Bovine Respiratory Disease (BRD) in Dairy Calves

Bovine Respiratory Disease (BRD) or calf pneumonia is the second most important disease of calves in Australia after calf scours. Estimates of the prevalence of BRD in dairy calves are pretty similar around the world at 20 - 25%. The short and long-term cost of BRD in calves is significant and arise from treatment costs (antibiotics/anti-inflammatories/labour) and a range of negative effects on subsequent health and production. Calves that have had BRD, when compared to herd mates that have not had BRD, are:

2.85 times more likely to die
2.30 times more likely to be culled prior to first calving
Have a reduced pre-weaning ADG of 70 g/day
Produce 121 kg less milk in their first lactation
1.20 times more likely to be culled before the end of their first lactation

The effects of BRD on age at first service, first service conception rate and heifer pregnancy rates have also been studied but are variable and not consistent with some studies showing negative effects but others showing no differences between calves with and without BRD.

A wide range of bacteria and viruses are involved in BRD making it a complex disease to control. The viruses commonly associated with BRD are BHV1 (Bovine Herpes Virus 1), BPV (Bovine Pestivirus), BRSV (Bovine Respiratory Syncytial Virus), Adenovirus and PI3 (Parainfluenza Virus). Bacteria commonly associated with BRD include Salmonella dublin, Mannheimia haemolyticia, Histophilus somni, Pasturella multocida and Mycoplasma bovis.

There is a long list of risk factors for BRD in dairy calves but the most important include inadequate colostrum intake resulting in poor immunity, poor calf shed ventilation, poor air quality (dust/ammonia / fungal spores), group housing, shared feeders and water sources and inadequate milk feeding (< 4 litres/day).

Accurate early diagnosis of BRD in calves is actually very difficult with calves showing very little signs of illness in the early stages of the disease. Once calves are obviously sick they often have pneumonia and there is already significant lung damage with permanent consolidation of lung that often never resolves. A combination of post-mortem examination, clinical examination, lung ultrasound and laboratory analysis of various samples is often needed to make an accurate diagnosis of BRD.

A simple BRD scoring system has been developed by the University of California that is designed to be used on farm by people rearing the calves to aid in the early diagnosis of BRD in pre-weaned calves. It assesses 6 easily measurable parameters and allocates a score to each of those parameters if
present.

1. Cough - 2 points
2. Eye discharge - 2 points
3. Temperature (>39.2) - 2 points
4. Abnormal respiration (rate / depth / effort) - 2 points
5. Nasal discharge - 4 points
6. Ear droop or head tilt - 5 points

Simply observe a calf for these 6 signs and add up the points if any are present. If you get to 5 points by any combination then the calf has BRD and requires immediate treatment. This simple system will accurately diagnose a calf with BRD in about 73 % of cases and accurately diagnose a calf as not having BRD in about 90 % of cases.

Early treatment of any calf identified with BRD is important. Draxxin KP is the drug of choice for treating BRD. A single dose will result in therapeutic levels of antibiotics in the lungs for 14 days.

Prevention of BRD revolves around a number of measures. Good colostrum management is essential (surveys show only about 30 % of Australian dairy farms hit all the targets for good colostrum management!) to confer good immunity to calves in the first few weeks of life.

The calf shed environment is critical - poor ventilation resulting in high levels of ammonia/dust / fungal spores will predispose calves to BRD. Sharing milk feeders and troughs between pens increases the risk of transmission and spread of BRD between pens if an outbreak does occur.