Insights into Digestibility

Dr Helen Masey-O'Neill presented a paper and a poster on starch digestibility of wheat for broilers. She and Dr Wiseman at the University of Nottingham investigated the drying temperature of wheat: in the UK, cereal crops must sometimes be dried at temperatures up to 100°C in order to prevent its germination or mould growth in storage.

The results suggest that there is no difference in starch digestibility when wheat is dried at high temperature except with 85°C and that, only in the case of one hard wheat variety, which appeared to be particularly sensitive. Dr Masey-O'Neill explained that water was limited in the experiment, and that this may have prevented any loss of the crystalline structure.

She explained that there is little information in the literature regarding the effect of the level of crude protein on starch digestibility. They carried out some preliminary work on this, concluding that protein components should be excluded from tests evaluating wheat where starch digestibility is the focus. Dr Masey-O'Neill commented that there are indications that protein level has a role in starch digestibility in the ileum, and that this warrants further investigation.

From Queen's University in Belfast, Dr Elizabeth McCann reported on her work into the effect of dietary glycerol inclusion on broiler performance and apparent metabolisable energy concentration. She concluded that glycerol can be utilised as an acceptable partial energy replacement for wheat, providing a much higher dietary AME than the control diet.

Phytase Effects

The effect of nutrient dilution in turkey diets on water intake and excretion was the subject of the paper by Wassem Mirza and colleagues at SAC. Mr Mirza explained that wet litter is quite a widespread practical challenge for the industry, particularly as it can trigger footpad dermatitis and other conditions of welfare concern.

He said that their results indicate that nutrient dilution reduces excreta moisture content and it also has a a positive effect on dry matter digestibility when the sand – which was used as a filler in the diets – was taken into account. Furthermore, dietary phytase, which had been included in half the diets, was found to increase water output compared to diets without phytase for the same bodyweight in turkeys fed isonitrogenous diets.

Farina Khattak and colleagues at SAC and Danisco Animal Nutrition investigated the response of chicks, with prior exposure to low- and high phytate diets, when subsequently fed diets supplemented with phytase and phytate.

The results led her and her co-authors to conclude that the total content of phytate is an important parameter to be considered when formulating poultry feed since this may irreversibly or otherwise modify the gastrointestinal tract, and thus performance, throughout the life of the bird.

Diet and Health Interactions

Chamira Palliyeguru and colleagues at Harper Adams University College reported the latest results in their project looking at the effects of different protein sources on the incidence of sub-clinical necrotic enteritis (NE) in broiler flocks. Caused by an overgrowth of Clostridium perfringens, sub-clinical NE causes major economic losses to the broiler industry.

To investigate the effects of trypsin inhibitor activity on NE and performance, they used three levels on non-toasted soy (0, 100 and 200 g/kg) as well as a diet containing potato protein as the main protein source.

Ms Palliyeguru reported that there was a a negative relationship between the protein digestibility of the diet and the incidence of subclinical NE in the broiler. She suggested this may have been due to the increased Clostridium perfringens population in the gut and/or a direct effect of trypsin inhibitor on the pathogenicity of C. perfringens toxins.

Effects of Feeding on the End Product

Despite several recent much-publicised examples of food poisoning outbreaks caused by Salmonella in the US in other foods, this group of bacterial pathogens are more usually associated with poultry products. Great attention needs to be paid at all stages of the food chain in avoiding contamination. This focus has achieved considerable success but the search for new and better preventative measures continues.

Soumela Savvidou of the University of Plymouth presented a paper looking at how liquid feed fermented with Lactobacillus salivarius (Ls) affects the susceptibility of broiler chickens to Salmonella enterica typhimurium Sal 1344 nal. She and her colleagues fed chicks according to one of the following treatments: Ls in the drinking water; Ls delivered in fermented liquid feed; liquid feed acidified with lactic acid (ALF) or a negative control.

The researchers found the proportion of S. typhimurium-shedding chicken was decreased significantly in both chickens fed FLF and ALF. The effect was stronger in FLF than ALF. As a means of controlling Salmonella typhimurium infection, providing lactic acid through FLF was better than in the drinking water, Ms Savvidou said. She added that the higher the number of Lactobacillus and the greater the production of lactic acid, the better the Salmonella status of the chickens.

Researchers from Reading University had been looking at how to improve the healthy image of chicken meat. Dr Caroline Rymer explained that enriching chicken meat with long-chain omega-3 polyunsaturated acids (LC n-3 PUFA) would be a viable way to increase the human population's intake of these essential fatty acids. While feeding broilers fish oils is effective but causes unpleasant taints to develop in the meat, while feeding an oil rich in C18:3n-3 does not lead to deposition of LC n-3 PUFA.

So the Reading group turned their attention to stearidonic acid (C18-4n-3), feeding broilers a diet containing an oil derived from soybeans genetically modified to produce a high concentration of C18n-3.

They found that feeding broilers stearidonic acid produced meat with a nutritionally significant concentration of long chain omega-3 PUFA or their immediate precursors with a much reduced negative effect on the meat's sensory characteristics compared with feeding birds fish oil.

June 2009