The link between hygiene and infection is indirect and the literature has no clear descriptions of and associations between measured variables in the calf environment. The evolution of poultry and pig production systems has come out very clearly in support of ‘all-in, all-out’ (AIAO) systems, with the quality of the animal-free stage of the system being dictated by the effectiveness of appropriate hygiene. This has clear implications for the design of sustainable calf systems. The UK has more than 80% of dairy herds on an all-year-round calving pattern, which means that calf housing systems will have a constant trickle of young calves entering the built environment. Herd sizes have increased from 75 to 148 milking cows from 1996 to 2018 (AHDB, 2019) and has led to an inevitable increase in the number of calves going through systems. There must be an increase in the epidemiological pressures. System designs have adapted, but with limited success.
Efficiency of cleaning
Apart from the question of using the correct cleaning products at the correct dilution for the correct period of application, the ability to satisfactorily clean surfaces competently is a system design issue. A primary requirement is to have enough animal space and time to leave a pen or groups of pens empty for enough time to clean a space effectively. This is already a major weakness, and is perpetuated by the design of new systems that are intrinsically weak because the balance between calf numbers, flow, and available space is not achieved. An example of this inherent weakness is in some systems designed around automatic calf feeders, with one machine linked to four feeders in four pens. If a pen cannot be left empty for enough time to effectively clean it, the system is inherently at risk of health failure. The data concerning the enteric health of youngstock on UK dairy units strongly suggest that effective hygiene is not routinely achieved. The experience of the broiler industry is that it is not possible to routinely clean a broiler shed in less than 48 hours without having a negative impact on subsequent crop health. The cattle sector needs to be more realistic about the time and knowledge required for effective cleaning.
Effective hygiene requires cleanable surfaces that will dry within a practical amount of time. Broken surfaces are not cleanable because penetration by disinfectants of the many fissures in a surface is not possible, thus cleaning will not eliminate all viable microorganisms. The important role of biofilms as a factor that can significantly increase the survival rate of pathogens outside the host is slowly becoming realised, and needs wider dissemination. Clinical isolates of Streptococcus pyogenes and Streptococcus pneumoniae cultured from biofilm provided viable cells up to 1 month post desiccation (Marks et al, 2014). Mycoplasma bovis is another pathogen that thrives in biofilm (Maunsell et al, 2011). The target for youngstock pens is to provide cleanable surfaces, which can be achieved by rendering walls to 1.2 m height, the use of epoxy resin paints (Figure 1), and to recognise when timber and steel partitions need to be replaced with new materials.
Moisture and floors
Moisture management is a key design requirement of all animal housing. Starting with the requirement for effective cleaning, solid floors should have a slope of 1 in 60 (1.5–2.0%) to facilitate the removal of dirty wash water. Drainage channels are required to intercept dirty water coming from each pen, to prevent diffuse pollution of the immediate area and significantly decrease the spread of pathogens by footfall and machinery. This is simple, easy to understand, and massively ignored. Producers are understandably reluctant to use water in a cleaning process if the dirty water contaminates adjacent pens, but the design answer is to provide facilities that can be individually cleaned. Drainage can be provided in existing concrete floors by cutting 100 mm wide x 75 mm deep channels with concrete saws, and creating a drainage channel lined with epoxy concrete.
Design for moisture management can significantly improve building performance and reduce variable costs. Many Grampositive bacteria and all the respiratory viruses ‘thrive’ in a moist environment and aerosol survival times are maximised in the 75–85% relative humidity range. Moisture management is a key requirement. Calves will produce 4–8 litres/day of liquid as faeces and urine, and 1–2 litres/day as moisture by respiration. A pen of 20 calves needs to contain or manage 80–160 litres/day of dirty liquids, up to 1000 litres or 1 m3 per week. A design standard that needs to be re-applied in the youngstock sector is the knowledge that, to provide drainage of liquids under straw, a slope of 1 in 20 (5%) is required. This requires a one-time effort to convince the producer and the builder that the extra effort will provide life-long added value.
The application of preferential floor slopes within a building for milk-fed calves can be across the complete floor area of a pen, or part of a pen where excess urine can be expected. This could be considered an absolute requirement where automatic feeders are used, with a change in floor profile within a 2–3 meter focus of the feed stance. The target is to provide a floor profile that collects urine in the immediate vicinity of the calf feeder and directs the liquid to the shortest route out of the pen. This also improves the cleanability of the area around the feeder, which is a hygiene hotspot in any calf pen.
Ventilation
Ventilation provides the balance between fresh air delivery and stale air removal. Ventilation is always a balance between inlet and outlet; if only one side of the equation is effective the whole system has less functionality. Ventilation is constantly referred to as a vital factor in the management of pneumonia, and just as constantly dealt with in a totally subjective manner, which is incorrect. The first design requirement is to acknowledge that, for most locations, natural ventilation of a building is powered by the wind for >90% of the time. This leads to two objective and predictable conclusions for any particular building:
- Wind comes from all directions at some point and at a moderately predictable frequency
- Wind driven ventilation will not occur from one or more sides of a building which is partially or completely protected by an adjoining or nearby structure or topographical feature.
The design requirement is for sidewall cladding that facilitates wind-driven airflow but controls air speed and the ingress of rain or snow. Details are available from AHDB (2018a, 2018b), RIDBA (2019).
One design example that needs to be widely re-introduced for youngstock housing is to understand the difference between York-shire board and space board (Figure 2). The building trade sells space board and calls it Yorkshire board; the latter is what is needed for youngstock housing in many locations, because space board does not reduce air speed adequately for youngstock, and does not eliminate moisture ingress to the same degree as Yorkshire board. Yorkshire board is typically two parallel lines of 150 mm boards with a 25–50 mm gap between each board, with the gap based on calculated inlet area requirement (AHDB, 2018a). It is very common to find that the gap is not a calculated width, and may be entirely inappropriate. The two lines of boards are separated by horizontal tantalised timbers with a distance equal to or more than the calculated 25–50 mm distance between adjacent boards.
Effective ventilation needs both inlets and outlets, preferably with at least a 2:1 balance between the two. Inlet area should provide diffuse inlets along the entire side of a building above animal height, with an absolute target of reducing internal air speed below 0.5 m/s and 0.2 m/s at animal lying height. This is clearly not possible when inlets are point sources such as a door which will only increase air speeds entering a building. The fact that external wind predictably comes from all points of the compass at some time of the year should be considered.
The primary outlets of naturally ventilated buildings are the sidewalls opposite the sidewalls where air enters. Thus all walls need to act as inlets and outlets at some point. Buildings where this is not the case will predictably create turbulent airflows within a building, as air that enters a building enters a chaotic phase created by solid divisions, deflection, and increased localised pressures. A target airflow pattern is a controlled inlet air flow across the whole inlet area of a sidewall, a parallel airflow across the interior of the building, and an outlet on the opposite wall that does not inhibit air flow patterns.
There will always be predictable periods of low or zero wind-speed, at which point there will be no fresh air entering a calf house. Competent design of ridge outlets are based on the understanding of thermal dynamics, whereby the sensible heat output from ruminant animals is sufficient to raise the air temperature inside the building and create the stack effect. The optimum design is a protected ridge with upstands, because the upstands create a negative pressure in the ridge for >90% of the time (Figure 3). They suck dirty air out of the roof space. Clear open ridges with caps to prevent rainwater ingress are very poor as they create a positive pressure at the ridge >90% of the time. They are popular because they are cheaper and people do not understand how ridges can work (Figure 4). The required areas of outlet are based on stocking density and liveweights (LW) and roof pitch. A reliable ballpark figure of outlet area for calves is 0.04 m2 per animal to 100 kg LW. However the monogastric calf produces only 200 W of sensible heat, and with large building volumes and a surfeit of concrete and steel there is seldom any stack effect (Figure 5). Thermal dynamics is one reason that the calf Igloo system can be beneficial to calf health and productivity, because the presence of 15 calves inside a volume of 22 m3 can create a stack effect.
A preliminary analysis of the ventilation capacity of 88 calf buildings on 66 dairy farms in Northern Ireland (AFBI Opti-house project, 2019, in prep) shows that only 9% of calf buildings were able to provide effective ventilation. Effective ventilation is a primary requirement of housed livestock systems, and it is questionable that quality assurance does not drive improvements in this area. There is good potential for improving animal health by improving ventilation, and the costs associated with designed improvements should be balanced against the real costs caused by current health and performance losses.
Mechanical ventilation
Producers understand that there can be a predictable increase in the severity and prevalence of respiratory issues associated with periods of still, moist air. People can understand a process where-by air quality must diminish when wind-driven fresh air delivery slows or stops. There is a very low probability of a stack effect in calf buildings, so most calf buildings need mechanical ventilation. A fan and duct system for 40–80 calves may cost in the region of £1500, and £1 per day in running costs. An effective covered open ridge on a 20 m building might cost another £1500. The investment needs to be balanced against a £700–900 loss of income from every retained heifer calf, injected twice or more and kept for two lactations (Morrison et al, 2013).
Fan and duct systems should be designed to fit specific sites and Nordlund (2008) published farm-based guidelines. Too many producers are sold ‘off-the-peg’ products in either a sense of false economy or because the seller is not fully knowledgeable about the system requirements. A common problem occurs where the lack of a effective ridge opening is ignored, which can lead to significant losses as the fan and duct system (positive pressure ventilation) serves to introduce fresh air amongst the calves, and forces the dirty air to be spread amongst stock as it finds passage out of the building. A further common failure is to provide a system that delivers fresh air above 0.2–0.3 m/s at calf height, creating draughts.
Information required to design a competent fan and duct system:
- Building length, width, eaves height and ridge height
- Maximum number and maximum weight of calves in the building volume
- Location of calf pens within the floor area (e.g. all on one side?)
- Practical height of bottom of tube above the floor
- Location of impediments to fan or tube location (e.g. roof trusses)
- Area and location of any outlets in the roof: ballpark requirement is 0.04 m2 per calf.
Hutches
Individual hutches have the advantage in terms of calf health of maintaining a physical separation between individual calves at a time when immune status is naïve. This is currently under pressure from concerns about other aspects of calf welfare, but maintaining very small groups sizes in AIAO facilities should be beneficial for calf health. There is clear evidence that calf productivity significantly improves under group housing compared with individual housing, due to increased feed intakes and socialisation that facilitates future re-grouping of calves. Evidence that supports grouping from day 0 is not so clear.
The strengths of hutch systems are that they are readily cleanable, provide plenty of access to fresh air, and are easy to use as an AIAO system. The principle design weakness occurs when drainage is ignored, leading to inherent dampness, diffuse pollution and pathogen spread at ground level. Successful hutch systems maintain porous floors or concrete bases that actively prevent dirty water spreading to adjacent hutches.
Conclusion
The last 10 years has seen a significant change in the understanding of the value of very young calves. Improvements in thermal competence via nutrition and insulation are being followed by upgrades to calf housing. Basic design guides have been available and updated for many years (AHDB, 2018a,b; RIDBA, 2019). However there is very little in the current ‘design’ process for livestock building beyond a token consideration of adequate floorspace and checking that the engineering of the steelwork is sufficient to with-stand a 1 in 50 years' weather event. Nothing more. The opportunity for improvement is vast.
KEY POINTS
- Pens and buildings need to be made cleanable, and any weaknesses of current systems should be discussed openly. Lack of appropriate time is a system weakness.
- Good drainage is one ingredient of good hygiene, and all floors can be changed with expected benefits of better biosecurity, reduced straw use and cleaning times, and lower ambient humidity.
- Ventilation: discuss the obvious. Fresh air cannot get through solid walls; elevated air speeds create a chill factor and can reduce immune competence; shared air spaces with older stock cannot be beneficial.
- Good ventilation requires diffuse inlet AND outlet areas. There is clear guidance in freely available AHDB publications, based on proven science.
- Most buildings for calves require fan and duct ventilation to act as a fresh air inlet for the predictable periods and locations where wind-driven natural ventilation is poor or absent.
- Discuss required changes in terms of financial investment, with payback from improvement to current financial losses caused by health and productivity issues.