Factors affecting microbial dynamics during aerobic deterioration of silages were evaluated in laboratory, pilot-scale and full-scale experiments. Yeasts usually caused the initial deterioration but in some samples with fairly good storage stability (>lo days) the activity was associated with the growth of moulds and bacteria. At a later stage, and especially at higher temperatures (>4OoC), the activity was caused by bacilli. The increase in pH as a result of lactate metabolism permitted the growth of Enterobacteria. Evaluation of storage stability in samples from different levels in a bunker silo indicated low stability in surface samples and fairly good stability in samples from 160cm depth. The surface samples contained higher numbers (10@1000 times) of yeasts but the pH levels were similar.The establishment of yeasts during storage is probably due to diffusion of oxygen by leakage through the plastic cover. Compared with a plastic cover (0.1mm polythene), a rubber seal improved storage stability in laboratory silage (pH 4.0) inoculated with lactic acid bacteria and infected with Candida albicans. An increase in acid content and a reduction in pH (3.7) by means of an efficient inoculant did not seem to increase the storage potential under the conditions described above. The content of adenosine triphosphate has been used as a measure of microbial activity during aerobic deterioration of silages. The main activity was concentrated at the surface (0-5cm). At 20"C, the activity was about ten times higher at the surface than at a depth of 30cm; above 30°C it was about 100 times higher.

Respiration losses, effect of sugar content, formic acid addition and inociilation were evaluated in relation to initial fermencation and silage quality in three experiments. Changes in the content of fermentable substrate during post-harvest respiration and initial fermentation were studied in the laboratory. Soluble carbohydrates were estimated as glucose, fructose, sucrose, fructans and starch by an enzymatic method.About 70*70 of the sugars remained after 30 h of conventional wilting, as opposed to less than 50% in a chopped sample kept in the dark. During the first days of fermentation the metabolic activity was very intensive. Sugars, which accounted for lOi^^o of the dry matter, were fermented within 4 d. There were indications, mainly in clover silages, that substances other than water-soluble carbohydrates were used as energy sources.Low-sugar crops were obtained by shading the fields. After 3 d the sugar in the grass had decreased to half of the original content. This effect was less pronounced in clover. The amount of available substrate and dry matter (DM) content had a major influence on silage quality. In an unwilted crop at least 25 g of water-soluble carbohydrate was needed per kg of fresh material to obtain an acceptable silage Correspondence; Mr K, Lurden Petiersson, Swedish University of Agricultural Sciences, Departmeni of Animal Nuiriiion and Management, Kungsangens gSrd. S-75323, Uppsala, Sweden;quality in the controls, while 20 g was sufficient in inoculated silage. Formic acid addition makes the fermentation less sensitive to water-soluble carbohydrate content. Inoculation of willed silage increased lactic acid production and decreased the pH. There was also less variation in silage quality.

Pettersson K, Svensson C, Liberg P: Housing, feeding and management of calves and Replacement heifers in Swedish dairy herds. Acta vet. scand. 2001, 42, 465-478. -A questionnaire was sent to 1500 randomly selected dairy herds in Sweden, asking for general information about the herds, including routines from birth to first calving and also routines at breeding, calving and during the grazing period. Fifty-eight percent of the questionnaires were returned. The preweaned calves were kept in individual calf pens in 68% and in group housing systems in 28% of the herds. Pens with slatted floors were the main housing system for replacement heifers from weaning to breeding, and tie stalls from breeding to first calving. Whole milk was used in 44% and milk replacements in 42% of the herds. The calves received, as a median, 2.5 litres of milk per meal and 2 meals per day. The median age at weaning was 8 weeks. Age was the single most common criteria used for deciding both weaning and breeding time. The median age when the heifers were first turned out to pasture was 6 months. Prophylactic anthelmintic treatment was used by 65% of the herds. The most common diet for replacement heifers before calving was a combination of grain, hay and silage. colostrum; wearing; rearing; breeding; feed plan; pasture.