Effects of Defatted Microalgae on Nutrient Digestibility and Retention in Broiler Chicks

Abstract Text:

This experiment was to determine the impact of supplemental 10% defatted microalgae (Nannochloropsis oceanica, 45% CP and 3.8% ether extraction, EE) from biofuel production in a corn-soybean meal basal diet (BD) on nutrient digestibility and retention in broiler chicks. Day-old hatchling Cornish Giant cockerels were divided into two groups (5 cages/group, 4-5 chicks/cage) and fed the BD or the microalgae diet for 6 wk. Starting wk 3, chicks were fed diets containing 0.2% chromic oxide as an indigestible marker.  Total excreta of individual cages was collected daily for consecutive 5 and 3 d during wk 5 and 6, respectively. At the end of wk 6, chicks were euthanized to collect ileal digesta from 1 chick/cage. Concentration of DM, CP, EE, AA, and chromic oxide in digesta, excreta, and diets were assayed. Apparent nutrient retention was calculated based on total excreta collection and chromic oxide as an indigestible marker. The latter was also used to estimate apparent ileal digestibility of nutrients. Data were analyzed by Student t-test. Chicks fed the two diets had similar ADFI and G:F ratio, although those fed the microalgae diet had 3-5% (P < 0.05) heavier BW than chicks fed the BD. Feeding the microalgae diet enhanced (P < 0.05) and decreased (P < 0.05) apparent retention and digestibility of DM by 3.3% and by 1.8%, respectively. Feeding the microalgae diet elevated (1.6 to 3.8%, P < 0.05) apparent retention of EE determined by the indirect method, but not by the direct method. Supplemental defatted microalgae did not affect apparent retention of CP determined by both methods at either time-point except for a 17.8% decrease (P < 0.01) by the 5-day total collection. Feeding the microalgae diet decreased (P < 0.05) apparent ileal digestibilities of 8 essential AA and 6 nonessential AA, ranging from 32% for isoleucine to 7% for glutamic acid. Feeding that diet decreased (P < 0.05) apparent retention of 6 essential AA and 5 nonessential AA, ranging from 16% for threonine to 0.6% for leucine. In conclusion, supplementing 10% of defatted microalgae in the corn-soybean meal diet did not show consistent effect on apparent retention or ileal digestibility of DM, EE, or CP determined by the two methods at the two time-points, but the diet decreased apparent retention or ileal digestibility of a number of AA. (Supported by USDA/DOE Biomass R&D Initiative Grant and a Cornell Hatch Grant).

Keywords: Algae, amino acid, broiler, digestibility, retention