He said calves must have fresh air, no draught (low air speed), a dry environment, and be within the correct temperature range, to grow and maintain their immune system.
There is generally an imbalance in one or more of the four elements; not enough fresh air, too much draught, too wet and too cold, said Mr Kavanagh, consultant vet with Cow Solutions, Tipperary.
Irish weather conditions, particularly in springtime, are so variable, and the temperature, wind speed, and humidity will often change hourly.
Because of this, there is, as such, no perfect calf shed but there are basic principles, which if followed, allow simple conversions of old sheds and improvements made in new ones that make them work.
“If you understand the needs of the calf at different stages of growth, then it is possible to adapt sheds very easily to successful calf rearing environments,” he said.
The temperature at which an animal has to burn additional energy to keep warm is referred to as the ‘lower critical temperature’.
Up to two weeks of age, the lower critical temperature is -5C.
Below this temperature, the calf is burning energy to maintain its core temperature and its immune system. The optimal temperature for the calf is 15C to 25C.
The lower critical temperature is affected by a number of factors including coat length, and whether the coat is wet or dry.
As cattle grow and become heavier, their lower critical temperature reduces, enabling them to withstand lower temperatures without becoming stressed.
Similarly, as growth rates increase, lower critical temperatures tend to reduce. For young calves up to three weeks old, the optimum temperature is over 15C.
At temperatures below -10C, the calf will require extra feed to stay warm, and for each one degree drop, the calf should get 2% more feed in the form of extra milk or increased milk powder concentration.
Increasing the depth of the straw bedding, providing other heat sources such as red lamps or linear quartz lamps, and calf jackets, can all help improve the temperature.
If calves are sick, they should have a warm sheltered area, to get out of cold draughts. Mr Kavanagh said Irish calf houses are made from materials with poor thermal properties such as concrete and tin, which do not hold the heat, and act like a deep freeze in cold weather.
During cold weather, calves under one month old need sheltered areas within large sheds to warm up in; these are micro-environments within a larger environment.
This is the principle of igloos and hutches.
The calf is sheltered in a micro-environment and the hutch can ventilate by the stack effect due to the heat generated by the calf. These systems fail if there is excess moisture due to poor drainage and wet bedding.
Bacteria and viruses are killed 10 times quicker by 100% fresh air than by 50% fresh air. Lack of fresh air increases the survival time of airborne bacteria and viruses, increases the concentration of toxic and noxious gases, and can reduce oxygen concentrations.
“There is too little fresh air in most calf houses. A calf house should have minimum cubic air capacity of 10 cubic metres per calf up to 100kg. Often, the solution is to create a large opening in the building that increases air speed but allows draughts to develop, creating more problems.
“Excessive air speed at calf height causes wind chill and should be avoided, particularly for young calves,” he said.
The increased speed of air around the calf reduces the insulation properties of its hair coat, thereby increasing the rate of heat loss from the body. If sustained or excessive, there will be a direct negative impact on productivity and immune competence.
This is compounded if the calf or calf bed is wet.
A one month old calf’s lower critical temperature is 0C, but if the airspeed is two metres per second, the lower critical temperature is 9C.
A windspeed of 2m/s will just make loose straw barely move and tremble.
“So, in a draught that we will barely feel, the calf is getting colder, more stressed and increasingly susceptible to pneumonia. Remember that the young calf is more at risk due to its lower critical temperature. As the calves age, they become more capable of withstanding the effects of draughts.”
“What is most important is to maintain the air quality around the calf. The calf spends more than 80% of its day lying down. The air change is needed approximately 25cm above the bedding. Due to poor air exchange in calf pens, there is a buildup of ammonia at calf nose level that damages the natural defences of the calf ’s airway.”
In an indoor environment, most problems are caused by insufficient outlet areas (minimum of 0.05sq m per calf) in the ridge or roof, and insufficient inlet areas (needs to be four times greater than the outlet area).
“Many of the modern cladding systems do not allow enough air in and buildings are smelly, dirty, warm and damp. Yorkshire boarding is an excellent solution, or cladding with at least 25% void.
“In a ridged building, as a general rule of thumb, allow a minimum of 50mm of ridge opening for every 3m of building width,” he said.
Roof pitch has a major impact on airflow; the steeper the pitch, the better. A pitch angle of 17%-22% is recommended, depending on the overall design and aspect of the building.
“Ironically, in Ireland, due to the nature of the construction of sheds and the prevailing weather, the air inside is often colder than outside, leading to an air sink rather than an airflow outwards.”
This is compounded by poor outlet size and design for the class of animals in the shed.
Cross ventilation is the easiest solution, where the shed is narrow enough for air at slow speed to cross the house and exit the far side, once there is sufficient inlet.
Air can also be mechanically blown into the shed in order to push out the stale air; positive pressure ventilation, by means of a fan and tube system. This system needs to be designed according to the dimensions of the building, fan size and speed and the position of the calf pens.
“Mechanical ventilation can ventilate an existing building, but always look to the simpler and cheaper solutions to improve the inlet and outlet dimensions.”
Fresh air is critical to control respiratory pathogens, and good ventilation keeps the areas dry. Mono-pitch buildings that are too deep (more than 9m) will struggle to ventilate properly, and it is common to see these buildings with poor drainage and inadequate inlet that prevents fresh air flow.
Moisture is produced by all livestock, in their breath, urine, faeces and sweat.
“Many calf houses retain moisture, due to inadequate drainage, leaking water troughs, water and urine pooling, excessive hosing and cleaning without good drainage, poor air change and drying, and condensation from non-insulated or tin roofs,” he said.
Excess moisture increases the risk of bacteria and virus survival, the risk of dirty water transmitting infection, the requirement for bedding, and it also reduces ambient temperatures.
At all times, the calf environment should be dry. Floors under straw need a 1:20 fall, and pens should drain separately. Straw can be expensive, and, in many situations, under-utilised.
Dry straw should cover the knees and hocks when the calf is lying down; this allows the calf to nest and maintain a micro-environment of 15C around its body.
It is not advised to use a straw blower when bedding calves under three months old. They have poor ability to trap and get rid of the dust particles from their airway.
A calf will require about 200kg of straw to bed it for a 25-week period, under well- drained conditions.
As a general rule, calves up to 150kg should have at least 1.5sq m of floor space.
“A pen of young calves with this floor space will look understocked, and there is a temptation to add calves.”
Calves should move in pairs, and remain with calves of the same age (not more than a week difference from the youngest to the oldest).
“This prevents older calves infecting more susceptible younger calves,” he says.
Increase group sizes by adding stable groups of calves, not adding individuals, as this is highly stressful. Preferably, in bought-in calf environments, try to maintain the stability of groups and practice all-in, all-out stocking, so pens can be cleaned per batch.