The nutritional value of biofuel co-products for poultry (PhD)

Abstract

A total of eight experiments were used to provide data about the nutritional value of wheat-distillers’ dried grains with solubles (DDGS) produced in the UK as a feedstuff for broilers and turkey. In the first study, 499 data sets were compiled and used to develop regression models to predict the amino acid (AA) contents of maize- and wheat-DDGS from their crude protein (CP) contents because of the variability in the chemical composition of DDGS among sources. Using a validation exercise, it was noted that the AA contents of maize- and wheat-DDGS can be predicted with reasonable accuracy using the mathematical equations generated in this study. Using a total of six experiments, the apparent metabolisable energy (AME), ileal amino acid (AA) digestibility and phosphorus (P) digestibility in wheat-DDGS without- or with exogenous enzymes was determined for broilers and turkeys.

The AME content in wheat-DDGS without or with enzymes were 15.0 or 15.5 MJ/kg, respectively, for broilers and 14.0 or 14.4 MJ/kg, respectively, for turkey. Nitrogen corrected-AME(AME_n) without or with enzymes were 14.0 or 14.5 MJ/kg, respectively, for broilers; 13.0 and 13.5 MJ/kg, respectively, for turkey. For broilers, apparent ileal AA digestibility (AIAAD) ranged from 35% (alanine (Ala)) to 75% (proline (Pro)) without protease, whereas the range was 42% (threonine (Thr)) to 82% (Pro) with protease supplementation. Supplemental protease improved (P < 0.05) the AIAAD of arginine (Arg) and Pro. Standardised ileal amino acids digestibility (SIAAD) ranged from 43% (aspartic acid (Asp)) to 84% (Pro), whereas the range was from 54% (Asp) to 93% (Pro) with added protease. Protease addition improved (P < 0.05) the SIAAD of Arg, leucine (Leu), phenylalanine (Phe), methionine (Met), valine (Val), and Pro. For turkey, AIAAD was lower than 50% for all AA except for glutamic acid (Glu) (70%) and Pro (81%) without protease whereas, SIAAD ranged from 41% (Thr) to 89% (Pro) without protease; and 56% (Arg) to 88% (Pro) with protease. Protease improved (P < 0.05) the AIAAD and SIAAD (except cystine (Cys) and Pro) from between 5 to 19 percentage points. Phosphorus digestibility (ileal) in wheat-DDGS was 94 or 96% without- or with phytase, respectively, for broilers or 76% or 82%, respectively, for turkey.

On the other hand, total tract phosphorus retention was 92% or 94%, respectively, for broilers and 71% or 81.6%, respectively, for turkeys. Phytase did not improve phosphorus digestibility or retention of wheat-DDGS for broilers and turkeys. The effect of enzyme supplementation on growth performance and gastrointestinal tract (GIT) characteristics of broilers receiving a wheat-soyabean meal (wheat-SBM) based diet containing up to 25% wheat-DDGS, was determined in a final experiment. Supplementation of a mixture of carbohydrases and protease modestly improved the growth performance of broilers from day 1 to 42 but phytase had no effect. In addition, enzyme supplementation had no marked effect on jejunal villi height and crypt depth, intestinal pH or caecal volatile fatty acids production in broilers.

Collectively, it was concluded from these experiments that mathematical models are a useful tool to predict the amino acids content of maize- and wheat-DDGS. The metabolisable energy (ME) in wheat-DDGS was comparable to those of wheat and maize grain for broilers and turkey; therefore, wheat-DDGS may be used as a substitute for wheat or maize in diets for broiler and turkey. The digestible P content in wheat-DDGS for broilers and turkey is greater than in most other major feedstuffs. The use of wheat-DDGS in poultry diet may therefore reduce the quantity of inorganic P compounds used, reduce P loss in manure and, overall, may reduce feed cost. Ileal AA digestibility in the wheat-DDGS for broilers and turkey was variable and generally low. It was recommended that the low digestibility of essential AA in wheat-DDGS should be accounted for when using wheat-DDGS as a feedstuff for poultry.