Dietary starch is the major energy source for broiler chickens, and knowledge about its digestive behavior can be important. In a digestibility trial with 720 broiler chickens, site, rate and extent of starch digestion were measured for 12 feedstuffs. Starch digestion was determined using the slaughter technique, which involves removal of the small intestine from the recently killed chicken, with manual collection of the contents. Starch digestion coefficients were calculated from remaining starch in three segments of the small intestine and in excreta. Mean retention time in four segments of the small intestine was measured. This enabled calculations for starch digestion rate (k(d)). Ileal starch digestibility varied from 33% (potato starch) to 99% (tapioca). Retention time for digesta in the postduodenal small intestine varied from 136 min (barley diet) to 182 min (potato diet). On the basis of starch digestion rates, a distinction was made between slowly digestible starch (k(d) < 1 h(-1)), gradually digestible starch (k(d):1-2 h(-1)) and rapidly digestible starch (k(d) > 2 h(-1)). Starch from common beans was digested most slowly (k(d): 0.5 h(-1)), and starch from tapioca was digested most rapidly (k(d): 4.3 h(-1)). Starch digestion rates of potato starch and legume seeds were lower than those of cereal grains and tapioca. Degradation of starch entering the hind gut of the birds did not occur. Milling of corn affected rate, but not the extent of starch digestion. We concluded that site of starch digestion within the small intestine is not an accurate indicator for starch digestion rate.

Current feed evaluation systems for poultry are based on digested components (fat, protein and nitrogen-free extracts). Digestible starch is the most important energy source in broiler chicken feeds and is part of the nitrogen-free extract fraction. Digestible starch may be predicted using an in vitro method that mimics digestive processes in the gastrointestinal tract of broiler chickens. An experiment was designed to use this method for predicting site, rate and extent of starch digestion in broiler chickens. In vitro starch digestion was studied in 12 experimental diets differing in starch sources. These diets were also used in a digestibility trial with broiler chickens. Correlations between in vitro and in vivo starch digestion were calculated. Starch digestion after 2 h incubation correlated well with in vivo starch digestion in the first half of the small intestine (r = 0.94). A 4-h incubation period resulted in a good correlation between in vitro starch digestion and ileal starch digestion (r = 0.96). In vitro starch digestion rate (h(-1)) correlated well with in vivo starch digestion rate (r = 0.87). In vitro starch digestion of individual starch sources was additive. It appeared that legume seeds and waxy corn contained two starch fractions, which were digested at different rates. We conclude that starch digestion rate in broiler chickens is well predicted by the in vitro method.

Zusammenfassung Der Einfluß von α‐Galaktosiden und α‐Galaktosidase im Futter auf ileale Verdauungsvorgänge beim Ferkel An sechs Ferkeln mit ileorektalen Anastomosen (IRA) wurde der Einfluß von α‐Galaktosiden (27,5 g/kg) mit und ohne Zusatz von α‐Galaktosidase (7,1 U/g) auf ileale Verdauungsvorgänge untersucht. Die ileale Verdaulichkeit von organischer Substanz, Rohprotein und NfE wurde um etwa 20% durch α‐Galaktoside im Futter gesenkt. Bei Stärke betrug dieser Wert nur ca. 3%. Durch den Zusatz von α‐Galaktosiden wurde die Flüssigkeitsretention und die mikrobielle Fermentation, gemessen anhand von ATP und flüchtigen Fettsäuren im Chymus, erhöht. Die höhere Flüssigkeitsretention und mikrobielle Aktivität stimulierte die Darmperistaltik, führte zu Zellwandschäden im Dünndarm und erniedrigte die Hydrolyse der Nährstoffe. Außerdem wurde ein Anstieg von fermentierbaren Substraten in den unteren Darmabschnitten beobachtet, der zu einer Veränderung der mikrobiellen Besiedlung und damit zu erhöhter Durchfallhäufigkeit führen kann. Die Zugabe des Enzyms α‐Galaktosidase konnte das Auftreten dieser negativen Phänomene nicht verringern.

In 5 trials with Dutch Black Pied or Dutch Black Pied X Holstein-Friesian cows the effects of feeding concentrates with rapidly and slowly degradable protein on rumen values were investigated. Samples of rumen fluid were taken before and 45, 90, 135 and 180 min after the morning concentrate feed. Rumen pH was not affected by protein degradability. Rumen ammonia content was higher when easily degradable protein was given than when slowly degradable protein was given; peak concentration varied from 10 to 12.5 and from 4 to 8 mmol/litre, respectively. Maximum concentration of lactate was not influenced by protein degradability. Rumen content of volatile fatty acids increased more rapidly when the slowly degradable protein rather than when the rapidly degradable protein was given. At all sampling times the molar acetate:propionate ratio was higher after feeding on slowly degradable protein than after rapidly degradable protein. (Abstract retrieved from CAB Abstracts by CABI’s permission)