Grad Student Competition
Effect of Salmonella Dublin latent carrier dry cow vaccination on bacterial shedding and intrauterine transmission
| Date/Time: |
9/13/2024
08:30
|
| Author: |
Rafael Castro Vargas |
| Clinic: |
Michigan State University |
| City, State, ZIP: |
East Lansing, MI 48823 |
Rafael Castro-Vargas, BVSc
1
;
Faith Cullens-Nobis, MS
2
;
Rinosh Mani, BVSc, MS, PhD, DACVM
1
;
Jennifer Roberts, DVM, DACT
3
;
Angel Abuelo, DVM, MS, PhD, DABVP, DECBHM
1
;
1Department of Large Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, MI, 48824
2Michigan State University Extension, East Lansing, MI, 48824
3Boehringer Ingelheim Animal Health, Duluth, GA, 30096
Introduction:
Salmonella Dublin latent carrier cows pose a significant risk for transmitting infection to newborn calves through intra-uterine transmission and bacterial shedding in feces and colostrum at calving. Vaccination of these latent carriers dams during late gestation can enhance the immunity against S. Dublin. This could reduce the activation of the dormant bacterium during the periparturient immune dysfunction period, thereby reducing the risk of early-life infection in the offspring until vaccination is possible. This study aimed to evaluate the extent to which vaccinating S. Dublin latent carrier cows at dry-off with a commercial live bacterial vaccine (Entervene-D, Boehringer Ingelheim) reduces bacterial shedding at calving and intrauterine infection in calves.
Materials and methods:
To identify latent carriers, 1,084 cows were screened across four commercial Michigan dairy farms with a previous history of S. Dublin and no vaccination against Salmonellae. Cows were classified as latent carriers when they showed three consecutive positive milk antibody ELISA tests conducted every two months. Subsequently, 148 latent carriers were randomly assigned to the vaccine or control group. The vaccine group received the commercial vaccine subcutaneously (s.c.) at dry-off, followed by a booster two weeks later. The control cows received saline s.c. at the same intervals. At calving, we collected fecal and colostrum samples from the dam and a pre-colostral serum sample from the calf. Bacterial shedding was evaluated in feces and colostrum both qualitatively (Yes/No) and quantitatively, using the bacterial enrichment culture method ISO 6579-1:2017 and qPCR quantification of gene vagC copy numbers, respectively. Intrauterine transmission was defined when a calf tested positive for serum antibody ELISA at birth. Results were evaluated via logistic regression for qualitative shedding and intrauterine transmission. A t-test was used to compare the number of S. Dublin copies estimated via qPCR.
Results:
Vaccination resulted in a lower risk of calves being born with S. Dublin antibodies (Relative Risk [95%CI]) = 0.19 [0.04 – 0.84]). However, no S. Dublin-positive isolates were identified through either bacteriological culture or qPCR in feces or colostrum.
Significance:
Vaccination of S. Dublin latent carrier cows at dry-off reduced intrauterine transmission to their calves. This strategy could decrease the transmission of S. Dublin in dairy farms. Additionally, the absence of S. Dublin positive fecal and colostrum samples from latent carriers warrants further evaluation of the traditional methods for identification of latent carriers or S. Dublin isolation, as well as the role of latent carriers in infecting newborn calves in the maternity area at birth.
