Calf health from birth to the end of the first grazing season in dairy-beef systems

Orla Keane Bernadette Earley

Beef production from the dairy herd has increased in recent years due to increasing dairy cow numbers and now contributes approximately 60% of beef output in Ireland. Typically, dairy-bred calves are sourced at approximately three weeks of age and are vulnerable to several infectious diseases, particularly during the calf-rearing phase. The most common diseases of calves one to six months of age are respiratory tract infections and gastrointestinal tract infections.

Reducing disease risk

To promote good calf health, management should focus on reducing the calf’s exposure to disease while strengthening its ability to resist infection. A clean, low‑risk environment from birth through the rearing period is essential. Key measures to achieve this include:

• Limiting the number of farms from which calves are purchased and selecting only farms and animals with a known high-health status.
• Thoroughly cleaning and disinfecting all calf accommodation and equipment before calves arrive and throughout the rearing period.
• Providing a clean, dry, straw‑bedded lying area that is free from draughts and has adequate ventilation.
• Housing calves in age‑based groups, ensuring that younger calves are not mixed with, or placed in areas occupied by, older calves.
• Vaccination programmes should be tailored to farm‑specific risks and reviewed regularly in consultation with a veterinary practitioner to reflect changes in disease prevalence. This includes emerging or re‑emerging threats such as bluetongue virus (BTV‑3), which has recently been detected in Ireland.

Housing requirements for calves

Housing for dairy‑beef calves should provide sufficient space, air volume and ventilation to support good health and performance. The legal minimum pen space requirement for group-housed calves less than 150 kg live weight is 1.5 m² per calf (DAFM). A space of 2.0 m² – 2.3 m² per calf is recommended, with most of this area designated for lying. Calf houses should provide adequate cubic air capacity, with a minimum of 7 m³ per young calf, rising to around 10 m³ per calf by two months of age, to help reduce relative humidity and airborne pathogens. Effective ventilation is essential, with a target of five to six complete air changes per hour, delivered primarily through natural ventilation using wind and stack effect, while avoiding draughts at calf level. Ridge outlets of approximately 0.04 m² per calf, combined with inlet areas two to four times larger are recommended to achieve this airflow. Floors should be well‑drained, ideally sloped at 1:20. Bedding depth should always be assessed using the “knee test”—when kneeling on the bedding, knees should remain dry; if not, additional straw is required. Maintaining adequate bedding depth reduces cold stress, supports lying comfort, and lowers the risk of disease by keeping calves dry and warm.

Respiratory tract infections

Pneumonia, or bovine respiratory disease (BRD), is a complex condition involving viruses and bacteria including mycoplasma species. While infection rates can be high, mortality varies depending on severity and management. The main viral agents involved are IBR, RSV, PI‑3 and BVD. Calves are more vulnerable to BRD when subjected to stress (e.g. disbudding or castration), overcrowding, poor ventilation, draughts, fluctuations in temperature, inadequate nutrition, or concurrent illness. In many cases, viral infection damages the respiratory tract, allowing mycoplasmas and secondary bacterial pathogens such as Mannheimia haemolytica to subsequently establish infection. Although antibiotics do not act against viruses or mycoplasmas, they are often used to control secondary bacterial infections and support recovery. To ensure appropriate treatment, nasal swabs should be submitted to a Regional Veterinary Laboratory to identify the causative organisms. Where pneumonia is a recurring issue, vaccination should be considered. The most comprehensive protection is achieved through a vaccination programme targeting IBR (BoHV‑1), RSV, PI‑3 and Mannheimia haemolytica.

Calf diarrhoea

Diarrhoea is the leading cause of mortality in young calves. Most cases are associated with six main causative agents: viruses (rotavirus and coronavirus), bacteria (Escherichia coli and Salmonella spp.) and protozoa (cryptosporidia and coccidia). Vaccination of the dam during late pregnancy results in active immunisation of cows and heifers and the transfer of passive immunity to the calf through colostrum ingestion. When administered in accordance with label instructions and combined with good colostrum management, these vaccines are effective in reducing the incidence and severity of diarrhoea caused by rotavirus, coronavirus, E. coli (K99), and Cryptosporidia. There is currently no vaccine available for the control of coccidiosis. Calves affected by diarrhoea lose large volumes of fluids and essential electrolytes, including sodium, potassium, chloride and bicarbonate, and may lose 10–12% of their body weight because of dehydration. Depending on the severity of disease, oral electrolyte solutions may be required once daily or up to four times per day. Milk feeding should continue alongside electrolyte therapy, as research has shown that continued milk intake does not worsen or prolong diarrhoea and provides essential energy and nutrients required for recovery.

Parasitic diseases

Coccidia: Coccidia is a risk to calves from approximately three weeks to six months of age. Signs include diarrhoea, dehydration, straining, loss of condition, rough coat and reduced growth. In severe cases, the dung may contain blood and mucus and if left untreated can result in calf deaths. The parasite is transmitted via the faecal-oral route. Therefore, strict hygiene and disinfection of calf pens are key in preventing disease. When disinfecting, it is important to remove all organic matter and use a disinfectant effective against coccidia. Feed and water troughs should be kept clean and raised to prevent faecal contamination. Bedding should also be kept dry. Veterinary medicines with efficacy against coccidia may prevent disease spread. Sick calves should be separated from unaffected calves and housed in a clean, warm, dry environment and oral rehydration administered. Immunity to coccidia develops reasonably rapidly, meaning coccidia is only rarely associated with disease in older animals. The treatment and control of coccidiosis in calves relies on the use of licensed anticoccidial products containing toltrazuril or diclazuril. These products are administered orally under veterinary guidance and are most effective when used as part of a group‑based control strategy combined with strict hygiene and housing management.

Stomach worms: Once calves start grazing, they are exposed to stomach worms. Stomach worm larvae can survive for many months on pasture. Therefore, worm numbers build up over time and are generally a greater problem in the latter part of the grazing season. Calves are susceptible to these parasites in their first grazing season when heavy infections can result in scour and ill-thrift, but more commonly they cause appetite suppression and reduced growth rates. Reducing infection from pasture is key to preventing disease, along with anthelmintic treatments when required. Newly re-seeded paddocks, silage after-grass and pasture grazed by older (immune) cattle or other animals (such as sheep) tend to have lower numbers of parasite larvae. Grazing different age groups (calves, yearlings etc) in a leader-follower system can also reduce the parasite challenge to calves. Control of gut worms is achieved by the administration of broad-spectrum wormers. Despite the large number of products on the market, there are currently only three classes of wormer available for the control of gut worms. These are benzimidazole (commonly known as white wormer (1-BZ)), levamisole (commonly known as yellow wormer (2-LV)) and macrocyclic lactones (commonly known as clear wormer (3-ML)). Within the macrocyclic lactone class are several related wormers, including ivermectin, moxidectin, doramectin and eprinomectin. The route of wormer administration is also important. Use of oral and injectable wormers results in less variation in drug uptake than pour-on products. With pour-ons, there is more variation in ingestion by licking and skin absorption due to hide thickness, hair length, dirt and weather conditions. Recent research has demonstrated widespread anthelmintic resistance in gut worms on Irish dairy calf-to-beef farms. The percentage of tested farms with resistance is shown in Table 1.

Table 1. Number of dairy-beef farms tested for anthelmintic (wormer) resistance and the % of farms with resistance.

Farmers interested in checking the efficacy of wormers against gut worms on their farm can sign up on the Teagasc website for the MARCS project. https://www.teagasc.ie/animals/amr/research/marcs-project/

Lungworm: Lungworm, or ‘hoose’ is one of the most important parasitic diseases. Lungworm larvae also reside on pasture and are picked up by grazing calves. Ingested parasites move from the gut to the lungs where they lay eggs that are coughed up and swallowed. The eggs hatch in the gut and larvae are passed out in the dung. The larvae are carried out of the dung pat by rain or on the spore of a fungus which grows on cattle dung. Infective lungworm larvae also build up on pasture over the grazing season. Lungworm outbreaks are unpredictable and often linked to grazing patterns and weather. Clinical signs include coughing and difficulty breathing, particularly when animals are moved. If left untreated it can result in calf deaths. Immunity to lungworm develops over time and calves are at greatest risk. The wormers used to control lungworm are the same as those used for control of gut worms although anthelmintic resistance in lungworm is believed to be rare. However, there has been limited testing for resistance in lungworm in Ireland and there are no established guidelines for the diagnosis of resistance in lungworm in the field. Lungworm is one of the few parasitic diseases for which a vaccine is available to prevent disease (Huskvac). The vaccine consists of two doses of inactivated lungworm larvae given 4 weeks apart and can be given to animals eight weeks and older. The use of wormers around vaccine administration must be avoided.

Conclusions

Successful dairy‑beef calf rearing depends on an integrated approach to disease prevention, housing, nutrition and parasite control, particularly during the vulnerable early-life stages. Respiratory and gastrointestinal diseases remain the principal threats to calf health and performance, but their impact can be substantially reduced through effective biosecurity measures, sourcing calves from a limited number of high‑health herds and maintaining high standards of hygiene and housing. Adequate space allowance, ventilation, bedding and drainage are essential to minimise environmental stress and reduce disease challenge, while timely vaccination and appropriate veterinary intervention play a critical role in controlling infectious disease outbreaks. As calves transition to grazing, strategic parasite control, informed by grazing management and awareness of emerging anthelmintic resistance, becomes increasingly important. A well‑planned and regularly reviewed herd health programme, developed in consultation with a veterinary practitioner, is central to protecting calf health and welfare, optimising growth rates and ensuring that calves reach their genetic and economic potential.

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.