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The voluntary intake and digestibility of four hays were measured with eight sheep using two 4 × 4 Latin squares. Measurements were made during the last 8 days of each 3-week period. The degradation characteristics of the hays were measured by incubating samples (in nylon bags) for 12, 24, 48 or 72 h in the rumen of four sheep fitted with rumen cannulae and given a good hay. The exponential p = a + b(1 − e−α) where p = degradation loss, t = time, and a, b and c are constants, was fitted. The potential degradability (defined as a + b) of the dry matter (DM) of the four hays was 0·76, 0·66, 0·54 and 0·46 with corresponding voluntary intakes of 71, 62, 52 and 45 ± 2·9 g DM per kg M075 per day. The in vivo digestibilities were 0·61, 0·59, 0·46 and 0·45 (s.e. 0·013) respectively and corresponded to 23-, 25-, 31- and 67-h degradation. Voluntary intake was better related to potential degradability (and degradability at 12, 24, 48 and 72 h) than to in vivo digestibility. It is concluded that the degradation characteristics of forages may have useful application in predicting voluntary intakes, and that potential degradability could be used to define the rumen (jegradable nitrogen content necessary with any particular forage.

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Ultrasound treatment, which involves the introduction of high‐intensity sound waves into a sludge medium, is one of several technologies which promote hydrolysis during sludge treatment. It has become well‐established with numerous full‐scale plants in Europe operating for several years. The basic principle involves the release of extra‐cellular material which then catalyses biological reactions and improves bacterial kinetics, resulting in lower sludge quantities and (in the case of anaerobic digestion) increased biogas production. Its use is most suited to plants containing large quantities of refractory material and/or cellular matter, such as waste activated sludge. This paper uses the data from several full‐scale part‐stream ultrasound plants and discusses the influence of the technology on numerous operating conditions, especially with respect to improved digestion and enhanced biogas production.

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