Strategic use of the bioactive properties of n–3 fatty acids and plant secondary compounds in the diet of ruminant farm animals
Creators: name: Giller, Katrin
Publisher: name: ETH Zurich
Year: 2021
Subjects: RUMINANT NUTRITION, RUMINANT FEEDING AND FEEDSTUFFS (ANIMAL NUTRITION)
Bioactive components
Oxidative stress
METABOLISM (ANIMAL PHYSIOLOGY)
REPRODUCTION (ANIMAL PHYSIOLOGY)
Meat Quality
Milk quality
Omega-3 fatty acids
Plant secondary compounds
Polyphenols
Carotenoids
Sustainable agriculture
Greenhouse gas emission
Rumen fermentation

description: Ruminant production systems are increasingly critically discussed for reasons that can be summarized as environmental, ethical, animal welfare, and human health concerns. Looking at the development during the past decades and the predictions for the ones to come, ruminant-derived food production will however still rather increase than decrease. The impressively enhanced production efficiency via breeding strategies in ruminants contributes to covering the growing demand for meat and milk on most continents. The flip side of this progress is an increased prevalence of oxidative stress and inflammation-related production diseases, promoting fertility problems and impaired productivity. These are at least in part modulated by drastic changes in the nutrition of high-yielding dairy cows and beef cattle e.g., intake of maize silage and concentrate at the expense of grass-based feeds. This has concomitantly shifted dietary nutrient composition and particularly resulted in a decreased supply with bioactive feed components such as the essential fatty acid (FA) α-linolenic acid (ALA) and various plant secondary compounds (PSC). The ALA is the only n–3 FA present in original ruminant diets and serves as a precursor for the long-chain n–3 FA eicosapentaenoic and docosahexaenoic acid. All three n–3 FA possess distinct functions in the modulation of cell signaling, inflammatory processes, and gene expression. Bioactive properties are also described for PSC, a chemically diverse group produced in the secondary metabolism of plants, comprising thousands of different molecules. Some PSC including polyphenols and carotenoids may induce antioxidant and anti-inflammatory processes. The tannins are especially associated with antinutritional effects such as a decreased nutrient digestibility but in turn may reduce greenhouse gas emissions, with the latter property also having been reported for dietary n–3 FA. Knowledge on the bioactive properties of these dietary components in monogastrics (especially humans and rodents, but also livestock species such as pigs and chicken) is more advanced than in ruminants but overall, effects and underlying mechanisms are not entirely known. 
This thesis presents an overview and results from various own studies on the effects of bioactive n–3 FA and PSC from feed supplements and alternative sustainably produced feedstuffs on a range of factors relevant for ruminant livestock production. In particular, effects on rumen fermentation, greenhouse gas emissions, tissue partitioning of FA, oxidative stress, inflammation, reproduction-related parameters, productivity, as well as meat and milk quality were investigated. The research was performed in a set of in vitro and in vivo experiments involving cattle, sheep, and goats, investigating mostly direct but also intergenerational effects.
The results show that most of the tested alternative feedstuffs rich in bioactive components e.g., food industry by-products and microalgae were suitable to maintain rumen fermentation processes and animal productivity. Replacement of the critically discussed soybean meal by more sustainable protein sources rich in bioactive components was successful in dairy cows and beef cattle without impairing productivity or meat and milk quality. The supply with bioactive components e.g., via fish oil and microalgae partially improved the nutritional value of meat and milk even though the sensory meat quality was impaired following fish oil supplementation. Importantly, differential effects of   n–3 versus n–6 FA as well as hydrolysable versus condensed tannins were observed on the mechanisms and the effectiveness of methane mitigation, respectively, which need to be further investigated in the future to exploit the full potential of these bioactive components. The detected differential partitioning of dietary n–3 and n–6 FA into a large range of different body tissues and fluids point towards tissue-specific requirements and functions of these FA that need to be further elucidated on a molecular level. A remarkable observation was the promotion of preimplantation embryo elongation with maternal fish oil supplementation, adding another aspect of how n–3 FA may beneficially affect reproduction. The herein presented antioxidant and anti-inflammatory effects observed in the studies with ruminants following intake of bioactive feeds differ from those observed in monogastrics but still indicate potential for beneficially modifying symbiotic microorganisms and ruminant host physiology. 
Overall, the work presented in this thesis extended the scarce knowledge about the biofunctionality of n–3 FA and selected PSC and their synergistic effects in ruminant molecular physiology. The variable results reported here and in the literature require further experiments that control for a broader range of factors with known or assumed influence on study results e.g., the type, dose, matrix, and duration of bioactive component supply, composition of the basal diet, animal species, sex, and age. Particularly interactions among bioactive components from the same or different categories are of relevance. Future research should compare long- and short-term effects to determine whether or not there is an adaptation of the rumen microbiome to bioactive feed components, thereby modulating their effects. Future advances in molecular ruminant nutrition will provide valuable insights to understand the underlying mechanisms of effects mediated by bioactive feed components to improve environmental, ethical, animal welfare, and human health aspects of ruminant livestock systems. The current body of evidence indicates that most of these aspects would benefit from increasing the ruminants' intake of n–3 FA (particularly ALA) and PSC through modification of their diets.