Introduction
The compost barn represents an interesting innovation in recent years in dairy and beef cattle housing techniques. The salient feature is the presence of a large bedding rest area that is regularly worked with harrows and/or tillers, in order to stimulate the composting process of the mass (aerobic fermentation) and to encourage the evaporation of liquids from the surface layers of the bedding.
CRPA has studied this housing technique within the framework of two projects financed by the RDPs of the Emilia-Romagna (dairy cattle) and Liguria (beef cattle) regions; In the period 2020-2022 in Liguria the feasibility of a compost barn for beef cattle has been investigated within the framework of an Operational Group INNOVABIOZOO, financed by the regional administration of Liguria with Measure 16.1 of the Rural Development Plan (RDP). This Operational Group has made it possible to verify in the field numerous aspects that condition the functioning of the compost barn, also analysing from an economic point of view the impact of the introduction of the compost barn on livestock farms.
The following is a summary outline of the key points arising from the investigations of the Operational Group, dividing them into merits (advantages) and demerits (criticalities). Obviously, for the merits, well-designed and implemented and adequately managed compost solutions are considered, while for certain shortcomings, sub-optimal solutions and situations are considered.
Advantages
1. Large resting area, totally free of subdivisions and obstacles, in which the animals can move freely and can lie down assuming the most natural positions, without constraints.
2. Soft, dry and comfortable resting surface, which favours the cattle's decubitus and cleansing of the body, but which also facilitates walking, favouring the health of limbs and feet and the behavioural manifestations typical of oestrus, and limiting skin changes.
3. Two other advantages derive from the previous points: on the one hand a high level of animal welfare, which may favour the longevity of the cows, with a reduction in the costs of replacement, and on the other hand a probable increase in the rate of heat detection, with evident benefits on the reproductive performance of the herd.
4. Housing system that easily adapts to cattle of different sizes (larger or smaller cows) or different categories (cows, heifers, heifers, etc.).
5. Reduced storage requirements for palatable material, since according to current regulations it is possible to store manure within the resting area, up to a quantity defined by the height of the bedding, in the same way as for permanent bedding.
6. Reduction of ammonia emissions from the lying areas, both with respect to bedded stalls and with respect to conventional permanent bedding.
Drawbacks
1. Not easy availability of optimal bedding materials (sawdust, shavings, straw pellets) at affordable prices, particularly when compared to farm-produced straw. This may be one of the major limitations of the system, as was shown in the economic analysis comparing compost barns and kennels.
2. Higher operating costs for bedding, labour and mechanical means for the care and management of the resting area compared to bunks.
3. Barns that tend to cost more, due to the large areas to be provided in the resting area, despite the simpler construction and smaller storage volumes for manure.
4. Sub-optimal operation, in the climates of Emilia and the Ligurian mountains, during the cold and humid period, due to the low level of evaporation of the liquid fraction of the litter, with possible serious detriment to hygiene in the resting area and the hygiene of the animals.
5. In the presence of a malfunctioning system, there is a risk of an increase in ammonia emissions and unpleasant odours, contrary to normal conditions.
6. Disastrous effects with overcrowding, i.e. when the unit housing surfaces of the initial design are not respected, putting more animals in the cowshed than could fit.
The projects have clearly shown how, from the point of view of building new stables, there is an increase in the unit construction cost with compost barn solutions compared to cubicle systems, which varies depending on the type designed and especially on the unit area allocated in the rest area.
Moreover, the eventual cost of renovating a bunk barn into a compost barn is also quite significant, especially due to the need to build new covered area and because of the inevitable demolition of masonry work and dismantling of equipment.
The annual running cost of the barn, with regard to the care and management of the resting area and the removal of effluent, also shows a clear increase from bunk stalls to worked litter stalls, mainly due to the cost items "bedding material", "machinery" and "labour".
One problematic aspect that was highlighted is the choice of bedding materials: traditionally less commonly used types of material in the dairy farming sector, such as sawdust, shavings or plant fibres of other origin, are better suited for compost barns, but these materials can have higher purchase costs than straw, especially farm-produced straw.
In addition, the quality of the litter, especially the moisture content aspect, can have obvious effects on the state of litter maintenance and animal hygiene.
The positive aspect of processed litter is certainly the fact that the animals spend, on hard concrete floors, a smaller proportion of their time standing in the average day; in fact, in the recommended types of compost barn there is only the feeding area that has a solid floor without litter, while in the most common bedded barns we also have the sorting aisle and connecting cross passages. All this can lead to a benefit in terms of the incidence of foot problems.
Another positive aspect arising from the tests conducted is the reduction in atmospheric emissions of certain climate-altering gases compared to permanent straw bedding solutions: this is true for ammonia, methane and carbon dioxide, while the opposite is true for nitrous oxide. In fact, daily turning operations induce an alternation of the biological processes of nitrification and denitrification operated by microorganisms and, therefore, nitrous oxide emissions tend to increase.
In conclusion, the compost barn solution can be a viable alternative to conventional bedding and permanent litter solutions, but requires special care in the choice of bedding and litter management. It can be assumed that during the winter months compost management will be temporarily discontinued, switching to conventional straw litter management, and then resumed with processed litter as soon as weather conditions improve (late winter or early spring).
Aithors: Paolo Rossi and Kees de Roest (CRPA)