7. Construction of cattle stable
General
The stable should be near the house in order to keep the pipeline from the gasplant to the kitchen short. The fodder trough must be easily accessible. Water for the animals should be near the trough. The milking place lies at the highest floor level of the stable, opposite to the biogas plant. The roof should not drain its rainwater onto the biogas plant.
The stable should allow easy collection of dung and urine to charge the biogas plant. Whenever possible, the existing stable should be kept and modified if necessary to fulfill the above requirements. In many cases a new concrete or tiled floor will do. A new stable should be constructed in cases the farmer wishes to modernize his live stock or if adaptation would demand intolerable compromises.
The size of the stable depends on the number of animals and whether they are freely moving or tied-up. A stable suitable for a biogas unit might require more space than the existing one. Later extension should also be possible without changing or affecting the biogas plant.
The Principles of Design
The ideal cattle stable is a zero-grazing unit with separation of milk cows, heifers and calves, roofed or non-roofed exercising area, separate milking stand, restricting fodder trough and solid floor with urine channel. The fodder chopper, the squeegee and the dipper are essential tools for operation of the stable.
A stable connected to a biogas plant has to fulfill the following indispensable criteria:
-solid floor with urine drain in order to collect dung and urine without soiling
-dung and urine collection point lies higher in level than the inlet of the biogas plant in order to avoid laborious handling and losses of substrate
-animals are fed from a trough with neck restriction in order to avoid spreading of too much of fibrous material on the floor which will then enter the plant.
Additional favourable criteria are:
-stable is roofed in order to avoid rain water washing away too much of urine and dung
-resting and exercising area are separated in order to limit the area of dung dropping and to keep animals clean
-calves, heifers and milk cows are separated because of their different sizes to allow an optimal design of the stable
-there is a separate milking stand in order to improve hygienic conditions and optimize milk production by undisturbed milking.
Fig.29: Principle design of the cattle shed.
The stable is divided into a resting area ( 1 ) and an exercising cum feeding area (2). Calves' boxes (3) and the milking stand (4) are at the far end. Milking cows are placed adjacent to it (5). The urine drain (6) ends in the urine chamber (7). The dung and mixing chamber (8), which is the inlet of the biogas plant, are placed beside. The fodder trough passes along the feeding area (9); a water trough (10) is provided between, Calves have smaller troughs (11). The chopping block is at the centre of the trough (12). A bar passes over the necks of the cattle in the sleeping area (13) to force the cows to move back when getting up to drop dung. The necks of the cattle are also restricted at the trough to prevent them from scattering fodder to the floor. This can be done by a bar (14) or by narrow standing poles (15). The floor of the stable is concreted (16) or laid out with concrete tiles (17). The dung is pushed into the mixing chamber daily with the help of the squeegee (18). Urine is taken by a dipper (19) and mixed with the dung before entering the biogas plant. There is a verge of timber (20) or concrete (21) at the end of the sleeping box.
The Floor
The condition of the floor influences most the operation of the gas plant. Smooth stable flooring with appropriate slope encourages and simplifies daily cleaning of the stable. The floor should be even without holes. It should not be slippery but plain and slightly rough. There is a 2% slope of the floor into the urine drain and of the urine drain into the urine chamber. The urine drain is shaped one sided at the lowest end of the slope floor. Its corner is bottle curved.
Normally, floor is of 10 cm concrete (mixture 1: 2: 4) on stone bedding. Anti-termite chemicals should be spread on the stone bedding where applicable. The concrete is firmly rammed or vibrated. A good solution are concrete tiles of 15~15~5 cm in size and 1: 2: 4 by mixture. They are laid into solid sand bedding without joints. The tiles should be cured for at least one week by keeping them moist and cast in steel moulds in order to maintain exact rectangular shape to avoid unwanted wide Joints.
The floor of the calves pen is preferably of wooden boards raised 30 cm above the concrete floor leaving 2,5 cm slats between for faeces to be pushed between in order to keep the place dry and clean.
The Feeding Trough
Well designed fodder troughs prevent too much waste fodder from entering the gasplant. The feeding trough must fit the anatomy of the animal. A trough which is too small increases work for feeding, too big a trough increases waste of fodder. The trough should have rounded bottoms and corners for easy reach of fodder. A drain pipe for cleaning and drainage of rain water should also be provided.
There are different ways to prevent the cows from scattering fodder from the trough to the floor where it could mix with the dung and enter the biogas plant. One alternative is vertical poles of 1,50 m height and 20 cm free space between. These are erected in front of the trough. The poles should be rounded and smooth so as not to cause friction at the cows neck. The distance from the inner side of the trough and the outer side of the poles should not exceed 16 cm in order to allow the cow to reach the full width of the trough. The other, cheaper and easier method, is to place a bar above the cow's necks to restrict movements of their heads. In both cases, the outer wall of the trough is shaped in such a manner that animals do not push fodder off the trough while eating. Troughs may or may not be placed under the roof of the stable. Wooden troughs wear quickly.
Compartment Walls
All walls should be strong and smooth. Movable wooden bars used for closing of door openings are not recommended because they might be lifted Off by the animals. Normal wooden doors with solid hinges are more appropriate. Built-in wooden poles have to be protected by burning their surface when surrounded by mortar or concrete.
Sleeping Boxes
Sleeping boxes should be clean and dry. Therefore, for defecating, the cow has to get In a position in which she can not soil the floor. A 15 cm raise of the floor above the level of the exercising area prevents the cow from entering the box In reverse. A 15 cm high timber or concrete verge forces the cow to lay fully inside the box.
The neck bar allows the cow to lay inside the box in full length but if she gets up for defecating she has to step back dropping dung and urine outside the sleeping box. The floor should be of concrete or tiles in order to avoid too much of sand or soil being collected with the dung. If bedding is wanted or required, it should neither be of straw nor of sawdust but dried slurry could be used instead. To train cows using the sleeping box, requires tying them up for the first few nights after being placed in the new stable.
Dung and Urine Chamber
When cleaning the stable, dung is pushed into the dung or mixing chamber, which is actually the inlet chamber of the biogas plant. Urine and water collects in the urine chamber from where it is taken out with the help of a dipper and mixed with the dung in the dung chamber. The mixed substrate is then released into the biogas plant.
The urine chamber is in fact a storage and dosing tank designed for the capacity needed to get the right TS-content for the slurry. If rain or washing water exceeds the required amount, the urine chamber overflows into the slurry distribution channel. If too little urine gets collected, which might be the case in dry places or seasons, the urine chamber has to be filled with water to the required amount.
The Roof
The roof should at least cover the sleeping boxes, the calves pen and the milking stand. In case with no sleeping boxes, part of the exercising cum resting area should be covered. If the roof covers the total area of the stable it should be 3 m high in order to allow ventilation and sunshine. The roof should not drain on the biogas plant.
Fig.30: Cattle foot bath. If cattle are regularly out grazing, they should pass a cleaning foot bath before entering the stable in order to prevent too much soil from entering the gasplant. A drainage pipe would allow easier cleaning.
