For beef cattle housed in uninsulated barns, it is important to design the deep litter area deeper than the dung alley in accordance with the bedding material used. If this step is not taken it may become necessary to remove the deep litter in the middle of winter when, because of cold weather, the re-establishment of composting cannot be guaranteed. If the wrong type of litter is used, the animals may sink into the deep litter and soil themselves. Also, the counter-pressure of aeration could be too high. These aspects were evaluated in a bench-scale study that simulated the functioning of deep litter in partially littered pens. The size of the test vessels was 60 cm by 60 cm. There were "ve di!erent litter mixes of straw, peat and wood chips involved in the trials. The simulation was based on the assumption that the space allowance per suckler cow in the pen was 3)5 m on deep litter and 4)0 m on dung alley and manure (27)5 kg day) was deposited evenly in the pen.
The height of deep litter increases by 4)1}5)2 mm day, depending on the litter mix, in a partially littered pen littered at the recommended rate (55% of the weight of manure) and having an optimal space allowance (equivalent to 3)7 kg manure m\ of deep litter). By the end of the housing period (8 months) an additional layer (0)10}0)20 m) of litter had accumulated. A depression of 0)62}0)86 m deep in the #oor underneath the deep litter would be enough to allow a housing period of 8 months. The carrying capacity of deep litter systems that comprise straw, peat and wood chips is high enough to prevent the steers, heifers or cows from sinking into the litter and getting dirty, provided there is not too much (more than 60% in weight) peat or equivalent material in the mix. The counter-pressure at an adequate aeration rate in a 1 m high deep litter system is 29 Pa, which will cause no technical problems.