High fibre feeds for pigs

Summary
In 1996-1998 three experiments were carried out to study the nutrient digestibility and utilisation of fibre rich feeds in growing pigs. Fresh clovergrass, clovergrass silage and whole crop barley-pea silage was originally planned to be fed at a low and a high level, but due to large interindividual variation, the measurements had to be carried out with registration of individual roughage intakes. The experiments were carried out as 2 types of classical digestibility experiments, where the overall nutrient balance was studied by separate collection of faeces and urine by urine catheter in intact pigs. In parallel, experiments were performed on ileum cannulated pigs to study partial digestibility and energy balance in respiration chambers. For each type of roughage to be studied, two balance trials with 18-41 days interval were carried out with 2x6 pigs fed roughage and 2x2 pigs only fed the basal diet. The ileum cannulated pigs were slaughtered at the end of the experiment for analyses of the gastrointestinal tract and its contents.

The intake of roughages was very variable but generally quite low. It accounted on average for 10-12% of the daily dry matter intake. The roughages had as expected lower dry matter, organic matter, and energy digestibility than the basal diet. The fresh clovergrass had a higher energy digestibility than the two types of silage. Inclusion of 10% of gross energy in the diet from clover grass led to a reduction in the rations energy digestibility of 2.1%, while clovergrass silages and the wholecrop silage led to reductions of 3.1 and 3.3%, respectively. No increment in energy loss from urine, methane, hydrogen, heat production or loss in retained energy was detected in pigs fed the roughages. The in vitro method that measures enzyme digestible organic matter (EFOS), generally underestimated the energy value of the rougages compared to the experimentally obtained values. More than 62% of the variation in the faecal digestibility of energy could be accounted for by the content of dietary fibre in the ration. The protein digestibility of all fibre rich feeds was low (< 45%), and the content of non-starch polysaccharides explained 44% of the variation. Less than 25% of protein was retained. The digestibility and utilisation of the rations’ mineral content showed some variation. Approximately 50% of calcium and phosphorus was retained, whereas less than 20% of zinc, and 15% of potassium and copper was retained.

The pigs’ requirement for maintenance and growth was met by the rations containing a relatively low amount of the fibre rich feeds. However, at a higher proportion of the dry matter intake coming from the fibre rich feeds, minerals supply will probably not be sufficient without adjustment of the mineral content of the basal diet.

The inter- and intra-individual variation in the intake of roughages makes the data concerning the influence on the gastrointestinal environment more difficult to interpret. There was a tendency for a marginally larger gastrointestinal tract without differences between the different types of roughage. This could indicate a larger requirement of energy for maintenance. Furthermore, intake of fibre rich feeds led to larger amounts of gas-trointestinal contents.

This project describes the nutrient digestibility, protein metabolism and energy value of 3 different types of fibre rich feeds. Some of these have not been tested before. Because of the low roughage intake, it was not possible to give more precise estimates of the energy value based on partial digestibility coefficients and specific energy losses in the form of gas- and heat production. The project also describes relations between roughage intake and nutrient digestibility, but no relation between fermentation of dietary fibre and recirculation of N was establised due to a limited level of fermentable substrate obtained from the fibre rich feeds. The experiments indicate how the fibre rich feeds influence the gastrointestinal environment but final conclutions are hampered by the low and variable rhougage intake. From the results of the present study it is possible to calculate overall nutrient balances for feed rations having a limited content of fibre rich feeds.

Based on the observations in the present study, we find that the fibre rich feeds provide a limited contribution to the overall nutrient supply. With a relatively low intake and an energy value of 50-70% of the basal diet, the fibre rich feeds will on average provide less than 7% of the energy supply. The type of roughages that has been investigated here, might have other benefits in organic pig production. However, the nutritive value of the feeds is evaluated to be limited.