Dietary Medium-Chain Fatty Acids for Sustainable Ruminant Nutrition

Abstract

In the current thesis, the potential of krabok oil was investigated to reduce methane production by ruminants. Typically, krabok oil has similar amounts of lauric acid (C12:0) compared to coconut oil but krabok oil also contains ~44% myristic acid (C14:0) and previous research indicated that C14:0 and C12:0 synergistically affected rumen methanogenesis when they were applied as pure fatty acids. In the current thesis it was attempted to assess this synergism in vitro and in vivo, with the use of two natural fatty acid sources, i.e., krabok- and coconut oil. In the first in vitro experiment, rumen methanogenesis and the biohydrogenation of unsaturated long chain fatty acids were assessed. The study consisted of five treatments, The results of this study indicated that both krabok and coconut oil reduced methane production which was coincided with a shift from acetate and butyrate production to propionate. The overall effect of either krabok oil or coconut oil on rumen biohydrogenation was limited. In a subsequent study was conducted to test the defaunating effect of krabok oil in vivo. Three rumen-cannulated beef cows were used to assess the potential of krabok and coconut oil to affect rumen protozoa numbers with experimental treatments arranged in a 3×3 Latin square design. The experimental diets consisted of a concentrate supplemented with either 25.5 g/kg of tallow (control) or the same quantity of coconut oil or krabok oil. Supplemental krabok oil as well as coconut were found to decrease the protozoa numbers, but the effect of coconut oil was more pronounced. The ciliate counts were not significantly different between treatment although the ciliate counts were strongly related to total protozoa counts. Except for propionic acid, the rumen concentrations of the remaining volatile fatty acids were similar between treatments. The two oils did not influence the amylolytic, cellulolytic or proteolytic bacteria counts. Cluster analysis of the denaturing gel electrophoresis profiles of ciliate communities showed a clustering of the coconut oil containing diet and the tallow containing diet. The third study were study in vivo used eight rumen-cannulated bulls, two bulls per treatment. All treatments contained 35 g supplemental fat per kg dry matter: a control diet with tallow; a diet with supplemental coconut oil; and a diet with supplemental krabok oil. The protozoal numbers were reduced by either source of medium chain fatty acids and the strongest reduction was observed when supplemental krabok oil was fed. The abundance of methanogenic Archaea was likewise affected by the experimental diets. The denaturing gradient gel electrophoresis profiles of the rumen archaeal population did not result in a grouping of treatments but in case the diets were supplemented with krabok oil, the richness and evenness were increased within the the archaeal community. The last experiment on vitro was study a dose-response relationship between krabok oil and methane production was also investigated using a fully automated gas production test. The experimental substrates contained either krabok oil (KO), whole krabok seed (WKS), the residue of WKS after fat extraction residue (FER) or FER+KO. Appropriate amounts of WKS or its derivatives were added to a basal substrate so as to attain either a low, medium or high content of KO. Both, the absolute (ml/g fat-free OM) and the relative (% of total gas production methane production were reduced at the highest inclusion level of WKS or its derivatives. At the same time, the highest inclusion levels FER, FER+KO, and WKS, but not KO, reduced total gas production and total volatile fatty acids. In current thesis, it was shown that krabok oil is instrumental in mitigating methane emission.