White, Gavin A.
(2007)
Influence of processing on starch digestibility and gut morphology in the weaned piglet.
PhD thesis, University of Nottingham.
Abstract
To overcome the `post-weaning growth check' commonly seen at weaning, the incorporation of antibiotic growth promoters (AGPs) to the diet has been a useful management tool. Recent legislation within the European Union banning the use of AGPs at sub-therapeutic levels in animal feed means that the quality of dietary ingredients used in weaner diets has assumed a much more fundamental role. In order to improve the availability of starch in the piglet diet, processing of cereals is widely practised. However, descriptions of processing techniques used in many studies are simply referred to by name, with no regard of the precise variables used. In addition, many of the feed materials are simply referred to as `cooked' which gives little indication of nutritional value.
Five trials were conducted in order to assess the use of raw and processed cereals on diet component digestion, digesta properties and gut morphology in newly-weaned piglets. The main objective was to examine the use of precisely controlled processing variables, such that starch digestibility was maximised with benefits for the gastrointestinal environment. A second aspect of the programme of work reported was the application of a number of analytical tests commonly used in the field of human food science, to examine the physicochemical properties of starch granules, and the changes they undergo upon processing. Using this approach, a comparison could be made between in-vitro (rheological) results and in-vivo (biological) responses.
Trials 1 and 2 examined variability between raw cereals. Wheat, barley, rye and triticale were assessed in Trial 1. Wheat (identical batch), naked oats, whole oats and maize were evaluated in Trial 2. Coefficients of apparent digestibility (CAD) for starch and nitrogen revealed considerable variation between the cereals. In Trial 1, there was a strong trend (P = 0.051) for starch digestion to be highest for the rye diet and lowest for triticale. CAD for starch was not significantly affected by cereal type in Trial 2. Despite having more viscous intestinal digesta than other animals (P = <0.001), pigs fed the rye-based diet did not experience any detrimental effects to animal performance.
Trial 3 examined the use of raw wheat, of either hard or soft endosperm texture. From 5 days post-weaning, piglets fed the soft wheat diet had a tendency (P = 0.063) to have higher feed intakes. In addition, pigs fed soft wheat diets had significantly less viscous tract digesta (P = 0.029) than those animals fed the diet based on hard wheat. There was no significant difference in CAD for starch between the two dietary treatments but CAD for nitrogen was found to be significantly higher (P = 0.006) in the distal region of the small intestine for pigs fed the soft wheat diet. The results from Trial 3 suggest that endosperm texture of wheat can have an effect on nutritional value, and that wheat of soft endosperm texture is more beneficial than hard wheat for the young piglet.
Trial 4 was a 2x2 factorial study examining wheat endosperm texture (hard vs. soft) and degree of micronisation (high cook vs. low cook). CAD for starch was not affected by endosperm texture, although degree of cook was an important factor with significantly higher starch digestion for the high cook diets, compared to low cook (P = 0.047). The use of micronised wheat lessened the reduction in starch digestibility seen on day 4 post-weaning in the small intestine, compared against the decline seen using raw wheat diets in Trial 3. In summary, Trial 4 demonstrated that micronisation can enhance the nutritional value of wheat for the weaned piglet, with degree of cook, a more significant factor than wheat endosperm texture.
Trial 5 assessed wheat endosperm texture (hard vs. soft) and degree of extrusion (high cook vs. low cook). Raw soft wheat was used as a control. Results showed that CAD for starch in the small intestine was noticeably higher than in the other animal trials. Starch digestion was significantly affected by endosperm texture (greater coefficients for soft than hard; P <0.001) and by degree of cook (high SME greater than low SME; P <0.001). The use of extruded wheat diets almost eliminated the drop in starch digestion at the 0.5 intestinal site seen on day 4 post-weaning. Wheat of soft endosperm texture responded better to extrusion processing than hard wheat under the conditions of Trial 5.
The use of computer modelling was able to demonstrate a correlation between in-vitro starch parameters and in-vivo starch digestion in the small intestine of the piglet.
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