In vitro fermentation capacity of hindgut microbiota in pigs in relation to dietary fibre

As pigs compete with humans for high quality feed ingredients such as grains, alternative feed sources need to be found. These alternative feed ingredients are usually high in indigestible carbohydrates, consisting mainly of non-starch polysaccharides (NSP) and are less suitable for human consumption. In order to find the most suitable feed ingredients for pig nutrition, they need to be well characterized regarding their nutritional value. This is possible with in vitro methods which mimic the hindgut degradation of these mainly indigestible feed ingredients. These in vitro methods either use enzymes or faecal inocula to incubate the feed ingredient to be tested. However, there is a lack of information on some general aspects of in vitro methods with pigs, such as the number of animals to use for inocula preparation, influence of enzymatic pre-digestion of feed ingredients, repeatability of fermentation results, adaptation time of donor animals etc.
The studies described in this thesis describe a number of experiments which were designed to test some of these above mentioned aspects in order to improve the in vitro procedure and therefore the predictability of feeding values of new feed ingredients (in the following called substrates). The first study compared two in vitro methods; one using enzymes and using inocula for fermentation and a combination of the two. The results showed a similar ranking order. Nonetheless, a combination of enzymatic pre-digestion with subsequent fermentation seems most suitable to best predict the nutrient availability of the tested substrate. The second study determined if 19 days of adaptation of donor animals is adequate to adapt them to a new diet, either high or low in NSP. The adaptation to the new diet was not completed and had the biggest influence on the slow fermentable substrate cellulose. The third study revealed that the results of a single fermentation run can be representative for the fermentation capacity of the donor animals. However, the optimal number of donor animals remains to be determined in order to receive results with a low variation coefficient. The last study compared the fermentation capacity of pigs raised on different organic farms. The results showed that animals across organic farms had a relatively similar and high fermentation capacity despite the different rations fed on single farms and varying farm management. This might be caused by the animals’ lifelong exposure to a high variety of fibre.
The results of this thesis show that in vitro fermentation methods can be further improved and need further attention regarding the optimal number of donor animals and their nutrition. It would be of special interest to compare the differences of fermentation capacity and energy yield between animals that are fed diets either high or low in NSP. Pig diets based on an improved in vitro methodology have the potential to increase economic profit for feed industry and farmers, but also to increase animal health and welfare.