The principal aim of dairy calf rearing is to efficiently produce healthy replacements that can reach their genetic production potential, there-by ensuring the longevity of dairy businesses. However, this goal must now be achieved while considering consumer perceptions of animal welfare and navigating rising costs, labour shortages and increasing sustainability pressures. Providing advice without accounting for all these factors will result in recommendations that have limited uptake within the industry. This article summarises research on calf management strategies, focusing on housing and its impact on calf health and welfare.
Common UK calf management practices
A questionnaire of UK farmers who reared dairy calves commercially was carried out in 2020, and had 216 responses (Mahendran et al, 2022). A key finding wasthe recognition of the low level of regular hands-on veterinary involvement in day-to-day health decision-making for calves. It may be that treatment protocols for calves are covered in herd health plans (HHPs) and farm staff feel appropriately trained to make treatment decisions. However, veterinary practices should ensure standard operating procedures (SOPs) for diagnosing and treating diseased calves are in place and are being used across farm clients. These should be a ‘live’ document that is regularly reviewed and revised depending on changing farm conditions, and not simply included in HHPs as a result of standard requirements. Given the impact of changing seasonal conditions for calves, a minimum of twice-yearly reviews might be advisable, with a rationale for quarterly reviews to changes in the weather and disease patterns to be considered when reviewing calf health SOPs.
Identifying sick calves can be challenging as a result of subtle clinical signs in early disease along with subclinical disease prevalence. Although weekly veterinary support can be helpful, such as through routine calf heath visits, formal health assessments need to be performed more regularly (at least daily), therefore relying on farm staff abilities. This reiterates the need for farmer training and up-skilling to enable them to detect sick calves early in the disease course and apply the correct treatment strategies to help reduce the negative production consequences. Farmer training has demonstrated success with other dairy diseases such as mastitis and metritis, leading to improvements in antimicrobial stewardship (Pempek et al, 2022; Garzon et al, 2023), as well as improving staff retention (Ju and Li, 2019). Integration of precision technologies should also be considered, such as accelerometers or automatic milk feeders (AMFs) (Figure 1) (Costa et al, 2021; Wilson et al, 2023). These can reduce labour requirements, with the use of demonstration farm networks providing an opportunity for farmers to see and evaluate the effectiveness of the technology working on commercial units to encourage their investment into them (Dutton-Regester et al, 2020).
Additional findings from the farmer questionnaire revealed that restricted milk feeding of calves (4–6 litres/day) remains highly prevalent (45.4% of surveyed farms), likely contributing to poor production outcomes in calves on UK dairies, including increased mortality, decreased growth and increaseddisease levels. This is especially noteworthy, given that calves with access to near ad libitum milk quantities chose to voluntarily consume a mean of 9.6 litres/day (Mahendran et al, 2023a).
Below-target growth was observed where restricted milk feeding was practised, exacerbated by the overall low concentrate feed intake many calves have before weaning. This suggests young calves (before six weeks of age) cannot compensate for low milk feeding rates by increasing concentrate intake.
While increasing milk provision for calves has a higher initial cost, this strategy offers long-term benefits, including improved heifer fertility and milk production (Heinrichs and Heinrichs, 2011; Soberon et al, 2012), as supported by research (Welk et al, 2023). These improvements should offset the increased rearing costs, though there is a significant time lag in recouping this investment.
Many farmers cite farm facilities and practicality as reasons for continuing low milk feeding. Encouraging the use of technologies such as AMFs could help overcome these barriers
By increasing the number of meals calves can consume to increase overall intakes. If using manual feeding (particularly with twice daily feeding), some care over maximum portion sizes is needed, with recommendations for no more than 5% of bodyweight to be fed at a time.
Individual compared to pair housing of calves
The importance of calf behaviour is often overridden by economical and practical realities when it comes to housing management on commercial dairy farms. Cattle are gregarious animals that naturally live in social groups (Chua et al, 2002) and will learn from each other, such as for solid feed consumption. Over the previous three decades, many calf housing recommendations have focused on individual housing to decrease pathogen exposure and associated disease occurrence and risk of death for calves (Svensson et al, 2006). Individual housing also prevents unwanted behaviours such as cross sucking from occurring (Kung et al, 1997). A greater focus on the impacts of stress and immune status, as opposed to exposure to pathogens alone, has contributed to a re-evaluation of the potential benefits of isolated rearing/individual housing (Van Reenen, 2000).
The authors carried out three studies to assess the impacts of individual compared to pair housing of calves (Mahendran et al, 2021; 2023b; 2023c). Overall, there were multiple positive benefits to housing calves in pairs during the pre-weaning period, particularly when this was done from birth. This included increased survivability between birth and the end of first lactation (73.8% compared to 63.7%), resulting in more milk produced from pair-housed calves overall (10 080 kg vs 9861 kg). There was also similar or lower disease prevalence during the pre-weaning period, higher activity levels and positive impacts on concentrate intakes for pair-housed calves. These studies showed no significant differences in average daily liveweight gain (although restricted milk feeding may have confounded this result), novel object approach times or heifer fertility between the pre-weaning housing types.
A potential negative long-term effect associated with pair-housing calves was that they did experience significantly more udder health events in the first lactation than individually housed calves (29.4% vs 17.7%), possibly linked to cross sucking activities, but this did not impact overall 305 day milk yields. There were other factors that may have influenced the prevalence of udder health problems, such as seasonal fly control, which were not investigated in this study. Client support may be needed with regard to feeding strategies to minimise the prevalence of cross sucking behaviours by ensuring calves are fed enough milk via a teat, and with enough environmental stimulation to reduce these unwanted behaviours.
Larger group housing of calves
Group housing can range from small groups (three to 12 calves) up to around 30 calves – the number depends on the farm size and calving pattern, with small farms that have infrequent calvings generally having smaller group sizes, and large block calving herds having larger group sizes. It is generally accepted that group housing requires considerably less time commitment compared to individual housing (<1 min per calf compared to 10 min per calf respectively), making it a more efficient way to house calves (Kung et al, 1997). It also helps satisfy public perception – over 75% of participants in one survey stated that group housing was more acceptable than pair and individual housing as they thought it allowed better socialisation, increased space provision and play interactions (Perttu et al, 2023).
The use of groups allows calves to develop normal social responses (Jensen et al, 2010), providing social support and social buffering (Cohen and Wills, 1985), which is important in reducing stress responses. Despite these positive impacts, there are disadvantages to group housing calves, with cross-sucking behaviours reported more frequently in groups with high numbers of calves (Lidfors and Isberg, 2003). Group housing can also increase competition behaviours around restricted resources, such as when milk feeding through limited teat numbers, with the potential for decreased feeding times and reduced milk in-takes, with ratios of one teat per three calves (von Keyserlingk et al, 2004).
Research on group-housed calves fed through an AMF (Mahendran et al, 2023b) demonstrated that calves given ad libitum milk consumed on average 9.6 litres per day, with a range of 0.3–17.9 litres/day. These calves did have good growth rates that met targets for heifers to reach puberty and first service weights, along with low overall disease levels. This highlights the success that this pre-weaning feeding strategy can have. However, the high mean milk volumes consumed may disincentivise farmer uptake as a result of higher overall milk powder costs. If farmers still wish to feed fixed-rate milk volumes, this work demonstrated calves preferred to consume approximately 3 litres of milk three times a day, again highlighting the high level of restricted milk feeding currently being used by many farms in the UK. In addition, heavier birthweight calves voluntarily consumed more milk, suggesting that fixed-rate feeding systems should take calf size into account, allowing larger calves to be provided with proportionally more milk. A suggested minimum quantity of milk equivalent to 20% of body weight is needed to enable calf potential for growth and organ development through anabolic metabolism (Hammon et al, 2020). This should provide confidence to those who worry about overfeeding calves, but appropriate meal volumes should be maintained along with slow drinking speeds to reduce the risk of milk overflowing or entering the rumen.
In terms of social interactions, there was an increasing amount of time being spent near the AMF, with more cross-sucking occurring around the feeder over the weaning period. These calves were weaned from 7–0 litres/day of milk over a 2-week weaning period, but the changes in behaviour seen suggest that this protocol may not be optimal. Slow, gradual weaning aims to increase a calf 's solid feed intake gradually, enabling rumen adaption and reducing the risk of reduced growth rates following weaning (Khan et al, 2007; Sweeney et al, 2010; Steele et al, 2017). However, the behavioural changes seen in this research suggest that improvements could still be made to the weaning protocols used, such as more gradual reductions in the milk volume available, and possibly longer total time periods (≥3 weeks) spent in the weaning phase.
The gender of the calf also influences behaviour around the milk feeder, with female calves experiencing more displacements, meaning they are unable to finish comsuming their allocated milk volumes. This resulted in higher refusal visits and led to more time spent waiting around the AMF. This suggests that single-sex groupings may be beneficial to optimise calf use of limited resources like an AMF by preventing inter-sex agonistic behaviours.
The internal housing environment and air quality
Within the UK, pre-weaned dairy calves are typically housed using three main building designs; sheds, mobile housing such as hutches or igloos, and polytunnels. Sheds are permanent structures, usually with an A-frame or monopitch design that generally give a large air space containing many animals. Many of these sheds rely on natural ventilation but often have inadequate inlet and outlet areas along with adjoining to other livestock buildings (Brown et al, 2021) which can compromise air quality within the shed. Hutches and igloos are prefabricated plastic housing units that are available in varying sizes to house between 1 and 12 calves (Figure 2). They are easily relocatable and cleanable, providing increased flexibility for housing. Polytunnels are a relatively low-cost housing option that provides a large covered area that generally has very good light levels within it because of the semi-transparent plastic or polypropylene sheeting used to create it. All of these housing types are thermodynamic and provide variable protection from the weather, resulting in exposure of calves to changeable environmental conditions. Multiple physical parameters can impact the environment, and more specifically air quality; temperature, humidity, airspeed, particulate matter and other airborne compounds such as ammonia and microorganisms.
An observational study (Mahendran et al, 2023d) found that even in the UK's temperate climate, calves spent extended periods exposed to either heat or cold stress depending on the season, with levels impacted by the type of calf housing used. Hutches placed outside without any additional roofing provided the least environmental stability, recording both the maximum and minimum temperatures along with the highest humidity levels in the research (Figure 3). This means that moisture control must be care-fully considered when siting hutches, with the provision of additional shading and airflow to reduce heat in the summer, and increased insulation to keep calves warm in the winter.
Shed housing had the most stable temperature and humidity levels, but small air particulate matter that can reach the lung alveoli (PM2.5) had the greatest levels in shed housing, along with the highest air bacterial levels compared with the other housing types. This may negatively impact calf respiratory health (Callan and Garry, 2002; Lago et al, 2006) and indicates that ventilation in sheds must be carefully designed to ensure optimal air exchange without the production of draughts.
Conclusions
Given the recent government grants available for improving calf housing, vets and consultants must remain up to date with the latest research findings and recommendations that could improve the quality of calf production in the UK. Much success in calf rearing comes down to the basics—feeding the calves plenty of milk to fuel their immune systems and growth, keeping them in clean and well-ventilated pens, and providing appropriate social interactions and environmental conditions to reduce stressors and optimise welfare parameters. Ensuring farmers have the knowledge and support to provide these things will help make genuine improvements in calf production abilities, which can only be a positive step for the industry.