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Rice-based Diets in Pigs–for protection against intestinal bacterial infections
by Associate Professor John Pluske and Professor David Hampson September 2005
RIRDC Publication No 05/143 RIRDC Project No. UMU-30A
Rice is a staple food for much of the world’s human population but has received relatively little attention as a possible feedstuff for the animal industries, in this case the Australian pig industry. Rice, once gelatinised, is highly digestible within the gastrointestinal tract of the pig that, in turn, could enhance performance over pigs fed wheat, the most commonly used grain used in Australia.
Furthermore, and based on previous studies conducted in Australia and overseas, rice has potential to ameliorate PWD, a disease which costs the Australian pig industry millions of dollars annually. The increasing pressure that governments are facing worldwide to ban the use of dietary growth promoting antibiotics and dietary heavy metals such as zinc and copper in pig diets has meant that alternative strategies for the control of PWD, and indeed other enteric diseases, need to be found. This has already occurred in the European Union, for example. Based on these previous studies, cooked white rice appears to offer promise as an alternative nutritional strategy to the current use of antimicrobial compounds for mitigating PWD. However, more research was needed in order to refine further dietary recommendations that could be made to the rice and pig industries regarding the feeding of rice to pigs to reduce PWD without recourse to antimicrobials in the diet.
The seven experiments conducted
in this programme are presented as chapters, as follows:
Results obtained
in this research project have demonstrated that cooked (processed) white
rice, either in medium-grain or long-grain form, included in diets for
weanling pigs can be used as a replacement for wheat without a loss of
production in the immediate post—weaning period. The decision to replace
a cereal such as wheat in diets for weanling pigs, therefore, is likely
to be one of price differential.
Cooking broken white rice, particularly in medium-grain and waxy rice that have lower amylose levels than long-grain rice, increases starch digestibility when measured at the end of the small intestine. This could be predicted with accuracy in vitro using a “fast digestible starch” assay modified for rice in our laboratory. Regardless of the type and variety of rice used, however, pigs fed cooked white rice partition more digested nutrients into carcass gain than pigs fed other cereals such as wheat and barley, although the type of proteins fed to pigs will also influence this. In this regard, the use of extruded rice plus sources of animal protein (eg, milk powders, fishmeal, meat and bone meal) appear the best dietary combination for production purposes. Feeding vegetable (plant) proteins typically increased the weight of the gastrointestinal tract as a consequence of increased fermentative activity in the large intestine, and reduced bodyweight gain and FCR. Determination of the energy (DE and NE) values of extruded medium-grain (Amaroo) and long-grain (Doongara) rice confirmed the superior energy value of these two rice types over existing cereals used in Australian feeding of pigs, such as wheat.
The effects of feeding cooked white rice on reducing faecal shedding of the bacterium (E. coli) responsible for causing PWD were generally unchanged, or even exacerbated, when the rice plus animal protein diets were fed compared to commercially-based diets that were considered a contributing factor to the incidence of PWD. The extent and duration of faecal shedding of enterotoxigenic E. coli found in the studies conducted was generally low, and this might have influenced the capacity of the rice-based diets to exhibit protective effects. It was hypothesised also that an imbalance in the amounts of carbohydrate versus protein entering the large intestine might have predisposed the pig to PWD, due to a change in the types of microbiota and subsequent production of compounds implicated in non-infectious diarrhoea. The results of Chapter 9 advocate the inclusion of a quantity of slowly or moderately fermentable dietary fibre to extruded rice-based diets consisting of animal protein to ameliorate the diarrhoea that is sometimes observed when feeding this diet, although in this instance 20 g kg- oat hulls depressed digestibility and production after weaning. Nevertheless, this proposition is consistent with European experiences of feeding processed rice to piglets after weaning. In this respect, it is feasible that the addition of rice bran and (or) rice hulls, or possibly the use of brown rice, in diets for piglets after weaning could achieve similar results.
An unfortunate consequence of the drought in the rice-growing regions of NSW for this particular project, however, was the inability to perform an on-farm trial implementing some of the findings and conclusions arising from this research project.
The major recommendations
arising from this project are as follows:
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