Infectious disease in the suckler herd

Natascha Meunier Michelle McGrath

Maria Guelbenzu

Disease is a major cause of financial and animal production losses on beef farms, and even though it’s difficult to put a value on it, the labour and stress involved in a disease outbreak should also be taken into consideration when evaluating individual farm disease risks. The likelihood and consequences of a disease need to be weighed against the costs of control and preventative measures. For example, some measures such as vaccination, may appear to have higher initial costs but may still be cheaper than the overall costs of treatments, labour, clinical and subclinical animal production losses should an outbreak occur.

Preventing disease is done through minimising animal exposure to pathogens (bacteria, viruses and parasites) and maximising an animal’s immune system. Minimising exposure is achieved by both preventing diseases moving onto the farm and protecting your animals from pathogens that are already present. Many diseases are spread from farm-to-farm through the movement and mixing of infected animals, which appear to be healthy but may be silently carrying diseases that could cause extensive harm to a herd if it has never encountered these diseases before. If you do need to purchase animals, buy in as few, and from as few herds, as possible. The risk of disease being introduced increases with more animals, and when animals are purchased from multiple sources. Newly introduced susceptible animals can also face potential disease risks from diseases already established in a herd.

To minimise disease exposure:

• Keep brought-in animals separate from the main herd for a minimum of five days (ideally 21- 28 days) and monitor them for any signs of illness.
• Good hygiene, cleaning and disinfection practices have the biggest potential to impact on-farm disease spread.
• Calving pens and creep areas should have dry, clean straw bedding with good ventilation and no draughts.
• Disinfect calf navels soon after birth to prevent infection from the environment.

The starting point to maximise an animal’s immune system is good quality colostrum consumed soon after birth in sufficient quantity. Calves are born with an immature immune system and rely heavily on colostrum for antibodies before they can produce their own. Calves who fail to receive adequate colostrum are more susceptible generally to disease. Hand-feeding or stomach tubing colostrum is advised for calves too weak to suckle or if abandoned or refused by the dam. Keep a store of frozen colostrum to ensure these calves can get colostrum as soon as possible.

Calf diarrhoea (scour)

Up to one month of age, scour is the leading cause of death in calves (All-Island Animal Disease Surveillance Report, 2024). It can have several causes such as bacteria, viruses or parasites but for all of these, good hygiene such as regularly replenishing bedding, cleaning feed/water troughs and stomach tubes is important to stop spread and prevent disease. Thoroughly clean and disinfect sheds between calving seasons to minimise the risk of infection between seasons. Use a disinfectant that is specifically targeted against cryptosporidium and coccidiosis, if these are problematic on farm.

Vaccines are available for rotavirus and cryptosporidium, common causes of scour, as well as E. coli, coronavirus, and Salmonella. These vaccines are given to the dam on various schedules, at least three weeks pre-calving, but are only effective in the calf if the colostrum is consumed soon after birth.

It is not possible to tell what has caused a diarrhoea by its appearance, but the age of onset can give some clue e.g. E. coli usually affects calves in the first week of life and coccidia is generally from 3 weeks old. Sampling and testing early in the disease onset can help guide treatment decisions and prevention measures. No matter the cause, early treatment which encompasses replacing lost fluids and salts to prevent dehydration from the scour is important; isolate the sick calf and dam from the group. Continue to allow the calf access to its dam for milk feeds but give additional electrolytes and fluids as a rehydration solution (four litres per day).

Coccidiosis can affect calves both in the shed or when at grass, and the oocysts (eggs) can survive for over a year. If calves had an outbreak the previous year while in a particular field, it is advised not to use that same field for new calves the following year. Water and feed troughs in these fields should be emptied and thoroughly cleaned. Consult with your veterinarian on preventative treatments for high-risk periods.

Bovine respiratory disease (BRD)

From one to twelve months of age, respiratory disease and pneumonia is a major cause of disease and mortality in calves. Pneumonia is a complex problem and is often referred to as being a ‘multifactorial disease’. This means that besides the infectious agents, a number of environmental and management factors and their interactions will determine the occurrence and severity of disease. Cattle succumb when the disease pressure overcomes their immune system. There is no single factor that will control pneumonia and multiple factors must be tackled together. Calves that suffer repeated and/or severe bouts of pneumonia may end up stunted for life due to permanent lung damage. Such calves may appear healthy after the signs resolve but do not achieve the same growth rates as their healthy peers.

Stress can suppress the immune system, so managing stressful periods well has an important role in preventing disease, particularly pneumonia. Weaning should be completed well ahead of other stressful periods such as transport, sales, mixing of groups, housing or other major handling (Further information: Weaning management of beef-suckler calves: health implications). Attempt a gradual weaning approach by phasing-in the separation. Pain relief and anti-inflammatories used during castration or disbudding are a means of reducing stress around these procedures.

Environmental factors that affect incidence of pneumonia include poor air quality, draughts, humidity and high population density, with the risk of respiratory disease increasing with crowding and mixing of age groups. In some situations, infectious agents can build up in the farm environment to such high levels that the immune system can be overwhelmed (even when it is not compromised).

Good ventilation, fresh air circulation without draughts, is important to remove pathogens, contaminants, ammonia and dust, which are irritant to the lungs. Upon entering the shed, a strong smell of ammonia and many cobwebs in the rafters are indicators that the ventilation needs to be reviewed. Increasing outlet widths or changing inlets for more airflow are options to explore to improve the air circulation. Dry, warm bed areas are vital for autumn-born calves to prevent chills.

Initial signs of pneumonia can be non-specific and include being off form, dullness, reduced feed intake and lack of gut fill. Other signs may include fever (over 39.5°C), increased respiratory rate, coughing, watery nasal discharge and severe breathing difficulties. Early diagnosis is crucial as by the time these later signs are noted the disease is advanced and treatment is less likely to be successful as damage to the lungs may be irreversible. Not all infected animals show obvious signs of disease but may still experience reduced growth and production (Further information: Health management of purchased weanlings and store cattle).

There are a number of viruses and bacteria that can contribute to pneumonia. Lungworm can also contribute to pneumonia and predispose calves to bacteria and viruses affecting the lungs. Bacterial infection often follows a viral infection and can cause severe damage to the lung tissue if left untreated or if treatment is started too late. Infectious bovine rhinotracheitis (IBR) is a particular challenge because once an animal becomes infected, it becomes a carrier of the disease for life. The virus establishes a lifelong latent infection and at times of stress such as transport, calving, nutritional stress, mixing stock etc, the virus may be reactivated and can be re-excreted leading to new infection in other susceptible cattle.

Currently vaccines are available to protect against many infectious causes including, IBR, BRSV, PI3V, Mannheimia haemolytica, Histophilus somni and Mycoplasma bovis. In some instances, vaccination does not prevent infection but decreases the severity of clinical disease if an animal becomes infected and/or decreases shedding of infectious organisms.  Vaccines take time to provide sufficient protection, so ideally farmers should plan to use them well in advance of when their animals need protection such as transport, housing or weaning. Vaccination protocols should be developed by the farmer and veterinary practitioner together. The exact programme will differ for each farm, depending on which infectious agents you want to protect against. It is important to remember that vaccination is only one part of disease prevention and cannot compensate for poor management or insufficient attention to biosecurity.

Parasites

There has been a great deal of attention focused on anthelmintic (wormer) resistance in recent years. This is an ongoing concern and frequent use and over-reliance on wormers should be avoided. On the other hand, the Irish climate remains very amenable to worm development and reducing usage without increasing monitoring or using other worm avoidance strategies and grazing practices carries risk of parasitic disease. In the case of anthelmintics, use as much as necessary and as little as possible.

Spring-born suckler calves are generally at low risk of parasitic disease from gut and stomach worms until weaning. Autumn-born calves are naïve from turn-out and need to be more closely monitored and managed for worms. There is gradual build-up of eggs and infective larvae on pastures as the grazing season progresses and this risk should be controlled by integrating treatment, worm avoidance strategies and grazing management. Liver and stomach flukes are a higher risk in the autumn and winter period, clinically seen as animals not thriving. Dung testing and abattoir reports can help guide treatment and management throughout the grazing season.

Hoose caused by lungworm, is usually seen in late summer and autumn but outbreaks can be very unpredictable. They often occur 2-3 weeks after the start of rainfall following a period of dry, warm weather. Strategic lungworm dosing may be needed in high-risk periods such as late autumn or a few weeks ahead of sales or housing to prevent pneumonia.

Clostridial disease

Farmers are advised to vaccinate for clostridial diseases, as the vaccines are relatively low-cost but the consequences of an outbreak of the disease can be devastating. Clostridia cause diseases such as blackleg, where animals are often found dead with no prior symptoms or sudden illness. These bacteria are widespread and found in soil and organic material, so vaccination remains the best option to prevent disease. There are several vaccines available, which usually require two doses as part of the course. Animals will not be fully protected unless the course is completed.

Bovine viral diarrhoea (BVD)

Ireland is very close to BVD freedom with only a small number of herds with BVD. While the risk of your herd being infected with BVD is small, there is still a risk, especially if there is movement of stock into your herd. Buying in (or even renting) an animal that is apparently healthy, but carrying the BVD virus remains a risk for spread of the disease into herds.

One of the new changes to the BVD programme in 2026 is the introduction of “forward tracing”. This may affect farmers who buy in stock even though their own calves tested negative. If a calf tests positive for BVD, the herd is immediately restricted. However, by that stage, the infected calf may already have been on the farm for some time and could have spread the virus to other animals. During this period, before the result is known, animals may also have been sold or moved off the farm. Forward tracing looks at this risk. It means that any animals moved out of the herd between the birth of the BVD-positive calf and the test result are traced. Where there is a risk that infection may have been passed on, the receiving herds are contacted, and the animals are blood tested to check their status.

Conclusion

Develop a flexible approach to herd health on your farm with your veterinary practitioner examining risks and preventative measures. Target those diseases likely to have a big impact on the herd, are most likely to occur, or are already present on the farm.

Compiled and edited by Mark McGee and Paul Crosson, Teagasc, Grange Animal & Grassland Research and Innovation Centre, and first published in BEEF2026 – Driving Sustainable Performance, additional reading from BEEF2026 is available here.