When talking about sugars and starches in broiler nutrition it is often the digestibility that is considered. but at what rate are these carbohydrates digested? here we take a more detailed look into the effects of slowly digestible carbohydrates in broiler nutrition. By Karel Thurman.
By Karel Thurman
Starch is one of the most important energy sources in a broiler diet. Up to 65% of the metabolisable energy in a broiler ration is imputed to carbohydrates. Both starch and sugars are digested to glucose, which is readily absorbed as energy source. Starch sources vary strongly in digestive characteristics depending on granular structure, amylose:amylopectin ratio and cristallinity. Also processing of the starch has an impact on these parameters. Not only the digestibility of the starch source may vary but also the rate at which starch is digested is an important factor determining the value of an ingredient. Some starches are very rapidly digested and absorbed in the proximal part of the small intestine, provoking a quick elevated level of plasma glucose. In Table 1 an overview is given of the digestion characteristics of a number of starch sources.
Disaccharides are contrarily to starch not organized in a granular structure and because of their simple structure, they are considered to be 100% digestible. However, a similar difference in digestion rate can be seen in sugars. Not all disaccharides are hydrolyzed at the same rate by the enzymes. Dextrose for example is known to be very rapidly digested and absorbed whereas the enzymatic affinity for other sugars is lower, leading to a more balanced glucose supply.
Slow digestible starches have a positive effect on broiler performances
Various researchers have studied the effect of starch sources on the performances of broilers. It has been shown that not only the digestibility but also the site and rate of starch digestion have a significant impact on the zootechnical performances in poultry. Weurding et al. (2003) have demonstrated that slowly digestible starch (SDS) can have positive effects on the feed efficiency, compared to rapid digestible starch (RDS) (Table 2). This was also confirmed by a study of Gutierrez del Alamo et al. (2009) who found that wheat starches with lower digestion rate resulted in better technical results. These data suggest that it might be important to take in account the starch digestion characteristics when formulating broiler diets.
Amino acid sparing effect of slow digestible starch
These effects are explained by the researchers both by a more continuous supply of glucose in the intestinal lumen. During carbohydrate digestion, the glucose peak is partly buffered by conversion of glucose in lactate by the epithelium cells. The lactate is afterwards delivered to the liver for conversion to glucose or fatty acids.
It is likely that more glucose is converted to lactate after rapid starch digestion. A more balanced carbohydrate digestion would hence need less energy consuming conversions and enables a more direct use of glucose resulting in a better feed efficiency.
When feeding slowly digestible carbohydrates, glucose is supplied not only at the proximal part of the lumen but also the epithelium cells in the distal part of the small intestine can benefit from glucose as a direct energy source. This prevents them from oxidizing valuable amino acids as e.g. glutamine to meet their energetic requirements. Research from Enting et al. (2005) also showed that the synchronization between amino-acid supply and energy supply results in better performance of the broilers. The explanation can be found via the effect of slow digestible carbohydrate sources on insulin level in the blood.
A novel sugar syrup
When talking about carbohydrate-feeding of broilers, often only starches are considered. BeneoCarb S (BCS) is a novel low glycemic sugar syrup. The product contains not only sucrose, fructose and glucose but also high levels (>65% on dm) of trehalulose and isomaltulose.
These are disaccharides of glucose and fructose but due to a slight modification in the structure they are more slowly digested than sucrose. The slow digestion and consequently slower release of glucose reduces the postprandial glucose peaks. Despite the reduced digestion rate, the sugars are completely digested in the small intestine and yield the same caloric value as sucrose. However, unlike sucrose, these sugars are digested also in the lower small intestine, providing a continuous supply of glucose in the lumen.
Because of the negative connotation of molasses in broiler nutrition, sugar syrups are rarely used for this application. However, since BeneoCarb S is very pure and contains almost no ash (<0,5%), it is an ingredient which is also highly suitable for inclusion in broiler diets.
BeneoCarb S in broiler diets
The potential use of this low-glycemic sugar syrup for poultry nutrition was evaluated in a broiler trial at the Institute for Agriculture and Fisheries Research (ILVO, Belgium) (2008). In this trial both inclusion level and period of administration of the product were evaluated. The effects of the diet on zootechnical results were evaluated. All diets were formulated iso-energetically and iso-proteic and were at the same first limiting AA content. It was mainly wheat starch which was replaced throughout this trial. In total 6 treatments were used in the trial:
T1: control diet – standard nutrient composition of practical diets
T2: diet with 3% BC, fed during 7 days
T3: diet with 3% BC, fed during 14days
T4: diet with 6% BC, fed during 7 days
T5: diet with 6% BC, fed during 14 days
T6: diet with 3% BC, fed during the whole fattening period (39 days)
The results for this trial can be seen in Table 3. During first period feed intake was not influenced by the inclusion of BeneoCarb S in the diet, but efficiency of growth was significantly improved especially during the first week of the trial. In the overall period, it was the treatment which received 3% of BeneoCarb S throughout the whole feeding period which showed the best performances.
This research indicates that low glycemic sugars have certainly a potential for use in poultry diets. They offer a readily available source of glucogenic energy but feature a balanced supply of the glucose. Because of the low ash content of this product, there will be no effect on the osmotic pressure in the intestinal lumen. This was investigated via a scoring of the litter quality in the trial. Because of the sweet taste of BeneoCarb S, the product can also be used for the improvement of the organoleptical profile of a diet.
Tailor made carbohydrate concept?
From this research it can be concluded that digestion rate of both sugars and starches has an important influence on the feed efficiency of broilers. Sourcing for carbohydrates with high digestibility but reduced rate of digestion, supplying energy synchronized with amino acid supply can help in achieving a better zootechnical performance. Via selection of ingredients with varying digestibility an optimal energy provision in line with the requirements of these high demanding animals can be achieved.
– Weurding, E., Veldman, A., Veen, W., van der Aar, P and Verstegen, M. (2001). Starch digestion rate in the small intestine of Broiler Chickens differs among feedstuffs. J. Nutr 131: 2329-2335
– Gutierrez del Alamo, A., Verstegen, M., Den Hartog, L., Perez de Ayala, P., Villamide, M. (2009). Wheat starch digestion rate affects broiler performance. Poultry Science 88:1666-1675
– Weurding, E. Enting, H. Verstegen, M. (2003). The relation between starch digestion rate and aminio acid level for broiler chickens. Poultry Science 82:279-284
– Enting, H., Pos, J., Weurding, E., Veldman, A. (2005). Starch digestion rate affects broiler performane. Aust Poult. Sci. Symp. 2005:17-20
Source: FeedMix vol 18 nr 1, 2010