORT đang được quan tâm rất nhiều hiện nay (80,76%) với 64,19% trại đã từng
có bệnh. Trong đó, Đồng Nai và Tiền Giang có tỷ lệ cao nhất. Đặc biệt, bệnh thường xảy ra ở giai
đoạn từ 3-10 tuần tuổi. Quy mô đàn càng lớn, nguy cơ bệnh ORT nổ ra càng cao. Bệnh thường xảy
ra quanh năm với tỉ lệ bệnh cao, dễ lây lan trong đàn. Bệnh xảy ra trên mọi lứa tuổi và thường
xuất hiện quanh năm chiếm (41,4%) Bên cạnh đó tỷ lệ bệnh ORT xảy ra cao nhất ở quy mô từ
>10.000 con (70,59%) . Có 34% trại có câu trả lời tỉ lệ bệnh lên tới 100% gà trong đàn. Các ca
bệnh thường ở thể nhiễm ghép với các biểu hiện triệu chứng hô hấp phức hợp cũng như đa bệnh
tích trên gà bệnh. Khi bệnh xảy ra, cần mất nhiều thời gian để điều trị: thời gian điều trị trên 7
ngày chiếm 40%. Chi phí điều trị giao động tùy vào lứa tuổi của gà và trung bình để điều trị cho
2.460 đồng/con. Ngoài ra, mặc dù có can thiệp điều trị nhưng vẫn có tỉ lệ chết sau điều trị. Các
trại vẫn sử dụng thuốc kháng sinh để phòng và điều trị bệnh ORT là chủ yếu (69,96%) dẫn tới việc
dễ dàng đề kháng kháng sinh.


INTRODUCTION
Up until January 2018, some provinces in the south of Vietnam, such as Tien Giang, Long An,
Ben Tre, Ba Ria – Vung Tau (BRVT) and Dong Nai have had the largest number of total chickens raised
in the southern area, reaching over 43 million chickens (Statistical Department, 2018). Along with the
fast development in the total number of chicken raised as well as farm infrastructures, diseases,
especially respiratory problems, have been constantly troubling the poultry industry throughout the

whole country. There are many different causes for respiratory diseases; they could be due to
microorganism factors such as viruses, bacteria, and fungi, or they could be due to farms’ management
Among those, bacteria Ornithobacterium rhinotracheale (ORT) plays an important part in causing
complex respiratory syndromes with high mortality (Umali et al, 2018). Duration of the disease O.
rhinotracheale is not only cause sudden death, rapid transmission but also causes severe respiratory
symptoms. (van Ampel và Hafez, 2010).
Until now in Vietnam, there have only been a few researches regarding ORT, namely Nguyễn Thị
Bích Liên et al (2014), Nguyễn Thị Lan et al (2016, 2017), and there is no official study regarding the
circulation of ORT in southern provinces in Vietnam.
Therefore, it is extremely necessary to investigate and evaluate the status of the disease as well as
the ability to prevent and treat chicken disease caused by ORT. This study’s aim is to build up data
which could be utilized for analyzing and diagnosing the disease in order to form a better procedure for
prevention and treatment of ORT disease.
MATERIALS AND METHODS
Research subjects
The research was conducted on farm with a questionaire in chicken farms with the scale of at least
500 chickens in some districts of 5 provinces: Tien Giang, Long An, Ben Tre, Đong Nai and BRVT.
Contents and research methods
All data regarding the total number of chickens raised as well as chicken farms were gathered
from the 2018 annual statistical results of Tien Giang, Ben Tre, Long An, Đong Nai and BRVT.
According to those results, around 10-20% of total chicken farms were surveyed based on the farm
scale of over 500 chickens per farm by a questionaire (Table 1).


Table 1. Number of expected surveyed chicken farms
Province

Number of surveyed chickens

Tien Giang

Long An
Ben Tre
Đong Nai
BR-VT
Total

Number of expected surveyed chicken

2,284,200
435,550
239,000
2,421,000
226,500
5,606,250

farms
327
78
111
322
25
863

The interview process was conducted directly at the farm with a prepared questionnaire to record
the information which is provided the necessary requirements of the experiment (Appendix attached).
Each farm filled in the questionaire with information about their own farm, then, those information
would be collected and statistically analyzed in order to evaluate the ORT disease status, damages
caused by the disease as well as methods to prevent and treat ORT in 863 chickens farms of Tien Giang,
Long An, Ben Tre, BRVT and Dong Nai. Accordingly, the farms were identified by: (1) Some mild
respiratory symptoms such as: transient nasal discharge, dyspnea, coughing, sneezing, neck lift (Roepke

et al., 1998). And the common particular lesions include pneumonia, pleuritis, tracheitis and
(casein)fibrinosuppurative airsacculitis, (Van Empel et al., 1997), (2) Veterinarian's diagnosis, (3) Test
results (if any).
Data analysis methods
After gathering information in the questionair, all data were digitalized, then analyzed using
descriptive statistics method by Excel 2010 and Minitab 16.
RESULTS AND DISCUSSION
1. ORT status by surveyed areas
1.1 Level of concern and awareness of ORT
Table 2. Level of concern and awareness about ORT
N = 863
ORT
Percent (%)

Aware
697
80.76

Not aware
166
19.23

Total
863
100

According to Table 2, farms that are concerned and aware of ORT accounted for a really high
percentage of 80.76%, equaling to 697/863 farms; whereas, only 19.23% of farms were not aware of the

disease. This result clearly showed that ORT has always been one of the most concerned problems for
chicken farms in the surveyed areas.
1.2 ORT status by provinces
Table 3. Number of farms with suspected ORT clinical signs by different provinces
Province

Total

Ben Tre
BRVT
Đong Nai
Long An
Tien Giang
Total

111
25
322
78
327
863

Number of farms
34
8
262
32
218
554

ORT
Percent (%)
30.63
32.00
81.37
41.03
66.67
64.19

There were 554 out of 863 farms (64.19%) said that their farms suffered from ORT before. This
result indicated that ORT has often occurred in the surveyed areas. The result from comparing the
disease percentages of 5 provinces showed that there was a significant difference found (P<0,001) with
Dong Nai and Tien Giang taking the highest disease percentages of 81.37% and 66.67%, respectively.
1.3 ORT status by the scale of chicken flocks
Chicken farm scales were classified into 3 large groups: scale of over 2000 chickens was
considered as industrial rearing, scale of 500-2000 considered as semi-industrial rearing, and scale of
lower than 500 chickens considered as household rearing (Farming Institute, 2004). In this study, the
status of ORT was evaluated by each scale shown in Table 4.
Table 4. ORT status by the scale of chicken flocks

N=863

ORT
Total

Farms

Percent (%)

500-2000

133

67

50.38

2000-5000

350

222

63.43

5000-10000

210

133

63.33

>=10000

170

120

70.59

Total

863

542

62.80


Out of 554 farms suspected of ORT, there were 12 farms that could not be collected precise data
from, therefore, they were omitted. According to Table 4, farms with the scale of over 10,000 chickens
had the highest percentage of being infected with ORT (70.59%), while only 50,38% of farms with the
scale of < 2000 chickens reported of being infected with the disease, which was the lowest. There was a
significant difference between the 500-2000 chickens group compared to others regarding the frequency
of being infected with ORT (P<0,05). It could be concluded that the inadequate management of the
farms as well as ORT treatment and prevention could be one of the contributing factors for increasing
the probability of ORT in farms with larger scales.
1.3 ORT status by age groups
According to the result, there were 554 farms reported of being infected with ORT before. Out
of these farms, data about ORT status by age groups were collected from 476 farms, which are shown in
Table 5.
Table 5. Percent of ORT by age groups

Age groups (weeks old)
<3
3-6
7-10
11-15
15-20

> 20
All ages
Total

Infected farms
46
113
192
55
23
17
30
476

Percent (%)
9.66
23.74
40.34
11.55
4.83
3.57
6.31
100

According to Table 5, the age group of 3-10 weeks old was most commonly seen being infected
with ORT. It was probably due to the fact that when chickens reached this age, their maternal immunity
has started to degrade while the acquired immunity from vaccination has not developed fully. Therefore,
they were more prone to different diseases, including ORT. (tai liệu tham khảo?)
1.4 ORT status by seasons
Out of 554 farms suspected of ORT, there were 10 farms that could not be collected precise data

from regarding the ORT status by seasons, therefore, they were omitted. From the results shown in
Table 3, it could be clearly seen that there was a significant difference of ORT status by different
seasons, in which the all year round group accounted for the highest percentage of ORT infection
(41.36%). According to Lopes et al. (2002), ORT infection often occurred in winter, spring and inbetween season where the temperature fluctuated regularly. However, with the current industrial rearing


system of chickens with a high density while biosecurity is not secured, ORT infection could happen all
year round.
Table 6. ORT status by different seasons in a year
Season
Infected season unclear
In-between season
Dry season
Rainy season
All year round
Total

Number of farms
130
51
56
82
225
544

Percent %
23.89
9.37
10.29
15.07

41.36
100

3. Investigate pathological characteristics
Through the survey, the clinical signs and typical lesions of ORT were collected through the
answers of 110 farms that had appeared ORT. Of these, 94 farms had detailed answers for clinical signs
and 16 had answers about typical lesions which is showed in Tables 7a and 7b
Table 7a. Clinical signs of ORT
(*)

A

B

C

Farm

1

10

1.0
6

10.6
3

%

A +C

B +C

C +D

A+B+C

A+B+D

A+C+D

A+B+C+D

4

A+
B
5

Total

7

30

9

12

1

1

14

94

4.25

5.31

7.44

31.91

9.57

12.76

1.06

1.06

14.89

100

Table 7b. Lesions of ORT
Lesion (*)

Farm
%

I
1
6.25

II
6
37.5

IV
4
25.
0

III + IV
1
6.25

IV +VI
1
6.25

IV + V
2
12.5

II + III +IV
1

6.25

Total
16
100

(*) Note: A (Nasal discharge), B (Neck lifting), C (wheezing), D (Prostration)
I (Pleuritis), II (tracheal casein accumulation), III (Airsacculitis with casein accumulation), IV
(Casein accumulation near bronchi branching), V (Nasal mucus), VI (Trachea hemorrhage)

The clinical signs and lesions of ORT in report are consistent with the description of Van Empel
(1997); Roepke et al. (1998) such as watery nose, wheezing and neck lift when they breathing or
pneumonia, air sacs, tracheal casein accumulation ... In addition, the majority of cases are complicated
transplant expression. Among them, dyspnea + neck lift are quite common (31.91%) in cases.

2. Damages caused by ORT in surveyed farms


Bệnh <5%; 15.31%
Bệnh 5% - <10%; 6.12%
Bệnh 80% -100%; 35.71%
Bệnh 10% - <15%; 7.14%
Bệnh
15% - <20%; 1.02%
Bệnh 60% - < 80%; 4.08%
Bệnh 20% - <30%; 5.10%
Bệnh 30% - <40%; 7.14%
Bệnh 40% - <60%; 18.37%

Figure 1. Percentage of ORT in farms

2.1 Disease percentage
When asked about the percentage of chickens infected with ORT, only 98 farms were capable of
providing an answer, with 34% said 100% while 15% answered 50% of the flock. The remaining
answers are shown in Figure 1. This result indicated that once a chicken is infected with ORT, there
would be a high chance that the whole flock would be affected as well.
2.2 Mortality after treating
When ORT clinical signs were observed in a flock, farms were provided with a diagnosis as well
as a treatment plan. However, there was still mortality recorded, which is shown in Figure 2. Out of 119
farms able to give an answer about flock mortality, 55% said that the mortality was only under 5%, 16%
said from 5-10%, and 13% said from 10-15%. The survey still recorded that ORT made high mortality,
decrease in body weight and performance at infected flocks. So the increasing of condemnation rate in
farms infected ORT.
According to Goovaerts et al. (1998), ORT mortality could reach up to 20%, whereas Van Veen et
al. (2000) stated that ORT mortality could occur to 50% or over in a flock due to damages caused by the
disease. In this survey, some case reports of O. rhinotracheale infection report a concomitant infection
with other respiratory diseases, such as ND, IB, Coryza or Candidosis. According to Chu et al. (2017),
when chickens infected Chlamydia psittaci and fungi that caused by Aspergillus spp. and ORT, the


mortality is about 20%. Meanwhile, infection between Chlamydia psittaci, Aspergillus spp., H9N2 and
ORT resulted in up to 40% mortality in chickens.

chết 80% -100%; 0.84%
chết 60% - < 80%; 1.68%
chết 40% - <60%; 1.68%
chết 30% - <40%; 3.36%
chết 20% - <30%; 5.88%
chết 15% - <20%;
chết <5%; 54.62%
2.52%

chết 10% - <15%;
13.45%
chết 5% - <10%; 15.97%

Figure 2. Chickens’ mortality
2.3 ORT treatment time

16.92%

14.99%

23.13%

44.97%

< 3 ngày
7-14 ngày

3-7 ngày
Kéo dài (>14 ngày)

Figure 3. ORT treatment time
There were a total of 467 farms infected with ORT giving an answer for an effective ORT
treatment plan. The results in Figure 3 showed that a treatment plan of over 7 days accounted for 40%,


whereas a treatment plan of 3-7 days took up to 45% (Figure 3). Therefore, it could be concluded that
ORT needs to be treated for a long time in order to be effectively eliminated.
2.4 ORT treatment cost
Table 7. ORT treatment cost

Age groups

Number of farms

(weeks old)
<3
3-6
7-10
11-15
16-20
21-50
Total

41
96
164
49
12
12
374

Total number of treated
chickens
186,8
278,4
479,4
144,9
36
123,1
1.248.600

Average cost/chicken (VND)
1,568
2,154
2,885
4,071
1,238
1,307
2.460

(*): thousand VND
According to Table 4, 374 infected farms were able to give an answer regarding to ORT
treatment cost by age groups. The results showed that the highest treatment cost was for the group from
11-15 weeks old with 4,071 VND/chicken, and the group from 7-10 weeks old took the second place
with the average cost of 2,885 VND/chicken. The average treatment cost for 1,248,600 ORT infected
chickens from 374 farms was 2,460 VND, equaling to 3,071,495,000 VND in total while the average
cost for medication and vaccination of a cycle of that broiler is 2,000 – 2,500VND, layer is 7,00010,000VND according to the record from the surveyed farms.
3. Investigation of methods to prevent and treat ORT infected chickens in surveyed farms
3.1 Methods to prevent ORT
There were only 90/863 farms that employed methods in order to prevent ORT, which were
equivalent to 10.43%. The most commonly seen method that farms utilized to prevent ORT was using
antibiotics with 76.67%; the other methods such as supplements, ILT vaccine and antibiotics
combination, or antibiotics and supplements combination accounted for a very small percentage, which
were all shown in Table 8.
Table 8. Methods to prevent ORT
Number of

ILT
9

KS
69

HT
3

KS + ILT
4

KS + HT
5

Total
90


farms
Percent %

10

76.67

3.33

4.44

5.56

100

(*) Note: ILT (ILT vaccine), KS (Antibiotics), HT (Supplements)
However, throughout the whole conduction of this research, it is found that ORT prevention with
antibiotics did more harm than good and this method has started to lose its efficiency as well. Therefore,
it is conclusive that using antibiotics could not be a long term as well as the most efficient method to
prevent ORT. As reported by Devriese et al. (2001), ORT bacteria strains have started to develop
resistance against 80-100% commonly used antibiotics in treating poultry diseases, such as ampicillin,
ceftiofur, tylosin, spiramycin, lincomycin, tilmicosin, flumequine, enrofloxacin và doxycycline. In
addition, our records show that there are not still the commercial ORT vaccine in Viet Nam. So some
famers used ILT vaccine to prevent for ORT disease although they did not know how its effect. Maybe
some cases ORT secondary - infected from ILT, so if prevention ILT effectively leading to reduce
opportunity development of ORT. It means reducing spreading of ORT in farms. Beside that maybe
famers did not know clearly about ORT disease so they thought that ILT vaccine may have prevented
ORT disease. Some these methods did not alway get good result, so that needing to provide a better
efficiency method, directly and sustainability like management or ORT vaccine for reducing ORT in
Vietnam soon as possible.
3.2 Methods to treat ORT
As treatment methods would have a direct impact on the final treating results as well as on the
performance of the chickens, in order to improve the chickens’ performance, farmers are ought to spend
their overall production budget appropriately, which would also include the ORT treating cost.
Table 9. Methods to treat ORT ORT
Number
farms
Percent %

of

ILT

KS

KS+HT

KS+ST

KS+HT+ST

KS+ND/IB/ILT

3

156

49

6

5

4

1.35

69.96

21.97

2.69

2.24

0.45

(*) Note: ILT (ILT vaccine), IB (IB vaccine) ND (Newcastle vaccine), KS (Antibiotics), HT
(Supplements), ST (Antiseptic).
There were 223 farms provided an answer regarding methods used to treat ORT (Table 9), in
which, a large proportion of farms used antibiotics for this purpose, accounting for 69.96%. Moreover,
there were also other treating methods that were employed by farms, namely combining antibiotics or


supplements with IB, ND and ILT vaccines. Nevertheless, according to van Empel and Hafez (2010),
the susceptibility of ORT to antibiotics was vastly different and depended mainly on the infecting ORT
strains. Morever, the treatment of O. rhinotracheale infections with antibiotics is very difficult because
of the variable susceptibility of strains. And O. rhinotracheale can acquire reduced susceptibility or
resistance against antibiotics (Devriese et al., 2001; Soriano et al., 2003). Therefore, this is not the
optimal method for treatment.
CONCLUSIONS AND RECOMMENDATIONS
ORT occurred rather frequently in the surveyed areas (64.19%), especially to the age group of 310 weeks old. In addition, the bigger the chicken flock scale, the higher the probability of chickens
being infected with ORT. The disease occurred all year round with a high morbidity and an extreme
spreadability. O. rhinotracheale infection report a concomitant infection with other respiratory
pathogens and that the severity of lesions is enhanced. Damages caused by ORT mainly came from the
treatment cost, the prolonged treatment period, the high mortality as well as chickens’ wellbeing after
being treated. Moreover, the currently main method for preventing and treating ORT still largely
depended on antibiotics, which would later lead to the increase of antibiotic resistance and antibiotic
residue in chicken meat.
In conclusion, it is necessary to conduct more in depth researches regarding the proportion of
ORT circulation by serological testing on farms as well as to identify the common ORT strains in
Vietnam in order to use the correct type of vaccine for a better protection.
REFERENCES
[1] Devriese, L., De Herdt P. & Haesebrouck, F. (2001). Antibiotic sensitivity and resistance in

Ornithobacterium rhinotracheale strains from Belgian broiler chickens. Avian Pathol. 30:205-208.
[2] Devriese, L.A., De Herdt, P., & Haesebrouck, F. (2001). Antibiotic sensitivity and resistance in
Ornithobacterium rhinotracheale strains from Belgian broiler chickens. Avian Pathology 30: 197200.
[3] Goovaerts, D., Vrijenhoek, M. & van Empel, P.C.M. (1998). Immuno-histochemical and
bacteriological investigation of the pathogenesis of Ornithobacterium rhinotracheale infection in
South Africa in chickens with osteitis and encephalitis syndrome. In Proceedings of the 16th meeting
of the European Society of Veterinary Pathology, Lillehammer, pp.81.


[4] Lopes, V.C., Back, A., Shin, H.J., Halvorson, D.A. & Nagaraja, K.V. (2002). Development,
Characterization,

and

Preliminary

Evaluation

of

a

Temperature-Sensitive

Mutant

of

Ornithobacterium rhinotracheale for Potential Use as a Live Vaccine in Turkeys. Avian Diseases 46:
162-168.

[5] Nguyễn Thị Bích Liên, Võ Thị Trà An, Trần Thị Ngọc Hân, Hồ Quang Dũng, Niwwat
Chansiripornchai (2014). Nhận dạng, phân lập và xác định mức độ mẫn cảm kháng sinh của vi khuẩn
Orninobacterium rhinotracheale ở gà. Tạp chí Khoa học Kỹ thuật Nông lâm nghiệp, 4: 23-25.
[6] Nguyễn Thị Lan, Chu Đức Thắng, Nguyễn Bá Hiên, Phạm Hồng Ngân, Lê văn Hùng, Nguyễn Thị
Yến (2016). Đặc điểm của vi khuẩn Ornithobacterium rhinotracheale (ORT) phân lập từ đàn gà nuôi
tại một số tỉnh phía bắc Việt Nam. Tạp chí KH Nông nghiệp Việt Nam 14(11): 1734-1740.
[7] Nguyễn Thị Lan, Chu Đức Thắng, Nguyễn Hữu Nam, Lê Văn Hùng (2017). Nghiên cứu lựa chọn
phương pháp chẩn đoán bệnh do Ornithobacterium rhinotracheale (ORT) trên gà. Tạp chí Khoa học
kỹ thuật thú y, 24(5): 69-74.
[8] Roepke D.C., Back A., Shaw D.P., Nagaraja K.V., Sprenger S.J. & Halvorson D.A. (1998). Isolation
and identification of Ornithobacterium rhinotracheale from commercial turkey flocks in the upper
Midwest. Avian Dis 42: 219-221.
[9] Soriano, V.E., Vera, N.A., Salado, C.R., Fernandez, P. & Blackall P.J. (2003). In vitro susceptibility
of Ornithobacterium rhinotracheale to several antimicrobial drugs. Avian Dis. 47:476-480.
[10] Umali, D.V., Shirota, K., Sasai, K. & Katoh, H. (2018). Characterization of Ornithobacterium
rhinotracheale from commercial layer chickens in eastern Japan. Poultry Science 97: 24-29.
[11] Van Empel và cs. (1997). Ornithobacterium rhinotracheale: An update. Proc Fachgruppe
“Geflügelkrankheiten” der Deutsche Veterinärmedizinische Gesellschaft. Hannover, Germany pp.2025.
[12] van Empel, P.C.M & Hafez, H.M. (2010). Ornithobacteriumrhinotracheale: A review, Avian
Pathology, 28(3): 217-227.
[13] Van Veen, L., Gruys, E., Frik, K. & van Empel, P. (2000). Increased condemnation of broilers
associated with Ornithobacterium rhinotracheale, Vet Rec. 147(15): 422-423.
[14] Cục thống kê (2018).
[15] Viện Chăn nuôi (2004).