This is a case of Bovine Respiratory Disease that developed after the introduction of a group of cattle purchased from a saleyard. This complex is associated with a number of viruses with secondary bacterial involvement. Vaccines prior to exposure are sometimes helpful in avoiding severe outbreaks. In this case 40 deaths occurred in 3 months from a herd of around 80 head.
The problem appeared to start in early March; two weeks after 34 calves were purchased from Dublin (South Australia) saleyard and introduced into the feedlot. These calves ranged from 8 weeks to 5 months of age and initial signs observed were cattle showing respiratory signs, illness and then death.
The producer is in an isolated area and purchases young beef & dairy calves from Dublin & Mt Pleasant market for fattening in his feedlot. Sheep are also kept on farm but appear unaffected.
A private vet was contacted who diagnosed respiratory disease complex and dispensed antibiotic for blanket treatment of the surviving cattle. Department of Primary Industries and Regions, South Australia (PIRSA) was resulting in a farm visit and investigation.
One Murray grey animal was available for post-mortem on arrival at the property; it had died about 2 hours previously after being unwell for approximately 10 days. Another 39 cattle had died prior to this in the previous 3 months. On arrival cattle were observed in a feedlot environment, with various ages and breeds mixed together as one group. Cattle appeared in light condition and some smaller cattle appeared unwell with a persistent cough. A group of these were later examined and blood samples collected.
Normal induction into the feedlot has been Vit B12 injections, Vitamin ADE injections for cattle under 4 months then 5-in-1 (Clostridial vaccine) after 6 months of age. This regime was under advice from a livestock agent. The owner decided to start using a vaccine (Bovi-Shield MH One (Zoetis)) when a veterinarian suggested the possibility of Bovine Respiratory Disease Complex (BRD).
The dead heifer had obvious and advanced pneumonic lesions with compromise of approximately 60% lung tissue with lesions ranging from full consolidation to reddish discolouration, and some abscesses. Pus was observed on some areas within tissue and bronchi (see photos). This animal had been treated with an antibiotic (oxytetracycline) the day before.
Histopathology revealed broncho-interstitial, fibrino-necrotic, suppurative and lymphohistiocytic, multifocal, severe, subacute pneumonia with hyaline membranes and type 2 pneumocyte hyperplasia.
This is suggestive of subacute bronchointerstitial pneumonia typically associated with multifactorial aetiology of bovine respiratory disease complex in young cattle. The presence of syncytial cells is suggestive of viral infection (e.g. BRSV, PI-3 virus, Bovine herpesvirus 1); however confirmatory viral inclusion bodies were no longer detectable in these subacute lesions.
Unfortunately cultures from fresh tissue and swabs were unrewarding in this case&emd;possibly due to prior antibiotic exposure.
Pestivirus testing of 5 in-contact cattle indicated that the virus had been circulating in the herd recently and there could be “persistently infected” (PI) calves on the property that may contribute to further ill health in the herd.
The purchase of young, stressed cattle from saleyards that have been mixed from a number of other properties, then introduced into a feedlot situation is a very risky process that at some point is bound to introduce diseases, including the possibility of exotic diseases.
Another virus that is increasingly becoming understood as a contributor to BRD and other feedlot / herd diseases is Pestivirus. Many commercial feedlots now have an induction process that starts on the farm of origin using initial vaccinations against BRD, Clostridials and Pestivirus - this seems to be producing good results. An example is the Elders “Feeder Guard” program utilising vaccinations of cattle on the farm of origin prior to arrival at feedlot with Pestigard, Bovi-Shield MH One, and Ultravac 5 in 1. Advice should be obtained from your veterinarian about the costs and benefits of this program.
Purchasing of calves from a saleyard is a risky process in terms of biosecurity and introduction of new diseases to your property. It is recommended cattle purchased should come with a completed Cattle Health Declaration, as well as NVDs.
Testing calves to identify Persistently Infected (PIs) animals is simple and inexpensive, a good website discussing pestivirus is www.swansvet.com and simple tests can be arranged through EMAI, see www.dpi.nsw.gov.au. Removal of PI cattle and ensuring no PI cattle are introduced may reduce the need for vaccinations.
Of concern is that so many cattle died and the owner was unsure of where to get quality diagnostic advice and diagnosis on farm. PIRSA maintains a presence in saleyards and conducts workshops and events in order to promote reporting and detection of events like this, since we are aware that producers tend to contact those they know and trust first for advice.