The environmental needs of a calf are fairly simple: physical comfort, good hygiene and reasonable shelter writes Martin Mulholland, Senior Dairying Technologist at the College of Agriculture, Food and Rural Enterprise (CAFRE).
Calf rearing is relatively straightforward if calves remain healthy and disease-free.
Key calf house design issues to minimise disease spread include: providing plenty of fresh air through good ventilation, controlling the speed of air movement at calf level to avoid draughts, good liquid waste drainage to avoid increasing humidity, and good feed supply and bedding management to allow the calf to manage low temperatures.
Modern dairy calf housing should provide such an environment to allow calves to be reared to meet growth rate targets for calving at 24 months of age in a labour efficient and cost-effective manner.
To meet growth rate targets of 0.85 kg/day throughout the heifer rearing period, it is essential that the calf housing environment is designed to minimize disease incidence and spread in the early stages of calf life.
How to keep the calf house environment healthy will be explored during a series of CAFRE Calf 2020 webinars. These will start on Thursday, November 17th, at 8.00 pm and will continue for three consecutive weeks until Thursday, December 3rd.
How calves can become infected
A calf can become infected by disease-causing organisms in several ways, including direct contact through either, calf mouth to mouth, faeces to mouth, mouth to feeder teat to mouth, or surfaces to mouth; short-range air transmission of droplets transmitted by coughing and sneezing; airborne diffusion in aerosols formed from water droplets or dust.
What can farmers do to minimize disease spread? Avoid overstocking calf houses as 90% of pathogens come from other calves.
Stocking densities should not be less than 6.0 m3 of air space per calf before weaning. In terms of floor space, the minimum floor space should be 1.5 m2 per calf up to 4 months of age.
Reduce humidity in the calf environment through good drainage and good ventilation. Pathogenic micro-organisms are released into the air within a calf house from infected calves and contaminated materials such as bedding and wall surfaces.
Use materials which are easily cleaned, such as smooth, hard plastics. Clean and disinfect calf rearing facilities between batches. Strictly apply veterinary-approved vaccination protocols.
How do you keep disease-causing organisms out of the calf house? The concentration of micro-organisms in a calf house air depends on the balance between the rate of release of micro-organisms into the air and the rate of clearance of micro-organisms from the air.
The number of micro-organism colony-forming units in a calf house air can range from 1,000 to 500,000 per cubic metre. By contrast, the number outdoors is typically <100 per cubic metre.
Good drainage is also a critical factor to keep the air as dry as possible and speed up the rate of micro-organism death.
Drainage channels should be installed as close as possible to the source of liquids to minimize the area of wet floor surfaces. Falls of at least 1 in 50 should be constructed to ensure rapid drainage of liquids to minimize evaporation and humidity.
Ventilation of calf housing is critical to minimize the spread of disease and control humidity while avoiding draughts.
It removes heat, moisture, chemical substances, and micro-organisms from a building. However, the number of micro-organisms removed by ventilation is considerably smaller than the numbers that die within a building.
In winter, the main function of ventilation is to remove moisture from the building and keep relative humidity down, ideally below 80% to reduce the survival time in the air of small aerosols containing micro-organisms.
Good ventilation should result in at least 6 air changes per hour in the calf house building.
An enclosed calf house should have air inlets of 0.045m2 and air outlet of 0.04m2 per calf. Ideally, the height difference between the inlets and outlets should be at least 1.5m and preferably 2.5m – depending on the width of the building.
The adequacy and performance of calf house ventilation can be assessed through measuring air space and ventilation inlets and outlets and by the use of smoke emitter pellets within the building. Smoke pellets will also readily indicate where draughts occur.
What about draughts? Draughts are most critical when a calf is housed in a small, enclosed pen with no opportunity to move away from the draught.
Where calves are reared in groups, they may have more opportunity to move away from draughts. Deep, dry, straw bedding has an important function in allowing a calf to nestle into a bed of straw and protect itself from draughts at floor level.
Extra bedding should be provided for young calves when temperatures are below 10oC. Bedding should ideally be topped up in the evening ahead of falling night-time temperatures.
Ventilation should never be compromised to prevent draughts. The impact of draughts may be minimized by providing deep straw bedding to allow the calf to nest. One can install double row space boarding (Yorkshire cladding) to baffle air inflow and install ceiling sheeting over the first two purlins to reduce down-draughts.
A farmer can re-position exposed pens to have solid pen sides facing onto draughts, and partially covering the back of pens next to outside walls to reduce down-draughts.
Calf jackets may also help as they can prevent heat loss through convection, conduction, radiation and evaporation. The benefits of calf jackets have been studied by the Agrifood and Biosciences Institute (AFBI), Teagasc and Harper Adams.
Teagasc found calf jackets to have no effect on growth rates or calf health.
AFBI calf measurements have shown skin temperatures to be raised by up to 5oC when calves are fitted with jackets. To avoid jackets becoming a disease transfer risk, however, washing and drying operations need to be factored into their use.
Feed intake should be increased in cold temperatures to replace energy being burnt for heat and to prevent growth rates being compromised.
The Agricultural and Horticultural Development Board (AHDB) recommend feeding an extra 50g of milk replacer per day for each 5oC drop in temperature below 10oC.