Introduction

Bovine respiratory complex (BRC) diseases are one of the main causes of economic losses in livestock farms¹. These losses are ascribed to decreased production efficiency, treatment costs, increased labor and death of animals due to pneumonia². The development of BRC is associated with environmental factors (management, stress and feeding), individual-specific factors (age, body condition and immunity), and the action of infectious agents (viruses, bacteria, and parasites)¹. Viral agents associated with BRC diseases include the IBR, PI3, BRSV and BVD viruses³.

Respiratory disease occurs when a pathogenic virus infects the host and allows opportunistic bacteria, normally present in the upper respiratory tract, to invade the lungs and cause severe pneumonia and death. These bacteria include Pasteurella multocida, Mannheimia haemolytica, Mycoplasma bovis, and Histophilus somni¹.

Epidemiological studies in the municipality of Montería, department of Córdoba, Colombia, determined the seroprevalence of viruses associated with BRC, the percentages being 74.7 % for IBR⁴, 29.4 % for BVD⁵, 13.5 % for PI-3⁶, and 13 % for BRSV⁷.

The aim of this study was to analyze the presence of the BVD, IBR, PI3, and BRSV viruses involved in the BRC diseases and the associated epidemiological factors in the two Creole bovine breeds at the Turipaná Research Center of AGROSAVIA, in the municipality of Cereté, Córdoba.

Material and methods

Results and discussion

The BVD, IBR, PI3 and BRSV viruses, which are part of the BRC complex, have been reported in different cattle farms in Colombia. However, this study is the first one that seeks to determine their prevalence in the Romosinuano and CCC creole breeds. These breeds are claimed to be resistant and well adapted to the ecological conditions of the low tropics on the northern coast of Colombia^9,10. However, both exhibited seroprevalence for the four viral diseases of the BRC, with CCC being the most susceptible (Table 1). The virus with the greatest presence in both races was the BVD virus, with a prevalence rate of 33.60 %, followed by the BRSV, with almost half the percentage (18.51 %), while the agents with the least presence were IBR and PI3, with prevalence rates of 12.8 % and 11.20 %, respectively.

As in this study, a high seroprevalence for BVD has been confirmed in other regions of Colombia; a previous study in the municipality of Montería reported 29.5 % seropositivity⁶, and another study carried out in the department of Cesar obtained results of 46 %¹¹.

BRSV is believed to be prevalent in cattle populations worldwide. Studies on this virus in animals with a history of infertility in Montería yielded seroprevalences of 13 %⁵, and of 31 % in newborn calves¹². In England, 83 % of cattle have antibodies, and in the United States, this is implicated in more than 50 % or respiratory diseases among fattening cattle¹³.

The prevalence of IBR in cattle has been reported historically in several regions of Colombia. In 1982, seropositivity was found to be 51.7 % in the Caribbean region; 21.5%, in the Andean region, and 20.6% in the Pie de Monte Llanero region¹⁴. Recently, prevalences of 55.5% were reported in the Magdalena region¹⁵, and of 35.65 % in the municipality of Toca - Boyacá¹⁶. Among the reports analyzed¹⁷, the highest seroprevalences for this virus have been reported in the municipality of Montería, where the seroprevalence in females with a history of infertility was 74.7 %⁴, and 60 % in newborn calves¹²; in the department of Antioquia, a prevalence of 68.9 %¹⁸ was reported in the Creole White Black-eared breed. Seroprevalences of 44.6 % were found in Argentina² and 81.8 % in Peru¹⁹.

Tables 2, 3, 4 and 5 show the univariate analysis of the factors studied on the different BRC diseases. The greater susceptibility of females to BRC diseases could be explained as a consequence of the high number of handlings carried out on females, due to a greater productive and reproductive demand. Factors associated with milking, artificial insemination and embryo transfer are considered to be stress factors that may render the females more susceptible to disease than the males²⁰.

Age was positively associated with BVD and PI3, with animals aged >1 year being most affected (2.39 and 3.55 times, respectively). Although cattle are susceptible to BVD infection at all ages, animals older than one year are more likely to be seropositive. This is probably due to decreased passive immunity resulting from maternal antibodies and from a longer exposure time to the pathogens involved in the disease²¹.

The herd type was also associated with BVD and PI3. In this sense, the Germplasm Bank herd was more affected than that of the breeding program (3.49 and 11.33 times for BVD and PI3, respectively). The higher susceptibility of the cattle in the Germplasm Bank may be accounted for by the higher population density in this group, which favors the aerogenic dispersion of these viruses; the higher humidity in the pastures used by these animals is another factor that favors the occurrence of the disease²².

The univariate analysis showed a statistical association between the race variable and BVD, RSV and PI3 viruses, with CCC being the most seropositive to these three infectious agents, compared to the Romosinuano breed. The CCC was 2.05 times more seropositive for BVD, 1.59 times more seropositive for BRSV, and 2.24 times more seropositive for PI3. However, multivariate analysis only revealed a statistically significant association between CCC and BVD (OR= 1.845, 95 % CI = 1.349-2.523, P<0.001). There are no studies that demonstrate that the CCC breed has a higher exposure to these infectious agents than Romosinuano. Therefore, this study suggests conducting specific immunological studies in order to further research breed-specific susceptibility to these diseases.

BVD and PI3 viruses were the only infectious agents that presented a statistical association with all the variables studied. However, since BVD was more frequent in the studied herds, the logistic regression model for viral diseases of the BRD complex was based on BVD.

The logistic regression model (Table 6) showed that BVD has an association with female sex, animals aged over one year, and the CCC breed, suggesting that these factors may significantly contribute to the development of these infections. The association between BVD, IBR and PI3 was also demonstrated. IBR-positive animals are 3.04 times more likely to have BVD, while PI3-positive animals are 3.81 times more likely. However, given the type of serological diagnosis and because this is a cross-sectional study, it is not possible to detect a causal relationship between the three diseases or to evaluate a time sequence in their occurrence. Although the final model showed epidemiological relevance, the log-likelihood and Hosmer-Lemeshow statistics indicated a poor model fit. Nevertheless, variable elimination was not considered because all the variables left in the final model have epidemiological significance, as confirmed by the univariate statistics. Further epidemiological studies on these issues are required.

Conclusions and implications

In conclusion, all the main viral agents involved in the BRD complex are present in the Creole livestock of the Turipaná Research Center. An action plan is recommended to control and prevent these diseases at the research center, with an emphasis on the control and prevention of BVD. In addition, further follow-up studies are required in order to understand the dynamics and co-endemicity processes of the BVD, IBR, BRSV and PI3 viruses in the Romosinuano and CCC breeds.