Influence of dietary fat inclusion on the ileal digestibility of amino acids in broilers : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Animal Science at Massey University, Manawatu, New Zealand

Abstract

The main focus of the present study was to examine nitrogen, dry matter and specific amino acid digestibility, particularly in the jejunum and ileum. Due to the fact that the gizzard and duodenum are primarily sites of digestion, and not absorption and due to limitations of the titanium oxide marker method, results from these segments are less applicable to the overall results. The general trend indicates that the presence of tallow in the diet increases digestibility significantly compared to diets without additional fat. The soybean oil diets generally had intermediary digestibility between the tallow and no-fat diets. Previous studies with similar fat sources indicated the opposite would be true. Differing digestibility of the different fat sources could likely be governing this effect. Future studies could involve birds of differing ages, as well as a more diverse set of fat sources to better determine which factors are affecting these digestibility rates. The speculated mechanism of action for this increased digestibility is an increase in digesta transit time caused by the increased fat content. Future studies could confirm this by using a marker technique to trace the rate of passage in the digestive tract between the different diets. Differences and digestibility between maize and wheat diets were expected, but it was unknown if there would be any major interactions between grain type and fat source in the diet in nitrogen and dry matter digestibility. The present study found no interaction. The decreases in digestibility seen by high NSP ingredients like wheat is likely related to the creation of insoluble gels in the gut. Thus, while fat and these gels may both increase the viscosity of gut contents, the composition of the viscous contents differ substantially, with the fat having less of an inhibitory effect on amino acid digestibility. The present study found no substantial interaction effects in the lower digestive segments between the grain effects (caused by NSP content) and fat effects. This indicates that, while the addition of both can alter digestive viscosity, there is no inhibitory effect exerted by either on the other. No significant effect of fat source was found on amino acid digestibility. This may be due to the fact that these samples were taken from the lower ileum, and the majority of amino acid absorption may have taken place in more proximal segments.--Conclusio