Determining the Extent of IBR, BVD and Bovine Brucellosis Based on Abortion History of Dairy Cattle’s Reared at College of Wondo Genet Forestry and Natural Resources, Sidama, Ethiopia

Abstract

The study was conducted in the Wondo Genet district of the Sidama region of Ethiopia to identify the cause of sporadic abortion occurrence in dairy cattle kept in the college. Serum samples were collected for the test from a total of 101 cattle with essential epidemiological data. Disease investigations were carried out on IBR gB ELISA for BoHV-1 antibody detection, BVD for antibody and antigen detection ELISA, and Rose Bengal plate test for Bovine brucellosis antibody detection. Of 101 serum samples examined for these diseases; IBR was found 28.7% (29/101) seropositive for bovine herpesvirus-1 antibody detection and the other two diseases (i.e. bovine brucellosis and BVD) showed negative (0%). Out of, 16 cows with a history of abortion, 10 (62.5%) were positive for the antibody detection of BoHV-1 which was statistically significant when compared to non-aborted groups (p=0.003). The farm had used bulls for breeding purposes and was positive upon examination for IBR. So that the seropositivity of this bull had a direct causal effect on the breeding cows on the farm as the disease was majorly transmitted through the reproductive tract. The result of the present study revealed that IBR is the most important disease in the area which is causing a significant economic loss on the dairy farm. Therefore, it requires further detailed studies on the level of antigen detection using some sophisticated test methods like real-time PCR.

Keywords: IBR; BVD; Bovine brucellosis; ELISA; Rose Bengal plate test

Introduction

Reproductive disorders have been found to be a major reason for decreased reproductive efficiency in cattle; and consequently reproductive efficiency is the major determinant of lifetime productivity of cows [1]. Emphasis has increasingly shifted to economically important diseases to the dairy producers and animal health problem stands out as the most prominent [2]. When the function of the reproductive system is impaired, cows fail to produce calves regularly [3]. Among the major reproductive problems that have direct impact on reproductive performance of dairy cows, abortion covers a significant economic implication which has infectious and non-infectious causes [4]. The exact proportion of cases due to infectious agents is not known, but in 90% of cases in which an etiologic diagnosis is achieved, the cause is infectious [5]. Based on available research evidence, nearly half of the cases of abortion/stillbirth worldwide are caused due to infectious agents [6], including Bovine Viral Diarrhea (BVDV), Brucella species, and Infectious bovine Rhinotracheitis (IBR) [7-9]. These pathogens can result in extensive economic losses, indicating the need for control measures to prevent infection or disease [10].

Upon closer examination of reproductive processes in the dairy cattle, the post-partum period is the most varied and vulnerable to problems and that incidentally coincides with the peak of milk production, uterine involution, and resumption of ovarian activity, conception and greater risk to infection [11]. These results in considerable economic loss to the dairy industry due to slower uterine involution, reduced reproductive rate, prolonged interconception and calving interval, negative effect on fertility, increased cost of medication, drop in milk production, reduced calf crop and early depreciation of potentially useful cows [12]. It is very difficult to diagnose those problems by one particular disorder or symptom because there is interrelation between predisposing factors such as management at calving, hygiene and parity, stage of gestation, nutrition and environment [2]. Therefore, the aim of this report was to determine and investigate abortion causing infectious disease at the studied farm.

The present study was conducted on identification of abortion causing agents in a large production system of dairy farm at Sidamaregion, Wondo Genet district. It is located atlatitude of 7o5’37”N and 38o37’48’’E longitude. According to Natural Resource Management and Regulatory Development of the Ministry of Agriculture and Rural Development [13], the agro-ecological region of the area is characterized with an altitude of 1723 meters above sea level having Tepid humid mid highland. The climate of the area is also characterized by two rainy seasons: a long rainy season from July to September and a short rainy season from February to April. The mean annual rainfall and temperature at the area is 1372mm and 19^oC, respectively.

To assess the sequel of abortion, following abortion history in the farm, blood sample was collected using10 ml plain vacutainer tubes from nearly all animals in the farm (n=101) with appropriate animal and farm level data. The collected blood samples were placed for an overnight period to separate serum and decanted into cryovials of 1.8ml volume. The samples weretransported into the National Animal Health Diagnostic and Investigation Center, now called Animal Health Institute, using cold chain facilitiesand stored at -20^oC until the test conducted. Three abortion causing diseases were defined for the test (IBR, BVD and Brucellosis).

IBR was tested using gB Competitive enzyme linked immune sorbent assay (C-ELISA) for Bovine herpes virus-1(BoHV-1) antibody detection based on the manufacturer recommendation. Similarly, BVD and Brucellosis were also examined based on the manufacturer’s instruction. Both antibody and Antigen detection ELISA were performed for BVD test due to the fact that persistently infected cows were unable to induce antibodies and aresero-negative for their lifetime and those cows which are infected at the time of gestation (viremic) were prone to manifest the antibody and in both cases the disease can cause abortion in cows [14-17]. Rose Bengal plate test was applied for brucellosis screening [18].

Based on the current study that causes abortion in the dairy farm, sero-positivity of BoHV-1 was 29/101 (28.7%). Of the total cows with the history of abortion (n=16); 10 (62.5%) were positive for IBR antibody. Because of latent infection induced by BoHV-1, detection of antibodies using IBRgB ELISA test could be sufficient for the determination of the BoHV-1 status of individual animals [19] and is indicative for the circulation of the causative agent, so that these animals were able to be a potential risk for disease transmission in the population.

Of the two bulls tested for IBR in the farm, the one which was actively contributing for breeding was sero-positive 1/2 (50%) for the disease. The semen of an infected bull may contain BoHV-1, and the virus can, thus be transmitted by natural mating and artificial in semination [20]. This bull was expected to spread the disease as the farm was exclusively using natural mating for breeding [21].

In the current study, age was significantly associated (P<0.001) with BoHV-1 sero-positivity. As age increasesthe chance of getting the disease was also increased as shown in table 1.This finding was in line with previous reports [22,23], that showed higher BoHV- 1 sero-positivity in adults than young animals. This result could be attributed either to continuous exposure for mating of adult animals than young’s, so that disease transmission through reproductive tract might be easily established or due to the effect of animal management practice where aged animals reared in a herd and calves were isolated and managed separately so that nearby contact for inhalational disease spread for aged animals might occur through shedding of the virus via various body secretions and excretions [24].The significance of the disease in the old age group is also contributed by the development of carrier states as age goes [25].

  

    
Variables
    
Total no. of animal tested
    
No. of positive (%)
    
X2
    
p-value
  
  

    
Sex
    
 
    
 
    
0.4517
    
0.502
  
  

    
Female
    
99
    
28(28.3%)
    
 
    
 
  
  

    
Male
    
2
    
1(50%)
    
 
    
 
  
  

    
Age
    
 
    
 
    
21.5382
    
<0.001
  
  

    
<=2years
    
33
    
0(0%)
    
 
    
 
  
  

    
2-5years
    
34
    
12(35.3%)
    
 
    
 
  
  

    
>5years
    
34
    
17(50%)
    
 
    
 
  
  

    
Parity
    
 
    
 
    
13.5148
    
0.001
  
  

    
Non
    
58
    
12(20.7%)
    
 
    
 
  
  

    
Primiparous
    
13
    
1(7.7%)
    
 
    
 
  
  

    
Pluriparous
    
30
    
16(53.3%)
    
 
    
 
  
  

    
Abortion history
    
 
    
 
    
11.3681
    
0.003
  
  

    
Non aborted
    
83
    
18(21.7%)
    
 
    
 
  
  

    
Aborted
    
16
    
10(62.5%)
    
 
    
 
  
  

    
Bulls
    
2
    
1(50%)
    
 
    
 
  

Table 1: Association of selected risk factors with IBR occurrence.