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Prevalence of Bovine TB among cattle in Central Province 2.6%: Study

12 Apr 2022

BY Ruwan Laknath Jayakody  The estimated prevalence of Bovine Tuberculosis (bTB) – a disease that carries the risk of transmission from cattle and buffaloes to humans and other susceptible animal species – among cattle in the Central Province is 22.6%.  This finding was made in a research article on the “Prevalence of bTB among cattle and buffaloes in the Central Province” which was authored by Y.H.P.S.N. Kumara, A. Amarasinghe, P.G.A. Pushpakumara, W.M.T.D. Rathnakumara and B. Alexander (all five attached to the Peradeniya University’s Veterinary Medicine and Animal Science Faculty’s Farm Animal Production and Health Department), H.M.S. Wasana (attached to the same University’s Postgraduate Institute of Agriculture) and G.A. Gunawardana (attached to the Gannoruwa Veterinary Research Institute’s Molecular Biology Division) and published in the Tropical Agricultural Research Journal 33 (2) in March 2022.  “The dairy industry plays a key role in livestock production. The Government has taken steps to increase milk production by introducing improved exotic cattle such as Holstein Friesian, Jersey, and their crossbreds. However, exposure of these cattle herds to a new tropical environment has posed the threat of attracting animal diseases,” Kumara et al. observed. Kumara et al. selected study sites in the Districts of Kandy, Matale and Nuwara Eliya in the Central Province in order to determine the prevalence of bTB. The study spanned from October 2013, to August 2016. Visible swelling at the injection sites was not observed in cattle with negative results. However, a noticeable swelling at the injection sites was observed in cattle with positive results. These observations were based on 72 hours after injecting Purified Protein Derivative (PPD).  Among the total of 616 cattle tested by injecting PPD, 139/22.6% were identified as reactors for the SICCT test and the majority (77.4%) were negative for the SICCT test.  In the present study, 248 cattle from the Nuwara Eliya District, 286 from the Kandy District and 82 from the Matale District were tested where only 85/34%, 54/19% and zero/0% showed reactions to the SICCT test from the respective Districts.  The highest number of reactors was recorded from a herd in the Nuwara Eliya District, where 57 cattle out of 91 tested (62.6%) were positive to the SICCT test. However, 10 herds which were tested for the SICCT (50%) (one herd from the Nuwara Eliya District, five herds from the Kandy District and four herds from the Matale District), were found to be negative and free from exposure to bTB within the study area.  A herd level prevalence of 50% (10/20) resulted in the large and medium-scale dairy farms that were tested in the study area. There were no significant associations observed with bTB prevalence and the tested parameters such as the herd category, the duration of the farm establishment and the type of management practice.  The individual level prevalence of 22.5% was observed (139/616) in the present study. A significant association of the prevalence of bTB with the body condition score, the breed, the origin of the cattle, and the reproductive status were observed.  A total of 33 cattle (six males and 27 females from eight herds) which showed positive results in the SICCT test were subjected to the rapid antibody (Ab) test. Only seven cattle (two males and five females from four different herds) out of 33 were positive for the rapid bTB Ab test.  Based on this study, a high prevalence of bTB was observed at both the individual and herd levels. The high prevalence (50%) of bTB at the herd level poses a high risk towards future dairy farming.  The findings also revealed that there was a significant association between the prevalence of bTB with breeds of cattle. The highest disease percentage for bTB was observed in the Ayrshire breed (63.6%) indicating five-fold more susceptibility than the other breeds (12.85%). However, a definitive risk factor for the Ayrshire breed has not been identified.  Herd level investigations suggested that cattle and buffaloes managed under intensive and/or semi intensive management systems may carry a high risk of bTB transmission among animals.  “Possible underlying causes for high herd prevalence of bTB could be intensification, stress, and overcrowding due to limited land availability. It is also suggested that these farming systems cannot avoid close contacts among animals and thereby create a favourable environment in the spreading of the disease from one animal to another. Water and feed sources were common for all the animals managed under the semi intensive management system in the study, where animals were herded to a common area in the yard for concentrated feeding every day. Horizontal transmission of the disease is inevitable in such situations,” Kumara et al. pointed out. The results revealed that the gender of an animal was not significantly associated with the status of bTB. “This could be due to the small number of male animals included in the study due to the low representation of male animals in dairy farming systems,” Kumara et al. added.  Among the individuals who tested positive for the SICCT, the highest percentage (34.7%) was the cattle with poor body condition scores. “This could mainly be due to the fact that animals with poor body condition scores are immune compromised and thus become susceptible to diseases. Animals with good body condition scores were the least (5%) affected by the disease. Hence, maintaining a good body condition score with optimum environmental conditions are of utmost importance in order to prevent the disease,” Kumara et al. emphasised. The results further indicated that the herd level prevalence of bTB was proportionate to the herd size. Therefore, the tendency of the spread of bTB in large-scale farms was higher than in medium-scale farms. 


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