Herd Health: Are your buildings fit for purpose?

Thursday 24 November 2011
Herd Health: Are your buildings fit for purpose?

Building design for optimum animal health was the hot topic for discussion at the most recent meetings of both the Stockport, and Burnley and Pendle Farmers group meetings organised by Myerscough College.

Jamie Robertson from the University of Aberdeen spoke at both meetings about his extensive experience of research and work with farmers at a practical level to understand more about how the housing of stock affects health and productivity.

The big three

Problems with livestock housing are almost always due to one or more of the following:

  1. Moisture – bacteria breed rapidly in damp conditions so the drier the building and bedding are kept then the fewer bacteria will be able to survive there
  2. Fresh air – fresh air is clean and reduces the survival time of airborne bugs.
  3. Air speed – the air needs to be moving quickly enough to prevent a build up of stale dirty air, but if the wind speed is too great the wind chill factor will be increased.

 

Dr Robertson spoke at a recent herd expansion conference on this same subject. The video above summarises key points made in the report below. Slides from his presentation can be seen HERE (pdf)

Financial impact

Jamie dived straight in with the financial impact of chronic health problems which are a direct result of the housed environment, namely pneumonia in calves. Extensive research has shown that for every calf showing symptoms of pneumonia it will cost the farmer £75 for treatment, lost production etc. Any growth performance that is lost due to the disease, and the resultant damage to the lungs, can never be recovered through the entire lifetime of the animal, so an infected calf will always remain small for its age.

This quickly adds up when you take into account that perhaps 10% of calves could be affected: in a group of 50, treatment alone will add up to at least £375. However for each calf in the group that is exposed to the pneumonia bug there will be a slight reduction in productivity even if they show no signs, and this can cost up to £22 per calf. This will cost a further £990 for the remaining calves in the group which are exposed and have to use their own immunity to deal with the infective load.

Use of vaccine

These figures certainly grabbed everyone’s attention and led to quite a discussion about the use of pneumonia vaccine. By vaccinating a group of calves it will reduce the amount of virus being shed into the building, and hence will reduce the risk of a pneumonia outbreak. In addition to this any calves that do succumb to the infection will show fewer symptoms as the infection will be less severe. Jamie stressed that whilst it is possible to use vaccination as a means of managing the risk, all farm situations are different and the benefits of vaccination will depend on each individual herd. As one group member wisely commented “you can’t vaccinate against bad management!”

“50% of naturally ventilated buildings had insufficient openings for the number of animals housed...” (MacCormack, Clark and Knowles, 1984)

This effectively means that 50% of livestock housing is unfit for purpose due to poor ventilation, which is quite staggering when you take account of the huge investment that farmers make each year in new buildings. However Jamie pointed out a number of low-cost, simple changes that can be made to improve existing buildings.

Moisture management

Air speed

Bugs causing diseases of the respiratory system are generally airborne and are spread via the air. However the viability of the bugs is negatively affected by fresh clean air. Research has shown that after one hour in 100% fresh air only 15% of bugs are still viable, whereas if the air is only 50% fresh then 50-60% of bugs remain viable and infective. This illustrates how important fresh air is in killing bugs.

 

Mechanical fans can be used to increase the speed of air moving over adult cattle. This will help to increase to rate at which moisture is removed from the building thus helping to control the growth of bacteria and viruses.

 

Another option to increase the proportion of fresh air available to housed livestock is to allow the stock outdoor access. Calf hutches are an ideal way of achieving this provided they are suitably sheltered from the wind to avoid wind chill.

 

Wind chill

 

Whilst it is essential that fresh air is available in a building, all possible steps must be taken to avoid wind chill, particularly in calf housing. The lower critical temperature (temperature below which an animal has to start producing heat to keep warm) of a new born calf will increase from 9 degrees celcius to 17 degrees celcius with an increase in air speed from 0.2m/s to 2m/s. If a calf is housed in a draught, even for a short period of time, the increase in stress will lead to depressed immunity thus leaving the calf more susceptible to pneumonia, scours etc.

 

Jamie showed a picture of a calf shed which looked fit for purpose. However on closer inspection it could clearly be seen that there was a gap under the doors which could potentially let in quite a draught blowing straight onto the calf beds. He suggested simply attaching some rubber belting to the bottom of the gate with pot rivets to prevent this problem.

 

Ventilation

 

Ventilation is driven by the stack effect whereby warm air in the building rises and leaves via the outlet and then cooler air is drawn via the inlet in to replace this. In order for the stack effect to be successful there must be sufficient heat in the building to make the air rise, as well as sufficient air inlets and outlets to allow air to flow through the building.

 

Common issues

 

Jamie then discussed common problems on many farms which prevent adequate ventilation, causing a build up of damp, stale air in buildings and the associated potential health problems.

 

  >   Lack of high level air outlets – by a general rule of thumb 0.1m2 of outlet is required per cow eg. in a shed with 100 cows a minimum of 10m2 air outlet is required. However it is essential that you calculate exactly what each building requires in terms of outlet and ensure this is achieved. One of the simplest ways of increasing the outlet is to remove the caps and open up the ridge. If the ridge lies directly over the cubicles this is not a feasible option as the beds are more likely to get damp so the alternative option would be to fix the caps higher up on metal legs (protected ridge vent).

  >   Inadequate inlet area – inlets must be at least twice the area of the outlets. You can open up the sides of buildings by removing solid sides and replacing with a porous material such as a mesh windbreak or space boarding. However if using space boarding the gap between the boards must not exceed 1 inch or the speed of the air coming into the building will be too great.

  >   Sharing airspace with older animals – this can mean that any bugs in the older animals are passed to the younger stock with lower immunity.

  >   Low heat production – a small number of calves in a large building will not produce sufficient heat to drive the stack effect. Additionally in buildings with a wet floor 20% of the heat energy will be absorbed thus compounding the problem If possible calves could be moved into a different building or could be housed in hutches located within the larger building.

 

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